Freshwater Fishes of North-Eastern Australia
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Freshwater Fishes of North-Eastern Australia
Brad Pusey, Mark Kennard and Angela Arthington
Centre for Riverine Landscapes, Griffith University Nathan, Qld 4111, Australia
Text © 2004 Brad Pusey, Mark Kennard, Angela Arthington and the Rainforest CRC Illustrations © 2004 B.J. Pusey All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owners. Contact CSIRO PUBLISHING for all permission requests. National Library of Australia Cataloguing-in-Publication entry Pusey, Bradley J. Freshwater fishes of north-eastern Australia. Bibliography. Includes index. ISBN 0 643 06966 6 (hardback).
ISBN 0 643 09208 0 (netLibrary eBook).
1. Freshwater fishes – Australia, North-eastern. 2. Freshwater fishes – Australia, North-eastern Identification. 3. Freshwater ecology – Australia, North-eastern. I. Kennard, Mark J. II. Arthington, Angela H. III. Title.
597.1760994 Available from CSIRO PUBLISHING 150 Oxford Street (PO Box 1139) Collingwood VIC 3066 Australia Telephone: Local call: Fax: Email: Web site:
+61 3 9662 7666 1300 788 000 (Australia only) +61 3 9662 7555
[email protected] www.publish.csiro.au
Front cover Hephaestus tulliensis (khaki grunter), photograph by G.R. Allen
Set in 9.5 Minion Cover design by Jo Waide Text design by James Kelly Typeset by J & M Typesetting Printed in Australia by Ligare
To my parents Pat and Jim (dec.) for fostering a love of natural history, and to my family, Moira, Michael and Olivia for their support and tolerance B.J.P.
To my loving partner Lorann and chiens lunatiques Sas´a and Max, for happy diversions and indulgences, and to my family, especially Jill and Colin, for inspiration and encouragement M.J.K.
To my New Zealand family and to Mark, Kirstie, Ayden, Huntley and Liveya, for their enduring love and encouragement A.H.A.
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Foreword
This book is the end product of the authors’ extensive research on the ecology and flow requirements of fishes in Queensland rivers. Production of the book has been a major initiative of the Co-operative Research Centre for Tropical Rainforest Ecology and Management (Rainforest CRC) via its fundamental research on biodiversity in the Wet Tropics region, and the CRC’s new Catchment to Reef research program. The Rainforest CRC and the Centre for Riverine Landscapes, Griffith University, have subsidised production of the book and worked together with the publishers, CSIRO Publishing, to achieve its high standard of presentation.
North-eastern Australia contains over 130 native species of freshwater fish which is approximately half of the freshwater fish fauna of the entire continent. This fauna is of great interest for its diversity, scientific importance and value. Many species occurring in this region also extend westward across much of northern Australia and southward through coastal New South Wales, Victoria, South Australia and Tasmania. This makes the book of singular importance as the only text covering the freshwater fishes of this vast region in the richness of detail presented here. The value of this baseline work is potentially enormous. Tropical Australia faces a number of serious problems directly stressing the environment we value so highly. There is increasing demand for water for agriculture and for urban use and we are likely to see our water resources further stressed by increasing climatic variability – one of the likely results of global climate change. There is also international concern about runoff from catchments causing a decline in the health of the Great Barrier Reef and its feeder streams. Fish are important indicators of ecosystem health and this book provides the sort of detailed information needed for a monitoring toolkit that can be used at the stream level by community groups, farmers and scientists concerned with these issues. We continue to lead the tropical world in these fields of science and application.
On behalf of the Rainforest CRC and Griffith University, I congratulate the authors on their dedicated efforts in producing this significant contribution to knowledge, and commend the book as an indispensable compendium, catalogue and baseline reference for anyone with a keen interest in this fascinating component of Australia’s unique biodiversity. Nigel Stork CEO, Rainforest CRC Cairns, Queensland February 2004
vii
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Table of contents
Foreword
vii
Acknowledgements
xiii
Introduction
1
Origins, structure and classification of fishes
3
Key to the native and alien fishes of north-eastern Australia
14
Study area, data collection, analysis and presentation
26
Ceratodontidae Neoceratodus forsteri – Queensland lungfish
49
Osteoglossidae Scleropages leichardti – Saratoga
60
Megalopidae Megalops cyprinoides – Tarpon
64
Anguillidae Anguilla australis, Anguilla obscura, Anguilla reinhardtii – Eels
71
Clupeidae Nematalosa erebi – Bony bream
92
Ariidae Arius graeffei, Arius leptaspis, Arius midgleyi – Fork-tailed catfishes
102
Plotosidae Neosilurus hyrtlii – Hyrtl’s tandan Neosilurus ater – Black catfish Neosilurus mollespiculum – Soft-spined catfish Porochilus rendahli – Rendahl’s catfish Tandanus tandanus – Eel-tailed catfish
112 121 129 133 137
Retropinnidae Retropinna semoni – Australian smelt
152
Hemiramphidae Arrhamphus sclerolepis – Snub-nosed garfish
161
Belonidae Strongylura krefftii – Freshwater longtom
166
Atherinidae Craterocephalus marjoriae – Marjorie’s hardyhead Craterocephalus stercusmuscarum – Fly-specked hardyhead
171 180
Melanotaeniidae Rhadinocentrus ornatus – Ornate rainbowfish Cairnsichthys rhombosomoides – Cairns rainbowfish Melanotaenia splendida – Eastern rainbowfish Melanotaenia duboulayi – Duboulay’s rainbowfish Melanotaenia eachamensis – Lake Eacham rainbowfish
197 205 211 221 231
ix
Melanotaenia utcheesis – Utchee Creek rainbowfish Melanotaenia maccullochi – MacCulloch’s rainbowfish
237 242
Pseudomugilidae Pseudomugil mellis – Honey blue-eye Pseudomugil signifer – Pacific blue-eye Pseudomugil gertrudae – Spotted blue-eye
247 254 269
Synbranchidae Ophisternon gutturale, Ophisternon spp.? – One-gilled swamp eels
272
Scorpaenidae Notesthes robusta – Bullrout
278
Chandidae Ambassis agrammus – Sailfin glassfish Ambassis agassizii – Agassiz’s glassfish Ambassis macleayi – Macleay’s glassfish Ambassis miops – Flag-tailed glassfish Denariusa bandata – Pennyfish
284 292 302 306 309
Centropomidae Lates calcarifer – Barramundi
313
Percichthyidae Macquaria ambigua, Macquaria sp. B – Yellowbelly Macquaria novemaculeata – Australian bass Guyu wujalwujalensis – Bloomfield River cod Maccullochella peelii mariensis – Mary River cod Nannoperca oxleyana – Oxleyan pygmy perch
326 337 345 348 353
Terapontidae Amniataba percoides – Barred grunter Leiopotherapon unicolor – Spangled perch Hephaestus fuliginosus – Sooty grunter Hephaestus tulliensis – Khaki bream, Tully grunter Scortum parviceps – Small-headed grunter
361 369 378 390 395
Kuhliidae Kuhlia rupestris – Jungle perch
401
Apogonidae Glossamia aprion – Mouth almighty
409
Toxotidae Toxotes chatareus – Seven-spot archerfish
419
Mugilidae Mugil cephalus – Sea mullet
426
Gobiidae Glossogobius sp. 1 – False Celebes goby Glossogobius aureus, Glossogobius giuris – Golden goby, Flathead goby Glossogobius sp. 4 – Mulgrave River goby Redigobius bikolanus – Speckled goby Awaous acritosus – Roman-nosed goby Mugilogobius notospilus – Pacific mangrove goby Schismatogobius sp. – Scaleless goby
434 440 445 449 456 461 465
x
Eleotridae Eleotris fusca, Eleotris melanosoma – Brown gudgeon, Ebony gudgeon Bunaka gyrinoides – Greenback gauvina Oxyeleotris lineolatus, Oxyeleotris selheimi – Sleepy cod, Striped sleepy cod Oxyeleotris aruensis – Aru gudgeon Giurus margaritacea – Snakehead gudgeon Hypseleotris compressa – Empire gudgeon Hypseleotris galii, Hypseleotris sp. 1 – Firetailed gudgeon, Midgley’s carp gudgeon Hypseleotris klunzingeri – Western carp gudgeon Gobiomorphus australis – Striped gudgeon Gobiomorphus coxii – Cox’s gudgeon Mogurnda adspersa, Mogurnda mogurnda – Purple-spotted gudgeon, Northern trout gudgeon Philypnodon grandiceps – Flathead gudgeon Philypnodon sp. – Dwarf flathead gudgeon
468 473 477 487 491 498 510 521 530 538 544 558 568
Conclusion: prospects, threats and information gaps
575
Glossary of terms used in the text
585
Bibliography
601
Appendix 1: Fish species composition in rivers of north-eastern Australia
655
Appendix 2: Studies undertaken in rivers of north-eastern Australia
674
Index
681
xi
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Acknowledgements
Department of Primary Industries, Fisheries), South East Queensland Water Board, South East Queensland Water Corporation, and the Wet Tropics Management Authority.
This book is a product of our research on the ecology and flow requirements of fishes in Queensland rivers, amply funded by the former Land and Water Resources Research and Development Corporation (LWRRDC, now Land and Water Australia), and generously supported by the former Queensland Water Resources Commission, and former Queensland Department of Primary Industries, Land Use and Fisheries Branch (now Queensland Departments of Natural Resources, Mines and Energy, and Queensland Department of Primary Industries, Fisheries, respectively), and Griffith University. Funding from the Co-operative Research Centre for Tropical Rainforest Ecology and Management (Rainforest CRC) supported our research, and the Rainforest CRC and the Centre for Riverine Landscapes, Griffith University, have subsidised this book to make it more affordable. Professor Nigel Stork, Chief Executive Officer of the Rainforest CRC and Jann O’Keefe sought publication outlets for the book and negotiated our contract with CSIRO Publishing. We sincerely thank Nigel and the Rainforest CRC for supporting our research and writing.
We also wish to thank all government agencies and agency staff (e.g. rangers) and the numerous landholders and aboriginal communities who allowed us access to field sites, supported our work and shared their knowledge and insights. The following colleagues, friends and family members have assisted in the field and in the laboratory - we are deeply indebted to one and all: Steven Balcombe, Mark Bensink, Jason Bird, David Blühdorn, Stacey Braun, Stuart Bunn, Peter Buosi, Damien Burrows, Harry Burton, Brian Bycroft, Hiram Caton, Nick Cilento, Paul Close, Dan Clowes, Diane Conrick, Anthony Cutten, Felicity Cutten, Huntly Cutten, Ellie Dore, Ashley Druve, Susan Dunlop, John Endler, John Esdaile, Simon Hamlet, Debbie Harrison, Karen Hedstrom, Alf Hogan, Peter James, Daniel Kennard, Paul Kennard, Alex Langley, Matthew Langworthy, Greg Lee, Bill Macfarlane, Stephen Mackay, Nick Marsh, Chris Marshall, Jonathan Marshall, Peter Mather, Greg Miller, John Mullen, Carl Murray, Peter Negus, Richard Pearson, John Peeters, Tony Pusey, Martin Read, Darren Renouf, Andrew Sheldon, Michael Smith, Errol Stock, Brian Stockwell, Celia Thompson, Chris Thompson, Rob Wager, Richard Ward, Selina Ward, Tony Watson, Gary Werren, Rob Williams and Tim Wrigley.
Preparation of this book has entailed a major review of existing literature and collation of the results of unpublished field research undertaken by the authors in freshwater systems throughout Queensland over the last 20 years. Many people and institutions have assisted with this research or provided funding support, in-kind resources, data and advice. We particularly wish to thank many institutions and individuals for their commitment to the study of freshwater fishes in Australia.
Sincere thanks are due to the following for stimulating discussions on the ecology of freshwater fish and for provision of literature, reports and data, access to specimens of fish species and identification of specimens, including fish parasites: Gerry Allen, John Amprimo, Steven Balcombe, Chris Barlow, Andrew Berghuis, Eldridge Birmingham, Steve Brooks, Culum Brown, Damien Burrows, Niall Connolly, Brendan Ebner, Craig Franklyn, Gary Grossman, Jeff Gunston and Bruce Hansen and many others from the Australia New Guinea Fishes Association, Michael Hammer, Gene Helfman, Brett Herbert, Alf Hogan, Jane Hughes, Paul Humphries, David Hurwood, Michael Hutchison, Inter-Library Loans staff at Griffith University, Peter Jackson, Jeff Johnson, Peter Johnston, Peter Kind, John Koehn, Helen Larson, Keith Lewis, Mark Lintermans, Chris Lupton, Roland Mackay, Chris Marshall, Jonathan Marshall, Mark McGrouther, Craig Moritz, Richard Pearson, Colton Perna, Claire Peterkin, Phil Price, Tyson Roberts, John Ruffini, John Russell,
First, we gratefully acknowledge research grants and inkind support from the following agencies: Australian Nature Conservation Agency, Australian National Parks and Wildlife Service, Australian Water Research Advisory Council, Co-operative Research Centre for Rainforest Ecology and Management, Co-operative Research Centre for Freshwater Ecology, Co-operative Research Centre for Sustainable Tourism, Land and Water Resources Research and Development Corporation, Moreton Bay Waterways and Catchments Partnership, Queensland Department of Environment and Heritage, Queensland Department of Natural Resources, Mines and Energy, Queensland Department of Primary Industries (Fisheries), Queensland Environmental Protection Agency, Queensland National Parks and Wildlife Service, Queensland Water Resources Commission, Walkamin Research Station (Queensland
xiii
Nick Schofield, Clayton Sharpe, Bob Simpson, Jim Tait, Rob Wager, John Ward, Alan Webb, Peter Unmack and Tom Vanderbyll.
acknowledge Mariola Hoffmann for preparing the maps presented in this book. We thank Elly Scheermeyer, Fiona McKenzie-Smith and Darren Renouf for assistance with references. We are also grateful to Maria Barrett, Petney Dickson, Jason Elsmore, Daina Garklavs, Keith Officer, Lacey Shaw, Deslie Smith, Stuart Taylor and many other staff at Griffith University for administrative support and the various tasks that supported the production of this book. We apologise to anyone we have neglected to thank.
We warmly thank the following colleagues for reading and commenting on various chapters: Culum Brown, Damien Burrows, John Endler, Alf Hogan, Helen Larson, Steven Mackay, Chris Marshall, Jonathan Marshall, Dugald McGlashan, Colton Perna, Tarmo Raadik, John Russell, Alisha Steward and Jim Tait. This book would no doubt have benefited from further expert feedback from other colleagues; unfortunately, time constraints precluded this.
Finally, we are indebted to CSIRO Publishing for taking on our book and are particularly grateful to Nick Alexander for his support throughout its production and to Briana Elwood for assistance with formatting and editing considerations.
We appreciate the assistance of Aubrey Chandica and Paul Martin with the provision of maps and gratefully
xiv
Introduction
flowing coastal rivers of Queensland and northern New South Wales, although the range of many extends westward across much of northern Australia and southward through coastal Victoria, South Australia and Tasmania.
North-eastern Australia contains the most diverse freshwater fish fauna in all of Australia, over 130 native species in about 30 families, approximately half of the fauna of the entire continent. This fauna includes some of the most ancient species in Australia – the Queensland lungfish, Neoceratodus forsteri, and the saratoga, Scleropages leichardti – as well as one of the most recently discovered Australian freshwater fish species, the Bloomfield River cod, Guyu wujalwujalensis, found far to the north of its nearest relatives, the cods and basses of south-eastern and south-western Australia. In addition to these freshwater fishes, the freshwater reaches of north-eastern Australian rivers support many species from otherwise marine or estuarine families, such as the Lutjanidae, Carangidae, Gerreidae, Scatophagidae, and even sharks and stingrays (Carcharhinidae and Dasyatidae, respectively). Unfortunately, five families (Belontiidae, Cichlidae, Cobitidae, Cyprinidae and Poeciliidae) and at least 23 species of alien fishes have been introduced into freshwater systems of north-eastern Australia, many of which have established self-sustaining populations, or may soon do so. Attempts to establish other families alien to the continent (e.g. Salmonidae) have so far failed in Queensland freshwaters. This book does not treat these two groups of species in any detail as there is very little information on the ecology of marine or estuarine vagrants in freshwaters, and in the case of alien species, major reviews of their distribution and ecology are currently being written by others. We are here primarily concerned with the native freshwater fishes occurring in easterly flowing drainages of the Australian drainage division known as the North-east Coast Division (Drainage I) as defined by the Queensland Department of Natural Resources, Mines and Energy (see Figure 1 in the section describing the study area). Species found only in rivers draining into the Gulf of Carpentaria and those occurring in Queensland sections of inland systems draining central and southern Australian (Lake Eyre, Bulloo-Bancannia and Murray-Darling drainage divisions) are not fully covered here. Our reasons for restricting the number of species covered are threefold: 1) the fauna of this drainage division is currently most at risk from human activities, 2) it is the fauna we know best and that which we have examined in detail or for which a substantial literature base exists, and 3) species omitted from this treatment are covered to lesser or greater extents in existing texts on Australian freshwater fishes. The 79 species covered in this book generally occur in easterly
The aim of this book is to provide information on the freshwater fish fauna of north-eastern Australia in a format that is rich in detail yet readily accessible to ecologists, ichthyologists, environmental managers and consultants, fishermen, hobbyists and the general public. Our treatment takes the reader on a journey – from a description of each species, and an account of its taxonomy, systematics and evolutionary history, biogeography, distribution patterns and abundance – to its macro-, meso- and microhabitat requirements, environmental tolerances, reproductive biology and development, movement biology and feeding ecology. We provide a pen and ink drawing of each species to illustrate characters for identification, an illustrated key to native and alien species and many figures and tables summarising detailed quantitative ecological information. Each chapter concludes with an account of the conservation status of the species, current threats, knowledge gaps and management issues. The increasing pace of development in north-eastern Australia, particularly agricultural and water resource development, currently places severe pressure on the region’s aquatic environment and biota, including fish. Although initiatives such as the Water Resource Planning process in Queensland, and the move towards regional Natural Resource Management Plans and conservation strategies, are intended to minimise the impacts of increasing development, these efforts are placing increasing demands on scientists and practitioners to provide high quality ecological assessments and technical advice. Managers, scientists and the public urgently need reliable quantitative information upon which to base conservation priorities, management strategies and monitoring protocols. Our coverage of the freshwater fish fauna of northeastern Australia is intended to support and strengthen these planning initiatives, to foster the application of scientific principles and sound ecological data in the management of Queensland aquatic ecosystems, and in consequence, to afford a high degree of protection to the region’s unique fish fauna. Several excellent books published in the last 25 years deal with the freshwater fish fauna of Australia (Merrick and Schmida (1984), Australian Freshwater Fish: Biology and
1
Freshwater Fishes of North-Eastern Australia
information they contain. All deal most comprehensively with the fauna of southern Australia, an emphasis reflecting the amount of information available at the time of production. Allen et al. (2002) [52] is a welcome and excellent addition particularly with regard to nomenclature, but its field guide format necessarily limits the amount of scientific detail on many topics needed for effective management of the fish of north-eastern Australia. The present treatment aims to complement these texts by providing reference material in a standard format that is both up-to-date and comprehensive, including published material (some dating back over 100 years but still relevant) and unpublished documents (government and consultancy reports, University theses) as well as the authors’ extensive published information and unpublished data sets.
Management [936]; Allen (1989), Freshwater Fishes of Australia [34]; and Allen et al. (2002), Field Guide to the Freshwater Fishes of Australia [52]). Other texts cover in varying detail the fauna of individual regions (Allen (1982), A Field Guide to the Inland Fishes of Western Australia [33]; Larson and Martin (1989), Freshwater Fishes of the Northern Territory [774]; Bishop et al. (2001), Ecological Studies on the Freshwater Fishes of the Alligator Rivers Region, Northern Territory: Autecology [193]; Herbert and Peeters (1995), Freshwater Fishes of Far North Queensland [569]; McDowall (1996), Freshwater Fishes of South-eastern Australia (2nd Ed.) [884]; Cadwallader and Backhouse (1983), A Guide to the Freshwater Fish of Victoria [270]; Koehn and O’Connor (1990), Biological Information for Management of Native Fish in Victoria [732]; Wager and Unmack (2000), Fishes of the Lake Eyre Catchment of Central Australia [1354]; Moffat and Voller (2002), Fish and Fish Habitat of the Queensland MurrayDarling Basin [959]), or selected components (Allen (1995), Rainbowfishes in Nature and in the Aquarium [38]).
We hope that this book will encourage greater research effort on the region’s fish fauna and provide a comprehensive information resource allowing other researchers to adopt a more quantitative and strategic framework for their research. We have endeavoured to identify knowledge gaps where they exist and suggest promising new avenues for research. We also hope that this book will have wide general interest and that readers will find this component of Australia’s unique fauna as interesting as we do.
Several books [34, 884, 936] have become the ‘standard’ reference texts for Australian freshwater fishes and essential research tools for many aquatic biologists, yet are now somewhat out of date, and limited in the amount of
2
Origins, structure and classification of fishes
The origin of fishes The bony fishes (Class Osteichthys) are the most successful and diverse group of vertebrates on Earth. Three major groups or subclasses make up the Osteichthys: the rayfinned fishes (Actinopterygii), the lungfishes (Dipnoi) and the predatory lobe-finned fishes (Crossopterygii). The Actinopterygii are the most speciose group of living fishes, containing more than 23 000 species, whereas the Dipnoi is restricted to four species in three genera: Lepidosiren from South America (1 species), Protopterus from Africa (2 species) and Neoceratodus from Australia (1 species). The subclass Crossopterygii is restricted to a single species Latimeria chalumnae, the coelocanth. (Some classification schemes group the Dipnoi and the Crossopterygii within a single subclass, the Sarcopterygii.)
and diversification during the Devonian period, similar to that observed in the Dipnoi and Crossopterygii. These early fishes, the palaeoniscoids, were characterised by a long slender body, a large mouth gape with many small teeth, small scales and a poorly ossified axial skeleton. By the end of the Devonian however, the mouth gape had shortened, the opercula bones had enlarged and the micromeric scales characteristic of early palaeoniscoids had been replaced by larger, rhombic scales. Over 40 separate families of palaeoniscoid fishes had evolved by the Permian period (250–290 m.y.b.p.). Actinopterygian evolution had given rise to the neopterygian fishes (to which belong the teleost fishes) by the end of the Permian. These fishes are characterised by a vertical suspensorium (where the lower jaws articulate with the upper jaws by a vertically oriented quadrate bone), free cheek bones, the condition where the dorsal and anal fin rays are supported by an equal number of small bones, fusion of the upper jaw bones along the midline and the development of pharyngeal tooth plates. The first teleostean fish evolved in the Triassic period (205–250 m.y.b.p.). These fishes are characterised by the presence of uroneurals (small bones that stiffen the dorsal lobe of the tail and support a series of dorsal fin rays), free movement of the premaxilla independent of the maxilla and development of unpaired toothplates on the basibranchials. These changes in jaw structure resulted in the evolution of a protrusible mouth, which when coupled with the previous change in the suspensorium, allowed huge diversification in feeding mode. Changes in fin structure (possession of rays and of uroneurals) greatly enhanced mobility and manoeuvrability. Thus, the stage was set for the explosive radiation evident in the extant teleost fishes. Many of the modern groups of teleost fishes, at the family level, had appeared by the Eocene period (45–57 m.y.b.p.) [820].
The evolutionary history of the bony fishes is described by John Long [820] and is very briefly summarised here. The origins of the Osteichthys date back to the Late Silurian (approximately 410 million years before present), a time when the seas were dominated by the Chondrichthyes (sharks and rays), Acanthodii (spiny-finned fishes) and especially Placodermi (armour-plated fishes). The Dipnoi originally arose in marine environments during the Devonian (355–410 m.y.b.p.), but have been confined to freshwaters since the early Carboniferous (~340 m.y.b.p.). The Dipnoi experienced a very rapid rate of evolutionary change during the Devonian and early Carboniferous periods, resulting in the evolution of many different species. During this period, there was a transition from gill-respiration to lung-assisted respiration and a transition from a shredding to a crushing feeding mode. In addition, there also occurred a change from the possession of two equallysized dorsal fins, separate anal fin and heterocercal caudal fin to the possession of a shortened first dorsal fin and merged second dorsal, caudal and anal fins (the condition observed today). Fossils of Neoceratodus forsteri, the Queensland lungfish, indicate that it has persisted in its present form for over 100 million years.
The origin of Australia’s freshwater fishes Australia’s freshwater fishes include both primary freshwater species (entire evolutionary history restricted to freshwater) and secondary freshwater species (freshwater forms secondarily derived from marine stocks). However, unlike other parts of the world, Australia has few primary freshwater fishes. These include N. forsteri, Scleropages jardinii, S. leichardti and Lepidogalaxias salamandroides, and possibly members of the Galaxiidae and Retropinnidae [888, 936]. These fish may have ancient Gondwanan origins. For example, fossils of Neoceratodus species have been found
The Crossopterygii also arose during the Devonian. This group of predatory fishes experienced rapid diversification during this period, especially during the Carboniferous, and persisted throughout the Mesozoic era (250–135 m.y.b.p.). Some crossopterygiian species reached an estimated size of 6–7m. The Actinopterygii (ray-finned fishes) first appear in the Late Silurian fossil record followed by significant radiation
3
Freshwater Fishes of North-Eastern Australia
in Cretaceous deposits in Australia and South America [52]. Similarly, the presence of bony-tongued fishes (Osteoglossidae, the saratogas) in South America, Africa, South-east Asia and Australia–New Guinea suggests that the origins of this family also predate the fragmentation of Gondwanaland [820]. Other families with a possible Gondwanan origin include the Retropinidae, Prototroctidae, Galaxiidae, Aplochitonidae and Percichthyidae [888, 936]. These families are predominantly restricted to the southern half of the Australian continent and are mostly inhabitants of cooler waters. The presence of the percichthyid Guyu wujalwujalensis, a possible Cretaceous relic [1091], in the Wet Tropics region, and of Macquaria species in the Fitzroy River basin and drainages of central Australia [52], suggests that these southern Gondwanan elements may have once been more widespread on the Australian continent.
with increasing latitude is less apparent, and spatial variation in species richness (at the basin level) is best explained by variation in the magnitude of mean annual discharge and seasonality/perenniality of the flow regime. More species occur in rivers with large mean annual discharge (which is not simply a function of catchment size) and less species occur in rivers with a highly seasonal flow regime [1093]. Second, Unmack [1340] observed that the extent of endemism (the unique occurrence of a species in a single region) varies across Australia, being greatest in western (east and west Kimberley, Pilbara and south-western Western Australia), southern (south-western Victoria and southern Tasmania) and central (Lake Eyre Basin and Murray-Darling Basin) regions. The only region east of these regions for which endemism is high is north-eastern Queensland, which includes the Wet Tropics region. Unmack’s analysis revealed a surprisingly high level of endemism in the fauna; 47% of the Australian fauna occurred in one region only. Third, classification analysis of regional variation in faunal composition divided the fauna into two major groups, basically equating to northern and southern Australia. The Fitzroy River south to the Queensland border was included in the southern group. The northern Australian group, excluding the arid central regions (Bulloo, Lake Eyre and Barkley Tablelands), divided into a cluster containing regions (Burdekin, north-eastern Queensland and southern Cape York Peninsula) located to the east of the Great Dividing Range and a larger cluster located to the west.
The majority of Australia’s freshwater fishes are secondary freshwater species derived from marine ancestors with tropical Indo-Pacific affinities [1409]. Some authors suggest that this component of the fauna is evolutionarily young and that colonisation of the Australian continent by marine ancestors probably occurred in the last 10 million years or so (a late Miocene origin at maximum) [52, 936, 1409]. However, others have suggested a more extended occupation of the Australian continent by some families. For example, Vari [1346] postulated that ancestral terapontid grunters may have populated the northern shores of the Gondwanan supercontinent. Crowley [343] suggested that freshwater invasion of Australian freshwaters by craterocephalid hardyheads occurred during the Cretaceous or Palaeocene (>60 million y.b.p.). Families typical of northern Australia and New Guinea such the Ariidae, Plotosidae, Terapontidae and Eleotridae have undergone substantial speciation in freshwater environments, yet elsewhere are almost entirely marine or estuarine. Freshwater habitats on the Australian continent have undergone enormous change during the period over which the teleost fishes arose, including several marine transgressions as well as changes in climate and periodic aridity. Undoubtedly such events have led to extinctions of freshwater fish species and opened the way for colonisation of freshwater habitats by estuarine fishes.
Unmack’s [1340] analysis of the biogeography of Australia’s freshwater fishes was restricted to freshwater fishes that complete their entire life history in freshwater (a definition more restricted than that used in this book). As a consequence, many diadromous species with an estuarine or marine interval in the life history, such as eels and many gudgeons or gobies, were not included. Their inclusion does not alter the broad outcomes of Unmack’s study however, except to perhaps emphasize the distinctiveness of those rivers draining east of the Great Dividing Range [1093]. Rivers of northern Australia tend to have more such species than do rivers of southern Australia. Moreover, a catadromous reproductive strategy (i.e. migration out of freshwaters to breed) is common in northern Australian fishes. Cappo et al. [278] suggested that the higher water temperatures of northern Australian rivers may confer a metabolic advantage to euryhaline species enabling more efficient osmoregulation. Gross et al. [481] examined global trends in diadromy and found catadromy to dominate in tropical regions and anadromy to dominate in temperate regions. They proposed such a pattern to be driven by latitudinal differences in the relative productivity of freshwater and marine habitats. In
Unmack [1340] recently examined the biogeography of Australia’s freshwater fishes and the major features of that analysis are summarised below. First, species richness decreases significantly with latitude, echoing a general global trend for greater freshwater fish diversity in tropical regions [1007, 1057]. In addition to this gradient, arid regions are less speciose. A more recent analysis of biogeographical patterns in north-eastern Australia by Pusey et al. [1093], revealed that the trend of decreasing diversity
4
Origins, structure and classification of fishes
SUPERORDER Acanthopterygii ORDER Perciformes SUBORDER Percoidei FAMILY Terapontidae GENUS Hephaestus SPECIES Hephaestus fuliginosus (Macleay, 1883)
tropical areas, the productivity of freshwater systems exceeds that of marine systems. The classification of fishes All living organisms are related to one another in some way, either closely as in the case of species within genera, or distantly as in the case of species within different phyla. Classification systems seek to organise a naming system that reflects this degree of relatedness. Ideally, such a system should reflect evolutionary history.
Some of these groups may be further subdivided. For example, the Cairns rainbowfish Cairnsichthys rhombosomoides is placed with the tribe or clade Bedotiini, within the subfamily Melanotaeniinae, within the family Melanotaeniidae. Subgenera may also be designated (e.g. the subgenus Chonophorus in the genus Awaous). Species may often be divided into subspecies (e.g. the various subspecies of Melanotaenia splendida such as Melanotaenia splendida splendida and Melanotaenia splendida inornata).
Classification systems have been in existence for millennia. The famous 19th century anatomist Georges Cuvier provides a fascinating account of the early development of fish classification from the time of the ancient Egyptians, to early Greek natural philosophers such as Aristotle, to the European naturalists of the 16th and 17th century such as Guillaume Rondelet and Hippolyte Salviani [354]. Indeed, natural classification schemes have probably existed since the development of human language and possibly reflected similarities in edibility, gross form and risk of injury to the hunter or gatherer. However, early classification schemes often poorly reflected the relationships between organisms. For example, the cetaceans (whales, dolphins etc.) were included with fishes in most classification systems well into the middle of the 17th century [354].
Note that in the sooty grunter example listed above, the species name is followed by the name of the authority that first described this species, and the date in which this occurred. In the case of H. fuliginosus, the name and date are enclosed within parentheses. This is a nomenclatural convention to denote that this species was first described under another name (Therapon fuliginosus) and that the present name was allocated following a revision of the species. The authority and date are not enclosed in parentheses when the original name stands unaltered.
Peter Artedi, a Swedish natural philospher of the early 18th century, attempted a consistent ichthyological classification scheme, building on the work of the English natural philosophers John Ray and Francis Willughby. Artedi’s scheme, based on the consistency of the skeleton, the opercula and the fin rays, was published in his 1738 treatise Ichthyologia, sive Opera omnia de piscibus (edited and published posthumously by his friend Carolus Linnaeus following Artedi’s death by drowning in an Amsterdam canal after a night of socialising at the age of 30). Linnaeus’s most significant achievement was to formalise a system of natural classification within a system of binomial nomenclature. In this system, closely related species were arranged within genera and closely related genera were arranged within families, and so on. It is a hierarchical system reflecting different degrees of relatedness and is the system we use today (with some modification and addition). Below is an example of a full classification for a common north-eastern Australian fish, the sooty grunter.
The freshwater fishes (including alien species) of northeastern Australia can be arranged in the following classification scheme (to family level only). This classification is based largely on that provided by Paxton and Eschmeyer [1041], and Long [820]. PHYLUM CHORDATA SUPERCLASS AGNATHA (JAWLESS FISHES) CLASS CEPHALASPIDOMORPHA Order Petromyzontiformes Mordaciidae (Shorthead lampreys) SUPERCLASS GNATHOSTOMATA (JAWED FISHES) CLASS OSTEICHTHYES (BONY FISHES) SUBCLASS DIPNOI Order Ceratodontiformes Ceratodontidae (lungfish) SUBCLASS ACTINOPTERYGII (RAY-FINNED FISHES) INFRACLASS NEOPTERYGII DIVISION TELEOSTEI Subdivision Osteoglossomorpha Order Osteoglossiformes Suborder Osteoglossoidei Osteoglossidae (saratoga) Subdivision Elopomorpha Order Elopiformes Megalopidae (tarpon)
PHYLUM Chordata SUBPHYLUM Gnathostomata CLASS Osteichthys SUBCLASS Actinopterygii INFRACLASS Neopterygii DIVISION Euteleostei
5
Freshwater Fishes of North-Eastern Australia
Eleotridae (gudgeons) Suborder Anabantoidei Belontiidae (gouramis – alien) Order Pleuronectiformes Suborder Soleoidei Soleidae (soles)
Order Angulliformes Suborder Saccopharyngidae Anguillidae (eels) Subdivision Clupeomorpha Order Clupeiformes Suborder Clupeoidei Clupeidae (herrings) Engraulididae (anchovies) Subdivision Euteleostei Order Cypriniformes Cyprinidae (carp – alien) Cobitidae (loaches – alien) Order Siluriformes Ariidae (fork-tailed catfishes) Plotosidae (eel-tailed catfishes) Order Salmoniformes Suborder Osmeroidei Retropinnidae (smelts) Galaxiidae (galaxiids) Order Cyprinodontiformes Suborder Cyprinodontoidei Poeciliidae (topminnows – alien) Order Beloniformes Suborder Exoceotoidei Hemiramphidae (halfbeaks) Belonidae (longtoms, needlefish) Order Atheriniformes Suborder Atherinoidei Atherinidae (hardyheads) Melanotaeniidae (rainbowfishes) Pseudomugilidae (blue-eyes) Order Synbranchiformes Synbranchidae (swamp eels) Order Scorpaeniformes Suborder Scorpaenoidei Scorpaenidae (stonefishes) Order Perciformes Suborder Percoidei Chandidae (glassfishes) Centropomidae (barramundi) Percichthyidae (bass, pygmy perch) Terapontidae (grunters) Kuhliidae (flagtails) Apogonidae (cardinal fishes) Toxotidae (archerfish) Kurtidae (nurseryfish) Cichlidae (tilapia – alien) Suborder Mugiloidei Mugilidae (mullet) Suborder Labroidei Cichlidae (tilapia – alien) Suborder Gobioidei Gobiidae (gobies)
Modern classification schemes strive to reflect the evolutionary history of a group rather than the overall gross similarity of taxa within a group. That is, they try to represent the phylogeny of that group. Therefore, species within a genus should be derived from a common ancestor and be more closely related to one another than to species in another genus. When species share a character that is derived (an apomorphic character) from a common ancestor, that character is said to be synapomorphic. Plesiomorphy, in contrast, refers to primitive characters. For example, in the terapontid grunters, the plesiomorphic condition of the gut is one of simple structure with no looping or coiling. The more derived condition is one in which the intestine is composed of more than one loop. Genera such as Hephaestus, Scortum, Pingalla and Syncomistes all share the synapomorphy of a gut possessed of at least six loops. Pingalla and Syncomistes both possess a gut composed of 11 loops. Thus, the derived or synapomorphic condition in these two genera is 11 loops whereas the plesiomorphic condition is six loops. Note that there are different levels of apomorphy. Every level of apomorphy defines the temporal order of modification occurring between the pre-existing (plesiomorphic) and emerging (apomorphic) characters of the transformation [868]. Although modern classification schemes strive to reflect the evolutionary history of a group, this is not always achieved. Occasionally a species, or number of species, is allocated to one genus by one researcher to be later found more closely allied to another genus. For example, many of the gudgeons of north-eastern Australia were first placed in the ‘catch-all’ genus Eleotris but were later found to be more properly placed within a larger number of genera. Such a generic grouping is therefore unnatural and does not accurately reflect the group’s evolutionary history. The genus is therefore termed paraphyletic. Modern classification schemes strive to arrange species or genera (or any level of classification) in monophyletic groups. Classification schemes are constantly being reviewed and changed as new evidence becomes available or when new evidence is inconsistent with current views. The introduction of modern genetic techniques such as DNA sequencing has been of special significance in this regard.
6
Origins, structure and classification of fishes
soft-rayed dorsal fin spinous dorsal fin (second dorsal) (first dorsal) dorsal spines dorsal scale sheath operculum soft ray dorsal filament posterior nostril adipose fin anterior nostril lateral line scales premaxilla caudal or tail fin
pectoral fin horizontal scale rows barbel
papilla maxilla
Figure 1.
pelvic fin ventral scutes genital papilla anal spines
caudal peduncle anal fin anal scale sheath
Basic external anatomy of a generalised bony fish.
Fish anatomy The classification of fishes is largely based on their anatomy. It is therefore necessary to have some understanding of the general anatomy and osteology of fishes in order to identify and classify them in the field or laboratory and to understand, in many cases, their ecology. Extreme diversity of form is a feature of the bony fishes more than any other vertebrate group and no description of a single species is adequate to convey all the morphological variation present within the group. Figure 1 illustrates the basic external morphology of a generalised bony fish.
gill rakers on upper limb gill rakers on lower limb gill filaments
The head region is clearly distinct from the body and distinguished by a bony gill covering termed the operculum. This structure covers the gill arches and gill filaments that function predominantly in gas exchange between the fish and its environment (Fig. 2). The gill arches are distinguished by a series of protrusions termed rakers on the anterior face of the arch. In some species, these rakers are long and flexible, in others they may be shortened and reduced to transverse plates or ridges, whereas in others they may be reduced to a series of papillae only. The gill rakers may function as sieving apparati in filter feeding species. Gill rakers may be confined to the first and second arches only and the shape and number are useful characters for distinguishing between different species.
Figure 2.
The structure of a gill arch of a bony fish.
located on the snout and are distinguished by reference to their relative anterior or posterior position. Sensory pores connected by canals may be present on the head of many fishes. Similarly, many fishes possess rows of sensory papillae or pit canal organs on the head, and these structures are usually located above and below the eyes, and on the cheek or preoperculum. Some fish possess barbels that aid in the detection of food. The number, length and position of the barbels are important characters used to distinguish between species. Barbel placement and nomenclature are shown in Figure 3.
The upper jaw is divided into two sections, the premaxilla and the maxilla (Figs. 1 and 7). Two pairs of nostrils are
7
Freshwater Fishes of North-Eastern Australia
V–VII; I, 11–15, indicating that this species possesses five to seven spines in the first dorsal fin and one spine and 11 to 15 soft rays in the second dorsal fin.
nasal barbel maxillary barbel
The anal fin is located on the ventral midline posterior of the anus. This fin may contain both spines and segmented rays. The final medial fin is the caudal or tailfin. Spines are absent from this fin and support is provided by a series of bones associated with the terminal vertebrae and by the fin rays (Fig. 4). The caudal fin may be of a variety of different shapes. The most frequent caudal fin shapes are illustrated in Figure 5.
inner mental barbel outer mental barbel
epurals (3) Figure 3. catfish.
procurrent rays
uroneurals (2)
Barbel placement and nomenclature in a plotosid
fin rays antepenultimate vertebra
The shape, position and orientation of the mouth are all useful characters for distinguishing between species. Position is most frequently described as terminal (end of the snout), supraterminal (upper surface of the end of the snout) or subterminal (lower surface of the end of the snout), often accompanied by descriptions of the angle of the gape (i.e. straight or oblique). In addition, the relative prominence of the upper and lower jaws is frequently used as a distinguishing character.
penultimate vertebra urostyle (ultimate vertebra)
hypurals (6)
Figure 4. Generalised diagram of the teleost caudal skeleton. (Redrawn after Cailliett et al. [276].)
Two sets of paired fins, the pelvic and pectoral fins, are present in most species. The pectoral fins are located in the anterior third of the body whereas the location of the pelvic fins may vary in position among species (and may often be an important diagnostic character) but invariably they are located in the anterior two-thirds of the body. These paired fins possess bony segmented fin rays. In many taxa, the first ray of the pelvic fin forms a thickened spine. Three to four medial rayed fins are also present. The first and second dorsal fins are located, as the name suggests, on the midline of the dorsal surface. A second dorsal fin is not present in some groups of fishes and, in some groups, the first dorsal fin is deeply notched to give the impression of two dorsal fins. A third fleshy adipose fin may be present in some species. The first dorsal fin is usually supported by a series of spines whereas the second dorsal fin may contain both spines and segmented rays. In the second dorsal, pectoral, pelvic and anal fins of some species (e.g. Craterocephalus spp.), a single unsegmented ray sometimes separates the fin spine and the segmented rays. The unsegmented ray is counted together with the segmented rays in this book. In taxonomic descriptions, counts of the number of spines present are usually distinguished from fin ray counts by the use of Roman numerals to denote spines. For example, the dorsal fin formula for the Cairns rainbowfish Cairnsichthys rhombosomoides is
a
b
c
d
Figure 5. Common shapes of the caudal fin: a) rounded; b) truncated; c) emarginate; d) forked.
8
Origins, structure and classification of fishes
actually exposed. In some species, the scales may extend out as a sheath onto the dorsal and anal fins (Fig. 1). There are two main types of scale: cycloid and ctenoid (Fig. 6). Another common type of scale is termed the lateral line scale. These scales have a small tube or canal on the surface that allows water to flow through to the lateral line sensory system. The number, position and type of lateral line scales are important characters for distinguishing between species. A fourth type of scale, the ganoid scale, which is rhombic in shape, is present in some primitive teleosts such as gars and sturgeons. As fish grow, the scales also grow by increments of bony tissue. Daily increments (circuli) are wide during periods of rapid growth and narrow during periods of slow growth. Successive periods of slow growth result in the narrow circuli being located in close proximity to form a growth ring or annulus. These periods of slow growth usually occur with a return frequency of one year, hence the term annuli, and can thus be used to age fish.
The external surface of many fishes is covered by a layer of scales, each deeply embedded in the epidermis and overlapping one another so that only about 30% of the scale is
a
circuli annulus focus ctenii
b focus
Fish osteology The principal components of the teleost skeleton are the axial vertebral column and caudal fin, the head (consisting of the cranium, upper and lower jaws and the gill coverings, which are comprised of the opercular bone series, preopercular and branchiostegal rays), the paired pectoral and pelvic fins, and the medial dorsal and anal fins (Fig. 7).
Radii Figure 6.
Teleost fish scales: a) cylocid; b) ctenoid.
lepidotrichia pterygiophore vertebra
neural spine hypurals
pectoral fin opercula bones preoperculum cranium premaxila
dentary maxilla
branchiostegal rays pectoral girdle
Figure 7.
haemal spine pleural rib pelvic girdle pelvic fin
Skeleton of a generalised perciform teleost fish. (Redrawn after Norman [996].)
9
Freshwater Fishes of North-Eastern Australia
small part, to successive changes in the structure of the suspensorium and separation of the previously fused maxilla and premaxilla, coupled with changes in the attachment points of the respective muscles [276].
The head is composed of many individual bones, either fused to one another, or free (although connected by cartilage) and articulating against one another (Fig. 8). The head can be divided into two separate components based roughly on this distinction [276]. The skull is comprised of the neurocranium (10–11 bones), the orbital region (19 bones, including the lachrymal), and the otic region (20 bones). These bones unite to form a solid housing to contain the brain and associated sensory systems (i.e. optic, olfactory and auditory systems), and the roof of the upper jaw, as well as a point of attachment and articulation for many of the bones within the branchiocranial series.
Finally, the last bony component of the branchiocranial region is the opercular series. This series is comprised of the operculum (large flat bones comprising most of the gill cover), the interoperculum, and the suboperculum and preoperculum (a large pair of bones anterior of the opercular bones that partially cover the hyomandubular and carry elements of the lateral line canal). The second major region of the branchiocranium is the hyoid region, comprised of the unpaired glossohyal and urohyal bones, the paired interhyals. epihyals and ceratohyal bones and the branchiostegal rays. These bones collectively comprise the back of the buccal cavity and the points of attachment of the gill arches. Each gill arch is comprised of five bones, the pharyngobranchial, epibranchial, ceratobranchial, hypobranchial and basibranchial, and collectively these arches form the third and final region, the branchial series.
The branchiocranial series is composed of over 60 separate bones organised into three distinct regions: the oromandibular region, the hyoid region and the branchial series. The oromandibular region is comprised of the upper jaw, the lower jaw, the suspensorium and the opercular series. The 36 bones that comprise this region are all paired (i.e. 18 pairs). The lower jaw is composed of two large pairs of fused bones, the dentary and the angular (or articular), a third pair of much smaller bones termed the retroangulars, and a fourth pair of bones termed the sesamoid angulars which are involved in the attachment of the mandibular adductor muscles responsible for mouth closure. The shape, size and orientation of these bones are often useful in the identification of different species or reveal the phylogenetic relationships between taxa. hyomandibular parietal parasphenoid sphenoid endopterygoid frontal nasal
There are several bones in the teleost skull that may bear teeth (Fig. 9). The structure, size, type, position and arrangement of teeth are all important characters used to distinguish between different species.
a supraoccipital exoccipital
premaxillary maxillary vomerine
post temporal
palatine
lachrymal premaxilla
pharyngeal mesopterygoidal operculum
dentary maxilla
first gill arch
suboperculum articular quadrate circumorbital
interoperculum preoperculum metapterygoid
b dentary
Figure 8. Superficial facial bones and suspensorium of a generalised teleost fish. Note that many of the bones mentioned in the text are covered or obscured by the superficial bones depicted here. (Redrawn after Calliette et al. [276] and Hildebrand [575].)
tongue pharyngeal basibranchial (hyoid)
The lower jaw articulates against the suspensorium, a series of pairs of bones comprised of the palatines, endopterygoids, metapterygoids, ectopterygoids, quadrates, symplectics and hyomandibulars. The phenomenal diversity and success of the teleost fishes is due, in no
Figure 9. Bones within the mouth or buccal cavity that may bear teeth in bony fishes: a) upper jaw, b) lower jaw. (Redrawn after Calliette [276].)
10
Origins, structure and classification of fishes
groups of fishes (e.g. synbranchid eels and percichthyid perches, respectively). Pterygiophores form the base of the two medial fins. They are imbedded in the epaxial (dorsolateral) and hypaxial (ventrolateral) musculature. At the proximal end of each pterygiophore is a small bone termed the basal against which the fin ray articulates. Each fin ray is controlled by three similar sets of muscles, the erector, depressor and inclinators, which control forward, backward and lateral movement, respectively. The caudal fin is composed of modified terminal and preterminal vertebrae, which support and strengthen the caudal fin (Fig. 4). In many teleosts, the urostyle (the terminal segment of the vertebral column) is comprised of the last two vertebrae fused into a single element. Modified neural spines and neural arches form plates termed the epurals and uroneurals, respectively, which when coupled with the modified haemal arches known as the hypurals, form a strong yet flexible base for the caudal fin rays.
The paired medial fins are part of two separate series of bones known as the pectoral and pelvic girdles. These structures form the point of attachment and articulation of the fins and the associated fin rays. The term girdle is most appropriate for the pectoral girdle as it almost encircles the entire body just behind the opercula. This series of bones is connected to the neurocranium by the posttemporal bone at attachment points on the epiotic and oposthotic bones [276] (Figs. 8 and 10). The nature of the posttemporal bone is important in the identification of different genera of terapontid grunter and the structure of the entire girdle is important in the systematics of the percichthyids (cods, bass and pygmy perches). The simpler pelvic girdle is inserted under the pectoral girdle and consists of a pair of plates called basipterygia to which the fin rays and pelvic spines (when present) attach and articulate.
Meristic and morphometric characters In addition to characters associated with skeletal anatomy, many systematic studies use a combination of meristic and morphometric characters to distinguish between species. Meristic characters include such characters as the number of fin spines and rays, number of gill rakers, number of lateral line scales, vertical scale rows, number of cheek scales. Note that these characters are all expressed as counts.
post temporal supracleithrum
cleithrum
Morphometric characters, in contrast, describe the condition or size of certain characters. For example, the size of the head or of the eye, or the distance between the snout and the start of the first dorsal fin (predorsal length) are all morphometric characters. Figure 11 depicts many useful and frequently used morphometric characters. Most morphometric characters vary in size with increasing fish size, therefore they need to be standardised in some manner so that comparisons may be made between specimens of differing size. The most frequent mechanism for standardising morphometric characters is to describe them as a proportion of fish length, usually standard length (the distance from the tip of the snout to the hypural crease). Another frequently used denominator is head length: thus it is not uncommon to see characters such as mouth gape or maxilla length expressed as a proportion of head length. In this way, the size of any particular character may be reasonably compared across fish of different size. Calliette et al. [276] provide a useful discussion of the issues associated with standardisation of morphometric characters.
scapula actinosts
coracoid Figure 10. The pectoral girdle of the percichthyid Guyu wujalwujalensis. (Redrawn after Pusey et al. [1091].)
The axial skeleton (which technically includes the skull) contains two types of vertebra. The precaudal vertebrae of the abdominal region bear ribs, intermuscular bones and neural spines but not haemal spines (Fig. 7). The caudal vertebrae bear few ribs and have prominent neural as well as haemal spines. The absolute number of caudal and precaudal vertebrae and the relative number of these bones are both important characters in the systematics of some
Standardisation by dividing by standard length or head length assumes that the relative size of a character remains constant with varying size of the fish. This is not always the
11
Freshwater Fishes of North-Eastern Australia
series of steps, to a final identification of an unknown fish. The key is based to a large extent on characters that do not require the use of a microscope or dissection to discern (i.e. number of gill rakers or vertebrae), however such characters are sometimes the most useful for separating species and their use is therefore unavoidable. Furthermore, small-bodied species cannot be examined with great accuracy unless a microscope or magnifying glass is used. We recommend that this key be used as a guide only, and that tentative identifications derived from it, be checked against the comprehensive description provided for the relevant species or sent to a relevant taxonomic expert at a museum.
case. For example, in a study examining the distribution of the rainbowfish Melanotaenia eachamensis in the Wet Tropics region of northern Queensland, Pusey et al. [1105] compared the meristics and morphometrics of many populations of rainbowfishes with those of known populations of M. eachamensis and M. splendida splendida. Very few morphometric characters were found to remain invariate with increasing size: predorsal length, body depth, snout length, and peduncle depth were the only characters to satisfy this criterion. Other characters: head length, head depth, eye diameter, mouth length and peduncle length, all varied with length in an exponential fashion, with an exponent less than one. Thus these characters were all relatively greater in smaller individuals than in larger individuals. In such cases, better standardisation may be achieved by dividing by standard length raised to the power best describing the relationship between that character and standard length.
The species covered in this key include both native and alien species (non-native, introduced from other countries) found in north-eastern Australia. The key contains some species not covered in depth in this book but which may be encountered in rivers of north-eastern Australia. Some species found occasionally in easterly flowing streams of Cape York Peninsula are more properly considered fauna of drainages discharging into the Gulf of Carpentaria, west of the Great Dividing Range; these species are not covered in this book other than inclusion in this key. When in doubt about a species’ identification, consult widely and use the services of museum specialists. The systematics of many groups of fishes is often in flux
Identification of the freshwater fishes of north-eastern Australia The identification of fishes can be a difficult task for the non-specialist and specialist alike. We have included a dichotomous key to aid in the identification of different fishes in the field and laboratory. A dichotomous key is basically a set of either/or questions that should lead, by a
total length caudal fork length standard length
snout length
body depth
caudal peduncle length
predorsal length head length
caudal peduncle depth
head depth
eye diameter maxilla length Figure 11.
Commonly used morphometric characters. (Redrawn after Pusey et al. [1105].)
12
Origins, structure and classification of fishes
have used generic or family level reviews. Figures 21, 22, 23, 24 were redrawn after Allen [34] and Figures 38, 39, 41, 42 were redrawn after Allen and Cross [43]. In those cases where undescribed species have been assigned species numbers, we have retained the numbering system presented in Allen et al. [52].
and the use of varied information sources is prudent. The use of limited or out-of-date systematic resources too often leads to circumstances where identification and distributional information become less than useful. Ideally, fish ecologists, aquatic biologists and consultants should try to keep abreast of changes in the systematics of freshwater fishes. The key included below is based on a number of different sources [34, 37, 43, 47, 773, 1346] but where possible we
13
Freshwater Fishes of North-Eastern Australia
Key to the native and alien fishes of north-eastern Australia (alien species are denoted by *)
1a 1b 2a 2b 3a
3b
4a 4b
5a 5b 6a 6b 7a
Body elongated and eel-like........................................................................2 Body not elongated and eel-like .................................................................4 Barbels present (alien)..................................................................Cobitidae Misgurnus anguillicaudatus* Barbels absent..............................................................................................3 Pectoral fins absent ..............................................................Synbranchidae Aa Gill opening a slit-like fold across ventral surface of head, not attached to isthmus...........................................................................B Ab Gill opening pore-like, triangular shaped, and internally attached to the isthmus .........................................................Monopterus albus Ba Colour blackish-green to reddish-brown; mottled; eye positioned forward of the middle of the distance between end of mouth and snout tip (note that there may be a number of undescribed species of Ophisternon present in freshwaters of Queensland and the species referred to as O. bengalense may not occur in Australia) .......................................................................Ophisternon bengalense Bb Colour brown to green; ventral surface lighter in colour; eye positioned posteriorly of the middle of the distance between end of the mouth and snout tip........................................Ophisternon gutturale Pectoral fins present...................................................................Anguillidae Aa Colouration mottled, dorsal fin originating well in front of vertical line through line anus (Fig. 1) ............................Anguilla reinhardtii Ab Colouration uniform, dorsal fin originating only slightly in front of anus (Fig. 2).......................................................................................B Ba Jaws reaching back to eye or slightly beyond, vomerine tooth patch broad, distribution does not extend north of the Burnett River ............................................................................................A. australis Bb Jaws reaching well beyond eye, vomerine tooth patch long and narrow, distribution does not extend far south of the Pioneer River .............................................................................................A. obscura Eyes not on the same side of head; body not greatly flattened ................5 Eyes on same side of head, body flattened .....................................Soleidae Aa Dorsal rays 66–78; caudal rays 16; anal rays 53–59; caudal fin narrow and pointed; lateral line scales 84–97 ...Brachirus salinarum Ab Dorsal rays 70–75; caudal rays 18–20; anal rays 55–60; caudal fin rounded; lateral line scales 77–81 .....................................B. selheimi Pectoral and pelvic fins thick and flipperlike (Fig. 3) .......Ceratodontidae Neoceratodus forsteri Pectoral fins not thick, fleshy and flipperlike, fin rays easily visible (Fig. 4)..........................................................................................................6 Barbels present on lower jaw, may or may not be present on upper jaw (Figs. 5 and 6) ..............................................................................................7 Barbels absent from lower jaw, but single pair of barbels may be present on upper jaw ............................................................................................... 9 Barbels short and paired (Fig. 5).........................................Osteoglossidae Aa Dorsal rays 20–24; anal rays 28–32......................Scleropages jardinii Ab Dorsal rays 15–19; anal rays 25–27 (Fitzroy River system only unless translocated)..........................................................S. leichardti 14
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Key to native and alien fishes of north-eastern Australia
7b 8a
8b
Barbels long, 3 or 4 pairs (Fig. 6)................................................................8 Barbels in 4 pairs; dorsal, anal and caudal fins fused to form one continuous pointed fin...........................................................................Plotosidae Aa Second dorsal fin originating either just anterior to or posterior to vertical line through anus (Fig. 7)....................................................B Ab Second dorsal fin originating well posterior to vertical line through anus (Fig. 8) ......................................................................................C Ba Jaws without teeth.............................................Anodontoglanis dahli Bb Jaws with teeth.....................................................Tandanus tandanus Ca Dorsal profile of head frequently concave; eyes relatively low set on side of head; tail more or less pointed; few dorsal rays in fused fin ......................................................................................................D Cb Dorsal profile of head straight or slightly convex; eyes set in higher position approaching dorsal profile; tail more rounded and extending relatively further onto dorsal profile ..........................................F Da Lateral line discontinuous .......................................Porochilus obbesi Db Lateral line continuous .....................................................................E Ea Dorsal fin with sharp spine and 4 soft rays; pectoral fin with sharp spine and 7 soft rays .........................................................P. argenteus Eb Dorsal fine with spine and 5–7 soft rays; pectoral fin with sharp spine and 9–11 soft rays.....................................................P. rendahli Fa Dorsal fin tall; dorsal spine reduced to flexible cartilaginous ray (Fig. 9) ........................................................Neosilurus mollespiculum Fb Dorsal fin short or moderately elongated; dorsal spine rigid (Fig. 10).............................................................................................G Ga Dorsal fin short; nasal barbels extending back beyond eye .....................................................................................N. brevidorsalis Gb Dorsal fin moderately elongated; nasal barbels not extending back beyond eye ........................................................................................H Ha Confluent dorsal, anal and caudal fin comprised of 120–160 rays; dorsal fin with 5–7 soft rays; pectoral fin with 11–13 rays; snout elongated...................................................................................N. ater Hb Confluent fins comprised of 115–135 rays; dorsal fin with 5–6 soft rays; pectoral fins with 10–11 rays; snout not elongated ...N. hyrtlii Barbels arranged in 3 pairs...............................................................Ariidae Aa Raker-like processes present on back of all gill arches ....................B Ab No raker-like process on back of first 2 gill arches .........................C Ba Barbels long (30–47% of SL); palatal tooth patches arrayed as in Fig. 11, vomerine and palatine patches in inner row separate in smaller specimens ..........................................................Arius berneyi Bb Barbels short (17–40% of SL); palatal tooth patches arrayed as in Fig. 12...................................................................................A. graeffei Ca Head broad; snout well rounded to squarish; maxillary barbels long (22.7–50% of SL); inner row of palatal tooth patch consisting of united palatine and vomerine patches as in Fig. 14.........A. leptaspis Cb Head rectangular; snout squarish or truncate; maxillary barbels short (16.6–24% of SL); inner row of palatal tooth patches composed of four separate patches as in Fig. 13.............................D Da Gill rakers on first arch 15–17, 16–19 on last arch, eye relatively large, 12.9–21.8% of HL ...................................................A. midgleyi Db Gill rakers on first arch 10–11, 11–14 on last arch, eye relatively small, 8.9–15.3% of HL .......................................................A. paucus
15
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Freshwater Fishes of North-Eastern Australia
9a 9b 10a 10b 11a
11b
12a
12b 13a 13b 14a
14b
15a 15b 16a 16b 17a 17b 18a
18b 19a
Single dorsal fin (Fig. 15), but may be notched to give the appearance of two separate fins (Fig. 16).........................................................................10 Two separate dorsal fins (Fig. 17).............................................................25 Mouth very small, oblique ........................................................................11 Mouth not very small and oblique or if small, head with short beak ....12 Lateral line present and curved, male anal fin not modified, oviparous (alien) .........................................................................................Belontiidae Trichogaster trichopterus* Lateral line absent, male anal fin modified to form intromittent organ (gonopodium), viviparous (live-bearing) (alien) .....................Poeciliidae Aa Body deep, 50% of SL, prominent dark blotch at base of caudal fin, body colour blue..........................................Xiphophorus maculatus* Ab Body not noticeably deep, <50% of SL (except perhaps in pregnant females), prominent caudal spot absent ..........................................B Ba Dorsal spine present, anal spine present, dorsal fin originating behind anal fin ..................................................Gambusia holbrooki* Bb Dorsal spine absent, anal spine absent, dorsal fin originating in front of anal fin.................................................................................C Ca Dorsal fin rays 7–8, caudal fin not elongated to form sword............ Poecilia reticulata* Cb Dorsal fin rays 11–14, ventral rays of caudal fin elongated to form sword ..................................................................Xiphophorus helleri* Ventral midline of breast or abdomen with series of serrations (skutes) .......................................................................................................Clupeidae Nematalosa erebi Ventral midline of breast or abdomen without series of serrations .......13 Either or both upper or lower jaw elongated to form beak-like structure.....................................................................................................14 Jaws not elongated to form beak-like structure.......................................15 Upper and lower jaws elongate (Fig. 18); well toothed; some teeth enlarged and needle-like ..............................................................Belonidae Strongylura krefftii Lower jaw elongate (Fig. 19); teeth small, granular or cardiform ............................................................................................Hemiramphidae Arramphus sclerolepis Dorsal fin without spines..........................................................................16 Dorsal fin with spines ...............................................................................17 Adipose fin present (may be very small) .............................Retropinnidae Retropinna semoni Adipose fin absent ...................................................................Megalopidae Megalops cyprinoides Single dorsal fin without notch ................................................................18 Single dorsal fin notched to give impression of two fins ........................20 Dorsal fin with more than 10 spines (alien) ................................Cichlidae Aa Dorsal rays 12–15, anal rays 10–12, lateral line scales 28–30, snout blunt ...........................................................................Tilapia mariae* Ab Dorsal rays 10–12, anal rays 9–10, lateral line scales 29–33, snout elongated and pointed ............................Oreochromis mossambicus* Dorsal fin with less than 10 spines ...........................................................19 Body rhombiform, dorsal fin roughly equal in size to anal fin, insertion point of dorsal fin level with anal fin...........................................Toxotidae Aa 5 or 6 (usually 5) dorsal spines ...............................Toxotes chatereus
16
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Key to native and alien fishes of north-eastern Australia
Ab
19b
20a 20b 21a
21b
4 dorsal spines; predominantly marine or estuarine ........................ .................................................................................Toxotes jaculatrix Body not rhombiform, dorsal fin longer than anal fin and inserted well forward of anal fin (alien)..........................................................Cyprinidae Aa Barbels present on upper jaw ..................................Cyprinus carpio* Ab Barbels absent on upper jaw.................................Carassius auratus* Head with conspicuous spines .................................................................21 Head without conspicuous spines............................................................22 Moderate size (10–20 cm), never transparent, mottled brown/black colour, more than 10 spines in dorsal fin .............................Scorpaenidae Notesthes robusta Small size (<10 cm); generally transparent or silver in colour; less than 10 spines in dorsal fin ......................................................................Chandidae Aa Gill rakers reduced to rudimentary stumps, about 7–9 on lower limb of first gill arch; enlarged and conspicuous pores on preorbital ...............................................................................Denariusa bandata Ab Gill rakers well developed, 15 or more on lower limb of first gill arch (including raker at angle); pores on preorbital, supraorbital and preopercular bones not conspicuous........................................B Ba Supraorbital spines usually 3–5 (rarely 2); nasal spine well developed ..........................................................................................C Bb Usually a single supraorbital spine (Fig. 20); nasal spine either well developed or absent ..........................................................................E Ca Hind margin of preoperculum with about 6–13 small serrae (mostly estuarine) ...................................................Ambassis vachelli Cb Hind margin of preoperculum usually smooth or weakly crenulate without distinct serrae .....................................................................D Da Soft anal rays usually 10, rarely 11; predorsal scales 16–18; eye relatively small, 10.7–12.7% of SL; caudal peduncle relatively short (16.1–20.8% of SL) and deep (14.4–16.3% of SL) ........A. marianus Db Soft anal rays usually 9; predorsal scales 11–14; eye larger, 13.0–13.9%; caudal peduncle more longer (20.6–22.2% of SL) and more slender (13.0–14.8% of SL) (mostly estuarine) .................................................................................A. gymnocephalus Ea Lateral line continuous from upper edge of gill opening to caudal fin base; predorsal scales 12–15; horizontal scale rows from anal fin origin to base of dorsal fin 9 or 10; second dorsal spine slightly less than or equal to third dorsal spine .......................................A. miops Eb Lateral line either terminating on anterior portion of body or interrupted in middle section...................................................................F Fa Nasal spine present; lateral line always well developed consisting of 8–13 tubed scales in anterior section and 9–14 in posterior section (mostly estuarine).........................................................A. interruptus Fb Nasal spine usually absent; lateral line often poorly developed consisting of 9–14 tubed scales in anterior section and 0–15 tubed or pitted scales in posterior section .................................................G Ga Rakers on lower limb of first gill arch 24–29; dorsal and anal soft rays usually 10 (occasionally 9 or 11); pectoral rays 14–15; base of pectoral fin frequently blackish…..….…………...……A. macleayi Gb Rakers on lower limb of first gill arch 15–20; dorsal and anal soft rays usually 8 –9 (rarely 7 or 10); pectoral rays 11–14; base of pectoral fin pale................................................................................H
17
Figure 20
Freshwater Fishes of North-Eastern Australia
Ha
22a
22b 23a 23b 24a
24b
Scales in longitudinal series from upper edge of gill opening to caudal fin base 28–34; spinous dorsal fin relatively tall, 29.1–41.8% of SL, usually >33%.…………………………………A. agrammus Hb Scales in longitudinal series from upper edge of gill opening to caudal fin base 24–26 (rarely 27); spinous dorsal fin usually shorter, 18.4–36.8% of SL, usually <33%….………..……………………I Ia Circumpeduncular scales usually 16, occasionally 15; height of spinous dorsal fin 24.0–36.8% of SL, mean 28.5% .......Ambassis sp. (formerly A. muelleri) Ib Circumpeduncular scales usually 14 or less; height of spinous dorsal fin 18.4–27.6% of SL, mean 23.8 ...........................A. agassizii Pelvic fin base in front, directly below, or immediately behind pectoral fin base (Fig. 21).........................................................................Percichthyidae Aa Small bodied (<7 cm); pelvic fins without extended filaments ........ Nannoperca oxleyana Ab Moderate to large bodied, pelvic fins with extended filaments ......B Ba Head broad and jaw depressed; no conspicuous open pores on lower jaw; naturally confined to the Mary River but widely translocated ...................................................Maccullochella peelii mariensis Bb Head deep and laterally compressed; lower jaw with or without conspicuous pores ...........................................................................C Ca Conspicuous pores on lower jaw absent......Macquaria novemaculeata Cb Conspicuous pores on lower jaw present........................................D Da Suboperculum and cleithrum without serrations; opercula spines without serrations; natural Queensland distribution restricted to the Fitzroy River and drainages of central Australia (extensive translocation into other drainages has occurred and central Australian population probably distinct species) ............................ .............................................................................Macquaria ambigua Db Suboperculum and cleithrum with serrations; opercula spines serrate; restricted to the Bloomfield River......Guyu wujalwujalensis Pelvic fin origin well behind pectoral fin base (Fig. 22)..........................23 Lateral line extends onto caudal fin...................................Centropomidae Lates calcarifer Lateral line does not extend onto caudal fin............................................24 Dorsal spines 10; mouth large extending to below eye ...............Kuhliidae Aa Maxilla reaching back to middle of eye; 9–10 soft anal rays; caudal only slightly emarginate; caudal pigmentation generally restricted to two dark blotches ..................................................Kuhlia rupestris Ab Maxilla not reaching back to middle of eye; 11–12 soft anal rays; caudal deeply emarginate, almost forked; caudal often entirely darkly pigmented ...........................................................K. marginata Dorsal spines 11 or more; mouth small to moderate in size, not reaching back to eye; caudal fin without blotches except in estuarine forms .................................................................................................Terapontidae Aa Post temporal bone covered with skin and scales, not expanded posteriorly and without serrated edge (Fig. 23) ..............................B Ab Post temporal bone exposed posteriorly, expanded and serrate posteriorly (Fig. 24) ..........................................................................E Ba Lateral line scales 55–62; limited to the Mitchell River .............................................................................Variichthys lacustris Bb Lateral line scales usually <55; widespread .....................................C Ca Body with 5–6 vertical black bars .....................Amniataba percoides
18
Figure 21
Figure 22
Figure 23
Figure 24
Key to native and alien fishes of north-eastern Australia
Cb Da
Body without vertical black bars .....................................................D Caudal fin with broad oblique black stripe across each lobe (estuarine) ...................................................Amniataba caudivittatus Db Caudal fin without black stripe...................Leiopotherapon unicolor Ea Lower opercula spine greatly developed, extending beyond edge of operculum (Fig. 25); caudal fin lobes with oblique dark stripes (estuarine) ................................................................Therapon jarbua Eb Lower opercula spine smaller, not extending beyond edge of operculum, caudal fin lobes without oblique stripes..............................F Fa Teeth flattened, strongly depressible................................................G Fb Teeth conical, nondepressible or only slightly depressible..............L Ga Body not noticeably elongate, head not noticeably small; predorsal scales <20..........................................................................................H Gb Elongate body; elongate caudal peduncle; head small; predorsal scales 20–25.......................................................................................K Ha Limited to easterly flowing drainages ...............................................I Hb Not occurring naturally in easterly flowing drainages.....................J Ia Lateral line scales 49–53; horizontal scale rows above lateral line 8–10; predorsal scales 16–20; check scales in 4–6 rows; confined to the Burdekin River.................................................Scortum parviceps Ib Lateral line scales 52–61; horizontal scale rows above lateral line 11–13; predorsal scales 14–18; check scales in 5–6 rows; confined to the Fitzroy River and possibly the Burdekin River also ........S. hillii Ja Body relatively deep, 43.5–47.6% of SL; limited to central Australian drainages .............................................................S. barcoo Jb Body relatively slender, 35.7–42.7% of SL; limited to Gulf of Carpentaria drainages ..........................................................S. ogilbyi Ka Lateral line scales 49–56; confined to Lake Eyre and Bulloo drainages....................................................................Bidyanus welchi Kb Lateral line scales 55–62; naturally limited to Murray-Darling Basin but widely translocated in Queensland ...............Bidyanus bidyanus La Medium sized grunter with vivid gold and black barring; generally limited to western drainages but also present in small number of eastern drainages of Cape York Peninsula; lateral line scales 52–60 ..................................................................................Hephaestus carbo Lb Large grunter with generally uniform colour; lateral line scales 43–52 ................................................................................................M Ma Pectoral fin base without dark band; pelvic fins reach back to anus when depressed; lateral line scales 46–52; confined to the Wet Tropics region...................................................................H. tulliensis Mb Pectoral fin base with dark band; pelvic fins do not reach back to anus when depressed; lateral line scales 43–51; widespread ........................................................................................H. fuliginosus 25a Pelvic fins inserted well behind level of pectoral fin base .......................26 25b Pelvic fins inserted approximately level or forward of pectoral fin base29 26a Three anal fin spines ....................................................................Mugilidae (Note – most mullet are estuarine species and this key allows identification to species level for those species commonly encountered in freshwater only, otherwise identification is to genus only) Aa Rear tip of maxilla not curved down below tip of premaxilla (Fig. 26) ................................................................................Mugil cephalus Ab Rear tip of maxilla curved down below tip of premaxilla (Fig. 27) ..B Ba Teeth present on vomer and palatines ........................Myxus petardi
19
Figure 25
Figure 26 Figure 27
Freshwater Fishes of North-Eastern Australia
Bb Ca
26b 27a
27b 28a
28b
Teeth not present on vomer and palatines ......................................C Scales cycloid, hind margin with digitations; rear tip of maxilla hidden when mouth closed................................................Valamugil Cb Scales cycloid or ctenoid, but without digitations on hind margin; rear tip of maxilla apparent when mouth closed........................Liza Anal fin with 1 spine .................................................................................27 Innermost pelvic fin ray not attached to belly by membrane; scales present on belly between pelvic fin attachment and anus (Fig. 28) ....................................................................................................Atherinidae Aa Vertical scale rows 27–30..........................Craterocephalus marjoriae Ab Vertical scale rows 32–35 ....................................C. stercusmuscarum (Note – this species is suggested to be composed of two subspecies defined primarily by distribution and that an undescribed species, growing to larger size than the nominal form, exists in the upper reaches of the North Johnstone and Barron rivers) Innermost pelvic fin ray attached to belly by membrane (Fig. 29; scales absent on belly between pelvic fin base and anus....................................28 Total anal fin rays usually 9–13; rigid fin spines absent; anal fin origin in posterior half of body (by SL) .........................................Pseudomugilidae Aa Body and median fins covered with small black dots; dorsal fin origin about ? eye diameter anterior to level of anal fin origin .........................................................................Pseudomugil gertrudae Ab Body and fins without small black dots; dorsal fin origin nearly full eye diamater anterior to anal fin origin ...........................................B Ba Rays in second dorsal fin usually 6 or 7; rays in anal fin 7–10 usually 9; origin of second dorsal fin about level with third or fourth anal ray.........................................................................................P. tenellus Bb Rays in second dorsal fin 7–11, usually 7 or 9; rays in anal fin 10–13, usually 10–12; origin of second dorsal fin about level with middle anal rays.............................................................................................C Ca Rays in second dorsal fin 7–11, usually 8 or 9; head pores relatively large and conspicuous; mandibular pores present; maxillary teeth usually exposed when mouth closed...................................P. signifer Cb Rays in second dorsal fin 6–9, usually 7, occasionally 8; head pores minute, inconspicuous; mandibular pores absent; maxillary teeth hidden when mouth closed ...................................................P. mellis Total anal fin rays usually 14–23 (except 10–12 in Iriatherina, which has a rigid fin spine on anal fin); rigid fin spines present (except in Rhadinocentrus and Cairnsichthys, both of which have more than 17 anal fin rays); anal fin origin in anterior half of body or about middle of body ............................................................................................Melanotaeniidae Aa No rigid fin spines present, all rays slender and flexible ................B Ab Rigid fin spines present, usually at the beginning of the first dorsal (except in Iriatherina), second dorsal, anal and pelvic fins ............C Ba Lower jaw prominent (Fig. 30); exposed lateral part of maxillae with single row of 15 or less widely separated teeth; horizontal scale rows at level of anal fin origin 8–9...............Rhadinocentrus ornatus Bb Jaws about equal; exposed lateral part of maxillae with numerous teeth arranged in several rows; horizontal scale rows at level of anal fin origin 10–11 .................................Cairnsichthys rhombosomoides Ca All spines of first dorsal fin relatively soft and flexible; soft anal fin rays 11–12; first few rays of second dorsal and anal fins extended as elongate filaments in adult males; exposed premaxillary teeth
20
Figure 28
Figure 29
Figure 30
Key to native and alien fishes of north-eastern Australia
restricted to a single row of 7–8 canines .............Iriatherina werneri Not as for Ca.....................................................................................D Colour pattern consisting of 8–9 horizontal rows of narrow dark stripes (sometimes broken and replaced by spots); the midlateral stripe not expanded to form broad black stripe; acidic waters on dune fields and lowland floodplains..…..Melanotaenia maccullochi Db Colour pattern not as in Da..............................................................E Ea Teeth of lower jaw in dense band without toothless groove separating row of teeth at front of jaw (Fig. 31); distinct black band (may be interrupted) running along middle of side.................................F Eb A toothless groove usually separating an enlarged row of teeth at front of jaws and dense band of smaller teeth behind (Fig. 32); distinct black band absent, usually replaced by a series of narrower stripes although the midlateral one may be expanded to form a diffuse dark band..............................................................................G Fa Soft rays in second dorsal fin usually 8–11; anal fin rays usually 15–19; black midlateral stripe always continuous; body slender, maximum depth not exceeding 34% of SL in males and 28% in females; Cape York Peninsula............................................M. nigrans Fb Soft rays in second dorsal fin usually 12–16; anal fin rays usually 18–23; black midlateral stripe frequently interrupted or at least faint just behind the pectoral fins; body deep, maximum depth of 45% of SL or greater in males, and 35% of SL in females .........M. trifasciata Ga Vomer with a few feeble teeth on lateral section; body slender, <31% in males and 28% in females; origin of first dorsal fin less than 46% of SL; snout length less than 7% of SL; restricted to Wet Tropics region...................................................................................H Gb Vomer with a solid band of teeth of well developed teeth; body deeper, >35% in males and 26–40% in females; origin of first dorsal fin greater than 47% of SL; snout length greater than 8% of SL .....I Ha Restricted to lakes and streams of the Atherton Tablelands at altitudes of 600 m.a.s.l. or greater ..................................M. eachamensis Hb Restricted to forested tributary streams of the Johnstone River at elevations of between 100 and 600 m.a.s.l ...................M. utcheensis Ia Deep bodied rainbowfish of streams and rivers, body depth of males (>50 mm) 29–48.8% of SL, of females 26.4–40.8% of SL; meristics and morphometrics extremely variable; range extends from Cape York Peninsula to possibly Baffle Creek, several subspecies recognised...........................................................M. splendida Ib Less deep-bodied, body depth of males 28–35.7% of SL, of females 26.3–31% of SL; not found north of about Baffle Creek ........................................................................................M. duboulayi 29a Spines of first dorsal sharp and rigid; 2 rigid spines at beginning of anal fin; lateral line scales usually present (sometimes reduced or absent) ...................................................................................................Apogonidae Glossamia aprion 29b Spines of first dorsal fin soft and flexible; a single flexible spine at the beginning of the anal fin, lateral line scales absent..................................30 30a Pelvic fins fused to form disc-like structure ................................Gobiidae Aa Head and body without scales............................Schismatogobius sp. Ab Head and body with scales ...............................................................B Ba Midlateral scales 49–100 or more ....................................................C Bb Midlateral scales 25–38 except in Chlamydogobius ranunculus Cb Da
21
Figure 31
Figure 32
Freshwater Fishes of North-Eastern Australia
which may have as many as 52 but usually 45 or less midlateral scales ..................................................................................................E Ca Lower jaw with one row of teeth, at least 2 canines present near middle of jaw; lower lip with a row of widely spaced conical teeth; upper lip with papillae or one or more clefts along margin (Fig. 33) ......................................................................Sicyopterus lagocephalus Cb Lower jaw with several rows of teeth, no canines; lower lip without teeth; upper lip without papillae or clefts along margin ...............D Da Gill arches and gill filaments papillose; broad dark bar or triangular marking below eye absent .......................................Awaous acritosus Db Gill arches and gill filaments not papillose; broad dark bar or triangular marking below eye present ...............Stenogobius psilosinionus Ea Midlateral scales 32–52, usually >38 ...Chlamydogobius ranunculus Eb Midlateral scales 25–38 .....................................................................F Fa Lower jaw with one row of teeth; operculum scaleless ...................................................................................Stiphodon alleni Fb Lower jaw with several rows of teeth; operculum scaled or scaleless ...........................................................................................................G Ga Opercle scaleless or with small inconspicuous scales restricted to uppermost part.................................................................................H Gb Opercle fully covered by scales ........................................................Q Ha First dorsal fin mostly black; caudal fin with 4–5 short blackish bars along lower edge (mostly estuarine).........Psammogobius biocellatus Hb First dorsal fin either clear or with black spot confined to rear half of first dorsal fin.................................................................................I Ia Short barbels present on chin.......................Glossogobius bicirrhosis Ib Short barbels absent on chin ............................................................J Ja Lines of sensory papilla below eye arranged in vertical lines (Fig. 34).....................................................................G. circumspectus Jb Lines of sensory papilla below eye arranged in horizontal lines (Fig. 35) .............................................................................................K Ka Breast scaled ......................................................................................L Kb Breast naked or nearly so..................................................................P La Predorsal scales large, 13–16 rows; infraorbital pore behind eye; 4 lateral line canal pores above preoperculum and operculum; lateral canal tube above operculum present ....................Glossogobius sp. 1 Lb Predorsal scales small, usually 17–30 rows; infraorbital pore behind eye; 2 lateral line canal pores above preoperculum and operculum (some populations of G. aureus may have 3–4 lateral canal pores); lateral canal tube above operculum present...................................M Ma Papillae lines from middle of upper jaw to infraorbital pore behind eye with distinct posterior branch under eye; longitudinal papillae lines under eye composed of multiple rows of papillae ....G. giurus Mb Papillae lines from middle of upper jaw to infraorbital pore behind eye without distinct posterior branch under eye; longitudinal papillae lines under eye composed of a single row of papillae...............N Na Scales absent from upper part of operculum .....................G. aureus Nb Scales present on upper part of the operculum..............................O Oa Predorasl scales 13–16 ................................................G. concavifrons Ob Preporsal scales 18–24 ............................................Glossogobius sp. 2 Pa Predorsal area naked or with rudimentary scales only; confined to Cape York Peninula and south New Guinea .........Glossogobius sp. 3 Pb Predorsal scales 10–12; confined to rivers of the Wet Tropics region
22
Figure 33
Figure 34
Figure 35
Key to native and alien fishes of north-eastern Australia
.................................................................................Glossogobius sp. 4 Midlateral scales 32–38; opercle covered with numerous small scales; head pores absent (predominantly estuarine but commonly found in freshwaters close to ocean)................................................R Qb Midlateral scales 25–28; opercle covered with a few large scales; head pores present...........................................................................W Ra Predorsal scales reaching close behind eye and almost entering interorbital space; anterior most scales on nape enlarged...............S Rb Predorsal scales reaching to preoperculum or less, never entering interorbital space; usually all scales small or equal in size, or absent from predorsal midline.....................................................................T Sa Second or third dorsal spine usually longest; predorsal scales 10-16; anterior most few enlarged; side of head with two longitudinal streaks; body with chequered pattern .............Mugilogobius mertoni Sb First dorsal spine usually longest; predorsal scales 13–22; anteriormost often not much larger than others; side of head with distinct reticulated pattern; body with oblique bars and blotches...M. filifer Ta Circumpeduncular scales modally 12; caudal fin with two dark spots at base ...................................................................M. notospilus Tb Circumpeduncular scales modally 13–20; two or more dusky diagonal bands may be present on caudal fin ........................................U Ua Predorsal scales 0–21 (most often 0–12); ctenoid scales on side of body restricted to caudal peduncle and patch under pectoral fin...................................................................................M. platynotus Ub Predorsal scales 14–30, never absent; ctenoid scales on side of body extending forward to below fifth ray of second dorsal or further..V Va Ctenoid scales on side of body extending continuously up to behind pectoral fin base, not broken into two areas..M. stigmaticus Vb Ctenoid scales on side of body usually separated by a distinct gap .....................................................................................M. platystomus Wa First dorsal fin without prominent black spot (although fin may be mottled darkly); no prominent oblique or vertical dark bar extending from eye, 3–5 short dark bars present on ventral most portion of sides between anus and caudal fin base (predominantly estuarine) ..........................................................................................X Wb First dorsal fin with prominent black spot either ringed in yellow or with anterior most part of fin yellow; prominent oblique or vertical dark bar extending from eye, short dark bars between anus and caudal fin base absent................................................................Y Xa Cylindrical in transverse section; body with blotches, rarely forming vertical bars; transverse bars across head; maxillary not reaching past middle of eye........................................Redigobius bikolanus Xb Laterally compressed, body with vertical bars; oblique bars radiating from eye; mouth large with maxillary extending well past eye; not found north of the Noosa River ........................R. macrostomus Ya Body with conspicuous oblique bar extending from below first dorsal fin ...........................................................................R. balteatus Yb Body without conspicuous oblique bar .........................R. chrysoma 30b Pelvic fins separate .......................................................................Eleotridae Aa Midlateral scales <50 (usually <45) .................................................B Ab Midlateral scales >45 (usually >60, except in Oxyeleotris nullipora which has 30–38) ..............................................................................K Ba Predorsal scales absent...............Hypseleotris sp. 2 (Lake’s gudgeon) Qa
23
Freshwater Fishes of North-Eastern Australia
Bb Ca Cb Da Db Ea Eb Fa Fb Ga Gb Ha
Predorsal scales present ....................................................................C Midlateral scales 33–47, usually greater than 33.............................D Midlateral scales 27–32, rarely 33.....................................................F Total rays in first dorsal fin 6.........................Ophiocara porocephala Total rays in first dorsal fin 7–9 .......................................................E Midlateral scales 30–36 .......................................Mogurnda adspersa Midlateral scales 37–48 .................................................M. mogurnda Head laterally compressed (Fig. 36) ................................................G Head moderately to greatly depressed (Fig. 37) ...............................J Head pores present.........................................Hypseleotris compressa Head pores absent ............................................................................H Transverse scales rows 11–13; midlateral scales 31–43 ...................... ................................................Hypsleotris sp. 1 (Midgley’s gudgeon) Hb Transverse scale rows 9–11; midlateral scales 27–32 ........................I Ia Series of transverse papillary rows above and below the eye (Fig. 38) .................................................................................H. klunzingeri Ib Series of transverse papillary rows above and below the eyes absent or only a single row present above the eye (Fig. 39)..............H. galii Ja Head more or less pointed; snout very elongate and greatly flattened; bony crests in interorbital space .............................Butis butis Jb Head more rounded; snout short and not greatly flattened; no bony crests in interorbital space .................................Giurus margaritacea Ka Lower rear corner of preopercle with an enlarged downward curved, strong spine (may be obscured by flesh) (Fig. 40) .............L Kb Lower rear corner of preopercle without enlarged spine ...............N La Gill rakers on first arch 8–10; <40 predorsal scales; 5–6 transverse lines of pit organ canals along lower edge of cheek........................... ...........................................................................Eleotris acanthopoma Lb Gill rakers on first arch 10–13; >40 predorsal scales; 7–12 transverse lines of pit organ canals along lower edge of cheek .......................M Ma Gill rakers on first arch 12–13; midlateral scales 46–56; >40 predorsal scales; 7–9 transverse lines of pit organ canals.....E. melanosoma Mb Gill rakers on first arch 10–12; midlateral scales 57–65; >42 predorsal scales; 8–12 transverse lines of pit organ canals...............E. fusca Na Scales small, usually >50 in midlateral series (except for O. nullipora) ..................................................................................................O Nb Scales larger, usually <45 in midlateral series..................................T Oa Second dorsal fin rays I, 8–9; colour uniform, mottled or distinct difference between dorsal and ventral sides.....................................P Ob Second dorsal fin rays I, 11–14; distinct chevron-like markings on sides ...................................................................................................R Pa Teeth of jaws more or less uniform, or some only slightly enlarged ................................................................................Bunaka gyrinoides Pb Teeth of jaws with outer row enlarged ............................................Q Qa Anal, pelvic and pectoral fins spotted or barred, narrow white stripe (or irregular white blotches) along midline; caudal fin slightly pointed; papillae below eye arranged in six distinct vertical lines Oxyeleotris selheimi Qb Anal, pelvic and pectoral fins without spots or bars (dorsal and caudal fins may be spotted); midlateral without white stripe; caudal fin rounded; papillae below eye arranged in 9 indistinct vertical lines plus 2 anterior oblique lines ..................................O. lineolatus Ra Midlateral scales 30-38 ....................................................O. nullipora
24
Figure 36
Figure 37
Figure 38
Figure 39
Figure 40
Key to native and alien fishes of north-eastern Australia
Rb Sa
Sb
Ta
Tb
Ua
Ub
Va Vb
Midlateral scales >55.........................................................................S Second dorsal I, 12–14; anal I, 10–12; predorsal scales 35–40; 3 head pores forward of eye, 4 pores on preopercle margin and 2 on operculum .................................................................................O. aruensis Second dorsal I, 11–12; anal I, 11–12; predorsal scales 37–45; 2 head pores forward of eye, 5 pores on preopercle margin and 5 on operculum ...............................................................................O. fimbriata Head strongly depressed, width about 1.5 times depth; mouth large in adults, reaching to, or beyond, middle of eye; side of head scaleless .....................................................................................................U Head rounded or truncate in side view, width about 0.8–1.2 times depth; mouth smaller, ending below or before anterior part of pupil; side of head scaled .................................................................V Pectoral rays 16–20, usually 18–19; total gill rakers on first arch 14–20; gill openings reaching forward to below eye ................................ .......................................................................Philypnodon grandiceps Pectoral rays usually 15–16; total gill rakers on first arch 11–12; gill openings restricted, reaching to below rear margin of preopercle ....................................................................................Philypnodon sp. Pectoral rays 18–19; midlateral scales 36–40 .....Gobiomorphus coxii Pectoral rays 14–16; midlateral scales 30–34 ...................G. australis
25
Freshwater Fishes of North-Eastern Australia
Study area, data collection, analysis and presentation
with the fishes of the North-east Coast Drainage Division (Fig. 1), a relatively narrow strip bounded by the Great Dividing Range and the Coral Sea. Although this drainage division represents only 5.8% of the continental area, its rivers discharge almost 25% of the total annual discharge of 34.6 x 107 ML [1409].
Study area Australia can be divided into 12 major drainage divisions based on climate, landform and the distribution of aquatic habitat types (Fig. 1) [52, 936, 1409]. The biogeography of Australia’s freshwater fishes is highly congruent with these drainage divisions [1340]. This text is primarily concerned
AUSTRALIAN DRAINAGE DIVISIONS
Philippin es
I II III IV V VI VII VIII IX X XI XII
Pacific Ocean
Malaysia New Gu inea
Solomo n Islands
Ind onesia Vanu atu Coral Sea
Australia
Ind ian Ocean
Fiji New Caledon ia New Zealand
Tasman Sea
North-east Coast Division South-east Coast Division Tasmania Division Murray-Darling Division South Australia Gulf Division South-west Coast Division Indian Ocean Division Timor Sea Division Gulf of Carpentaria Division Lake Eyre Division Bulloo-Bancannia Division Western Plateau Division 152°31'00" -42°00'00"
Arnhem Land
Alligator Rivers Region Darwin
Kimberley
VIII IX
Pilbara
XII
I
VII
X Brisbane
XI Perth
V
IV II
VI
Sydney Adelaide
Canberra Melbourne
N
116°00'00" -40°01'00"
0
500
1,000
III Hobart
Kilometres
Figure 1. Map of Australia showing the major drainage divisions and some localities mentioned in the text. Base data reproduced with the permission of the Queensland Department of Natural Resources, Mines and Energy.
26
Study area, data collection, analysis and presentation
QUEENSLAND DRAINAGE BASINS Gulf of Carpentaria & Wester n Cape York Peninsula 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928
928
927 137°13'00" -11°20'40"
101 926 102 924
925
Easter n Cape York Peninsula
Settlement Mornington Island Nicholson Leichhardt Morning Flinders Norman Gilbert Staaten Mitchell Coleman Holroyd Archer Watson Embley Wenlock Ducie Jardine Torres Strait Islands
101 102 103 104 105 106 107
Jacky Jacky Olive-Pascoe Lockhart Stewart Normanby Jeannie Endeavour
Wet Tropics 108 109 110 111 112 113 114 115 116
Daintree Mossman Barron Mulgrave-Russell Johnstone Tully Murray Hinchinbrook Island Herbert
South-eastern Queensland
Central Queensland 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135
Black Ros s Haughton Burdekin Don Proserpine Whitsunday Island O'Connell Pioneer Plane Styx Shoalwater Water Park Fitzroy Curtis Island Calliope Boyne Baffle Kolan
136 137 138 139 140 141 142 143 144 145 146
Burnett Burrum Mary Fraser Island Noosa Maroochy Pine Brisbane Stradbroke Islands Logan-Albert South Coast
103
923
Coen 922 104
Gulf of Carpentaria and Western Cape York Peninsula
Eastern Cape York Peninsula 106
921 920 105
107
919
108 109
911
110
Cairns 918
914
Wet Tropics
111
910
112 113 114 115 117
116 912
917
916
Townsville 118 119
913
121
120
122 123 124
IX
915
Mackay 125
I
Mount Isa
Central Queensland 126
129
Rockhampton 127 128
X
131 132 133 134 135
130
137
South-eastern Queensland 139
Maryborough
136 138
140 141
IV
XI
Brisbane
142
144
143
146
N
145
154°00'45"
0
250
500
-29°45'00"
Kilometres Figure 2. Map of the coastal drainage basins of Queensland and some locations mentioned in the text. Drainage basins designations and numbering follow the Queensland Department of Natural Resources, Mines and Energy. Base data reproduced with the permission of the Queensland Department of Natural Resources, Mines and Energy.
27
Freshwater Fishes of North-Eastern Australia
The North-east Coast Division contains almost one half of all species of freshwater fishes found in Australia. Moreover, many of the fishes of the North-east Coast Division are widespread, occurring across northern Australia to the Kimberley region or southward into the South-east Coast drainage Division, which extends down through New South Wales, Victoria and into South Australia. In addition, some fauna are shared with the Murray-Darling Drainage Division. The material presented in this book concerning the ecology of fishes of the North-east Coast Division has broad relevance for eastern Australia.
specifically for Australian climatic conditions, they do serve to illustrate the diversity of climate present across the continent. North-eastern Australia (as defined here) traverses the tropical zone (from Cape York Peninsula south to about Mackay) and the area further south which is transitional between the tropical type and the warm temperate type [1361]. Figure 3 illustrates some aspects of the climatic diversity present in north-eastern Australia. The climate of eastern Cape York Peninsula is typified by rainfall and temperature data recorded at the township of Coen. Mean monthly maximum temperatures rarely fall below 28°C and mean monthly minima drop below 20°C only during the period June to September. Very little rainfall occurs over the period April to November. The period of greatest rainfall is related to the development of the southern monsoonal trough and most occurs in association with the passage of tropical cyclonic weather systems. The climate of the Wet Tropics region is also monsoonal. Only minor seasonal variation in climate is experienced in Cairns, located at sea level. Mean monthly maxima exceed 33°C in December only and fall below 27°C in June and July only. Minimum monthly temperatures average about 20°C and fall below 17°C in July and August only. Maximum temperatures at Atherton, located at an elevation of 753 m.a.s.l. on the Atherton Tablelands to the immediate west of Cairns, are slightly lower and vary more throughout the year. The range in monthly mean temperatures at Atherton exceeds that for Cairns. Mean monthly temperatures may approach 10°C during the drier months and short periods of frost may occur then also. Both Cairns and Atherton experience the majority of rainfall during the summer monsoonal period but also experience consistent rainfall during the period May to November. Moisture laden south-easterly winds deposit substantial rain during this period as they cross the coast and are forced over the mountainous terrain typifying this area. This region contains Queensland’s two highest mountains (Mts. Bartle Frere and Bellenden Kerr, both exceeding 1500 m in height) and is notable for being the wettest region in Australia [27]. Although rainfall is basically seasonal in occurrence, there is little seasonal signal in the number of rain days per month [27].
The North-east Coast Division (Figs. 1 and 2) extends through more than 18° of latitude. Accordingly, there is an enormous diversity of climate, flow regime, landform and river type across this gradient. On the basis of these physical features, the North-east Coast Division can be further subdivided into four secondary drainage divisions (Fig. 2), which also correspond with variations in fish species composition (Appendix 1) [1340]. These four subdivisions are: Eastern Cape York Peninsula, the Wet Tropics region, Central Queensland, and south-eastern Queensland; each is composed of a number of separate drainage basins. The majority of drainage basins are relatively small, with few exceeding 10 000 km2. Note that some of these drainage basins are composed of more than one, albeit small, separate river systems. Throughout this book, the four secondary drainage divisions of the Northeast Coast Division, and the separate drainage basins within them, are used as the basic spatial template for discussions of fish species distribution and ecology. We follow the drainage basin designations and numbering system used by the Queensland Department of Natural Resources and Mines. Climate Bridgewater [226] provides an overview of the Australian climate in which he notes that of the seven major global climate types identified by Walter and Leith [1361], four occur in Australia. These are: • Tropical type, characterised by some seasonality in temperature and a concentration of rainfall in the warmer months; • Subtropical dry type, characterised by very low rainfall, high summer maximum temperatures and low winter minima; • Transitional zone with winter rainfall, characterised by very little summer rainfall, typically no winter cold season but permanent summer drought; and • Warm temperate type, characterised by no noticeable winter and year-round rainfall.
Climate records for Ayr located near the mouth of the Burdekin River are typical for central Queensland and reveal a climate dominated by maximum temperatures and rainfall during the period December to April (Fig. 3). Diel variation in temperature, particularly during the drier months, is a feature of the region and although frosts are not common at sea level, they may occur in the headwater areas of the Burdekin River. Rainfall is erratic in incidence, strongly influenced by cyclonic weather systems and varies greatly from year to year [1089].
Whilst these are very broad categories intended for characterisation of global climate regimes rather than
28
Study area, data collection, analysis and presentation
Discharge regimes A river’s discharge regime is defined by the temporal variation in the amount of water being carried within its channel as a result of temporal variation in climate (rainfall, temperature and evaporation). In addition, evapotranspiration and groundwater inputs also markedly affect discharge regime. Flow regimes vary markedly throughout north-eastern Australia. The Normanby River in Cape York Peninsula has a distinctly seasonal flow regime with most (86%) discharge occurring in January, February or March (Fig. 4). Wet season flows break out of the stream channel and inundate floodplain waterbodies. Very little flow occurs from June to November and the river contracts to a series of large isolated within-channel pools. Notably however, while reduced flows during the dry season are predictable in occurrence, wet seasons flows are less predictable in timing and magnitude. The coefficient of variation (CV) of mean annual discharge (standard deviation of the mean/mean x 100) is high (up to 105% [697]) indicating that many years lack a summer flood (‘failed wet seasons’).
The climate of south-eastern Queensland, typified by that recorded at Gympie in the Mary River drainage, and Beaudesert in the Albert/Logan River drainage, is more seasonal. Mean monthly thermal maxima and mean monthly minima vary by about 10°C and 15°C, respectively, throughout the year. The pattern of rainfall is less strongly dominated by the summer monsoon and frequently influenced by the northward extension of temperate weather systems [1095]. As detailed above, this region is transitional between the tropical and warm temperate climate types identified by Walter and Leith [1361]. In summary, the climate of north-eastern Australia changes with latitude. Although maximum summer temperatures vary little across the latitudinal gradient encompassing north-eastern Australia (cf. Coen and Beaudesert), the extent of diel variation increases significantly from about 10°C in the north to about 15°C in the south. Moreover, the difference between mean summer and winter temperatures increases as one moves south, mainly as a result of a decrease in mean monthly thermal minima. Seasonality is defined more by temporal variation in rainfall at low latitudes in the north whereas temporal variation in temperature defines seasonal shifts in climate in the south. 35
Coen
30
500 400
25
35
The flow regime of rivers of the Wet Tropics region is in stark contrast to those of Cape York Peninsula. Rivers of this region vary little in discharge from year to year (i.e. 500
Cairns
30
400
25
5
35
200 15
100 0
Ayr
30
500 400
25
100
10 5
35
500
Gympie
30
400
100
10
35
0
Beaudesert
30
500 400 300
20
200
2
0
200
0
15
15 100
200 15
300 20
10
300
25
25
15
400
5
0
300 20
500
20
200
10
30
300 20
15
Atherton
25
300 20
35
100
10
™
100
10
™
™
5
0
Month
5
0
Month
5
0
Month
Figure 3. Plots of mean daily minimum temperature (closed squares), mean daily maximum temperature (open squares) and mean monthly rainfall (open circles) for each month at selected locations in eastern Queensland. The period of data record from which means and ranges were calculated was >80 years for each location except Cairns (~50 years). Data source: Queensland Bureau of Meteorology.
29
Freshwater Fishes of North-Eastern Australia
they exhibit low annual CV values). For example the Mulgrave and Johnstone rivers have CV values of 28% and 34%, respectively [1096, 1100]. Rivers of this region are perennial. The Johnstone River may cease to flow in as few as 1 in every 50 years. Wet season flows dominate the monthly hydrograph as they do in the Normanby River (Fig. 4) but discharge during the dry season remains high, contributing about 25% of mean annual flow. Two features of the region contribute to this pattern. First, rainfall remains high during the dry season (Fig. 3). Second, much of the catchments of some rivers of the Wet Tropics region are composed of porous basalt, which acts as a large aquifer contributing significant amounts of the groundwater throughout the year. Thus even small tributary systems such as the upper North Johnstone River at Malanda are perennial. Dry season flows tend to remain very stable and there is a low likelihood of spates occurring during the period June to October [1093, 1096]. It should be noted that the Mulgrave and Johnstone rivers are located in the centre of the Wet Tropics region. Rivers to the north and south grade into more seasonal flow regimes characterised by a reduced contribution of dry season flows to the annual total. 300 250
200 Normanby Riv er Gauge105101A 2
150
(2,302 km )
The flow regimes of rivers of central Queensland, such as the Burdekin River, are similar to those of eastern Cape York Peninsula (Fig. 4). Most of the discharge occurs during a well-defined summer wet season, with very little discharge occurring outside of the months April to November. The flow regimes of the Burdekin and Fitzroy rivers have been identified as amongst the most variable in the world [1076]. Wet season flow are dominated by one or rarely two large flood events associated with cyclonic weather systems which may occur at any time from December to April [1089]. Wet seasons fail regularly in this region leading to substantial year-to-year variation. The CV of annual flow in the Burdekin River itself exceeds 100% whereas in some tributary systems, particularly in the south-west, annual flows may be even more variable [1089]. In contrast to the perennial flow regimes typical of the Wet Tropics region, the flow regimes of rivers of central Queensland are typified by long periods of very little flow occasionally punctuated by extreme flood events. The flow regimes of rivers in south-eastern Queensland are different to that described for rivers further north. The majority of stream flow occurs in the summer months of
Lower Mulgrav e Riv er Gauge111007A 2
40
30
(520 km )
Upper Nth Johnstone Riv er, Gauge112003A 2
(165 km )
200 150
100
20
50
10
0
0
100 50 0
1500 1250
300 Burdekin Riv er Gauge120002C
Mary Riv er Gauge138001A
250
2
2
(36,260 km )
(4,755 km )
1000
200
750
150
500
100
250
50
0
0
40
30
Albert Riv er Gauge 145196A 2
(722 km )
20
10
Month
0
Month
Month
Figure 4. Variation in mean total monthly discharge for selected eastern Queensland Rivers. The catchment area (km2) upstream of each gauging station is given in parentheses. The period of data record from which means were calculated was >20 years for each gauge. Data source: Queensland Department of Natural Resources, Mines and Energy.
30
Study area, data collection, analysis and presentation
Figures 5 and 6 and Table 1 for details of drainage basins and rivers examined within these regions), the details of which are in the process of being published (see also [706, 707, 708, 1100, 1107, 1108, 1109]). This study was undertaken over the period 1994–1997 in the Wet Tropics region and 1994–2003 in south-eastern Queensland. It involved quantitative sampling of fish assemblages at 416 locations, 959 separate samples (location and sampling occasions) and the collection of over 199 000 individual fish from 68 species (almost all of which were returned alive to the water at the site of collection).
January to March, followed by a second minor peak in discharge between April and July as a result of northern penetration of low-pressure temperate weather systems [1095]. The incidence and magnitude of these secondary peaks in flows is quite unpredictable, as are summer wet season flows, and thus rivers of this region tend to show high annual CV values (100% or greater) [1100]. Tributary streams tend to be considerably more variable than lowland river systems and variability in discharge decreases markedly with distance downstream [1095]. Despite the high variability in summer wet season flows and therefore of total mean annual discharge, flows during the dry season period of July to October are relatively stable and vary little [949, 950, 951, 1095].
To simplify discussion of species frequency of occurrence, abundance and biomass, data has been summarised for rivers and streams in the Wet Tropics region grouped according to drainage basin designation (Fig. 5), and for south-eastern Queensland, also according to geographic proximity and geomorphological similarity (Fig. 6 and Appendix 1). Rivers and streams sampled in the Sunshine Coast region (Noosa Basin 140 and Maroochy Basin 141) generally drain sandy acid-wallum landscapes and have been grouped together. Short coastal streams of the Logan-Albert Basin draining into Redland Bay (Basin 145a – Appendix 1) are small catchments quite dissimilar to the Logan-Albert River proper and so have also been grouped with other morphologically similar coastal streams of the greater Moreton Bay region (i.e. those in the Pine Basin – 142) (Figure 6). All other rivers and streams have been grouped according to their drainage basin designation (Mary River – Basin 138; Brisbane River Basin – 143; Logan-Albert River – 145a,b; South Coast rivers and streams – Basin 146) (Fig. 6).
Study basins and site locations The species summaries in this book are based on many different sources of information gathered by many individuals and groups. Our own studies have occurred in a variety of areas including basins in Cape York Peninsula [697, 1099, 1101], the Wet Tropics region [49, 1085, 1087, 1091, 1096, 1097, 1100, 1104, 1107, 1108, 1109], central Queensland [1079, 1081, 1082, 1089, 1098] and southeastern Queensland [84, 99, 104, 205, 699, 700, 701, 702, 704, 709, 1095, 1100, 1107]. The reader is referred to these studies for more detail concerning site location and sampling methods. Much of the information contained in this book, especially that concerning habitat use, variation in abundance and biomass, and aspects of life history, is drawn from a recent comparative study undertaken in the Wet Tropics region and south-eastern Queensland (see
Table 1. Sampling intensity in rivers and streams of the Wet Tropics region and south-eastern Queensland. See Figures 5 and 6 and Appendix 1 for river basin and sub-basin locations and designations. Region/River
Number of locations
Number of samples
Number of fish species collected
51 56 11
83 190 11
32 37 19
7959 27 267 717
118
284
39
35 943
50 29 20 111 68 20
225 42 37 165 174 32
27 24 21 28 28 21
83 198 2557 4310 26 536 43 162 3558
Wet Tropics region Mulgrave Russell River (Basin 111) North and South Johnstone rivers (Basin 112) Tully River (Basin 113) Sub-total South-eastern Queensland Mary River (Basin 138) Sunshine Coast rivers and streams (Basins 140b; 141) Moreton Bay rivers and streams (Basins 142; 145a) Brisbane River (Basin 143) Logan-Albert River (Basin 145b,c) South Coast rivers and streams (Basin 146)
Number of individuals collected
Sub-total
298
675
38
163 321
Total
416
959
68
199 264
31
Freshwater Fishes of North-Eastern Australia
146°06'00" -16°55'00"
Cairns
111 Mulgrave-Russell Basin
Mulgrave-Russell Rivers Johnstone River Tully River
Innisfail 112 Johnstone Basin
N
145°30'00" -18°01'00"
113 Tully Basin 0
10
20
kilometres
Figure 5. Location of study sites in the Wet Tropics region of northern Queensland. Base data reproduced with the permission of the Queensland Department of Natural Resources, Mines and Energy.
32
Study area, data collection, analysis and presentation
152°28'00" -24°52'00"
Fraser Island Mary River Sunshine Coast rivers and streams Moreton Bay rivers and streams Brisbane River Logan-Albert Rivers South Coast rivers and streams
138 Mary Basin 140 Noosa Basin !! !
! ! ! !
!
!
'' '
'
141 Maroochy Basin
'
!!
'
''
!!
'' ' ' ''
'' ' ' ' ' ' ' ' '
' '
' '
' ' '
'
' '
' '
N
=
' ''
!
'
Moreton Island = = = = = = = = = = == = = = '=
' ' '' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '' ' ' ' ' ' '
Bribie Island
' ' ' ' ' '
'
'''
'
!
'
' ' '
143 Brisbane Basin
!
' ''
''
'
' ''' '
142 Pine Basin Moreton Bay
Brisbane = ' = = =
North Stradbroke Island
South Stradbroke Island
146 South Coast Basin 153°58'00"
0
35
70
-28°14'00"
kilometres 145 Logan-Albert Basin Figure 6. Location of study sites in south-eastern Queensland. Base data reproduced with the permission of the Queensland Department of Natural Resources, Mines and Energy.
33
Freshwater Fishes of North-Eastern Australia
lowland reaches of rivers in the Wet Tropics region further constrained our ability to sample these habitats by these methods. The ecology of fishes in lowland river reaches of north-eastern Australia remains one of the least studied aspects of this field in Australia and offers exciting potential for further research. The majority of study locations in both the Wet Tropics region and south-eastern Queensland were relatively undisturbed. However, some of the sampling in south-eastern Queensland was undertaken as part of a project to examine the effects of human activities on freshwater fish assemblages [709, 1255], and some sites in this region were therefore impacted to varying degrees by land use activities (e.g. land clearing, grazing, cropping and urbanisation), water resource development and local riparian and in-stream habitat degradation.
Site selection and spatial distribution The location of the individual sampling sites in the Wet Tropics region are shown in Figure 5 and that of sampling locations in south-eastern Queensland in Figure 6. Fish and habitat sampling was conducted with the intention of characterising as much of the environmental and biological variation possible in each selected stream reach within the hierarchical organisation of habitats characteristic of river networks. In south-eastern Queensland streams, at least two contiguous hydraulic habitat units (i.e. riffles, runs and pools) were usually sampled in each reach in order to encompass this variation (Fig. 7), except during dry periods when surface waters occasionally contracted to shorter isolated pools. In rivers of northern Queensland, a single hydraulic habitat unit was usually sampled at each location. Study sites in the Wet Tropics region were, on average, 34.1 ± 0.9 m in length and 347.1 ± 17.6 m2 in wetted area, and those in rivers of south-eastern Queensland were of similar size: 38.6 ± 0.5 m stream length and 313.3 ± 10.6 m2 wetted area. Note that all error terms are listed as Standard Error throughout this book unless otherwise stated.
Study sites were sampled over a range of seasonal and hydrological conditions effectively encompassing the range of flow conditions expected in these rivers and regions (Fig. 8). Although fish assemblages were not sampled during large floods, samples were frequently collected as soon after flooding as practicable. The reader should note that we sometimes present summaries of information in which sampling occasions are grouped (e.g. length-frequency data). We have used traditional seasonal groups (i.e. summer, autumn, winter and spring) for data collected in south-eastern Queensland but not the Wet Tropics regions, as application of such seasonal categories is not appropriate in the latter region due to its tropical climate (see above).
Study sites were arrayed widely throughout each catchment from headwaters to downstream reaches, however study site location was constrained by our choice of sampling methodology (back-pack electrofishing and seine-netting – see below). This limited our ability to sample fish assemblages effectively and quantitatively in large lowland river reaches with a depth of greater than 1.5 m. In addition, the presence of estuarine crocodiles in
River
Reach
Hydraulic unit In-stream habitat sampling point
Distance upstream (m)
40 Pool
Riffle
Sampling location Run
35
Bank habitat sampling segment
30 25
Flow
20 15 10 5
Hydraulic unit
0 E
D
C
B
A
1/6w 2/6w 3/6w 4/6w 5/6w
Right bank
Transect
Left bank
Figure 7. Spatial scale at which individual hydraulic units within each river reach were defined for sampling fish and habitat. Also shown are the sampling points within each hydraulic unit where measurements of in-stream habitat and bank habitat structure were undertaken.
34
Study area, data collection, analysis and presentation
25
These data were collected as part of the process for determining distribution and abundance at larger spatial scales. The following data were estimated for each individual collected during electrofishing and recorded on data sheets: • Mean water column velocity (portable flow meter) • Focal point velocity (portable flow meter) • Total water column depth (graduated stick) • Focal point depth (graduated stick) • Proportional substrate composition in one square metre immediately below the fish (i.e. mud, sand, fine gravel, coarse gravel, cobbles, rocks and bedrock) • Distance to nearest potential refuge (i.e. microhabitat structure) • Distance to bank
Wet Tropics (n=284) South-eastern Queensland (n=675)
20 15 10 5 0
Summer
Autumn
Winter
Spring
Summer
Month/Season
For fish less than 0.2 m from the nearest refuge, the type of potential cover with which it was associated was recorded (note that 0.2 m is an arbitrary distance only). The cover elements identified were: the substratum itself, submerged aquatic macrophytes, filamentous algae, leaf litter, emergent vegetation, submerged bank-side vegetation, submerged overhanging vegetation, large woody debris, small woody debris, undercut banks and root masses. Fish >0.2 m from the nearest potential cover were recorded as being in open water.
Figure 8. Distribution of sampling occasions in months and seasons throughout the study period.
Collection and quantification of fish abundance levels Fish assemblages at each site were intensively sampled using the procedures detailed in Pusey et al. [1107]. Each hydraulic unit was blocked upstream and downstream with weighted seine nets (11 mm stretched-mesh) to prevent fish movement into or out of the study area. The site was sampled using a combination of repeated pass electrofishing (Smith-Root model 12B Backpack Electroshocker) and supplementary seine netting until few or no further fish were collected. Usually four electrofishing passes and two seine hauls were required to collect all fish present within a site. The intensive sampling regime described here has been demonstrated to provide accurate estimates of species composition and abundances in wadeable stream sites [1107].
Two problems with this method can be identified immediately. First, it relies on the investigator being able to see the fish in question and to see its position within the habitat milieu prior to it being stunned. Second, it must be assumed that the observed microhabitat use does not differ from a hypothetical condition that might exist without the presence of the observer and his or her electrofishing gear. These are potentially important biases and we sought to minimise their influence in three ways. First, microhabitat data was only collected when water clarity was sufficiently high to allow observation. Second, microhabitat data was not recorded or used if the position of the fish was unknown prior to it being stunned. Third, microhabitat data was only recorded for fish collected during the first electrofishing pass, the assumption being that the behaviour of fish changed significantly after they had experienced the observer and the electrofisher for the first time. In addition, we have, on occasions, conducted snorkelling surveys and recorded habitat use data prior to electrofishing in an attempt to assess the accuracy of habitat use data recorded during electrofishing. Habitat use data generally matched quite closely for the two methods. One possible exception is the estimation of focal point depth and velocity for fish located in the bottom-third of the water column but not in actual contact with the substrate, especially when depth exceeds 1 m.
All fish collected were identified to species, counted, measured (standard length to the nearest mm) and all native fish were returned alive to the point of capture. Alien fish were euthanased (using benzocaine – MS222), and were not returned to the water (in accordance with the Queensland Fisheries Act 1994). The weight of each fish (both native and alien species) was estimated by reference to previously unpublished and existing relationships between body length and mass for each species. Fish abundance and biomass data were transformed to numerical densities (number of individuals.10m–2) and biomass densities (g.10m–2) at each site. Quantification of fish microhabitat use Microhabitat use data for many of the fish species covered in this text were colleted during sampling in the Mulgrave and Russell rivers in the Wet Tropics region and in the Mary and Albert rivers in south-eastern Queensland.
35
Freshwater Fishes of North-Eastern Australia
1:100 000 topographic maps using a digital planimeter and also using Geographical Information System (GIS) data. Riparian cover was estimated from multiple measures (usually three) at each site on each occasion, using a handheld densiometer. Estimates of variables describing habitat structure at the meso- and microhabitat scale within each site and on each occasion were based on multiple samples within a combined bank transect and random points scheme. An imaginary grid (40 rows and five
Quantification of habitat structure at macro-, mesoand microscales A range of catchment and local scale environmental variables describing habitat structure (Table 2) was measured at each site and on most sampling occasions according to a standard protocol briefly described in Pusey et al. [1100] and more fully here. Catchment descriptors for each site (upstream catchment area, elevation, distance from stream source and distance to river mouth) were estimated from
Table 2. Environmental variables estimated at each sampling location. Variable/Measurement Unit Catchment variables Upstream catchment area (km2) Distance from stream source (km) Distance to river mouth (km) Elevation (m.a.s.l.) Site physical characteristics Wetted stream width (m) Riparian cover (%) Water depth (cm) Mean water velocity (ms–1) Site gradient (%) Substrate composition (% surface area) Mud Sand Fine gravel Coarse gravel Cobble Rock Bedrock Microhabitat structure (% surface area) Aquatic macrophytes Filamentous algae Overhanging vegetation Submerged vegetation Emergent vegetation Leaf litter Large woody debris Small woody debris Undercut banks (% bank) Root masses (% bank) Water chemistry Water temperature Dissolved oxygen pH Conductivity Turbidity
Description Estimated using 1:100 000 topographic maps and digital planimeter or GIS Estimated using 1:100 000 topographic maps and digital planimeter or GIS Estimated using 1:100 000 topographic maps and digital planimeter or GIS Estimated using 1:100 000 topographic maps and digital planimeter or GIS Horizontal distance measured perpendicular to stream flow from bank to bank at existing water surface using tape measure. Hand-held densiometer. Vertical distance from existing water surface to channel bottom measured using graduated stick. Speed at which water moves downstream. Measured with a Swoffer current velocity meter at 0.6 of water column depth. Measured for each hydraulic habitat unit using staff, dumpy and tripod. (Visually estimated) <0.06 mm (particle size) 0.06 mm–2.0 mm 2.0 mm–16.0 mm 16.0 mm–64.0 mm 64.0 mm–128.0 mm >128.0 mm (Visually estimated) Submerged aquatic macrophytes and charaphytes. Overhanging terrestrial vegetation in contact with water surface. Submerged terrestrial vegetation along river margins (e.g. grasses and annual weeds). Semi-aquatic vegetation (e.g. sedges and rushes). Accumulations of leaf litter and fine woody material (<1 cm stem diameter) Woody debris >15 cm minimum stem diameter. Woody debris of <15 cm maximum stem diameter. Bank overhanging water by at least 30 cm, and no more than 10 cm above water surface, expressed as a proportion of wetted stream perimeter. Submerged bankside root masses, expressed as a proportion of wetted stream perimeter. Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems DT50 data logger). Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems DT50 data logger). Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems DT50 data logger). Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems DT50 data logger). Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems DT50 data logger).
36
Study area, data collection, analysis and presentation
random points (i.e. a sample size of 20 or more) with those taken at a much reduced number of points (3) revealed little difference [1093].
columns) was imposed on each site (Fig. 7) and the mesoand microscale variables listed in Table 2 were measured at a series of previously selected random points across the grid. The distance between the cross-sectional lines on the imaginary grid was dependent on the length of the study site, according to the formula: grid length interval = study site length/40. Thus, grid lines were spaced at approximately 1 m intervals on average. The interval between longitudinal grid lines was determined by the formula: grid width interval = wetted stream width/6. Thus vertical grid lines A and E in Figure 7 were one-sixth of the stream width away from the left and right banks, respectively, whereas grid line C was always in the centre of the wetted stream width. In general, this scheme resulted in 20 measures for each parameter at each site. Habitat variables were measured or estimated at each of these randomly selected points. Substrate composition was estimated by eye for a 1 m2 quadrat centred on each survey point according to a modified Wentworth scheme described in Pusey et al. [1095] and detailed in Table 2. Average values (depth and current velocity), or average proportion of mean wetted site area (substrate composition and microhabitat elements) were then estimated. With practice, the location of each point is quickly committed to memory and the process is rapid and efficient. A pilot study prior to the main sampling program revealed that the in-stream habitat sampling scheme described above often failed to include microscale habitat elements located close to the bank (such as woody debris, macrophyte beds, banks of leaf litter). In order to fully capture such elements, a series of graduated bank transects was also established on both banks. Transect width was set at: width = stream wetted width/10 and the length of segments within each transect set as length = site length/4. Microhabitat cover for each element and substrate composition were estimated by eye and expressed as a proportion of the area enclosed within each segment of the bank transect. The extent of bank associated root masses and undercuts was expressed as a proportion of bank length in each segment. Thus eight measures of these parameters were estimated at each site
Inter-regional comparison of habitat structure and water quality Figure 9 summarises the distribution of study sites within each region across various macro- and mesoscale habitat variables. These data represent the frequency distributions of mean estimates of habitat parameters for each site across the range of sites examined. Over 70% of sites in both regions were located in streams with a catchment area of less than 200 km2. A greater number of larger streams were examined in south-eastern Queensland than in the Wet Tropics region, reflecting differences in catchment area of the rivers examined (see Fig. 2). Catchment size also influenced the distribution of sites with respect to distance downstream from the stream source and upstream from the river mouth. More sites distant from the river mouth were examined in south-eastern Queensland than in the Wet Tropics region. Sites in south-eastern Queensland were distributed more evenly across the elevation gradient than were sites in the Wet Tropics region. Rivers of the Wet Tropics tend to have a short lowland section and then rise very steeply to their headwaters (see [1096]). Some of these rivers have an upper low gradient section located at high elevation (>500 m) on the Atherton Tablelands. Despite these differences at the landscape or macrohabitat scale, study sites were arrayed similarly across the gradients of stream width, gradient and riparian cover. Approximately 20% of sites in south-eastern Queensland had localised patches greater than 1.25 m deep whereas such depths were uncommon in streams sampled in the Wet Tropics region. Mean site depth varied little between regions however. Although sites within both regions covered similar ranges in maximum current velocity recorded in each site, comparatively fewer sites in the Wet Tropics region had average current velocities less than 0.01 m.sec–1 (i.e. still water). This reflects the differences in regional hydrology. Rivers and streams of the Wet Tropics region rarely cease to flow.
Estimates of proportional cover and substrate composition derived from both schemes were then combined to give an overall representation of the habitat structure of each site by weighting the area characterised by each method (i.e. estimates derived from bank transects characterised 20% of the wetted area whereas the random points scheme characterised habit structure in the middle 80% of wetted area).
Substrate composition differed slightly between the two regions (Fig. 10). Coarse gravel was the dominant particle size in streams of south-eastern Queensland, whereas rocks were the dominant particle size in streams of the Wet Tropics. Bedrock was present in streams of this region also, but was almost absent from streams of south-eastern Queensland. The average contributions of mud, sand and fine gravel were very similar in both regions.
Ambient water quality conditions (Table 2) at each site on most sampling occasions were characterised by the mean of three measurements for each parameter taken at each site. A pilot study comparing measures taken at each of the
The two regions differ substantially with respect to the types and abundance of different cover available to fishes. Aquatic macrophytes and filamentous algae both
37
Freshwater Fishes of North-Eastern Australia
Figure 11 shows the frequency distribution of the random points measures of current velocity, depth, substrate composition and microhabitat cover elements. This figure differs from data presented in Figures 9 and 10 wherein the distribution of overall site means is presented. For example, although aquatic macrophytes comprised, on average, less than 1% of the area of sites in the Wet Tropics region (Fig. 10), 6% of the random point measures were positioned over a 1 m2 quadrat containing aquatic macrophytes. Comparing the same data for sites in south-eastern Queensland indicates that aquatic macrophytes were more commonly encountered and more extensive in areal coverage in this region. Data in Figure 11 is intended to allow
comprised about 10% of the area of sites located in streams of south-eastern Queensland but were essentially absent from study sites in the Wet Tropics region (Fig. 10). Whether this is due to regional differences in hydrology, canopy cover or nutrient status is unclear. Submerged vegetation (para grass in the Wet Tropics region) was, on average, more common in streams of the Wet Tropics region but note that median values differ little between regions. It is worth noting that para grass (Urochloa (=Brachiaria) mutica) is able to establish in well-shaded streams and is a potentially significant threat to the maintenance of habitat structure in rainforest streams [108, 250, 1092] and to freshwater fishes [94].
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Figure 9. Macro and mesoscale habitat characteristics of study sites located in rivers of the Wet Tropics region (solid bars, n = 118 locations and 284 mesohabitat unit samples) and south-eastern Queensland (open bars, n = 278 locations and 790 mesohabitat unit samples).
38
Study area, data collection, analysis and presentation
microhabitat preference would require that microhabitat availability at only those sites in which a species occurred, rather than across all sites examined (as is presented in Figure 11), was used to base the comparison. To present this information for individual species and study river was beyond the scope of this text (see also section on Macro, meso and microhabitat use below).
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Figure 11. Microhabitat availability in the Mulgrave and Russell rivers, Wet Tropics region (closed bars, n = 5589 habitat sampling points), and the Mary and Albert rivers, south-eastern Queensland (open bars, n = 9456 habitat sampling points). Note that these data represent the frequency distribution of random points measurements of different microhabitat parameters.
0
Microhabitat structure
The ranges of water quality parameters encountered during the study period are shown in Figure 12. Streams of the Wet Tropics region tended to be warmer than those in south-eastern Queensland, reflecting the latitudinal gradient shown in Figure 3. Very few sites were examined in which temperature might be thought to be approaching extreme levels. Similarly, most sites examined where welloxygenated. Streams of the Wet Tropics region tended to be slightly more acidic than those of south-eastern Queensland, although most were circum-neutral in acidity. Water clarity was high in both regions except in the tannin-stained aquatic habitats of the coastal wallum (Banksia dominated) ecosystems of south-eastern Queensland. The two regions differ most with respect to
Figure 10. Box plots of variation in the substrate composition and microhabitat structure of mesohabitats in rivers of the Wet Tropics region of northern Queensland (closed circles, n = 284 mesohabitat unit samples) and south-eastern Queensland (open circles, n = 790 mesohabitat unit samples). The lines at the top, middle and bottom of each box represent the 75th percentile, median and 25th percentile, respectively. Upper and lower bars represent 90th and 10th percentiles and means are represented by symbols.
the reader to assess the match between micohabitat use by individual species and the availability of different microhabitats. Note however, that a quantitative assessment of
39
Freshwater Fishes of North-Eastern Australia
[1420]; an updated version of which is available online at www.marine.csiro.au/caab.
electrical conductivity. Streams of the Wet Tropics region rarely exceeded 100 µS.cm–1 whereas the majority of streams examined in south-eastern Queensland exceeded 250 µS.cm–1. 40
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Description This section is intended to provide the reader with a detailed mechanism for confirming the identification of a specimen determined through use of the dichotomous key provided. We present standardised diagnoses and descriptions (meristics, morphometrics and colour patterns) of species in life and in preservative. Where possible, we provide length/weight relationships based on our own data or sourced from the published literature. Geographical or subspecific variation in appearance is discussed and features allowing differentiation between closely related species are highlighted. Wherever possible, we have used the original description or subsequent taxonomic reviews as our main source of information. However, when such sources contain limited or erroneous data, we have used alternative sources or our own data sets. A drawing is provided for each species that should enable the reader to check meristic and morphometric characters listed in the text. In most cases, these drawing were of preserved specimens and the size, sex, locality and date of collection are given. Occasionally, figures were based on photographs of specimens. The year in which the figure was drawn is also given.
40
Systematics The nomenclatural history and details of synonomy are given. Wherever possible, the results of morphological or genetic studies examining phylogenetic and phylogeographic relationship are presented and discussed. The chapters are arranged in approximate phylogenetic order (after Paxton and Eschmeyer [1041]) and the systematics of a particular family or genus is described in the summary for the first species listed in each family or genus.
20 0
Turbidity (NTUs)
Figure 12. Water quality in streams of the Wet Tropics region (closed bars, n = 233 mesohabitat unit samples) and southeastern Queensland (open bars, n = 778 mesohabitat unit samples).
Distribution and abundance A detailed account of the distribution of each species is presented based on literature accounts and our own survey results. The distribution of all fish species in coastal drainage basins of Queensland is given in Appendix 1 and the combined reference sources for these data are given in Appendix 2. We present information on distribution at a variety of scales from global, national, regional and individual river basins. We have not included maps detailing the distribution for each species. Information regarding the distribution of a particular species is often drawn from a variety of sources, yet some basins may not have been sampled adequately and it may be unknown whether a species does occur there. Maps tend to give an overall impression of distribution and do not highlight those basins in which a species may be naturally absent or those
Data presentation and format of species summaries Nomenclature We have primarily followed the nomenclatural conventions used in Allen et al. [52] except where we have received advice to the contrary from other taxonomists. Common or vernacular names are given where available and follow those given in Allen et al. [52]. Common names often vary markedly across a species’ range, with the attendant risk of confusion between different researchers. If common names are to be used and the potential for confusion removed or minimised, we recommend the adoption of standardised common names. We have also listed a unique code number of each species. This code is derived from CSIRO’s Codes for Australian Aquatic Biota (CAAB)
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25% of sites examined, some fish with limited distribution may be dominant (high rank) in those sites in which they occur, perhaps because they have highly restricted habitat requirements, but contribute little to abundance over all sites examined. Similar summaries are given for biomass data. For each species the average and maximum numerical density and biomass density, respectively, for those sites in each basin in which each species occurred are also presented and discussed (note that biomass data was not collected for a small proportion of samples in south-eastern Queensland).
for which inadequate data exists. We feel it important that these factors be identified and that readers have the necessary information to make their own judgements about patterns of distribution. We have presented data concerning the abundance of species in a variety of ways. First, data collected by us over the period 1994–2003 is presented in a consistent tabular format to facilitate comparison within and across drainage basins and between regions. For example, Table 3 lists data for the Fly-specked hardyhead Craterocephalus stercusmuscarum fulvus in drainages of south-eastern Queensland. Data are listed for each basin and for all basins combined. The proportion of the total number of locations in which this species was collected is given as an indication of how widespread each species is. For example, C. s. fulvus is a relatively widespread species in south-eastern Queensland, occurring in about one quarter of all locations examined. Note that although this species is moderately common in many river basins, especially the Mary River, it is absent from the Logan-Albert River and rare in some other streams and rivers. The proportional contribution of this species to the total number of fish collected is given as % abundance, as an indication of how abundant this species is relative to other species found in the region or within individual basins. Similarly, an indication of its ranked abundance is also given. For example, C. s. fulvus was the 10th most abundant species collected in rivers of southeastern Queensland but contributed only 2.8% of the total number of fish collected, and much less of the total biomass. Also listed in parentheses are the equivalent summaries at only those sites in which this species occurred, to give an indication of the local abundance and biomass of each species. For example, C. s. fulvus is relatively more common and contributes more to the total number of fish collected in this reduced number of sites. Although this is to be expected for a fish occurring in only
Second, we have attempted to summarise the findings of studies in which quantitative electrofishing estimates of abundance and biomass are not available but in which abundance data are presented as catch per unit effort or as relative abundance. We identify potential problems associated with comparison across studies employing different methodologies. Information drawn from the literature concerning distributional limits and abundance must be interpreted with care, taking into account differences in concentration of sampling effort and study site location, as well as differences in survey methodology (i.e. electrofishing, seine-, gill- and hand-netting, bait trapping, visual census, ichthyocides). Different methods are often selective with respect to the particular species or size of fish they collect. However, abundance information derived from our sampling of wadeable streams is directly comparable, as it has been collected using standardised quantitative sampling methods. The distributional information summarised in Appendix 1 has been drawn from many studies undertaken over a relatively long period. Some literature sources used were published in the 1880s, for example. The abundance and distribution of many species, particularly migratory
Table 3. Distribution, abundance and biomass data for Craterocephalus stercusmuscarum fulvus. Data summaries for a total of 4608 individuals collected from rivers in south-eastern Queensland over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton rivers and Bay rivers streams and streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
25.8
62.0
3.4
15.0
36.0
—
10.0
2.82 (7.96)
3.82 (6.90)
0.04 (2.27)
1.55 (14.47)
5.05 (11.90)
—
0.59 (40.39)
10 (6)
9 (7)
22 (5)
9 (2)
6 (2)
—
14 (1)
0.21 (0.69)
0.27 (0.63)
0.01 (0.03)
0.24 (0.41)
0.63 (1.24)
—
0.11 (0.43)
19 (10)
14 (10)
14 (6)
10 (7)
10 (7)
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13 (3)
Mean numerical density (fish.10m–2)
0.99 ± 0.13
1.06 ± 0.17
0.03 ± 0.03
0.51 ± 0.16
0.88 ± 0.18
—
0.39 ± 0.37
Mean biomass density (g.10m–2)
0.68 ± 0.32
0.71 ± 0.14
0.03 ± 0.03
0.25 ± 0.03
0.58 ± 0.15
—
0.34 ± 0.34
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Freshwater Fishes of North-Eastern Australia
Table 4. Macro/mesohabitat use by Craterocephalus s. fulvus in rivers of south-eastern Queensland. Data summaries for 4608 individuals collected from samples of 232 mesohabitat units at 76 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
species, is known or suspected to have contracted in recent years due to deteriorating catchment condition, increasing human pressures and an increase in the number of artificial barriers to fish movement caused by dams, weirs and other infrastructure. The impacts of anthropogenic disturbances on fish species’ distributions and abundances are treated in detail in the section on Conservation status, threats and management requirements.
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Macro, meso and microhabitat use We have presented data concerning macro- and mesoscale habitat use in a consistent tabular form in order to facilitate comparison between species within regions or within species across regions. Ontogenetic variation in habitat use is examined for some large-bodied species and additional information available in the literature is also discussed. For example, Table 4 lists the habitat use of C. s. fulvus in rivers of south-eastern Queensland. The minimum and maximum values for each parameter are given to provide an indication of the range of conditions over which a species may be found. These data can be used in conjunction with information concerning a species’ distribution within a catchment or region (e.g. Table 3) to gain a better understanding of distribution and habitat use at large and local spatial scales. For example, C. s. fulvus occurs in catchments ranging from only 19.3 to 1540 km2 in area (Table 4), yet data presented in Table 3 indicates that it is not necessarily evenly distributed across that range. The average of each habitat parameter calculated across all sites in which each species occurred is also presented. In addition, we have included an estimate of mean habitat conditions weighted by the density of fish at each site. In effect, each fish is the sample unit rather than the site. Weighting the mean by density gives an approximation of particular habitat conditions in which this species is most abundant and which may be especially favoured or selected by a species. For example, the difference between the average and weighted average values for site gradient, mean water velocity and the proportional contribution of sand to the substrate composition (Table 4) indicate that, although C. s. fulvus occurs on average, in streams with a gradient of 0.3%, an average current velocity of 0.14 m.sec–1 and 18.4% sand substrate, this species is more abundant in sites in which the gradient and current velocity are comparatively reduced and sand is more abundant.
Max.
Mean
W.M.
19.3 10211.7 9.0 270.0 4.0 311.0 0 240 0.7 46.8 0 80.0
1540.1 73.5 193.1 83 12.3 28.9
996.0 56.1 220.8 89 11.5 24.1
2.86 1.08 0.85
0.30 0.43 0.14
0.17 0.43 0.09
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec–1) 0 Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
99.6 100.0 56.7 70.9 65.8 41.1 76.0
8.4 18.4 21.9 30.1 16.8 3.0 1.4
7.5 31.8 22.6 24.7 12.1 0.9 0.4
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
64.5 65.9 26.7 65.7 43.3 43.3 31.0 15.5 50.0 58.8
19.8 11.8 1.5 8.6 2.3 9.1 3.8 3.0 8.5 12.1
23.2 15.5 0.9 15.0 3.5 6.9 2.9 2.4 3.9 6.9
0.20 m.sec–1). An example of microhabitat use histograms for C. stercusmuscarum collected from the Wet Tropics region and south-eastern Queensland is given in Figure 13. The microhabitat use data presented does not necessarily give an indication of habitat preference thus must be interpreted with caution. Preference for a particular depth class or sediment particle size for example, requires that fish use such microhabitats more frequently than predicted by chance due to the relative availability of that habitat element in the environment. Although it is possible to represent a species preference for certain habitat configurations by standardising habitat use data in relation to data on habitat availability, we have not done this in a systematic quantifiable manner here as such a method of standardisation still does not ensure that habitat preference information is transferable across sites with varying habitat structure. The microhabitat use summaries presented here were usually generated from a large
Mesoscale data describe the type of habitat (e.g. riffle, run or pool) in which an individual species is found whereas the microhabitat data reveal the type of conditions which species occupy within that habitat. Microhabitat use data is presented as a series of frequency histograms showing the proportion of the total number of fish collected within different categories (e.g. current velocity between 0.11 and
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consistent tabular format detailing minimum, maximum and mean values. Mindful of the potential for geographic variation in water quality tolerance, we have presented data for different populations wherever possible. The number of samples upon which the summaries are based is also given in most cases. We have relied extensively on the information provided by Bishop et al. [193] concerning ambient water quality conditions experienced by fishes in the Alligator Rivers region. In such cases, the number of samples from which summaries are based, varies between parameters. We have not listed sample size when these data are presented. Note however, that the research by Bishop et al. [193] occurred over a two year period, study locations were sampled many times over a range of seasonal and hydrological conditions and sample size for some parameters was often very large (>100 replicate measures). These data are therefore very comprehensive and represent the most detailed examination of the habitat requirement of fishes in north-western Australia. We also present summaries derived from the published work of other researchers, particularly that of Hamar Midgley ([944, 946]). In such cases where minimum, maximum and mean values are not explicitly stated we have reanalysed the data presented in the original reports.
number of fish collected from a large number of sites and sampling occasions and hence environmental conditions. They do therefore represent a general guide to the microhabitat conditions commonly used by each species. 60
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Figure 13. Microhabitat use by Craterocephalus s. stercusmuscarum in the Wet Tropics region (solid bars) and C. s. fulvus in south-eastern Queensland (open bars). Summaries derived from capture records for 78 individuals from the Johnstone and Mulgrave rivers in the Wet Tropics region and for 558 individuals from the Mary River, south-eastern Queensland, over the period 1994–1997 [1093].
We must place several caveats on the extent to which data describing ambient water quality conditions represents tolerance per se. First, the data represents the conditions in which fish occur. However, the fact that a species occurs in particular conditions does not indicate that it prefers such conditions nor does it indicate that its biology is unaffected by those conditions. Sublethal stresses may impact on the fitness of an individual, yet it may, for whatever reason, be forced to endure such conditions (e.g. during circumstances when fish may be restricted to isolated pools during extended periods of zero flows). Second, if the lethal tolerance levels of a particular species are exceeded at a site, then it will no longer occur there, and as a consequence this site will not be included in the sample. Third, the majority of study sites were selected on the basis that they were largely undisturbed, thus we intentionally avoided sites with poor water quality. The main exception to this was for a subset of moderately to highly degraded sites in south-eastern Queensland.
Environmental tolerances The tolerance of north-eastern Australian freshwater fishes to extremes in water chemistry or toxicants is unknown for most species. We review experimental data for each species where available. In the absence of such data we have presented summaries of ambient levels of five major water quality parameters (temperature, dissolved oxygen, pH, conductivity and turbidity) drawn from our own field studies and the research of others. Data are presented in a
It is important to note that environmental tolerances are likely to vary between life history stages (i.e. eggs and larvae might be especially vulnerable) and may vary considerably between different geographic populations and between populations occurring in different habitat types. For example, populations occurring in wetlands may be more tolerant of hypoxia than are populations occurring in streams, and populations occurring in high elevation, well-shaded streams may be less tolerant of
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10
0
0
Substrate composition
Microhabitat structure
43
Freshwater Fishes of North-Eastern Australia
appropriately applied to all species. These different maturity classifications are compared in Table 5. Another method used to quantify reproductive development in individuals and populations is the Gonadosomatic Index (sometimes referred to as Gonosomatic Index) and abbreviated as GSI. It is a measure of the relative contribution of the weight of the developing gonads to the total weight of the individual and is estimated according to the formula: GSI = gonad weight/total body weight x 100. Ideally, body weight should refer to the body weight minus the weight of any material within the gut. It is an effective way of comparing temporal changes in reproductive development. For example, in some species the spawning period is highly concentrated within a short period. Temporal changes in GSI will reflect this, being low for most of the year, then rapidly increasing as the spawning period approaches, and peaking during the spawning period. Other species with a more protracted spawning period show a more gradual increase in GSI values. GSI values are effective for comparing the reproductive investment of individuals or populations. High GSI values are indicative of high investment into reproduction. Short-lived species often have high GSI values as they have a limited time in which to reproduce. Longer-lived species may be able to spawn over several years and therefore do not need to invest so much effort in reproduction in any one year. Female fish typically have higher GSI values than males.
elevated temperatures than are populations occurring in lowland open streams. Notwithstanding these caveats, the information presented here is the first comprehensive and consistent examination of the water quality requirements of the fish of north-eastern Australia. Experimental examination of sublethal and lethal effects of varying water quality is urgently required. Reproduction In this section we review all known published studies for each species. In addition, we present previously unpublished data concerning the life history of a small number of species; the reader is referred to Pusey et al. [1108] for details of methods used. In addition to the review of reproductive biology, summary data are listed in standardised tabular format allowing the reader to quickly access information and identify knowledge gaps. Data listed covers various aspects of reproductive biology such as fecundity, spawning phenology, critical environmental thresholds, and cues and age at maturity. Information concerning embryology and larval development is also presented where available. The methods and terminology used in studies of fish reproductive biology often vary greatly. We have attempted to standardise terminology as much as possible, particularly that relating to fecundity. In many species, especially those characterised by small size at maturity, the intraovarian eggs are not all at equivalent stages of development. Rather, groups of eggs develop in concert, are simultaneously ovulated, and then oviposited in a batch. Another batch then begins to develop. We have used the term batch fecundity to refer to the number of large ovulated or near ovulated eggs within an ovary in such species. Total fecundity refers to the number of ovulated and follicular eggs other than primary oocytes (i.e. all yolked eggs) present within the ovaries of an individual female. It is an instantaneous estimate of fecundity. Total fecundity can sometimes be taken to mean the total number of eggs produced in a spawning season which may be much higher for batch, repeat or protracted spawners. There is no real way to estimate this latter version of fecundity unless individual females are followed throughout their reproductive life.
Movement Fish move over a variety of spatial scales and for a range of biological and ecological incentives. Some fish may only move within their own home range, which may be as small as a single pool or riffle, juveniles of some species may undertake mass upstream dispersal movements, whereas others may have a spawning migration into freshwater habitats other than those occupied in periods outside of the spawning season. Others may migrate out of freshwater to estuarine or marine ecosystems. Migratory movements may occur in the larval, juvenile or adult phase. Movement is a critical aspect of the ecology of many riverine fishes and one that is very easily disrupted (e.g. by artificial barriers), often with deleterious effects. Mallen-Cooper [852] provides a very useful summary of migration in freshwater fishes and McDowall [890] discusses in depth the various types and functions of diadromous migration undertaken by fishes. We provide a review of the movement/migration biology of each species (i.e. migration pattern, time of year, age at which migrations occur, critical habitats, anthropogenic factors impeding movement) where such information is available. A better understanding of the movement biology of the fishes of north-eastern Australia is urgently required and represents one of the greatest impediments to better management of the fauna.
A number of schemes have been developed to characterise the developmental stages of reproductively mature fishes based on the visible appearance and size of the gonads. Variation in the proportional contribution of different reproductive stages to the total adult population can then be used to estimate the timing and length of the spawning period, and whether maturation occurs in one habitat or another for example. However, the various schemes available and used in studies of species occurring in northern Australia are not always consistent with one another or
44
Table 5. Generalised classifications of maturity stages in fishes, with approximate correspondence between them (modified from Bagenal and Braum [120]). Note that allocation of a given individual to a particular maturity stage is partly subjective, species dependent (different fish species have varying reproductive morphology) and dependent on whether specimens are fresh or preserved (it is difficult to extrude eggs and milt in preserved specimens). Pollard [1061], Bishop et al. [193]
Davis [360]
Beumer [173]
Milton and Arthington [949, 951]
Pusey et al. [1093, 1108]
I Virgin. Very small sexual organs close to vertebral column. Testes and ovaries transparent, colourless to grey. Eggs invisible to naked eye.
I Immature. Young individuals which have not yet engaged in reproduction; gonads of very small size.
I Immature virgin. Testes and ovaries thin and threadlike, translucent and colourless; sexes usually indistinguishable.
I Immature virgin. Testes are strap-like with little folding and twisting, translucent and almost colourless. Ovaries are narrow and small, colourless and generally translucent. Some opaque white oocytes are visible to the naked eye in larger ovaries.
I Juveniles. Immature individuals where sexes are indistinguishable. Gonads are very small.
I Juveniles. Gonads small, testes almost indistinguishable, extremely thin and almost colourless. Ovary thin, translucent, without visible oocytes (X40 magnification).
I Immature. Gonads not visible or small, thin and strap-like.
II Maturing virgin. Testes and ovaries translucent, grey-red. Length half, or slightly more than half, the length of ventral cavity. Single eggs can be seen with magnifying glass.
II Resting stage. Sexual products have not yet begun to develop; gonads of very small size; eggs not distinguishable to the naked eye.
II Developing virgin and recovering spent. Testes thin and strap-like, translucent and greyish, sometimes with melanophores. Ovaries more rounded, translucent and colourless, eggs not evident to the naked eye.
II Developing virgin and recovering spent. Testes of developing virgins are thicker, translucent and white, and they begin to twist and fold. Testes of recovering spent fish are thicker, the main body of the testes showing numerous translucent regions and the lobes tending to be opaque off-white and rough in texture. Ovaries are more rounded, the ovary wall is thick and opaque, and oocytes are creamy white and opaque.
II Inactive. Immature (sexes distinct) and recovering individuals. Gonads small. Oocytes distinguishable under X40 (L. unicolor) and X10 (M. splendida) magnification.
II Inactive. Immature virgins and recovering spent fish. Testes thin, strap-like and creamy-white. Ovaries small, regularly shaped and elongated. Oocytes distinguishable (X10 magnification).
II Early developing. Testes elongate, whitish sac; ovary pale orange, with few oocytes, visible at X20 magnification.
III Developing. Testes and ovaries opaque, reddish with blood capillaries. Occupy about half of ventral cavity. Eggs visible to the eye as whitish granular.
III Maturation. Testes change from transparent to a pale rose colour; eggs are distinguishable to the naked eye; a very rapid increase in weight of the gonad is in progress.
III Developing. Testes thickening, opaque and greyish-white, smooth texture. Ovaries thickening, opaque and pale yellowish, eggs small but visible to the naked eye.
III Developing. Testes are increasing in size, the main body becoming opaque and white, and the tips of lobes and lateral margins becoming creamy-white. Ovaries increase in size, the ovary wall becoming thinner and translucent, and oocytes of various sizes are present, larger oocytes being creamy white and opaque.
III Maturing. Gonads increased in size. Testes swollen, pale, twisted and folded and occupying at least half of the body cavity. Ovary swollen to fill width of abdominal cavity, oocytes visible to naked eye.
III Developing virgin and resting adult. Testes grey-white; Ovaries orange, often with red flecks, eggs opaque, just visible to the naked eye, small oil droplets present in larger oocytes.
IV Maturing. Testes enlarged, opaque and whitish, smooth texture. Ovaries enlarged, opaque and yellowish, eggs large.
IV Maturing. Testes are large, occupying half of the body cavity, and the lobes and lateral margins are creamy-white and rough in texture. Ovaries occupy over half of the body cavity, and the current season’s oocytes are distinct in size from reserve oocytes and are opaque and yellow.
III Maturing. Gonads increasing in size. Ovary of M. splendida visible to the naked eye and of L. unicolor distinguishable under X10 magnification. Tips of filaments on oocytes of M. splendida first begin to appear.
IV Developing. Testes reddish-white. No miltdrops appear under pressure. Ovaries orange reddish. Eggs clearly discernible; opaque. Testes and ovaries occupy about two-thirds of ventral cavity.
IV Late developing. Testes opaque, white to grey-white, no milt present; ovaries orange, eggs clearly visible, opaque, larger oil droplets present throughout oocyte.
Study area, data collection, analysis and presentation
Nikolsky [993]
45
Kesteven [713]
Nikolsky [993]
Pollard [1061], Bishop et al. [193]
Davis [360]
Beumer [173]
Milton and Arthington Pusey et al. [949, 951] [1093, 1108]
V Gravid. Sexual organs filling ventral cavity. Testes white, drops of milt fall with pressure. Eggs completely round, some already translucent and ripe.
IV Maturity. Sexual products ripe; gonads have achieved their maximum weight, but the sexual products are still not extruded when light pressure is applied.
V Mature. Testes fill most of the body cavity, opaque and creamy-white, smooth texture. Ovaries fill most of body cavity, opaque and yellow, eggs large.
V Mature. Testes are generally opaque and creamy-white, but regions of the main body are still slightly translucent, and the testes occupy up to two-thirds of the body cavity. Ovaries occupy most of the body cavity, the ovary wall is very thin and translucent, and oocytes are large and yellow, tending to become translucent.
VI Spawning. Milt and roe run with slight pressure. Most eggs translucent with few opaque eggs left in ovary.
V Reproduction. Sexual products are extruded in response to very light pressure on the belly; weight of the gonads decreases rapidly from the start of spawning to its completion.
VI Ripe. Testes fill body cavity, opaque and pure white, smooth and crumbly texture, milt extruded by pressure on abdominal wall. Ovaries distend body cavity, translucent pale golden, eggs large and extruded by pressure on abdominal wall
VI Ripe. Testes are opaque and white, and milt can be extruded by applying pressure to the abdominal wall. Ovaries distended the body cavity. Oocytes are large, translucent and lemon coloured, and can be extruded by slight pressure on the abdominal wall.
IV Ripe. Gonads have achieved maximum size and weight with oocytes plainly visible in ovaries. This stage culminates in running ripe fish when milt or oocytes may be readily extruded from L. unicolor in response to light pressure on the abdominal region. L. unicolor oocytes have a single distinct oil-vacuole, while M. splendida oocytes are completely enveloped by the filaments and have between 14 and 30 oilvacuoles.
IV Ripe. Gonads have reached maximum size. Testes opaque and white; milt can be easily extruded with slight abdominal pressure. Ovary distends body cavity. Oocytes large, translucent yellow, easily extruded with slight pressure on abdomen.
VIII Spent. Testes and ovaries empty, red. A few eggs in the state of reabsorption.
VI Spent condition. The sexual products have been discharged; genital aperture inflamed; gonads have the appearance of deflated sacs. The testes usually containing some residual sperm, and the ovaries a few left-over eggs.
VII Spent. Testes thin and flaccid, greyish, sometimes white areas (residual sperm). Ovaries thin and flaccid, translucent and colourless to pale yellowish, sometimes contain large opaque-yellow residual eggs.
VII Spent. Testes are thin and flaccid, irregular in texture, and become translucent while regions remain opaque and white (residual sperm). Ovary wall is opaque, and ovaries are flattened and irregular in shape. Some large residual eggs may be present. These tend to become opaque and creamywhite, and reduce in size as they are reabsorbed.
II Recovering spent. Testes translucent, greyred. Length half, or slightly more than half, the length of ventral cavity. Single eggs can be seen with magnifying glass.
II Resting stage. Sexual products have been discharged; inflammation around the genital aperture has subsided; gonads of very small size. Eggs not distinguishable to the naked eye.
VII Spawning/spent. Not yet fully empty. No opaque eggs left in ovary.
46
V Spent. Gonads virtually empty. Testes normally with some residual sperm and ovaries with some remaining oocytes.
V Spent. Gonads reduced in size, irregularly shaped. Testes thin, flaccid and virtually translucent. Ovary reduced, small and flaccid, some enlarged oocytes remain but are irregularly distributed within ovary.
V Gravid. Testes white, and extrude milt with pressure; ovaries yellow-orange with some translucent, round eggs, oil globules forming single polarized mass. VI Running ripe. Testes extrude milt without pressure. Ovaries with large numbers of ovulated eggs.
Freshwater Fishes of North-Eastern Australia
Kesteven [713]
Study area, data collection, analysis and presentation
Trophic ecology Dietary information for each species was obtained from a variety of sources including published literature, unpublished governmental and consultancy reports and unpublished data sets held by colleagues and collated elsewhere [705]. In instances where the dietary data from each study was presented separately for different sites, seasons and/or size classes for an individual species, we summarised the diet composition for each species within each study as a weighted average (weighting based on abundance). Means were weighted by abundances so as to represent the average condition for a given species and study. A full list of sources for the diet data used in the present study is given in the bibliography.
except when no volumetric, gravimetric or abundance data was available for a particular species. Frequency data was transformed so as to approach proportional representation by first ranking different items on the basis of their frequency (i.e. the most frequent was ranked 1, the second ranked 2, etc.), then inversed and divided by the sum of all inverse ranks. For example, the proportional contribution of the most frequently encountered item equals 0.66 when the diet is composed of only two items and 0.54 when there are three items. Dietary data was summarised to the maximum taxonomic resolution possible but we were constrained by the minimum level to which diet categories were distinguished in the literature and the manner in which diet items were pooled in many studies. Nevertheless, we distinguished between food sources of autochthonous and those of allochthonous origin, and between animal and vegetable material, and we grouped items according to general similarities in prey habitat occupation and size. We were able to distinguish 15 functional diet categories (Table 6).
Dietary information can be summarised in a variety of forms, each method being subject to varying degrees of bias and accuracy in estimating the relative importance of individual dietary items to the total diet. The volumetric contribution of individual items to a total diet, per cent abundance (the numerical proportion of each diet item), per cent dry weight and per cent wet weight were the most commonly used method for data presentation across the range of studies examined. We assumed that these methods estimated diet similarly. In studies where dietary data was expressed using more than one of these methods for a single species, the method approximating the volumetric and then gravimetric contribution was preferred over abundance data, although in the overwhelming majority of such studies both methods indicated similar dietary habits. We avoided using frequency of incidence data
We also discuss major spatial and temporal patterns in the diet of each species where such information was available in the literature. Ontogenetic variation in fish diets was examined for large-bodied species for which sufficient data was available. In these cases, age classes were recognised (termed juveniles and adults) and the body size delimiting each age class was presented. Very little information on the trophic ecology of larval fishes is available in the literature but was discussed where possible.
Table 6. Dietary categories used throughout the text. Diet category
Description
Unidentified
Includes the unidentified fraction, together with unidentified items often referred to as ‘other’ or ‘miscellaneous’ Terrestrial insects (primarily Hymenoptera, especially Formicidae), arachnids and other terrestrial invertebrates (e.g. annelids, isopods, gastropods) Aerial forms of adult aquatic insects (primarily Diptera and occasionally Trichoptera, Ephemeroptera and Odonata) and water surface invertebrates (e.g. Araneae, Gerridae and Collembola) Mammals, birds, reptiles and amphibians Terrestrial wood, bark, leaves, buds, fruits, seeds and pollen Includes organic detritus and occasionally mud or sand Includes aquatic macrophytes and charophytes Includes filamentous and non-filamentous epiphytic algae and phytoplankton Includes larval and adult stages of all aquatic insects occurring in the benthos and water column Bivalves and aquatic gastropods Decapod crustaceans Copepoda, Cladocera, Ostracoda and Chonchostraca Includes amphipods, isopods, oligocheate and polycheate worms, nematodes, Nematomorpha and Hirudinea Hydracarina, Rotifera, Hydra Includes bones, scales and eggs
Terrestrial invertebrates Aerial and surface aquatic invertebrates Terrestrial vertebrates Terrestrial vegetation Detritus Aquatic vegetation Algae Aquatic insects Molluscs Macrocrustaceans Microcrustaceans Other macroinvertebrates Other microinvertebrates Fish
47
Freshwater Fishes of North-Eastern Australia
existing and potential threats for each species or for different populations based on published data, recovery plans, consultancy reports, and our own information and interpretations. Each chapter concludes with a forecast of the future conservation status of the species and/or our perception of the major management issues needing attention by means of restoration, recovery or conservation actions.
Conservation status, threats and management The current conservation status of each species is given as listed in the Action Plan for Australian Freshwater Fishes by Wager and Jackson [1353], and the Australian Society for Fish Biology Conservation Status of Australian Fishes – 2003 [117]. We also report the conservation status of species listed under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and State legislation, where applicable. Following this we summarise
48
Neoceratodus forsteri (Krefft, 1870) Queensland lungfish
37 046001
Family: Ceratodontidae
Description Neoceratodus forsteri is a large species growing to 1500 mm, commonly to about 1000 mm [52]. Larger fish weighing 20 kg are not unusual [672, 690]. The largest lungfish caught by Illidge [626] from the Burnett River, south-eastern Queensland, in the 1890s weighed ~12.3 kg. O’Connor [1008] recorded a range of 825–1125 mm for 109 fish from the Mary River, south-eastern Queensland. Brooks and Kind [238] reported that lungfish from the Burnett River spanned 345–1420 mm TL and weighed 485–25 000 g, with a mean length of 906 ± 199.63 mm and mean weight of 7523 ± 4563 grams; most (80%) lungfish exceeding 1200 mm TL were females. The equation best describing the relationship between length (TL in mm) and weight (W in g) for 2361 individuals from the Burnett River (range 450–1305) is W = 9.96 x 10–6 L2.98, r2 = 0.956, p<0.0001; both sexes follow similar growth patterns except that females grow to larger size [238]. Figure: composite, drawn from photographs; drawn 2003.
tail is long and pointed. Pectoral fins large, fleshy and flipper-like; pelvic fins are situated well back on the body and are also fleshy and flipper-like. Each paired fin has an archipterygium (‘ancient wing’) with segmented axis and preaxial and postaxial branches [763]. Thin cartilaginous fin rays are formed in the dermis of the skin, separate from the cartilaginous archipterygium; these rays support the fin web [763]. The skeleton is partly ossified, partly cartilaginous, the vertebrae are pure cartilage, the ribs are hollow tubes filled with cartilaginous substance [742]. Large cycloid scales cover the body, ten rows on each side, grading to small scales on fins, each scale embedded in an epithelial pocket; scales overlap extensively such that vulnerable areas of the body are covered by a thickness of at least four scales. The third row of scales from the dorsal surface of the body is marked by a relatively indistinct lateral line that perforates the thick overlying scales at intervals [742]. Two unusually large and thick interlocking scales cover the back of the head where the bony skull is thin. Mouth small and subterminal in position; the anterior naris partly outside the upper lip and partly within; posterior part of the naris inside the mouth cavity. Dentition (see also Trophic ecology, below) is unusual; two incisors, restricted to upper jaw, are flat, slightly bent and
The following description of N. forsteri is taken largely from Allen et al. [52], Kemp [688, 690] and Krefft [742]. Adult fish have a wide flat head, and stout elongated body. Dorsal fin commences on the middle of the back and is confluent with the caudal and anal fins; the diphycercal
49
Freshwater Fishes of North-Eastern Australia
after the mottling has disappeared. The belly of a small lungfish is a muddy pink colour. Juveniles are capable of rapid colour changes in response to light but this ability is gradually lost as the pigment becomes denser [688].
denticulated on hind margin; these are followed by dental plates on upper and lower jaws [742]. Eyes small; snout and lips naked; well-endowed with sense organs (pores). Sense lines over the head show a series of pits connected by a subdermal canal. The distinguishing feature of N. forsteri is the possession of lungs used to breathe air, and gills used for respiration in water [1380]. Gills are developed on all branchial bars; the lung is a single long sac situated above and extending the length of the coelomic cavity, formed by a ventral outgrowth of the gut [478, 488, 1318]. Internally, the lung is divided into compartments by septa formed by infolding of the walls; each compartment is further divided to form a spongy alveolar region; blood capillaries run through this region of increased surface area, close enough to the air space in the lung to effect gaseous exchange [478]. The lung is connected with the pharynx by the pneumatic duct; a buccal force-pump like that of Amphibia fills the lung with air; exhalation is effected by contraction of smooth muscles in the walls of the lung [478].
Systematics When Krefft [742] first described the Queensland lungfish in 1870 he believed it to be a giant amphibian “allied to the genus Lepidosiren”. He also recognised the similarity of its dentition to fossil tooth plates of a creature known as Ceratodus thought to have been like a shark, hence the generic name (meaning ‘horned tooth’). The newly discovered fish became known as Ceratodus forsteri, after William Forster (Minister for Lands in the New South Wales Government) who provided two specimens to Krefft for scientific description [1381]. In 1871, Günther [488] published the first anatomical description of the lungfish in the journal ‘Nature’ and was adamant that the teeth of the living fish were indistinguishable from those of fossil forms. This view persisted until 1891 when Teller [1306] described a fossil calvarium (skull), associated with typical ceratodont tooth plates. This skull differed significantly from the skull of the extant fish [688] and Teller [1306] accordingly reserved Ceratodus for the fossil forms and gave the recent genus a new name, Epiceratodus. By then, however, de Castelnau [374] had described a living lungfish from Australia that he believed differed from Ceratodus forsteri in both body proportions and teeth. He named it Neoceratodus blanchardi, but within a year retracted this designation, recognising that he had described a juvenile lungfish (610 mm long) with teeth no different, on fuller examination, to those of C. forsteri [375]. By the laws of priority, the living species became known thereafter as Neoceratodus forsteri [688].
Neoceratodus forsteri has an unusually large karyotype (2n = 54), very large chromosomes and cells, and the cells have high nuclear DNA relative to other vertebrates but less than reported for lungfishes of the family Lepidosirenidae [1153]. Joss [672] has discussed the phylogenetic and physiological significance of these findings, for example, large cell sizes result in lowered capacity for gaseous exchange and consequently very reduced metabolic rate, which in turn is correlated with a slow growth rate and long life cycle. Adult fish are usually dark brown or olive-brown over most of the body with an underbelly that varies in colour from whitish to muddy salmon-pink [690]. The pink colour is much brighter during the breeding season, especially in males, otherwise there are no obvious distinguishing sexual characteristics [688]. The pink colour of the flesh has given rise to the common name of ‘salmon’ in some writings. Longman [824] noted that N. forsteri from the Burnett River had a narrow white margin to the paired fins and that this feature was also observed by Bashford Dean. Longman also noted a narrow whitish margin on the scales surrounding the eye [824].
Neoceratodus forsteri is one of five extant representatives of the ancient and once speciose air-breathing Dipnoi (lungfishes) that flourished in the Devonian (c. 413–365 m.y.b.p.) and is the most primitive surviving member of this lineage [420, 1153]. It is the only extant member of the family Ceratodontidae, confined to Australia [52]. Fossil tooth plates discovered at Lightning Ridge, New South Wales, are indistinguishable from those of living N. forsteri indicating that this species was already present in the Early Cretaceous (c. 140–165 m.y.b.p.) [689, 693]; an opalised tooth discovered at Walgett, New South Wales, places this species in the Upper Cretaceous [294]. Neoceratodus forsteri is therefore the oldest living dipnoan species [693], the South American and African lungfishes of the family Lepidosirenidae being more recently derived [169]. Fossil records indicate that in the Miocene (15 million years ago) there were nine species of lungfishes in Australia, living in lakes and rivers in central, eastern and northern Australia [688]. Neoceratodus
Juvenile fish have different body proportions to those of mature fish. The head is rounder, the fins relatively smaller and the trunk more slender. The mouth is initially terminal but shifts back as the fish grows. The dorsal fin reaches to the back of the head in young juveniles and gradually moves caudally, until it extends only to the middorsal region in the adult fish. Juveniles are distinctly mottled with a ground colour of gold or olive-brown. There are also patches of intense dark pigment which persist long
50
Neoceratodus forsteri
Other translocations of N. forsteri were made into the North Pine River (eight individuals), a lagoon near the Albert River (five individuals), the upper Coomera River (16 individuals) and the Condamine River near Warwick (21 individuals) [1317]. All translocations were undertaken because O’Connor [1008] and others (e.g. Illidge [626] and Bancroft [123]) believed that the species was becoming extinct within its natural distribution [164, 841]. The fate of these translocations is poorly documented. There have not been any recent surveys to ascertain whether the introductions into the Coomera River were successful. No lungfish have been recorded during surveys of the Condamine River [664], nor has recent extensive sampling at numerous locations in the Albert River yielded N. forsteri [1093]. Thomas Bancroft wanted to establish a hatchery at Blue Lake on North Stradbroke Island for production of N. forsteri but failed to raise the necessary interest and funds [841]. However, a few lungfish were released into Blue Lake and 18-Mile Swamp on the island, evidently unsuccessfully [690, 1316, 1317]; no past or recent surveys of these freshwater systems have recorded this species [84, 105, 154, 1316]. On the mainland, introductions of N. forsteri, both official and independent of any authority, have resulted in viable populations in several sizeable waterbodies including Lake Manchester and Gold Creek Reservoir near Brisbane [690] and the impoundments of Somerset and Wivenhoe dams situated in the middle Brisbane River [688]. According to Thomson [1317] stocks in Enoggera Reservoir and the Brisbane River have thrived and provided a source of specimens for scientific research all over the world. However, Kemp [164] has stated that the population in Enoggera Reservoir declined after spraying of water hyacinth (Eichhornia crassipes) in 1974 eliminated the main spawning substrate for N. forsteri. Every specimen caught in Enoggera Reservoir recently has been very old [1422]. This species has also been stocked in impoundments in the Logan and Caboolture rivers.
forsteri was one of them. It once extended to the centre of the Australian continent (Lake Eyre drainage) prior to the Pleistocene (c. 1.6 m.y.b.p.) [1257]. Neoceratodus forsteri displays low allelic diversity at allozyme and mtDNA loci and minimal genetic differentiation between populations from the Mary, Burnett and Brisbane (possibly a translocated population) catchments; average heterozygosity across all loci was found to be 0.03 [420]. Frentiu et al. [420] suggested that this low level of genetic variation at allozyme and mtDNA loci could be attributed to population ‘bottlenecks’ associated with periods of range contraction, probably during the Pleistocene, and/or in recent times during the periods of episodic or prolonged drought that are known to reduce some reaches of these river systems to a series of isolated pools [1093, 1095]. Long generation times [238] and the vulnerability of juvenile lungfish to predators [127, 1380] are thought to contribute to slow recovery of lungfish populations after periods of population contraction [420]. The minimal level of genetic differentiation between the geographically separate Mary and Burnett river populations was attributed to historical connection of these systems, probably at the height of the Pleistocene when sea levels were lower than at present [420]. Hughes et al. [606] attributed similar patterns of genetic variation in the Oxleyan pygmy perch, Nannoperca oxleyana, to historical confluence and admixture of drainages in this area of south-eastern Queensland. Distribution and abundance Neoceratodus forsteri is restricted to river systems of southeastern Queensland [52], where it occurs naturally in the Burnett and Mary rivers and possibly also the Brisbane River [690]. There is disagreement as to whether the Brisbane River population formed part of the species’ natural range at the time of European settlement, or is the product of translocations made in 1895 and 1896 for acclimatisation purposes [1008, 1317]. O’Connor [1008] reported several transfers of N. forsteri into the Brisbane River basin. Five fish went into a dam near Cressbrook connecting with the Brisbane River during floods, two individuals into a pond in the city Botanic Gardens (adjacent to the Brisbane River) and eight individuals into Enoggera Reservoir on Enoggera Creek, draining into the estuary of the Brisbane River [1008]. Kemp [690] believes it unlikely that the five lungfish introduced into Cressbrook Dam could be responsible for the whole of the lungfish population in the Brisbane River, for several compelling reasons. However, genetic analysis of allozyme and mtDNA loci has shown that the Mary and Brisbane river populations share a rare haplotype (haplotype G), a finding that Frentiu et al. [420] believe is ‘most consistent with a translocation scenario’.
The most recent surveys of N. forsteri in its natural range are those of Brooks and Kind [238]. They captured N. forsteri in the Burnett River from the Ben Anderson Barrage (AMTD 23.9 km) to approximately AMTD 335 km, and also within the Boyne River to the wall of Boondooma Dam and upstream to the gorge sections of both the Auburn River and Barambah Creek. They could find little evidence that N. forsteri occurs upstream from Barambah Gorge, despite extensive sampling in Barambah Creek and in Bjelke-Petersen Dam, Silverleaf Weir and Joe Sippel Weir [238]. Neoceratodus forsteri was one of the most regularly encountered fish species during surveys conducted between January 1997 and February 2000, when the total catch of lungfish (by targeted boat
51
Freshwater Fishes of North-Eastern Australia
Environmental tolerances There is very little quantitative information on the environmental tolerances of N. forsteri. Kemp [692] stated that this species prefers deep pools at temperature of 15–25°C. Laboratory experiments have shown that 25°C is close to the preferred temperature for juveniles (27–51 g in weight) of this species, and that it is relatively cold hardy, living in areas of the Brisbane River with an annual thermal range of 11–31°C [479]. Tolerance of a similar thermal range (10–30°C) is indicated by field data recorded by Brooks and Kind [238] at sites sampled for evidence of spawning. Data in Table 1 summarise records from sites where evidence of spawning activity was obtained (14/15 sites) and hence, mature N. forsteri had been present. Neoceratodus forsteri occurs in neutral to mildly basic waters of low to moderate conductivity and relatively high dissolved oxygen concentration. Brooks and Kind [238] found that water transparency was significantly higher at sites where spawning had occurred, however this could be a consequence of the preference for spawning in dense macrophyte beds that are more likely to be found in relatively clear water.
electrofishing and monofilament panel nets) was 2888 individuals [238]. Catches varied over time (annually and seasonally) and among river sections but the overall pattern was an increase in mean catch per unit effort (CPUE) with distance downstream from AMTD 321 km at the township of Ceratodus [238]. Higher catches at some sites during winter or spring surveys were attributed to spawning aggregations, whereas high catches in autumn were thought to reflect aggregations in deeper waterholes at the onset of the dry season [238]. Macro/meso/microhabitat use Neoceratodus forsteri lives in slow-flowing rivers and still water including reservoirs with some aquatic vegetation along the banks, and is most common in deep pools [52]. Their preferred depth is 3–10 m [692]. According to Kemp [692], lungfish live in groups, under submerged logs, in dense banks of aquatic macrophytes or in underwater caves formed by removal of substrate under tree roots in the river bank. This species is found over mud, sand and gravel bottoms. In the Mary River, N. forsteri is closely associated with overhanging vegetation, submerged woody debris, and dense macrophyte beds, whereas areas of open water were largely avoided [238]. In the Burnett River, very young fish <100 mm TL were captured in habitats similar to those used for spawning (see below), as were juveniles <300 mm TL, usually within dense beds of aquatic macrophytes over sand and gravel substrates [238]. However, the largest juveniles were captured amongst Hydrilla verticillata, a species rarely used as a site for spawning. Most juveniles were captured at depths less than 300 mm with the largest fish captured at the greatest depths [238]. Immature N. forsteri (300–700 mm) were most often captured in areas of dense submerged wood, undercut banks and dense aquatic macrophytes [238]. We have electrofished several individuals of similar size in large slow-flowing pools in the main channel of the Mary River in relatively shallow water (~1.3 m), close to the bank, among large log piles interspersed with aquatic macrophytes over sand and fine gravel substrates [1093]. We collected a further two fish (single individuals on two separate occasions) among submerged terrestrial grasses in fast-flowing runs in Wide Bay Creek (<0.45 m mean depth, >0.27 m.sec–1 mean velocity), a large tributary of the Mary River. It is presumed that these fish were in the process of moving through these likely sub-optimal habitats after dispersing from dry-season refuges as both sampling occasions coincided with periods of elevated discharge immediately following prolonged dry periods (> nine months) during which time Wide Bay Creek had dried out to a series of isolated pools.
Günther [488, 489] suggested that the possession of a lung enabled N. forsteri to live in aquatic habitats subject to seasonal stagnancy. He wrote ‘when the fish is compelled to sojourn in thick muddy water charged with gases which are the product of decomposing organic matter (and this must be the case very frequently during droughts which annually exhaust the creeks of tropical Australia), it commences to breathe air with its lung’ [488]. This view persisted for almost 100 years until finally dispelled by Grigg [480] in 1964. His field measurements at 22 sites in the Mary and Burnett rivers revealed dissolved oxygen concentrations ranging from 7–13.2 ppm under ‘the very situations considered by Günther and others to provide challenging respiratory problems’ [480]. Oxygen supersaturation at many sites was attributed to convection due to diurnal temperature fluctuations, circulation by wind, influxes of well-oxygenated water from riffles/runs and the presence of abundant aquatic vegetation [480]. Grigg [480] showed that juvenile and mature N. forsteri are more active at night, and surface to breathe more often at night or during flooding ‘when the fish would be forced into activity as it fights the current’. Respirometry studies on juvenile fish confirmed that individuals forced into activity supplemented aquatic respiration via the gills by surfacing to take air [480]. Neoceratodus forsteri is incapable of surviving complete desiccation [480], and does not survive dry seasons by secreting a mucous cocoon and burying itself in bottom muds, as does Protopterus [1256]. However, N. forsteri can survive out of water for several days if the surface of the skin is constantly moist, using the lungs to respire [672].
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Neoceratodus forsteri
Neoceratodus forsteri has complex courtship behaviour observed during studies in the wild [235, 477, 687] and in captivity [688, 760, 762, 764]. Grigg [477] described three distinct phases, firstly a searching phase when the fish ranged over a large area, possibly searching for potential spawning sites. Kemp [687] also described pairs of fish performing circling movements at the surface of the water close to beds of aquatic plants. During this phase, N. forsteri breathes air more frequently and usually more noisily than normal, possibly reflecting a greater physiological requirement for oxygen [125]. Individual fish have been observed to breathe air at regular intervals of about 20 minutes, with air breathing accompanied by a distinct loud burp made in the air with the lips clear of the water [687]. Kesteven [714] suggested that noisy breathing is a form of mating call, and Kemp [687] observed that lungfish seem to do their noisy breathing in concert, even responding to each other, close to but not within the areas where eggs are laid [688]. The next phase involves behaviour described by Grigg [477] as ‘follow the leader’ during which one fish, presumably the male, shows interest in the cloaca of the female, nudging her with his snout. The same fish occasionally took a piece of aquatic plant into its mouth and waved it about. Brooks [235] observed that up to eight individuals may be involved in follow-the-leader behaviour. Grigg [477] suggested that nudging the female probably stimulates her to spawn. In the third phase, the fish dive together through aquatic vegetation, the male following the female and presumably shedding milt over the eggs. When spawning actually occurs a pair of fish lie on their sides or become entwined [688]. Grigg [477] observed that spawning fish shake their tails from side to side possibly to facilitate the flow of reproductive products. Brooks [235] observed this behaviour immediately prior to the completion of spawning and proposed that it could serve to disperse the eggs. Lambkin [762] described slightly different spawning behaviour of N. forsteri held in large outdoor ponds.
Table 1. Physicochemical data for Neoceratodus forsteri at 14 sites in the Burnett River surveyed between 1995 and 2000 [238]. Parameter Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (Secchi depth in cm)
Min.
Max.
Mean
10.0 6.9 7.0 421.0 50.0
30.0 15.6 9.1 1165.0 150.0
19.9 10.5 7.9 716.0 77.4
Reproductive biology Neoceratodus forsteri spawns and completes its entire life cycle in freshwater systems and has been bred in captivity [477, 673, 685, 686, 687, 688, 691, 1038]. It is a slow-growing species, with age at first breeding of populations in the Burnett River estimated to be 17 years for males and 22 years for females [238], however, Johnson [664] remarked that these estimates may be exaggerated and recommended more work on this aspect of reproductive biology. Length at maturity varies widely in both sexes (Table 2). In the Burnett River, males became mature at 738–790 mm TL (mean 767 mm) and females at 814–854 mm TL (mean 834 mm) [238]. Neoceratodus forsteri may commence to spawn from mid-July, August or September and spawning may continue to November/December but eggs are most abundant during September and October [688]. Spawning can occur at temperatures between 16 and 26°C and usually commences within three months of the winter solstice [687]. Kemp [687] noted that spawning precedes spring rains and is completed before heavy rains [125], that is, before the increased stream flows characteristic of December and January in south-eastern Queensland [1095]. Aside from stream flow and the availability of submerged aquatic vegetation, the stimulus for spawning is believed to be day length [687]. Brooks and Kind [238] remarked that very little attention has been given to the influence of flow rates on spawning site selection. Brooks [235] demonstrated that flowing water is not essential for spawning of this species, but suggested that eggs laid at depths >0.3 m in still water typically settle deep in aquatic macrophytes and die as a result of low dissolved oxygen levels. Viable eggs were collected in both still and flowing water in the Burnett River [238]. Highest densities of early stage eggs were associated with intermediate flow velocities (0.2 m.sec–1), low turbidity, a broad range of temperatures (maximum 36°C), high dissolved oxygen levels, depths of 400–600 mm and moderate to high densities of aquatic macrophytes 160–350 mm in height [235, 238]. Kemp [685] noted that temperatures of 10 and 30°C. were lethal to cleaving eggs.
Eggs of N. forsteri are usually deposited singly, occasionally in pairs, very rarely in clusters [687]. The male fish fertilises each egg as it emerges and the eggs are deposited in dense aquatic vegetation [687, 688]. The newly laid egg is enclosed in a jelly envelope and is sticky for a short while until silt and small aquatic organisms have covered it, and it remains sticky for long enough to become attached to submerged vegetation [688]. Eggs are also negatively buoyant and may fall to the substrate if not attached to vegetation or some other type of substrate; such eggs are considered unlikely to survive to hatching. Neoceratodus forsteri is selective in the choice of spawning site [688, 691]. Kemp [687, 688] recorded eggs on aquatic plants rooted in sand or in gravel in slow or fast flowing water (but not in still water), in areas where the vegetation was
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Freshwater Fishes of North-Eastern Australia
[124]. The epithelial cells of embryonic N. forsteri are sensitive to mechanical stimuli and excitable, similar to the skin impulse system of embryonic and larval Amphibia [208]. Bone et al. [208] suggested that this sensory system may permit embryos to escape precociously from the jelly envelope when attacked by predators. Newly hatched larvae of N. forsteri develop a ciliary current over the skin surface which continues for more than six weeks of larval life, and the gill surfaces under the opercula also become ciliated [1379]. Whiting and Bone [1379] suggested that the ciliary current could provide respiratory exchange across the skin and gills without necessitating any movements of the jaw or branchial apparatus, which are welldeveloped at this stage. A secondary role of the current may be to keep the skin of unprotected larvae free of debris, parasites, and predatory protozoans that may attack and erode the fins of larval lungfish [1379]. Both roles of the ciliary current may be adaptive for larvae that are totally unprotected by a nest or burrow, nor guarded by the male parent, as occurs in other dipnoans.
shaded or in full sun, and on plants with and without epiphytic algae, but not on aquatic plants ‘infested with slimy algae’ or in stagnant water or in areas where there was loose debris on the water surface. She considered that plant growth form (e.g. dense masses of vegetation), location (e.g. plants situated against a bank) and morphology (e.g. the roots of bottlebrush, Callistemon sp. and water hyacinth, Eichhornia crassipes) were important features of spawning sites [687]. In Enoggera Reservoir, eggs deposited into the root mass of water hyacinth clumps were laid over an area of 1–5 m2, on the roots and occasionally in partly submerged floats of the plant, in positions varying from near the surface to a depth of 1 m [687]. Some eggs were laid so high on the root mass of water hyacinth that a drop in water level would leave them exposed [687]. Brooks and Kind [238] found that structurally complex plant species contained higher densities of eggs than those with less complex growth forms, concluding, as have Kemp [687, 688] and other observers [691], that the suitability of a spawning site does not depend upon the particular plant species but on the provision of suitable microhabitat for both eggs and larval lungfish, and food supplies for the newly hatched fish. Illidge [626] reported finding the eggs of N. forsteri deposited on the sides and bottom of submerged logs.
The larvae of N. forsteri are reported not to feed for 2–3 weeks, while yolk is still present [686]. By the time the yolk is fully utilised, a spiral valve has developed in the intestine and the fish starts to feed. They have been described as essentially bottom feeders and approach their food in jerky movements [1165]. Small N. forsteri show a gradual change in body form as they develop but there is no externally detectable metamorphosis and no obvious point at which they can be termed adult as opposed to larvae [686]. Johnston and Bancroft [667] described a very young specimen of N. forsteri as measuring 17 mm at six weeks posthatching. Bancroft [128] recorded wide variation in the (preserved) length at age of N. forsteri held in captivity: 12 fish aged three months were 23–40 mm long (presumably total length), 18 fish aged five months were 26–44 mm, at eight months 25 fish were 26–55 mm, at 10 months 17 fish 40–62 mm, and at 12 months 19 fish were 33–72 mm long. Young lungfish come to the surface to breathe air when they are about 25 mm long [480, 690]. They are reported to do so only when stream water is laden with silt, as in times of flood, when it is stagnant, drying out and low in oxygen or when the fish is unusually active [480, 690].
Neoceratodus forsteri spawns during the day and at night [688]. It does not make a nest and there is no guarding or parental care once the eggs are laid [687]. Female N. forsteri have a large ovary and the potential to lay many eggs, but produces hundreds of eggs at most in the wild [687], whereas in captivity Hegedus [564] recorded 200 eggs laid at one time and Moreno [964] (cited in Kemp [687]) reported 500–600 eggs at a single event. This species does not necessarily spawn every year, however, a good spawning season occurs every five years, irrespective of environmental conditions (Kemp, pers. comm. to Brooks [235]). The following account of egg development is based largely on Kemp [686, 687, 688]. The newly laid egg is hemispherical in shape, delicate, heavily yolked and enclosed in a single vitelline and triple jelly envelope. The egg itself is about 3 mm in diameter, and with the jelly envelope has a total diameter of 1 cm. Cleavage is rapid, with the largecelled blastula stage reached in 36 hours and the smallcelled blastula stage reached after a further 18 hours. Head structures and pigmentation start to appear by day 17 and hatching occurs from 23–30 days [688]. Upon hatching the young fish is close to 10 mm, ‘inconspicuous and beautiful’ [1379]. During its first week of life it lies on its side, hiding in the weeds and moving only when stimulated by touch, but from time to time swimming spontaneously [123, 626, 687, 688, 1379]. Recently emerged larvae often retreat back into the gelatinous envelope when disturbed
The collection of juvenile N. forsteri has proved difficult ever since the species was first discovered in 1870, despite numerous attempts to collect small lungfish using a wide array of gear (including liming and use of dynamite). Bancroft [123, 125] feared that no juveniles survived their many predators in a normal year and, like Welsby [1373], erroneously thought that juveniles buried themselves in the mud for up to three years. Concern about the perceived lack of juvenile recruitment led to the many translocations of N. forsteri described above. However, from 1876
54
Neoceratodus forsteri
The reproductive biology of N. forsteri has many unusual features. Joss [672] is investigating the idea that surviving lungfish may be neotenic, i.e. they are larvae that have grown and become reproductively mature without metamorphosing.
onward, a spate of records of juvenile N. forsteri (61 cm in length or less with weights of 2 kg or less) appeared in the literature; full details are recorded by Kemp [688]. According to Kemp, numerous juvenile N. forsteri were caught in the Mary and Brisbane rivers in the early 1980s, in sand and gravel substrates near banks of aquatic vegetation. They were captured using electrofishing methods, a previously unavailable technique. However, in recent surveys in the Burnett River, Brooks and Kind [238] caught only 23 juveniles <300 mm TL, 19 by push-net and four by electrofishing. They concluded that juvenile recruitment of N. forsteri had been poor since 1996, coinciding with poor conditions for spawning (e.g. few aquatic macrophytes in shallow water) in 1997, 1998 and 1999. The eggs, larvae and juveniles of N. forsteri are vulnerable to aquatic predators (shrimps, insects such as beetles and odonates, and small fish) [1380].
Movement Neoceratodus forsteri is reputed to be a sluggish and inactive fish but is capable of rapid escape movements using its strong tail [688, 690]. This species is usually quiet and unresponsive by day (except in the breeding season) but becomes more active in the late afternoon and evening when it moves around feeding [480, 688]. Movements are usually slow and sinuous, using the tail with or without the use of the fins [688]. The fins are used to brace the body of the fish against the substrate when the fish is feeding, a behaviour displayed by N. forsteri when only a few
Table 2. Life history data for Neoceratodus forsteri. Age at sexual maturity (years)
Spawning of Burnett River populations commences at 15–17 years in males, 20–22 years in females [18, 238, 664]
Minimum length of ripe females (mm)
In the Burnett River, females mature at 814–854 mm TL (mean 834 mm) [238]
Minimum length of ripe males (mm)
In the Burnett River, males mature at 738–790 mm TL (mean 767 mm) [238]
Longevity (years)
Adults long-lived, at least 20–25 years [1380], with a claim that they possibly live to 60–100 years of age [18]
Sex ratio
1:1 [238]
Spawning activity
Spawn from mid-July, August or September to November/December; occasionally January to March [235]; eggs are most abundant during September and October [688]
Critical temperature for spawning
16–26°C [687]
Inducement to spawning
Day length; spawning usually commences within three months of the winter solstice; usually occurs before heavy rains, but may occur during or after rain [687]
Minimum GSI of ripe females (%)
?
Minimum GSI of ripe males (%)
?
Fecundity (number of ova)
Females produce hundreds of eggs at most in the wild; 200 and 500–600 eggs laid at one time in captivity [687]
Fecundity/length relationship
?
Egg size (diameter in mm)
3 mm; total diameter of 10 mm inclusive of jelly envelope [687]
Frequency of spawning
Females may release eggs in batches when spawning conditions and habitats are suitable; if unsuitable, female may not spawn [688]
Oviposition and spawning site
Both still and flowing water; highest densities associated with intermediate flow velocities (0.2 m.sec–1), low turbidity, a broad range of temperatures, high dissolved oxygen levels, depths of 0.4–0.6 m and moderate to high densities of aquatic macrophytes 0.16–0.35 m in height [238]
Spawning migration
None in natural river conditions; adults migrate out of impoundments into suitable riverine spawning sites [238]
Parental care
None [687, 688]
Time to hatching
4–5 weeks after oviposition [127]; 23–30 days [688]
Length at hatching (mm)
10 mm [1379]
Length at feeding
?
Age at first feeding
2–3 weeks [686]
Age at loss of yolk
Around 2–3 weeks [686]
Duration of larval development
No externally detectable metamorphosis [686]
Length at metamorphosis
–
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Freshwater Fishes of North-Eastern Australia
centimetres long [688]. This species is able to slither through wet grass with the assistance of a downhill slope but cannot support its body weight on the fins without the additional support of water [626]. Lungfish do not crawl up onto land or projecting logs to bask, as sometimes reported in early literature [690, 1380].
Another individual was located in the same position during 23/34 tracking events over the period August 1998 and January 2001. It moved upstream between October and December 1999 and between September and December 2000, that is, at times corresponding to the spawning season. This fish entered shallow, heavily vegetation glides during each movement event and remained within the glide for several weeks before returning to the same rock outcrop it had left [238]. Increased flow rates resulted in a tendency towards increased downstream movement of individual fish. There was also evidence of upstream movements during the spawning seasons of 1999 and 2000, especially during August–October 1999, when several fish were returning from long distance movements downstream following increased flows earlier in the year [238].
Grigg [480] demonstrated experimentally that more frequent air breathing was correlated with periods of greater activity at night, when N. forsteri uses the lung as a supplementary organ of respiration. To breathe air, the fish may rise to the surface and exhale air through the mouth, then inhale and dive forwards, or rise to the surface, breathe, and reverse back into the water [688]. In juveniles, facultative air breathing develops when the fish are 25 mm long [686]. Neoceratodus forsteri is essentially a sedentary species exhibiting strong site fidelity within a restricted area, such that home ranges rarely extend beyond a single pool or occasionally, two adjacent pools [238]. Brooks and Kind [238] recorded the following details during radio-tagging studies in the Burnett and Mary rivers. Of 12 individuals (685–1070 mm TL, weight 2750–10 100 grams) tracked every 3–4 weeks between 1998 and 2001, only four were located more than 1000 m from the site of release. Movements of all tracked fish were independent of water temperature and stream discharge. The pattern of movement involved strong fidelity to particular sites within pools (usually against the banks or adjacent to large rock formations) during daylight, and free movement of fish throughout the pools at night, resulting in extensive overlap of individual home ranges. Two fish moved through the downstream riffle and continued downstream but all other movements were in the upstream direction, and at times, four individuals moved upstream into a series of pools containing dense beds of aquatic macrophytes, negotiating a large riffle zone to do so [238].
Tag and recapture studies confirmed the patterns of movement of N. forsteri described above [238]. Movement data were collected for 124 recaptured fish (25 females, 30 males and 69 unsexed fish, 470–1240 mm TL) at liberty for periods from 7–928 days (mean 352 ± 239 days). Fish tagged in impounded areas moved distances ranging from 16 900 m downstream to 35 400 m upstream, compared to the longest distance moved in a natural riverine area (2900 km). Approximately 20% of all recaptures of tagged fish occurred within 100 m of the tagging location, 50% were caught within 1000 m and only 17 fish (13%) moved more than 5000 m. Mean movement between release and recapture was 206 (± 5500 m) and there was no significant difference in the number of individuals making movements upstream or downstream, nor any differences in movement direction or distance between male and female fish. One tagged fish was captured in the Walla Weir fish lock, however none of the radio-tagged fish entered this device. Some fish captured in Jones Weir moved out of the main channel upstream into the Boyne River during the 1999 spawning season, and also into the Auburn River [238].
Movements of radio-tagged N. forsteri within impounded sections of the Burnett River were strikingly different [238]. The mean total range of five lungfish released downstream from Walla Weir (i.e. within the river reach impounded by Ben Anderson Barrage) was 28 740 m compared to 6450 m within Walla Weir, and 1667 m in the riverine section at Goodnight Scrub. Larger fish ranged over wider areas but total ranges were similar for both sexes. Mean monthly movements in this group of fish ranged from zero in the month immediately following release to more than 9 km in January 2001, with fish regularly traversing the area from below Walla Weir (AMTD 74.5 km) to Ben Anderson Barrage (AMTD 23.9 km). One individual traversed the 48 km distance from Walla Weir to Ben Anderson Barrage on at least four occasions.
These movement studies suggest that N. forsteri does not follow a set migratory path but may actively seek out suitable spawning habitat between July and December [238]. Mature fish in impounded areas appear to move out of artificially ponded habitat and upstream into shallow, free-flowing reaches to spawn. Movements within Walla Weir (lower Burnett River) shortly after it was closed and the natural river became impounded were little different to those of lungfish in unimpounded reaches [238]. The limited movements of lungfish in this pondage were interpreted as the normal localised movements of mature, resident individuals habituated to spawning close to, or within, their home range [238].
56
Neoceratodus forsteri
that had passed into the gut without being crushed by the tooth plates. Recent accounts indicate that in captivity adult N. forsteri consume a wide range of animal foods, fish, insect larvae, crustaceans, molluscs, worms, tadpoles, dead toads, meat, offal, egg yolk, dried dog or poultry food, Vallisneria spiralis, Hydrilla verticillata, filamentous algae and water hyacinth rootlets [694]. Jaw movements generally crush the food but vary with the type of food being eaten [688]. Soft foods such as worms and plants are partially crushed with a few quick bites and then swallowed, such that the plant fragments found in faeces can still be identified [688]. Molluscs are often pushed out and pulled back in several times, and particles of food may escape from the operculum, even in mature fish [688]. Movement of the prey in and out of the mouth accompanied by strong adduction of the jaws to crush prey between the massive tooth plates is typical of lungfishes and is described in detail for Lepidosiren [152]. These crushing movements are accompanied by hydraulic transport of the food, achieved by movements of the hyoid apparatus, to position the prey within the oral cavity (analogous to the functions of the tongue in tetrapods [152]). Neoceratodus forsteri displays the most primitive version of these biomechanical feeding adaptations and behaviours [152].
The distribution of N. forsteri is restricted in the Burnett River catchment by natural barriers to movement, for example within the gorge areas of the Auburn River and Barambah Creek [238]. Man-made barriers also restrict the movements of this species, for example, Boondooma Dam presently constrains its distribution within the Boyne River [238]. The presence of tidal barriers (e.g. in the Burnett River, Mary River and Tinana Creek) may further impact on lungfish by preventing or hindering recolonisation of freshwaters if displaced by floods to brackish estuarine areas downstream of tidal barrages. Fish strandings leading to death also occasionally occur within and downstream of dams and weirs in the Burnett River spillway due to rapid reductions in discharge and flaws in the design of the spillways [700]. Trophic ecology Although no quantitative dietary data is available in the published literature, anecdotal observations clearly indicate that the diet of N. forsteri changes with development and is correlated with a change in dentition [684]. When feedings begins, dentition is of the ‘hold and catch’ type consisting of simple groups of isolated cusps, three in each tooth plate. The larvae are essentially bottom feeders [1165] taking microcrustaceans (Daphnia, brine shrimp) and small Tubifex worms, occasionally supplemented with filamentous algae [684, 685]. Large items as big as the fish itself may be captured, only to escape via the gill slits, and digestion is often ineffective, such that live worms have been reported to leave the gut via the anus, or by breaking through the gut and body walls [688]. During larval growth, the sharp tooth cusps fuse in ridges radiating from a point situated posterolingually; cusps are added to the labial ends of the ridges and more ridges are added posteriorly, producing a total of seven ridges in each tooth plate [684]. Each tooth grows in thickness, the tooth plate grows outwards and is resorbed from the inner angle at the same time, and more cusps grow between the ridges, thus forming the crushing surface. Vomerine teeth grow in the same way by fusion of isolated cusps and the addition of new cusps at the labial end of the tooth plate, and they too thicken over time [684]. Initially vomerine tooth plates are low-based with long cusps but they develop into highbased low cusped incisiform tooth plates in adult fish.
Conservation status, threats and management Early accounts suggest that N. forsteri is a valuable food fish, however Spencer [1257] described the flesh as very oily, coarse and disagreeable, and seldom eaten except by those who could afford ‘nothing better’. Spencer felt that consumption by humans would be unlikely to cause rapid extermination of this species [1257]. That was in 1892. Today, over 100 years later, other human activities threaten the Queensland lungfish, particularly water resource development [18, 253, 323, 472, 1418, 1422]. The taking of N. forsteri has been prohibited since the lungfish was declared a protected species under the Queensland Fish and Oyster Act 1914, and it was placed on the CITES list in 1977 [692]. Neoceratodus forsteri is currently protected from fishing, and collection for educational or research purposes requires a permit in Queensland under the Fisheries Act 1994, and from the Commonwealth Government [692]. Unfortunately, N. forsteri was listed as Non-Threatened in the 1993 Action Plan for Freshwater Fishes [1353]. By 1995, numerous individuals and organisations were deeply concerned about the possible impact of the construction of a new weir (Walla Weir) on the lower Burnett River within the core distribution and prime habitat of N. forsteri [18, 323, 472, 1418, 1422]. A nomination put forward in 1997 to have the species listed as Endangered under the Endangered Species Protection Act 1992 was unsuccessful.
Illidge [626] reported that adults of N. forsteri use the vomerine teeth to gnaw the bark of trees growing in the water and also consume moss and grass fallen into the water and the seed-pods of Eucalyptus. Whitley [1380] noted that the blossoms of Eucalyptus falling on the surface are eagerly consumed, and Spencer [936] reported that the alimentary canals of lungfish examined in late September (1891) were filled with the fruit of Eucalyptus tereticornis
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Freshwater Fishes of North-Eastern Australia
This nomination was assessed by the Commonwealth Endangered Species Scientific Subcommittee as not meeting the relevant criteria as ‘its numbers have not been reduced to such a critical level, and its habitats so drastically reduced, that it is in immediate danger of extinction’ [18]. In Queensland, N. forsteri was not even listed as threatened under the Queensland Nature Conservation Act 1992. An independent review of the impacts of the Walla Weir proposal on N. forsteri and the Elseya turtle recommended the establishment of a long-term program of research to ascertain its status [207]. The Boardman review [207] recommended collection of baseline data on distribution, genetic diversity, population size and age structure, migration, spawning sites, hatching rates and juvenile recruitment. Studies on the habitat requirements of juveniles and the effect of fluctuating water levels were also recommended [207]. The research program, led by Brooks and Kind [238], yielded many essential facts relating to the ecology of N. forsteri and paved the way for a new nomination for its protection as Vulnerable under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). After considerable delay, Neoceratodus forsteri was included in the category of Vulnerable under section 78 of the EPBC Act in late 2003 [18]. However, this species is not listed under the World Conservation Union (IUCN) ‘Red’ List or the Australian Society for Fish Biology (ASFB) ‘Conservation Status of Australian Fishes’ listing.
Brooks and Kind [238] established that there has been a marked decline in the quality and extent of breeding habitat of N. forsteri in the Burnett River due to impoundment of 26% of the core distribution. While impoundments provide habitat and feeding grounds for this species, the particular conditions suitable for successful spawning rarely occur within impounded areas. Generally, spawning habitat is characterised by relatively shallow water and dense macrophyte cover [238], whereas impoundments tend to be steep-sided with deep water and fluctuating water-levels, conditions that are not suitable for the growth of macrophytes. Brooks [235] observed that a rapid reduction in water level (250 mm) in Bingera Weir on the lower Burnett River (AMTD 54.5 km) exposed many shallow spawning areas (predominantly beds of Vallisneria) and caused the death of a large number of eggs. Furthermore, impoundments probably do not provide suitable nursery habitat for juveniles of N. forsteri (<300 mm) as the young fish remain for some time after hatching in habitats similar to those used for spawning, primarily dense aquatic macrophytes [238]. Juveniles are believed to be susceptible to stranding or loss of sheltered habitat and food supplies caused by rapid decreases in water level, until such time as they move into deeper water [18]. Increases in water level may have little effect on juvenile N. forsteri until macrophytes die three to four weeks after inundation [238].
This species is potentially threatened in much of its core distribution in the Burnett and Mary rivers: 26% of this core distribution is presently impounded by weirs and dams, with a further 13% likely to be impounded if proposed water infrastructure developments for the Burnett River catchment go ahead [238]. Water infrastructure developments are also planned for the Mary River. The effects of new dams and weirs are likely to be significant. Barriers to movement and altered flow regimes downstream of dams for irrigation purposes could lead to the disruption of existing population structure and cause loss of genetic variation, leading to inbreeding depression, possibly culminating in extinction [420]. There has been debate as to whether the Queensland lungfish in the Brisbane and North Pine rivers are natural or translocated populations and the status of most of these populations is unknown. The conservation value of self-maintaining translocated populations of N. forsteri is also unclear. In areas where it occurs naturally, this species has inherently low genetic variation [420], and, as only limited numbers of individuals from one natural site were used to establish the translocated populations, these new populations are likely to have particularly low genetic diversity. It is possible that only the natural populations possess the full evolutionary potential of the species [18, 420].
Queensland lungfish are slow-growing, with age of first breeding estimated to be 15–17 years for males and 20–22 years for females. Adults have a high survival rate and are long-lived (at least 20–25 years [1380]), with a claim that they possibly live to 60–100 years of age [18]. Large adults have recently been found to be relatively common in various localities, and there is no evidence of decline in adult numbers, however, it is suspected that recruitment into the adult population is inherently low. Juveniles are more difficult to observe and locate than adults and little is known of their distribution, abundance and ecology. From recent surveys in the Burnett River, Brooks and Kind [238] concluded that juvenile recruitment of N. forsteri had been poor since 1996, coinciding with poor conditions for spawning (e.g. few aquatic macrophytes in shallow water) in 1997, 1998 and 1999. Johnson [664] remarked that for a long-lived species with naturally low mortality rates, successful spawning and juvenile recruitment is not essential every year, and may only occur irregularly, possibly in medium to long-term cycles, even in natural systems. The length of these cycles could easily mask potentially deleterious impacts on recruitment for many years, whereas large adults could remain common for decades and give no indication of incipient population decline in the longer term.
58
Neoceratodus forsteri
The vulnerable status now afforded to N. forsteri by the Commonwealth EPBC Act has not inhibited further water resource development in the Burnett River. The proposed Burnett River Dam situated at AMTD 131.2 km (a place called Paradise) has been approved by the Commonwealth and Queensland Governments. The maximum height of the dam wall will be 37.1 m and at full supply level it will have a capacity of 300 000 ML, a length of 45 km and extend over an area of 2950 ha [253]. The Environmental Impact Statement for the Burnett River Dam places little emphasis on the requirements of N. forsteri. Environmental flow releases from the dam are expected to maintain spawning sites and juvenile habitat downstream [253], however the impounded area may not provide either [238]. Monitoring of N. forsteri abundance, health and recruitment in the impoundment and downstream has been recommended as part of the development plan for the new dam [253]. Consideration will be given to the translocation of N. forsteri into areas of the catchment where natural and man-made barriers prevent access to potentially useable habitat [253]. The development of Water Resource Plans for the Burnett and Mary River catchments represents an opportunity to address the possible implications of altered flow regimes for lungfish habitat, movement, spawning and recruitment processes [701]. The ultimate fate of the Queensland lungfish, Neoceratodus forsteri, probably the world’s oldest living vertebrate species, remains to be seen.
There are concerns that the Queensland lungfish is threatened by alien and translocated native fishes that have been introduced into the Burnett and Mary river systems, and are capable of predating on eggs and young and competing with adults for breeding habitat [700, 701]. Introduced fishes may also contribute to future declines in the number of breeding adults [18]. One of the alien species, the Mozambique mouthbrooder or tilapia (Oreochromis mossambicus) has been declared a noxious and threatening alien species in Queensland [79, 95, 103]. It is present in Boondooma Dam on the Burnett River [593] and could become established within the natural range of N. forsteri in this catchment. Details of its ecology and impacts in Australia can be found in Arthington and Blühdorn [86] and related publications [79, 95, 103]. In summary, there have been losses or reductions in quality of the breeding and nursery habitat of N. forsteri amounting to 26% of the core habitat in the main channels of the Burnett and Mary Rivers [18, 238]. In addition, the breeding and nursery habitat of this species will continue to be threatened by further water infrastructure development and associated agricultural land use in these highly populated areas. The impact of alien and translocated fishes in these river systems is not known, but could well result in a further population reduction. On the basis of these losses and threats, there is sufficient evidence to indicate that the adult breeding population of N. forsteri will undergo a substantial decline over the next three generations. Therefore, the species has been categorised as ‘Vulnerable’ under the EPBC Act [18].
59
Scleropages leichardti Günther, 1864 Saratoga
37 088002
Family: Osteoglossidae
Description Dorsal fin: 15–19; Anal fin: 25–27; Dorsal profile straight, non-sloping; jaw steeply inclined, mouth pointing dorsally. Figure: composite, drawn from photographs; drawn 2003.
eggs in the buccal cavity. Colour: brown to dark green dorsally with silver sheen, grading to pale green ventrally. Dorsal and lateral scales with one or two pink spots near margin. Medial fins dark with faint pink spots. Whitley [1386] cites a personal communication in which a cardinal red specimen is described. Scleropages leichardti is unlikely to be confused with any other species except S. jardinii, but given the restricted distribution of the former (see below), confusion is unlikely.
Scleropages leichardti grows to large size, reaching a maximum length of approximately 1000 mm but more commonly to about 500 mm [52]. The body is long and compressed with the dorsal and anal fins positioned posteriorly. The body is moderately deep (24% of SL) [42], slightly more so in females [938]. Length-weight relationships, where weight is in g and total length is in mm, for female and male fish, respectively are: W = 5.649 x 10–7L3.432 and W = 5.272 x 10–7L3.432; pooled n = 125 [938]. Head length less than one-quarter of standard length (greater than one-quarter in S. jardinii). The mouth is dorsally oriented, steeply sloping and extends back to rear margin of eye (in contrast to S. jardinii in which it projects back well beyond reach of the eye) [42]. We have noted from inspection of photographs that the jaw extends past the rear margin of the eye in some specimens and this character may not be very useful. External sexual dimorphism is lacking in this species [938], however mouth size may be greater in females given that this sex incubates the
Systematics Osteoglossidae is an ancient group of primary freshwater fishes with a distribution (Africa, South America, Southeast Asia and Australia) suggestive of an origin well prior to the fragmentation of the Gondwanan supercontinent [573]. Fossil osteoglossids are known from Eocene deposits [52, 1413] and Saville-Kent [1197] provides a figure of an extinct osteoglossid Phareodus queenslandicus from tertiary clay shale in south-eastern Queensland. The family contains four extant genera: Arapaima Müller, Heterotis Rüppell (ex Ehrenberg), Osteoglossum Vandelli and Scleropages Günther. Scleropages contains two Australian species S. leichardti Günther, S. jardinii (SavilleKent) and a third species S. formosus (Schlegel and Müller)
60
Scleropages leichardti
scattered locations east of the Great Dividing Range on Cape York Peninsula including the Olive, Pascoe and Lockhart rivers [571, 1349], Harmer Creek and an unnamed lake in the Shelburne Bay area [571].
from Indonesia, Malaysia, Thailand, Cambodia and Vietnam. Scleropages leichardti was first collected in 1845 by the German explorer Friedrich Leichhardt while encamped on the McKenzie River. It was subsequently described by Günther in 1864 but the type locality was listed as the Burdekin River [490]. Günther consistently misspelt Leichhardt’s name throughout the description and in the trivial name but according to the rules of International Code for Zoological Nomenclature the trivial name stands as leichardti without the extra ‘h’ [165]. Nonetheless, the trivial name frequently appears as leichhardti [165, 1042]. The only synonym is Osteoglossum guentheri Castelnau, 1876 and the type locality for this species is also listed as the Burdekin River [286, 1042].
Macro/meso/microhabitat use Quantitative information on habitat use by S. leichardti is lacking. Qualitatively, it has been stated that S. leichardti prefers long deep turbid waterholes, with a reduced flow rate and abundant snags, undercut banks and overhanging vegetation [753, 936, 942, 1386]. It may do well in impounded waters [160]. This species spends considerable time at the water’s surface patrolling the river banks, retreating to deeper water or snags and undercuts when threatened [470, 1386]. Access to deep water may be important at times of high water temperature (>31°C) [934].
The vernacular name for S. leichardti is often listed as spotted barramundi [470, 1181, 1386]. Whitley [1386] believed the name was a corruption of the aboriginal word burrumundi, while Grant [470] believed the original aboriginal name was burrumunda, later corrupted to barramunda, then barramundi. However, Saville-Kent used the term barrimundi in his 1892 description of S. jardinii [1197]. The name barramundi has been used for both Australian species of Scleropages, Lates calcarifer and Neoceratodus forsteri [470]. We recommend, in order to avoid the confusion so common with vernacular names, that barramundi be used as the common name for Lates calcarifer only and that the names saratoga and northern saratoga be used for S. leichardti and S. jardinii, respectively.
Environmental tolerances Few data are available concerning the environmental tolerances or ambient water quality conditions experienced by S. leichardti. The range of water quality conditions in which this species was recorded by Midgley [942] was: 22.5–31°C, 3.6–8.3 mg O2.L–1, pH 7.2–8.3 and 12–90 cm Secchi disc depth. Lake and Midgley [756] believed S. leichardti tolerant of high turbidity levels and gave a Secchi disc depth of 3.8 cm as the most turbid conditions in which they had recorded this species. These authors report that S. leichardti can live in water temperatures of 7–40°C but that prolonged exposure (three to four weeks) to temperatures less than 10°C results in death.
Distribution and abundance Scleropages leichardti is endemic to the Fitzroy River system [52]. Within this river, S. leichardti occurs in the Dawson, McKenzie, Don, Isaacs and Connor rivers [160, 942]. Midgley [942] recorded S. leichardti from only three of 19 study sites and qualitatively recorded it as rare at each site. Berghuis and Long [160] found it to be more widespread, occurring in six of 19 sites, but this species was not abundant, comprising 0.6% of the total catch only, at an average catch rate of 0.0125 fish.m–1.hr–1. This species is thought to be highly territorial [52, 934] and rarely reaches high abundance [938].
Reproduction Scleropages leichardti exhibits a significant degree of parental care; the female incubates the eggs in the buccal cavity and guards the young until they are old enough to leave. Spawning is by direct pairing, after a prolonged courtship period [934], occurring from September to November (but mostly in October) when water temperatures exceed 22–23°C (Table 1). The eggs are large (10 mm diameter), few in number, and maturation is delayed until the fourth or fifth year of life when large size is attained (Table 1).
Errors in specifying the type locality (i.e. Burdekin River instead of Fitzroy River) have been promulgated sufficiently to result in the distribution being extended to this river in some texts [470]. This species has been translocated into some catchments of the Burdekin basin and many other water storages in south-eastern Queensland (e.g. Mary, Brisbane, Logan-Albert and Burnett rivers) [593, 1349].
Longevity is unknown but probably exceeds six to seven years. Whitley [1386] cites a personal communication in which efforts to catch a particularly distinctive red specimen had occurred for at least seven years. Whitley even speculates at a life span measured in decades [1386]. Long life, delayed maturation, low fecundity and large egg size are features common to most fishes exhibiting parental care.
Scleropages jardinii is patchily distributed across northern Australia west of the Great Dividing Range [52] and a few
Spawning has not been observed (the mechanics of fertilisation and transfer of the eggs to the buccal cavity are
61
Freshwater Fishes of North-Eastern Australia
three days [934]. The young quickly establish small territories but will shoal together if abundances are in excess of habitat suitable for the establishment of territories. It is noteworthy that territorial behaviour is assumed so early in life and it is tempting to speculate that the female’s first patrols, in which the young are released, involve some assessment of the quality of juvenile habitat. Furthermore, occasional displays of aggression to other incubating females may be intended to reduce juvenile competition for territories.
unknown), but probably occurs at dusk [934]. Larval development is rapid; hatching occurs after 10–14 days at 22–30°C. During the incubation period, the female does not eat nor show signs of aggression to non-incubating females, although aggression towards other incubating females, which may be distinguished from non-incubating fish by a conspicuous white chin, may occur [934]. The larvae hatch at an advanced state of development, closely resembling the adult form with the exception of the possession of a large yolk sac. Growth is rapid and a length of 35–40 mm is attained after four weeks. It is at this size that the young make their first forays away from the female. The female moves close to the river-bank where the young are released. They remain close to the mother’s head as she slowly patrols the riverbank, returning rapidly to the safety of the buccal cavity when required. The interval between the first release of the young and the final release is about
Juvenile growth is rapid also. Under culture conditions, a length of 110–110 mm may be reached six weeks after incubation ceases [934] and length of 150–200 mm may be reached after six months [1194]. A length and weight of 560 mm and 1700 g, respectively, may be reached after three years under culture conditions [756] but these growth rates probably exceed that experienced in the wild [938].
Table 1. Life history data for Scleropages leichardti. Information on reproductive biology drawn from a number of studies undertaken principally under culture conditions. Age at sexual maturity (months)
Maturation commences at three years but spawning occurs at four years of age [756], five years [938]
Minimum length of ripe females (mm)
360 mm TL [797]; >560 mm, growth rates of cultured fish greater than that of wild fish [934, 938]
Minimum length of ripe males (mm)
355 mm TL [797]; >560 mm , growth rates of males may be greater than females [756]
Longevity (years)
? at least 7 years [1386], probably in excess of 8 years
Sex ratio
?
Peak spawning activity
Mid-October [756], September/October [934], October/November [1194]
Critical temperature for spawning
>23°C [756], 22–23°C [934]
Inducement to spawning
? Temperature
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
Low: 30–130 [14]; 78–173 [756]
Fecundity/length relationship
78 eggs at 476 mm TL, 110 eggs at 550 mm TL, 173 eggs at 660 mm TL [756]
Egg size
10 mm [756]
Frequency of spawning
Once per season for females, twice or more for males with long recovery period (several weeks) between spawnings
Oviposition and spawning site
Unknown, spawning probably takes place at night [934]
Spawning migration
?
Parental care
Buccal incubation by female, incubation and brooding may last 5–6 weeks [126, 756, 934]
Time to hatching
10–14 days at 23-30°C [756]; 5–6 weeks [14]
Length at hatching (mm)
15 mm [934], newly hatched larvae 36 mm TL [756]
Length at feeding
At maximum 35–0 mm TL [934]
Age at first feeding
At maximum, 30 days post-hatch
Age at loss of yolk sac
?
Duration of larval development
Hatch at advanced state of development, larvae with adult appearance with the exception of presence of large yolk sac [756]
Length at metamorphosis
? 15–25 mm
62
Scleropages leichardti
Movement Other than that described above, little is known of the movement biology of this species. Scleropages leichardti has not been recorded moving through fishways.
expressed. However, given the large number (15 and rising) of impoundments in the Fitzroy River basin, it seems critical to determine whether such habitats are indeed beneficial to this species. Any fish exhibiting the life history traits of delayed maturation and reduced fecundity as shown by S. leichardti will be more vulnerable than early maturing highly fecund species. Scleropages leichardti is exploited by both recreational fishers and the aquarium fish industry (collection of brood stock only), the extent of which is controlled by bag limits and collecting restrictions [1194]. This species is widely translocated in Queensland and the collection of broodstock may also place pressure on this species.
Trophic ecology No quantitative information on the trophic ecology of S. leichardti is available. This species has been described as a surface feeder on insects, crustaceans, frogs and fish [52]. Scleropages jardinii in the Northern Territory has a diet dominated by aquatic insects (54%), terrestrial insects (12%), terrestrial plant material (10%) and fish (9%) [191]. Sambell [1194] believed that S. leichardti were less adept at catching small fish than S. jardinii because of the dorsal orientation of the eyes.
Water regulation has greatly altered the natural flow regimes of the various rivers in the Fitzroy River basin [380]. The extent to which these changes interfere with the reproductive phenology of adults and the development and recruitment success of juveniles remains unknown. Similarly, many aquatic habitats of the river are seriously degraded [380]. Loss of riparian integrity and of bank associated structures (i.e. woody debris, root masses and undercuts) is likely to impact on this species by reducing food supply (i.e. terrestrial insects) and habitat quality. The fact that this species is territorial suggests that localised reductions in abundance are unlikely to be naturally remediated by colonisation in anything but the medium to longer term.
Conservation status, threats and management Scleropages leichardti was listed as Rare in 1993 [1353] and more recently as Lower Risk–Near Threatened [117]. Midgley [942] expressed concern about declining numbers of this species in 1979, but in more recent research in the Fitzroy River, Berghuis and Long [160] believed that the population was secure because the creation of impoundments in the Fitzroy River basin had increased the area suitable for this species. However, Berghuis and Long failed to collect S. leichardti at sites close to those established by Midgley and failed to collect any specimens in the upper Dawson River, although unpublished data apparently suggests that this species still commonly occurs there. Moreover, Midgley’s study included impounded waters and S. leichardti was absent from these habitat types despite being present in earlier years. The two studies are difficult to use to determine the current status of S. leichardti given differences in sampling regime and the manner in which abundances were
Given the endemic status of this species, its phylogenetic significance, and unique biology, we find it very surprising and alarming that so little is known about S. leichardti. This in itself is one of the most serious threats to the continued survival of this species, especially given that it is restricted to one of the most developed river basins in Queensland.
63
Megalops cyprinoides (Broussonet, 1782) Tarpon, Oxeye Herring
37 054001
Family: Megalopidae
anterior margin of the eye. The lower jaw is prominent, its two branches separated by a bony gular plate. Eyes large and covered by an adipose eyelid. Scales large; lateral line well-developed with tubes branching. Pectoral fins set low on profile and with long axillary process. Axillary process also present on pelvic fins. Well-vascularised swim bladder present and lying below and in contact with skull. Tail deeply forked. The extended filament of the dorsal fin is absent in specimens below about 56 mm in length. Colour in life: bluish-green to olive dorsally grading through silver on flanks and white on belly. Fins frequently a pale yellow. Colour in preservative: essentially the same as in life except silver colour of flanks and yellow colour of fins less vibrant.
Description First dorsal fin: 16–21, last ray forming prominent filament; Anal fin: 24–31; Pectoral fin: 15 or 16; Pelvic fin: 10 or 11; Gill rakers on first arch: 15–17 + 30–35; Lateral line scales: 36–40; spines on fins absent [37, 422]. Figure: composite, drawn from photographs of adult and juvenile specimens, Burdekin River; drawn 2002. Megalops cyprinoides is a large fish with a fusiform, compressed body, unlikely to be confused with any other species except in the juvenile stage, when it may be confused with juvenile clupeids. Maximum sizes reported for this species vary from 1000 mm [936, 977] to 1300 mm [37] and as large as 1500 mm [470]. Fish of this size are rarely collected (especially from freshwaters) and maximum sizes of less than 500 mm are more the norm [193, 313]. Coates [313] reports a length/weight relationship for tarpon from the Sepik River of W = 9.96 x 10–6 L3.1; n = 156, r2 = 0.95 where W = weight in g and L = SL in mm. Bishop et al. [193] report a length weight relationship for tarpon in the Alligator River region of W = 2.4 x 10–2 L2.83; n = 155, r2 = 0.833 where W = weight in g and L = CFL in cm.
Megalops cyprinoides produce a leptocephalus-like larva that is flat, band-like, transparent and with a forked tail. Larvae develop teeth early in life at about 11 mm [594, 1347]. Although M. cyprinoides provides excellent sport on light line, opinions vary as to its culinary quality. Early accounts suggest it is good eating but Grant [470] dismisses it as poor quality even after extensive preparation. This species is an important component of the subsistence fisheries of Papua New Guinea [313].
The mouth of M. cyprinoides is terminal, toothless in the adult stage, oblique and large, extending back beyond the
64
Megalops cyprinoides
Megalops cyprinoides has been recorded from most drainages of the eastern side of Cape York Peninsula including the Olive, Claudie, Lockhart, Pascoe, Stewart, Starke, Howick, McIvor, Endeavor, Harmer, Normanby and Annan rivers [571, 697, 1349] as well as some smaller streams (Massey Creek and Three Quarter Mile Creek) [571] and dune lakes of the Cape Flattery region [1101]. Tarpon are found in most rivers of the Wet Tropics region, being been recorded from the Daintree, Saltwater, Mossman, Barron, Russell/Mulgrave, Johnstone, Moresby, Tully/Murray and Herbert River drainages [583, 584, 643, 1177, 1183, 1184, 1185, 1187, 1349]. This species was not collected from the smaller systems of the Hull River, or Maria and Liverpool creeks [1179].
Systematics Megalops cyprinoides has been variously placed within the Elopidae (the giant herrings) or Megalopidae, with the latter being currently accepted [406]. Both families are ancient: Merrick and Schmida [936] suggest that megalopid fossils have been found in Upper Jurassic deposits, Wilson and Williams [1413] list fossil Elopidae in Late Cretaceous deposits, and Long (1733] provides a drawing of a fossilised otolith of the extinct Megalops lissa from the Miocene. The extant Megalopidae contains a single genus comprised of two species: Megalops atlanticus and M. cyprinoides. Phylogenetic relationships among the superorder Elopomorpha, a grouping which includes all teleost fishes that possess a specialised leptocephalus larva (including the Megalopidae and Anguillidae), are discussed in Obermiller and Pfeiler [1437] and Inoue et al. [1434].
Further south, M. cyprinoides has been recorded in the Black Alice River [275], St. Margarets Creek [1053], the Houghton River [255], the Baratta wetlands [1046] and the Burdekin River [587, 591, 847, 940, 1098]. Its distribution in the Burdekin River extends upstream to include the Bowen River although it is no longer common in this system due to the barrier imposed by the Clare Weir. It is still common in wetlands of the Burdekin delta (C. Perna, pers. comm.).
Megalops was first erected by Lacepède in 1803 with the type species for the genus being M. filamentosus (=cyprinoides). Megalops cyprinoides was first described and placed in the genus Clupea by Broussonet in 1782, based on material collected during Captain Cook’s voyages in the Pacific. Not unexpectedly, given the large range of this species, there are numerous other synonyms for M. cyprinoides. These include: M. cundinga Hamilton 1822, M. curtifilis Richardson 1846, M. indicus Valenciennes 1847, M. macropthalmus Bleeker 1851, M. macropterus Bleeker 1866, M. oligolepis Bleeker 1866, M. setipinnis Richardson 1843, and M. stagier Castelnau 1878.
Megalops cyprinoides has been recorded from the Pioneer River [1081] and the Shoalwater Bay region [1328]. Tarpon were formerly widespread in the Fitzroy River but the numerous impoundments on this system have reduced its present distribution [659, 942, 1274]. Impoundments have similarly affected this species in the Burnett River [11, 700, 1173, 1276]. Tarpon have been recorded from the Burrum, Mary, Noosa, Brisbane and Logan-Albert rivers [168, 643, 701, 702, 881, 1349] and from Moreton Bay [881, 969] and North Stradbroke Island [988]. This species has been recorded from artificial habitats (e.g. golf course lakes) in the Gold Coast region of southern Queensland (J. Tait, pers. comm.).
Distribution and abundance Megalops cyprinoides is a very widespread species, its range extending from east Africa to South-east Asia including Japan, Australasia and some islands of the west Pacific. The Australasian distribution is similarly large. This species occurs in rivers of both northern and southern Papua New Guinea and Irian Jaya [37, 42, 46, 51, 316, 495]. The Australian range includes rivers of the Kimberley region [45], being recorded from the Fitzroy [620, 779], Carson and Ord rivers [620]. This species is widespread across the Northern Territory and has been recorded from the Victoria [946] and Daly [945] river systems, drainages of the Alligator Rivers region [193, 772, 1064, 1416], and drainages of Arnhem Land [944]. Tarpon have been recorded from the Leichhardt River in the Gulf region of Queensland [1093] and is probably present in most rivers of this region. Rivers draining the western side of Cape York Peninsula in which M. cyprinoides has been collected include the Embley, Mitchell, Coleman, Ducie, Watson, Archer, Edward, Holroyd, Wenlock and Jardine rivers [41, 571, 643, 1349]. Its distribution in the Mitchell River extends as far upstream as the Walsh River [1186]. Tarpon have also been recorded from swamps and lagoons of the Weipa area [571].
Lake [748] lists M. cyprinoides as a member of the freshwater fish fauna of New South Wales and later suggested that it was restricted to the northern rivers of the state [755]. Krefft reported catching M. cyprinoides on fly in the Hawkesbury River in the early 1860s [741]. It appears to be uncommon or no longer present in New South Wales as it was not collected in the recent comprehensive NSW Fisheries survey [554]. Macro/meso/microhabitat use The life history of Megalops cyprinoides is complex, involving a variety of different habitats at different life stages. The habitat requirements of the larval and juvenile forms are more fully described in the sections on reproductive and movement below. Subadult and early-maturing adult
65
Freshwater Fishes of North-Eastern Australia
Table 1. Physicochemical data for the tarpon Megalops cyprinoides. Summaries are drawn from two separate studies undertaken in northern Australia [193, 697]. Note the difference in units used to described turbity.
forms are found in a variety of freshwater habitats and may penetrate many hundreds of kilometres upstream. Roberts [1147] reported M. cyprinoides 905 km upstream in the Fly River of Papua New Guinea and Coates [313] reports it present 530 km upstream in the Sepik River (although it may have been present further upstream where little sampling was undertaken). Similarly extensive upstream distributions have also been reported for Australian rivers (see above). In the Sepik River, tarpon have been recorded from the main river channel, major lowland tributaries, oxbow floodplain lakes and on the floodplain itself [313]. However, it was reported that the floodplain was not the preferred habitat, that tarpon were absent from low order streams and deep water habitats were preferred. In contrast, tarpon in the Alligator Rivers region have been recorded from escarpment habitats near the headwaters. The majority of fish collected by Bishop et al. [193] were from lentic habitats such as floodplain, lowland muddy and corridor lagoons as well as the main channel. These authors noted that M. cyprinoides was most abundant in lagoons with plentiful submerged and floating-attached macrophytes, but that at times would move out of such habitats to feed extensively on migrating rainbowfishes. Bishop et al. [193] noted a preference for deeper waters also.
Parameter
Min.
Max.
Mean
Alligator Rivers region (n = 20) Water temperature (°C) 23 34 Dissolved oxygen (mg.L-1) 1.9 9.7 pH 5.3 9.1 Conductivity (µS.cm-1) 2 200 Turbidity (cm) 4 270
86
Normanby River floodplain (n = 12) Water temperature (°C) 22.9 29.4 Dissolved oxygen (mg.L-1) 1.1 7.1 pH 6.1 8.2 Conductivity (µS.cm-1) 9.8 391 Turbidity (NTU) 2.1 8.1
23.9 3.6 7.1 220.6 5.3
29.8 6.2 6.5
with dissolved oxygen levels of 0.2 mg O2.L–1 [583]. This species is obviously very tolerant of low levels of dissolved oxygen primarily because of its ability to extract oxygen directly from the atmosphere. Megalops cyprinoides was not recorded in a large fish kill in Magela Creek for which hypoxia was implicated as the primary cause [187] and Bishop et al. [193] attributed its survival to its ability to breath air.
Coates [313] observed that tarpon fed extensively underneath floating mats of Salvinia. This same behaviour has been observed in floodplain habitats of the Burdekin River delta (C. Perna, unpubl. obs.). Floodplain water bodies experience precipitous declines in water quality, especially dissolved oxygen levels, when floating weeds such as Salvinia and water hyacinth (Eichhornia crassipes) proliferate. In such cases, tarpon (which is a facultative airbreather), and other species capable of accessing the relatively well-oxygenated layer of surface water (e.g. the alien Gambusia holbrooki), are the dominant species.
Air breathing in M. cyprinoides has not been studied but has been for M. atlanticus [444], a summary of which is included below. This species is a bimodal breather with gas exchange occurring across the walls of the swim bladder. Species of Megalops are the only marine nektonic species to use bimodal breathing and the only marine fishes to use respiratory gas bladders. The wall of the gas bladder in M. atlanticus has four rows of highly vascularised tissue. The extent of vascularisation of the bladder in M. cyprinoides is greater in fish collected from hypoxic waters than in welloxygenated waters (C. Perna, pers. comm.). In M. atlanticus, air is expelled from beneath the opercula as the fish rises to the surface. If denied access to air after exhalation, M. atlanticus cannot maintain neutral buoyancy. Air is inhaled by expansion of the buccal and opercular cavities, accompanied by abduction of the gular plate. The inhaled air is forced into the gas bladder, after the mouth closes, by compression of the buccal and opercular cavities. This behaviour of rising to the surface and gulping air has been termed ‘rolling’ and has been observed to occur in leptocephalus-like larvae also [594]. Bishop et al. suggested that rolling was more frequently observed when oxygen levels were low [193]. Air breathing, or at least the ‘rolling’ behaviour associated with air breathing, has been observed in larval M. cyprinoides also [302].
Environmental tolerances Megalops cyprinoides is a tropical species and the water temperatures given in Table 1 reflect this distribution. However, given that its distribution extends down the east coast to at least Brisbane, this species may be able to tolerate lower water temperatures than indicated here. The closely related M. atlanticus has been recorded from temperatures as low as 12°C [444]. Megalops cyprinoides has been recorded across a wide range of dissolved oxygen concentrations and is tolerant of hypoxic conditions (Table 1). Oxygen levels in floodplain habitats of the Burdekin River delta, in which this species is common, frequently descend as low as 0.2–1% saturation (C. Perna, pers. comm.). Hogan and Graham recorded this species in wetlands of the Tully Murray River
66
Megalops cyprinoides
The related species M. atlanticus is not an obligate air breather, surviving for at least two weeks when denied access to air. This species will however, breath air in normoxic waters, presumably to maintain buoyancy [444]. Air breathing frequency in M. atlanticus increases with increasing temperature and decreasing oxygen saturation. At temperatures above 29°C, the frequency of air breathing is independent of oxygen levels [444]. The frequency of air breathing in M. atlanticus increases with increasing sulphide concentrations also. High levels of sulphide inhibit respiration by disrupting the function of both haemoglobin and cytochrome c. Megalops atlanticus is tolerant of very high levels of sulphide (240 µmoles.L–1) when air breathing frequency is higher than that recorded for anoxic conditions.
probably achieves sexual maturity in the second year of life when lengths in excess of 300 mm are attained. Juvenile individuals smaller than that observed by Bishop et al. [193] have been recorded from freshwaters elsewhere. Taylor [1304] reports the presence of a 66 mm juvenile in a freshwater lagoon with connection to an estuarine mangrove habitat in Arnhem Land. Small fish of this size have been collected from lagoons of the Burdekin River delta also (C. Perna, pers. comm.). In an early dry season survey of the fishes of Gunpowder Creek, approximately 200 km from the river mouth of the Leichhardt River, we collected numerous M. cyprionoides between 25–50 mm SL [1093]. Obviously such small fish must be capable of rapid extensive movement. The spawning habitat of M. cyprinoides is unknown other than it occurs in the near-shore marine or estuarine environment. This species produces a leptocephalus-like larva that undergoes most of its development in saline supralittoral tidal swamp environments. Opinions differ as to whether the leptocephali actively migrate into such habitats [29] or are simply passively carried in on rising tides [302], however Wade [1347] demonstrated that postlarvae were capable of independent movement and migration. Davis [370] studied the temporal dynamics of supralittoral swamp fishes near Darwin and found M. cyprinoides to be very common, accounting for 13% of all fish collected during the early wet season. Leptocephali were present in the tidal swamp from October to March, although peak numbers occurred in December and January. Initially, numbers appeared greatest during the full moon phase until numbers increased sufficiently to swamp any apparent temporal variation in recruitment. Juvenile fishes (i.e. those having undergone metamorphosis) were, in contrast, present only from December onwards and abundances levels were correlated with tidal phases. Megalops cyprinoides was the most numerically dominant species during neap tides and was amongst the top three species with respect to length of residency. Russell and Garrett [1174] also found M. cyprinoides larvae during December in supralittoral swamps of the Norman River estuary, northern Queensland; they were uncommon however.
Megalops cyprinoides has been recorded across a reasonably wide range of pH (5.3 to 9.1) (Table 1). We have collected adult M. cyprinoides from dystrophic dune lakes of the Cape Flattery region, where pH levels may frequently be in the range of 4–5 [1101]. The conductivity levels depicted in Table 1 indicate fresh waters but given that both larvae and adult tarpon occur in marine and estuarine environments, salinity tolerance must extend across a wide range. Larval tarpon are able to withstand abrupt transfer from brackish to freshwater but acclimation is generally a gradual process [29]. The range of water clarity across which it has been collected suggests that tarpon are tolerant of elevated turbidity. However, the extent to which high turbidity interferes with the ability of tarpon to locate prey remains unknown. The conditions in which M. cyprinoides has been recorded and the tolerances inferred from these conditions plus insights gained from comparison with M. atlanticus, suggest that tarpon are hardy and well-adapted to inhabit seasonal wetlands that experience substantial fluctuations in dissolved oxygen, turbidity, pH and sulphide levels. Reproductive biology Detailed information on many aspects of the reproductive biology of Megalops cyprinoides is lacking, principally because this species moves out of freshwater environments to spawn. Bishop et al. [193] records some information on reproductive biology of this species, however sample sizes were not large. Most fish collected were immature, with the length frequency distribution being essentially unimodal with a mean of 246 mm CFL. The smallest fish collected by these authors was 137 mm CFL occurred in the mid-wet and mid-dry seasons, suggestive of a recruitment pulse occurring during the mid-wet when estuarine connections occur. Male maturation commenced at the end of the dry season. Based on growth estimates provided by Alikunhi and Nagaraja Rao [29] and Bishop et al. [193], M. cyprinoides
Fecundity estimates are unavailable for M. cyprinoides. Hollister [594] cites data for a 56 kg M. atlanticus producing 12 million small (0.67–0.75 mm), non-buoyant, nonadhesive eggs. Given that M. cyprinoides does not reach such large size, it is unlikely to be a fecund as its congener. Nonetheless, this species probably produces hundreds of thousands of small eggs similar to M. atlanticus. Estimates of reproductive effort in M. cyprinoides indicate a maximum female GSI of about 7% [313]. Bishop et al. [193]
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Freshwater Fishes of North-Eastern Australia
Table 2. Life history data for the tarpon Megalops cyprinoides. Age at sexual maturity (months)
12–24 months
Minimum length of ripe females (mm)
Alligator Rivers region – 300 mm CFL (estimate only) [193] Sepik River – 410 mm female recorded with developed gonads [313]
Minimum length of ripe males (mm)
Alligator River region – 300 mm [193]
Longevity (years)
?
Sex ratio (female to male)
?
Occurrence of ripe fish
?
Peak spawning activity
Summer wet season [193] India – suggestions of a year-round breeding phenology with a peak during the monsoonal months [1347]
Critical temperature for spawning
?
Inducement to spawning
?
Mean GSI of ripe females (%)
7% [313]
Mean GSI of ripe males (%)
<1%, although maturity stage low [193]
Fecundity (number of ova)
?
Fecundity/length relationship
?
Egg size
?
Frequency of spawning
Possibly several times over life span
Oviposition and spawning site
Near-shore marine
Spawning migration Parental care
None
Time to hatching
?
Length at hatching (mm)
?
Length at free swimming stage (mm)
11
Length at metamorphosis (mm)
17
Duration of larval development
Up to several weeks
Age at loss of yolk sack
?
Age at first feeding
Probably very soon after hatching
list much smaller values (<1%) for fish from the Alligator Rivers region. However, it must be borne in mind that the entire sample was collected from freshwaters and that complete gonad maturation probably occurs in marine or estuarine habitats.
anus, and a change in the shape, appearance and size of the head. Further details on metamorphosis and early development can be found in Tsukamoto and Okiyama [1444]. Movement From the above discussion, it is evident that movement is a feature of many phases during the life history. After metamorphosis, juvenile tarpon migrate out of supralittoral habitats and move upstream. It is unknown whether this movement is made en masse or involves single individuals. However, the 32 juveniles we recorded in Gunpowder Creek were all between 32 and 50 mm SL, suggesting that migration may have been coordinated within this age class. Moreover, it indicates that substantial upstream movements are made at very small size.
The smallest size recorded for the larvae of M. cyprinoides is about 11 mm [1347], such fish already have well-developed teeth, a long and well-developed alimentary canal and the air bladder is a club-like evagination of the alimentary canal. Growth is gradual until the leptocephalus achieves a length of 25–26 mm whereupon the body commences to shrink back to a length of about 16 mm [1347]. This latter process is protracted, taking up to seven weeks. However, Alikunhi and Nagaraja Rao [29] suggest that shrinkage may occur over the space of as little as seven days when larvae are acclimated to freshwater over 24 hours. Larvae can tolerate direct transfer from brackish to freshwater although acclimation usually occurs over a longer period [1347]. Outstanding features of metamorphosis other than shrinkage in body length include: forward migration of the dorsal and anal fins and of the
Megalops cyprinoides have been recorded moving through, or attempting to move through, various fishway structures in Queensland rivers [11, 158, 159, 232, 587, 740, 1276]. However, in all cases numbers have been low. For example, Russell [1173] recorded only eight individuals ascending the fishway on the Burnett River barrage over a 32-month
68
Megalops cyprinoides
period. Ascending fish were between 33 and 180 mm in length. A further two fish, both 30 mm in length, were recorded moving downstream through this fishway. Kowarsky and Ross [740] detected small numbers of fish between 139–370 mm in length, ascending the fishway on the Fitzroy River barrage during March and April only. Similarly small numbers were recorded moving through the fishway on the Burnett River barrage in these months, and Broadfoot et al. [232] recorded 18 individuals moving through the Kolan Weir fishway at times of little flow. In most of these studies, the size range of fishes sampled (when given) indicates that the majority of upstream migrating fish are of relatively small size. For example, sizes ranges for fish trapped in the Tinana, Kolan, Burnett and Fitzroy barrage fishways were 106–206 mm (TL), 89–142 mm (CFL), 30–180 mm (TL) and 139–370 mm (TL), respectively. Hogan et al. [587] recorded much larger fish (300–450 mm TL) attempting to ascend the Clare Weir fishway on the Burdekin River under a variety of flow condition (65 466–127 467 ML.day–1). In the Sepik River, M. cyprinoides enter the river at lengths of about 100 mm between April and July, and individuals less than 250 mm in length move upstream between May and August (i.e. the early dry season) [313].
classified it as a marine species that was widely distributed throughout the estuary in the wet and early dry seasons only. Trophic ecology The dietary summary provided in Figure 1 was drawn from three separate studies. The first was undertaken by Bishop et al. [193] in the Alligator Rivers region and included 79 individuals ranging in size from about 150 mm to 400 mm CFL; the second was by Kennard [697] in floodplain lagoons of the Normanby River and included 25 individuals ranging in size from 180 to 400 mm SL [697]; and the third included three individuals of 400, 420 and 640 mm SL collected in the lower Burdekin River [1080]. The diet of M. cyprinoides, although reasonably diverse, is dominated by aquatic insects and fish (chandids, rainbowfishes, plotosid catfishes, Pseudomugil tenellus and Hypseleotris compressa). The extent of piscivory varied between studies, with fish comprising 31% of the total for tarpon from the Alligator Rivers region and 21.6% of the diet of fish from the Normanby River floodplain. Fish were absent from the guts of three fish collected in the Burdekin River. Both Bishop et al. [193] and Kennard [697] showed that piscivory varied in importance with season. Fish were most important in the early, mid- and late wet season diets in the Alligator Rivers region. Bishop et al. noted that tarpon would establish feeding stations where they preyed heavily on migrating rainbowfishes. Fish accounted for 22% of the early dry season diet of tarpon in the Normanby River but were almost absent (1.8%) in the late dry when terrestrially derived prey were more important (16.2%).
An extensive upstream migration is not necessarily an obligate part of the life history. For example, tarpon less than 350 mm TL are common in wetland habitats of the Burdekin River delta: they may however be entrained in pumping works and artificially delivered into these systems (C. Perna, pers. comm.). Nonetheless, it appears that many small individuals do migrate upstream where they make use of main channel and off-channel habitats. If upstream movements by juveniles occurs during periods of low flow late in the wet season or in the early dry season, it is unlikely that access to many off-channel waterbodies exists at this time. Further lateral movement may occur when water levels rise at the beginning of the following wet season.
Unidentified (15.4%)
Fish (29.0%) Terrestrial invertebrates (4.6%) Aerial aquatic invertebrates (1.6%) Terrestrial vegetation (1.3%) Detritus (3.3%)
Bishop et al. [193] found that M. cyprinoides less than 300 mm CFL were most common in floodplain, lowland and corridor lagoons but that fish larger than this were often recorded from lowland sandy creeks during the wet season. Such a shift in habitat use may presage a downstream spawning migration. These authors believed that adult tarpon migrate back upstream after spawning, citing as evidence observations of spent females congregated below, and trying to negotiate, a roadside culvert. Coates [313], in contrast, suggested that no upstream migration was made after spawning and that spent fish remained in estuarine, near-shore marine environments. Cyrus and Blaber [356] found that the distribution of M. cyprinoides in the estuary of the Embley River varied seasonally and
Microcrustaceans (4.0%)
Macrocrustaceans (6.0%) Aquatic insects (34.6%)
Figure 1. The average diet of the tarpon Megalops cyprinoides. The summary is derived from three separate studies undertaken in northern Australia (see text for details) and mean contributions have been weighted by sample size.
Terrestrially-derived foods are important in the diet, accounting for about 8% overall. We observed that two adult tarpon from the dystrophic dune lakes of Cape Flattery region consumed little other than terrestrial insects.
69
Freshwater Fishes of North-Eastern Australia
faces many of the same pressures. These are principally associated with degradation of estuarine and supralittoral habitats necessary for larvae and juveniles and the need to move freely between different habitats throughout their life history. Although tarpon are frequently found in offchannel habitats of less than optimal water quality and condition, access to such habitats may not always be assured. Water resource developments that interfere with upstream or downstream movement are likely to impact on this species in the long term. Similarly, infrastructure sufficiently large enough to capture large flood events may affect tarpon by reducing the extent of lateral flooding.
The presence of microcrustacea in the diet is noteworthy given the size of M. cyprinoides. This food type comprised 8.4% of the overall diet of fish in the Normanby River (11.4% and 0% in the early and late dry seasons, respectively). Microcrustaceans (Cladocera) were present and important (14%) in the diet of Alligator River tarpon in the mid-dry season only. The diversity of diet evident in Figure 1 is of interest not only for the range of prey consumed but also the range of habitats from which prey are obtained (i.e. surface, midwater and benthos). A diversity of feeding styles is also evident, for this species is not only capable of preying upon fast-moving fishes but also upon fishes with protective spines, as well as planktonic microcrustaceans, macrocrustacean (prawns) and a range of small benthic insect larvae.
Given the piscivorous nature of M. cyprinoides, this species is probably of significance in determining the assemblage structure and abundance of smaller fishes in some habitats, particularly enclosed off-channel wetlands. In the wetlands of the Burdekin River delta, this species may play a significant role in controlling the abundance of pest species such as Gambusia holbrooki (C. Perna, pers. comm.) and its absence may allow Gambusia to achieve abundance levels sufficiently high to impact on other native species.
Coates [313] described the diet of tarpon from the Sepik River [313]. Fish were also important in this river (17%) but included a less diverse range of species being dominated by Giurus margeratacea and Oxyeleotris spp. Prawns comprised 20% of the diet and terrestrial insects a further 13%. The contribution made by terrestrially-derived prey was probably higher as some insect orders were grouped in a prey class termed ‘larger insect larvae’. Insect larvae comprised about 40% of the diet. Such a diet is well within the range depicted in Figure 1.
Given the scant information available about the ecology of the adult form, it is difficult to say what pressures may be faced by this life history stage. This species forms only a minor component of the bycatch from commercial barramundi harvesting [501] and does not appear under threat from this activity. Recreational fishing is similarly not expected to pose any major threat given the poor culinary value of this species: most individuals are released after capture.
Noble [994], reporting on the laboratory rearing of M. cyprionoides larvae, noted that post larvae preferred copepods over other prey, and also noted the preponderance of copepods in the diet of larvae reported in other Indian studies of this species. As larvae grow, foraging is focused first on large microcrustaceans, then on such prey as isopods with an eventual transition to prawns.
There remain many aspects of the ecology of this species for which information enabling effective management is lacking. Megalops cyprinoides is not unique in this regard. Absence of data should be regarded as a threatening process in itself. There is potential for fishway studies to increase our knowledge of this species’ ecology, provided that information other than simply length and number of fish passing through the fishway is collected.
Conservation status, threats and management Megalops cyprinoides is classified as Non-Threatened [1353]. However, the ecology of this species parallels that of the barramundi in many ways, and accordingly it
70
Anguilla australis Richardson, 1841 Shortfinned eel
37 056001
Anguilla obscura Günther, 1872 Pacific shortfinned eel
37 056004
Anguilla reinhardtii Steindachner, 1867 Longfinned eel
37 056002
Family: Anguillidae
to about half the distance of the jaw teeth; anterior nostrils long, projecting forwards over upper lip; eyes small in immature specimens, increasing in relative size at maturity; gill openings small and vertically orientated. Dorsal fin confluent with caudal and anal fins, originating slightly in front or level with the anal fin, without spines. Pelvic fins absent; pectoral fins small and ovate, positioned just behind gill openings. Scales inconspicuous, deeply embedded in thick, fleshy skin, skin covered in characteristic slime. Lateral line distinct.
Description Anguilla australis Dorsal fin confluent with caudal fin and anal fin, originating slightly in front or level with anal fin; Pectoral fin: 14–16 rays; Pelvic fins absent; Scales indistinct; Vertebrae: 109–116 [52, 178, 401]. Anguilla australis is a medium to large sized eel. Beumer [178] lists a maximum length of around 1100 mm TL and weight of 3.2 kg. Merrick and Schmida [936] list a maximum weight of 6.8 kg but suggest it is usually much smaller. Males attain smaller maximum size (up to 500 mm TL and 250 g) than do females [178, 891]. The largest specimen we have collected in south-eastern Queensland was 350 mm SL [1093]. The equation describing the relationship between length (TL in mm) and weight (W in g) for a population in the Douglas River (eastern Tasmania) [1244] is: Log W = 3.4 Log L – 3.477, r2 = 0.984, p<0.001, n = 80, range = ~ 80–520 mm TL.
Small juvenile eels (known collectively for all Anguilla species as ‘glass eels’) recently metamorphosed from the leptocephalus stage and in the process of moving into estuaries and lowland rivers are transparent but can be distinguished from other eel species in south-eastern Australia by the position of the origin of the dorsal fin. Fully pigmented juvenile eels (known as ‘brown elvers’) rapidly assume adult colouration after entering freshwaters (often called ‘yellow eels’ by this stage). The uniform colouration of elvers and adults of A. australis is characteristic of this species in south-eastern Australia and varies from coppery or golden to olive-green on the dorsal and lateral surfaces, becoming paler greyish to silvery-white on the ventral surface. The dorsal surface of mature adults
Anguilla australis has an elongate, cylindrical body and a small head; mouth large, extending to below the eye; toothless groove between maxillary teeth absent; vomerine teeth forming a broad club-shaped patch extending back
71
Freshwater Fishes of North-Eastern Australia
the mean and maximum length of this species were 242 and 1350 mm SL, respectively, with 85.6% of the sample being less than 350 mm SL [1093]. Of 5121 specimens collected from streams of south-eastern Queensland over the period 1994–2000, the mean and maximum length of this species were 239 and 1300 mm SL, respectively, with the majority (80% of individuals) 350 mm SL or less [1093].
becomes darker and contrasts markedly with the silver belly (often referred to as ‘silver eels’) on commencement of the downstream migration to oceanic spawning grounds [52, 177, 178, 401, 936]. Anguilla obscura Dorsal fin confluent with caudal fin and anal fin, originating slightly in front or level with anal fin; Pectoral fin: 14–20 rays; Pelvic fins absent; Scales indistinct; Vertebrae: 101–107 [37, 52, 178, 401].
Equations describing the relationship between length (SL or TL in mm) and weight (W in g) are available for the following populations:
Anguilla obscura is a medium to large sized eel reported to reach 1200 mm TL but is more commonly around 600 mm TL [33, 754]. The largest specimen collected in the Normanby River, eastern Cape York Peninsula, was 600 mm SL [697]. The largest specimen collected in the Wet Tropics region of northern Queensland was 800 mm SL, but the average length of 21 individuals was 171 mm SL [1093]. Beumer et al. [183] collected a 1050 mm TL female from the South Johnstone River. No length–weight equation is available for this species but it is generally similar in size and shape to A. australis.
Mulgrave and Johnstone Rivers (Wet Tropics) [1093]: W = 4.91 x 10–8 SL3.686; r2 = 0.953, p<0.001, n = 100, range = 93–890 mm SL. Douglas River (eastern Tasmania) [1244]: Log W = 3.548 Log TL – 3.567, r2 = 0.996, p<0.001, n = 71, range = ~ 50–1200 mm TL. Mouth large, extending well behind the eyes; maxillary teeth separated by a toothless groove; vomerine teeth forming a narrow patch extending backward around the same distance as the jaw teeth; the dorsal fin originates well forward of the anal fin. The glass eel stage of A. reinhardtii can be recognised by the position of the origin of the dorsal fin, which is characteristic of this species throughout eastern Australia (but see below). The distinct mottled or marbled colouration is also characteristic of this species: dorsal surface varying from olive-green to brownish, becoming paler laterally and ventrally. Median fin dark brown; pectoral fins commonly yellowish. Adults usually lose their mottled pattern and become bright silvery after commencement of the downstream migration to oceanic spawning grounds [37, 52, 178, 401, 936].
Mouth large, extending well behind the eyes; toothless groove between maxillary teeth absent; vomerine teeth forming a narrow patch extending backward around three-quarters or less of the distance of the jaw teeth; eyes dorsally positioned in large adult specimens. Dorsal fin origin slightly in front or level with the anal fin. Colour varying from silver or yellowish to dark brown on the dorsal and lateral surfaces, becoming paler on the ventral surface. The uniform colour and position of the origin of the dorsal fin are diagnostic of this species in north-eastern Australia [37, 52, 401, 936]. Anguilla reinhardtii Dorsal fin confluent with caudal fin and anal fin, originating well forward of anal fin; Pectoral fin: 16–20 rays; Pelvic fins absent; Scales indistinct; Vertebrae: 104–110 [52, 178, 401]. Figure: drawn from photographs of mature specimen 815 mm SL, lowland creek, North Johnstone River, September 1995; drawn 2002.
A fourth eel species, A. megastoma, may occur occasionally in north-eastern Australia [1085, 1087]. This species is most similar to A. reinhardtii in having a mottled colouration and a dorsal fin originating well forward of the anus. It differs in having a larger mouth (33–45% of HL versus 20–31% in A. reinhardtii) and lacking a tooth groove between the maxillary teeth [37].
Anguilla reinhardtii is a very large eel. Merrick and Schmida [936] list a maximum documented length of 2000 mm TL and weight of 16.3 kg, but recount reliable reports of this species attaining 3000 mm TL in deep isolated lakes where downstream migrations may be prevented for long periods of time. Beumer [178] listed a maximum length of around 1650 mm TL and weight of 22 kg. This species is more common to 1000 mm TL and males are thought to reach smaller maximum size (up to 650 mm TL and 600 g) than females [52, 178]. Of 1376 specimens collected from rivers of the Wet Tropics region,
Systematics Anguillidae is presently considered to contain 15 species within a single genus Anguilla [52]. It is a very widespread family occurring in temperate and tropical waters of the northern Atlantic, Indian and western Pacific oceans, and coastal rivers of adjacent landmasses. Up to six species of Anguilla have been recorded in Australia, five of which occur in the north-eastern part of the continent. Anguilla bicolor McClelland, 1844 [874] is widespread in the Indian Ocean and western Pacific region including New Guinea;
72
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
the Burdekin River used in the description of A. marginipinnis by Macleay, 1883 [847] was recognised by Schmidt [1205] as A. obscura, the remaining specimens being synonymous with A. reinhardtii. Refer to Ege [401] for a detailed examination of the synonymy of A. obscura and A. reinhardtii.
in Australia it occurs only in the Kimberley region of northern Western Australia and is not treated further here. Anguilla megastoma Kaup, 1856 [679] is widespread in the central and western Pacific region including New Guinea; in Australia it is known only from a single specimen (~700 mm TL) collected by us in the Daintree River in the Wet Tropics region of northern Queensland [1085, 1087]. Anguilla marmorata Quoy and Gaimard, 1824 is widespread in the Indo-West Pacific region including New Guinea [37]. In Australia a single glass eel of this species was recently recorded in the lower Daintree River by DPI fisheries staff (M. Hutchison pers. comm.). It would appear that the Australian records of A. megastoma and A. marmorata are extra-limital and these species will not be treated further here.
The lepocephalus larval stage characteristic of the Anguillidae and other Anguilliformes such as conger, moray and snake eels, occurs in only three other groups of fishes, the Elopiformes (tarpon and ten pounders), Sacchopharyngiformes (bobtail eels, swallowers and whiptail gulpers) and the Notacanthiformes (deep sea spiny eels). All are marine and for this reason, Anguillidae is considered to be derived from marine stocks and given that two-thirds of all Anguilla species are tropical, probably from tropical marine stocks [1330]. Seven of the world’s 15 species of Anguilla occur around the western Pacific.
Anguilla australis was first described by Richardson in 1844 [1137]. In 1928, Schmidt [1205] revised the taxonomy of the Australian eels and, on the basis of small but consistent differences in dorsal fin insertions and vertebral counts, proposed two subspecies: A. australis occidentalis in Australia and A. australis orientalis in New Zealand. Griffin [475] reviewed the New Zealand anguillids in 1936 and renamed the Australian subspecies A. a. australis and the New Zealand subspecies A. a. schmidtii. In his comprehensive review of the genus in 1939, Ege [401] agreed with these subspecific designations and this view remained generally accepted for almost four decades until questioned by Jellyman [645] and McDowall [891]. In 1999, Dijkstra and Jellyman [382] presented mitochondrial DNA data demonstrating a lack of genetic differentiation between Australian and New Zealand populations and concluded that the subspecies should therefore be considered a single species, A. australis.
Ege [401] presented an early phyologeny based on morphometrics and meristics but subsequent molecular analyses [63, 1330] have revealed that the external morphological characters used by Ege (including dorsal fin length) are adaptive and may not reflect phylogenetic relationships [63]. Studies of mtDNA sequence divergence in some species of Anguilla have indicated that A. celebesensis [1330] or A. marmorata [137] is most similar to ancestral forms, but a subsequent study which included all 15 species of Anguilla revealed A. borneensis from Borneo Island as the most likely basal species [63, 1333]. The following scenario has been proposed to explain the phylogeny and biogeography of Anguillidae [63, 1330, 1333]. An ancestral stock similar to A. borneensis, which evolved around present day Indonesia in the Cretaceous-Eocene period, gave rise to two stocks. In one, the leptocephalus larvae dispersed widely via the east to west flowing Paleocircumglobal Equatorial current in the Tethys Sea, giving rise to the precursor of the Indo-Pacific species A. rostrata (North America), A. anguilla (Europe and northern Africa) and A. mossambica (eastern Africa). The second stock included the ancestor of the Oceania lineage that dispersed south-westwards by the South Equatorial Current to form A. australis and A. dieffenbachii in Australia and New Zealand. A second divergence event within the ancestral stock was thought to have occurred during the Oligocene (30 m.y.b.p.), giving rise to A. japonica which dispersed northward via the North Pacific Gyre, and the Indo-Pacific species including A. obscura and A. reinhardtii. The position of A. reinhardtii is ambiguous [63] but it appears that this species and A. australis are only distantly related (relatively) and arrived on the Australian continent at different times.
The absence of genetic variation in A. australis glass eels from New Zealand led Smith et al. [1251] to conclude that all individuals in this species are derived from a single spawning population. However, these authors found significant genetic variation among A. australis populations from different localities in New Zealand, which they suggested was due to selection, perhaps mediated by water temperature, in the juvenile to adult phase (i.e. after recruitment into the freshwater environment). Steindachner [1262] first described A. reinhardtii in 1867 and A. obscura was first described by Günther [489] in 1871. Perhaps as a result of their widespread distribution in the south-western Pacific and eastern Australia, and their sympatry with other anguillids, both species appear in the literature under several different names, all due to erroneous determinations rather than being specifically connected with the descriptions of supposed new species [401]. For example, one of the co-types (syntype) from
73
Freshwater Fishes of North-Eastern Australia
It was present in low numbers at sites in which it occurred (13th most abundant species forming 1.29% of the total abundance at these sites). In these sites, A. australis most commonly occurred with the following species (listed in decreasing order of relative abundance): G. holbrooki, R. semoni, M. duboulayi, A. reinhardtii, and H. compressa. Anguilla australis was the 27th most important species in terms of biomass, forming only 0.02% of the total biomass of fish collected by us and contributing less than 0.1% to the total biomass collected within individual drainage basins. Across all rivers, average and maximum numerical densities recorded in 47 hydraulic habitat samples (i.e. riffles, runs or pools) were 0.14 individuals.10m–2 and 2.00 individuals.10m–2, respectively. Average and maximum biomass densities at 33 of these sites were 0.63 g.10m–2 and 7.41 g.10m–2, respectively. Other surveys in south-eastern Queensland have recorded this species in similarly low numbers [643, 768]. Fishway studies [1276, 1277] and targeted surveys [912, 915] have revealed that although glass eels are relatively common in south-eastern Queensland, only a very small proportion appear to recruit to the adult population [912, 1169]. Less than 1% of eels collected by commercial harvesting in freshwaters of south-eastern Queensland are A. australis [1169]. Russell [915] concluded that large barriers present in many of the lowland streams in this area may prevent A. australis from reaching freshwaters as the upstream migration period of juveniles occurs predominantly in the winter months when river discharges are low. McKinnon et al. [912] suggested that an increased recruitment success of A. reinhardtii relative to A. australis in south-eastern Queensland freshwaters, despite equivalent levels of abundance in the estuarine population, may arise because A. reinhardtii is better adapted to higher temperatures in tropical and subtropical areas than cooler areas further south, which appear to suit A. australis.
Distribution and abundance Anguilla australis This species is widespread in the western Pacific including New Caledonia, New Zealand, Chatham Islands, Norfolk Island, Lord Howe Island and coastal drainages of eastern Australia between the Burnett River in south-eastern Queensland, south and west to Mt. Gambier in South Australia [52, 178, 401]. The veracity of several isolated records of this species in the Murray-Darling Basin [52, 178] is uncertain [1338]. It is also present in streams on Flinders and Vansittart islands in Bass Strait and is widespread in coastal drainages of Tasmania [52, 178, 423]. Anguilla australis is also present on Bribie and Moreton islands, off the south-eastern Queensland coast. A Queensland Museum record of this species from the Pioneer River in central Queensland is probably erroneous as it was based on a very small glass eel that was most likely A. obscura [1081]. Records of A. australis in Japan are undoubtedly escapees from aquaculture facilities [1283]. Anguilla australis is relatively uncommon in Queensland but has been recorded in most basins from the Burnett River south to the border with New South Wales. Glass eels and elvers have been collected in the Burnett River [1276, 1277] but it is not clear whether individuals recruit to the adult population in freshwater reaches of this river. It has not been recorded from the Elliott River but a few Queensland Museum records exist for small streams of the Burrum Basin [661]. We collected only 122 individuals (80% of which were less than 120 mm SL) during surveys of streams and rivers from the Mary River south to the Queensland–New South Wales border [1093]. Although it was present at 10.1% of all locations sampled (Table 1), it was only the 24th most abundant species collected (0.07% of the total number of fishes collected) and was not common or widespread within individual drainage basins.
Table 1. Distribution, abundance and biomass data for Anguilla australis in rivers of south-eastern Queensland. Data summaries for a total of 122 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively, at those sites in which this species occurred. Total
% locations
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
10.1
4.0
20.7
10.0
1.8
23.5
10.0
0.07 (1.29)
0.01 (0.32)
0.31 (1.64)
0.16 (2.05)
0.01 (0.71)
0.21 (1.35)
0.25 (3.53)
24 (13)
22 (13)
13 (8)
19 (8)
24 (10)
17 (12)
16 (7)
0.02 (0.89)
0.01 (0.11)
0.08 (42.43)
–
0.02 (0.81)
0.06 (1.12)
0.03 (0.14)
27 (8)
24 (12)
9 (2)
–
24 (8)
19 (7)
14 (7)
Mean numerical density (fish.10m–2)
0.14 ± 0.04
0.05 ± 0.02
0.08 ± 0.03
0.09 ± 0.03
0.21 ± 0.02
0.17 ± 0.07
0.03 ± 0.02
Mean biomass density (g.10m–2)
0.63 ± 0.26
0.08 ± 0.04
1.39 ± 0.00
–
1.08 ± 0.65
0.68 ± 0.34
0.03 ± 0.00
% abundance Rank abundance % biomass Rank biomass
74
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
[1099], it rarely exceeded 5% of the total number of fish collected at each site. This species is widespread and relatively abundant in the Wet Tropics region, however. It was recorded in all drainage basins examined in an extensive survey of the region; present in 77% of all sites examined and contributed 6.2% of the total number of fishes collected [1085, 1087]. Subsequent surveys in the region have collected this species from every drainage examined [643, 979, 1179, 1183, 1184, 1185].
Anguilla australis is widespread but not overly common in freshwaters of northern New South Wales and appears to be more abundant in freshwaters toward the southern end of its range in southern New South Wales, Victoria and Tasmania [188, 437, 814, 1066, 1201]. Sloane [1245] reported that this species was widespread and abundant in Tasmanian streams and maximum numerical densities of 14 individuals.10m–2 and maximum biomass densities of 230.1 g.10m–2 have been recorded [759, 1245].
Its ubiquity in the region is matched by its distribution within river systems. Anguilla reinhardtii occurred in over 90% of all locations sampled in the Johnstone and Mulgrave/Russell rivers (Table 2). Overall, it was the seventh most abundant species collected over the period 1994–1997 but was proportionally more abundant in the Mulgrave than the Johnstone River, perhaps because the latter is characterised by steep cascades and waterfalls in its middle reaches. The sequential reduction in abundance upstream in the Johnstone River reduces the mean density of this species estimated over all sites. Note however, that the proportional contribution of eels to total biomass collected is higher in the Johnstone River, presumably because these same barriers selectively filter out smaller individuals. Density values estimated for these rivers (Table 2) approximate those seen in rivers of south-eastern Queensland as do biomass densities (Table 3). Although this species is the most dominant with respect to biomass in these Wet Tropics rivers, the proportional contribution of eels to the total biomass (43%) is lower than that seen in south-eastern Queensland probably because rivers of the Wet Tropics region contain more large-bodied species than do rivers to the south [1093].
Anguilla obscura This species is widespread in the south-western tropical Pacific from New Guinea east to the Society Islands. It is also present in coastal drainages of north-eastern Australia between the Jardine River near the tip of Cape York Peninsula, throughout eastern Queensland as far south as the Burnett River in south-eastern Queensland [37, 183, 597, 1349]. A reliable record of A. obscura occurring on Fraser Island also exists (M. Hutchison, pers. comm.). Although widespread in most drainage basins of northeastern Queensland, A. obscura is usually uncommon [569]. For example, over the period 1994–1997, we collected 24 individuals only from rivers of the Wet Tropics, making this species the 32nd most abundant species collected in this region (from a total of 38 species). Estimates of average density were low (0.17 ± 0.04 individuals.10m2, 1.15% of total abundance, n = 20 sites) although the contribution of A. obscura to total biomass was relatively high (27.2 ± 19.7 g.10m-2, 9.6% of total biomass, n = 20 sites) by virtue of its large size. Anguilla reinhardtii This species occurs in New Caledonia, New Guinea and in coastal drainages of eastern Australia between the Jardine River near the tip of Cape York Peninsula, southwards throughout eastern Queensland, New South Wales to the vicinity of Melbourne in Victoria. A record of this species in the Murray-Darling Basin has been reported from the lower Goulburn River, a tributary of the Murray River, Victoria [607]. It is also present on Fraser, Bribie, Moreton and North Stradbroke islands, off the south-eastern Queensland coast, on Lord Howe Island off the central New South Wales coast and in northern and eastern Tasmania [37, 178, 423, 597]. Anguilla reinhardtii has also been reported from the north-western coast of New Zealand, where it may have been present in low numbers since the early 1970s and is thought to have increased in abundance in recent years [649, 895].
Table 2. Distribution, abundance and biomass data for Anguilla reinhardtii in the Wet Tropics region. Data summaries for a total of 1768 individuals collected from rivers in the Wet Tropics region over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total % locations % abundance Rank abundance % biomass Rank biomass
Anguilla reinhardtii has been collected from all river basins in eastern Cape York Peninsula but appears to be relatively uncommon except in the most southern drainages of this region [1223]. Although present at all locations sampled in the Normanby River by Kennard [697] and Pusey et al.
75
Mulgrave River
Johnstone River
92
95.4
92.9
5.0 (9.0)
8.9 (13.9)
3.3 (6.5)
6 (4)
10 (9)
7 (7) 43.1 (45.4) 1 (1)
40.9 (41.1) 46.3 (47.5) 1 (1)
1 (1)
Mean numerical density (fish.10m–2) 0.32 ± 0.03
0.56 ± 0.06 0.19 ± 0.02
Mean biomass density (g.10m–2)
90.8 ± 27.5 44.7 ± 7.8
60.1 ± 10.6
Freshwater Fishes of North-Eastern Australia
south to the Queensland–New South Wales border. Surveys undertaken by us between 1994 and 2003 in south-eastern Queensland [1093] collected a total of 7694 individuals and A. reinhardtii was present at 69.5% of all locations sampled (Table 3). Overall, it was the eighth most abundant species collected (4.7% of the total number of fishes collected) and was the eighth most abundant species at sites in which it occurred (6.2%). In these sites, A. reinhardtii most commonly occurred with the following species (listed in decreasing order of relative abundance): P. signifer, R. semoni, M. duboulayi, C. marjoriae and G. holbrooki. It was generally widespread in each major river basin surveyed in south-eastern Queensland occurring in over 60% of locations sampled. The Brisbane River is an exception and the presence of Wivenhoe Dam (a large dam in the central part of the catchment) probably restricts the upstream dispersal of A. reinhardtii [704].
This species is widespread and generally common throughout coastal drainages of central Queensland and has been recorded in almost all rivers of the region. It was the eighth most abundant species collected by electrofishing in the Burdekin River and contributed 3.3% of the total collected by this method [1098]. Notably, this study showed that A. reinhardtii is generally restricted to the lower reaches of the river downstream of the Burdekin Falls Dam and to its lowland tributaries. Some large individuals still occur upstream of the dam and in Lake Dalrymple [1082], although their numbers are declining as such individuals emigrate at times of high flow and because recruitment is denied by the presence of the dam. Berghuis and Long [160] found A. reinhardtii to be contrastingly rare in the Fitzroy River, collecting only four specimens over a two-year period. These authors cautioned however, that A. reinhardtii was widespread in this river and that the sampling methods used (gill netting and baited traps) were ineffective methods for sampling eels. Addition of electrofishing to the suite of methods used is essential if the distribution and abundance of A. reinhardtii and the impact of the numerous weirs and reservoirs in this river are to be quantified. The problem of method bias was also identified in a review of the fish fauna of the Pioneer River [1081]. Although electrofishing revealed this species to be widespread and common, studies lacking this collecting method greatly underestimated its distribution and abundance.
This species achieved the highest relative abundances in the Logan-Albert and South Coast basins where it formed 7.8% and 13.9% of the total catch, respectively. By virtue of the large size attained by this species and its relative abundance, A. reinhardtii dominated the total biomass of fishes collected in each basin (except for small streams of the Moreton coastal region) and overall comprised 66.9% of the total biomass. Across all rivers, average and maximum numerical densities recorded in 709 hydraulic habitat samples (i.e. riffles, runs or pools) were 0.43 individuals.10m–2 and 12.37 individuals.10m–2, respectively. Average and maximum biomass densities at 538 of these sites were 46.98 g.10m–2 and 671.81 g.10m–2, respectively. Small eels (≤150 mm SL, corresponding to three years or younger [1244]) were present in equivalent numerical densities to larger fish (>150 mm SL, 3+ years [1244]). Mean densities of 0.35 and 0.32 individuals.10m–2 were observed for these two size classes, respectively, in hydraulic habitats where this species occurred in south-eastern
In south-eastern Queensland, this species is also widespread and generally common. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that it had been collected at 19 of 63 locations surveyed (11th most widespread species in the catchment) and formed 0.5% of the total number of fishes collected (14th most abundant). South of the Burnett River it is present and generally common in all other drainage basins
Table 3. Distribution, abundance and biomass data for Anguilla reinhardtii in rivers in south-eastern Queensland. Data summaries for a total of 7694 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively, at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert South Coast River rivers and streams
69.5
86.0
65.5
60.0
45.9
94.1
90.0
4.71 (6.20)
3.81 (4.69)
5.24 (9.59)
0.90 (2.52)
1.81 (4.24)
7.83 (9.60)
13.86 (16.44)
8 (8)
10 (7)
6 (5)
12 (6)
12 (7)
6 (5)
3 (2)
66.88 (68.84) 77.92 (80.82) 95.80 (97.13) 25.62 (27.86) 44.46 (58.04) 47.26 (47.96) 75.59 (76.36) 1 (1)
1 (1)
1 (1)
2 (2)
1 (1)
1 (1)
1 (1)
Mean numerical density (fish.10m–2)
0.43 ± 0.03
0.26 ± 0.02
0.25 ± 0.07
0.12 ± 0.02
0.36 ± 0.07
0.72 ± 0.09
0.44 ± 0.10
Mean biomass density (g.10m–2)
46.98 ± 3.59
46.08 ± 5.14 87.47 ± 39.58 27.74 ± 18.65 57.22 ± 13.40 45.52 ± 5.70 34.52 ± 11.36
76
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
Table 4. Macro/mesohabitat use by Anguilla australis in rivers of south-eastern Queensland. Data summaries for 122 individuals collected from samples of 47 mesohabitat units at 28 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
Queensland (n = 306 and 517 samples for small and large eels, respectively) [1093]. In contrast, the larger size class formed much greater biomass densities (mean and maximum biomass of 49.38 and 690.98 g.10m–2, respectively) than small eels (mean and maximum biomass of 0.94 and 13.14 g.10m–2, respectively) (n = 503 and 293 samples for large and small eels, respectively) [1093].
Parameter
Anguilla reinhardtii appears to be relatively common and widespread in coastal rivers of New South Wales and Victoria [188, 437, 814, 1066, 1201]. Sloane [1245] reported that A. reinhardtii was less widespread than A. australis in Tasmanian streams but was common in northern and eastern coastal streams. Maximum numerical densities of 4.0 individuals.10m-2 and maximum biomass densities of 1146.6 g.10m–2 were recorded in these rivers [1244, 1245]
2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
Mean
W.M.
6.0 3.0 4.0 0 1.2 11.1
1426.4 100.0 152.0 180 21.9 91.0
254.2 36.0 54.4 42 8.2 45.4
208.8 31.7 50.9 38 5.1 53.2
Gradient (%) 0 Mean depth (m) 0.10 Mean water velocity (m.sec–1) 0
Macro/mesohabitat use Anguilla australis is reported to be essentially a still water species but is found in a variety of lotic and lentic habitats including coastal and insular streams, lakes, swamps and lagoons, and in large lowland rivers. Glass eels and elvers commonly occur in estuarine areas and the freshwaterestuarine interface of lowland rivers, and the final stage of the life cycle is spent in oceanic waters [52, 178, 936, 1093]. Glass eels have also been collected in the surf zone of open beaches in New South Wales and Victoria [171]. In rivers and streams of south-eastern Queensland, A. australis occurs at low to moderate elevations (0–180 m.a.s.l.) but most commonly at less than 40 m.a.s.l. (Table 4). This species most frequently occurs in the middle to lower sections of rivers and short coastal streams (within 50 km of the river mouth), but has been recorded up to 152 km upstream from the mouth of the Logan River (Table 4). It is present in small to moderate-sized streams and rivers (range = 1.2–21.9 m width) but is more common in streams around 5 m wide and with moderate riparian cover. In streams of south-eastern Queensland, A. australis most commonly occurs in runs characterised by moderate gradient (<0.65% weighted mean gradient), moderate depth (0.31 m weighted mean depth) and moderate mean water velocity (weighted mean = 0.14 m.sec–1). We have also collected this species in shallow fast-flowing riffles and deeper slow-flowing pools (Table 4). This species is most abundant in mesohabitats with fine substrates (sand and gravel) and where submerged leaf-litter beds, woody debris, undercut banks and particularly root masses are common.
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0.1 0 0 0 0
2.30 1.05 0.55
0.58 0.42 0.14
0.65 0.31 0.14
90.8 100.0 42.6 78.2 52.4 44.0 20.2
7.8 25.5 14.6 25.8 17.0 4.5 4.6
6.9 43.5 9.6 21.2 13.6 2.1 3.1
20.1 25.1 11.9 58.2 18.8 49.9 29.9 15.3 56.7 56.7
2.4 2.3 1.4 5.6 1.1 12.8 9.1 4.2 11.7 20.9
2.1 1.6 1.1 5.9 1.4 12.5 8.1 4.1 11.5 23.8
pools of the Normanby River, located up to 160 km upstream of the river mouth [697]. We have also recorded a single very large individual of this species in the upper Burdekin River near Charters Towers [1093]. Glass eels and elvers commonly occur in estuarine areas and the freshwater-estuarine interface of lowland rivers, and the final stage of the life cycle is spent in oceanic waters [52, 936, 1093]. In the Wet Tropics region, this species is restricted to lowland reaches and small swampy tributaries at an elevation less than 20 m.a.s.l. It also occurs in floodplain wetlands of this region [583, 584, 1085, 1087]. Anguilla reinhardtii is reported to prefer more flowing waters in comparison to other Australian anguillids but it is found in a wide range of lentic and lotic habitats including coastal and insular streams, lakes, swamps and lagoons, and in large lowland river and floodplain habitats. Glass eels and elvers commonly occur in estuarine areas and the freshwater-estuarine interface of lowland
Anguilla obscura is reported to occur in generally similar habitats as A. australis including the lower reaches of rivers and brackish coastal lagoons [52, 936]. We have collected this species in floodplain lagoons and main river channel
77
Freshwater Fishes of North-Eastern Australia
rivers, and the final stage of the life cycle is spent in oceanic waters [52, 178, 697, 936, 1093]. Glass eels have also been collected in the surf zone of open beaches in New South Wales and Victoria [171]. Unlike other eels, large adults of this species also commonly occur near the surface in the deep offshore waters of large impoundments [936].
Table 5. Macro/mesohabitat use by Anguilla reinhardtii in the Wet Tropics region. Data summaries for 1376 individuals collected from 92 locations in the Johnstone and Mulgrave rivers between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
Anguilla reinhardtii in the Wet Tropics region occurs over a wide range of macrohabitat conditions ranging from large, low gradient rivers and very small, adventitious streams located at low elevation near the river mouth to headwater streams and cascades located distant from the river mouth and at elevations greater than 700 m.a.s.l. (Table 5). The average macrohabitat is a stream about 11 m wide, at an elevation of less than 100 m.a.s.l., about 40 km from the river mouth, with a gradient of 0.95%, with an intact riparian canopy. Comparison of average and weighted average values suggest that this species of eel is more abundant in similar streams with a slightly more open canopy, higher gradient and located at about 70 m.a.s.l. (Table 5). Ontogenetic variation in macrohabitat use occurs in the Wet Tropics region. Large adult eels (>500 mm SL) occur more commonly more distant from the river mouth than do smaller adult (300–500 mm SL) or juvenile and subadult (>300 mm SL) eels (weighted means = 43, 41 and 37 km, respectively), at higher elevation (155, 121, 52 m.a.s.l., respectively), in higher gradient (1.13, 0.95, 0.93%, respectively), deeper (0.36, 0.32, 0.31 m) streams with a more extensive riparian canopy (43.3, 36.3, 29.6%). These data suggest that A. reinhardtii either migrates upstream as it grows or that small eels are excluded from habitats favoured by large eels, or both.
Parameter
Min. 2
Catchment area (km ) Distance from source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
0.13 0.5 8.1 5 2.0 0
Gradient (%) 0 Mean depth (m) 0.1 Mean water velocity (m.sec–1) 0
Anguilla reinhardtii occurs in streams of a diverse substrate composition reflecting the wide distribution of this species in rivers of the Wet Tropics. The largest size class tends to be more abundant in reaches dominated by sand (15.6%) fine gravel (21.5%) and rocks (21%) whereas juveniles were most abundant in reaches with a substratum dominated by cobble (29%) and rocks (21%). Juvenile and subadult eels occupied reaches with an intermediate substrate type. This species occurs in reaches with a wide variety and availability of instream cover, even in streams choked by introduced para grass. It does not achieve high abundance in such streams however, and younger eels appear to be less abundant than older age classes in streams with abundant para grass (weighted means = 6, 11.8, 13% for juvenile, subadult and adult eels, respectively) (Table 5). Few other ontogenetic differences in the abundance of instream cover elements were evident [1093].
Max.
Mean
W.M.
515.5 67.0 104.5 790 53.7 90
67.5 14.0 40.8 95.1 11.3 39
70.3 15.3 38.6 68.1 12.4 31.5
7.33 0.87 0.56
0.76 0.36 0.18
0.95 0.32 0.25
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48.0 88.0 73.0 73.0 55.0 81.0 98.0
4.2 14.6 21.7 14.0 14.6 23.2 7.7
2.3 12.2 17.6 16.5 19.4 28.0 4.0
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
23.7 6.9 33.0 91.0 10.0 81.2 12.5 11.4 35.0 67.0
0.9 0.2 2.0 8.6 2.8 8.8 1.8 1.5 5.7 12.4
0.6 0.1 2.0 7.2 1.8 6.9 1.5 1.4 4.6 9.2
400 m.a.s.l. (Table 6). It most commonly occurs around 100 km upstream of the river mouth and at elevations around 75 m.a.s.l. It is present in a wide range of stream sizes (1.1–46.8 m width) but is more common in streams of intermediate width (9.3 m weighted mean width) and with low to moderate riparian cover (<40%). Juvenile A. reinhardtii were more common at low elevations and closer to the river mouth than adults (weighted mean elevation 65 and 110 m.a.s.l. for juveniles and adults respectively; weighted mean distance to river mouth 96 and 127 km for juveniles and adults, respectively), reflecting the progressive upstream movement of this catadromous species with growth [1093]. We observed generally little ontogenetic variation in the mesohabitat use of A. reinhardtii in south-eastern Queensland. Except for the very largest individuals which were most common in deep slowflowing pools, juveniles and adults were most common in main channel rapids, riffles and runs characterised by high gradients (weighted mean 1.3%), relatively shallow depths
Anguilla reinhardtii is widely distributed in rivers and streams of south-eastern Queensland, ranging between 0.5 and 303 km from the river mouth and at elevations up to
78
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
(weighted mean 0.26 m), and high water velocities (weighted mean 0.29 m.sec–1) (Table 6, [1093]). These data tend to support the earlier generalisation that A. reinhardtii prefers faster-flowing waters than other Australian eels. Juveniles and adults were collected in mesohabitats with similarly coarse substrates, dominated by coarse gravel, cobbles and rocks. There was apparently little selection for mesohabitats with particular submerged cover attributes and little ontogenetic variation in this pattern (Table 6, [1093]). This is unsurprising given the frequency with which A. reinhardtii occurred in rapids and riffles where submerged cover other than that provided by the coarse substrate is generally uncommon [1093].
(usually less than 0.2 m.sec–1) but occasionally in higher mean and focal velocities (Fig. 1a and b). It was usually collected in shallow water depths, most often between 10 and 40 cm (Fig. 1c). A benthic species, it usually occupied the lower third of the water column, most commonly in direct contact with the substrate (Fig. 1d). It usually occurred over sand, fine gravel and coarse gravel (Fig. 1e). This species showed no preference for areas close to the stream-bank as an equal number of fish were collected in areas less than and greater than 1 m from the bank [1093]. It was most frequently collected in close association with the substrate, and less commonly near aquatic macrophytes, woody debris, undercut banks and root masses (Fig. 1f).
Table 6. Macro/mesohabitat use by Anguilla reinhardtii in rivers of south-eastern Queensland. Data summaries for 7694 individuals collected from samples of 709 mesohabitat units at 203 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
(a)
(b) 40
30
30
20
20 10
Parameter Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
5.0 10211.7 3.0 270.0 0.5 303.0 0 400 1.1 46.8 0 95.8
Mean
W.M.
10
0
818.7 1159.5 47.2 56.1 110.2 100.2 74 76 9.4 9.3 39.5 36.1
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
60
40 30
Gradient (%) 0 Mean depth (m) 0.06 Mean water velocity (m.sec–1) 0
3.02 1.05 0.87
0.54 0.39 0.16
1.34 0.26 0.29
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
100.0 100.0 82.7 82.1 66.8 65.0 76.0
5.0 15.6 18.6 26.7 23.1 9.1 2.0
1.9 6.2 10.4 26.3 35.2 18.5 1.4
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
69.6 65.9 26.7 65.7 50.0 92.6 37.6 26.8 96.3 100.0
9.3 6.9 1.3 4.8 1.5 11.8 4.1 3.2 12.5 17.9
7.7 6.9 0.8 5.0 0.9 6.9 3.0 2.2 4.9 10.0
40
20 20 10 0
0
Total depth (cm) 30
(e)
30
20
20
10
10
0
0
Substrate composition
Microhabitat use Microhabitat use of A. australis in rivers of south-eastern Queensland generally reflected the pattern observed in mesohabitat use. This species was most frequently collected from areas of low to moderate water velocity
Relative depth
(f)
Microhabitat structure
Figure 1. Microhabitat use by Anguilla australis. Data derived from capture records for 46 individuals collected in the Mary and Albert rivers, south-eastern Queensland over the period 1994–1997 [1093].
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Freshwater Fishes of North-Eastern Australia
results of conflict with a larger individual [1093]. In southeastern Queensland, the presence of bite marks on eels is much less common, except during very dry periods when densities of eels are higher and opportunities for interactions between eels are presumably more frequent [1093].
In streams of the Wet Tropics region, various aspects of microhabitat use by A. reinhardtii change subtly as this species ages. Most individuals collected were from current velocities of between 0.1 and 0.3 m.sec-1, reflecting the average current velocities present in those sites in which it occurs. There is little ontogenetic difference in the pattern of microhabitat use with respect to current velocity except a greater number of large adult eels (>500 mm SL) occurred in faster currents up to about 1 m.sec–1 (Fig. 2a). About half of all eels collected were from areas experiencing no current at all and most (>80%) were from areas with current velocities less than 0.2 m.sec–1 (Fig. 2b). This species was collected over a wide range of depths but all age classes were most commonly collected from depths less than 0.6 m (Fig. 2c). Juvenile and subadults (<300 mm SL) were most commonly collected from depths of between 0.1 to 0.3 m, and adults (300–500 mm SL) and large adults (>500 mm SL) from depths of 0.4 to 0.6 m, although proportionally more large fish were collected from depths greater than 0.6 m than any other size class (Fig. 2d). Juvenile and subadults were more commonly collected (80% of this size class) in the bottom 10% of the water column (Fig. 2d), often in direct contact with the substratum. About 60% of adult fish were collected from the bottom 10% of the water column and only ~35% of large adult eels were collected in this depth zone. Despite these differences, this species was most frequently collected from the bottom 50% of the water column. All age classes were collected over a variety of substrate types, reflecting the composition evident at larger spatial scales (Table 5). There was a slight tendency for juveniles and subadults to occur more frequently over a substratum dominated by gravel and cobbles and for adult fish to be more frequent over a substratum dominated by rocks and sand. Few of any size class were collected over areas of mud or bedrock (Fig. 2e). The three age classes differ most in their use of cover. Juveniles and subadults were most frequently collected from within the interstices of the substratum or insinuated well within banks of leaf litter. Large adult fish also used leaf litter as cover but were more frequently recorded in association with woody debris, undercut banks and root masses. Adults were intermediate between these age classes with respect to cover although both this age class and juvenile and subadult fish appear to avoid undercut banks. In north-eastern Queensland it is very rare to collect an eel, even a small individual, which does not have a recent bite mark of another eel somewhere on its body. Such marks suggest that eels of all sizes interact aggressively with one another, and are perhaps indicative of substantial territorial behaviour. In many cases, these bite marks, although not deep, are very clear and their length and width give a reasonable indication of the size of the aggressor. Such marked eels usually display the
(a)
60
(b)
30 40 20 10
20
0
0
Mean water velocity (m/sec) 30
(c)
Focal point velocity (m/sec) 80
(d)
60
20
40 10
20
0
30
0
(e)
Relative depth
Total depth (cm)
(f)
20
40
10
20
0
0
Substrate composition
Microhabitat structure
Figure 2. Microhabitat use by Anguilla reinhardtii juveniles and subadults (<300 mm SL: solid bars, n = 509), adults (300–500 mm SL: hatched bars, n = 85) and large adults (>500 mm SL: open bars, n = 176) in the Wet Tropics region. Summaries derived from capture records from the Johnstone and Mulgrave rivers, northern Queensland, over the period 1994–1997 [1093].
In streams of south-eastern Queensland, A. reinhardtii was collected from a wide range of water velocities including very fast-flowing water, although adults were more common in slower flowing water than juveniles (Fig. 3a and b). Focal-point velocities were slightly lower than mean velocities, reflecting the benthic habit of this species (Fig. 3d) and usual refuge within coarse substrates where
80
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
velocities are lower (Fig. 3f). This species was usually collected in water depths less than 50 cm with adults slightly more common in deeper water than juveniles (Fig. 3c). Anguilla reinhardtii was usually found among coarse substrates (coarse gravel, cobbles and rocks, Figure 3e), reflecting their availability in the rapids, riffles and runs where this species most commonly occurred (see above). Adults were more common close to the river-bank than juveniles (44% of adults collected within 1 m of the bank versus 27% of juveniles [1093]) but both age classes were almost always found in close association with some form of submerged cover; usually within the interstices of coarse substrates (Fig. 3f). Juveniles were more common in this microhabitat type whereas adults were slightly more common among woody debris, undercut banks and root masses. 40
(a) 40
30
30
20
20
10
10
0
0
40
Environmental tolerances Anguillid eels are a notoriously hardy group of fish but quantitative information on tolerances to water quality extremes is lacking. Harris and Gehrke [553] classified A. australis and A. reinhardtii as tolerant of water quality degradation. Anguillids are very tolerant of hypoxic conditions [417] and able to survive out of water for long periods by absorbing oxygen from the atmosphere through the skin, as long as it remains moist [891] or by gulping air [417]. Maturing eels in freshwater possess a significant hypo-osmoregulatory ability [394]. In south-eastern Queensland, A. australis has been collected over a relatively wide range of physicochemical conditions reflecting those expected for streams and rivers of this region. (Table 7). It appears to tolerate low dissolved oxygen concentrations (field minimum of 2.6 mg.L–1). We have collected this species in slightly acidic to basic water conditions (pH range 5.9–8.5) (Table 7) and at temperatures ranging from 8.4 to 27.8°C. The maximum turbidity at which this species has been recorded in southeastern Queensland is 112.3 NTU, but it more commonly occurs in less turbid waters (mean 10.9 NTU). We have collected this species in freshwaters up to 1231.7 µS.cm–1 conductivity.
(b)
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
Anguilla obscura has been recorded over a range of water quality conditions (Table 7) reflecting its distribution in northern rivers and floodplain habitats [697, 1093]. It is tolerant of moderate hypoxia (e.g. in floodplain lagoons of the Normanby River) and occurs most commonly in slightly acidic waters. The conductivity values presented in Table 7 indicate that it occurs in very freshwaters but it obviously tolerates much higher salinity levels given its life history.
80 30
60
20
40
10
20
0
0
Total depth (cm)
Relative depth
(e)
In the Wet Tropics region, A. reinhardtii occurs across a range of water quality conditions typical of rainforest streams and rivers of this region (Table 7). The minimum temperature recorded (13.3°C) occurred during July in a stream located on the Atherton Tablelands, whereas the maximum (32.7°C) was recorded in November at a site with little riparian cover and at a time of reduced flow. Streams of this region tend to be well-oxygenated throughout the year and to be of very low conductivity. This species occurs across a wide pH range but the average value is circumneutral. Occasional periods of high turbidity occur in streams of the Wet Tropics region in association with periods of intense rainfall and usually in streams receiving drainage from agriculture. Such turbid periods are usually transitory and on average this species occurs in clear waters. Given the very wide distribution of this species in rivers of the Wet Tropics region, the values given in Table 7 approximate those expected for streams and
(f) 40
30
30 20
20 10
10 0
0
Substrate composition
Microhabitat structure
Figure 3. Microhabitat use by Anguilla reinhardtii in southeastern Queensland. Data derived from capture records for 810 juvenile (<150 mm SL: solid bars) and 911 adult (>150 mm SL: open bars) individuals collected in the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
81
Freshwater Fishes of North-Eastern Australia
rivers of the region. In south-eastern Queensland, A. reinhardtii has been collected over a relatively wide range of physicochemical conditions also reflecting those expected for streams and rivers of this region. (Table 7).
Australian statutory health limits (0.5 µg.g–1 wet weight) leading Beumer and Bacher [181] to conclude that consumption of these species would be well within ‘acceptable daily intake’ recommended by the World Health Organization.
Table 7. Physicochemical data for Anguilla australis, A. obscura, and A. reinhardtii. Data summaries are from a number of studies conducted in a range of rivers and habitats across north-eastern Australia (the number of sites from each study is given in parentheses). Parameter
Min.
Max.
Anguilla australis South-eastern Queensland [1093] (n = 39) Temperature (°C) 8.4 27.8 Dissolved oxygen (mg.L–1) 2.6 10.4 pH 5.9 8.5 Conductivity (µS.cm–1) 110.0 1231.7 Turbidity (NTU) 0.5 112.3
Reproduction, development and movement biology Anguillids are considered by many to be catadromous: adults undertake distinct spawning migrations from freshwaters, downstream and seaward to distant oceanic spawning grounds in the Coral Sea, and the young migrate back to freshwaters to complete their life cycle. The emerging view however, is that catadromy is not obligatory for some anguillids, including at least one Australian species [1048, 1331, 1332, 1333]. Rather, catadromy in anguillids is facultative, with freshwater, estuarine and marine residents more appropriately considered as contrasting ecophenotypes [1331, 1332]. Evidence from strontiumcalcium ratios in otoliths of adult eels of several species (A. anguilla, A. japonica, and A. reinhardtii) has revealed that some individuals appear to have an exclusively marine history and never enter freshwater, others may move repeatedly between freshwater and the estuary during their extended occupancy in coastal catchments, and others enter freshwater and remain there until adulthood before making the return spawning migration to the ocean [1048, 1331, 1332, 1333]. It has been postulated [1331, 1333] that latitudinal variation in the productivity of riverine versus marine habitats, or the presence of other potentially competing marine anguilliformes, may explain apparent regional variation in the frequency of individuals remaining in marine environments versus those entering estuaries or freshwaters. However, hypotheses about the duration and frequency of marine residency and of contrasting ecophenotypes are based mainly on examination of temperate zone populations. Further research is required before these hypotheses can be extended to tropical eel populations. Nevertheless, it has been speculated that individuals with a primarily ocean-based life history may contribute substantially to future recruitment [1331, 1332]; a view with important implications for the management of anguillid species that are currently the focus of intensive freshwater and estuarine fisheries for live export and aquaculture operations (see Conservation status, threats and management, pp. 90).
Mean
18.4 7.3 7.4 386.2 10.9
Anguilla obscura Normanby River [697] (n=3) Temperature (°C) 23.9 29.4 Dissolved oxygen (mg.L–1) 2.0 6.2 pH 6.1 8.1 Conductivity (µS.cm–1) 97.8 250.3 Turbidity (NTU) 3.3 8.6
25.8 3.5 6.9 188.9 6.2
Wet Tropics region [1093] (n = 15) Temperature (°C) 19.9 27.4 Dissolved oxygen (mg.L-1) 5.6 8.8 pH 4.5 7.9 Conductivity (µS.cm-1) 6.0 63.8 Turbidity (NTU) 0.3 7.2
23.9 7.1 6.4 38.9 1.32
Anguilla reinhardtii Wet Tropics region [1093] (n = 200) Temperature (°C) 13.3 32.7 Dissolved oxygen (mg.L–1) 5.1 12.4 pH 4.5 8.5 Conductivity (µS.cm–1) 5.6 67.6 Turbidity (NTU) 29.7 0.1
22.7 7.2 7.1 34.4 3.6
South-eastern Queensland [1093] (n = 440) Temperature (°C) 8.4 31.7 19.5 Dissolved oxygen (mg.L–1) 0.3 16.2 7.6 pH 5.6 9.1 7.6 Conductivity (µS.cm–1) 19.5 2247.0 456.4 Turbidity (NTU) 0.4 331.4 8.8
Beumer and Bacher [181] suggested that A. australis and A. reinhardtii could be effective indicators of local mercury concentrations in inland waters of Victoria as both species are carnivorous, feeding at all levels of the food chain, and because they probably have a relatively small home range during their yellow eel phase in freshwaters. In their 1982 study, total mercury concentrations in the axial tissues of most individuals examined were found to be below
What follows is an overview of the current understanding of the life cycle of the three Australian species of Anguilla considered in this text, with a focus on the freshwater ecophenotype described above. Sloane [1244] estimated ages of A. australis and A. reinhardtii from the Douglas River in eastern Tasmania using the marginal growth increments of burnt otoliths. An
82
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
annual growth ring was formed in the otoliths of both species at the end of winter, occurring slightly earlier in A. australis. The main period of growth in both species coincided with increasing water temperatures (15–22°C) during late spring and early summer. In Victoria, heightened activity of both species also occurred during spring and summer coinciding with elevated discharges and inundation of marginal areas due to rains occurring in late winter and spring [175]. Estimates of growth rates and ages based on otolith annuli indicated substantial interspecific, intraspecific and spatial variation in growth [252, 1244]. Nevertheless, available data from Australian streams indicates that A. australis appears to have a slower growth rate and live for a shorter period of time than does A. reinhardtii. Sloan [1244] estimated that a 250 mm TL individual of A. australis would have spent approximately 12 years in freshwater, whereas a similarly sized individual of A. reinhardtii would require only seven years. The largest A. australis specimen aged in his study was about 500 mm TL and was estimated to be approximately 32 years old; an equivalent sized A. reinhardtii would be about 21 years old. Age estimates of the largest specimens of A. reinhardtii were variable but individuals between 1000 and 1200 mm TL were estimated to be between 35 and 45 years of age [1244]. A validation of otolith age determination in A. reinhardtii is provided by Pease et al. [1438]. Further information on sexual and spatial variation in size and age of A. reinhardtii is available in Walsh et al. [1445].
Quantitative estimates of fecundity in Australian anguillids are not available. A single large migrating female of A. reinhardtii estimated to contain several million eggs has been collected and A. australis is thought to be similarly fecund [936, 1393]. Fecundity estimates of A. dieffenbachii from New Zealand varied between 1 and 20 million eggs for fish between 700–1500 mm TL, intraovarian eggs were 0.33 mm diameter or larger, and the gonads contributed 8–10% of body weight at the commencement of migration [891, 1324, 1325]. The fecundity of A. australis from New Zealand ranged from about 1.5 to 3 million eggs in migrating females between 500 and 800 mm, intraovarian eggs were 0.22 mm diameter, and the gonads contributed about 3.5% of body weight [891, 1324, 1325]. DeSilva et al. [377] report that migrating A. australis from southeastern Australian estuaries had GSIs up to 3.2%.
Very little information is available concerning the sexual development and fecundity of Australian anguillids. The sex of eels is very difficult to determine by external examination, but in A. reinhardtii and other species, gender can be established by internal macroscopic examination of the gonads [891, 1360]. Histology is necessary to accurately define stages of gonadal development, particularly in individuals less than around 600 mm in length [1360]. The anatomy of anguillids is unusual in that female fishes are without oviducts (the gymnovarian condition), the eggs pass directly into the peritoneal cavity and then through pores or funnels to the exterior [891, 1308]. The gonads of some individuals of A. obscura [183] and A. dieffenbachii [818], but not A. reinhardtii [1360], have been reported to show signs of intersexuality. Walsh et al. [1360] provide details on the macroscopic and microscopic structure and development of the gonads in freshwater and estuarine specimens of A. reinhardtii from New South Wales. This species displayed asynchronous gamete development, the most advanced cells present in the gonads of migrating males were spermatocytes; those of females were pre-vitellogenic oocytes [1360]. Gonadal development was positively correlated with body size in females, this relationship less apparent in males [1360]. Walsh et al. [1360] estimated that that sexual differentiation in A. reinhardtii
The size and age at which eels commence the spawning migration varies widely, perhaps in response to the wide range of habitat conditions occupied, and the distance to the spawning grounds [1360]. Larsson et al. [776] suggested that European eels are triggered to migrate when the proportion of body lipid exceeds a threshold necessary to accomplish the migration and final development of the gonads. Sloane [1246] reported that migrating adult A. australis (almost all female fish) in Tasmania varied in length (range 840–1110 mm TL, mean 945 mm TL) and age (range 18–30 years, mean 22.1 years). De Silva et al. [377] reported the average length, mass and age of females as 832 mm TL, 1051 g and 17.2 years, respectively. No equivalent data for male A. australis are available. Beumer et al. [183] collected mature females of A. obscura ranging from 595–1050 mm TL. Walsh et al. [1360] observed that sexual maturity in A. reinhardtii occurred over a wide size range in both sexes, but estimated that the minimum size at which this species commenced migration was 740 mm TL in females and 440 mm TL in males, but noted that such estimates may be inflated given the small number of eels examined (71 males and 637 females) [1360]. Migrating male A. australis and A. dieffenbachii in New Zealand are reported to also be generally smaller and younger than females [891, 1323]. It has been suggested
occurred at approximately 590 mm TL. Female A. australis and A. reinhardtii are often collected in freshwaters in greater numbers than males [936, 1360, 1445] and sexspecific variation in habitat choice has been observed elsewhere [891, 1025]. Observed sex ratios are probably strongly influenced by the sampling methods used and the habitats in which the populations were sampled [1360]. It has been suggested that environmental factors such as salinity may influence sex determination in Australian eels [1027] but sex determination may also be controlled in part by genetics [891].
83
Freshwater Fishes of North-Eastern Australia
that the larger size and hence higher fecundity of female eels would be selectively advantageous, given the high risks associated with the long migration to the spawning grounds; males on the other hand are able to produce large quantities of sperm at comparatively smaller size and so would be favoured by an ability to grow rapidly to a size large enough to make the spawning migration [566, 567, 891].
collections of leptocephali indicate that in the three Australian species considered here, spawning occurs in the Coral Sea off the north-eastern Australian coast, possibly in the area encircled by New Caledonia, Fiji, Tahiti and the Solomon Islands [64, 178, 645, 891, 912, 1308]. It is uncertain whether the spawning locations of the Australian species are geographically separated in this area [64]. Little is known of the route or duration of the long oceanic migration to the spawning grounds, but for eels originating from south-eastern Australia, the distance to the spawning grounds may be up to 5000 km [177, 912]. Walsh et al. [1360] suggested that the comparatively early stages of gonadal development at migration observed in both sexes of A. reinhardtii may indicate that this species needs to travel further or may take longer to reach the spawning grounds than some other anguillid species (but see Shiao et al. [1439]. Silver eels of other species have been recorded swimming at speeds up to 2–2.5 km.hr–1 and 50–60 km per day, suggesting that it may take over three months for eels from some parts of Australia to reach the spawning grounds [177, 645, 912]. Tsukamoto et al. [1333] suggested that adult eels probably do not migrate in schools to the spawning grounds on the basis of body form and behaviour of adult eels and the fact that migrating adults have occasionally been collected singly at sea. Adult migrating eels appear to undertake vertical migrations at sea [1259, 1307], possibly in response to variations in light and water temperature, and are capable of swimming at great depths. Tesch [1307] tracked A. anguilla at depths ranging from less than 50 m to at least 400 m below the water surface and the remains of anguillids have been found in the stomachs of benthic fish caught at depths of over 700 m [1126]. It is unknown how adult eels locate the spawning ground but navigation may be facilitated by an ability to orientate to the earth’s magnetic field [1155, 1307, 1308]. Volcanic seamounts, which may have unique geomagnetic and geopotential anomalies, may function as cues for orientation also [1333, 1443].
Immediately preceding and during the early stages of the spawning migration, a range of morphological, biochemical and physiological transformations take place. A distinct counter-shading colour pattern develops, the snout becomes chisel-shaped, the head becomes dorsoventrally flattened, the eyes increase in size, the pectoral fins enlarge and the tail becomes paddle shaped. Such changes are assumed to improve locomotory mechanics and survival in the marine environment. Biochemical adjustments include changes in the mobilisation and composition of stored fatty acids in response to the energetic demands of long-distance migration, maturation and gonad recrudescence. Physiological adjustments include osmoregulatory and ionoregulatory changes associated with transition from fresh water to saline water [377, 394, 891]. Downstream migrations of Australian eels may occur over an extended period but appear to reach a peak during summer and autumn. The cues for movement are not well understood but eels are often, but not always, observed moving during flood conditions, which may trigger or at least facilitate downstream movements [55, 210, 232, 936, 1246, 1393]. Other factors such as temperature and day length may also be important [1246]. Cyclical annual variation in the number of eels undertaking downstream migrations has also been reported [936]. The downstream and seaward migration of eels can result in a substantial loss of organic matter (in the form of fish flesh) from the freshwater environment, particularly in areas of low productivity [1249]. Beumer [177] reported that silver eels congregate briefly in estuaries and then migrate seaward to the spawning grounds. These outward migrations may be influenced by lunar phase and light intensity. Males are thought to leave estuaries earlier than females but swim more slowly (perhaps because they are smaller), thereby arriving at the spawning grounds at approximately the same time as females [177]. A similar pattern has been observed in New Zealand eels [891] and Tsukamoto et al. [1333] suggested that aggregation in space and time of reproductively mature adults would facilitate physiological synchronisation of the sexes and improved reproductive success.
Eels are believed to cease feeding during the oceanic migration, and are thought to invest much of their energy reserves into gonad production and final maturation so that they are ready to spawn upon reaching the spawning grounds [891]. Jellyman [645] estimated that spawning of A. australis occurred between June and September on the basis of the collection dates of leptocephali of known sizes, together with data on growth rates of Northern Hemisphere eels. Evidence from A. japonica suggests that spawning does not occur continuously over the long spawning season, but that eels are synchronised to spawn periodically once a month during the new moon [1443]. Nothing is known of the spawning behaviour or the precise conditions where spawning occurs but it is thought to take
The precise location of spawning of Australian eels is unknown as very few adult eels have been collected at sea. Projections based on knowledge of oceanic currents and
84
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
interactions between oceanic currents and movement of leptocephali and glass eels. McKinnon et al. [912] proposed a model whereby the East Australian Current bifurcates, transporting leptocephali northwards along the Queensland coast and southwards along the southern Queensland and Northern New South Wales coasts.
place at considerable depths, possibly at about 350 m. The adults are thought to perish soon after spawning; it is extremely unlikely that they undertake a return migration to freshwater [891, 1308]. The eggs are small and pelagic, floating upwards towards the surface [891, 936, 1308]. The maximum diameter of intraovarian eggs of A. rostrata (up to 950 mm TL) was 0.37 mm, but more commonly ranged between 0.2–0.3 mm [335]. Few details are available on many aspects of embryological and larval development of anguillids as the eggs of very few species have been successfully fertilised, hatched or reared in captivity (but see [819, 1049, 1072, 1073]). Lokman and Young [819] managed to successfully hatch the eggs of A. australis after about 45 hours of incubation at room temperature. Larvae were around 2.5 mm at hatching and grew to about 5.3 mm after five days but larvae did not survive beyond this point [819].
Once they reach the edge of the continental shelf in eastern Australia, active swimming may be required for leptocephali to detrain from the oceanic currents [645]. In New Zealand waters, detrainment may occur several hundred kilometres off the continental shelf but it is unknown how larvae gain an awareness of the direction and proximity of land and hence orientate towards it [645]. Very little information is available concerning the duration of the oceanic transport of leptocephali before metamorphosis, but it may be highly variable and depend at least in part on the relative location along the eastern Australian coast of detrainment and metamorphosis [645, 1225]. Based on data from microstructure and microchemistry of A. australis otoliths, the unvalidated age at the commencement of metamorphosis was estimated at 138–198 days for glass eels collected in south-eastern Queensland [66]. Shiao et al. [1225] estimated that glass eels collected in estuaries from the Albert River north to the Fitzroy River were significantly younger than those collected further south, suggesting that leptocephali metamorphosed earlier and were faster growing in north-eastern Australia than in south-eastern Australia. McKinnon et al. [912] estimated the mean ages at metamorphosis for glass eels of A. australis and A. reinhardtii collected from the Albert River estuary were 153.4 days ± 16.8 SD and 124 days ± 15.8 SD, respectively. For further comparative data see also Shiao et al. [1439].
Leptocephali larvae are very rarely collected in the ocean, but several Indo-Pacific eel species have been collected in trawls at depths ranging from around 30 to 200 m [655]. These leptocephali are small (usually less than about 50–60 mm TL), have slender heads, peculiar large forward-pointing teeth, and a flat, ribbon or leaf-shaped body that is gelatinous and transparent [891]. Leptocephali may gain their nutrition by active feeding on plankton or by absorption of nutrients in the seawater through the skin, the latter being postulated to explain the unusual flattened shape and high surface area of the body of leptocephali [891, 1055]. Australian eel leptocephali are thought to be transported from the spawning grounds to the Australian continental shelf by oceanic currents [64, 171, 645, 912]. Leptocephali are generally believed to be transported passively and to be very weak swimmers, their flattened shape possibly facilitating transport on oceanic currents, but several researchers [288, 891, 1032] have reported that leptocephali undertake vertical migrations and may be capable of swimming across current flows.
During metamorphosis, a reduction in body length and width and a loss of teeth occurs, and feeding is thought to cease for a short period [1308]. Anguilla australis leptocephali range from 53–54 mm TL immediately preceding metamorphosis [401]. As leptocephali transform into glass eels they absorb the gelatinous body, and assume the characteristic elongate and slender eel shape, but remain transparent: they are now known as glass eels [891]. Early-stage glass eels may vary between about 47–73 mm for A. australis and 46–65 mm TL for A. reinhardtii [401].
The warm South Equatorial and East Australian currents are thought to carry leptocephali from the tropical spawning grounds [64, 171, 645], but interactions with the cooler currents of the Central Tasman Mass, North Bass Strait Mass and the Sub-Antarctic Current at certain times of year, and longer term changes in the El Niño Southern Oscillation Cycle and hence oceanic currents, may influence the species composition, timing, abundance and size of glass eels delivered to the eastern Australian coast [171, 1047] and elsewhere [303, 649, 895]. Mechanisms for the delivery of leptocephali and glass eels of A. reinhardtii and A. obscura to the north-eastern Australian coast are poorly understood, as is the effect that the fringing Great Barrier Reef has on
Following metamorphosis, glass eels move shoreward; one Northern Hemisphere species has been observed drifting in a vertical position close to the water surface [1410]. The time between metamorphosis in A. australis and A. reinhardtii, and the age at recruitment to the upper Albert River estuary in south-eastern Queensland has been estimated at 40.8 ± 7.8 and 39.8 ± 5.6 days, respectively, giving total approximate ages for glass eel recruitment to this part
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Freshwater Fishes of North-Eastern Australia
assignation of developmental stages based on pigmentation). The degree of pigmentation is related to the time since metamorphosis, with developmental rates probably more related to ambient temperature than salinity or other environmental factors [464]. Other morphological changes occurring during this period include the development of a new set of teeth, the formation of the stomach and the development of an extra loop in the intestine [891, 936].
of the estuary of 194.2 ± 22.8 and 164.1 ± 14.8 days for each species, respectively. Arai et al. [66] estimated that glass eel recruitment of A. australis to the upper Albert River estuary occurred between 186–239 days [66]. The seasonal phenology of invasions to particular coastal localities is associated with the southward and westward movement of leptocephali on oceanic currents and recruitment of glass eels along the Australian coastline and hence may vary with latitudinal and longitudinal position [171, 464, 1247]. Several studies have shown that A. reinhardtii recruitment to tropical and subtropical estuaries of Queensland and northern New South Wales occurs over extended periods throughout the year [171, 740, 1169]. Anguilla australis recruitment to temperate estuaries in southern New South Wales, Victoria and Tasmania occurs over similarly long periods [171, 464, 1247]. Each species shows distinct, but often not exclusive, seasonal peaks in glass eel abundance [171, 1047, 1169]. Seasonal and interannual variation in recruitment may serve to temporally isolate the recruitment into freshwater habitats of sympatric species such as A. reinhardtii and A. australis [913, 1047].
Mass invasion of coastal and estuarine waters is followed by a secondary upstream migration into freshwaters. This two-stage process involves semi-passive tidal advection and active swimming of glass eels into and within estuaries [912]. A period allowing the eels to acclimate to reduced salinity is followed by an active upstream swimming phase undertaken by later developing glass eels and early pigmented elvers. These secondary migrations are thought to commence at or near the upper tidal limit of brackish lowland rivers [464, 648, 1247, 1308]. These mass-invasions of glass eels are known colloquially in England, Australia and elsewhere as ‘eel-fares’ [180, 418, 500, 1382, 1393] and is the origin of the term elvers [180]. Glass eels and elvers may remain in estuaries prior to the upstream migration for a period of about two weeks [647, 648, 1047]. They can however move considerable distances during this period: mark-recapture data for A. australis in the Albert River revealed that this species moved large distances (up to 12 km) over a relatively short period of time (2–3 days) [912]. Upstream migrations may take place for extended periods throughout the year but their phenology is highly variable [401, 936, 1205, 1243, 1247], perhaps as a result of the variability inherent in the numbers and timing of glass eel invasion. Fishway studies in Queensland indicate that the upstream movement of glass eels and elvers of A. reinhardtii is protracted but concentrated during spring and summer [232, 740, 1173, 1275, 1276]. Various cues initiating upstream movement such as interactions between prevailing light conditions (time of day and day length), water temperature, salinity and river discharge have been suggested, although the process is poorly understood [1047, 1243, 1247, 1248, 1277, 1356].
Interspecific, seasonal and interannual variation in the relative abundance, age and size of glass eels observed in estuaries along the eastern Australian coast and elsewhere has been attributed to such factors as: differences in adult spawning locations and spawning times; variation in the relative spawning success of adult eels and consequent recruitment pulses; variation in primary and secondary productivity and hence food availability for leptocephali; the intensity and direction of offshore and inshore oceanic currents; and the actual distance from the spawning location to the site of estuarine invasion [171, 381, 912, 1047]. In addition to these largely extrinsic factors, a range of other localised environmental factors (and possibly biological factors) may be important [464]. Eels are known to have extremely sensitive olfactory organs [1308] and some species are thought to be attracted to estuaries by the presence of particular organic chemoattractants in the water discharging from estuaries [337, 873, 1252, 1253, 1254, 1326, 1327]. Other factors such as lunar periodicity, light intensity, variation in tidal magnitude (and hence tidal flow), water temperature, turbidity, salinity and the magnitude of freshwater discharge have also been identified as potentially important cues for glass eel invasion of estuaries and longitudinal movement within rivers [171, 464, 912, 913, 1047, 1233] (see McKinnon et al. [912] and Tesch et al. [1308] for recent discussions).
Elvers and developing eels colonise a range of freshwater habitats and are capable of penetrating far upstream (see Macro/mesohabitat use, pp. 77). Jellyman [646] estimated that movement rates of elvers in New Zealand streams were around 1.5–2 km per day. Eels are renowned for their ability to overcome obstacles to movement such as dams, weirs and waterfalls, which impede but do not prevent upstream passage [178]. Elvers are able to climb such obstacles by adhering, through friction and surface tension, to damp surfaces. Eels have also been observed
During their residency in estuaries and brackish lowland rivers, glass eels acclimate to the reduced salinities and develop rapidly into fully pigmented elvers (see Strubberg [1271] for details of a widely used scheme for the 86
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
1274, 1275, 1276]. The swimming abilities of glass eels of A. australis and A. reinhardtii may be well below that needed to negotiate the high water velocities frequently observed in fishways in Queensland and elsewhere [182, 496, 543, 1274]. Hydraulic flume experiments [769] indicate that the maximum sustained and burst swimming speeds of A. australis glass eels (mean 54.2 mm TL) were 0.29 and 0.79 m.sec–1, respectively, and those of A. reinhardtii (mean 51.2 mm TL) were 0.32 and 0.75 m.sec–1, respectively [769]. On the basis of these results, Langdon and
slithering up wet banks and traversing short distances over damp ground to bypass such obstacles [500, 711, 936, 1356]. Eels are sensitive to barriers to movement however, and small individuals may have difficulty ascending fishways. Many fishways on weirs and tidal barrages in Queensland are characterised by high water velocities, high turbulence and, in the case of some vertical-slot designs, have smooth-sided walls in each vertical slot which may prevent or impede the ability of glass eels to climb along the wetted margins within the fishway [769,
Table 8. Life history information for three Australian species of Anguilla. Information is listed for individual species where available, otherwise it is listed under Anguilla spp. as many aspects of the life cycle may be generally similar. Age at sexual maturity
A. australis – ? Migrating females 840–1110 mm TL (mean 945 mm TL) [1246] A. reinhardtii –? Migrating females 832 mm TL (mean length) [377]
Minimum length of ripe females (mm)
A. australis – ? No fully mature females have been collected (but see age of migrating females above) A. obscura – ? Mature individuals ranged between 595–1050 mm TL [183] A. reinhardtii – ? No fully mature individuals have been collected but the mean length of maturing females (Stage 3 of Walsh et al. [1360]) was about 1025 mm TL
Minimum length of ripe males
A. australis – ? No fully mature fish have been collected A. reinhardtii – ? No fully mature individuals have been collected but the mean length of maturing males (Stage 3 of Walsh et al. [1360]) was about 550 mm TL
Longevity
A. australis – ? >32 years [1244] A. reinhardtii – ? >45 years [1244]
Sex ratio
A. australis – ? Females often more abundant in freshwaters than males [936, 1360] A. reinhardtii – ? Females often more abundant in freshwaters than males [936, 1360]
Peak spawning activity
A. australis – ? Outward migration to spawning grounds occurs over an extended period during summer and autumn; spawning possibly occurs between June and September [645] A. reinhardtii – ? Outward migration to spawning grounds occurs over an extended period during summer and autumn; timing of spawning is unknown
Critical temperature for spawning
?
Inducement to spawning
A. australis – ? Cues for migration to spawning grounds probably involve a combination of biological (e.g. body size, lipid concentration, stage of gonadal development) and environmental (temperature, day length, discharge) factors
Mean GSI of ripe females (%)
A. australis – ? Up to 3.5% in migrating eels [891, 1324, 1325]
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
A. australis – ? 1.5–3 million eggs in migrating eels [1324] A. reinhardtii – ? ‘several million’ eggs [936, 1393]
Fecundity/length relationship
?
Egg size
A. australis – Intravovarian eggs of migrating eels 0.22 mm diameter [891, 1324, 1325], 1.55 mm post-fertilisation [819]
Frequency of spawning
Anguilla spp. – Adults probably spawn once and then die [891, 1308]
Oviposition and spawning site
Anguilla spp. – ? Probably in the Coral Sea and at considerable depths [891, 1308]
Spawning migration
Anguilla spp. – Facultative catadromy (see text for details)
Parental care
Anguilla spp. – None known
Time to hatching
A. australis – ~45 hours [819]
Length at hatching (mm)
A. australis – ~2.5 mm TL [819]
Length at feeding
?
Age at first feeding
?
Duration of larval development
A. australis – Variable, mean 153.4 days ± 16.8 SD for specimens from Albert River [912] A. reinhardtii – Variable, mean 124 days ± 15.8 SD for specimens from Albert River [912]
Length at metamorphosis
A. australis – 47–73 mm TL (early-stage glass eels) [401] A. reinhardtii – 46–65 mm TL (early-stage glass eels) [401]
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Freshwater Fishes of North-Eastern Australia
substrate [936]. Some anguillids also show marked diel variation in activity; A. australis and A. dieffenbachii in New Zealand were demonstrated to be nocturnally active (associated with foraging) and to seek refuge within the substrate during the day [453, 1191].
Collins [769] recommended that mean and maximum velocities through fishways should not exceed 0.30 and 0.75 m.sec–1, respectively. To further facilitate passage, several researchers [747, 769, 954, 1275, 1277] have advocated the inclusion of roughening substrates within the cells of existing and future vertical slot fishways, and the construction of eel passes that may specifically permit the passage of glass eels and elvers.
Trophic ecology Anguilla australis is a carnivorous species, relying on generally small-sized food items as juveniles and switching to larger diet items and a more diverse array of food types with growth (Fig. 5). The diet of elvers and subadults (≤200 mm TL) is dominated by aquatic insects (86.0%); small amounts of molluscs (11.0%) and macrocrustaceans (3.0%) are also consumed. Adult fish consume a wide range of food types, probably reflecting the wide array of habitats in which this large mobile predator can forage. Aquatic insects (30.0%), fish (22.9%), and material foraged from the water’s surface (terrestrial vegetation (7.4%), terrestrial invertebrates (4.5%) and terrestrial vertebrates (3.1%)) were the most important diet items consumed by adults. Large crustaceans (6.5%), molluscs (5.8%, aquatic algae (5.1%) and microcrustaceans (4.4%)
A number of studies in south-eastern Australia [175, 1208, 1244], have described a trend of decreasing abundance and concomitant increasing size and age of A. australis and A. reinhardtii with increasing distance from the sea, although this is less evident in rivers and streams of south-eastern Queensland [1093]. This pattern may be due to an avoidance of habitats characterised by low permanence, lower winter temperatures and reduced food availability (in the form of catadromous forage fish such as galaxiids) in high elevation upland streams [1, 1208, 1244]. Predation by larger eels may be important also. Migrating eels must pass through a series of environmental ‘filters’ imposed by physical barriers, sub-optimal habitats and biological interactions on their progressive movement upstream. Little information is available concerning the local movement patterns of Australian eels during the long period of residence in freshwaters. Beumer [175] undertook a study of the local movement of A. australis in a lentic freshwater wetland of coastal Victoria. Of 1051 eels tagged and released, 194 were recaptured over the two-year study period. The maximum linear distance travelled was 3715 m for two individuals at liberty for 36 and 79 days, respectively. Three individuals recaptured after just 24 h had moved between 145 and 200 m. There was no relationship between eel size and number of days at liberty or distance moved. Instead, movement activity was closely related to variations in water temperature and feeding. The majority of individuals exhibited limited movement (77% of fish moved 400 m or less within 150 days of liberty) leading Beumer [175] to estimate a home range of around 400 m for this species. Pease et al. [1438] concluded that A. reinhardtii has a very restricted home range of 300 m or less. Beumer [175] and others (see Tesch et al. [1308]) have suggested that eel home range size is strongly related to the size of the waterbody in which they occur. The presence of large eels may influence the movement of smaller eels. In a defaunation experiment in river reaches of the Wet Tropics region, the removal of a large individual was usually accompanied by the subsequent appearance of a number of smaller eels. Interestingly, the combined biomass of these interlopers was often very similar to the biomass of the eel removed [1093]. Movement activity may be much reduced at low temperatures (below 10°C) when eels are thought to become dormant, burying themselves in the
A. australis juveniles (n = 24) Macrocrustaceans (3.0%) Molluscs (11.0%)
Aquatic insects (86.0%)
A. australis adults (n = 513) Unidentified (1.9%)
Terrestrial invertebrates (4.0%) Terrestrial vertebrates (3.1%)
Fish (22.9%) Terrestrial vegetation (7.4%) Detritus (0.1%) Aquatic macrophytes (0.5%) Algae (5.1%)
Other microinvertebrates (0.1%) Microcrustaceans (4.4%)
Macrocrustaceans (6.5%)
Molluscs (5.8%) Other macroinvertebrates (8.3%)
Aquatic insects (30.0%)
Figure 4. The mean diet of Anguilla australis juveniles (≤~200 mm SL) and adults (>~200 mm SL) (sample sizes for each age class are given in parentheses). Data derived from stomach contents analysis of fish from New South Wales [1133, 1134], Victoria [175, 595] and Tasmania [758, 1244].
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Anguilla australis, Anguilla obscura, Anguilla reinhardtii
vegetation (7.7%) and terrestrial invertebrates (4.3%) were also consumed. Bunn et al. [248] noted that the isotopic signature of a small number of eels from Bamboo Creek, a degraded lowland tributary of the Johnstone River, indicated a diet dominated by terrestrial insects. Anguilla reinhardtii is likely to be an important top predator in many aquatic environments of north-eastern Australia, given its size, high local density and predatory habit. Beumer [175] observed that A. reinhardtii in a coastal Victorian wetland fed throughout the year and that feeding activity was greatest in spring and summer. Beumer [175] reported that A. reinhardtii was cannibalistic and Sloane [1244] observed the remains of A. australis in the stomachs of A. reinhardtii and further suggested that
also formed minor components of the diet of this species. Anguilla australis has been reported to go without food for up to 10 months and may cease feeding at low water temperatures [936]. Beumer [175] observed that A. australis in a coastal Victorian wetland fed throughout the year but that feeding activity was greatest in spring and summer. Sagar and Glova [1191] reported diel feeding activity in A. australis in New Zealand: individuals of all sizes fed between dusk and dawn irrespective of size, but smaller individuals were more crepuscular. Beumer [175] reported the presence of unidentified eels in the diet of A. australis in coastal Victoria, and suggested that cannibalism may be a feature characteristic of eel species. Very little information is available concerning the diet of A. obscura but it is likely to be very similar to that observed for A. reinhardtii and A. australis. The diet of three individuals from the Wet Tropics region of northern Queensland (330–400 mm SL) comprised terrestrial invertebrates (33.0%), molluscs (21.0%), aquatic insects (13.0%) and unidentifiable material. These data most likely do not adequately represent the true diet of A. obscura.
A. reinhardtii juveniles (n = 76) Fish (0.8%) Macrocrustaceans (3.4%)
Unidentified (3.0%) Terrestrial invertebrates (2.7%) Detritus (0.5%) Aerial aq. Invertebrates (0.5%)
Unidentified (33.0%) Molluscs (21.0%)
Aquatic insects (89.2%)
A. reinhardtii adults (n = 321)
Aquatic insects (13.0%)
Unidentified (0.9%)
Terrestrial invertebrates (4.3%) Terrestrial vertebrates (0.7%) Terrestrial vegetation (7.9%)
Fish (28.2%)
Detritus (0.5%) Aquatic macrophytes (0.1%) Algae (4.6%)
Terrestrial invertebrates (33.0%)
Figure 5. The mean diet of Anguilla obscura. Data derived from stomach contents analysis of three individuals from the Wet Tropics region of northern Queensland [1097]. Aquatic insects (30.3%)
The diet of A. reinhardtii is generally similar to that of A. australis with carnivory and ontogentic variation features of the diet (Fig. 6). The diet of elvers and subadults (≤200 mm TL) is dominated by aquatic insects (89.2%). Only small amounts of microcrustaceans (3.4%), terrestrial invertebrates (2.7%) and fish (0.8%) are consumed occasionally. Adults prey upon a wide range of food types, including macroscopic items such as fish (28.2%), macrocrustaceans (21.4%) and terrestrial vertebrates (0.7%). Aquatic insects (30.3%) were an important component of the diet of this species and aquatic algae (4.6%), terrestrial
Macrocrustaceans (21.4%) Molluscs (0.7%)
Other macroinvertebrates (0.4%)
Figure 6. The mean diet of Anguilla reinhardtii juveniles (≤~200 mm SL) and adults (>~200 mm SL) (sample sizes for each age class are given in parentheses). Data derived from stomach contents analysis of fish from eastern Cape York Peninsula [599, 697, 1099], the Wet Tropics region of northern Queensland [1097], central Queensland [1080], south-eastern Queensland [80, 205], New South Wales [1133, 1134], Victoria [175] and Tasmania [1244].
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Freshwater Fishes of North-Eastern Australia
species for export and aquaculture operations is becoming increasingly prevalent in eastern Australia. The world aquaculture production of freshwater anguillids is currently thought to exceed 216 000 t per annum, worth over US$915 million and is based largely on the culture of the European eel A. anguilla, and the Japanese eel, A. japonica [462]. Despite a decline in eel stocks in many areas over recent years due to a combination of overfishing and environmental changes impacting on recruitment [289, 290], commercial eel production has increased substantially due in part to improved aquaculture techniques and sourcing of alternative seedstock [462, 464]. Interest in the potential for eel culture in Australia has increased over recent years [462, 464]. Currently, eel production is based on A. australis and A. reinhardtii and total production is estimated as 5000–7000 t per annum, worth AUD$4–6.5 million (as at 2002) [462]. The vast majority of production in Australia comes from the harvest of elvers and subadults from wild riverine fisheries. These life stages are then transferred to semicontrolled lentic waterbodies (e.g. lakes, swamps and wetlands) where they are grown under natural conditions until they reach a marketable size and are exported to Europe and Asia [464, 1240].
interspecific competition for food and space between these species may be intense at times in the Douglas River, Tasmania. The frequent observation of eel bite marks on eels in the Wet Tropics and the observation of replacement by smaller eels following defaunation, also support suggestions that eels compete intensely for food and space. Conservation status, threats and management Anguilla australis, A. obscura and A. reinhardtii are listed as Non-Threatened by Wager and Jackson [1353]. We suggest that these listings remain valid on the basis of existing data. The status of A. megastoma in north-eastern Queensland is uncertain as a single individual has been collected from the Daintree River only [1085, 1087]; the presence of this species in north-eastern Australia requires confirmation. The widespread distribution of north-eastern Australian eels and their complex life cycle: involving marine and freshwater stages, distinct migration phases, remote spawning grounds, extended larval stage and long period to sexual maturity suggests that they may face and be vulnerable to a range of threats throughout the long lifespan. The frequently high local abundance of these largebodied species in freshwaters, together with their usual position at the top of the aquatic food chain, indicates that eels may play an important role in the structuring of fish and aquatic invertebrate communities and the transfer of energy within trophic levels at local scales. Although it is premature to label eels as ‘keystone’ species, it is difficult to conclude that the presence of a 20 kg, highly mobile predator ranging over 400 m of stream, is without effect. Any natural or anthropogenic impacts on the distribution and abundance of eels may have far-reaching consequences for other aquatic and semi-aquatic species.
Recent interest has focused on the potential for harvesting of wild glass eels for subsequent grow-out in aquaculture facilities [462, 464]. Recent major studies by Gooley et al. [464] and Gooley and Ingram [462] have attempted to evaluate the status of glass eel stocks in eastern Australia, but the high spatial and temporal variability in glass eel recruitment to eastern Australian estuaries has precluded a reliable estimate of the total eel stocks in this region [462]. Effective informed management of the glass eel fishery in Australia is also hampered by an absence of fundamental information on basic life-history attributes of Australian anguillids, an absence of long-term data on eel stocks in Australian waters and hence the ability to accurately assess the determinants of variability in glass eel recruitment, and ignorance about the role that eels play in the ecology of rivers.
The movement of millions of glass eels and elvers across marine/estuarine/freshwater ecosystem boundaries represents an enormous transfer of marine-derived carbon, the significance of which is unknown but potentially high. The migration of adult eels out of freshwaters and estuaries represents a similarly large transfer of energy across ecosystem boundaries. Despite the undoubted climbing ability of eels, the imposition of barriers to movement by structures such as dams, weirs and tidal barrages is an important determinant of eel distribution and abundance. Changes to the natural flow regime (e.g. timing, magnitude frequency and duration of flows), independent of the imposition of barriers, may also impact on eels by affecting possible cues for downstream migration of adults, and cues for the recruitment of glass eels into estuaries and the upstream migration of glass eels and elvers to freshwaters.
It has been suggested that commercial harvesting of particular eel species may be undertaken with minimal environmental impact in areas where a disproportionate ratio of migration of A. australis to A. reinhardtii into estuaries occurs, compared with recruitment into the catchment proper. Areas at the extremes of the natural range of each species have been suggested as candidate locations for intensive eel harvesting (e.g. south-eastern Queensland in the case of A. australis). Although, numbers of A. australis recruiting to the adult population in freshwaters of south-eastern Queensland may represent only a very small proportion of the number of glass eels attempting to
Overfishing is one of the most serious threats to eel populations in Australia as commercial harvesting of several
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Anguilla australis, Anguilla obscura, Anguilla reinhardtii
biodiversity [184, 912]. Large quantities of small-bodied and juvenile fish species (some of commercial importance), cructaceans and other aquatic invertebrates are frequently caught during passive netting of glass eels and mortalities are reported to often be very high [912]. Semiaquatic reptiles and mammals and birds are also occasionally captured during eel harvesting [184]. Options for bycatch reduction are the subject of continuing research and management planning [22, 462].
do so, it would seem that additional impact on glass eel abundance in estuaries by harvesting would further decrease the likelihood that A. australis will enter freshwaters. Clearly further evaluation and long-term monitoring are required before it could be concluded that commercial harvesting of glass eels could be undertaken in an ecologically sustainable manner in these areas or elsewhere. Eels have traditionally been an important source of food for the indigenous rainforest people of the Wet Tropics region. Concern about a decline in eel numbers over the last 50 years has been expressed to the senior author by some elders. That such concern exists in the absence of widespread harvesting of glass eels in this region suggests that other factors may currently place pressure on these species.
The wide distribution of Australian eels in the Asia-Pacific region necessitates the coordinated management of eel stocks across state and national boundaries, an imperative facilitated by the establishment in 1997 of the Australia and New Zealand Eel Reference Group (ANZERG), comprised primarily of Government aquaculture and fisheries representatives [914]. It is hoped that ANZERG will help to ensure conservation and management of South Pacific eel stocks in an environmentally sustainable manner.
Bycatch of aquatic and semi-aquatic biota during intensive glass eel harvesting in estuaries and lowland rivers is another potential source of impact on aquatic ecosystem
91
Nematalosa erebi (Günther, 1868) Bony bream, Bony herring, Australian river gizzard shad
37 085019
Family: Clupeidae
collected by seine-netting but also list a maximum Total Length of 419 mm (in their Table 3). A maximum length of 350 mm SL was recorded by us in a sample of 3123 fish from the Burdekin River [1093]. Note that the type of length measurement used varies between studies. By applying conversion factors (1.14 for CFL, 1.23 for SL) [422], estimates of maximum total length for the Northern Territory and Burdekin River populations of 410 mm and 430 mm may be made. These data suggest little difference in maximum size across this species’ range.
Description Dorsal fin: 14–19; Anal: 17–27; Pectoral: 14–18; Pelvic: 8; Vertical scale rows: 40–46. All fins spineless. Last ray of dorsal fin elongated to form a long filament in larger fish. Distinct line of scutes present on ventral margin, particularly between pelvic and anal fins. Head scaleless. Snout blunt and rounded, mouth small, lower jaw with central notch that fits a central groove in the upper jaw on closure. Body deep and laterally compressed. Scales cycloid, easily dislodged [52, 936]. Nematalosa erebi is easily recognised and unlikely to be confused with any other species except in northern lowland rivers that may be colonised briefly by other clupeid species. The sexes are externally indistinguishable. Figure: composite, drawn from photographs of adult specimens, 221–262 mm SL, Burdekin River, November 1991; drawn 2002.
Bishop et al. [193] list the relationship between length (CFL in cm) and weight (in g) as: W = 0.012 L3.12; n = 845, r2 = 1.0, p<0.001. Harris and Gehrke [553] list the relationship between weight (g) and length (CFL in mm) as W = 0.862 x 10–5 L3.1227. Arthington et al. [101] list the relationship between length (SL in cm) and weight (g) as W = 0.017 L3.113; n = 1223, r2 = 0.964, p<0.001 for bony bream in Barambah Creek, a tributary of the Burnett River. These data indicate that there is little indication of differences in size and shape across this species’ range. However, these relationships predict weights in excess of those listed by Puckridge and Walker [1075] for a sample of 27 gravid female fish from the River Murray, suggesting northern populations may be heavier for a given length.
Nematalosa erebi is a moderate-sized fish with most specimens between 150–300 mm SL. Maximum size is suggested to be 470 mm (TL) and 2.0 kg [936]. Bishop et al. [193] recorded a maximum length of between 355 and 365 mm FL for a sample of 723 fish from the Alligator Rivers region in the Northern Territory. Puckridge and Walker [1075] recorded a maximum length of between 360 and 380 mm TL for a sample of approximately 600 fish
92
Nematalosa erebi
Nematalosa elongatus (Macleay), Fluvialosa bulleri Whitley, 1948; Fluvialosa paracome Whitley, 1948; Fluvialosa richardsoni (Castelnau), and Fluvialosa erebi (Günther). The type specimen was collected from the Mary River, Queensland. The large number of synonyms reflects, in part, the extent to which different populations were classified as distinct species [678].
The larvae of N. erebi are small and eel-like and easily distinguished from the larvae of other species with the possible exception of the larvae of Retropinna semoni. Smelt have a higher myomere count, however (54 versus 45) [1075]. The yolk sac of bony bream is absorbed very early in ontogeny (<3.5 mm TL). The larvae are largely unpigmented except for a line of melanophores along the dorsal border of the gut (visible throughout larval development), a single melanophore located anterior to the cleithrum (after 6 mm TL) and a fine line of melanophores along the hindmost two-thirds of the gut [1075].
Distribution and abundance Nematalosa erebi is arguably the most widespread of Australia’s freshwater fishes, rivalled only by the spangled perch. This species has been recorded from the Pilbara and Kimberley regions of Western Australia, throughout the Northern Territory including its arid interior, the arid interior of South Australia (i.e. rivers of the Lake Eyre basin including Lake Eyre itself [455, 1341] and of the Bullo-Bancannia basin [947]) and most major basins of Queensland as far south as the Albert River. Its presence in New South Wales and Victoria is limited to the MurrayDarling Basin [52]. Various texts [34, 52] indicate that the distribution of N. erebi does not extend north of the Burdekin River on the east coast but this is not entirely true. The distribution includes the Wet Tropics region [1087], northward to the Stewart River [571, 1099] and including the Annan [599], Endeavour [571] and Normanby [697, 1099] rivers. This species was not recorded from the McIvor, Starke or Howick rivers within this range, or from the Lockhart, Pascoe, Claudie or Olive rivers further to the north, during the extensive CYPLUS surveys of 1993 [571]. Whilst these data do suggest that its distribution is not continuous in this part of Queensland, focused surveys (using gill nets and boat electrofishing) are needed to confirm the absence of bony bream. Nonetheless, several other species are absent from these rivers also (sooty grunter for example) whilst several species not typical of rivers of the east coast are present in some of these rivers (coal grunter for example), and this area would appear to be one of biogeographic significance. Various texts list the distribution of bony bream as extending into southern Papua New Guinea, but Allen [37] believed its occurrence there doubtful and based on misidentification of either N. papuensis (Munro) or N. flyensis Wongratana, both of which are morphologically very similar to bony bream.
Colour in life: bright silvery-white, sometimes greenishgrey on back. Fins either clear or opaque white. A reddish tinge to the body, and particularly the head region (see Figure 48 in Merrick and Schmida [936]), occurs and may be associated with breeding. This colour variation has been observed in the Burdekin River population also [1093] and is thus not restricted to the Murray River population [678]. Colour in preservative: white to light tan, silvery appearance retained but greatly subdued. Systematics The family Clupeidae is composed of over 200 species of small to medium sized, silvery fish commonly called sardines, pilchards, herrings or sprats. The family is found mainly in the shallow inshore habitats of the Indo-Pacific although many species occur in freshwater and estuarine habitats. About 32 species from 15 genera are known from Australia [1042]. Clupeids are the single most important family in the fisheries of the world, comprising nearly 20% of the total catch [52]. A small bony bream fishery exists in the lower Murray (predominantly in Lake Alexandrina), landings of 1000 t were recorded in 1990. Catches are destined for use as crayfish bait [678]. Human consumption is limited, although bony bream were canned as food for the troops during WWII [884]: no doubt contributing to the war effort and hastening the conflict’s end. Diagnostic characters include: the presence of specialised scales on the belly (scutes); the absence of fin spines; silvery, easily shed cycloid scales, the absence of a lateral line, and a small terminal mouth without teeth (or if present, teeth are very small) [1042]. Only two Australia clupeids occur exclusively in freshwaters: Nematalosa erebi (Günther) and Potamalosa richmondia; although others such as Nematalosa come (Richardson) and Herklotsichthys castelnaui (Ogilby) are occasionally found in freshwaters.
Nematalosa erebi is an abundant species. This species comprised 7.5% of the 27 742 fishes collected in the NSW Rivers Survey and was the second most abundant species [553]. This figure underestimates its abundance however, given it was absent from two of the four major regions sampled. Bony bream comprised 17.8% of the catch from the Murray-Darling Basin and was approximately five times more abundant in the Darling River than it was in
The genus Nematalosa was described by Regan in 1917, the type species being Clupea nasus Bloch, by subsequent designation. The bony bream was originally described as Chatoessus erebi by Günther in 1868. Additional synonyms include Chatoessus richardsoni Castelnau, 1873; Chatoessus elongatus Macleay, 1883; Chatoessus horni Zeitz, 1896;
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In an extensive study of the fishes of the Fitzroy River, N. erebi was encountered at all sites examined (21 sites) and was the most abundant species collected [160]. It was present at all sites on all occasions except one and abundances did not vary greatly between sampling occasion over a three year period. This observation of stable population size is in contrast to that observed by us in the Burdekin River and in Barker/Barambah Creek in the Burnett River drainage [101]. Extreme flooding in the Burdekin River, associated with Cyclone Joy in 1991, resulted in greatly depressed abundance levels. However, it was not known whether this reduction was due to flood-associated mortality and removal, or whether populations had simply moved downstream following their detritus/periphyton food source. Whatever the case, population sizes had recovered substantially within 12 months. Seasonal reductions in abundance, from maximum catches of 200–300 fish per sample in summer to less than 20 fish per sample in winter, were recorded in Barker/Barambah Creek [101]. A marked decline in seine-netting catches over the period June to August, corresponding to the period of lowest water temperatures, also occurred in the lower Murray River [1075]. Winter reductions in abundance may be related to increased susceptibility and frequency of infection by pathogens (see below). Body condition has been shown to deteriorate over the winter months [101].
the Murray. This species was frequently the most abundant species at individual sites [1201]. Puckridge and Walker [1075] believed that in contrast to many other species, bony bream had not declined in abundance since the advent of flow regulation in the Murray River. However, this assertion was based on fisheries landings that showed an increase over the period 1970–1990 (approximately). In contrast, Gehrke [435] showed that the abundance of N. erebi was significantly lower in regulated reaches than in unregulated reaches of the MurrayDarling River. Recruitment may have been modified in regulated reaches also, as a smaller proportion of the population was composed of small fish. Bishop et al. [193] recorded N. erebi from 21 of 26 regularly sampled sites within the Alligator Rivers region of the Northern Territory. Overall, it contributed 2.6% to the total number of fish collected and was in the top quartile of species ranked by abundance. Abundance levels varied between habitat types, being most abundant in lowland backflow billabongs (5.48%) and least abundant in escarpment habitats (0–0.5%). Bony bream comprised 48% of the total gill-netting catch in a study undertaken in the Normanby River [1098]. Similarly high abundances were recorded by Kennard [697] in floodplain lagoons of the Normanby River. Nematalosa erebi comprised 42% of the 1301 fish from six lagoons and 43% of 318 fish from two main river sites collected by gill-netting. No N. erebi were collected by electrofishing in this study. Only six individuals were collected by electrofishing in an extensive survey of the freshwater fishes of the Wet Tropics region despite its occurrence at relatively high abundance in the lower reaches of these rainforest rivers [1087].
Macro/meso/microhabitat use Nematalosa erebi has been recorded from a wide array of habitats ranging from salt lakes, lowland rivers, floodplain billabongs and lagoons, impoundments to rainforest streams. Merrick and Schmida [936] suggest that the only riverine habitats not used by N. erebi are ‘higher, cooler, faster flowing, clear upper reaches’. They caution however that this may reflect low abundance of their preferred food resources; macrophytes and detritus. In fact, in the Wet Tropics region, bony bream are naturally found in mesohabitats typified by high elevation (100 m.a.s.l.), cool clear water of moderate flow. Translocated populations also do well at much higher elevations (i.e. on the Atherton Tablelands). It seems that the array of habitats occupied by bony bream is limited only by access and possibly by minimum water temperatures.
The estimation of bony bream abundance is highly influenced by sampling methodology. For example, bony bream comprised only 1% of the electrofishing catch (total n = 3630) in a three-year study of the fishes of the Burdekin River, whereas it comprised 36% of the seinenetting catch (total n = 121 987) and an enormous 64% of the gill-net catch (total n = 1720). These data indicate the care needed when comparing abundance levels between studies. Moreover, in the case of gill-netting, net placement has a large influence on total bony bream catch. For example, nets set perpendicular to the bank will catch significantly more bony bream than nets set parallel [1093]. It is noteworthy that despite its high abundance elsewhere in the Burdekin River, N. erebi is either absent or at very low abundance in off-channel lagoon habitats of the lower Burdekin River (Perna and Cappo, unpubl. data). Perna (pers. comm.) attributed this pattern to the effects of degraded water quality and weed infestation in these lagoons.
Nonetheless, abundance levels do vary spatially, corresponding to spatial variation in mesohabitat characteristics. In the Burdekin River, bony bream abundance was negatively associated with moderate to fast water velocity (>0.3 m.sec–1) and the proportional contribution of gravel and cobble to substrate composition (the latter possibly resulting only because of autocorrelation with the former) [1098]. However, bony bream do occur in fast flowing boulder strewn habitats such as occur in many rivers of the Wet Tropics. It is likely that water velocity/abundance 94
Nematalosa erebi
maximum value of 38°C is probably approaching the upper limit for this species. The minimum value listed (15°C) was for a rainforest stream during winter. Only one individual was collected at this time. Glover [455] lists minimum and maximum water temperatures of 14 and 30°C, respectively, for central Australian populations of N. erebi. Merrick and Schmida [936] list bony bream as being able to tolerate temperatures as low as 9°C.
relationships vary from location to location, if they exist at all. Substantial ontogenetic variation in habitat use by bony bream in a large floodplain river of the Northern Territiory was described by Bishop et al. [193]. Small juvenile fishes were most commonly collected from corridor and lowland channel lagoons and to a lesser extent, corridor anabranch lagoons and pools in sandy creekbeds. Larger juveniles and small adults were more widely dispersed across a range of lowland lagoon habitats. Larger adults were more restricted to corridor and floodplain lagoons and of these only the largest were recorded from escarpment habitats. No bony bream were collected from escarpment stream habitats. Reproductively active fish (stage VI and VII) were collected from muddy lowland lagoons.
Table 1. Physicochemical data for Nematalosa erebi. Data derived from different studies across the northern distribution of bony bream (see text). Dissolved oxygen values listed for the Alligator Rivers region are surface values, bottom values are given in parentheses. Turbidity values are given as NTU except where designated by * where water clarity is given as Secchi disc depths in centimetres. ** denotes that water conductivity is given as the concentration in mg.L–1 of total dissolved solids.
Surprisingly, given this species’ wide distribution and abundance, little information on its microhabitat usage or preferences is available. It is not frequently collected by back-pack electrofishing and consequently, we have very meagre habitat records for this species. Nonetheless, this species is infrequently associated with microhabitat cover elements such as woody debris and macrophyte beds, preferring to take refuge amongst the relative protection of its fellows. Comparison of seine- and gill-netting catches in the Burdekin River [1093] suggest that fish below 250 mm SL are most common in open shallow areas (30–150 cm) whereas fish larger than this are rarely found in such shallow habitats. Bony bream form a large part of the diet of many piscivorous water birds [1167] and avoidance of shallow habitats may reduce predation. Extremely high numbers of bony bream may be collected by seine-netting over sand/fine gravel in moderate depths, particularly when water clarity is sufficiently elevated to provide refuge. For example, catches of 500–1000 individuals per haul (50 m seine, 9 mm stretched mesh) were not uncommon during a study in the Burdekin River [1093]. Although bony bream may be observed throughout the water column, they are most commonly found in the lower one-third.
Parameter
Min.
Max.
Mean
Alligator Rivers region [193] Water temperature (°C) 23.0 38.0 31.0 Dissolved oxygen (mg.L–1) 2.7 (0.2) 9.7 (9.5) 6.3 (3.9) pH 5.1 8.6 6.2 Conductivity (µS.cm–1) 2.0 198.0 Turbidity (cm)* 1 360 65 Cape York Peninsula (n = 6) [1094] Water temperature (°C) 21.0 27.0 24.0 Dissolved oxygen (mg.L–1) 7.3 11.0 8.8 pH 6.43 8.44 7.21 Conductivity (µS.cm-1) 80.0 420.0 180.1 Turbidity (NTU) 0.7 5.4 2.0 Normanby River floodplain lagoons (n = 12) [697] Water temperature (°C) 22.9 33.4 25.9 Dissolved oxygen (mg.L–1) 1.1 7.7 3.46 pH 6.0 9.1 7.05 Conductivity (µS.cm–1) 80.0 412.0 184.1 Turbidity (NTU) 2.1 120.0 14.5 Wet Tropics region (n = 8) [1085] Water temperature (°C) 23.6 32.7 Dissolved oxygen (mg.L–1) 5.76 8.14 pH 7.10 8.0 Conductivity (µS.cm–1) 8.3 67.6 Turbidity (NTU) 1.7 29.7
Environmental tolerances Despite the near ubiquity and importance of bony bream in northern Australian freshwaters, information on the physicochemical tolerance of this species is lacking. Inferences must therefore be based on water quality information from sites in which N. erebi have been collected. The normal caveats about the extent to which such data adequately describe tolerance therefore apply. The range in average temperature values listed in Table 1 reflects the fact that the studies from which these data were derived were all conducted in northern Australia. The 95
27.2 6.77 7.54 42.6 11.9
Burdekin River (n = 43) [1098] Water temperature (°C) 15.0 31.0 Dissolved oxygen (mg.L–1) 4.0 12.0 pH 6.66 8.46 Conductivity (µS.cm–1) 50.0 780.0 Turbidity (NTU) 0.3 20.0
25.1 7.92 7.64 395.0 4.0
Fitzroy River (n = 11) [942] Water temperature (°C) 24.0 29.0 Dissolved oxygen (mg.L–1) 4.8 11.0 pH 6.9 8.8 Conductivity (mg.L–1)** 70 770 Turbidity (cm)* 4 160
26.2 7.35 7.91 205 76.3
Freshwater Fishes of North-Eastern Australia
invasion) were believed responsible for the near-absence of N. erebi from floodplain lagoons of the Burdekin River delta (C. Perna, pers. comm.). Bishop et al. [193] observed N. erebi in a fishkill at Leichardt Lagoon in the Alligator Rivers region when surface DO levels dropped to 0.1 mg.L–1.
It is probable that substantial local adaptation to low water temperatures occurs. For example, Puckridge et al. [1078] list data showing that bony bream occur in waters as cold as 12°C in the Murray-Darling River. However, rates of infection by the fungus Saprolegnia parasitica and the bacterium Aeromonas hydrophila, which leads to mycotic dermatitis, increased dramatically when water temperatures descended to 12°C. These authors suggested that low winter water temperatures depress the immune response of bony bream allowing mycotic dermatitis to develop. Increased rates of infection by the protozoan parasite Chilodonella hexasticha in central Australian populations of bony bream have also been associated with decreased winter water temperatures [767]. Lake [754] believed that hypolimnetic releases from the Hume (Murray River) and Burrinjuck (Murrumbidgee River) dams that lowered summer water temperatures to 16 to 18°C (a 6°C drop below expected river temperatures) had resulted in a decline in abundance of bony bream for several hundred kilometres downstream.
Nematalosa erebi has been recorded from waters of a moderately large range of acidity: 5.1 to 9.1 pH units. The pH range within each study area listed in Table 1 is somewhat smaller however, ranging from 0.9 units (Wet Tropics) to 3.5 units (Alligator Rivers region) and averaging only 2.2 pH units. In general, N. erebi occurs more frequently in neutral to slightly basic waters although it is evident that this varies between regions (i.e. the Alligator Rivers’ population), suggesting localised adaptation, within limits, to the existing array of habitats of varying water quality. It is notable that N. erebi has not been recorded from highly acidic habitats such as dune lakes [1101]. Herbert and Peeters [569] implicate elevated pH resulting from drainage works exposing potential acid sulphate soils as the major cause of some massive kills of bony bream in northern Queensland. Notably, the disjunction in distribution along the east coast of Cape York Peninsula discussed above, involves rivers draining extensive peaty swamps and dune fields notable for their low pH (i.e. <5) [1101].
The substantial range in maximum temperatures listed in Table 1 (27 to 38°C) in large part reflects the climatic differences between regions and the time of year in which samples were collected. For example, the maximum temperature recorded for rivers of the Cape York region (27°C) is much lower than that for floodplain lagoons in the same region, simply because the former sites were sampled in the winter dry season only whereas the latter were sampled over the full climatic year. Although N. erebi is evidently able to tolerate water temperatures as high as 38°C (for at least short periods) and is routinely found at temperatures between 27 and 35°C, we suggest that it preferentially avoids very warm waters, if possible. For example, water temperatures in excess of 31°C were routinely recorded in sites located on the upper Burdekin River at the end of the dry season (November) but such sites lacked bony bream. This species is the most common (in terms of abundance and biomass) of the river’s fishes and was present at such sites when temperatures were lower. The simplest explanation is that N. erebi avoid habitats of high water temperature if egress from such sites is possible.
Nematalosa erebi tolerates waters of a wide range of salinities, ranging from the highly dilute waters of rainforest streams of the Wet Tropics regions to more conductive waters of the Burdekin River (Table 1). However, the values presented in Table 1 are all indicative of very fresh water. Elsewhere this species has been recorded from salt lakes with salinities approaching that of sea water. Ruello [1167] reported that bony bream were present in Lake Eyre when surface salinity was approximately 39‰ but also included accounts of bony bream persistence at salinities approaching double this value. Whatever the case, the existing data indicates an extremely wide salinity tolerance befitting the most widely distributed Australian freshwater fish. Not unsurprisingly, N. erebi has been recorded from a wide variety of water clarities with a tendency to be most common in waters of moderate turbidity, perhaps reflecting more their preferred habitat (slow-flowing lowland rivers) rather than water clarity per se. Burrows et al. [256] recorded bony bream in the Belyando River in turbidities as high as 581 NTU. The extent of long-term persistence in such turbid waters is unknown as are reproductive, energetic and trophic responses (i.e. fecundity, condition and diet).
Bony bream have been recorded from waters with a large range in dissolved oxygen concentrations although the average values listed in Table 1 indicate that N. erebi are most commonly collected from well-oxygenated waters. Nonetheless, N. erebi have been recorded from hypoxic waters such as floodplain lagoons of the Alligator Rivers region and of the Normanby River. However, such conditions are far from optimal. Bony bream tend to reduce activity greatly under hypoxia, the extent to which this inhibits food intake or growth in hypoxic habits is unknown. Low oxygen levels (in concert with prolific weed
Information on the tolerance of bony bream to toxicants is, in general, lacking. We have observed highly significant
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toxic effects of copper and indirect effects of copper on its microalgal food source.
reductions in the abundance of N. erebi in stream reaches receiving mine effluents containing elevated concentrations of copper [1093] possibly in response to the direct
Table 2. Life history data for Nematalosa erebi. Data drawn from the work of Puckridge and Walker [1075] in the lower Murray River, Arthington et al. [101] in the Burnett River drainage and Bishop et al. [193] in the Alligator Rivers region. Age at sexual maturity (months)
Murray River – 12–24 months (males) and 24 months(females); median lengths 159 and 199 mm TL, respectively Burnett River – gender discernible at 115 mm SL and 127 mm SL for males and females, respectively Alligator Rivers – 12–15 months (males) and 12–15 months (females); length at first maturity 130 and 140 mm CFL, respectively
Minimum length of ripe females (mm)
Murray River – approximately 150 mm TL Burnett River – 202 mm SL although spent fish as small as 187 mm recorded Alligator Rivers – 140 mm CFL
Minimum length of ripe males (mm)
Murray River – approximately 130 mm although a small number of precocious males approximately 110 mm TL observed Burnett River – 204 mm SL although spent fish as small as 117 mm SL recorded Alligator Rivers - 130 mm CFL, no precocious males observed
Longevity (years)
Probably up to 5 years
Sex ratio (males to females)
Murray River – 0.86: 1; females more abundant in larger size classes Burnett River – 0.70: 1; females more abundant in larger size classes Alligator Rivers – 1:1
Peak spawning activity
Murray River – December to February Burnett River – GSI values elevated from October to March, some ripe individuals present in April Alligator Rivers – spawning continuous but majority occurring from December to March
Critical temperature for spawning
Murray River –18–20°C Burnett River – 22°C Alligator Rivers – data not given but likely to be >24–28°C
Inducement to spawning
Murray River - unknown but apparently unrelated to flooding Burnett River – unknown but postulated to involve interactive effects of temperature and daylength
Mean GSI of ripe females (%)
Murray River – 8–9% Burnett River – 5.8 ± 0.3% (SE) Alligator River – 4–5%
Mean GSI of ripe males (%)
Murray River – data not given Burnett River – 3.2 ± 0.1% (SE) Alligator Rivers – 3–4%
Fecundity (number of ova)
Murray River – 33 000–880 000 Alligator Rivers – 80 000–230 000
Fecundity/length relationship
Murray River – log F = 3.923 + 3.725(log TL in mm); n = 27, r2 = 0.88, p<0.001
Egg size (mm)
Murray River – 0.83 ± 0.04 mm (water-hardened) Alligator Rivers – 0.41–0.43 mm (in situ oocytes)
Frequency of spawning
Females homochronic, males may remain on spawning grounds longer and participate in several spawnings. Heterochrony possible in northern populations
Oviposition and spawning site
Murray River – shallow sandy embayments Alligator Rivers – muddy lagoons
Spawning migration
Inferred – see section on movement
Parental care
None
Time to hatching
Unknown but likely to be rapid
Length at hatching (mm)
Unknown but likely to be 2–3 mm
Length at feeding
Yolk sac absorption complete by 3.5 mm TL
Age at first feeding
?
Age at loss of yolk sac
?
Duration of larval development
?
Length at metamorphosis
Squamation commences at 26 mm TL, complete by 35–40 mm TL
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(October–December). Elsewhere in northern Queensland, temporal changes in population age structure suggest a more protracted breeding season. New recruits were present in both wet and dry season samples in the Burdekin River [1080] and in both early and late dry season samples in floodplain lagoons of the Normanby River [697]. It would be most instructive to determine whether spawning phenology becomes more pronounced, or commences earlier in the year, with increasing latitude over the length of the Murray-Darling system and to assess whether other life history adjustments are necessary as a result.
Overall, and as expected for such a widely distributed and abundant species, N. erebi appears highly tolerant of a wide range of environmental conditions. However, by the same token, we find it disturbing that there a few experimental data on the tolerances of this species. Its potential as a biomonitor, which given its huge distribution across a range of regions, rivers and habitats, its abundance and trophic position (see below) is considerable, cannot be realised until such data are available. Reproduction Nematalosa erebi has a reproductive biology similar to many of the clupeid fishes. It matures early in its life, usually in its first or second year. Female fish mature more slowly than do males and may attain greater size. The data presented in Table 2 suggests that female fish may mature more slowly in southern populations. There is no strong evidence however to suggest that they mature at much greater size than do northern populations. The data presented in Table 2 suggests that individual female fish may spawn up to four, but more commonly three, times over their life span. However, given the intensity of predation on this species (by both birds and fishes, and in northern rivers by crocodiles also), it is unlikely that all but a very few spawn more than once. Sex ratios tend towards unity in the northern population whereas females were found to be more abundant (mostly because of a dominance of females in the upper size classes) in the Murray and Burnett rivers. However, Puckridge and Walker [1075] found proportionally more males than females in the vicinity of spawning grounds leading them to suggest that males may stay on the grounds longer than females.
A short, pronounced breeding season in the southern population appears to indeed be related to a number of other life history adjustments. GSI values of female fish in this region were approximately double those observed in the northern population. The population in the Burnett River appears to have an intermediate female GSI value, consistent with the hypothesis that selection for a short breeding season also results in selection for comparatively elevated instantaneous reproductive effort. It would be instructive to know whether northern populations spawn more than once in a season. Although the estimates of fecundity in the Northern Territory population are based on only three specimens, the data suggests that fecundity may be lower there than in the Murray River, thus leading to the observed reduction in GSI values. Although egg size appears greater in the southern population, which may also lead to increased GSI values, it must be emphasised that the estimates of egg size in the Murray River population are based on ovulated, water-hardened eggs whereas Bishop et al. [193] based their estimate on the size of follicular oocytes.
Geographical variation in spawning phenology is apparent. Populations in the Murray River have a well-defined summer breeding season, the timing of which is unrelated to flooding. Recruitment may benefit from coincidence with flooding however [1075]. In contrast, year-round spawning, with a peak in the early wet season, was observed in the tropical Alligator River. An intermediate phenology was observed in the Burnett River, south-eastern Queensland, where maximum GSI values were recorded over the period October to March/April; although reproductively active fish were present in all sampling occasions except from June to August (the coldest months). Minimum temperatures associated with spawning ranged from 18–20°C in the Murray River, 22°C in the Burnett River and 24–28°C in the Alligator River. These studies suggest that water temperature exerts some influence on spawning phenology, with spawning in southern populations being limited to the warmer summer months. Llewellyn [814] reported that bony bream in New South Wales spawn early in the year
These data suggest that the life history of bony bream is relatively flexible, as might be expected for a species with a distribution encompassing wet tropical, wet/dry tropic, subtropical, arid and temperate environments. Puckridge and Walker [1075] noted that N. erebi was much more fecund than other related gizzard shads, and further, that the rate of increase in fecundity with increasing size was also much greater. These authors suggested that these features enabled very rapid recovery of population size after unfavourable environmental conditions. Such a rapid recovery was observed in the Burdekin River following extreme flooding associated with the passage of Cyclone Joy over the catchment in January 1991. Flooding reduced bony bream abundances by almost 80%. Population levels had increased to 77% of pre-flood levels within a year and returned to pre-flood levels after 18 months. Recovery was initially achieved through equal contributions by immigration and production but production was the greatest
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use described by Bishop et al. [193] indicates substantial movement by juvenile fish also. Long-term monitoring of fishes in the Burdekin River [1082] revealed that recolonisation of reaches after a large flood was partly achieved by the immigration of both small (<75 mm SL) and intermediate-sized fish (75–250 mm SL). These data suggest that small and intermediate sized fish make substantial movements not associated with reproduction. Such fish may track spatial and temporal variation in their detrital/ microalgal food base.
contributor in the second half of the recovery period [1082]. Spawning takes place in shallow still-water habitats. In the Murray River, spawning was suggested to take place in sandy embayments whereas the population in the Alligator River spawns in muddy lagoons. Spawning in lagoons of the Normanby River was also recorded by Kennard [697]. In the upper Burdekin River, which lacks off-channel lagoons, spawning probably takes place in backwaters. The eggs are apparently demersal at the time of spawning but later become buoyant [1075].
Puckridge and Walker [1075] implied the existence of movement associated with reproduction in the Murray River by designating certain areas as spawning grounds. Similarly, the distinction between adult and juvenile habitats in the Alligator Rivers region [193] suggests that adults make spawning-associated migrations into spawning grounds. It seems to us that focused studies on the movement biology of N. erebi would be a fruitful area of research and one that is needed to identify the precise mechanisms by which river regulation impacts on this species [435].
Larval development is, at least initially, rapid, particularly with regard to absorption of the yolk sac. This suggests that bony bream larvae may be highly reliant on the presence of an abundant phyto/microzooplankton bloom early in its life. Movement Information on the movement biology of this species is limited and derived primarily from studies on fishway efficacy or inferred from studies of reproductive biology.
Trophic ecology The dietary information presented in Figure 1 is summarised from a total of 11 different studies drawn from the lower Murray River (number of individuals = 98) [115]; the Pilbara region (n = 9) [358]; Cooper Creek in central Queensland (n = 90) [246]; a tributary of the Burnett River in south-eastern Queensland (n = 499) [99, 205]; the Burdekin River (n = 514) [1093]; the Wet Tropics region (n = 14) [99, 1097]; Cape York Peninsula (n = 118) [697, 1099] and the Alligator Rivers region (n = 471)
Stuart [1274] found that N. erebi was the second most abundant fish moving (upstream movement recorded only) through a fishway located 64 km from the mouth of the Fitzroy River. Up to 400 fish were recorded moving through the fishway, of a modified slot design, each day. Movement through the fishway occurred throughout the year but was least in late summer/early autumn. Nearly all (~95%) of the fish collected were less than 100 mm in length, with the remainder being greater than 250 mm length. Fish as small as 25 mm were found to negotiate the fishway although comparison of the size distributions of samples from the top and bottom of the fishway and of fish congregated below the fishway revealed that the processes of entry and passage through the fishway both selectively reduced the numbers of small individuals. Movement was predominantly diurnal, an observation that has also been made on populations in the Murray River [854]. Upstream movement in fishways will apparently cease, followed by a return to the base of the fishway, if the upstream passage cannot be negotiated before sundown [854]. Clearly therefore, N. erebi must be able to negotiate any fishway (or natural obstacle) within the space of a single diurnal period.
Terrestrial invertebrates (1.0%) Microcrustaceans (10.7%)
Unidentified (8.0%)
Molluscs (1.8%) Aquatic insects (5.1%)
Algae (14.7%)
Aquatic Macrophytes (1.4%)
Juveniles comprised the bulk of N. erebi recorded moving through a fishway on the Burnett River [1173]. Large congregations of juvenile fish below small barriers such as road crossings and culverts are commonly observed in the Mary River in south-eastern Queensland with the inference being that such fish had been prevented from upstream migrations. The ontogenetic variation in habitat
Detritus (57.3%)
Figure 1. Mean diet of Nematalosa erebi. Data derived from a total of 1813 individuals drawn from 11 different studies (see text).
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Freshwater Fishes of North-Eastern Australia
[193]. Note that the total sample is numerically dominated by fish from north-eastern and northern Australia (the summary means upon which Figure 1 is based are weighted by abundance) and substantial geographical and habitat-based variation in diet occurs (see below). Also, note that the samples contain both juvenile and adult fish and ontogenetic variation in diet is a feature of the trophic ecology of this species.
Microplankton, aquatic insects, and small molluscs collectively comprise about one-fifth of the average diet. In the Murray River, microcrustacea contributed 55% of the diet of juveniles and 27% of the diet of adults [115]. A similarly high contribution (35%) was reported for fish from Cooper Creek [246]. This food source was completely absent from, or contributed less than 1% to, the diet of bony bream from the Burdekin River or rivers of the Wet Tropics and Cape York Peninsula. Notably, however it was present and relatively important in the diet of some neosilurid catfishes in the Burdekin River and its absence from bony bream was not therefore due to an absence of this food source from the system. It should be emphasised here that although small amounts of Cladocera and copepods were present in the food class collectively termed ‘microcrustacea’, this class was dominated by ostracods. The consumption of microcrustacea therefore does not here reflect a planktivorous feeding habitat but rather one dominated by grazing on the benthos. This feeding strategy is in contrast to many other species of gizzard shad.
Nematalosa erebi is primarily a detritivore/algivore. The algal contribution is dominated by microbenthic algae such as desmids and diatoms. The contribution of detritus to the diet, whilst certainly significant, may not be as great as is depicted in Figure 1 due to methodological constraints on the estimation of the relative contribution of different food types. For example, in our analysis of the diet of N. erebi from the Burdekin River, we did not quantitatively distinguish between detritus and microalgae. Microalgae were present and important in these fish however, and probably contributed about one-third of the volume of the food class collectively termed ‘detritus’. Kennard [697], in contrast, did distinguish between microalgae and organic detritus in a study of fishes in floodplain lagoons of the Normanby River and found no contribution by microalgae to the diet. Thus some accounts of a high contribution by organic detritus to the diet of bony bream must be considered as indicating real importance and may reflect the effect of habitat structure (i.e. lagoons versus river habitats) on trophic style.
Ontogenetic variation in diet is pronounced. For example, the greater consumption of microcrustacea by juvenile fish compared to adults in the Murray River has already been described above. In the Burdekin River, small N. erebi (<80 mm) fed almost exclusively on chironomid midge larvae, and as such, were trophically similar to the juveniles of most other species in this system. The same observation has been recorded for bony bream in floodplain lagoons of Cooper Creek [246].
The relative contribution of benthic microalgae to the diet apparently varies geographically also. For example, no algae were recorded from the diet of either adult or juvenile fish from the Murray River [115], whereas algae contributed 10% of the diet of fish from Cooper Creek, between 11 and 22% of the diet of fish from the Burnett River drainage, 36% of the diet of fish from the Alligator River, 50% of the diet of fish from the Annan River [99] and 92% of the diet of fish from the Pilbara region [358]. A more pronounced consumption of aquatic vegetation is an outstanding feature of the differences in trophic ecology of fishes in northern Australian compared to southern Australia [705]. The full extent and relative importance of detrivory and algivory in this species remains to be determined although such work, using isotopic tracing, is underway in Cooper Creek (S. Bunn and P. Davies, pers. comm.) and in the Border Rivers region of eastern Queensland (Medeiros and Arthington, pers. comm.). Until such results are known, it is probably safe to say that at least half of the adult diet is composed of benthic microalgae, but also that the relative importance of algae to the diet varies between rivers and also within the riverine landscape and with ontogeny.
Nematalosa erebi is consumed by a wide variety of other species and is probably the most frequently consumed prey species in freshwater habitats. Herbert and Peeters [569] suggest that N. erebi forms over 90% of the diet of stocked barramundi in Lake Tinaroo on the upper Barron River. Nematalosa erebi are also consumed in large numbers by piscivorous birds such as cormorants and pelicans [1167]. Bony bream are an important component of aquatic food webs as their consumption by high trophic level consumers results in very rapid transmission of aquatic primary production (microalgae) and of terrestrial primary production (organic detritus) through the aquatic food web. In addition, bony bream have been suggested to be able to elevate nutrient levels in impoundments [569], presumably by increasing the resuspension of organic sediment and attached nutrients during feeding or by faecal liberation. This species may therefore potentially alter the trophic status of an impoundment if biomass is high. In riverine systems, the movement of large schools of bony bream may result in substantial export or import of nutrients.
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Nematalosa erebi
mortality. Further, the apparent intolerance of bony bream to low pH, suggests that floodplain developments that disturb potential acid sulphate soils are likely to negatively impact on this species.
Conservation status, threats and management Nematalosa erebi is listed as Non-Threatened by Wager and Jackson [1353]. Given its wide distribution and generally high abundance, it is probably secure. However, river regulation does impact on abundance levels and possibly also on recruitment processes [435] and some aspects of water resource management may therefore threaten this species. Nematalosa erebi is a widespread, mobile, highly abundant consumer, trophically located near the base of the riverine food web. As such, it is ecologically very important. By virtue of its detrivorous and algivorous habits and the fact that it forms the principal prey species for many piscivorous fishes, N. erebi is an important component of the aquatic food web and in the transfer of energy and carbon between trophic levels. As such, impacts on abundance and population size structure may have far reaching effects for entire aquatic systems. Declines in the abundance of this species would, in all likelihood, foreshadow or even cause major changes in the abundance of other aquatic organisms.
Movement is an integral part of the biology of this species. The imposition of barriers in the riverine landscape may prevent fish from tracking resources, accessing spawning areas or replenishing populations perturbed by natural or anthropogenic disturbance. Fish passage devices such as fish ladders obviously allow the passage of bony bream but must allow both upstream and downstream movement, and for the passage of individuals of all size classes, and must be negotiable within the space of a single diurnal period. Further research is required to elucidate the reproductive responses of bony bream to different flow events, particularly the mortality response of larvae to elevated flow. From a perspective of environmental flow management, a critical consideration is the extent to which modified flow regimes alter the distribution and availability of food resources, such as microcrustacea during early growth, and organic detritus and microalgae later in life. The latter may be highly susceptible to disturbance resulting from the mobilisation of fine particle substrates. In addition, increased turbidity may negatively impact on periphyton growth, reducing the abundance of this food source. Increased sedimentation may also reduce the quality of the detrital food base (i.e. by smothering or dilution of organic particles by inorganic particles).
Several aspects of its biology need consideration in any sphere of environmental management. First, although abundant and widely distributed, N. erebi may be negatively impacted by low water temperatures (depressing reproduction and immune responsiveness), low oxygen concentrations and by low pH. Hypolimnetic releases from storages are therefore likely to have severe consequences for this species. Seasonal or diurnal oxygen depletion, such as occurs in nutrient enriched or weed infested off-channel habitats, is also likely to lead to increased
101
Arius graeffei Kner and Steindachner, 1866 Arius leptaspis (Bleeker, 1862) Arius midgleyi Kailola and Pierce, 1988 Fork-tailed catfish
37 188005 37 188006 37 188010
Family: Ariidae
The equation describing the relationship between length (SL in mm) and weight (in g) for both male and female fish from the Clarence River is: W = 2.045 x 10–6 L3.39; r2 = 0.941, p<0.001 [1141]. Bishop et al. [193] report a length (CFL in cm)/weight (g) relationship of W = 9.21 x 10–3 L3.189; r2 = 0.98, n = 41, p<0.001. The description below is drawn from Kailola [676]. Body robust, elongate; anterior profile straight, moderately steep, elevated slightly before dorsal fin; mouth moderately broad and slightly curved; snout rounded, moderately fleshy upper lip extending beyond mouth gape, teeth usually concealed when mouth closed; shallow groove may be present between nostrils, posterior nostril ovate to elliptical, anterior nostril with flap just concealing opening; eye ovate, dorsolateral, positioned slightly anterior of middle of head. Maxillary barbel extending past head to base of pectoral fin or just beyond. Jaw teeth in arched curved band, fine, sharp and depressible, arranged in six to nine irregular series, edentulous space separating each side of mandibular tooth band. Palatal teeth villiform, patches arranged as in Figure 1. Raker-like processes on the back of all arches. Head shield finely and somewhat sharply granulated, arranged in series along each side of dorsomedian groove, radiating outward and over occipital process; shield beginning over
Description Ariidae is a large family of mostly marine catfishes. Six species (Arius graeffei, A. leptaspis, A. midgleyi, A. berneyi (Whitley, 1941), Arius paucus Kailola, 2000 and Cinetodus froggatti Ramsay and Ogilby, 1866) regularly occur in freshwaters of northern Australia [52, 675]. Only the first three species are treated here. Arius leptaspis does not occur in easterly flowing rivers of northern Australia but is included here because separation of these species has proved difficult in the past. The descriptions below are most comprehensive for A. graeffei and A. midgleyi as these species are more likely to be encountered in the area covered by this book and because descriptions of A. leptaspis have in the past been contaminated by inclusion of other species within the series examined [676, 1304]. Arius graeffei Dorsal fin: I, 7; Pectoral: I, 10–11; Anal: 15–19; Caudal fin: 15 (7+8) primary rays; Gill rakers on first arch: 17–22, 6–8 on upper limb; Free vertebrae: 45–48. Figure: composite, drawn from photographs of specimens 250–350 mm SL, Burdekin River; drawn 2002. Arius graeffei is a medium to large-sized catfish, commonly reaching 350 mm SL, occasionally to 600 mm [52, 676].
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Arius graeffei, Arius leptaspis, Arius midgleyi
before base of occipital process. Pelvic fin shape variable as in A. graeffei. Colour in life: dorsal surface dark grey, blackish or coppery-brown, becoming paler ventrally, series of vertical rows of golden dots often present on upper flanks. Medial and pelvic fins often with a white margin. Colour in preservative: similar but vertical rows of dots greatly subdued [52, 676, 677, 936].
middle of eye. Dorsal and pectoral spines thick, with pattern of longitudinal striae, posterior margin of dorsal spine usually smooth, occasionally with low serrae near tip; pelvic spines stoutly serrate on posterior margin. Pelvic fin shape variable; in males base narrow, fin rays rarely reaching anal fin origin; in females, base broad, inner elements become thickened and develop a pad or hook with sexual maturity, fin rays frequently reaching fourth to sixth anal ray. Colour in life: dark brown, deepblue, fawn or dark ochre above, becoming yellowish-cream or white on undersides, occasionally stippled on belly. Maxillary barbels black or dark brown, mental barbels dark or pale. Piebalding or blotching and albinism have been reported [936]. Colour in preservative: similar but blue and irridescence lost.
Arius midgleyi Dorsal fin: I, 7; Pectoral: I, 9–11; Anal: 16–19; Gill rakers on first arch: 15–17; Gill rakers on last arch: 16–19; Free vertebrae: 47–50 [675, 677]. Arius midgleyi is a large catfish that may reach 1.3 or 1.4 m in length and 28 kg in weight but is usually <500mm SL [52, 677, 697]. The description below is drawn entirely from Kailola and Pierce [677]. Body sleek and robust, rather compressed, tapering posteriorly. Snout broad and truncate, lateral head profile triangular and narrow, predorsal flat, interorbital region flat. Mouth broad, curved; lips thin at front of jaws and thick at corners; teeth in upper jaw either not or partly visible when mouth closed although often just visible at sides of mouth. Nostrils ovate, placed well forward, anterior nostril directly before or slightly lateral to posterior nostril, on which skin flap just conceals opening. Eye rounded to oblong, dorsolaterally placed, visible when viewed from above. Barbels thin and tapered, maxillary barbel reaching just beyond head to pectoral fin base (16–25% SL). Jaw teeth small, sharp and depressible, embedded in tissue, arranged in irregular series (16–24 in upper jaw, 10–15 in lower jaw); lower jaw band separated by narrow edentulous space at symphysis. Palatal tooth patches arrayed as in Figure 1. Gill rakers rigid and sharp tipped, as long as gill filaments. Raker-like process absent from posterior face of first arch and usually second arch; 11–17 on rear of third arch; low thick pad of tissue usually present on posterior face of second arch but absent from all others. Head shield usually concealed by tissue in small fish and often in larger fish also; when exposed, shield very granular, extending forward to above eye, to origin of gill opening and over occipital process. Dorsomedial head groove distinct, long and lanceolate. Numerous fine papillae distributed on snout, anterior two-thirds of head and occasionally on breast. Dorsal and pectoral spines sharp, moderately to very thick, anterior border roughened by granules and low dentae; posterior border of dorsal spine with no or few serrae, when present restricted to upper half. Pectoral spine with up to 20 short, saw-like serrae on posterior margin. Sexual difference in pelvic fins as described above. Colour in life: highly variable, perhaps relative to habitat and locality; dorsal surface ochre, brown, olive-brown, or smokey to dark blue, grading abruptly to white or cream
Figure 1. Palatal tooth patch arrangement. Redrawn after Allen [34].
Arius leptaspis Dorsal fin: I, 7; Pectoral: I, 9–11; Anal: 16–20; Gill rakers on first arch: 13–22 [52, 676]. Arius leptaspis is a medium to large-sized catfish, commonly reaching 350 mm SL, occasionally to 600 mm [52, 193]. The equation describing the relationship between length (CFL in cm) and weight (W in g) is W = 1.46 x 10–2 L3.1; r2 = 0.966, n = 740, p<0.001 [193]. Body robust, elongate; anterior profile straight, moderately steep, elevated slightly before dorsal fin; snout rounded, head not greatly flattened, mouth moderately broad and curved; moderately fleshy upper lip extending just beyond mouth gape. Maxillary barbel extending well past head, often beyond base of pectoral fin, 22–51% of SL [677]. Palatal teeth villiform, patches arranged as in Figure 1. Raker-like processes not present on the back of all arches. Head shield extensive and finely granulated, occipital process broad, dorsomedian groove terminating well
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Freshwater Fishes of North-Eastern Australia
described as Hexanematichthys leptaspis by Bleeker in 1862 [200] from material collected in southern New Guinea but was later placed within Arius by Paxton et al. [1042]. All references to this species east of the Great Dividing Range are apparently attributable to A. graeffei [1142].
ventrally. Pectoral and pelvic fins dark above, pale below; anal fin brown or bluish-brown, sometimes with white margins. Maxillary barbels dark, mental barbels pale. Piebalding sometimes observed. Colour in preservative: as above except pale ventral surface tends to a fawn colour. Fins and barbels as in life except blue fades to dark brown.
Arius midgleyi was described by Kailola and Pierce in 1988 [677] from material collected across a range of rivers from the Fitzroy River in Western Australia to the Flinders and Mitchell Rivers of the Gulf of Carpentaria region. Hamar Midgley first recognised the existence of this species and referred to it as ‘shovel nosed catfish’ in his reports on the freshwater fishes of northern Australia [944, 945, 946]. Arius midgleyi is similar to A. leptaspis and many of the specimens included in the series used by Taylor [1304] to describe A. leptaspis from the Arnhem Land region were the former species [677]. In addition, specimens of A. graeffei were also included in the series used by Taylor to represent A. leptaspis [676]. Taylor [1304] believed that A. graeffei and A. leptaspis represented a single species; a suggestion refuted by Kailola [676]. Material from the Flinders River within the type series of A. midgleyi was recently found to contain yet another species, A. paucus [675].
Arius midgleyi is most similar to A. leptaspis but is easily distinguished by differences in size (A. midgleyi is larger), relative size of barbels (shorter in A. midgleyi), head shape (square in A. midgleyi), head width (narrower in A. midgleyi) and head shield (described above). Systematics Ariidae is a large, circum-globally distributed, tropical and subtropical, family of fishes, commonly referred to as sea catfishes, containing approximately 80 species within about 14 genera [37, 52, 677]. The family has a long history of occupation of freshwater environments: fossil ariids appear in North American Eocene freshwater deposits [1413]. Arius contains more than 40 species, of which about 18 species occur in freshwater habitats of Australia and New Guinea [52, 677]. Arius was first formally described by Valenciennes in 1840 [677] although Taylor [1304] suggests that the genus had been described previously by Lacépède in 1803 as Tachysurus (type species T. sinensis) based on a Chinese painting of an unknown catfish. Wheeler and Baddockway [1376] showed that Tachysurus is of uncertain status but definitely not an ariid catfish. Kailola and Pierce [677] suggested that division of Arius into distinct subgenera is probably warranted.
Arius paucus is very similar to A. midgleyi, differing only in the number of gill rakers on the first arch (10–11 versus 15–17 in A. midgleyi), the number of rakers on the last arch (11–14 versus 16–19 in A. midgleyi) and the size of the eye (8.9–15.3% of HL versus 12.9–21.8% of HL in A. midgleyi). Distribution and abundance Arius graeffei This species occurs in New Guinea and Australia and is widely distributed across northern and south-eastern Australia, extending from the Ashburton River in the Pilbara region of Western Australia to the Hunter River in New South Wales [52, 676]. The southern limit of this species may have contracted recently as A. graeffei has not been recorded from the Hunter River in recent years [553] and is uncommon in the Richmond and Clarence rivers (0.6% of total catch for the North Coast region) [553] despite once being common [1140].
The nomenclatural history of the three species covered here is complex. Arius graeffei was described in 1867 from material collected in Samoa (location doubtful) in 1866 [725] but the name was rarely used and became replaced by A. australis, described by Günther in the same year [486] from material collected in the Hunter River of New South Wales. Notably, it no longer seems to occur in this river. Castelnau also described this species as A. curtisii in 1878 from material collected in the Moreton Bay region of Queensland [284]. Kailola [676] resolved the nomeclatural problem, reinstating A. graeffei as the valid name and demoting A. australis and A. curtisii to junior synonym status. Reference to this species under the names Tachysurus graeffei, Netuma australis, Neoarius curtisii, Neoarius australis and Pararius graeffei may be found also [1042]. An extra ‘i’ is frequently seen in misspellings of the species epithet.
Records of A. graeffei in rivers draining to the southern portion of the Gulf of Carpentaria region are remarkably scant, being limited to the Flinders River [676]. Whether this represents a real disjunction in distribution (this species is present in Arnhem Land [676, 1304]), or reflects the limited survey work undertaken in the area, is unclear. This species was not recorded from the Gilbert River in recent research [643]. Arius graeffei has been recorded from the Mitchell (including its tributary systems the
The nomenclatural history of A. leptaspis is less torturous; however the name has frequently been given in error to eastern populations of A. graeffei. This species was first
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Arius graeffei, Arius leptaspis, Arius midgleyi
The distribution of A. leptaspis in Queensland is patchy and somewhat restricted. This species has been recorded from the Flinders and Norman rivers of the Gulf region [979] and the Mitchell, Coleman, Archer, Embley, Wenlock, Ducie and Jardine rivers [41, 356, 571, 1349]. It does not occur west of the Great Dividing Range and early records of its presence here are attributable to A. graeffei.
Palmer and Walsh rivers), Coleman, Chapman, Archer, Watson, Embley, Wenlock, Ducie and Jardine rivers of western Cape York Peninsula [41, 356, 571, 643, 676, 1186, 1349]. Despite apparently occurring in rivers of the east coast of Queensland [52], there are no reliable literature accounts of its presence in any rivers from Cape York Peninsula to the Burdekin River region with the exception of a single record for the estuarine portion of the Barron River in the Wet Tropics region [1187]. Halliday et al. [501] report the presence of sea catfishes in the bycatch of several fisheries operating in the Wet Tropics region but did not identify which species were involved. This species has been recorded from the Haughton River [255] and from several locations in the lower Burdekin and Bowen rivers [586, 591, 847, 940, 1046, 1098]. Arius graeffei apparently once occurred in floodplain lagoons of this catchment [847] but no longer does so ([1046], C. Perna, pers. comm.). It may no longer occur upstream of the Collinsville Weir in the Bowen River [591, 956] despite having once occurred there [940]. This species comprised <0.1% and 3.2% of the total seine- and gill-netting catches in a study undertaken in the Burdekin River over the period 1989–1992.
Arius midgleyi This species is reported to occur in southern New Guinea and northern Australia [52] but Kailola [675] states that it is endemic to Australia. The Australian distribution extends seemingly continuously from the Fitzroy River in the Kimberley region of western Australia to the Calvert River near the Northern Territory–Queensland border [677]. This species is listed as rare in the Robertson and Calvert rivers [677], both of which drain into the southwestern portion of the Gulf of Carpentaria. Kailola and Pierce [677] intimate that A. midgleyi is present but rare in drainages between Arnhem Land and the Flinders River, but provide no locality information. It is important to note that Kailola [675] believed that the distribution of A. midgleyi and A. paucus were clearly disjunct, with the latter occurring eastward of and including the Roper River and including all rivers draining into the Gulf of Carpentaria. However, the material forming the type series contained very little material from Cape York Peninsula and the references cited by Kailola [675] to support statements about the distributional limits of A. paucus do not specifically include surveys undertaken in this region. Whilst acknowledging the fact that A. paucus may extend eastward into rivers of Cape York Peninsula, we feel it prudent to retain the name A. midgleyi for this taxon in this discussion until further evidence to the contrary becomes available.
Arius graeffei occurs in the Pioneer River [1081], and is common and widely distributed in the Fitzroy River Basin, Queensland. Berghuis and Long [160] recorded it from eight of 11 primary study sites and two of eight secondary sites, and it was the second most abundant species (after N. erebi) in gill-netting catches. Midgley found this species at nine of 15 sites in the river where its abundance varied between common and abundant [942]. The distribution of A. graeffei in the Fitzroy River Basin includes the Fitzroy, McKenzie, Don, Dawson, Isaac and Connors rivers and Princhester Creek [160, 659, 740, 942, 1274].
Arius midgleyi is widely distributed north of the Flinders River in westerly flowing rivers of Cape York Peninsula occurring in the Gilbert, Staaten, Mitchell (including its tributaries the Lynd, Walsh and Palmer rivers), Edward, Coleman, Holroyd and Archer rivers [571, 643, 677, 1186, 1349].
South of the Fitzroy River, A. graeffei has been recorded from the Boyne [1349], Kolan [232, 1349], Burnett [11, 102, 1173, 1276], Isis [1305], Mary [159, 643, 847, 1349], Noosa [1349], Brisbane [662, 1349] and Logan-Albert rivers [1349]. This species also occurs on Fraser Island [77]. Arius leptaspis This species occurs in northern Australia and southern New Guinea [52]. In north-western Australia, the distribution of this species extends from the King River in Western Australia through to the Northern Territory–Queensland border [193, 944, 945, 1304]. Arius leptaspis is widely distributed in the Alligator Rivers region occurring at 20/26 sites regularly examined by Bishop et al. [193]. Notably, A. graeffei was infrequently collected in this study and was restricted to the Nourlangie Creek system.
Arius midgleyi occurs in only two easterly flowing rivers of Cape York Peninsula, the Olive River [571] and the Normanby River [697, 1099, 1349]. Both rivers are notable for the number of species present that are more typical of rivers west of the Great Dividing Range. This species is common in the Normanby River, contributing almost 40% to the total gill-net catch, and occurs in both floodplain lagoons and the main river channel [697]. All three ariid catfishes discussed here appear to have disjunct or patchy distributions across the southern
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Freshwater Fishes of North-Eastern Australia
was about 100 m wide, a maximum of 4 m deep, with a current velocity of about 0.25 m.sec–1, with abundant macrophyte growth in shallow areas and a dominant substrate of fine silt. Greatest densities were recorded from a shallow (1–2 m) backwater area with much reduced flow, rocky substratum and little aquatic vegetation. Allen et al. [52] suggest that brooding male A. midgleyi prefer areas of deep water.
portion of the Gulf of Carpentaria region, in common with a moderate number (10–13) of other species [41]. Allen and Hoese [41] speculated that this disjunction may be a result of lower contemporary winter temperatures relative to more northern rivers and a substantial predicted drop in temperature during the Pleistocene. Kailola and Pierce [677] believed that the observed distribution pattern may equally be due to inadequate sampling effort in the region, but acknowledged that climate change during the Pleistocene may have contributed to presentday patterns of distribution.
It is not uncommon for the three species of Arius to occur in the same river (see Distribution section) and at least A. leptaspis and A. midgleyi frequently occur in the same habitat [944, 946]. Kailola and Pierce [677] suggest that A. midgleyi may be more typical of upstream reaches and is displaced upstream by A. leptaspis or A. graeffei. Allen et al. [52] also state that A. midgleyi is common in upstream reaches. Further examination of this suggestion may provide some insight into the factors that determine abundance and distribution of these species. Comparison of patterns of macrohabitat distribution in the Normanby River, which contains A. midgleyi only, with those in the Mitchell River, which contains all three species, may prove fruitful.
Macro/meso/microhabitat use Both Arius graeffei and A. leptaspis are reported to occur in freshwater and estuarine habitats [52] whereas A. midgleyi is an exclusively freshwater species occasionally occurring near the upper tidal limit [677]. Arius graeffei may penetrate into marine waters also [52, 284, 676]. Bishop et al. [193] report that A. leptaspis in the Alligator Rivers Region was common or moderately common in floodplain, corridor and muddy lowland lagoons but only occasionally occurred in perennial escarpment and sandy creek habitats. This species was widespread occurring in 20 of 26 regularly sampled study sites. Weak ontogenetic variation in habitat use was also reported for juvenile A. leptaspis with a shift from lowland muddy lagoons to floodplain lagoons and then corridor lagoons with increasing size [193]. Arius graeffei in contrast, occurred only in muddy lowland and corridor lagoons and was uncommon.
Environmental tolerances Data listed in Table 1 represent the range of ambient water quality conditions in which these catfishes occur. As such they should not be construed as representing upper and lower tolerance limits. The temperature ranges reported here are indicative of tropical or subtropical conditions. The minimum value reported here of 20.9°C for A. graeffei is lower than the 22–23°C lower limit suggested responsible for determining the distributional limits for many species in the southern portion of the Gulf of Carpentaria region [41]. Moreover, winter water temperatures in the Clarence River, where A. graeffei is reportedly common, descend as low as 15–16°C [1140]. Juvenile A. graeffei are reported to withstand temperatures as low as 10°C [936] but the lower temperature limits for A. leptaspis and A. midgleyi are unknown. Kailola and Pierce [676] believed them to be lower than 22–23°C. Low winter temperatures may play some role in determining distribution for although these catfish species may be able to tolerate temperatures of 20–23°C, they may not be able to breed at these temperatures.
The use of off-channel floodplain habitats seems typical of the three catfishes as A. midgleyi has been recorded from such habitats also [697]. The early-dry season population of A. midgleyi in floodplain lagoons of the Normanby River was dominated by fish between 200–300mm SL [697]. Such fish are probably transitional between 0+ and 1+ year classes [677] and are most likely to have invaded such habitats when water levels were high. Elsewhere A. midgleyi has been reported from fast-flowing rivers, billabongs, creeks, deep pools and desiccating waterholes [677]. This species reportedly does well in impoundments. Kailola and Pierce [677] remark that it is rarely numerically dominant except in impounded waters such as Lake Argyle on the Ord River, where it makes up about 70% of the catfish population. Arius graeffei also does well in impoundments in Queensland [1081]. Arius graeffei and A. leptaspis have also been reported from a similarly wide array of habitat types [586, 591, 940, 944, 946, 1046, 1098, 1140].
The dissolved oxygen concentrations listed in Table 1 are indicative of fairly well-oxygenated waters although hypoxic conditions may be present, especially at depth, in floodplain habitats in which A. graeffei, A. leptaspis and A. midgleyi occur. Arius leptaspis has been recorded in fish kills for which low dissolved oxygen levels (<0.1 mg.L–1) were implicated as a major cause [187].
Rimmer [1140] noted that A. graeffei was widespread in the lower Clarence River of northern New South Wales. The river where Rimmer undertook his study on reproduction
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Arius graeffei, Arius leptaspis, Arius midgleyi
Table 1. Physicochemical data for Arius graeffei, A. leptaspis and A. midgleyi. The summary provided for A. graeffei is based on a single study undertaken in Burdekin River [1098], those for A. leptaspis are based on two studies undertaken in the Northern Territory [193, 944] and those for A. midgleyi are based on two studies (data combined) undertaken in rivers of the Northern Territory [944, 946], a study in the Normanby River [1093] and a study undertaken in floodplain lagoons of the Normanby River [697]. Note that the units used to quantify water clarity differ between studies. Parameter
Min.
Max.
Mean
31 6.5 7.0 160 190
29.3 5.3 6.6 117
33 9.4 7.8 463 2.6
26.9 7.7 7.3 196 1.7
The three ariid catfishes discussed here appear to be tolerant of a moderate range of pH values although riverine populations tend to occur in neutral to slightly basic waters on average. Floodplain populations of A. leptaspis and A. midgleyi may tolerate slightly acidic conditions. Arius graeffei occurs in slightly acidic waters on Fraser Island [77]. Overall, these species appear to tolerate a range of pH. The conductivity values presented in Table 1 are all indicative of freshwaters. However, A. leptaspis and A. graeffei have both been recorded from brackish estuaries or estuaries and near shore marine habitats, respectively [52, 356], and are therefore able to withstand more saline conditions than reported here. All three species tolerate a range in water clarity, although data presented in Table 1 indicate a preference for clear waters.
Arius graeffei Alligator Rivers region Temperature (°C) 28 Dissolved oxygen (mg.L–1) 4.4 pH 6.1 Conductivity (µS.cm–1) 10 Secchi depth (cm) 15 Burdekin River ( n = 9) Temperature (°C) 20.9 Dissolved oxygen (mg.L–1) 10.8 pH 8.2 Conductivity (µS.cm–1) 790 Turbidity (NTU) 5.4
Reproduction Ariid catfishes exhibit a high degree of parental care of their young: the eggs and larvae are incubated in the buccal cavity of the male [1143]. The eggs are large (>10 mm) and relatively few in number (Table 2), traits that are typical of species exhibiting parental care. Reproductive investment (in terms of GSI values) is low in A. leptaspis but higher in A. graeffei from the Clarence River as a result of relatively greater fecundity (Table 2). The significance of this difference is unclear.
Arius leptaspis Alligator Rivers region (n = ?) Temperature (°C) 26 34 Dissolved oxygen (mg.L–1) 0.1 9.7 pH 4.8 9.1 Conductivity (µS.cm–1) 4 478 Secchi depth (cm) 1 360 Roper River (n = 4) Temperature (°C) 25 29 Dissolved oxygen (mg.L–1) 6.0 6.7 pH 7.2 8.2 Conductivity (µS.cm–1) Secchi depth (cm) 400 50
30.3 5.8 6.1
24.9 7.9 6.7 117.5 2.35
Prior to incubation, the epithelium of the buccal cavity, particularly that covering the palatal tooth patches, grows rapidly and thickens greatly, presumably to protect the eggs. In addition, epithelial structures associated with mucus production increase in number and activity and serum immunoglobulins become detectable in the mucus: both changes may confer some protective function for the incubating eggs [1143]. Feeding ceases in males during incubation. In many female ariids, including those discussed here, the pelvic fin becomes enlarged and thickened in the period leading up to spawning [1143]. Rimmer and Merrick [1143] cite several early studies in which it was believed that these structures function either to hold the eggs after they are extruded and prior to being taken into the buccal cavity by the male, or they function as ‘claspers’ enabling the copulating fishes to remain in very close proximity. The exact means by which the eggs are fertilised prior to buccal incubation has not been observed.
26.3 3.8 7.3 297.9 12.8
Gonadal enlargement is rapid in A. graeffei from the Clarence River and occurs within a rapidly short period (September to November): the spawning season appears to be similarly contracted (November to December) and synchronised year-to-year [1140]. Gonad development in
76 26 6.4 7.8 170
Arius midgleyi Roper and Victoria rivers (n = 17) Temperature (°C) 23 29 Dissolved oxygen (mg.L–1) 3.0 9.5 pH 7.0 8.7 Conductivity (µS.cm–1) Secchi depth (cm) 50 500 Normanby River (n = 4) Temperature (°C) 24 26 Dissolved oxygen (mg.L–1) 7.2 9.2 pH 6.2 7.16 Conductivity (µS.cm–1) 92 150 Turbidity (NTU) 0.1 5.4 Normanby River floodplain (n = 15) Temperature (°C) 22.9 33.4 Dissolved oxygen (mg.L–1) 1.1 7.1 pH 6.0 9.1 Conductivity (µS.cm–1) 81 412 Turbidity (NTU) 2.1 120
25.8 7.2 8.1 242
107
Freshwater Fishes of North-Eastern Australia
A. leptaspis from the Alligator Rivers region [193] occurs over a similarly well-defined period but peak GSI values differed in incidence from year-to-year. Spawning may be more protracted than that seen in A. graeffei however [193]. Arius midgleyi may breed slightly earlier than A. leptaspis or A. graeffei. In Lake Argyle on the Ord River, stage II to IV and stage V females of A. midgleyi are present in July and September, respectively [677]. Kailola and Pierce [677] cite a personal communication from Hamar Midgley that early breeding may occur in rivers also. Arius midgleyi is reported to have a faster growth rate than other northern ariid catfishes and may reach 200–300 mm in length in the first year. All three species breed prior to the onset of the wet season, perhaps stimulated by increasing temperature and daylength, and this may allow young to take advantage of the enhanced production, particularly of small fish species, that occurs during the wet season. A slightly earlier spawning season and faster growth may enable A. midgleyi to predate other sympatric ariid species as well as other fish species.
small-scale movement to deeper water during the incubation phase [677]. However, the fact that Kennard [697] collected large numbers of individuals in floodplain habitats of the Normanby River soon after the cessation of the wet season suggests that this species undertakes extensive lateral (and probably longitudinal) movements onto the floodplain during periods of floodplain inundation. Moreover, movement appears to be an integral component of the life history of other ariid catfishes [1143] and particularly of A. graeffei. This species is frequently recorded in fishway studies and is often dominant in such studies [11, 157, 158, 159, 232, 740, 1173, 1274, 1276, 1305]. Upstream movement by A. graeffei through the fishway on the Fitzroy River barrage occurs over a wide range of conditions and throughout the year [1274]. Water temperature range from 18–29°C but fish mostly moved when water temperatures exceeded 23°C and very large numbers (>1000 fish.day–1) were observed in the fishway when water temperature exceeded 27°C. This species migrated upstream over a wide range of discharge (18–195 757 ML.day–1) but highest numbers were recorded at times of low flow (1% exceedance). Stuart [1274] estimated that up to 12.2 t of A. graeffei moved through the Fitzroy River fishway per month and that the highest capture rates coincided with the highest tides for each month. This species used the fishway more at night than during the day and smaller fish were less able to ascend the fishway than larger fish. An earlier study on this structure also reported that upstream migration occurred throughout the year but was greatly reduced in July/August [740].
The exact location of spawning is unknown for these ariid species although males are reported to congregate in deeper water during incubation. Spawning behaviour remains undescribed but vigorous pursuit of males by females has been reported for a related species [1143]. Coates [314] reported that an observed positive relationship between egg size and female length, and of embryo size and male length, in New Guinean ariid catfishes, was suggestive of non-random mating and positive assortment on the basis of size. This seems plausible given that only large males could accommodate very large egg masses within their buccal cavities.
A similar study in the Burnett River revealed that A. graeffei ascended the fishway located on the tidal barrage from January to May over a temperature range of 29°C to 22°C, respectively, and over a range of discharge from 0 to 300 ML (mean daily flow averaged over each month). Peak numbers were recorded in May. Fish descended the fishway over the same period [1173]. Further upstream, A. graeffei also migrated up the fishway on the Ben Anderson Weir [1276]. They did so over a range of flow conditions (1–94% exceedance flows) but mostly during times of low flow. It migrated throughout the year except in the coldest months, July and August.
The eggs and developing young are held within the distended male buccal cavity for an extended period: the young to hatch at an advanced state of development with a functional alimentary canal and feeding structures [193, 1142]. Feeding on plankton while in the parent’s mouth commences shortly after hatching; the observation that A. graeffei juveniles increase in weight by 20% in the interval between hatching and the cessation of buccal incubation suggests that substantial feeding occurs during this phase. Hatching difficulties under in vitro culture conditions associated with herniation of the chorion have been reported to lead to high mortality (up to 90%) for A. leptaspis [936] and A. graeffei [1142] but have not been observed in naturally incubated embryos [1142] possibly because the male frequently churns the eggs within the buccal cavity at the time of hatching [1144].
Upstream movement of A. graeffei of between 200–350 mm length (but dominated by fish between 200–250 mm) through the fishway on the Kolan River barrage was attempted mostly in spring and summer over a range of conditions [232]. A weak positive relationship between discharge and movement was recorded (r2 = 0.103, p<0.05), however, this relationship was dominated by two large peaks in movement recorded at flows of 200 and 5500 ML.day–1. Ignoring these two events, more fish moved at times of low flow.
Movement The limited information available on the biology of A. midgleyi does not suggest extensive migration other than 108
Arius graeffei, Arius leptaspis, Arius midgleyi
Table 2. Life history information for three species of ariid catfish. Summary information for A. graeffei is based on Rimmer [1140, 1141] and Bishop et al. [193], that for A. leptaspis is based on Bishop et al. [193], and that for A. midgleyi on Kailola and Pierce [677] unless otherwise noted. Age at sexual maturity (months)
A. leptaspis – 24 months A. midgleyi – 36 months (estimate only)
Minimum length of ripe females (mm)
A. graeffei – 280–285 mm (length at first maturity, i.e. 50% of population mature) A.leptaspis – 300 mm (length at first maturity, i.e. 50% of population mature) A. midgleyi – 500 mm
Minimum length of ripe males (mm)
A. graeffei – 270–275 mm (LFM) A.leptaspis – 270 mm CFL (LFM), some precocious males 187–240 mm CFL
Longevity (years)
A. leptaspis – possibly up to 5 years
Sex ratio
A. graeffei – 1:0.82, males in excess A.leptaspis – generally 1:1, although males or females in excess on occasions
Peak spawning activity
A. graeffei – November, peak in GSI values pronounced, late wet/early dry season in Northern Territory A. leptaspis – late dry/early wet season, precedes flooding A. midgleyi – September–October (estimate only)
Critical temperature for spawning
A. graeffei – 26°C A. leptaspis – 26°C [936]
Inducement to spawning
A. graeffei – possibly temperature and increasing photoperiod (>13.7 h) A. leptaspis – ?, not cued by flooding
Mean GSI of ripe females (%)
A. graeffei – 12–16% A. leptaspis – 4.3 ± 2.6% (SD)
Mean GSI of ripe males (%)
A. graeffei – 0.28% maximum A. leptaspis – <1%
Fecundity (number of ova)
A. graeffei – 40–122, average 70.5. Brood size 1–83 A. leptaspis – 26–70, average 42. Average brood size 28 A. midgleyi – 100–180, possibly as high as 400
Fecundity/length relationship
A. graeffei – F = 0.478 (SL in mm) – 81.6; n = 40, r = 0.89, p<0.001
Egg size (mm)
A. graeffei – 11–13.7 mm, average 12.2 mm, fertilised eggs 12.3–15.2 mm A. leptaspis – 11.9–15.7 mm, average 13.8 mm A. midgleyi – 10 mm
Frequency of spawning
A. graeffei – spawning season short, females total spawners A. leptaspis – spawning season may be protracted
Oviposition and spawning site
A. leptaspis – unknown but ripe fish found in most lagoon habitats
Spawning migration
A. graeffei – may move into deeper water to breed A. leptaspis - ? A. midgleyi – may move into deeper water to breed or incubate
Parental care
A. graeffei – buccal incubation and extensive parental care A. leptaspis – buccal incubation and extensive parental care A. midgleyi – buccal incubation and extensive parental care
Time to hatching
A. graeffei – 4–5 weeks A. leptaspis – 4 weeks, 2–4 weeks at 32°C [936]
Length at hatching (mm)
A. graeffei – 20–27 mm TL A. leptaspis – 24 mm CFL, juveniles up to 60 mm CFL remain in buccal cavity A. midgleyi – ?
Length at feeding
A. graeffei – shortly after hatching 20–27 mm TL
Age at first feeding
A. graeffei - feeding occurs shortly after hatching [1143] A. leptaspis – feeding occurs shortly after hatching [1143]
Age at loss of yolk sac
A. graeffei – 6–8 weeks A. leptaspis – 6–8 weeks [936]
Duration of larval development
A. graeffei – 6–8 weeks A. leptaspis – 6–8 weeks [936]
Length at metamorphosis (mm)
A. graeffei – 50 mm A. leptaspis – 50–60 mm
109
Freshwater Fishes of North-Eastern Australia
A consistent observation in the fishway studies cited above is that the number of fish able to reach the top of the fishway is lower than the number entering at the bottom, and that only the largest fish appear to be able to ascend these structures [11, 232, 1274, 1276]. Despite the presence of fishways on some tidal barrages and weirs, catfish migrations are impeded in some rivers [157, 1305]. A common feature of almost all fishway studies, with the exception of Russell [1173], is that they provide information on upstream movement only. Complementary information on the reproductive status of migrating fishes is rarely gathered and there is limited potential to examine why fish are migrating.
A. graeffei (juveniles) n = 186 Fish (4%) Microcrustaceans (14%) Unidentified (34%)
Macrocrustaceans (10%)
Terrestrial invertebrates (5%) Other macroinvertbrates (25%)
Detritus (3%) Aquatic macrophytes (5%) Filamentous algae (1%)
A. graeffei (adults) n = 116 Fish (12.4%) Unidentified (27%) Macrocrustaceans (17.2%)
Rimmer [1140] cites studies [403] suggesting that estuarine or near-shore marine populations of A. graeffei migrate upstream into freshwaters to spawn. The fishway studies cited above contain many fishes that are, judging by their size, large enough to reproduce. However, the fact that migrations occur over a much longer time frame than the short spawning period reported by Rimmer [1140] indicates that some impetus other than reproduction stimulates movement.
Molluscs (0.5%)
Terrestrial invertebrates (9.4%)
Aquatic insects (6.4%) Filamentous algae (11.6%) Aquatic macrophytes (3.8%)
Terrestrial vegetation (10.4%) Detritus (1.4%)
A. leptaspis n = 633 Fish (15.3%) Unidentified (26.4%) Macrocrustaceans (13.5%)
Arius leptaspis has not been recorded from fishways and little is known of its movement biology except that that it disperse widely in the Alligator Rivers region [193]. Given that this species occurs in estuarine habitats, there is probably significant movement between this habitat and upstream areas.
Terrestrial invertebrates (6.2%) Terrestrial vertebrates (1.3%) Aquatic insects (20.7%) Filamentous algae (1%)
Terrestrial vegetation (12.4%) Detritus (0.9%) Aquatic macrophytes (2.4%)
A. midgleyi n = 109
Trophic ecology Information on the trophic ecology of A. graeffei, A. leptaspis and A. midgleyi is drawn from several sources. Sumpton and Greenwood [1279] examined the diet of juvenile (<100 cm TL) A. graeffei in the estuary of the Logan-Albert River. These data and dietary information from studies undertaken in the Barker-Barambah system, a tributary of the Burnett River, (n = 53) [1080], the Burdekin River (n = 25) [1093] and Nourlangie Creek, in the Alligator Rivers region (n = 38) [193] were used to summarise the adult diet. Information on the diet of A. leptaspis was sourced entirely from Bishop et al. [193]. Information on the diet of A. midgleyi included data from riverine (n = 8) [1099] and floodplain lagoon populations (n = 101) [697] of the Normanby River.
Unidentified (11.9%)
Terrestrial invertebrates (16%) Fish (47%) Terrestrial vertebrates (3%)
Macrocrustaceans (8.3%)
Terrestrial vegetation (4.9%) Detritus (1.4%) Aquatic macrophytes (1.4%) Filamentous algae (1.4%) Aquatic insects (4.3%)
Figure 2. The average diet of three species of fork-tailed catfish. See text for data sources.
that piscivory is acquired early in life. Plant material is only a minor component of the diet, as are terrestrial insects. The diet is notable for its diversity, including plant, invertebrate and vertebrate food, the diversity of feeding styles employed and the wide array of habitats from which it is procured (i.e. benthos, water column and water surface).
Juvenile A. graeffei in estuarine reaches of the LoganAlbert River consume a wide variety of food types, but particularly polychaete worms (expressed as other macroinvertebrates in Figure 2). Planktonic microcrustacea and shrimps and prawns were also important, collectively comprising 39% of the total diet. Although fish were only a minor component of the diet it is interesting to note
The diet of adult A. graeffei is similarly diverse but differs from that of juveniles by an increased consumption of fish, plant matter (both aquatic and terrestrial), macrocrustacea and terrestrial invertebrates. Such changes are not
110
Arius graeffei, Arius leptaspis, Arius midgleyi
unusual for northern Australian fishes of large size. Geographic differences in diet were moderately large, involving differences in the relative importance of particular food types and changes in foraging style. For example, A. graeffei from Barker-Barambah Creek consumed macrophytes and algae (8% and 24%, respectively) whereas these food types were absent from, or contributed less than 3% to, the diet of fish from the Burdekin River [1093] or the Alligator Rivers region [193]. Similarly, terrestrial vegetation was either absent from, or unimportant (<5%) in, the diet except in those fish from the Alligator Rivers region where this food type contributed 22% to the total. Fish were a minor component of the diet of fish from Barker-Barambah Creek (5%) but important in the Burdekin River and the Alligator Rivers region (12% and 22%, respectively). Macrocrustacea varied similarly in importance (5%, 39.5% and 19.6% for Barker-Barambah Creek, the Burdekin River and the Alligator Rivers region, respectively).
of these species ensures that most populations are secure. Some authors have expressed concern about the impact of dams and weirs on populations of A. graeffei in south-eastern Queensland [157, 1305] and despite their abundance in fishway structures, smaller size classes appear less able to negotiate these structures [11, 232, 1274, 1276]. Dissociation of freshwater habitats from estuarine reaches may have consequences for the maintenance of populations of A. graeffei and A. leptaspis populations in some rivers. These species are clearly warm-water fishes: impoundments that alter a river’s thermal regime are likely to impact on this species, particularly those rivers in the south-eastern portion of the range of A. graeffei where its lower thermal tolerance may be just above winter minima. River regulation reducing flood frequency and magnitude and hence floodplain inundation, or restricting movement between floodplain habitats and the main channel, is likely to impact on this species. Degradation of floodplain habitats is highly likely to impact on these catfishes, and this effect is already visible in the Burdekin River delta where reductions in the extent and integrity of riparian forests and poor water quality are correlated with the absence of A. graeffei (C. Perna, pers. comm.).
The average diet of A. leptaspis is not greatly different from that of A. graeffei (Fig. 2). However, comparison of the diet of these species in the Alligator Rivers region suggests more extensive partitioning of resources. For example, A. leptaspis consumed more fish and macrocrustaceans, less terrestrial plant material and more aquatic insect larvae than did A. graeffei. Nonetheless both species are macrophagic omnivorous feeders. The diversity of fish species consumed by A. leptaspis is very high, including neosilurid catfishes, Porochilus rendahli, Melanotaenia spp., Ambassis spp., Leiopotherapon unicolor, Toxotes chatareus, Glossogobius giuris, Hypseleotris compressa, Oxyeleotris lineolatus, Strongylura krefftii, Nematalosa erebi and conspecifics.
Despite the potential for water infrastructure to impact on these catfishes, A. graeffei and A. midgleyi do well in impounded waters, and in some circumstances, so well that a commercial fishery is supported (e.g. Lake Argyle on the Ord River). Elsewhere, ariid catfishes appear in the bycatch of near-shore and estuarine fisheries and are frequently amongst the most abundant species in the bycatch. In a study of the effects of netting on non-target fishes, comparison of relative abundance and biomass of ariid catfishes revealed that although the relative abundance varied little (7.8% versus 9.7% for open and closed rivers, respectively), ariid catfishes comprised 25% of the biomass in rivers closed to fishing compared to 13% in rivers open to commercial netting. Notably however the total fish biomass in rivers open to commercial fishing was greater (across all rivers, regions and seasons) than in closed rivers [501].
Fish comprised about half of the diet of A. midgleyi in both riverine and floodplain habitats of the Normanby River (Fig. 2); a finding in close agreement with the observation by Kailola and Pierce [677] that this species is primarily carnivorous. The remainder of the diet is dominated by terrestrial invertebrates and macrocrustacea, supporting other observations that these items are important in the diet [677, 944]. Terrestrial vegetation, detritus and aquatic plant matter are far less important in the diet of A. midgleyi than in either A. leptaspis or A. graeffei.
The southern limit of the distribution of A. graeffei appears to have contracted northward in the last two decades and populations in northern New South Wales appear to have declined in abundance, the reasons for which are unclear but may signal a general decline in the health of these rivers.
Conservation status, threats and management Arius leptaspis, A. graeffei and A. midgleyi are all listed as Non-Threatened [1353]. The wide northern distribution
111
Neosilurus hyrtlii Steindachner, 1867 Hyrtl’s tandan
37 192011
Family: Plotosidae
tapering posteriorly. Predorsal distance 24–30% of TL. Dorsal spine stout, slightly curved, weakly serrated on inside edge, occasionally serrate on both sides [1304]. Pungent spine on pectoral fins more strongly serrated on inside edge. Dorsal profile straight or slightly convex. Premaxilla with small sub-ovate patch of pointed teeth on either side of the midline; palatine teeth only slightly larger with mixed molariform and conical teeth arranged in a small triangular patch; teeth in lower jaw conic anteriorly, molariform posteriorly. Gill rakers on anterior face of first arch slender; anterior face of second arch with large papillae-like rakers, broad at base grading into transverse ridges; posterior face of first arch with two rows of papillae, the anterior row noticeably larger; transverse ridges on posterior face of second arch and anterior face of third arch longer than arch width, slightly overlapping the base of the gill filaments.
Description First dorsal fin: I, 5–6; Second dorsal and anal fins confluent with caudal fin, 115–135 rays; Pectoral: I, 10–11; Pelvic: 12–14; Gill rakers: 19–24 [34, 1304]. Figure: mature specimen 185 mm SL, upper Burdekin River, April 1995; drawn 2001. A moderately large species of catfish, commonly reaching 300 mm SL but more commonly between 100–200 mm SL. Largest specimen collected from the Burdekin River was 454 mm SL [1093]. The largest specimens collected by Bishop et al. in the Alligator Rivers region were about 400 mm TL [193]. Merrick and Schmida [936] list maximum weight as 2.0 kg, far greater than maximum weight recorded by us (920 g) [1093]. The relationship between length (mm SL) and weight (g) for Neosilurus hyrtlii from the Burdekin River is W = 4.786 x 10–6 L3.11, r2 = 0.990, n = 251, p<0.001. Sexual dimorphism is limited: females grow to larger size than males and possess a thick and rounded genital papilla, in contrast to a conical pointed papillae characteristic of male fish [1030].
Colour in life: variable depending on location, age and water clarity. Small specimens are frequently (although not always) silver laterally with bright to dull yellow fins. This colour form, frequently referred to as N. glencoensis, is rarely observed in fish greater than 200 mm SL. Larger specimens are most commonly a dark brown/grey dorsally grading to white on ventral surface of body and head with
Head broad, slightly flattened, possessing four pairs of barbels. Nasal barbels barely reaching beyond eye, mental barbels reaching to gill opening. Snout obtusely pointed and wider than long. Eye set in front half of head. Body 112
Neosilurus hyrtlii
Queensland estuaries and near-shore marine habitats. The family contains approximately 31 species in 10 genera [48]. Five genera occur in freshwaters of Australia: Tandanus (2 spp. but see comments in appropriate section); Neosiluroides (1 sp.); Anodontoglanis (1 sp.); Porochilus (3 spp.) and Neosilurus (6 spp. although more may be present) [48, 936, 1042]. Merrick and Schmida [936] list nine species of undescribed Neosilurus, Allen [34] lists three, and no undescribed species were included in Allen et al. [52]. However, Allen et al. [52] remark that further research on the many geographic populations of N. hyrtlii is needed as there is a strong possibility that the nominal species may be composed of more than one taxon.
dorsal fin and joined dorsal/caudal/anal fin being dark brown/black (rarely yellow). Pectoral and anal fin greyishwhite. Specimens from highly turbid waters show little colour except a dull grey [1093]. During spawning, both sexes are a bright silvery-white laterally and on the head, and the fins are a bright vivid yellow [1030]. Colour in preservative: yellow pigments typically lost, body brown/grey to pale tan, white ventrally. Neosilurus hyrtlii and N. ater are frequently syntopic in many river systems and in some rivers other plotosid catfishes may also be collected from the same habitat (i.e. N. mollespiculum and P. rendahli in the Burdekin River). These latter two species are easily distinguished due to possession of unique morphological characters (see respective chapters). Taylor [1304] provides a key distinguishing several species of neosilurid catfish and the couplet separating N. ater and N. hyrtlii (listed as N. glencoensis) is reproduced here:
Neosilurus hyrtlii, the type species for the genus, was first described by Steindachner in 1867 from material collected in the Fitzroy River, Queensland [1262]. Synonyms are numerous and include Silurichthys australis Castelnau, 1875; Neosilurus australis Castelnau, 1878; Eumeda elongata Castelanu, 1878; Neosilurus robustus Ogilby, 1908; Copidoglanis glencoensis Rendahl, 1922 and N. mortoni Whitley, 1941. Reference to this species under the names N. glencoensis, Tandanus hyrtlii and T. robustus may be found also, the former being the most common.
Second dorsal short, 24–37 rays to middle of caudal fin, length from origin to tip of caudal fin 20–30% SL, head length 17–21% SL, posterior face of first gill arch with two rows of papillae, snout shorter than post-orbital length of head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .N. hyrtlii Second dorsal long, 39–52 rays to middle of caudal fin, length from origin to tip of caudal fin 30–40% SL, head length 21–25% of SL, posterior face of first gill arch with only a single row of papillae, snout longer than post orbital length of head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .N. ater
Distribution Neosilurus hyrtlii is extremely widely distributed and can attain high levels of abundance. It occurs in the Pilbara region from the Ashburton River north [33, 936] and has been recorded from most major rivers of the Kimberley region (Charley, Lawley, Fitzroy, Meda, Isdell, Carson, Berkely, King Edward, King George, Mitchell, Roe, Prince Regent, Drysdale, Berkley and Ord rivers) [30, 45, 388, 619, 620]. This species is widely distributed in the Northern Territory from the Daly River across to Arnhem Land [193, 243, 772, 774, 1304].
Systematics Plotosidae is a family of catfishes within the order Siluriformes, a large group (~2500 spp.) of predominantly freshwater species that occurs on all continents except Antarctica. Other notable families within the Siluriformes include the Bagridae, Clariidae, Loricariidae, Ariidae and Siluridae. Some members of these families are among the largest of freshwater fishes. The Ariidae and Plotosidae are the only siluriforms that occur naturally in Australia or New Guinea. The Plotosidae includes both marine/estuarine and freshwater forms and is distributed in the IndoWest Pacific from Japan to Australia and east to Fiji [52]. Generic boundaries and affinities remain obscure [48] and the family is currently being revised. Marine forms are distinguished by the presence of a dendritic organ protruding from behind the anus. This organ is also present in one genus of New Guinean freshwater plotosid (Oloplotosus). Australian and New Guinean genera tend to be restricted to freshwater. Plotosus is an exception, with three species occurring in estuarine or marine waters and one species (P. papuensis Weber) occurring in freshwater. Plotosus lineatus (striped catfish) is common in
Bishop et al. [193], in their extensive study of the fish fauna of the Alligator Rivers region, found that N. hyrtlii was widespread and abundant, occurring in escarpment pools and streams (3/10 sites), lowland sandy creek-bed pools (1/7 sites), back flow billabongs (10/11 sites), corridor billabongs (2/7 sites) and floodplain billabongs (2/6 sites) and contributing 11.4, 0.3, 1.3, 0.1 and 0.1% of the total number of fish collected from these sites, respectively. Over the period of the study, N. hyrtlii contributed 3.2% of the total number of fish collected. Overall, it was present in all major habitat types in this region but was abundant only in escarpment habitats and in these habitats, abundant only in the early and late dry seasons when escarpment habitats function as important dry season refugia. Woodland and Ward [1416] recorded N. hyrtlii (grouped with N. ater and possibly P. rendahli as ‘plotosid
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Freshwater Fishes of North-Eastern Australia
Tully, Maria and Herbert river drainages [583, 584, 585, 599, 643, 1085, 1087, 1096, 1179, 1184, 1187, 1349]. This species rarely achieves high levels of abundance in these systems however. For example, it was ranked 51st of more than 60 species in the extensive survey of Pusey and Kennard (comprising only 0.01% of the total number of fish collected) [1085] and was ranked 18th and 27th in the South Johnstone and Mulgrave rivers, respectively, where it contributed 0.1% of the collective total from these rivers [1096]. Neosilurus hyrtlii has also been recorded from floodplain lagoons in the Wet Tropics region [585, 1131].
catfishes’) as moderately abundant in isolated pools in Magela Creek. The presence of this species was persistent through time as the pools contracted during the dry season, and unlike some other species, local extinctions of this species were not observed. Castelnau [287] included Plotosus elongatus among the fauna of the Norman River in the Gulf of Carpentaria region. Castelnau had previously used this name for Tandanus tandanus, however [283], a species not found in the Gulf region. From his description, it is most likely that he was alluding to N. hyrtlii and N. ater. We have recorded this species from Gunpowder Creek, a tributary of the Leichhardt River [1093]. Neosilurus hyrtlii is widely distributed in drainages entering the Gulf of Carpentaria [34].
Further to the south, N. hyrtlii occurs in the Black-Alice [176, 1349], Ross [1030] and Burdekin rivers [1098]. In a three-year study (1989–1992), this species contributed 6.1%, 1.0% and 2.9% of electrofishing, seine-netting and gill-netting catches and was the 5th, 6th and 6th most abundant species, respectively [1098]. It is widespread in this river system, being recorded from the main channel, upstream and downstream of the Burdekin River Falls; in the northern tributary streams, such as Keelbottom Creek, Fanning River, Star River and Running River; as well as the turbid south-western tributaries such as the Belyando River [256, 260, 1098, 1349, 1408] and floodplain lagoons of the delta area (C. Perna, pers. comm.). In the Belyando River, N. hyrtlii was recorded from four of five sites and comprised 37.6% of the total catch (gill-, dip- and seinenetting, fish traps and electrofishing) [256].
Neosilurus hyrtlii also occurs in the internal drainages of central Australia and has been recorded from the Georgina, Diamantina, Cooper, Bulloo and Finke rivers [34, 455, 456, 457, 605, 1341, 1349]. This species occurs in the Paroo and Warrego rivers, tributaries of the Darling River [605, 1069, 1201] and in the Condamine River [1069]. In a recent survey of the Cooper, Barcoo, Georgina and Diamantina drainages, N. hyrtlii was recorded from 11 of 12 sites and comprised 17.8% of the catch from these sites [121]. Neosilurus hyrtlii has been recorded from the Embley, Dulhunty, Jardine, Wenlock, Archer, Edward, Holroyd, Mitchell, Palmer and Coleman rivers and Kupandhanang Swamp near Weipa on the western side of Cape York Peninsula [571, 643, 991, 1349]. On the eastern side of Cape York Peninsula, this species has been recorded from the Olive, Lockhardt, Claudie, Stewart, Massey Creek, Rocky, Normanby, McIvor and Endeavour drainages [571, 697, 1093]. Neosilurus hyrtlii comprised 0.8% of the electrofishing catch and 1.3% of the gill-netting catch from floodplain lagoons of the Normanby River (being recorded from 6 of 6 lagoons), but was more abundant in gill-netting catches from the main river channel itself (3.4% of catch) [697]. This species is widespread in the Normanby River, (occurring in all 13 sites examined) extending well upstream into the headwaters. It may achieve greater abundances in the river channel (4.4% of the total catch [1093]) than in floodplain lagoons [697]. This species was even more abundant in the more ephemeral Stewart River were it comprised 8.1% of the total fish catch and was recorded from four of five sites [1093].
Neosilurus hyrtlii has been recorded from the Pioneer River [1081], drainages discharging into Shoalwater Bay [1328, 1349], most tributary systems of the Fitzroy River (its type locality) including the highly intermittent Isaacs River [160, 283, 284, 1093, 1274, 1349], the Burnett [205, 700, 1173, 1276], Elliot [700], Isis [700, 1305], Calliope [915] and Kolan rivers [232, 1328], Baffle Creek [826], and even in some freshwater lakes of Fraser Island [77]. It is not common in these southern rivers, however. For example, N. hyrtlii comprised only 0.07% of the catch from a total of 203 samples from 63 sites in the Burnett River [700]. Neosilurus hyrtlii has been recorded from the Mary River [1093, 1349] but is uncommon in this system where it was recorded from only six of 50 locations sampled over the period 1994–1997 (a total of 225 samples) and comprised only 0.07% of the 83 198 fish collected. It was persistent at those sites in which it occurred however and contributed an average relative abundance of 1.01 ± 0.15% of the total at these sites. Mean (±SE) and maximum densities were 0.135 ±0.029 fish.10m–2, respectively. Average and maximum biomass densities at these sites were 2.25 ± 0.45 g.10m–2 and 12.4 g.10m–2, respectively, comprising on average, 0.23 ± 0.06% of the total biomass [1093].
Neosilurus hyrtlii is widely but patchily distributed in the high-gradient, swiftly flowing rivers of the Wet Tropics region, being thus far recorded from the Endeavour, Annan, Daintree, Barron, Mulgrave/Russell, Johnstone,
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within a single season. Use of such habitats by small juveniles may extend over several flood events.
Despite being recorded from the Brisbane River in the past [662], it has not been detected in a recent survey of 111 separate locations (a total of 165 samples) throughout the catchment [704, 1093]. Similarly, it has not been detected in recent surveys in the Albert/Logan River (68 locations, 174 samples). Thus, its southern limit on the east coast appears to be the Mary River. It was not recorded in the extensive surveys of the northern coastal rivers of NSW undertaken as part of the NSW Rivers Survey [1201].
While the information presented above for the Normanby River suggests that N. hyrtlii is more abundant in riverine rather than off-channel lentic habitats, this species has frequently been reported from floodplain and wetland habitats across its range. Neosilurus hyrtlii is a benthic species found over a wide range of water depths and most frequently observed in close association with the substrate. During the day, adult N. hyrtlii tend to be confined to deeper waters (>2 m) although when cover in the form of woody debris or undercut banks is abundant, adult fish may be found in much shallower waters (40–60 cm). At night, the extent of dendency on cover is much reduced and adult N. hyrtlii may be observed foraging over sandy open reaches as shallow as 30 cm [1093]. In the Burdekin River, very small juveniles (<60 mm) are common in sandy glides as shallow as 5 cm. In such cases, fish are invariably sheltering under leaf litter (often single isolated leaves), macrophytes or mats of colonial blue-green algae (Gloeotrichia sp.). Adult N. hyrtlii are frequently observed foraging singly at night but just as frequently observed foraging in small shoals. It is not uncommon when gill-netting at night to collect 20 to 30 similarly sized individuals in one net but few in other nets. Underwater observations by us reveal that shoaling is very common in juvenile N. hyrtlii (<20 cm SL). Shoals may contain up to 100 individuals (although 40 to 50 is more common) and rather than being well-coordinated cohesive groups, such shoals are best characterised as a rolling ball of fish constantly being joined or left by individuals for varying lengths of time. Although N. hyrtlii is occasionally recorded from reaches with coarse substrates, it is most frequently collected from areas with a muddy or sandy substratum. It is essentially a still-water species, although it is capable of ascending reaches with substantial water velocities. Its benthic habit probably ensures that velocities experienced are much less than average water velocities. We have observed, on one occasion, an adult N. hyrtlii moving through a rapid/run section with an average water velocity of about 0.5 m.sec–1. Passage was affected by a series of short bursts between isolated woody debris or root masses. Once such cover was accessed, the pectoral fins were extended and apparently locked in this position, anchoring the fish in place for several minutes, after which another upstream sortie was made.
In summary, N. hyrtlii is extremely widely distributed and its distribution closely matches that of other very widespread species such as L. unicolor, A. percoides and N. erebi. Although present in the perennial rivers of the Wet Tropics region, it is rarely abundant. Neosilurus hyrtlii achieves its greatest abundance in more seasonal, low gradient rivers such as the Burdekin and Normanby rivers. In part, its distribution is probably limited by its tolerance to low water temperatures, much the same as is reported for L. unicolor. Herbert et al. [571] include it amongst a large group of species from Cape York Peninsula characterised as ‘colonising species’. Macro/meso/microhabitat use It should be evident from the discussion above that N. hyrtlii occurs in a wide variety of macrohabitats ranging from small permanent or intermittent tributary streams through large lowland low gradient seasonal rivers of Cape York Peninsula and central Queensland, to high gradient perennial rivers of the Wet Tropics region, to floodplain lagoons and wetlands typical of many rivers of northern Australia. Thus, from a macrohabitat perspective, N. hyrtlii makes use of virtually every aquatic habitat available within a river with the exception of the estuarine reaches. It also use dune lakes [77]. Habitat use varies with season and age in the Alligator Rivers region [193]. Over all sampling occasions, Neosilurus hyrtlii was recorded from all muddy lowland lagoons sampled, some sandy lowland creeks, and corridor and floodplain lagoons. However, this species was recorded from sandy creeks only during the late dry season whereas in the late wet/early dry seasons, N. hyrtlii was recorded from lowland lagoons, floodplain lagoons and perennial streams of the escarpment. Juveniles were mainly found in lowland lagoons and sandy creeks. In contrast to the downstream and lateral movements reported by Bishop et al. [193], Orr and Milward [1030] reported upstream spawning migrations of N. hyrtlii in Campus Creek, a tributary of the Ross River, Townsville. Use of such habitats by adult fishes is transitory and limited to the spawning period, however, several spawning runs associated with separate flood events may occur
Environmental tolerances Experimental data concerning the environmental tolerances of this species are lacking. Data presented in Table 1 are derived from field studies and represent the range of conditions in which N. hyrtlii has been found.
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be more tolerant of lower temperatures as winter temperatures as low as 8°C have been recorded in the Finke River [767]. Northern populations may not tolerate temperatures below 20°C. Low water temperatures probably play an important role in limiting the southern distribution of N. hyrtlii.
Neosilurus hyrtlii occurs predominantly in warm waters as would be expected given its distribution. The maximum water temperature in which N. hyrtlii has been recorded is 38°C (waterholes of Cooper Creek) [121] and similarly high temperatures (36°C) have been recorded in the Alligator Rivers region (Table 1). This species clearly tolerates temperatures in the mid-30s for extended periods.
Neosilurus hyrtlii is found over a wide range of dissolved oxygen (DO) levels. The average dissolved oxygen concentration in the three lotic studies included above (Cape York Peninsula, Burdekin River and Mary River) are all close to saturation and range from 7.5 to 8.7 mg O2.L–1. In contrast the remaining studies listed in Table 1 (Alligator Rivers region and Normanby River floodplain lagoons) dealt largely or entirely with lentic habitats and it can be seen that average dissolved oxygen levels experienced by N. hyrtlii in such habitats are substantially lower and on occasions very much lower (<1.2 mg O2.L–1). Hogan and Graham [583] recorded N. hyrtlii in a lagoon of the Tully floodplain in which DO was as low as 0.35 mg O2.L–1. Perna (pers. comm.) recorded N. hyrtlii in floodplain lagoons of the Burdekin River delta in which average DO levels were 42% saturation but for which occasional minimum saturation levels plummeted to 0.2%. From these data it is obvious that N. hyrtlii is tolerant of hypoxic conditions. Nonetheless, Bishop [187] recorded N. hyrtlii (as Neosilurus sp. B) among the dead in a large fish kill for which hypoxia was suggested to be the primary cause. The effects on growth and reproduction that might arise from long-term exposure to levels of between 1.5–3.5 mg O2.L–1 or whether such profoundly depressed DO levels are inimical to eggs, larvae and small juveniles are unknown. Given that reproduction in many areas appears concentrated in seasonally flowing streams, it is probable that these early life stages are intolerant of grossly depressed dissolved oxygen levels. Johnson [666] reported large fish kills involving N. hyrtlii in inland Queensland waters in the first two decades of the 20th century. Such kills were invariably associated with the winter low-flow period and Johnson attributed the cause of these kills to infection by the fungal pathogen Saprolegnia. It is probable that low water temperatures and the poor water quality (particularly low dissolved oxygen) existing at the time and remarked upon by Johnson [666] were also important.
With the exception of the Mary River, minimum water temperatures in sites in which it has been recorded are between 21 and 23°C. The minimum temperature recorded for the Mary River population is much lower than this, as is the average temperature in this river. It is likely that 12°C closely approximates the lower limit for this species, although populations in inland drainages may Table 1. Physicochemical data for Hyrtl’s tandan Neosilurus hyrtlii. Turbidity values are listed as NTU except for the Alligator Rivers region (ARR) where they are listed as Secchi disc depths in cm. Data listed for the ARR were from readings taken from the bottom of the water column. Elsewhere, they are derived from the midpoint of the water column. n refers to the number of samples. Parameter
Min.
Max.
Alligator Rivers region [193] Temperature (°C) 23 36 Dissolved oxygen (mg.L–1) 1.0 9.7 pH 5.2 7.3 Conductivity (µS.cm–1) 4 620 Turbidity (cm) 1 170 Cape York Peninsula (n = 8) [1093] Temperature (°C) 21 28 Dissolved oxygen (mg.L–1) 7.3 11.2 pH 6.55 8.35 Conductivity (µS.cm–1) 75 420 Turbidity (NTU) 0.4 5.4
Mean 29.4 3.7 6.0 31 24.7 8.7 7.28 157.8 1.9
Normanby River floodplain lagoons (n = 6) [697] Temperature (°C) 22.9 33.4 26.2 Dissolved oxygen (mg.L–1) 1.1 7.1 3.52 pH 6.0 9.1 7.06 Conductivity (µS.cm–1) 81 412 192 Turbidity (NTU) 2.1 120 15.5 Burdekin River (n = 33) [1080] Temperature (°C) 21 33 Dissolved oxygen (mg.L–1) 2.6 11.0 pH 6.76 8.46 Conductivity (µS.cm–1) 56 790 Turbidity (NTU) 0.25 16.0
25.5 7.50 7.74 430.3 3.2
Mary River (n = 21) [1093] Temperature (°C) 12.8 32.2 Dissolved oxygen (mg.L–1) 5.2 11.4 pH 7.0 8.67 Conductivity (µS.cm–1) 123 1855 Turbidity (NTU) 1.5 15
19.4 8.02 7.93 817.7 5.7
Neosilurus hyrtlii has been recorded from a wide range of water acidity (5.2–9.1 pH units), although the pH range within studies is considerably smaller (average range = 2.07 units) (Table 1). The greatest pH range reported in Table 1 (3.1 pH units) was recorded in studies in which floodplain lagoons were the dominant habitat type sampled. Neosilurus hyrtlii occurs over a wide range of water conductivity: 4–1855 µS.cm–1; it should be considered a freshwater species. Given that it lacks a dendritic organ to 116
Neosilurus hyrtlii
are known. Bishop et al. [193] found that length at first maturity (the size at which 50% of the sample were mature) was 135 mm for both male and female fish, and that no fish below 130 mm with gonads at or greater than stage III were present in the population. These authors cautioned that very few fish in their sample possessed gonads at a state of development greater than stage III. Similarly, only 15% of a sample of 288 N. hyrtlii from the Burdekin River possessed gonads at a state of development of stage IV or greater [1093]. The minimum size of stage III fish from the Burdekin River was 91 and 118 mm SL for male and female fish, respectively. Minimum sizes for stage V fish were 124 and 120 mm SL for male and female fish, respectively. Sexual maturity is reached at a relatively small size, probably at about 12 months of age. However, Orr and Milward [1030], in their study of spawning and migration behaviour in a tributary of the Ross River, found that actively spawning fish were larger (and probably older)
allow osmoregulation in saline environments, it is unlikely to tolerate conductivities in excess of 4000 µS.cm–1 for prolonged periods. A substantial range (0.25–120 NTU) in water clarity is characteristic of the habitats in which N. hyrtlii occur. Burrows et al. [256] recorded this species from the Belyando River in which turbidity was as high as 581 NTU and remains so for extended periods of time. Its nocturnal habitat and possession of barbels to facilitate prey detection probably enable N. hyrtlii to forage effectively in habitats of low light availability due to elevated levels of suspended inorganic material. The tolerance of eggs and early life history stages to high levels of suspended sediment is unknown. Reproduction The reproductive biology of Neosilurus hyrtlii has not been studied in great detail although some of the key elements
Table 2. Life history information for Neosilurus hyrtlii. Data listed are drawn primarily from a medium-term study undertaken in the Alligator Rivers region of the Northern Territory [193], a medium term study of changes in population size structure in the Burdekin River [1093], and a short-term study undertaken in a tributary of the Ross River in northern Queensland [1030]. Information about larval development is based on material identified to genus only, as spawning aggregations observed by Orr and Milward contained both N. hyrtlii and N. ater. It is assumed here that early development in both species is identical. Age at sexual maturity (months)
12 months (?)
Minimum length of ripe females (mm)
LFM = 135 mm (median length of mature fish) [193]
Minimum length of ripe males (mm)
LFM = 135 [193]
Longevity (years)
five years (?)
Sex ratio (female to male)
1:1 occasional excess of females after spawning season [193]
Occurrence of ripe fish
Stage IV in late wet to late dry, stage V early wet [193]; stage V in November [1093]
Peak spawning activity
Start of the wet season [193, 1030]
Critical temperature for spawning
Unknown but likely to be >25°C
Inducement to spawning
Rising water levels
Mean GSI of ripe females (%)
19.1% [1030], 3.6 ± 3.4% [193]
Mean GSI of ripe males (%)
Unknown
Fecundity (number of ova)
3630 eggs in one female 205 mm TL
Fecundity /length relationship
?
Egg size (mm)
1.3 ± 0.9 mm intraovarian [193], 2.6 mm water-hardened [1030]
Frequency of spawning
Unknown, may be several spawning events in one season but unknown whether single individual spawns more than once [1030]
Oviposition and spawning site
Tributary streams [1030, 1093], spawning sites unknown in Alligator Rivers region, gravel beds suggested to be important [193]
Spawning migration
Upstream [1030]
Parental care
None
Time to hatching
60 hours at 26–27°C [1030]
Length at hatching (mm)
5.7–6.0 mm [1030]
Length at free swimming stage
?
Length at metamorphosis (mm)
25 mm [1030]
Duration of larval development
28 days [1030]
Age at loss of yolk sack
?
Age at first feeding
?
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Freshwater Fishes of North-Eastern Australia
reported that one female, of 205 mm TL with a GSI of 10.1%, contained an estimated 3630 eggs with an average diameter of 1.3 mm. Water-hardened eggs are reportedly much larger: 2.6 mm [1030]. The eggs are non-adhesive and strongly demersal and rapidly settle amongst the interstices of the sediment probably preventing downstream removal in the current. Egg density in the sediment has been estimated at 2000 eggs.m-2 [1030].
than indicated above. Male fish were 170–220 mm in length whereas female fish were 200–300 mm [1030]. The minimum size of stage VI male N. hyrtlii in the Burdekin River was 217 mm SL whereas the minimum size of stage V females was 433 mm SL [1093]. Admittedly, the sample sizes used here are very small (n = 2 for males and n = 3 for females), but collectively these data suggest that although sexual maturation may occur in the first year, reproduction, especially in female N. hyrtlii may be delayed until the second year. Although ageing studies have not been undertaken for this species, the large size attained suggests by N. hyrtlii suggests it may live for up to five years.
Embryonic development is rapid with hatching occurring after about 60 hours at 26–27°C [1030]. Gastrulation occurs 10 hours after fertilisation, myomeres and optic vesicles are recognisable after 30 hours; heart, otic capsules and lenses after 40 hours. The larvae are 5.7–6 mm long at hatching and poorly developed. The medial finfold is present but the eyes are unpigmented. Barbel development occurs 48 hours post-hatching and is complete after 10 days. Fin rays appear after 4–6 days and full fin development is complete after 28 days. The yolk is completely absorbed after 10 days post-hatch. Metamorphosis is complete at 25 mm length and the adult form attained after six weeks [1030].
Spawning occurs during the summer wet season. Orr and Milward [1030] reported several different spawning events associated with individual flood events. It was not known whether individual fish participated in more than one spawning event. Gonad recrudescence in the Alligator Rivers region commences in the late dry season (stage IV fish present) [193]. In the Burdekin River, stage IV fish (and greater) were present in November samples only and absent from samples collected in May (although some apparently spent males were present in May of one year) [1093].
25
Beumer [176] suggested that Neosilurus spp. are dependent on increases in water level, with accompanying changes in turbidity and temperature, to stimulate spawning. Migration and spawning are clearly linked to flooding in north-eastern Australia [1030, 1093]. The extent to which temperature influences spawning is questionable, although it probably plays an important role in stimulating gonad recrudescence. Water temperature tends to decrease during floods [1093] and is thus not likely to be a useful cue for reproduction. However, unseasonal floods are not uncommon across this species’ range, and may stimulate mass migrations akin to that seen during the spawning period [1030]. It would be instructive to know whether rising water levels outside the summer period also stimulate spawning and whether temperature plays some role in determining whether spawning occurs during such ‘false runs’.
20
15
10
5
0
Standard Length (mm) Figure 1. Size structure of Neosilurus hyrtlii populations in the main channel of the upper Burdekin River (closed bars, n = 151) and in tributary streams of the upper Burdekin River (open bars, n = 79).
The available information on the extent of reproductive investment is conflicting. Bishop et al. [193] report mean female GSI values during the spawning season of only 3.6 ± 3.4% (n = 6) whereas Orr and Milward [1030] report a mean female GSI of 19% (n = 8). This disparity can probably be reconciled by the fact that running ripe fish were not present in the Alligator Rivers sample whereas Orr and Milward’s sample was derived from a spawning aggregation and presumably contained stage VI fish only. Fecundity data are lacking except Bishop et al. [193]
Movement In the Alligator Rivers region of the Northern Territory, substantial movements between different types of habitat occurs (see section on macrohabitat use) but given that Bishop et al. [193] were unable to identify spawning sites, it is not known which movements are associated with reproduction. This species was rarely observed migrating
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en masse in this region [190] as observed in north-eastern Australia. In the Ross River near Townsville, adult fish migrate upstream into small intermittent tributaries [1030]. In the upper Burdekin River (i.e. above the Burdekin Falls Dam), the great majority of small juveniles collected over the period 1989–1992 were from tributary streams such as Keelbottom Creek and the Fanning River (Figure 1), suggesting that N. hyrtlii makes upstream spawning migrations in this system also. The general paucity of fish greater than 80 mm in length in these tributary streams suggests that dispersal from the natal to the adult habitat occurs in the first year. The abrupt decrease in the number of fish greater than this length in tributary streams, coupled with the similarly abrupt increase in representation by fish greater than 80 mm SL in the main channel, suggests that emigration occurs either over a relatively short time period or that it occurs over a narrow size range.
Queensland. These include: Arthington et al. [98] (n = 28, Herbert and Tully rivers); Hortle and Pearson [599] (n = 1, Annan River); Pusey et al. [1097] (n = 10, Mulgrave and Johnstone rivers); Pusey et al. [1099] (n = 36, Pascoe, Stewart and Normanby rivers of Cape York Peninsula); Kennard [697] (n = 32, floodplain lagoons of the Normanby River); Bishop et al. [193] (n = 187, Alligator rivers region); and Pusey et al. [1093] (n = 202, Burdekin River). The latter two studies included data from both wet and dry seasons, whereas the remainder were confined to the dry season only. Molluscs (6.3%) Unidentified (18.3%) Microcrustaceans (13.7%)
Stuart’s [1274] study of fish movements through the fishway located on the Fitzroy River barrage found that N. hyrtlii (and P. rendahli) only contributed a very small proportion of the fishes moving through this structure (124 of a total of 23 000). Other studies of fishways located on tidal barrages have also found N. hyrtlii to be a minor component of the fauna using such structures [1173, 1276], probably because N. hyrtlii tends not to occur in estuarine or tidal reaches. Nonetheless, these studies have revealed significant insight into movement biology of this species. For example, small fish seem equally able to ascend fishways under most flow conditions as do larger fish [1274, 1276]. However, small fish (<150 mm TL) moved upstream during periods of low flow only (18 ML.day-1), whereas larger fish moved upstream under a wider array of flow conditions. Ascent occurred predominantly at night. Very few fish moved through the Fitzroy River fishway outside the period November to March (peak in January) [1274]. Similarly most movement through the Ben Anderson Barrage on the Burnett River occurred in spring and early summer: no movement occurred in March, April, July or August [1276]. No movement in the Fitzroy River was recorded when water temperatures were below 22°C [1274], whereas movement in the Burnett River occurred over the range of 15–25°C [1276].
Detritus (15.0%)
Terrestrial invertebrates (1.0%) Aerial aquatic insects (1.0%) Aquatic macrophytes (1.0%) Aquatic insects (44.3%)
Figure 2. The average diet of Neosilurus hyrtlii. Summary based on gut contents analysis of 496 individuals derived from seven separate studies (see text).
The average diet of N. hyrtlii is dominated by aquatic invertebrates, principally chironomid larvae, trichopteran larvae and ephemeropteran nymphs. Detritus comprised 15% of the diet. Microcrustacea were an important component of the diet, comprising 14% of the total. Molluscs (both bivalves and gastropods) were also important. The diet depicted in Figure 2 suggests a benthic feeding habit consistent with its body morphology. However, the presence of terrestrial invertebrates and the adult forms of aquatic insects suggests that it may occasionally forage at the water’s surface. There is substantial geographic variation in diet. For example, the contribution of detritus to the diet ranged from 0% in the Herbert/Tully River sample to 65.2% in the sample from floodplain lagoons of the Normanby River. Detritus was present but unimportant (3.3%) in the diet of riverine fish of Cape York Peninsula. This difference may reflect the different availability and quality of food sources in lentic and lotic environments. However, the diet of Northern Territory fish, containing many individuals from lowland muddy lagoons also, did not contain detritus to any significant degree (1%). These fish, in contrast, consumed appreciable amounts of microcrustaceans (20.6% - principally Cladocera). Microcrustaceans
Huey [605] recently examined dispersal by N. hyrtlii in the dryland Warrego River and Cooper Creek using electrophoretic and DNA sequencing techniques. Substantial levels of gene flow within catchments but not between catchments was detected suggesting that juveniles did not disperse very widely during periods of flood. Trophic ecology Information on the diet of N. hyrtlii is available from seven separate studies, six of which were conducted in
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by large predatory fish such as barramundi, fork-tailed catfish and tarpon [697].
contributed only 3.3% of the total diet of N. hyrtlii from lagoons of the Normanby River. Microcrustaceans were almost absent from riverine samples of this region (1.1%), yet contributed 14% of the diet of N. hyrtlii from the Burdekin River. Cladocera were present but relatively unimportant and the bulk of this prey class for these fish was composed of benthic ostracods.
Conservation status, threats and management Neosilurus hyrtlii is listed as Non-Threatened by Wager and Jackson[1353]. Given its wide distribution and generally high abundance, this species is probably secure and likely to remain so in the future. However, it should be recognised that the wide distribution of this species may be partly artefactual, obscuring the existence of more narrowly distributed, undescribed taxa that may be of greater conservation significance. Genetic studies may help to resolve this uncertainty. The limited data available suggests that movement is an important feature of the biology of this species and access to tributary streams appears to be important for reproduction, in north-eastern populations at least. Accordingly, the development of water infrastructure that inhibits upstream movement, or which captures high flow events and therefore removes the probable stimulus for spawning migrations, is likely to negatively impact on this species. Finally, the ecology of this species is not well understood. For example, the information concerning reproduction is limited as is information on the movement biology of this species. Effective management is hampered by these knowledge deficits.
Small bivalve molluscs were present in the diet of N. hyrtlii from the Burdekin River (11.4%), lagoons of the Normanby River (4.9%), the Mulgrave/Johnstone rivers (3.2%) and the Herbert/Tully River (2%). Small gastropods contributed more than 1% of the diet only in the Mulgrave/Johnstone River (25.3%) and Normanby River lagoons (8.6%). Overall, the diet of N. hyrtlii is composed primarily of very small prey items such as chironomid and trichopteran larvae, Cladocera, ostracods and detritus. Larger prey such as fish or macrocrustaceans were absent from the diet. This species forages on much smaller prey than might be expected on the basis of body and mouth size [1097, 1099] and the extent of ontogenetic variation in diet is not great as a consequence [1099]. Such a diet is not unexpected for a nocturnally feeding benthic species. Neosilurus hyrtlii is preyed upon
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Neosilurus ater (Perugia, 1894) Black catfish, Butter Jew, Narrow-fronted tandan
37 192009
Family: Plotosidae
extending to or almost to base of caudal rays; canals of head opening through a moderate number of pores; a cluster of about 5–25 temporal pores between eyes, axillary pore present. Premaxilla with a small rectangular patch of tiny pointed teeth on each side of midline; teeth on palate about four times as large, with rounded crowns, arranged in a large semicircular to triangular, posteriorly truncated patch. Teeth in lower jaw pointed anteriorly, molariform posteriorly. Maxillary and nasal barbels reaching to or very slightly behind eye; outer mental barbel longest, extending to base of pectoral fin. Slender gill rakers present on anterior faces of first and second arches, those of first arch about half length of gill filaments, those of second arch shorter, about as long as arch width; posterior face of first arch with a row of enlarged papillae along anterior edge; posterior faces of second to fourth arches and the anterior face of third to fifth arches with transverse, low, adnate, opposing ridges [34, 52, 1304].
Description First dorsal fin: I, 5–7; Second dorsal fin and anal fin confluent with caudal fin; Upper procurrent dorsal rays: 39–52; Anal plus lower caudal rays: 84–103; Pectoral: I, 1–13; Pelvic: 12–15, outer ray simple or very shallowly branched; Gill rakers: 24–30, 18–23 on lower limb [34, 52]. Figure: mature specimen, 202 mm SL, upper Burdekin River, April 1995; drawn 2002. A large catfish commonly reaching 400 mm in length, but more commonly around 250 mm. Allen et al. [52] list a maximum length of 470 mm, Bishop et al. [193] list 508 mm TL as maximum size in the Alligator Rivers region, and we have recorded one individual in the Burdekin River of 700 mm SL [1093]. The relationship between weight (in g) and length (TL in cm) for N. ater from the Alligator Rivers region is W = 7.3 x 10–3 L3.04; r2 = 0.947, n = 106, p<0.001. The relationship between weight (g) and length (SL in mm) for N. ater from the Burdekin River is W = 5.07 x 10-6 L3.109; r2 = 0.99, n =224, p<0.001. Note the differences in unit length.
Colour in life: usually mottled grey to black, often yellow/tan ventrally in region between head and origin of anal fin. During spawning the colour of this region may intensify to an intense orange/gold [1030]. Colour in preservative: almost uniformly brown to black, sometimes mottled.
Post-orbital length of head markedly shorter than snout length; head length 21–25% of SL. Second dorsal fin long, length from origin to tip 30–40% SL. Lateral line
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ater to be present in four of six lagoons examined and both main channel sites located on the Normanby River, where it comprised 1.2% and 0.6% of the electrofishing catch and 0.3% and 1.5% of the gill-netting catch, respectively.
Systematics Neosilurus ater was originally described as Lambertia atra by Perugia in 1894, from material collected in Inawi, Papua New Guinea. Formal placement within Neosilurus as N. ater was by Weber and de Beaufort in 1913 [1372]. This species has also been described as N. mediobarbis by Ogilby in 1908 [1017]. No other synonyms are known but reference to this species as Lambertichthys ater [1398] or Tandanus ater [1304] may be found.
Neosilurus ater is similarly widespread in the Wet Tropics region although apparently patchily distributed in the northern section of the region. This species has been recorded from the Daintree River [643, 1085, 1185], being present in four of 15 sites surveyed by Russell et al. [1185], but is apparently absent from the Mossman and Mowbray rivers and Saltwater Creek to the immediate south [1185]. This species is widespread and abundant in the Barron River being recorded from over half of all sites surveyed [1187], including those upstream of the Barron Falls. Its presence upstream of the Falls is probably due to translocation [1186] although separation of the upper Mitchell and Barron rivers is topographically minor and anecdotal accounts of connection during periods of extremely high rainfall exist [229]. Whether interbasin movement occurs at these times is unknown. Neosilurus ater is present in the following drainages: Mulgrave River (20/45 sites) [1184], Johnstone River (6/73 sites) [1177], Liverpool Creek (6/29 sites), Maria Creek (2/17) and Hull River (1/5) [1179], Moresby River (3/17 sites) [1183], the Tully/Murray rivers [585, 1085], and Herbert River (7/11 wetland sites) [584, 643]. It is not overly abundant and is limited to lowland reaches of these rivers. The abundance of this species may be underestimated if daytime electrofishing is the sole means of sampling. Recent studies examining the trophic ecology of lowland fishes of the Mulgrave River have revealed N. ater to be abundant and dominant in nocturnal gill-net catches (T. Rayner, pers. comm.).
Distribution and abundance Neosilurus ater occurs in northern Australia and southern Papua New Guinea and Irian Jaya [36, 42, 52, 576]. Although recorded as present in the Sepik River in northern New Guinea [316], a subsequent taxonomic survey of this river did not include N. ater [46]. This species is very patchily distributed in the Kimberley region, being recorded from the Lawley, King Edward, Carson and Drysdale rivers only [620], but its distribution across the Northern Territory appears to be continuous [193, 772, 774, 1304], extending to some of the larger off-shore islands [1353]. With the exception of the Gregory River [643] there are very few records of N. ater in rivers draining into the southern portion of the Gulf of Carpentaria. Further to the east, N. ater has been recorded from the Mitchell River [571, 643] and is widespread in this system, being recorded from its major tributaries the Walsh and Palmer rivers [571] and extending up into the headwaters [1186]. This species has also been recorded from the Coleman, Archer, Holroyd, Wenlock and Jardine rivers [41, 571] and Kupandhanang Swamp near Weipa [571] on the western side of Cape York Peninsula. Whether the absence of N. ater from Gulf rivers between the Mitchell and Gregory rivers represents a real and significant disjunction in distribution, or is simply due to inadequate sampling, remains to be demonstrated. However, given the widespread distribution detailed here, it is most probable that the distribution of N. ater is continuous across most of northern Australia.
Beumer [176] recorded a number of species of neosilurid catfishes from the Black-Alice River north of Townsville but did not distinguish between species. There is little doubt that N. ater was one of the species recorded in this river. It has been recorded from the Ross River also [1030]. Neosilurus ater is both widespread and abundant in the Burdekin River, having been recorded from every major tributary system (i.e. Cape/Campaspe, Belyando/Suttor, Broken/Bowen) [256, 586, 591, 1098], from the headwaters to the freshwater/estuarine interface, including wetlands of the Burdekin River delta (C. Perna, pers. comm.) and Baratta Creek [1045]. In a three-year study of the fishes of the Burdekin River [1098], this species was the seventh most frequently collected species in gill-netting catches and 13th most frequently collected species in both electrofishing and seine-netting catches. In another study in that drainage but restricted to the Belyando/Suttor River, N. ater comprised 2.5% of the total number of fishes collected by a range of methods including gill-, seine- and dip-netting, traps and electrofishing [256].
The distribution of N. ater in rivers of north-eastern Queensland is nearly continuous from the Claudie River of Cape York Peninsula, south to the Pioneer River. This species has been recorded from the Claudie, Lockhart, Pascoe, Stewart, Rocky, Starke, McIvor, Normanby, Endeavour and Annan rivers [571, 599, 697, 974, 1099, 1223] as well as a number of small creek systems such as Harmer, Black, Massey and Scrubby creeks [571]. It is notable that N. ater has been recorded from dystrophic dunelake systems (both Shelburne Bay and Cape Flattery) [571, 1101]. In a study of the fish fauna of floodplain lagoons of the Normanby River, Kennard [697] found N.
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be observed foraging over sandy open reaches as shallow as 30 cm. Adult N. ater are frequently observed foraging singly at night but just as frequently are observed foraging in small shoals. It is not uncommon when gill-netting at night to collect 20–30 similarly-sized individuals in one net but few in other nets. Although occasionally recorded from reaches with coarse substrates, this species is most frequently collected from areas with a muddy or sandy substratum. It is essentially an inhabitant of still to slowlyflowing waters, although it is capable of ascending reaches with substantial water velocities. Its benthic habit probably ensures that focal velocities experienced are much less than average water velocities. Woody debris and undercut banks provide important daytime cover for N. ater and it is unusual to observe this species not in association with such microhabitat elements. Juvenile N. ater make use of smaller cover elements such as leaf litter or aquatic macrophytes.
The southern range limit of N. ater is the Pioneer River [1081]. It has not been collected from the Fitzroy or the Burnett rivers despite extensive survey and fishway work in these rivers. Macro/meso/microhabitat use From the discussion above, it should be evident that N. ater inhabits a wide array of aquatic habitats ranging from acidic, dystrophic lakes, through to large rivers and their floodplain wetlands. It has been recorded from small permanent tributary streams [41] and intermittent tributary streams [1030]. In the latter case, use of such streams is restricted in adult fishes to the spawning season only, and in juveniles to the period required to achieve metamorphosis (see Table 1). Neosilurus ater is widespread in the Alligator Rivers region. Bishop et al. [193] recorded this species in 24 of 26 regularly sampled sites, occurring in floodplain lagoons, corridor lagoons, escarpment main channel water bodies and perennial streams, and most lowland muddy lagoons and sandy creek-bed habitats. Habitat use varied seasonally. During the dry season, N. ater was most common in escarpment habitats, floodplain lagoons and main channel corridor lagoons, and was absent from lowland habitats. At the commencement of the wet season, N. ater moved out of these refugial habitats and colonised all available lowland habitats. Return migrations to refugial habitats occurred in the late wet season. This pattern of habitat use is in contrast to that reported for N. ater in the Ross River of north-eastern Queensland. During the dry season, N. ater were confined to permanent water in the lowland sections of the river and made short migrations upstream for spawning at the commencement of the wet season [1030].
Environmental tolerances Experimental data concerning the environmental tolerances of this species are lacking. Data presented in Table 1 are derived from field studies and represent the range of conditions in which Neosilurus ater has been found. Neosilurus ater occurs predominantly in warm waters. The maximum water temperature in which N. ater has been recorded is 33.4°C (Table 1). The maximum water temperature recorded for the Alligator Rivers region was accompanied by a surface water temperature of 36°C [193]. This species clearly tolerates temperatures in the low to mid30s for extended periods. Minimum water temperatures in which N. ater has been recorded are between 21 and 23°C. Low water temperatures probably play an important role in limiting the southern distribution of N. ater. Neosilurus ater is found over a wide range of dissolved oxygen levels. The average dissolved oxygen concentration in the two lotic studies included above (Cape York Peninsula and Burdekin River) range from 8.0 to 8.5 mg O2.L–1 and are both close to saturation. In contrast, the remaining studies listed in Table 1 (Alligator Rivers region and Normanby River floodplain lagoons) dealt largely or entirely with lentic habitats and it can be seen that average dissolved oxygen levels experienced by N. ater in such habitats were substantially lower and on occasions very much lower (<1 mg O2.L–1). Hogan and Graham [585] recorded N. ater in lagoons of the Tully/Murray River floodplain with DO levels of 1.3 mg O2.L–1. Perna (pers. comm.) recorded N. ater in floodplain lagoons of the Burdekin River delta in which average DO levels were 42% saturation but for which occasional minimum saturation levels plummeted to 0.2%. From these data it is obvious that N. ater is tolerant of hypoxic conditions. Nonetheless,
River gradient appears to be an important determinant of macrohabitat use by N. ater. In rivers of low gradient such as the Mitchell, Normanby or Burdekin rivers (notwithstanding the presence of the Burdekin River Falls), N. ater occurs over the full length of the river. In rivers of higher gradient, such as those of the Wet Tropics region, this species is restricted to the lowland reaches. Allen [33] comments that N. ater prefers areas of faster flowing water in main channels. Neosilurus ater is a benthic species and is most commonly observed in close association with the substrate. It may be found over a wide range of water depths [1093]. During the day, adult N. ater tend to be confined to deeper waters (>2 m) although when cover in the form of woody debris or undercut banks is abundant, adult fish may be found in much shallower waters (40–60 cm). At night, the extent of dendency on cover is much reduced and adult N. ater may
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Neosilurus ater occurs over a wide range of water conductivity: 2–790 µS.cm–1; it should be considered a freshwater species. Given that it lacks a dendritic organ to allow osmoregulation in saline environments it is unlikely to tolerate conductivities in excess of 4000 µS.cm–1 for prolonged periods.
Table 1. Physicochemical data for the Black catfish Neosilururs ater. Turbidity values are listed as NTU except for the Alligator Rivers region where they are listed as Secchi disc depths in cm. Data listed for this region were taken from the bottom of the water column. Elsewhere, readings were taken from the midpoint of the water column. n refers to the number of samples upon which summaries are based. Parameter
Min.
Max.
Alligator Rivers region [193] Temperature (°C) 23 32 Dissolved oxygen (mg.L–1) 0.6 6.2 pH 4.5 6.8 Conductivity (µS.cm–1) 2 70 Turbidity (cm) 2 360 Cape York Peninsula (n = 6) [1093] Temperature (°C) 21 26 Dissolved oxygen (mg.L–1) 7.3 11.2 pH 6.2 7.2 Conductivity (µS.cm–1) 80 200 Turbidity (NTU) 0.1 5.4
A substantial range (0.3–120 NTU) in water clarity is characteristic of the habitats in which N. ater occur. Burrows et al. [256] recorded this species from the Belyando River in which turbidity may be as high as 581 NTU and remains so for extended periods of time. Its nocturnal habitat and possession of barbels to facilitate prey detection probably enable N. ater to forage effectively in habitats of low light availability due to elevated levels of suspended inorganic material. The tolerance of eggs and early life history stages to high levels of suspended sediment is unknown.
Mean 27.2 3.4 5.9 95 24.3 8.5 6.8 125.7 1.9
Bishop [187] recorded N. ater among the dead in a large fish kill for which hypoxia was suggested to be the primary cause. The effects on growth and reproduction that might arise from long-term exposure to levels of between 1.5–3.5 mg O2.L–1 or whether such profoundly depressed DO levels are inimical to eggs, larvae and small juveniles are unknown. Given that reproduction in many areas appears concentrated in seasonally flowing streams, it is probable that these early life stages are intolerant of extremely low levels of dissolved oxygen.
Reproduction As is the case for N. hyrtlii, the reproductive biology of N. ater is poorly documented and what little is known is derived primarily from research undertaken in the Alligator Rivers region [193] and in an intermittent tributary of the Ross River in Townsville [1030] (Table 2). Bishop et al. [193] determined that length at first maturity (length at which 50% of the sample is mature) was 260 and 280 mm TL for male and female fish, respectively. This is approximately twice the size at which male and female N. hyrtlii mature [193]. Maturation at lengths in excess of 200 mm SL occurs in the Burdekin River also [1093]. Gonad recrudescence commences in the mid-dry to early wet season, peaking in the early wet season in the Alligator Rivers region. Average GSI values during the breeding season were estimated to be 6% ± 2.5% and 1.7% ± 0.9, for female and male fish, respectively. GSI values decreased rapidly after a short breeding season that occurred during the wet season. Running ripe fish were found in a variety of habitats, both lentic and lotic. Bishop et al. [193] cite unpublished observations by H. Midgley of running ripe plotosid catfishes congregating in large numbers in Magela Creek soon after flow commenced. This observation parallels that of Orr and Milward [1030] who describe upstream spawning migrations by N. ater (and N. hyrtlii) in the Ross River.
Neosilurus ater has been recorded from a wide range of water acidity (4.5–9.1 pH units), although the pH range within studies is considerably smaller (average range = 1.9 units) (Table 1). This species has been recorded from acidic dune lakes in which pH was 5.01 [1101]. This species most frequently occurs in waters of near-neutral acidity although some populations, such as those occurring in dune lakes [1101] and floodplain wetlands [193] tolerate much lower pH levels.
The fact that N. ater and N. hyrtlii make simultaneous spawning migrations into the same habitats [1030] suggests the existence of very strong mechanisms for reproductive isolation. Orr and Milward [1030] observed that these species assume substantially different body and fin colouration during the spawning run (see descriptions), and this may help to prevent inappropriate mate choice. Moreover, N. ater apparently swim together in pairs immediately prior to spawning with the head pointed
Normanby River floodplain lagoons (n = 6) [697] Temperature (°C) 22.9 33.4 26.3 Dissolved oxygen (mg.L–1) 2 6.3 3.4 pH 6.4 9.1 7.3 Conductivity (µS.cm–1) 81 412 120 Turbidity (NTU) 3.4 120 22.6 Burdekin River (n = 29) [1093] Temperature (°C) 21.5 33 Dissolved oxygen (mg.L–1) 4.2 11.0 pH 6.8 8.5 Conductivity (µS.cm–1) 56 790 Turbidity (NTU) 0.3 16
26.0 8.0 7.7 426.3 3.565
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season is short in duration. Greater research effort is required to assess whether individual females spawn more than once, a life history tactic that may be advantageous in areas where spawning is restricted to intermittent streams in which discharge is unpredictable in incidence and duration.
downward coupled with frequent tumbling and intertwining, whereas in N. hyrtlii, the male follows the female, holding the snout adjacent to the female’s flank, followed by a short dart ahead to arch the body around the female’s snout [1030]. Neosilurus ater is moderately fecund for its size, producing between 2540 and 26 070 (average = 7890) small eggs with an intraovarian diameter of about 1.6 mm. Water-hardened eggs are apparently slightly larger. The eggs are demersal and non-adhesive. Bishop et al. [193] report that in addition to the presence of well-developed eggs in the ovaries of mature fish, many clusters of small, undeveloped eggs of about 0.16 mm diameter could be found. This raises the possibility that N. ater is a serial spawner. However, the steep decline in average GSI values through time observed in the Alligator Rivers region suggests that the spawning
Ripe N. ater were collected from a variety of habitats in the Alligator Rivers region but the exact site of spawning was unknown [193], in contrast to reports by Orr and Milward [1030], who observed spawning in an intermittent stream with a gravel/sand bed. Limited evidence concerning the location of spawning sites for the neosilurid catfishes of the Burdekin River, although far from comprehensive, suggests that both N. ater and N. hyrtlii migrate upstream into tributaries (Fig. 1) whereas N. mollespiculum remains in the main
Table 2. Life history information for Neosilurus ater. Data listed are drawn primarily from a medium-term study undertaken in the Alligator Rivers region of the Northern Territory [193], a medium term study of changes in population size structure in the Burdekin River [1093], and a short-term study undertaken in a tributary of the Ross River in northern Queensland [1030]. Information about larval development is based on material identified to genus only, as spawning aggregations observed by Orr and Milward contained both N. hyrtlii and N. ater. It is assumed here that early development in both species is identical. LFM = length at first maturity. Age at sexual maturity (months)
24 months (?)
Minimum length of ripe females (mm)
LFM = 280 [193]
Minimum length of ripe males (mm)
LFM = 260 [193]
Longevity (years)
5 years (?)
Sex ratio (female to male)
1:1 [1030], variable excess of females after spawning season
Occurrence of ripe fish
Stage IV in late wet to late dry, stage V early wet [193]; stage V in November [1093]
Peak spawning activity
Start of the wet season
Critical temperature for spawning
Unknown but likely to be >25°C
Inducement to spawning
Rising water levels
Mean GSI of ripe females (%)
10.5% [1030], 6.0 ± 2.5% [193]
Mean GSI of ripe males (%)
1.7 ± 0.9% [193]
Fecundity (number of ova)
Average = 7890 (n = 13), range = 2540–26 070 [193]
Fecundity /length relationship
?
Egg size (mm)
1.4 mm intraovarian (range = 0.85–1.64) [193], 2.0 mm water-hardened [193], 2.6 mm water-hardened [1030]
Frequency of spawning
May be several spawning events in one season but unknown whether single individual spawns more than once [1030]
Oviposition and spawning site
Tributary streams [1030, 1093], main channel [1093] – gravel beds
Spawning migration
Upstream [1030]
Parental care
None
Time to hatching
60 hours at 26-27°C [1030]
Length at hatching (mm)
5.7–6.0 mm [1030]
Length at free swimming stage
?
Length at metamorphosis (mm)
25 mm [1030]
Duration of larval development
28 days [1030]
Age at loss of yolk sack
?
Age at first feeding
?
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Freshwater Fishes of North-Eastern Australia
5, Annan River; Pusey et al. [1097], n = 49, Mulgrave and Johnstone rivers; Pusey et al. [1099], n = 50, Pascoe, Stewart and Normanby rivers of Cape York Peninsula; Kennard [697], n = 21, floodplain lagoons of the Normanby River; Pusey et al. [1093], n = 164, Burdekin River; Bishop et al. [193], n = 260, Alligator Rivers region. The latter two studies included data from both wet and dry seasons whereas the remainder were confined to the dry season.
channel [1093] (see pp. 129–132). Separation of spawning grounds of at least one species and differences in mating behaviour of the remaining two may be sufficient to maintain reproductive isolation in these catfish species. Embryonic and larval development are assumed to follow the same pattern as described for N. hyrtlii. Figure 1. Size structure of Neosilurus ater populations in the main channel of the upper Burdekin River (closed bars, n =108) and in tributary streams of the upper Burdekin River (open bars, n = 51) [1093].
Figure 2. The average diet of Neosilurus ater. Summary based on stomach contents analysis of 549 individuals derived from six separate studies (see text).
30 Molluscs (9.5%) Microcrustaceans (5.3%) Unidentified (29.0%)
20
10
Detritus (12.0%)
0 Aquatic insects (39.8%)
Terrestrial vegetation (1.5%) Aquatic macrophytes (2.2%) Fish (0.7%)
Length (mm) The average diet of N. ater is dominated by aquatic invertebrates (~40%), detritus (12%), molluscs (~10%) and microcrustacea (~10%). Other items were unimportant overall, although each may have been significant in each individual study. For example, fish comprised one-third of the diet of N. ater from the Annan River but did not contribute more than 1% in any other study.
Movement Other than the study by Orr and Milward [1030] demonstrating upstream migrations associated with spawning, little is known of the movement biology of N. ater. This species has not been recorded in studies undertaken in fishways. Clearly, upstream migrations by adults for spawning must be followed by a return migration by spent individuals, followed later by downstream dispersion of juveniles. The data presented in Figure 1 suggests that the juveniles return to the main channel at relatively small size, as juveniles between 120–240 mm SL are absent from tributary streams. In the Alligator Rivers region, substantial movements between expanded wet season habitats (principally in the lowlands) and dry season refugia (principally in upstream escarpment habitats) have been reported [193].
Ontogenetic and geographic variation in diet is pronounced in N. ater. Pusey et al. [1099] provided information on the diet of small (<150 mm SL, n = 31) and large (>150 mm SL, n =19) N. ater in rivers of Cape York Peninsula. Small fish relied more on aquatic invertebrates than did large fish (62% versus 38%, respectively), consumed more filamentous algae (6.6% versus 0%, respectively), consumed less microcrustaceans (almost entirely ostracods) (5.9% versus 22%, respectively) and much less molluscs (0% versus 20%, respectively). Although the consumption of larger prey items such as molluscs increased with increasing fish size (undoubtedly as a result of an increased ability to handle and process such prey), increasing body size was not necessarily associated with increasing size for all prey items. For example, very small ostracods were an important food source for N. ater in rivers of Cape York Peninsula. Notably, these small
Neosilurus ater, like N. hyrtlii, is most active at night. Most movement probably occurs at night, with the exception of spawning runs, which have been observed during daylight hours. Trophic ecology Information on the trophic ecology of N. ater is available from six separate studies, five of which were conducted in Queensland. These include: Hortle and Pearson [599], n =
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Neosilurus ater
prey items were not ingested incidentally along with organic detritus, as detritus was not recorded in the diet of fish from Cape York rivers.
Table 3. Comparative importance (% of total for each region) of selected food items in the diet of N. hyrtlii and N. ater. Items are included only if substantial differences in proportional contribution occurred.
Detritus was very important in the diet of N. ater from some of the other study areas. This food source contributed 60% of the total diet of fish from the Mulgrave and Johnstone rivers of the Wet Tropics region (n = 49) and 48% of the diet of catfish from floodplain lagoons of the Normanby River (n = 21) but did not contribute more than 7% of the diet in any other study area. Notably, microcrustaceans contributed very little to the diet in these studies, further emphasising the fact that when benthic microcrustaceans occur in the diet at appreciable levels, this is a result of active selection and processing rather than inadvertent ingestion as a by-product of detrivory. In addition, the type of microcrustacean eaten by N. ater varied between studies. For example, Cladocera (and to a lesser extent Conchostraca) were the dominant microcrustacean in the diets of fish from the Alligator Rivers region and from the floodplain of the Normanby River, reflecting the abundance of these taxa in lentic waters. The microcrustacean component of the diet of fish from riverine study areas (Burdekin River and rivers of Cape York Peninsula) was dominated by ostracods. The amount and type of molluscs eaten by N. ater varied between studies also. For example, in the Mulgrave and Johnstone rivers, small gastropods were twenty times more important than were bivalve molluscs (12.5% versus 0.6%, respectively). In contrast, bivalve molluscs were ten times more important than were gastropods (20.6% versus 2%, respectively) in the Burdekin River, and approximately equal contributions were recorded in the diet of fish from lagoons of the Normanby River (7.7% versus 6.9% for bivalve and gastropod molluscs, respectively). Molluscs were either absent or unimportant (<1%) in the diet of fish from the Annan River and the Alligator Rivers region.
Dietary item
N. hyrtlii
N. ater
Alligator Rivers region Microcrustaceans (Cladocera)
20.6
7.6
Normanby River floodplain Detritus Terrestrial invertebrates Aquatic insects
65.0 10.4 6.0
48.0 1.5 25.4
Cape York Peninsula Microcrustaceans (ostracods) Molluscs
3.3 0
12.1 7.6
Wet Tropics region Detritus Molluscs
32.0 28.5
60.0 12.8
Burdekin River Detritus Microcrustaceans (ostracods) Molluscs
22.0 14.0 11.4
5.6 1.4 22.6
between studies. Similarly, interspecific differences in the proportional contribution of detritus, molluscs and microcrustacea occur in the Wet Tropics region and the Burdekin River also. These data suggest that these two morphologically similar species do indeed partition the available food resources. Significantly however, this apparent partitioning is not consistent across the various studies. For example, while microcrustaceans are an order of magnitude more important in the diet of N. hyrtlii from the Burdekin River than in N. ater, and three times more important in the Alligator Rivers region, the reverse condition was observed in rivers of Cape York Peninsula where microcrustacea were more important in the diet of N. ater. Similarly, molluscs were more important in the diet of N. ater from Cape York and the Burdekin River whereas this food item was more important in the diet of N. hyrtlii from the Wet Tropics region. Contrasting patterns of partitioning with respect to detritus are also evident in Table 3. The mechanisms or factors responsible for these variable patterns of dietary segregation are unknown but the data serve to illustrate that these two morphologically similar, frequently sympatric and syntopic, catfishes are able to partition food resources effectively. Moreover, these data suggest that both species are able to employ a range of foraging strategies when circumstances dictate. Investigation of the mechanisms allowing the coexistence of these two species, and additional species such as N. mollespiculum and Porochilus rendahli, is warranted.
The average diet of N. ater, taken across all studies, is extremely similar to that of N. hyrtlii: both being dominated by aquatic invertebrates, molluscs, microcrustaceans and detritus. However, when comparison of the diet of each species is restricted to individual studies, it can be seen that substantial dietary segregation occurs (Table 3). For example, microcrustaceans were more important in the diet of N. hyrtlii in the Alligator Rivers region than N. ater from this region. In lagoons of the Normanby River, N. ater consumed less detritus, less terrestrial insects and more aquatic invertebrates than did N. hyrtlii, whereas in rivers of this region, N. ater consumed more microcrustacea and molluscs than did N. hyrtlii. Note that the type (Cladocera versus Ostracoda) and location (planktonic versus benthic) of the microcrustacean food differed 127
Freshwater Fishes of North-Eastern Australia
important for reproduction, in north-eastern populations at least. Accordingly, the development of water infrastructure that inhibits upstream movement, or which captures high flow events and therefore removes the probable stimulus for spawning migrations, is highly likely to negatively impact on this species. Finally, the ecology of N. ater is poorly documented. For example, the information concerning reproduction is limited as is information on movement biology and the mechanisms allowing coexistence of closely related species. Effective management is hampered by these knowledge deficits.
Conservation status, threats and management Neosilurus ater is listed as Non-threatened [1353]. Given its wide distribution and generally high abundance, this species is probably secure and likely to remain so in the future. However, available information suggests the existence of two disjunct populations, one restricted to north-western Australia and the other to north-eastern Australia. Whether this represents a true separation of these populations and whether significant genetic differentiation has occurred is unknown. Movement is an important feature of the biology of this species and access to tributary streams appears to be
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Neosilurus mollespiculum Allen & Feinberg, 1998 Soft-spined catfish
37 192023
Family: Plotosidae
of eye; inner mental barbel slightly shorter. Teeth slender, conical, arranged in several rows on upper and lower jaw; lunate patch of larger teeth on palate. Dorsal profile of head strongly convex in adult specimens. Dermal fold on chin forming deep groove across region between lower lip and ventral gill opening; branchiostegal membranes broadly united to each other and partly free from isthmus.
Description First Dorsal fin: I, 4 (spine flexible and last ray consisting of 2–3 small closely clustered rays arising from the same pterygiophore); Second dorsal and anal fin confluent with caudal fin: Upper procurrent caudal rays 28–33; Caudal rays: 8–9; Anal: 71–82; Pectoral: I, 13; Pelvic: 13–14. Gill rakers on lower limb of first arch: 12–16. Dorsal and pectoral fin spines weak, flexible and generally lacking serrations except occasionally in juveniles. Figure: composite, drawn from photographs of adult specimens, one of which is the paratype depicted in Allen and Feinberg [48]; drawn 2002.
Colour in life: variable, ranging from dark charcoal-grey or nearly black through to yellowish-grey brown dorsally and lighter ventrally. Young individuals tend to be darker than adults. Colour in preservative: pale grey to yellowish or tan, often darker grey on back and top of head.
Neosilurus mollespiculum is a moderate-sized to large catfish that may reach 410 mm SL (440 mm TL [52]) but is most commonly 150–200 mm SL. The relationship between length (SL in mm) and weight (g) is W = 5.31 x 10–6 L3.085: r2 = 0.98, n = 99, p<0.001 [1093]. The following description is drawn largely from the original description [48]. Head length about one-quarter of SL (22–24% SL); eye small (13–20% of HL), set in middle of head (snout length = 45–53% of HL) and close to dorsal profile. Nasal barbel 21–34% of HL usually reaching about 2/3 distance between snout and anterior margin of eye; maxillary and outer mental nasal about equal, reaching to below level of middle
Systematics Neosilurus mollespiculum has only recently been described [48] although it has long been recognised as a distinct taxon – Allen’s Neosilurus sp. C. [34]. This taxon was composed of two species, both lacking rigid spines in the dorsal and pectoral fins, namely N. mollespiculum and N. pseudospinosus. Prior to the description of two separate species, Allen [34] figured the distribution of Neosilurus sp. C. (p. 63) as extending across the Northern Territory, the Gulf of Carpentaria in Queensland, Cape York Peninsula and south to the Burdekin River. Neosilurus
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Burdekin Falls. In the upper Burdekin River, this species occurs in tributary rivers as well as the main channel [1082, 1098]. It has also been collected from the Bowen River, the major lowland tributary of the Burdekin River [1098]. The only major tributary system of the Burdekin River in which this species has not been recorded is the Cape River and Belyando/Suttor system in the south-western portion of the catchment. Burrows et al. [256] did not collect this species from the turbid waters of the Belyando River despite collecting N. ater, N. hyrtlii and P. rendahli. Neosilurus mollespiculum probably does occur in the south-western tributaries of the upper Burdekin River and its apparent absence is probably due to misidentification. Despite its widespread distribution, few researchers working in the catchment have recognised this species.
pseudospinosus has been recorded from rivers of the Kimberley region and from the Victoria and Daly River systems of the Northern Territory only, whereas N. mollespiculum is limited to the Burdekin River [48]. The two species are closely related and superficially resemble N. ater, which contrastingly possesses rigid spines on the dorsal and pectoral fins, and a higher gill raker count on the lower limb of the first brachial arch (18–23 versus 12–16 for N. ater and N. mollespiculum, respectively) [48]. Neosilurus mollespiculum differs from N. pseudospinosus in having a smaller average number of procurrent caudal rays (31 versus 37), a slightly shorter dorsal fin base (13–19% of SL versus 19–26% SL) and shorter nasal barbels (24–32% of HL versus 33–58% HL) [48]. The etymology of the species epithet is from the combination of the Latin for soft spine in reference to the characteristic soft, flexible dorsal spine.
Neosilurus mollespiculum is frequently sympatric with both N. hyrtlii and N. ater and appears to have almost identical habitat requirements. Reference to the meso/microhabit requirements of these species will adequately cover those of N. mollespiculum. However, this raises the interesting question of how such closely related species are able to coexist in the Burdekin River.
Distribution and abundance Neosilurus mollespiculum is endemic to the Burdekin River drainage. Allen and Feinberg [48] examined several specimens in the Australian Museum that were supposedly collected from Lillesmere Lagoon in the Fitzroy River and from the Mary River in the early 1900s. The paucity of additional collecting data associated with these specimens led Allen and Feinberg to conclude that the locations were in error and that the distribution of this species does not extend outside the Burdekin River. Lillesmere Lagoon is, in fact, located in the Burdekin River drainage. An extensive series of freshwater fishes was collected from the Mary River and the Burdekin River, including Lillesmere Lagoon, in 1883; the description of which was published the following year by Macleay [847]. Although plotosid catfishes were not mentioned in Macleay’s paper, several other errors in labelling and attribution are associated with this collection (M. McGrouther, pers. comm.) and it is most likely that the specimens of N. mollespiculum labelled as being from the Fitzroy River and the Mary River were indeed part of this collection.
Environmental tolerances Information on the environmental tolerances of Neosilurus mollespiculum are drawn from water quality measurements at sites in which this species has been collected. Table 1. Physicochemical data for the soft-spined catfish Neosilururs mollespiculum. n refers to the number of site sampling occasion combinations for which data were available.
In a study of the Burdekin River undertaken by Pusey et al. [1098] N. mollespiculum was the 15th, 10th and 9th most abundant species in electrofishing, seine-netting and gillnetting samples, respectively and contributed 1.0%, 0.1% and 1.1% of the catches by these methods, respectively. It was the second most abundant of the catfishes (total standardised catch over study period for N. hyrtlii, N. mollespiculum, N. ater, P. rendahli and T. tandanus = 1431, 226, 111, 30 and 7, respectively).
Parameter
Min.
Max.
Burdekin River (n = 23) [1080] Temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
21.5 4.2 6.76 56 0.25
33 10.0 8.46 790 6.0
Mean 25.7 7.73 7.71 408.8 2.7
Neosilurus mollespiculum occurs in warm, relatively welloxygenated, fresh waters of near neutral acidity and low turbidity. Tolerance to high levels of suspended sediment appears limited given the data presented in Table 1 and the fact that this species appears to be absent from the more turbid tributaries in the south-west of the Burdekin River catchment. However, as discussed above, this latter finding may have more to do with a failure to distinguish between this species and N. ater or N. hyrtlii than an apparent avoidance of turbid waters. The data listed in Table 1 for N. mollespiculum are almost identical to the values listed
Macro/meso/microhabit use Neosilurus mollespiculum occurs throughout the Burdekin River system, both upstream and downstream of the
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Neosilurus mollespiculum
for N. ater and N. hyrtlii (see respective chapters), a finding that is not wholly unexpected given the similarity in distribution and habitat requirements of these species in the Burdekin River. The extent to which the tolerances of N. mollespiculum match the broad range seen for N. hyrtlii are unknown however.
15
10
Reproduction Very little is known of the reproductive biology of N. mollespiculum. It is likely that many aspects of its reproductive biology parallel those observed for N. hyrtlii and N. ater. For example, spawning probably occurs during the wet season. The only occasion that we have detected mature stage V or VI females was in November 1991 (Fig. 1), prior to the period in which elevated flows are normally expected to occur [1093]. Note however, that similarly mature fish were not recorded in November of the preceding year.
5
0
Length (mm) I
II
III
IV
Figure 2. Population size structure of Neosilurus mollespiculum in the main channel (closed bars, n = 53) and tributary streams (open bars, n = 33) of the upper Burdekin River.
V
40
Movement Nothing is known of this aspect of the biology of N. mollespiculum. Data presented in Figure 2 suggests that spawning migrations into tributary streams do not occur, but such a conclusion is definitely provisional until more information is available.
30
20
Trophic ecology Information on the trophic ecology of N. mollespiculum is drawn from a single study, composed of three sampling occasions, conducted over the period November 1990 to November 1991 (n = 114) [1093].
10
0 Nov. 90
May 91
The diet of N. mollespiculum is extremely similar to the average diet of both N. hyrtlii and N. ater. It is primarily composed of benthic invertebrates, particularly insects such as chironomid larvae, mayfly nymphs and caddisfly larvae. This species consumes less detritus (3.5%) than either N. hyrtlii (14.4%) or N. ater (11.4%) but more filamentous algae (7.1% versus 0.7% and 1.1%, respectively). Molluscs comprise only 1.6% of the diet of N. mollespiculum as opposed to 6.3% and 9.5% in N. hyrtlii and N. ater.
Nov. 91
Figure 1. Temporal changes in maturation in populations of Neosilurus mollespiculum in the upper Burdekin River [1093].
Neosilurus mollespiculum may not migrate upstream into tributary streams to spawn as occurs in N. hyrtlii and N. ater. Comparison of population size structure in the main channel of the upper Burdekin River with that of tributary systems, such as Keelbottom Creek and the Fanning and Running rivers, reveals that small juveniles (<80 mm SL) were present in the main channel only. Separation of spawning and juvenile habitats may be an important mechanism allowing coexistence of these species.
This comparison is based on the average diet of N. hyrtlii and N. ater determined by pooling dietary information from a number of different regions. Comparison of the diet of these species from the Burdekin River, whilst revealing that the generalisations made above still hold true to an extent, also reveal a much finer dietary segregation in these three species when in sympatry. For example,
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Freshwater Fishes of North-Eastern Australia
Microcrustaceans (7.7%)
Molluscs (1.6%)
Macrocrustaceans (0.9%)
Unidentified (34.0%)
Detritus (3.5%) Aerial aq. Invertebrates (1.0%) Aquatic insects (43.4%)
Algae (7.1%) Fish (0.9%)
the diet of N. ater (1.4%) but more important in the diet of N. mollespiculum (7.7%) and N. hytlii (13.9%). Dietary partitioning may be another mechanism allowing the coexistence of these three closely-related species. It should be added however, that no N. mollespiculum were collected in May 1992 after the commencement of a prolonged drought in the Burdekin catchment, although N. ater and N. hyrtlii remained present, albeit at reduced densities. These species may compete intensely for resources when they are limited: this assertion remains untested however, as do most inferences about the biology of this species. Conservation status, threats and management Neosilurus mollespiculum is listed as a Poorly Known Species by Wager and Jackson [1353] and remains unlisted by ASFB [117]. Listing by Wager and Jackson was for the taxon known as Neosilurus sp. C., prior to the recognition of N. mollespiculum and M. pseudospinosus as distinct species. Its status should be revised in view of its restricted distribution. This species appears currently secure within the Burdekin River but any proposed development of water infrastructure in the catchment, and changes in flow regime associated with regulation, may impact on this species in the future. Much greater research effort is needed to define the biology of this narrowly endemic species.
Figure 3. The average diet of the soft-spine catfish Neosilurus mollespiculum (n =114 individuals) [1093].
detritus comprised only 5.6% and 3.5% of the diet of N. ater and N. mollespiculum but accounted for 22% of the diet of N. hyrtlii. Macrocrustacea (shrimps and prawns) were completely absent from the diet of N. hyrtlii but present, although relatively unimportant (~1%) in the diet of N. ater and N. mollespiculum. Molluscs were relatively unimportant in the diet of N. mollespiculum (1.6%), important in the diet of N. hyrtlii (11.5%) and very important in the diet of N. ater (22.6%). In contrast, microcrustaceans (mainly ostrocods) were a minor component of
132
Porochilus rendahli (Whitley, 1928) Rendahl’s catfish
37 192012
Family: Plotosidae
than post-orbital head length; profile often deeply concave; dorsal spine short; lateral line continuous (discontinuous in P. obbesi); canals of head opening from relatively few pores; temporal pores, between the eyes, few in number, usually one on each side of the midline, axillary pore present. Branchiostegal membranes rather broadly united, premaxilla with small rectangular patch of tiny pointed teeth on each side of the midline; teeth on palate large, rounded and arranged in semicircular to shallowly crescentic patch. Teeth in lower jaw pointed in front, molariform behind. Nasal barbel extending to, or beyond, posterior end of head; maxillary barbel reaching well behind eye; outer mental barbel reaching to, or beyond, base of pectoral fin base; the inner mental barbel, slightly shorter. Gill rakers on anterior face of first gill raker slender, those of middle of anterior face of second arch short, chubby, broad at the base, grading above and below into transverse ridges; posterior face of first arch with two rows of papillae along arch near margins, the anterior row slightly larger; second arch posteriorly with papillae more or less connected transversely across arch into ridges. Anterior nares on end of snout, above upper lip (in P. obbesi the nostril is situated on the upper lip), anterior to and slightly lateral to nasal barbel, without vestige of projecting tubule.
Description First dorsal fin: I, 5–7 (most commonly 5), spine pungent, weakly serrate or roughened; Second dorsal fin and anal fin confluent with caudal fin; Upper procurrent dorsal rays: 24–31; Anal plus lower caudal rays: 79–97 (Allen et al. [52] list a total of 104–127 rays); Pectoral: I, 9–11, spine pungent, serrae straight to slightly recurved; Pelvic: 10–13, Gill rakers on first arch: 22–26, of which 5–7 are on upper limb [52, 1304]. Figure: composite, drawn from photographs and after Taylor [1304]; drawn 2003. Porochilus rendahli is a small catfish that may achieve a maximum size of about 240 mm TL [1304]. Specimens this large are rare and P. rendahli is more commonly less than 150 mm in length. For example, the maximum length (SL) in a sample of 292 fish from Arnhem Land and Groote Eylandt was 187 mm and 96% of this sample was less than 127 mm SL [1304]. Bishop et al. [193] recorded a maximum size of 195 mm (TL) in a sample of 328 fish. These authors provide the following relationship between weight (W in g) and length (TL in cm): 4.4 x 10–3 L3.16; r2 = 0.98, n = 328, p<0.001. The following description is drawn largely from Taylor [1304]. Head length (17.5–20.8% SL), usually shorter than maximum body depth (19.3–22.2% SL); snout shorter 133
Freshwater Fishes of North-Eastern Australia
River [1349] suggests it may be more widespread in the region. The distribution on the western side of Cape York Peninsula is more or less continuous. The Mitchell River and its tributaries, the Walsh and Palmer rivers [571, 643, 1186], and the Edward, Holroyd, Archer, Wenlock and Jardine rivers [41, 52, 571, 1349] all contain P. rendahli. The related species P. obbesi also occurs in the Jardine and Olive rivers [41, 571].
Colour in life: variable, ranging from light grey to nearblack, sometimes with mottling, to yellow/tan with golden sheen [52]. Colour in preservative: dark grey to brown dorsally, grading lighter ventrally, lower head and abdomen pale. Taylor [1304] commented on the extent of variation in some characters within the series he examined. Specimens from Groote Eylandt differed from mainland specimens (Roper River area) in having fewer gill rakers on the first arch, more vertebrae, a crescentic to shallowly triangular palatal tooth patch rather than semicircular to deeply triangular palatal tooth patch and longer barbels. In addition, the number of temporal pores on the head varied from two to eight across the series. Given the wide distribution of this species (see below), it is probable that even greater variation exists. It is our belief that this species is frequently confused with juveniles of other plotosid catfishes and as a consequence, its distribution and macrohabitat requirements are not fully documented.
It is patchily distributed on the east coast of Australia, with P. rendahli being recorded only from the Pascoe, Stewart, Normanby and Endeavour rivers [52, 182, 697, 1349], Three Quarter Mile/Scrubby Creek [571] and the Cape Flattery region [1101] of Cape York Peninsula. It is broadly sympatric but not syntopic with P. obbesi in the dune fields of Cape Flattery [1101]. Porochilus rendahli is apparently absent from the northern part of the Wet Tropics region, being present in the Barron [608, 1085, 1349], Mulgrave [1093], Johnstone [643, 1093], Tully [1085] and Herbert rivers [643] only. This species is widely distributed in the Burdekin River, occurring throughout the catchment [586, 1098, 1349] including the highly turbid Belyando/Suttor River [256] and floodplain lagoons of the Burdekin River delta (C. Perna, pers. comm.).
Systematics Porochilus was erected by Weber in 1913 to contain the type species P. obbesi from the Lorenze River in southern Papua New Guinea [1042]. The genus was originally thought to be monotypic but is now known to contain four species: P. obbesi (northern Australia and southern Papua New Guinea), P. maraukensis (southern Papua New Guinea), P. argenteus (central Australia) and P. rendahli (northern Australia) [37, 52]. Porochilus rendahli was first described as Copidoglanis obscurus by Rendahl in 1922 [1127]. This name had however been proposed for another catfish, now recognised as Plotosus limbatus Valenciennes, 1840, by Günther in 1864. Whitley then proposed the name Copidoglanis rendahli in 1928 [1042]. Since then, this species has been referred to as Tandanus rendahli [1304] and most commonly as Neosilurus rendahli [936, 1042]. The first reference to this species being placed within the genus Porochilus appears to be Allen and Hoese [41], who state that ‘Feinberg and Nelson, who are revising the freshwater Plotosidae, include this species in the genus Porochilus’. Subsequent publications by Allen [52, 1304] have consistently employed the name Porochilus rendahli.
Further to the south, P. rendahli has been reported from the Fitzroy River and streams of the Shoalwater Bay area [1349], Burnett [700, 1349], River [701], Mary [701, 1349], Pine [1349] and Brisbane rivers [1349]. It is extremely uncommon in these southern rivers and it is unlikely that the distribution extends further south than the Brisbane River. Porochilus rendahli is usually uncommon in the east-coast river systems in which it has been recorded. For example, this species was the 16th (of 22) most frequently collected species in electrofishing samples in the Burdekin River [1098]. Porochilus rendahli contributed only 13 of a total of 35 851 fishes collected from 281 samples in the Mulgrave/Russell, Johnstone and Tully rivers [1093]. In a more extensive survey of the Wet Tropics region, only 12 specimens from a total of 7325 fish were collected [1085]. This species contributed 0.1% only of the total electrofishing catch in floodplain lagoons of the Normanby River [697].
Distribution and abundance Porochilus rendahli is widely but patchily distributed across northern Australia. This species occurs in a few rivers of the Kimberley region (Yeeda, Fitzroy, Drysdale and Ord rivers) [52] and in coastal rivers of the Northern Territory including Groote Eylandt [52, 193, 772, 774, 1304]. Records from rivers of the southern portion of the Gulf of Carpentaria are scant but its presence in the Leichhardt
High levels of abundance do occur occasionally. For example, this species comprised 10.5% of the total number of fishes collected from highly turbid waterholes of the Belyando/Suttor River [256]. Bishop et al. [193] described P. rendahli as being common to moderately abundant in the Alligator Rivers region.
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Porochilus rendahli
Table 1. Physicochemical data for Porochilus rendahli. Turbidity values are listed as NTU except for the Alligator Rivers region (ARR) where they are listed as Secchi disc depths in cm. Data listed for the Alligator Rivers region were recorded from the bottom of the water column. Elsewhere, they are derived from the midpoint of the water column.
Macro/meso/microhabitat use Porochilus rendahli has been recorded from a variety of habitats including both riverine and off-channel. This species is widely distributed in the Burdekin River, inhabiting the main channel both upstream and downstream of the Burdekin Falls, floodplain lagoons of the delta, intermittent tributary streams of the upper Burdekin river and low gradient in-channel lagoons of the Belyando River, but rarely occurs in the higher gradient Bowen/Broken River [1082]. In the Normanby River, it has been recorded from both the main channel and floodplain lagoons [697, 1099]. In the Alligator Rivers region, P. rendahli was collected from 17 of 26 regularly sampled sites and occurred in all muddy lowland lagoons and floodplain lagoons, and some corridor lagoons and perennial escarpment streams [193]. Juvenile P. rendahli were collected from lowland muddy and floodplain lagoons.
Parameter
Min.
Max.
Alligator Rivers region [193] Temperature (°C) 23 34 Dissolved oxygen (mg.L–1) 2 9.5 pH 5.2 7.3 Conductivity (µS.cm–1) 2 620 Turbidity (cm) 1 170
Mean 28 3.8 6 31
Normanby River, river and floodplain lagoon (n = 2) [1093] Temperature (°C) 22.9 26 Dissolved oxygen (mg.L–1) 2.0 7.3 pH 6.9 7.2 Conductivity (µS.cm–1) 80.9 152 Turbidity (NTU) 3.4 5.4
Porochilus rendahli is a benthic species that prefers habitats with low water velocities, and is most common in reaches with a muddy substrate [52, 193]. This species is frequently associated with aquatic vegetation [52] and achieves greatest abundance in areas with dense submerged macrophytes [193].
Cape Flattery (n = 1) [1101] Temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
Environmental tolerances The data presented in Table 1 are drawn from measurements of ambient conditions in sites in which P. rendahli occurs. As such, the usual caveats concerning extrapolation of this data to indicate upper and lower tolerance levels apply. Moreover, summaries based on more than one sample are restricted to the Alligator Rivers region and the Burdekin River. However, as the information available for this species is very limited, we have included data from several individual sites from other basins also.
Burdekin River (n = 7) [1093] Temperature (°C) 15 28 Dissolved oxygen (mg.L–1) 4.2 11 pH 7.22 8.3 Conductivity (µS.cm–1) 258 435 Turbidity (NTU) 1.3 4.75
32 7.4 5 385
22.9 7.3 7.7 339 3.0
the Belyando River in which high levels of very fine suspended sediment maintained very high turdidity levels (mean = 397 NTU) for extended periods.
Porochilus rendahli occurs in warm waters (Table 1) as would be expected given its distribution. The southern limit of this species is probably determined by low water temperature. The data presented in Table 1 suggest that P. rendahli is tolerant of low levels of dissolved oxygen. Indeed, levels of dissolved oxygen saturation in floodplain lagoons of the Burdekin River delta average 47% saturation only and may drop to as little as 0.4% overnight (C. Perna, pers. comm.). A well-developed tolerance to hypoxia is not unexpected for species inhabiting tropical lagoons with abundant macrophyte growth.
Reproduction What little is known about the breeding biology of P. rendahli is drawn entirely from the work of Bishop et al. [193] in the Alligator Rivers region. This species matures at small size: length at first maturity (LFM) reported to be 100 mm and 110 mmTL for male and female fish, respectively, although stage IV or V fish as small as 99 mm TL were observed in some populations. The breeding season is limited to the early wet season although gonad recrudescence commences in the mid dry season when temperatures exceed 28°C. Spawning apparently occurred in muddy lowland lagoons. Average GSI values for male and female fish during the spawning season were 0.7 ± 0.1% and 5.2 ± 1.7%, respectively. Estimated fecundity from a sample of eight fish was about 900 eggs (range = 240–3465) with an average diameter of 1.3 mm.
Porochilus rendahli has been recorded across a wide range of pH (5–8.3). Again, a tolerance to low pH levels is not unexpected given this species’ pattern of macro and mesohabitat use. Porochilus rendahli has been recorded from very fresh and moderately clear waters. However, Burrows et al. [256] found P. rendahli to be abundant in lagoons of
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Freshwater Fishes of North-Eastern Australia
Movement Little is known about this aspect of the biology of P. rendahli, except that migration into lowland muddy lagoons for spawning has been reported in the Alligator Rivers region [193]. Trophic ecology Information on the trophic ecology of P. rendahli presented in Figure 1 is drawn from three separate studies: Bishop et al. [193] in the Alligator Rivers region (n = 397); Pusey et al. [1099] in rivers of Cape York Peninsula (n = 3) and Pusey et al. [1082] in the Burdekin River (n = 10). The diet of P. rendahli is relatively simple, being dominated by aquatic invertebrates and microcrustaceans. The aquatic invertebrate component is dominated by chironomid midge larvae and small ephemeropteran nymphs. Microcrustaceans varied in importance and composition across the three studies, being absent from the Cape York sample, contributing 10% in the Burdekin River sample (comprised mainly of ostracods), and contributing 31% of the total in the Alligator Rivers sample (dominated by Cladocera) [193].
Fish (0.4%) Other microinvertebrates (0.4%) Unidentified (20.8%)
Microcrustaceans (30.1%) Terrestrial invertebrates (0.1%) Aerial aq. Invertebrates (0.5%) Detritus (3.2%) Terrestrial vegetation (0.1%) Algae (0.2%)
Macrocrustaceans (0.5%) Molluscs (0.8%)
Aquatic insects (43.1%)
Figure 1. The average diet of Porochilus rendahli. Summary drawn from three separate studies (see text) and a combined total of 410 individuals.
Conservation status, threats and management Porochilus rendahli is classified as Non-Threatened by Wager and Jackson [1353]. Given the paucity of information on this species, it is difficult to identify specific threats to this species. Broad issues of relevance include reclamation, isolation and degradation of off-channel wetlands, and the imposition of barriers to movement. An increased effort to document the biology of this species, and of plotosid catfishes in general, is needed.
Such a simple diet clearly reflects the constraints imposed by a benthic habitat and small size. Of importance in this regard is that the diet of P. rendahli is almost identical to that of the juvenile forms of the larger plotosid catfishes Neosilurus ater, N. hyrtlii and N. mollespiculum.
136
Tandanus tandanus Mitchell, 1838 Eel-tailed catfish
37 192006
Family: Plotosidae
Description First dorsal fin: I, 6; Second dorsal fin and anal fin confluent with caudal fin: 140–150 rays; Pectoral: I, 10; Pelvic: I, 5; Scaleless; Gill rakers on first arch: 23–32 [34, 270, 936, 1069]. Figure: mature specimen, 175 mm SL, Little Mulgrave River, November 1994; drawn 1995.
Wet Tropics [1093]: W = 1.18 x 10–4 L2.645, r2 = 0.554, p< 0.001, n = 215, range = 86–323 mm SL (but note the low exponent and low r2 value);
Tandanus tandanus is a large, robust fish. A maximum length of around 900 mm TL and weight of 6.8 kg has been recorded but this species is more common to 500 mm and 1.8 kg [270, 748, 749]. Of 529 specimens collected by electrofishing and seine-netting in streams of the Wet Tropics region over the period 1994–1997 [1093], the mean and maximum length of this species was 171 and 400 mm SL, respectively. The modal length of 191 fish collected largely from gill-netting samples in the Burnett River was 420 mm SL [99]. Of 2349 specimens collected by electrofishing and seine-netting in streams of south-eastern Queensland over the period 1994–2000 [1093], the mean and maximum length of this species were 107 and 500 mm SL, respectively, with the majority (80% of individuals) 150 mm SL or less.
Burnett River [205]: W = 4.4 x 10–6 SL3.244, r2 = 0.997, p<0.001, n = 242, range = 33–474 mm SL;
Burnett River [99]: W = 4.0 x 10–3 SL3.329, r2 = 0.953, p<0.001, n = 199, range = 190–520 mm SL;
Gwydir River (and elsewhere in the Murray-Darling Basin) [359, 362]: W = 2.96 x 10–6 TL3.223, r2 = 0.992, p<0.001, n = 858, range = ~30–590 mm TL. Note that this equation tended to underestimate the weight of large fish and a parabolic relationship was more suitable for fish greater than 350 mm TL. This equation takes the form W = 0.0225 TL2 – 11.278 TL + 1637.8, r2 = 0.941, p<0.001, n = ~397. All of the above studies recorded little difference in lengthweight relationships between the sexes. Tandanus tandanus has a broad, slightly flattened head and posteriorly tapering and compressed body. The mouth is relatively small and inferior, with thick, fleshy lips surrounded by four pairs of barbels. Anteriorly pointing tubular nostrils are located on front border of upper lip.
Equations describing the relationship between length (SL or TL in mm) and weight (W in g) are available for the following populations: 137
Freshwater Fishes of North-Eastern Australia
Vomerine teeth are small, conical and arranged in a semicircular patch. The first dorsal fin is positioned anteriorly on the body and preceded by a pungent, serrated spine. The second dorsal and anal fins are confluent with caudal fin, originating on the middle of the back. Pectoral fins are located ventrally and also preceded by a pungent, serrated spine. The entire body is scaleless with smooth, slimy skin; the lateral-line is well-defined and straight. This species is sexually dimorphic with the urinogenital papilla of females triangular and that of males longer and cylindrical. Colour may vary from olive-green to brown, dark grey or purplish on back and sides and fading to creamy-white on ventral surface. Also ontogenetic colour variation, with juveniles and subadults usually grey or brown with dark brown mottling on sides; mottling is less prominent in adult specimens. Preserved colouration brown to dark grey, sides with lighter mottling [4, 21, 59, 76, 79, 81, 97]. Systematics The genus Tandanus, originally proposed as a subgenus of Plotosus, was erected by Mitchell [955] in 1838 to contain T. tandanus. Tandan is an aboriginal word [797]. The two nominal species Tandanus are endemic to Australia and have disjunct distributions. Tandanus bostocki Whitley, 1944 [1389] is confined to coastal drainages of south-western Australia and T. tandanus is widely distributed throughout eastern and inland Australia. The taxonomy and phyletic structure of T. tandanus is complicated and remains unresolved despite recent investigation. Lake [754] speculated that the Tandanus species present in the Daintree River may be a distinct species due to its extreme isolation from other populations of T. tandanus. Merrick and Schmida [936] noted that northern populations did show some differences in growth and habitat preference but considered them conspecific with the nominal form. Musyl [980], using electrophoretic techniques, identified several genetically distinct populations: the nominal form in the Murray-Darling Basin and the Hunter, Mary and Brisbane rivers; a subspecific form of T. tandanus in the Fitzroy River of central Queensland; and an undescribed species in the Bellinger and Nymboida rivers (a tributary of the Clarence River). A fourth distinct form from the Tully River was identified electrophoretically by Keenan et al. [682], confirming Lake’s initial suspicions that the Wet Tropics region may harbour an undescribed species of Tandanus. This taxon exhibits significant differences at 50% of loci examined (C. Keenan, pers. comm. cited in [310]). Additional electrophoretic examination of populations of T. tandanus in northern New South Wales also emphasised the distinctiveness of the Bellinger River catfish (fixed differences between it and Murray-Darling and Nymboida River
138
catfish at 17% of allozyme loci surveyed) [982]. Further, this study demonstrated that the catfish present in the Nymboida River were sufficiently distinct from Murray/ Darling stocks (fixed differences at 8% of allozyme loci surveyed) to warrant species level elevation, although there was evidence of past, although not recent, hybridisation between these stocks [982]. Importantly, these authors found little accompanying morphological variation between stocks and interpreted this as indicative of cryptic speciation. Note however, that the Wet Tropics population was not included in the morphometric analysis in this study, although they are superficially very similar in external morphology and colouration [1093]. Jerry and Woodland [651] examined genetic differentiation within the catfish populations of northern New South Wales at a finer spatial scale than that of Musyl and Keenan [982]. They found that the Bellinger River form also occurred in the Macleay, Hastings and Manning rivers and exhibited very little genetic differences across these rivers. They confirmed that the Nymboida River form was indeed a separate species and that it occurred in the Tweed, Clarence and Richmond rivers. In contrast, significant genetic structuring was evident in these populations, and genetic similarities between them, particularly those in the Tweed and Clarence rivers, and the population present in the Namoi River (the type locality of T. tandanus) may have arisen from hybridisation with Murray/Darling stocks of T. tandanus translocated into the area in the early 1900s [651]. Collectively, these studies indicate the presence of several distinct taxa: 1) the nominal form in the Murray Darling Basin and rivers of south-east Queensland; 2) the Bellinger River form; 3) the Nymboida or Clarence River form (including putative hybrids); 4) a subspecies of T. tandanus in the Fitzroy River; and 5) the Tully River form of the Wet Tropics region. Obviously, further research is required to fully resolve the systematics of this species, especially those populations of central and northern Queensland, particularly in light of the widespread present practice of translocation of this species throughout Queensland [982]. It is possible however, that the extent of translocation undertaken in the past may be so great (see below) as to obscure any definitive resolution of the systematics and biogeography of this species complex. Whilst mindful of the existence of distinct forms of T. tandanus in Queensland, and of the fact that no formal description or allocation of names has yet occurred for any such distinct forms, the present discussion retains this name as applicable to all populations in north-eastern Australia.
Tandanus tandanus
Queensland. Tandanus tandanus was the eighth most abundant species collected in an extensive survey of the Wet Tropics region and occurred in eight of 10 major drainage basins, being absent from the Bloomfield River and short coastal streams of the Cardwell area only [1085, 1087]. Subsequent survey work has confirmed its presence in all major drainages of the region from the Daintree River south to the Murray River [1093, 1096, 1177, 1179, 1183, 1184, 1185, 1187]. It is apparently absent from the Mowbray River [1185] but probably occurs in this drainage. This species has not been recorded from the Herbert River [584, 643]. This species is widespread within rivers of the Wet Tropics region. It was recorded from 36% of all sites examined by Pusey and Kennard [1085, 1087] and a similarly widespread distribution was recorded by Russell and co-workers [1177, 1179, 1183, 1184, 1185, 1187] and in recent investigations in the Mulgrave and Johnstone rivers (Table 1). It is apparently slightly more widespread in the Mulgrave River than the Johnstone River but this more properly reflects the greater proportion of sites in the latter river located at high elevation. It is only moderately abundant in the Mulgrave and Johnstone rivers, being the 12th most abundant species overall (7th and 14th in the Mulgrave and Johnstone rivers, respectively). This species is a major component of the biomass present within streams of the Wet Tropics region being the second most important species overall (behind A. reinhardtii). Across both rivers, average and maximum numerical density estimates were 0.21 ± 0.03 fish.10m–2 and 3.91 fish.10m–2, respectively. Average and maximum biomass density estimates were 27.2 ± 3.5 g.10m–2 and 80.6 g.10m–2 [1093]. Tandanus tandanus most commonly occurs with (in decreasing order of abundance) M. s. splendida,
Distribution and abundance Tandanus tandanus is a widespread species occurring in coastal and inland drainages of eastern Australia from Cape Tribulation in the Wet Tropics region of northern Queensland south to the Shoalhaven River in central New South Wales. Inland, it was once present throughout much of the Murray-Darling Basin. In eastern Queensland it is native to most coastal drainages from Myall Creek (just north of Cape Tribulation) south to the border with New South Wales, but there appears to be a 400 km gap in the natural distribution of this species between (and including) the Herbert River and the O’Connell River in central Queensland [1069, 1085, 1349]. It is also present in lakes and streams on Fraser Island [1349] and North Stradbroke Island off the south-eastern Queensland coast. In coastal New South Wales it is native to most drainages from the Queensland border south to the Manning River [553, 814]. There have been many introductions and translocations of hatchery-reared and wild fish to rivers within and beyond the natural distribution of T. tandanus [95, 1350]. In northern Queensland, fish (some from Enoggera Dam in the Brisbane River basin) have been translocated to Lake Tinaroo impoundment in the Barron River basin where they have become established in small numbers. They have also been stocked in Freshwater Creek and the Lake Morris impoundment (Barron River), the Atherton Tablelands section of the North Johnstone River including tributaries such as the Beatrice River and above Millaa Millaa Falls [310, 582, 908]. Hundreds of fish bred in 1984/85 at the Walkamin Research Station hatchery were released into unspecified streams on the upper Atherton Tablelands (Fisheries Research Branch (1985), cited in Clunie and Koehn [310]); these streams could potentially include those flowing into the Barron, Johnstone, Tully or Herbert River basins. In central Queensland, catfish have been successfully introduced into the Burdekin River, a catchment in which they do not naturally occur [1082]. This species has also been stocked in impoundments in the Fitzroy River basin [823].
Table 1. Distribution, abundance and biomass data for Tandanus tandanus in the Wet Tropics region. Data summaries for a total of 572 individuals collected from rivers in the Wet Tropics region over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively, at those sites in which this species occurred.
On the basis of genetic evidence it has been suggested that T. tandanus populations in the Brisbane River, south-eastern Queensland, may have been introduced from the Murray-Darling Basin [682]. In coastal New South Wales, successful introductions of T. tandanus into the Hunter, Hawkesbury and Shoalhaven rivers have extended the southerly range of this species [442, 443, 859, 860, 1069], although this species may be indigenous to the latter two rivers [437]. Clunie and Koehn [310] document numerous other introductions and translocations of this species in New South Wales, ACT, Victoria and South Australia.
% locations % abundance Rank abundance % biomass Rank biomass
Tandanus tandanus is widely distributed and relatively common in the Wet Tropics region of northern
139
Total
Mulgrave River
Johnstone River
43.3
50
41
1.6 (5.4)
2.6 (8.5)
1.3 (3.8)
12 (7)
7 (5)
14 (10)
13.1 (31.7) 2 (2)
20.1 (27.2) 10.4 (31.7) 2 (2)
2 (2)
Mean numerical density (fish.10m–2) 0.21 ± 0.03
0.33 ± 0.08 0.15 ± 0.02
Mean biomass density (g.10m–2)
41.4 ± 8.5
27.2 ± 3.5
19.6 ± 2.6
Freshwater Fishes of North-Eastern Australia
P. signifer, M. adspersa, C. rhombosomoides and H. compressa. Anguilla reinhardtii is frequently abundant (2nd most abundant) when syntopic with T. tandanus in the Mulgrave River [1093].
and formed 1.0% of the total number of fishes collected (12th most abundant). It has not been collected from the Elliott River but is present and moderately common in rivers of the Burrum Basin [157, 491, 736, 987, 1305]. With the exception of small coastal streams of the Tin Can Bay region, T. tandanus is present in most other streams south to the Queensland–New South Wales border. Surveys undertaken by us between 1994 and 2003 in south-eastern Queensland [1093] collected a total of 3050 individuals of T. tandanus and it was present at 61.7% of all locations sampled (Table 2). Overall, it was the 14th most abundant species collected (1.9% of the total number of fishes collected) and was the 11th most abundant species at sites in which it occurred (2.6%). In these sites, T. tandanus most commonly occurred with the following species (listed in decreasing order of relative abundance): Psuedomugil signifer, Retropinna semoni, Melanotaenia duboulayi, Craterocephalus marjoriae and Gambusia holbrooki. It was most widespread in the Mary River where it occurred at 78% of locations surveyed, but was also relatively widespread in streams of the Moreton region, the Brisbane River and the Albert-Logan Basin (present at 60% or more of all locations surveyed). This species achieved the highest relative abundances in the Brisbane River where it formed 2.4% of the total catch and 4.2% of the catch at those sites in which it occurred. It was also moderately common in other basins of the south-eastern Queensland region. By virtue of the relatively large size attained by this species, T. tandanus formed a high proportion of the total biomass of fishes collected. It was the 2nd most important species, forming 15.4% of the total biomass of fish collected and 26.8% of the biomass at those sites in which it was present. The greatest relative biomass was observed in the streams of the Moreton Coast and in the Brisbane River. Across all rivers, average and
Tandanus tandanus is very patchily distributed in rivers and streams of coastal central Queensland. It has been translocated to the Burdekin River where it is essentially restricted to the site of introduction (Valley of Lagoons) [1082]. We have collected only two individuals outside this area over the period 1989–1997 [1093]. It is uncommon and contributed 0.2% of the total electrofishing catch (and was absent from seine-netting and gill-netting catches) over the period 1989–1992 [1098]. This river has a high diversity of plotosid catfishes (three species of Neosilurus and Porochilus rendahli) and T. tandanus may compete with these species and be limited in the extent to which it may expand its distribution. This situation may not persist if more impoundments are located on the upper Burdekin River as neosilurid catfishes appear unable to spawn in standing waters whereas T. tandanus may (see below). This species is present but uncommon in the Pioneer River [658, 1081]. It appears to be uncommon in short coastal streams between Sarina and Yepoon, having been collected only in Plane Creek [779], some streams of the Shoalwater Bay area and in Water Park Creek [1328]. It is widespread and generally moderately common in the Fitzroy River basin [156, 160, 404, 405, 658, 659, 942, 1173, 1180, 1351], Calliope River [915], Boyne River (possibly translocated) [593], Baffle Creek [826] and the Kolan River [232, 658]. This species is widespread and generally common in south-eastern Queensland. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that it had been collected at 30 of 63 locations surveyed (7th most widespread species in the catchment)
Table 2. Distribution, abundance and biomass data for Tandanus tandanus. Data summaries for a total of 3050 individuals collected from rivers in south-eastern Queensland over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
61.7
78.0
37.9
60.0
59.5
67.6
50.0
1.87 (2.63)
1.69 (2.07)
0.78 (3.04)
1.30 (2.80)
2.44 (4.22)
2.04 (3.03)
1.18 (3.42)
14 (11)
13 (11)
10 (9)
11 (11)
11 (8)
9 (7)
15.35 (26.78) 12.66 (26.89)
11 (9) 0.79 (14.83)
47.44 (63.72) 37.77 (41.45) 16.32 (22.21) 13.38 (28.53)
2 (2)
2 (2)
4 (2)
1 (1)
2 (2)
3 (3)
2 (2)
Mean numerical density (fish.10m–2)
0.24 ± 0.02
0.22 ± 0.02
0.06 ± 0.01
0.14 ± 0.03
0.33 ± 0.06
0.26 ± 0.03
0.09 ± 0.02
Mean biomass density (g.10m–2)
19.03 ± 1.44
16.18 ± 1.74
3.61 ± 0.00 102.02 ± 41.04 33.20 ± 6.44
18.13 ± 2.10
9.52 ± 4.93
140
Tandanus tandanus
The widespread distribution within rivers of the Wet Tropics region presented above is reflected in the wide range of macrohabitat conditions detailed in Table 3. This species occurs in small second order streams of small catchment area (1 km2) through to fifth order streams of several hundreds of square kilometres (Table 3). Such streams range in size from about 2 to 40 m in width and occur at elevations ranging up to 722 m.a.s.l. Note however, that populations occurring at high elevation (i.e. the Atherton Tablelands) are probably translocated. Although this species occurs in streams with very little riparian cover, the mean and weighted mean values (34.7% and 41.7%, respectively) suggest that it occurs most commonly and is most abundant in streams with an intact riparian zone.
maximum numerical densities recorded in 600 hydraulic habitat samples (i.e. riffles, runs or pools) were 0.24 individuals.10m–2 and 4.66 individuals.10m–2, respectively. Average and maximum biomass densities at 451 of these sites were 19.03 g.10m–2 and 208.79 g.10m–2, respectively. Highest numerical densities and biomass densities were recorded from the Brisbane River and streams of the Moreton Coast, respectively. Juvenile and subadult fish (≤150 mm SL, corresponding to two years or younger [359, 362]; hereafter termed juveniles) were present in greater densities (mean and maximum density of 0.26 and 4.66 individuals.10m–2, respectively) than adult fish (>150 mm SL, 2+ years [359, 362]) (mean and maximum density of 0.09 and 0.75 individuals.10m–2, respectively) in hydraulic habitat units where this species occurred in south-eastern Queensland (n = 408 and 282 samples for juveniles and adults, respectively) [1093]. Conversely, adult fish formed greater biomass densities (mean and maximum biomass of 27.64 and 208.79 g.10m–2, respectively) than juveniles (mean and maximum biomass of 3.04 and 41.10 g.10m–2, respectively) (n = 266 and 399 samples for adults and juveniles) [1093].
This species occurs in streams of a wide range of gradient from lowland channels with a gradient less than 0.1% to cascade sections of streams with a gradient exceeding 7%. It most commonly occurs in and is most abundant in Table 3. Macro/mesohabitat use by Tandanus tandanus in the Wet Tropics region (juveniles and adults combined). Data summaries for 223 individuals collected from 54 locations in the Mulgrave/Russell, Johnstone and Tully rivers between 1994 and 1997 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
Tandanus tandanus is widespread and moderately common in coastal rivers of northern and central New South Wales [282, 437, 438, 441, 484, 553, 814]. This species was once present throughout much of the MurrayDarling Basin [1069] where it was historically very common [778], being rare or absent only upstream of Wagga in the Murrumbidgee River and upstream of Mulwala in the Murray River. Recent surveys [553, 807] and reviews by Morris et al. [965] and Clunie and Koehn [310] reveal that since the late-1970s and early-1980s, it has undergone dramatic declines in distribution and abundance throughout much of the basin, although it is still present and locally common in some parts of the Queensland section of the upper Darling River (Condamine River) and in many impoundments in New South Wales and Victoria. Refer to Morris et al. [965] and Clunie and Koehn [310] for more details on the present distribution and population status of this species in southern Australia.
Parameter 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
Mean
W.M.
1.0 1.5 8.1 10 1.9 0
334.9 67 104 722 39.1 85
71.4 16 40.2 74 10.9 34.7
80.9 17.6 41.9 59.6 11.2 41.7
Gradient (%) 0.05 Mean depth (m) 0.19 Mean water velocity (m.sec–1) 0
Juveniles of this species have been reported to form loose schools but adults are usually solitary, except when breeding [270]. Macro/mesohabitat use Tandanus tandanus is found in a variety of lotic and lentic habitats including small coastal streams, rainforest streams, large rivers and in dune lake and stream systems. It is also common in some artificial lakes and impoundments.
141
7.33 0.87 0.45
0.84 0.40 0.17
0.75 0.42 0.17
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48.0 52.0 72.0 56.0 41.0 76.0 98.0
5.6 15.3 21.1 14.1 13.1 21.9 9.1
2.8 12.4 24.2 14.8 14.9 23.8 7.3
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
7.0 6.8 33.0 75.0 10.0 47.6 12.5 11.4 35.0 75.0
0.4 0.2 2.1 7.1 0.5 7.9 2.0 1.8 8.0 16.4
0.4 0.1 1.4 6.7 0.6 10.8 1.7 1.8 11.4 21.5
Freshwater Fishes of North-Eastern Australia
streams of a gradient less than 1% (Table 3). Such streams tend to be about 0.40 m deep and with current velocities of 0.17 m.sec–1 and are best typified as riffle/runs. Although this species may be found in stream reaches dominated by mud and sand, the average substrate composition in sites in which it occurs tends to be highly diverse containing approximately equal proportions of sand gravel and cobbles and a slightly elevated proportion of fine gravel and rocks. These latter two substrate types are proportionally more important in sites in which this species is abundant.
Table 4. Macro/mesohabitat use by Tandanus tandanus in rivers of south-eastern Queensland (juveniles and adults combined). Data summaries for 3050 individuals collected from samples of 600 mesohabitat units at 183 locations in south-eastern Queensland streams between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Tandanus tandanus occurs in streams with moderately abundant in-stream cover (Table 3). It is not common in streams with abundant introduced para grass, however. Leaf litter is moderately abundant in sites in which this species is common and the disparity between the mean and weighted mean values for undercut banks and root masses, suggest that this species is more abundant in sites in which these microhabitat elements are common.
Min.
5.6 10 211.7 4.0 270.0 0.5 335.0 0.0 460 1.8 46.8 0.0 91.1
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec–1) 0
In rivers and streams of south-eastern Queensland, T. tandanus is widely distributed, ranging between 0.5 and 335 km from the river mouth and at elevations up to 460 m.a.s.l. (Table 4). It most commonly occurs within 200 km of the river mouth and at elevations around 110 m.a.s.l. It is present in a wide range of stream sizes (1.8–46.8 m width) but is more common in streams of intermediate width (6–10 m) and with low to moderate riparian cover (<40%). There is little ontogenetic difference in the macrohabitat use of T. tandanus, possibly suggesting that juveniles do not disperse far from the natal habitat [1093]. However, some ontogenetic variation in mesohabitat use is evident, with juvenile fish collected more frequently in relatively shallow, moderately flowing runs and adults more commonly collected in deeper runs and pools (weighted mean velocity = 0.14 m.sec–1 and 0.12 m.sec–1 for juveniles and adults, respectively; weighted mean depth = 0.34 m and 0.41 m for juveniles and adults, respectively) [1093]. Adults and juveniles were collected over a similarly wide range of substrate conditions, but both age-classes were most common in mesohabitats dominated by sand, fine gravel, coarse gravel and cobbles. Juveniles and adults were especially common in mesohabitats with abundant aquatic macrophytes, filamentous algae, leaf litter undercut banks and root masses (Table 4). However, adults appear to prefer mesohabitats with a greater availability of undercut banks (weighted mean 16.1% versus 8.9% for adults and juveniles, respectively) and root masses (18.7% versus 13.9% for adults and juveniles, respectively) [1093].
Max.
3.02 1.10 0.87
Mean
W.M.
796.8 1216.7 46.6 56.8 146.6 175.7 97 110 8.9 7.6 38.6 38.5 0.38 0.41 0.13
0.31 0.35 0.13
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
57.1 100.0 72.4 78.2 66.8 57.1 76.0
4.5 16.9 21.1 26.8 21.3 7.8 1.6
3.8 14.9 20.4 30.3 21.8 7.6 1.3
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
69.6 65.9 45.0 65.7 39.1 92.6 37.6 22.5 96.3 100.0
11.0 8.4 1.5 4.8 1.3 12.9 3.7 3.3 13.9 19.0
12.2 10.8 1.3 4.9 1.6 10.5 3.2 3.3 10.4 15.0
benthic pool-dwelling species [553] and it has been reported to occur over sand or gravel substrates in billabongs, ponds, lakes and turbid slow-flowing streams and rivers, and where aquatic and fringing vegetation is common [270, 310, 814, 1069]; it has also been reported to be more abundant in lakes and backwaters than in flowing water [749]. Richardson [1133] reported that juvenile fish in the Tweed River, northern New South Wales, were more common in deep, slow flowing sites with mud-gravel substrates, aquatic plant cover and deposits of organic detritus. Adults had similar habitat preferences but were more common in areas with bedrock substrates. Microhabitat use Both juvenile and adult T. tandanus in the Wet Tropics region occur most frequently in water velocities of less than 0.3 m.sec–1 although juveniles are more frequently found in faster flowing water than adults (Fig. 1a). Both
Tandanus tandanus has been reported to occur at elevations greater than 600 m.a.s.l. in the Condamine River [310]. Harris and Gehrke classified T. tandanus as a 142
Tandanus tandanus
aquatic macrophytes and leaf litter than are juveniles (Fig. 1). Very small juveniles (<60 mm SL) are frequently found in very swiftly flowing water, sheltering under the straplike leaves of Aponogeton spp. In summary, adult T. tandanus in the Wet Tropics region tend to occur most frequently in deeper, slow waters over a mixed substrate with a high proportion of mud and sand, and in association with root masses, undercut banks and woody debris, whereas juveniles tend to occur more commonly in shallow, swiftly flowing waters associated with the substrate, leaf litter or macrophytes.
age classes are benthic in habitat occupying the lower onethird of the water column and often in direct contact with the substratum (Fig. 1d); they consequently experience reduced focal velocities compared to average current velocity (Fig. 1b). Adult and juvenile T. tandanus partially segregate with respect to depth and substrate composition with juveniles being more frequently collected from shallow areas (10–40 cm) (Fig. 1c) with coarse substrates (Fig. 1e) whereas adults prefer deeper areas with slightly finer substrates. Adults are more frequently collected from large woody debris, root masses and undercuts and less frequently from amongst the substrate, associated with
(a) 60
(b)
(a)
40 30
60
40
40
20
20
0
0
40
20 20 10 0
0
Mean water velocity (m/sec)
(c)
Focal point velocity (m/sec) 60
(d)
25
30
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 80
20 60
40
15
20 10
20
0
0
25
(b)
60
(e)
Total depth (cm) 40
20
40
10
(f)
5
20
0
0
Total depth (cm)
Relative depth 30
30
(e)
10
20
10 5
10
0
0
Substrate composition
20 15
20
15
Relative depth
(f)
10
5
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Tandanus tandanus juveniles (solid bars) and adults (open bars) in the Wet Tropics region. Summaries derived from capture records for 76 juvenile (≤150 mm SL) and 89 adult (>150 mm SL) individuals from the Johnstone and Mulgrave rivers, northern Queensland, over the period 1994–1997 [1093].
Microhabitat structure
Figure 2. Microhabitat use by Tandanus tandanus juveniles (solid bars) and adults (open bars) in south-eastern Queensland. Summaries derived from capture records for 550 juvenile (≤150 mm SL) and 167 adult (>150 mm SL) individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
143
Freshwater Fishes of North-Eastern Australia
(1996), cited in [310]) and may explain anecdotal accounts of fish kills following snow melts [310]. Laboratory experiments [749, 752] revealed that juvenile fish (60–80 mm, probably sourced from the Murray-Darling Basin) became motionless and lay on their sides at very low temperatures (4°C), and did not recover if exposed to this temperature for more than a few days. Fish did however, survive shortterm (~1 hour) exposure to temperatures as low as 1°C [749, 752]. The deaths of adult catfish (up to 1.8 kg) were observed in artificial outdoor ponds exposed to winter temperatures around 4°C [749, 752]. When gradually acclimated, fish in the laboratory survived for several days at temperatures greater than 35°C but became very distressed and lost their equilibrium at 38°C, surviving when temperatures were subsequently reduced [749, 752].
In rivers of south-eastern Queensland, T. tandanus was most frequently collected from areas of low water velocity (usually less than 0.2 m.sec-1) (Fig. 2a and b). Juveniles (≤150 mm SL) have been recorded at maximum mean and focal point water velocity of 1.44 and 1.01 m.sec-1, respectively. Adults (>150 mm SL) have been recorded at lower maximum mean and focal point water velocities (0.66 and 0.48 m.sec–1, respectively) than juveniles. This species was collected over a wide range of depths but juveniles were common in water depths between 10 and 50 cm; adults were collected more frequently in deeper water (Fig. 2c). Both age classes are benthic in habit and most commonly occupy the lower water column or occur in direct contact with the substrate (Fig. 2d). It is found over a wide range of substrate types but most often over sand, gravel and cobbles, with little difference in substrate use between age classes (Fig. 2e). Adult T. tandanus were more commonly collected close to the stream-banks (within 1 m) than juveniles (75% of adults versus 49% of juveniles) [1093], and almost always in close association with some form of submerged cover (Fig. 2f). Substantial ontogenetic variation in the use of microhabitat structures was evident: juveniles were most frequently collected in close association with the substrate, aquatic macrophytes (especially Vallisneria nana and Potomogeton spp.), filamentous algae and leaf litter beds; adults were more commonly collected in undercut banks, root masses and large woody debris (Fig. 2f).
Tandanus tandanus appears to tolerate a wide range of dissolved oxygen concentrations, fish in south-eastern Queensland having been collected in waters ranging from 0.3–17.1 mg.L–1 (Table 5). Field experiments revealed that subadult fish (200–300 mm) introduced to saline pools in the Wimmera River, western Victoria, showed acute LD50s at dissolved oxygen concentrations of 0–2% saturation (Ryan et al. (1999), cited in [310]). In contrast, T. tandanus in the Wet Tropics region has been recorded from welloxygenated streams only (Table 5). Significant fish kills involving this species in the upper North Johnstone River downstream of Malanda have been associated with organic contamination and high levels of BOD. It is possible that substantial variation in tolerance to hypoxia occurs across this species’ range.
Several workers have reported a strong association between T. tandanus and aquatic vegetation in the Murray-Darling Basin and elsewhere, but a reliance on this habitat component is not universal; Clunie and Koehn [310] concluded that the significance of aquatic macrophytes to this species was unclear and warranted further investigation.
This species has been collected in acidic and basic conditions in streams of south-eastern Queensland (range 4.8–9.1) and the Wet Tropics region (range 5.1–8.4) (Table 5). Southern populations also appear tolerant of high levels of suspended sediment. The maximum turbidity at which this species has been recorded in south-eastern Queensland is 250 NTU, but it appears to prefer less turbid waters (mean 6.3 NTU). This species is also relatively common in the naturally turbid waters of the upper Darling River, where it has been recorded at turbidities up to 910 NTU (D. Moffat, pers. comm., cited in [310]). Streams of the Wet Tropics in which this species occurs are generally very clear and the high value reported in Table 5 (29.7 NTU) was associated with a summer thunderstorm and was transient only.
Environmental tolerances Tandanus tandanus is reputedly a hardy species [748, 749], an observation supported by some limited experimental and field evidence of the environmental tolerances of this species. In Queensland rivers it has been collected over a relatively wide range of physicochemical conditions (Table 5). Populations from south-eastern Queensland appear tolerant of a relatively wide range of temperatures (8.4–33.6°C), whereas those of rainforest streams of the Wet Tropics have been collected over a smaller range (17–29.9°C). In the Murray-Darling Basin, low water temperatures due to cold water discharges from impoundments have been implicated in fish kills and a decline in range in the upper Murray and Murrumbidgee rivers [270, 310, 749, 1069, 1224]. The stress of low water temperatures may predispose T. tandanus to infection (Bowmer et al.
We have collected T. tandanus in streams with relatively high conductivities (up to 3580 µS.cm-1) (Table 5). This species is able to tolerate relatively high salinities: experimental acute and chronic LD50s have been observed as 13.6 ppt and 17.8 ppt, respectively [311, 641]. Field experiments revealed that subadult fish (200–300 mm)
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Reproduction The reproductive biology and early development of southern populations of T. tandanus is comparatively well studied but there is little information available for this taxon in the Wet Tropics region (Table 6). This species spawns and completes its entire life cycle in freshwater and will breed in outdoor ponds [750, 751, 809] and impoundments [99, 310, 359]. Eggs fertilised in outdoor ponds have also been reared in aquaria [751].
introduced to saline pools in the Wimmera River, western Victoria, showed acute LD50s at salinities between 23.4 ppt and 26.4 ppt (Ryan et al. (1999), cited in [310]). Juvenile fish were reported by Ryan et al. to be significantly less tolerant than adults to elevated salinities, these authors speculating that young fish had poorly developed osmoregulatory abilities and insufficient time to acclimatise to elevated salinities through their life history. Waters of the Wet Tropics region where this species occurs are very dilute (Table 5).
Sexual maturity is reached within five years of age. Davis [359, 361], in his study of T. tandanus from the Gwydir River, observed that fish of both sexes commenced gonadal development (reproductive stage III) at two years of age. Fifteen per cent of male fish examined were sexually mature (reproductive stage V) at three years of age and at weights between 600–700 g (equivalent to about 380–395 mm TL); all males were mature by five years of age and at weights over 1.2 kg (equivalent to about 460 mm TL or greater). Some females in this study tended to mature at a slightly smaller size (27% of females were of reproductive stage V at weights of 400–500 g, equivalent to 335–355 mm TL) but all females examined had reached sexual maturity at the same age and size as males [359, 362]. Bluhdorn and Arthington [205] observed that female fish in the Burnett River, south-eastern Queensland, also mature at a slightly smaller size than males; the smallest mature female (reproductive stage V) was 299 mm SL and the smallest mature male was 384 mm SL. Richardson [1133] reported that male fish in the Tweed River, northern New South Wales, matured at 370 mm TL and females matured at 390 mm TL. Sexually precocious females (~150 mm, 50–80 g) have been reported from a small overcrowded dam in New South Wales (P. and J. Norman, pers. comm., cited in Clunie and Koehn [310]).
There have been several large fish kills in eastern Queensland waters that have included T. tandanus [10, 16, 1093]. Despite investigation by the Queensland Environmental Protection Agency in some cases, the cause(s) of these fish kills could not usually be established with any certainty, although hypoxic or anoxic conditions associated with large accumulations of organic matter following flow events were often implicated [10, 16, 1093]. Several instances of fish kills have been reported from agricultural areas in the Murray-Darling Basin and elsewhere, although the causes are usually unclear [81, 221, 310]. Pesticide runoff from cotton growing areas has been implicated in some fish kills [81]. Tandanus tandanus sampled from tributaries of the Darling River in central New South Wales have been found to contain endosulfan residues up to 0.31 mg/kg wet weight [998, 1002]. These levels lie within the concentration range shown to cause ultrastructural changes in the gills and liver of T. tandanus exposed to endosulfan under experimental laboratory conditions [999, 1000, 1001]. Olsen [1026] detected relatively high residues of organochlorine insecticides (DDT = 1090 µg.kg-1 and Dieldrin = 280 µg.kg-1) in T. tandanus from South Australia.
Tandanus tandanus has an extended breeding season during spring and summer in south-eastern Queensland; ripe (stage V) and spent fish in the Burnett River were present between October and March [99]. Similar temporal patterns in GSI values were observed with peak monthly mean GSI values occurring in October for females (~6.2%) and remaining elevated until about January. Male GSI values showed a similar temporal pattern but were much lower (<1%, but note that these were estimated from maturing fish of stage IV only) [99]. Peak GSI levels for female fish in the Tweed River, northern New South Wales were also recorded in October [1133], with spawning suspected to occur through to February [1135]. The phenology of spawning in southern Australia is generally similar (if slightly more concentrated and later in the year) in Queensland rivers. Females from Murray-Darling populations were reported to have the highest standardised ovarian weights and the largest
Table 5. Physicochemical data for Tandanus tandanus in the Wet Tropics region and south-eastern Queensland over the period 1994 to 2003 [1093]. Parameter
Min.
Max.
Wet Tropics region (n = 133) Water temperature (°C) 17 Dissolved oxygen (mg.L–1) 4.9 pH 5.1 Conductivity (µS.cm–1) 6 Turbidity (NTU) 0.2
Mean
29.9 11.6 8.4 62 29.7
23.1 7.0 7.2 33.9 3.4
South-eastern Queensland (n = 380) Water temperature (°C) 8.4 33.6 Dissolved oxygen (mg.L–1) 0.3 17.1 pH 4.8 9.1 Conductivity (µS.cm–1) 19.5 3580.0 Turbidity (NTU) 0.2 250.0
19.5 7.6 7.7 488.9 6.3
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Freshwater Fishes of North-Eastern Australia
intraovarian eggs in November and December, and ripe fish were most abundant in January and February, leading Davis [359, 361] to conclude that spawning was concentrated in summer from January to March. Note however that a small number of ripe fish were present as early as September [359, 361]. Overall sex ratios for 2+ fish (n = 976) from the Gwydir River have been reported as 0.94 females for every male [361]. Sex ratios for adult fish (minimum 250 mm TL, n = 191) from the Burnett River were reported as 0.78 females for every male [99].
areas, elevated discharges may occur during the summer breeding period and it has been suggested that the consequent inundation of floodplains and shallow backwaters may encourage food production and facilitate growth of fish larvae and juveniles [361]. However, it appears that this species may require stable low flows for spawning and nest-building. In artificial ponds, fluctuating water levels that expose nests before the eggs are laid can result in the abandonment of nests and although another nest may be built, a sequence of several interruptions will result in a resorption of oocytes and the failure of a female to breed in a particular year [750].
The spawning stimulus for T. tandanus is unknown but Davis [361] suggested that increasing temperature was the primary factor stimulating spawning. The October peak in reproductive activity in Burnett River populations occurred at surface water temperatures of 23°C and ripe females were not recorded at temperatures below 20°C [99]. This species (possibly the male [1158]) constructs a nest in which the female deposits the eggs. Nest building may occur between one and four weeks prior to actual spawning [310]. Critical temperatures for the commencement of nest-building and spawning in southern populations have been reported as 24°C [361, 750], running ripe males have been observed at 18°C (Raadik, pers. comm., cited in Clunie and Koehn [310]), fish have been observed on nests at bottom temperatures of 13.8°C and the first eggs were laid at water temperatures of around 21°C [310]. Spawning cues are probably not associated with rising water levels or flooding [361] but this may hasten spawning for fish in artificial outdoor ponds [750]. In southern
In the Wet Tropics region, nest construction commences in late September or October [1093] and very small individuals are present in November or December (Figure 3). In south-eastern Queensland, we have observed nests in early September [1093] and the peak spawning period in spring and early summer in this region coincides with increasing water temperatures, increasing day length and a reduced likelihood of elevated discharges. However, length-frequency data (Figs. 3 and 4) indicate that very small juvenile fish (<30 mm SL) were present in streams of both northern and south-eastern Queensland for an extended period from spring through summer in the Wet Tropics region and spring to autumn in south-eastern Queensland. Juveniles from 30–60 mm SL were most common in south-eastern Queensland streams in the summer months, suggesting that the development of
30
40
Spring (n = 445)
30
Summer (n = 735)
Aug. - Dec. (n = 244) 20
Jan. - April (n = 92) May - July (n = 193)
AutumnWinter (n = 1169)
20
10
10
0
0
Standard Length (mm) Figure 3. Temporal variation in length-frequency distributions of Tandanus tandanus, from sites in the Mulgrave and Johnstone rivers of the Wet Tropics region sampled between 1994 and 1997 [1093]. The number of fish from each period is given in parentheses.
Standard length (mm) Figure 4. Seasonal variation in length-frequency distributions of Tandanus tandanus, from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
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Tandanus tandanus
T. tandanus in the upper Noosa River, south-eastern Queensland: ‘… we noticed a violent commotion in the water under an overhanging bank, and on investigation with a paddle we had the good luck to pick up four large and healthy River Jewfishes (Tandanus tandanus), the marriage ceremonies of which we had thus cruelly and wantonly interrupted.’
larvae and juveniles occurred not only during low-flow conditions normally experienced during spring and early summer in this region, but also during higher flows normally occurring in mid- to late summer [1093]. A prolonged spawning season is not evident in streams of the Wet Tropics region (Fig. 3). It is noteworthy that southeastern populations are dominated by individuals less than 90 mm SL whereas the northern is skewed towards larger individuals.
The abundance of adult males in individual runs or pools in streams of the Wet Tropics region often seems to be in excess of the number of nests particularly if nests are located close to areas of undercut banks or extensive root masses [1093]. It is unknown whether males compete for nest sites, whether they assess potential mates or indeed whether females assess the suitability of males and their nests, or whether small males have alternative mating strategies when faced with a shortage of potential nesting sites.
Nesting occurs in a wide range of habitats including runs and pools in small to medium sized stream in south-eastern Queensland [1093], flooded and shallow portions of large streams and still backwaters in southern Australia [751, 933, 1093], and also in shallow impoundments (e.g. Wivenhoe Dam and North Pine Dam [1093]). Merrick and Midgley [933] observed a nest in water depths of 0.6 m and mean water velocities of 0.05–0.07 m.sec–1 in the Mary River, south-eastern Queensland. However, microhabitat characteristics of nest sites do vary widely and we have observed active nests in south-eastern Queensland streams in water depths ranging from 0.2–1.8 m and velocities ranging from 0–0.1 m.sec-1 [1093]. Clunie and Koehn [310] have reported nests in water depths ranging from 0.35–1.6 m in a Victorian Lake. Nest location in streams of the Wet Tropics region appears to be non-random and associated with the thalweg track. Nests are more frequently situated at the downstream end of a run than in the upper half and their location may be associated with areas of downwelling. The extensive engineering that takes place during nest construction may even create areas of greater exchange between surface and hyporheic waters.
Demersal, non-adhesive eggs are deposited in the nest and these settle within the interstices of the substrate. It is unknown whether fertilisation occurs in the water column before egg settlement within the nest or subsequently as the male swims over and inspects the nest after each bout of egg deposition by the female [749, 933, 936]. After spawning, the female moves away and the male guards and maintains the nest [310, 933]. Males have been observed aggressively chasing away intruders (including alien species such as redfin – Perca fluviatilis [310]) and fanning the nest with their fins to clear away sediment and debris. This possibly also facilitates egg settlement within the substrate [310, 748, 1093, 1158]; however, both sexes may guard the nest in artificial ponds [749]. We have also observed single adult fish periodically making forays onto the nest after taking refuge in adjacent undercut banks and root masses (usually within 3 m of the nest) in the Daintree and Mary rivers [1093]. The same nest may be used in consecutive years, although it is unclear whether by the same pair of fish [310, 933]. Three separate size classes of larvae sampled within a nest in a Victorian lake [310] indicate that multiple spawnings may also occur in the same nest, with the male possibly attracting a number of females to the nest over a breeding season [310]. It is also possible that several males used the same nest over the breeding season [310].
The nest is usually characterised by a circular, saucershaped depression in the substrate, 0.5 to 2 m in diameter, and made of coarse sand or gravel with a central depression, usually of coarser material such as coarse gravel and sometimes rocks and sticks [270, 310, 750, 933]. Human refuse such as bottles and cans have been recorded in the central portion of some nests [310]. Some nests are simply slight depression in beds of aquatic charaphytes (Chara spp. and Nitella spp.) with very little exposed substrate [310, 1093]. Larger fish are reported to construct larger nests [310]. Nests can also be oval or U-shaped (nest shape may depend on locality, with fish in the Bellinger River, northern New South Wales, usually constructing U-shaped nests (Bishop, cited in [982]). In an artificial outdoor pond, spawning has also been reported in the absence of a nest but instead occurred directly on gravel [749].
Descriptions of gonad morphology and histology are available in Davis [359, 360] and Machin [831]. Fecundity for T. tandanus varies with fish size, linearly with weight and exponentially with length for fish from the Gwydir River [359, 361] (Table 4). In this study, estimates of total fecundity for mature and ripe fish ranged from 2000 eggs for fish of 675 g to 20 600 eggs for fish of 2275 g [359, 361]. In artificial ponds fish ranging in weight from 1250 to
Elaborate courtship and spawning displays have been reported to occur directly above or near the nest [283, 933, 1158, 1387]. In 1917, Ogilby [1023] published the following observations of reproductive behaviour of
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Freshwater Fishes of North-Eastern Australia
Incubation periods appear relatively short and have been reported to range from 8 to 11 days (at 15–21°C) [748] and 6 to 7 days (at 19–25°C) in southern Australia [749, 751]; the duration of egg development is likely to be shorter in warmer water temperatures in northern rivers. Photographic images and brief descriptions of larval development are available in Lake [749, 751]. Larvae are comparatively poorly developed at hatching, ranging in size from 7.0 to 7.4 mm TL and lacking barbels and pectoral fins. Barbels appear as tiny buds three days after hatching [751]. At seven days larvae were reported to be 12 mm and had distinguishable barbels [749, 752] but larvae at 12 days have also been reported to attain lengths of only 10.5–11.0 mm TL [751]. Larvae were free swimming at
2000 g were estimated to contain between 18 000 and 26 000 eggs [750] suggesting they were more fecund than wild fish of equivalent size (9000 to 15 000 eggs for fish from the Gwydir River [359, 361]). Intraovarian eggs are a clear dark amber colour and range in size from about 2.0–3.0 mm diameter, increasing with the size and also fecundity of the fish [361, 751]. Eggs range from 3.1–3.4 mm in diameter when water-hardened [749, 751]. The developing eggs are spherical, light green to yellow in colour, the perivitelline space is small, the yolk is granular in appearance without major oil globules and the chorion is thick (0.15–0.2 mm), slightly rough and transparent [749, 751]. Photographic images of egg development are available in Lake [749, 751]. Table 6. Life history information for Tandanus tandanus. Age at sexual maturity
4–5 years [359, 361]
Minimum length of gravid (stage V) females (mm)
335–355 mm TL [359, 361]; 299 mm SL [205]; 390 mm TL [1133]; 150 mm TL [310]
Minimum length of ripe (stage V) males (mm)
380–395 mm TL [359, 361]; 384 mm SL [205]; 370 mm TL [1133]
Longevity
At least 8 years (may be considerably longer) [359, 362]; 11–12 years [310, 1209]
Sex ratio (female to male)
0.94:1 [361]; 0.78:1 [99]
Occurrence of ripe (stage V) fish
September–March; slightly later in cooler southern states [99, 270, 359, 361]
Peak spawning activity
October–January in the Burnett River [99]; October in the Tweed River [1133]; January–March in the Murray-Darling Basin [359, 361]
Critical temperature for spawning
? >20°C [99, 361, 750]
Inducement to spawning
? Increase in water temperatures; water level rise may hasten spawning [361, 750]
Mean GSI of ripe (stage V) females
Maximum 6.2% [99]
Mean GSI of ripe (stage V) males
Maximum <1% (stage IV only) [99]
Fecundity (number of ova)
Maximum total instantaneous fecundity = 26 000 (increases with fish size) [359, 361, 750]
Total fecundity (TF)/Length (mm TL) or Weight (g) relationship
TF = 5.2 x 10–8 L4.19, r = 0.593, n = ~37, p<0.001 [359, 361]; TF = 7.947 W – 1156, r = 0.547, n = ~37, p<0.001 [359, 361]
Egg size (diameter)
Intraovarian eggs from ripe fish 2.0–3.0 mm, eggs size increasing with size and fecundity of the fish [359, 361]; Water-hardened eggs 3.1–3.4 mm [749, 751]
Frequency of spawning
Annually [732]
Oviposition and spawning site
Non-adhesive, demersal eggs deposited in an oval or U-shaped gravel nest and settle within interstices of substrate. Nest usually circular, saucer-shaped depressions (0.5–2 m diameter), composed of fine - coarse gravel (maximum substrate size 5 cm). Nest constructed by male 1–2 weeks prior to spawning. [750, 933, 936]
Spawning migration
None known
Parental care
Usually male but both sexes may guard, clean and fan nest until eggs hatch. Nestguarding adults observed to take refuge in adjacent undercut banks and root masses in the Daintree River, northern Queensland and the Mary River, south-eastern Queensland [750, 933, 936, 1093]
Time to hatching
6–7 days (at 19–25°C) [750, 751]; 8–11 days (at 15–21°C) [748]
Length at hatching (mm)
7.0–7.4 mm TL [751]
Age at free swimming stage
12–14 days [751]
Age at loss of yolk sack
?
Age at first feeding
19 days [751]
Length at first feeding
?
Length at metamorphosis
14–16 mm TL [751]
Age at metamorphosis
23–24 days [749, 751]
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Tandanus tandanus
and adult fish in pool-overfall type fishways in the Brisbane River basin (details on abundance, timing or direction of movements unclear). Small numbers of adults have been recorded in fishways on tidal barrages in the Kolan [11, 232], Burnett [1173, 1276, 1277] and Mary rivers [158, 159]. Fish appeared to be making upstream movements as they were reported to be ascending the fishways in the Fitzroy, Kolan and Burnett River studies [232, 1173, 1276, 1277]. Stuart and Berghuis [1276, 1277] recorded low numbers of adult T. tandanus migrating upstream in May and August and throughout the spring months. These authors suggested that these fish were moving upstream after being displaced downstream of the tidal barrage by flood events [1276, 1277]. Reynolds [1131] speculated that the lack of a distinct spawning or dispersal migration indicates that local populations of this species are likely to be susceptible to local anthropogenic disturbances.
12–14 days and fed at 19 days, with the pectoral fin buds visible by this time [751]. Larvae reached 15 to 19 mm by 17–21 days and larval development was almost complete at 23 days [749, 751]. Following metamorphosis, growth is rapid, reaching 90 mm TL in the first winter, 300–400 mm TL by 16 months, 170–360 mm by 30 months, 250–480 by 42 months and 500 mm by the sixth year [362, 752, 936]. The lifespan of T. tandanus is unknown and estimates vary depending on the method of age determination used; lifespan may also vary among populations due to genetic and environmental factors [310, 1209]. Estimates of fish from the Gwydir River using dorsal spine annuli validated with fish of known age and tagging data, recorded a maximum age of eight years [359, 362]. Elsewhere, maximum ages based on otolith analysis have been estimated as 11–12 years [1209] and 12 years (T. Raadik, pers. comm., cited in Clunie and Koehn [310]. Movement Limited information on the movement patterns of T. tandanus is available. This species has been suggested to be generally sedentary with a small home range [359, 362, 1133]. Adults are mainly active at night with peak activity occurring during dusk and early evening [359]. Adults may be territorial, especially during breeding season [933]. Adult fish have been reported to usually remain within the one locality and return to within 100 m if displaced from it [359, 362]. Tagging return data from adult fish in the Tweed River revealed that of the 8% of fish recaptured, none had moved more than 50 m after being at liberty for almost six months [1133]. This species does not usually undergo long distance movements although a downstream movement of approximately 14 km was documented for an individual fish tagged during a low flow period and recaptured following a large flood in the Murray River, South Australia [1128, 1131]. In this study of 425 tagged fish, 60% of 85 recaptured fish had not moved from the original tagging location and 37% moved less than 10 km up or downstream throughout the study period. During low flow periods only, the maximum movements upstream and downstream were 4 and 8 km, respectively. One individual was recaptured five times over a 27-month period [1128, 1131]. Upstream movements have also been documented during floods in the Namoi River, New South Wales [143]. Larvae and juveniles probably emigrate from the adult nesting habitat and colonise adjacent areas [1131]. Five small juveniles (15–20 mm SL) were collected in an overnight drift-net set downstream of riffle and located at least 100 m upstream or downstream from the closest nest site in a tributary of the Mary River [1093]. There are several instances where juveniles and adults of this species have been recorded using fishways on weirs and tidal barrages. Johnson [658] collected juvenile
Trophic ecology Diet data for T. tandanus juveniles (≤~150 mm SL) and adults (>~150 mm SL) is available for individuals sampled from rivers and streams in the Wet Tropics region of northern Queensland [1097] and central Queensland [1080], and from rivers, streams and impoundments in south-eastern Queensland [80, 99, 100, 103, 205], coastal central New South Wales [555], and the Murray-Darling Basin [359, 363]. Tandanus tandanus is a carnivorous species, juveniles relying on generally small-sized food items, switching to larger food items with growth (Fig. 5). The diet of juvenile fish is dominated by aquatic insects (61.9%), fish (13.6%), microcrustaceans (10.4%) and terrestrial invertebrates (9.5%). Small amounts of detritus, molluscs and macrocrustaceans are also consumed (Fig. 5). Spatial variation in the diets of juvenile fish is apparent, with microcrustaceans, fish and terrestrial invertebrates occurring in the diets of juvenile fish collected during the filling phase of an impoundment in the Gwydir River (Murray-Darling Basin) [359, 363]. The diets of juveniles from streams in south-eastern Queensland [80] and the Wet Tropics region [1097] were composed primarily of aquatic insects (>83% in both studies). Adult fish consume a wide range of food types including large crustaceans (27.2%), aquatic insects (25.5%), particulate detritus (16.4%), molluscs (14.9%), terrestrial invertebrates (7.3%) and fish (4.7%). The role of detritus in the diet of T. tandanus is unclear: it may simply be ingested incidentally during benthic foraging, or intentionally as some workers report it to be composed of particulate organic matter as well as benthic algae (e.g. filamentous algae, diatoms and desmids) [917], all of which may be assimilated by this species. Anatomical features of T. tandanus suggest specialisation for benthic
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Freshwater Fishes of North-Eastern Australia
We can find no published information on the feeding ecology of T. tandanus larvae, although 27-day-old larvae in aquaria are reported to consume cladocerans, copepods and chironomid larvae [751].
T. tandanus (juveniles), n = 290 Terrestrial invertebrates (9.5%)
Fish (13.6%)
Detritus (2.2%)
Microcrustaceans (10.4%)
Conservation status, threats and management Recent detailed reviews of the conservation status, threats and management requirements of T. tandanus are available in Morris et al. [965] and Clunie and Koehn [309, 310]. These reports highlight the fact that despite longheld concerns about the declining distribution and abundance of T. tandanus, particularly in the southern Australia, this species has generally received little formal recognition as a threatened species until very recently. As early as 1971, Lake [754] identified T. tandanus as a species whose distribution and/or abundance had been considerably reduced. In 1984, Cadwallader et al. [273] listed this species as Indeterminate – Possibly Threatened in Victoria but this classification was upgraded to Vulnerable in 1990 [731, 1004] and T. tandanus is now listed under the Flora and Fauna Guarantee Act 1988 [310]. In 1991, Lloyd et al. [816] considered T. tandanus to be Vulnerable in the Murray-Darling Basin. In 1993, Wager and Jackson [1353] listed Tandanus sp. A from the Bellinger River as Rare, but T. tandanus was listed as Non Threatened. In 1997, T. tandanus was declared a protected fish in South Australia by regulations under the Fisheries Act 1982 [310]. In 2001, this species was listed as a member of an Endangered Ecological Community in the lower Murray River [1005] and in the lowland catchment of the Darling River [329] under the New South Wales Fisheries Management Act 1994. This species is not listed for protection under Queensland legislation. Size limits and bag limits are in place for this species in all states [616].
Macrocrustaceans (0.9%) Molluscs (1.4%)
Aquatic insects (61.9%)
T. tandanus (adults), n = 962 Fish (4.7%) Microcrustaceans (0.1%) Macrocrustaceans (27.2%)
Unidentified (2.1%) Terrestrial invertebrates (7.3%) Aerial aq. Invertebrates (0.1%) Terrestrial vertebrates (0.1%) Terrestrial vegetation (1.0%)
Detritus (16.4%)
Aquatic macrophytes (0.6%) Algae (0.3%)
Molluscs (14.9%)
Aquatic insects (25.5%)
Other macroinvertebrates (0.1%)
Figure 5. The mean diet of Tandanus tandanus juveniles (≤~150 mm SL) and adults (>~150 mm SL) (sample sizes for each age class are given in parentheses). Data derived from stomach contents analysis of fish from the Wet Tropics region of northern Queensland [1097], central Queensland [1080], south-eastern Queensland [80, 99, 100, 103, 205], coastal New South Wales [555, 1133], and the Murray-Darling Basin [359, 363].
foraging, enabling the ingestion of macroscopic food items together with particulate matter containing small invertebrates. These features include a broad, flattened head, inferior mouth, presence of barbels, grinding dental apparatus, fleshy gill rakers and long, convoluted intestine [917]. Chemoreception and the high density of sensory papillae around the head and mouth might play an important role in food location [270, 917]. Davis [359, 363] reported however, that there was little evidence of mechanical breakdown of ingested food items in his study and attributed this to the small, poorly developed teeth of T. tandanus, and the lack of significant modification of the gill rakers for grasping or crushing. Davis [359, 363] concluded that this species is an opportunistic carnivore capable of open foraging for large mobile prey and ‘grubbing’ in the substrate, enabling it to exploit a wide range of food sources (see also Clunie and Koehn [310] and references therein).
Morris et al. [965] and Clunie and Koehn [310] recommended that the conservation status of T. tandanus be upgraded. These authors specifically recommended that T. tandanus be listed as Endangered under the IUCN Red List, Vulnerable under the National Environment and Protection and Biodiversity Act 1999, Vulnerable under the Australia Society for Fish Biology listing of the conservation status of Australian Fishes [117], Vulnerable under the New South Wales Fisheries Management Act 1994, but no change to the current listing in other States. The most recent (2003) listing of the conservation status of Australian Fishes by the Australia Society for Fish Biology [117] includes Tandanus n. sp. from the Bellinger River as Data Deficient. However, as at December 2003, we are not aware if the conservation status of this species has been upgraded according to the recommendations of Morris et al. [965] and Clunie and Koehn [309].
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Tandanus tandanus
T. tandanus and the significance of the threats. Nevertheless, it was clear that certain factors such as those associated with water infrastructure development have contributed to the decline of catfish over large spatial scales, whereas other factors such as interactions with alien fish and the impacts of agricultural chemicals are likely to have affected this species at more localised scales [310]. A recovery plan [309] has been prepared for T. tandanus in which a detailed list of recovery and management actions is recommended.
Clunie and Koehn [310] thoroughly reviewed existing and potential threats to T. tandanus, particularly for populations in the Murray-Darling Basin. Potential threats to this species included those associated with water infrastructure development (changes to flow regimes, changes to thermal regimes and barriers to fish movement), introduced species (particularly carp and redfin), water quality and habitat degradation (due to sedimentation, salinity, algal blooms, agricultural chemicals, riparian vegetation degradation, removal of woody debris, and declines in abundance of aquatic vegetation), diseases and other potential impacts associated with the aquaculture industry and translocations (e.g. genetic implications), and commercial and recreational fishing pressures. Clunie and Koehn [310] cautioned that many of the threats faced by T. tandanus were potentially synergistic and complex, and this together with lack of detailed information on many aspects of the ecology of this species, made it difficult to accurately diagnose the specific causes of decline of
Similar threatening processes as those described above probably occur throughout much of the range of T. tandanus in Queensland, however this species is not obviously in decline yet. Greater effort is needed to define the phyletic structure of T. tandanus populations in Queensland in order to identify stocks that may be of enhanced conservation significance and to provide a more rigorous underpinning for any future translocation activities.
151
Retropinna semoni (Weber, 1895) Australian smelt
37 101001
Family: Retropinnidae
origin just before and opposite to anal fin base on posterior half of body. Small adipose fin located above posterior anal rays. Slender caudal peduncle and moderately forked, round-lobed caudal fin. Ventral keel extending along abdomen from behind pelvic fins to vent. Nuptial tubercles present on body and head, larger in males and also occurring on fins. Colour variable but usually olive-green to orange with fine black spots (melanophores) on dorsal surface. Minimal fin pigmentation and body often translucent with silvery peritoneum and vertebral column externally visible. Silvery spot on operculum, dark patch on caudal peduncle and occasionally, a purplish sheen along sides. Male specimens from south-east Queensland rivers often bright orange-red during spring reproductive period, particularly in tannin-stained waters. Specimens from some tributaries of the Mary River in south-eastern Queensland are often infested with numerous small (<2 mm diameter) encysted trematode metacercaria which appear as brownish-black spots beneath the skin. Dove [1432] provided a list of parasite taxa recorded from R. semoni in south-eastern Queensland. Emits a distinct cucumber odour when freshly caught. Preserved colouration usually opaque silvery, tan, or yellow-brown [34, 270, 887, 893, 936, 1093].
Description Dorsal fin: 7–11 rays; Anal: 13–19; Pectoral: 8–12; Caudal: 18–19 segmented rays; Pelvic: 6; Vertical scale rows: 50–70; Gill rakers on first arch: 16–25; Vertebrae: 45–53 [34, 270, 887, 893]. Retropinna semoni is a small fish known to reach 100 mm TL but more common to 50–60 mm TL [270, 893]. Fish in northern populations are commonly smaller than those in more southern areas [893]. Of 10 963 specimens collected in streams of south-eastern Queensland, the mean and maximum length of this species were 37 and 68 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 475 individuals (range 21–63 mm SL) sampled from the Mary River, south-eastern Queensland, is W = 0.5 x 10–5 SL3.227, r2 = 0.956, p<0.001 [1093]. Retropinna semoni is an elongate species with compressed body, relatively large eyes and rounded snout. Moderately large, terminal mouth extending back to below middle of eye. Small, cycloid and easily dislodged scales present on body but not head; extent of scale coverage on body varies among populations and may be reduced in populations from southern inland areas. Lateral line absent. Dorsal fin
152
Retropinna semoni
Systematics Retropinnidae contains four species from two genera Retropinna and Stokellia, occurring in coastal marine and freshwaters of south-eastern Australia, New Zealand and the Chatham Islands. Although phylogenetic relationships are unclear, the family Retropinnidae is thought to be closely related to other Southern Hemisphere salmoniformes including Protroctidae, Aplochitonidae and Galaxiidae [887, 889].
of the Murray River in eastern South Australia. Retropinna semoni is also present on Fraser and Moreton islands off the south-eastern Queensland coast. Inland, it occurs throughout much of the Murray Basin and northern tributaries of the Darling Basin. It is also present in Cooper Creek in the Lake Eyre drainage basin [52, 270, 507, 733, 814, 893, 1113, 1201, 1340]. Attempted introductions of R. semoni to Tasmania and Papua New Guinea have reportedly not been successful [887].
The systematics of the Retropinnidae has a very confused history, probably due largely to the high degree of variability in morphologic and meristic characters frequently observed within and among taxa [887]. Aspects of the taxonomy and relationships of members of the family have been discussed by McCulloch [877], Stokell [1268], Woods [1417] and McDowall [885, 887]. In the most recent and complete revision of the Retropinnidae, McDowall [887] provided a detailed history of the taxonomic problems of the family, listed the numerous generic and specific synonyms, and included full descriptions of all recognised species.
In central Queensland, R. semoni has been reported as far north as the Fitzroy River [754] but it has not been collected during numerous subsequent surveys of this basin [160, 404, 405, 823, 942]. The next most northerly record for this species is approximately 150 km further south in Baffle Creek [1349] and it is also present in the Kolan River [1349]. It appears to be quite uncommon in both rivers and has not been reported from fishway studies or riverine surveys of these basins [232, 658, 826]. Retropinna semoni is widely distributed in south-eastern Queensland and is present in most major rivers and streams from the Burnett River south to the border with New South Wales. It is generally very common in this region and often locally abundant, forming schools of thousands of individuals [1093]. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that it has been collected at 22 of 63 locations surveyed (10th most widespread species in the catchment) and formed 5.2% of the total number of fishes collected (fourth most abundant). It has not been recorded from the Elliott River and appears to be uncommon in the Burrum Basin [701, 736].
Retropinna Gill, 1862 [448] contains three species, two of which occur in Australia; the remaining members of the family occur in New Zealand [887, 893]. The Australian retropinnids have disjunct distributions with Retropinna semoni (Weber, 1895) [1370] present on the mainland and R. tasmanica McCulloch, 1920 [877] confined to Tasmania. Distribution and abundance Retropinna semoni is a relatively widespread and common species occurring in coastal and inland drainages of eastern and southern Australia. This species occurs in coastal catchments from central Queensland, south through New South Wales and west through Victoria to near the mouth
Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 21 615 individuals from 52% of all locations sampled (Table 1).
Table 1. Distribution, abundance and biomass data for Retropinna semoni in rivers of south-eastern Queensland. Data summaries for a total of 21 615 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
51.7
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams 70.0
13.23 (20.02) 11.15 (14.72)
13.8
15.0
2.03 (38.24)
0.58 (12.26)
Brisbane River
Logan-Albert River
42.3
77.9
3.52 (8.84) 25.08 (34.15)
South Coast rivers and streams 60.0 14.05 (21.13)
3 (1)
3 (2)
9 (1)
14 (3)
9 (2)
1 (1)
2 (2)
1.10 (1.39)
0.77 (0.94)
0.04 (0.51)
—
0.43 (0.68)
2.02 (2.57)
0.59 (0.64)
7 (5)
6 (5)
13 (5)
—
14 (7)
5 (4)
5 (5)
Mean numerical density (fish.10m–2)
2.23 ± 0.48
2.48 ± 1.01
0.29 ± 0.10
0.43 ± 0.37
0.93 ± 0.15
2.64 ± 0.32
0.69 ± 0.17
Mean biomass density (g.10m–2)
1.54 ± 0.19
1.39 ± 0.29
0.15 ± 0.11
—
0.56 ± 0.12
2.10 ± 0.29
0.42 ± 0.18
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Freshwater Fishes of North-Eastern Australia
Table 2. Macro/mesohabitat use by Retropinna semoni in rivers of south-eastern Queensland. Data summaries for 21 615 individuals collected from samples of 532 mesohabitat units at 153 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
Overall, it was the third most abundant species collected (13.2% of the total number of fishes collected) and was very common at sites in which it occurred (20.2% of total abundance). In these sites, R. semoni most commonly occurred with the following species (listed in decreasing order of relative abundance): P. signifer, M. duboulayi, C. marjoriae and G. holbrooki. Retropinna semoni was the 7th most important species in terms of biomass, forming 1.1% of the total biomass of fish collected. This species was most widespread and abundant in the Mary, Brisbane, LoganAlbert and South Coast basins, where it occurred in over 40% of locations sampled and formed more than 3.5% of the total number of fish collected in each basin. It was less common or widespread in the short coastal streams of the Sunshine Coast or Moreton Coast. Across all rivers, average and maximum numerical densities recorded in 532 hydraulic habitat samples (i.e. riffles, runs or pools) were 2.23 individuals.10m–2 and 246.54 individuals.10m–2, respectively (the latter being recorded in a small (47.7 m2), isolated tributary pool of the Mary River) [1093]. Average and maximum biomass densities at 441 of these sites were 1.54 g.10m–2 and 61.96 g.10m–2, respectively.
Parameter
Min.
Max.
Mean
W.M.
5.0 5.0 9.0 0 1.4 0
10 211.7 270.0 300.0 300 46.8 93.4
965.1 53.7 142.9 87 9.2 39.2
621.9 45.8 159.4 94 6.2 31.1
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec-1) 0
3.02 1.04 0.87
0.62 0.37 0.19
0.77 0.23 0.20
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
74.0 100.0 70.7 78.2 66.8 65.0 70.0
3.6 13.2 18.9 27.9 24.7 9.9 1.7
1.3 11.5 22.3 27.0 24.4 10.9 2.6
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
86.1 63.6 20.0 40.9 50.0 90.0 37.6 22.5 85.0 100.0
9.4 7.4 1.4 4.2 1.2 11.2 3.6 3.0 10.9 16.7
13.0 14.3 0.7 3.7 1.0 7.4 1.8 1.8 4.0 8.5
2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Macro/mesohabitat use Retropinna semoni is found in a variety of habitats including still or slow-flowing aquatic habitats in large lowland floodplain rivers (e.g. backwaters, swamps and billabongs), upland rivers and streams, small coastal streams, dune systems (Fraser and Moreton islands), lakes (including inland salt lakes) river impoundments (dams and weirs) and brackish river estuaries [52, 270, 814]. In New South Wales this species has been classified as a riffledwelling species [553, 1200]. Retropinna semoni can be widespread within river systems, occurring from estuaries to headwaters. An altitudinal range of 0 to 760 m.a.s.l. has been recorded for this species in eastern Victorian rivers [1111, 1112]. In south-eastern Queensland we have collected this species between 9–300 km upstream from the river mouth and at elevations up to 300 m.a.s.l. (Table 2), but it more commonly occurs within 160 km of the river mouth and at elevations less than 100 m.a.s.l. It is present in a wide range of stream sizes (1.4–46.8 m width) but is most common in streams around 6 m width and with low riparian cover (~31%). This species has been recorded in a range of mesohabitat types but it most commonly occurs in high gradient (weighted mean = 0.77%) riffles and runs characterised by shallow depth (weighted mean = 0.23 m) and high mean water velocity (weighted mean = 0.20 m.sec-1) (Table 2). It is more commonly found in deeper slow-flowing pools during extended periods of low flow, when the availability of riffle and run habitats is diminished and longitudinal
connectivity is restricted [1093]. Retropinna semoni is most abundant in mesohabitats with intermediate to coarse-sized substrates (fine gravel, coarse gravel and cobbles) and often where submerged aquatic macrophytes and filamentous algae are common. Microhabitat use In rivers of south-eastern Queensland, microhabitat use of R. semoni is strongly influenced by discharge-related variations in habitat availability. During periods of high flow, individuals use moderate to high-flow environments with maximum mean and focal point water velocity of 1.35 m.sec–1 (Fig. 1a and b). We have also frequently observed aggregations of fish in slackwater eddies within areas of high flow [515, 1093]. During periods where habitat choice is restricted by low flows, this species is frequently collected in areas with water velocities less than 0.05 m.sec–1. This species was collected over a wide range of
154
Retropinna semoni
(a) 20
15
15
10
10
5
5
0
0
Mean water velocity (m/sec) 40
Larvae are reported to be planktonic, usually congregating at the water surface [951, 952]. King [718] sampled larvae in major tributaries of the lower Murray River and reported their presence in a range of habitat types including anabranch and floodplain billabongs, and on the floodplain proper during flood periods, but reported their preference for deeper billabong habitats.
(b)
20
(c)
40
30
30
20
20
10
10
0
0
(d)
Total depth (cm)
(e) 30
Environmental tolerances Harris and Gehrke [553] classified R. semoni as tolerant of poor water quality and habitat degradation, but this species is widely reported as being fragile and intolerant of handling [270, 797, 893]. In south-eastern Queensland this species has been collected over a relatively wide range of water quality conditions (Table 3). Temperatures at sites in which this species was collected ranged between 8.4 and 31.7°C, some sites had very low dissolved oxygen concentrations (minimum 0.6 mg.L–1), mildly acidic to basic waters (range 6.0–9.1), and moderately high conductivity (maximum 1624.2 µS.cm–1). The maximum turbidity at which this species has been recorded in south-eastern Queensland is 144.0 NTU.
Focal point velocity (m/sec)
Relative depth 40
(f)
30 20 20 10
Table 3. Physicochemical data for Retropinna semoni. Data summaries for 20 852 individuals collected from 339 samples in south-eastern Queensland streams between 1994 and 2003 [1093].
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Retropinna semoni. Data derived from capture records for 3603 individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
depths but usually less than 60 cm (Fig. 1c) and frequently less than 30 cm during low flows. A pelagic schooling species, it most commonly occupies the mid to upper water column or near the water surface (Fig. 1d) [515]. It is found over a wide range of substrate types but most often over coarse gravel and cobbles (Fig. 1e). Retropinna semoni often schools in mid-stream and in open water: 64% of individuals sampled in south-eastern Queensland rivers and streams were collected in areas greater than 1 m from the stream-bank and 14% of fish were collected in areas greater than 0.2 m from the nearest available cover (Fig. 1f) [1093]. This species was more commonly collected in open water during periods of high flow and was most frequently found in close association with coarse substrates, aquatic vegetation and leaf litter during low flows (Fig. 1f) [1093].
Parameter
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
8.4 0.6 6.0 51.0 0.4
31.7 16.2 9.1 1,624.2 144.0
Mean 19.7 8.0 7.7 387.4 5.5
Hume et al. [607] collected R. semoni over a wide range of water quality conditions in their extensive survey of fish in the Goulburn River, a tributary of the Murray River in central Victoria. Sites in which this species was collected were characterised by the following water quality conditions: dissolved oxygen 3.6–16.8 mg.L–1, pH 3.7–9.8, conductivity 50.4–7800 µS.cm–1 and turbidity 0.4–680.0 NTU [607]. Retropinna semoni is euryhaline and has frequently been recorded at the base of tidal barrages (refer to section on Movement) and in brackish and estuarine waters. It has also been recorded in saline lakes in inland Victoria at salinities up to 8.8 ppt [301]; juveniles have been recorded at salinities ranging between 0.04 to 2.8 ppt [300]. Studies of salinity tolerances of adult R. semoni revealed that experimental chronic (four-day) LD50s have been observed as 58.7 ppt [1405, 1406]. Death occurred between 50 and 66 ppt, but fish showed no signs of distress and continued to
155
Freshwater Fishes of North-Eastern Australia
[1093] and the Brisbane River [951] were generally similar in size at equivalent reproductive stages. Length at first maturity (equivalent to reproductive stage III) for fish from the Tweed River, northern New South Wales was reported as 30 and 32 mm LCF for males and females, respectively [1133]. The smallest ripe fish reported from the lower Goulburn River in inland Victoria were 36 mm LCF [607]. Fish in aquaria are reported to breed at lengths between 40–60 mm TL [797].
swim and feed normally until death. Williams [1406] cautioned that salinity tolerance information derived from experiments on adult fish may not necessarily be transferable to other life stages, and that the tolerances of eggs and larvae are likely to be much lower than those observed for adult fish. Ham [502] conducted lower temperature tolerance experiments on R. semoni from south-eastern Queensland. Fish acclimated for seven days at 15°C were observed to lose orientation at temperatures of about 2.5°C, move spasmodically at 1.5°C and cease movement completely at about 1°C [502]. Fish acclimated for seven days at 10°C were reported to have a significantly greater tolerance of low water temperatures, losing orientation at temperatures of about 2.2oC and ceasing movement completely at about 0.7°C [502]. Based on the results of a series of experiments on the upper thermal tolerances of R. semoni from the Latrobe River in coastal eastern Victoria, Harasymiw [537] established that the minimum LD50 temperature for fish acclimated over varying periods and temperatures was 31°C. It was concluded that fish could tolerate exposure to a maximum temperature of 29°C for extended periods [537].
50
Males 45
Females
40 35 30 25 20
Retropinna semoni appears to be intolerant of elevated concentrations of suspended sediments. Tunbridge (cited in Doeg and Koehn [386]) reported dead and dying fish at sites in the Thomson River affected by sediment concentrations of 190–200 mg.L–1.
I
II
III
IV
V
Reproductive stage Figure 2. Mean standard length (mm SL ± SE) for male and female Retropinna semoni within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland, between 1994 and 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 3.
Reproduction Quantitative information on the reproductive biology of R. semoni is available from field and aquarium studies [607, 749, 797, 951, 952, 1093, 1133]. Details are summarised in Table 4. Although facultative anadromy has been reported in some retropinnids [887, 893], R. semoni spawns and can complete its entire life cycle in freshwater and it has been bred in captivity in freshwater [515, 797, 952].
Retropinna semoni commences spawning in winter and may continue through to summer, but spawning appears to be concentrated in late winter and spring. In the Mary River, immature and early developing fish (stages I and II) were most common between October and May (Fig. 3). Developing fish (stages III and IV) of both sexes were present almost year-round. Gravid males (stage V) were present from May through to October and gravid females were present from May through to February, however gravid fish from both sexes were most abundant between July and September (Fig. 3). The temporal pattern in reproductive stages generally mirrored that observed for variation in GSI values. Peak monthly mean GSI values (9.4% ± 0.8 SE for males, 12.4% ± 1.3 SE for females) occurred in August for both sexes and GSIs remained elevated for longer in females than in males (Fig. 4). The mean GSI of ripe (stage V) fish was 7.8% ± 0.4 SE for males and 11.8% ± 0.5 SE for females [1093]. Reproductive activity and GSIs for fish from tributaries of the Brisbane River [951] and the Tweed
In both sexes only the left gonad develops [887]. Maturation commences at a relatively small size. Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, south-eastern Queensland, were 29.8 mm SL and 39.7 mm ± 0.7 SE, respectively for males and 25.8 and 38.2 mm ± 0.7 SE, respectively for females (Fig. 2). Gonad maturation in both sexes was commensurate with somatic growth up until stage III, after which the mean length did not differ substantially between each reproductive stage (Fig. 2). Gravid (stage V) females were slightly larger than males of equivalent maturity (minimum 33.2 mm SL, mean 45.8 mm ± 0.6 SE for females; minimum 32.3 mm SL, mean 42.5 mm ± 0.8 SE for males). Fish from the Mary River
156
Retropinna semoni
River, northern New South Wales [1133, 1135], were generally very similar to values observed for fish from the Mary River [1093]. Sex ratios during the breeding season for populations from the Brisbane River have been reported as 2–4 females for every male [951].
14
Males 12
Females 10
Reproductive stage I
II
III
8
IV
V
6
Males 100
4
(12) (10) (7) (11) (44) (16) (8) (12) (35) (8) (10) (18)
2 80
0 60 40
Month
20
Figure 4. Temporal changes in mean Gonosomatic Index (GSI% ± SE) of Retropinna semoni males (open circles) and females (closed circles) in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 3.
0 Females 100
(14) (15) (6) (8) (53) (17) (13) (14) (53) (18) (14) (8)
80
Retropinna semoni has an extended spawning period but it is unknown whether this species is a protracted, serial or repeat spawner [614]. In south-eastern Queensland, the peak spawning period in winter and early spring usually coincides with pre-flood periods of low and relatively stable discharge. However, breeding may also continue through the months of elevated discharge at the commencement of the wet season in December/January. In southern Australia, the peak spawning period of R. semoni during spring also often coincides with elevated river flows. However, Humphries et al. [615] demonstrated that larvae in the Campaspe River were present for up to nine months of the year, indicating that spawning can take place over a wide range of flow conditions. Hume et al. [607] reported that spawning success in the Goulburn River was independent of flooding and greater in years of comparatively low flows during spring. Furthermore, King [718] reported high larval abundances in major tributaries of the lower Murray River during years of high and low flow and found no evidence for greater spawning or recruitment success during flooding. Milton and Arthington [951] suggested that low flow conditions during the reproductive period are likely to increase the potential of larvae to encounter high densities of small prey, avoid physical flushing downstream due to high flows and thereby maximise the potential for recruitment into juvenile stocks. A similar low-flow recruitment hypothesis has been proposed for this species in the Murray-Darling
60 40 20 0
Month Figure 3. Temporal changes in reproductive stages of Retropinna semoni in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in parentheses.
The spawning stimulus is unknown but the winter reproductive period in south-eastern Queensland corresponds with low water temperatures, possibly reflecting the salmoniform affinities and largely temperate distribution of this species [951]. Spawning appears to occur earlier in the year in south-eastern Queensland [951, 1093] than in southern Australia [607, 749], reflecting the latitudinal gradient in temperature. Studies from both regions reveal that spawning commences at temperatures exceeding about 15°C [607, 951, 952]. In aquaria, spawning has been reported to occur at water temperatures between 21 and 24°C [1210].
157
Freshwater Fishes of North-Eastern Australia
hardened [952]. The demersal eggs are spherical, transparent, amber in colour, and strongly adhesive [797, 952]. The perivitelline space is large and several large and many small oil droplets are present in the yolk [952]. Details of embryological development are available in Milward [952]. Eggs are reported to hatch after six to 10 days at 21 to 24oC [797] and after nine days at 15.5 to 18.0°C [952]. Details of larval morphology and photographs of larval stages can be found in Serafini and Humphries [1218] and Milward [952]. Newly hatched larvae are small (4.61 mm TL), elongate and eel-like, and are capable of swimming at this stage [952]. Three days after hatching, the yolk sac is completely absorbed and larvae range between 5.29–5.51 mm TL [952]. The mean length of flexion and post-flexion larvae is reported as 9.6 mm (measured to end of notochord) and 11.9 mm SL, respectively [1218].
Basin [614, 615, 718]. Length-frequency data indicate that small juvenile fish (less than 20 mm SL) were most common in streams of south-eastern Queensland during spring, further suggesting that the development of a larval cohort occurred during low-flow conditions usually experienced during this time (Fig. 5) [1093]. 30
Spring (n = 2178)
25 Summer (n = 2819)
20
AutumnWinter (n = 5966)
15
Length at age data using evidence from scale annuli from fish in the Brisbane River [951] indicate that 1+ fish (males and females) were 44–45 mm SL and 2+ fish were greater than 51.5 mm SL, with females slightly larger than males in this age group. Milton and Arthington [951] reported that R. semoni reached sexual maturity within one year of age (estimated at six to nine months). Growth rates for populations from inland Victoria were similar with Hume et al. [607] reporting that R. semoni reached 36–42 mm in one year and that this age class dominated the breeding population in this region. Pollard [1059] estimated that fish in a western Victorian saline lake grew to approximately 50 mm in the first year. The maximum length of fish collected in south-eastern Queensland was 68 mm SL [1093], suggesting an age of 3+ years, but given that this species is thought to attain a larger size in southern populations (possibly up to about 100 mm TL), it is likely that this species lives even longer in southern parts of its range.
10 5 0
Standard length (mm) Figure 5. Seasonal variation in length-frequency distributions of Retropinna semoni from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
Total fecundity for fish from the Mary River is estimated to range from 106–1203 eggs (mean 530 ± 41 SE, n = 99 fish) [1093]. Fecundity for fish from the Brisbane River ranges from 98–1050 eggs (mean 362 ± 36 SE, n = 115 fish) [949]. Milton and Arthington [951] reported significant relationships between body length, body weight and fecundity (Table 4). Fish of 35 mm SL produced about 160 eggs, whereas fish of 55 mm SL produced about 600 eggs [951]. In aquaria, R. semoni is reported to deposit up to 120 eggs [797]. It is uncertain whether this species spawns only once during the breeding season or whether multiple batches of eggs are produced.
Movement There is limited quantitative data available concerning the movement biology of R. semoni. Unlike R. tasmanica, which is probably anadromous [52, 893], R. semoni appears to undertake facultative amphidromous and potomadromous movements [893]. Movements between estuaries, brackish lowland rivers and freshwaters do occur, but probably not for the purposes of reproduction. Although it has been recorded in estuarine areas and small numbers of individuals have been collected in fishways located on tidal barrages, spawning in estuarine waters has not been reported for this species. Russell [1173] collected 10 individuals descending a tidal barrage fishway on the Burnett River over a 2½-year period. Johnson [658] reported small numbers of juvenile and adult R. semoni moving upstream through a tidal barrage fishway in the Mary River. Berghuis [158, 159] observed aggregations of
In the wild, spawning may occur in aquatic vegetation [270] whereas fish in aquaria have been observed scattering eggs onto the gravel substrate [515, 797]. No parental care of eggs has been reported. Eggs are relatively small. The mean diameter of 818 intraovarian eggs from stage V fish from the Mary River was 0.73 mm ± 0.01 SE [1093]. The diameter of newly-laid eggs is reported as 0.80 mm and the eggs swell to an average diameter of 0.95 mm when water-
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fish (often in large numbers) below tidal barrages in the Mary River system, although few individuals were collected at the top of fishways on these structures suggesting limited upstream movement through these fishways.
way on the Barwon River in the Darling Basin was reported to occur during low flows in October and November [1334]. Young-of-the-year fish (15–45 mm TL) in the Murray River were observed attempting to ascend a vertical-slot fishway on the Torrumbarry Weir during daylight hours between November and February, a period of relatively low discharge. Fish were probably attempting to disperse to upstream habitats but apparently had difficulty ascending the fishway [854, 858]. Upstream migrations of R. semoni do not appear to be limited to periods of low flow. Upstream movement of approximately 2500 subadults was recorded through a fishway in the Nepean River, central New South Wales, in March during a period of elevated flows (discharge of 140 ML.day-1) [483]. No fish were observed moving at lower flows [483]. Small aggregations of R. semoni have also been reported below a weir spillway on the Lerderderg River, Victoria, between June and July, a period of relatively high discharge [182]. During periods of reduced flows, individuals in rivers of
Facultative potamodromy appears a common feature of the movement biology of R. semoni and probably serves as a dispersal mechanism for juveniles and subadults. Mass migrations within freshwater have frequently been documented and very large aggregations downstream of barriers to movement have been reported. In the Mary River, south-eastern Queensland, a large aggregation of youngof-the-year fish (at least 5000–10 000 individuals estimated to be around 20–25 mm TL) were observed immediately downstream of small barrier to movement (disused road culvert) in the main river channel. These fish were presumed to be attempting to move upstream during a period of stable low flows in spring (mid-September). Upstream movement of juveniles through a barrage fishTable 4. Life history information for Retropinna semoni. Age at sexual maturity
6–9 months [951]
Minimum length of gravid (stage V) females (mm)
33.2 mm SL [1093]; spawning fish in aquaria 40 mm TL [797]
Minimum length of ripe (stage V) males (mm) 32.3 mm SL [1093] Longevity
2+ years [951], possibly 3+ [1093]
Sex ratio (female to male)
2:1–4:1 [951]
Occurrence of ripe (stage V) fish
Winter through to summer (May to February) [1093]
Peak spawning activity
Winter and spring (July–September) [951, 1093]
Critical temperature for spawning
15°C (field) [607, 951, 952], 21–24°C (aquaria) [797]
Inducement to spawning
? Probably temperature [951]
Mean GSI of ripe (stage V) females (%)
11.8% ± 0.5 SE [1093]
Mean GSI of ripe (stage V) males (%)
7.8% ± 0.4 SE [1093]
Fecundity (number of ova)
Total fecundity = 106–1203, mean = 530 [1093]; 98–1050, mean = 362 [951]
Total Fecundity (TF) / Length (mm SL) or Weight (g) relationship
TF = 0.005 L2.92, r2 = 0.74, p<0.001, n = 47 [951] TF = 385.3 W0.09, r2 = 0.79, p<0.001, n = 47 [951]
Egg size (diameter)
Intraovarian eggs 0.73 mm [1093]; newly laid eggs 0.80 mm [952]; water-hardened eggs 0.95 mm [952]
Frequency of spawning
?
Oviposition and spawning site
Adhesive, demersal eggs scattered over gravel substrate or attached to aquatic vegetation [270, 515, 797]
Spawning migration
None known
Parental care
None known
Time to hatching
Varies with temperature. 6–10 days (at 21–24°C) [797]; 9 days (at 15.5–18.0°C) [952]
Length at hatching
Newly hatched prolarvae 4.61 mm TL [952]
Length at free swimming stage
Capable of swimming at hatching [952]
Age at loss of yolk sack
3 days
Age at first feeding
Approximately 3 days [614]
Length at first feeding
?
Age at metamorphosis
?
Length at metamorphosis
Flexion larvae 9.6 mm; post-flexion larvae 11.9 mm [1218]
Duration of larval development
? Possibly 14 days [718]
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Freshwater Fishes of North-Eastern Australia
Conservation status, threats and management The conservation status of R. semoni was listed as NonThreatened by Wager and Jackson [1353] in 1993 and this species remains generally common throughout most of its range in eastern Australia. Potential threats to R. semoni in south-eastern Queensland are similar to those identified for many other small-bodied fish species in this region, for example Atherinidae, Melanotaeniidae, Pseudomugilidae and Eleotridinae.
south-eastern Queensland appear to retreat to refugia (pools) or less transitory habitats within the main river channel. Occasionally, large numbers of fish have been observed trapped in small isolated tributary pools during extended periods of low flow in this region [1093]. Feeding ecology Diet data for R. semoni is available for 1277 individuals from coastal rivers of south-eastern Queensland [80, 205] and New South Wales [1133, 1134], floodplain waterbodies of Cooper Creek [246] and inland rivers and floodplain lakes of the Murray-Darling Basin [267, 396, 607, 805, 1062]. This species is a microphagic carnivore. Aquatic insects comprised mostly of drifting larval stages of Diptera, Ephemeroptera and Trichoptera formed 44.2% of the total mean diet and planktonic microcrustaceans comprised a further 21.7% (Fig. 6). A substantial proportion of the diet is composed of allochthonous material, mostly terrestrial invertebrates (15.0%) and winged adult forms of aquatic insects (4.1%). Small amounts of fish (unidentified fish eggs) and algae are also consumed occasionally. Some spatial variation in the diet of R. semoni is evident, apparently related to habitat type and hence food availability. For example, in studies of lentic and floodplain habitats (e.g. lowland rivers and floodplain lakes and billabongs [246, 396, 607, 805, 1062]) fish were observed to consume large amounts (>30% in each study) of microcrustaceans (zooplankton) in comparison to fish collected from lotic habitats [80, 205, 267, 1133, 1134] (<2.5% in each study). The diets of fish in lotic habitats were dominated by aquatic insects (>53% in each study). Retropinna semoni has been observed foraging during the daytime [1093] and also nocturnally [858]. This species is reputedly an important forage fish for other larger fish and avian predators [270, 887]. Fish (0.8%)
Unidentified (12.8%)
Microcrustaceans (21.7%)
Terrestrial invertebrates (15.0%)
Other macroinvertebrates (0.2%)
Aerial aq. Invertebrates (4.1%) Terrestrial vegetation (0.7%) Algae (0.5%)
Aquatic insects (44.2%)
Figure 6. The mean diet of Retropinna semoni. Data derived from stomach contents analysis of 1277 individuals from coastal south-eastern Queensland [80, 205], coastal New South Wales [1133, 1134], floodplain waterbodies of Cooper Creek [246] and inland rivers and floodplain lakes of the Murray-Darling Basin [267, 396, 607, 805, 1062].
160
Alien fish species (particularly Gambusia holbrooki and other poeciliids) threaten many small native species with similar habitat and dietary requirements in south-eastern Queensland streams. Retropinna semoni may be particularly at risk in degraded stream habitats supporting large populations of G. holbrooki, also an inhabitant of the upper water column and a microphagic carnivore [78, 80, 92, 94, 96]. Riparian and in-stream habitat degradation (e.g. riparian clearing, native and alien weed infestations and sedimentation) may affect terrestrial and aquatic food supplies of importance to small stream species such as R. semoni. Extensive infestations of introduced para grass, Brachiaria mutica, may also constrain the foraging behaviour of this surface-feeding species in degraded urban streams [94]. Several aspects of in-stream habitat degradation can affect the availability of suitable spawning substrates; for instance, aquatic weeds can out-compete native submerged macrophytes used for spawning, and excessive sedimentation may clog the interstices of gravel substrates and smother the demersal eggs of R. semoni [108, 1092]. Many field observations suggest that the natural movements of this species between estuaries, brackish lowland rivers and freshwaters, and within river systems may be severely constrained by in-stream barriers (e.g. dams, weirs, tidal barrages, even road culverts). The dispersal movements of both juvenile and adult fish may be affected. Flow modifications (particularly rapid fluctuations in water levels or aseasonal flow releases) during the months of spawning and larval development may have severe impacts on recruitment by damaging or exposing fish eggs attached to submerged vegetation, or flushing eggs and larvae downstream. Microscopic invertebrate prey are also likely to be reduced in abundance by flow-related habitat disturbances, or flushed downstream during spates and aseasonal flow releases. The environmental tolerances of R. semoni are so poorly documented that the effects of degraded water quality, such as low dissolved oxygen levels and increased turbidity, are difficult to evaluate. In some respects this species is known to be hardy (e.g. it is euryhaline and tolerates a wide thermal range) yet it is physically fragile and intolerant of handling.
Arrhamphus sclerolepis Günther, 1866 Snub-nosed garfish
37 234006
Family: Hemiramphidae
subspecies, A. s. sclerolepis and A. s. krefftii. Arramphus sclerolepis sclerolepis has fewer anal rays than A. s. krefftii (modal count = 15 versus 16), fewer vertebrae (46 or 47 versus 49), more gill rakers (23 or 24 versus 19–21) and a proportionally shorter jaw at larger sizes [320].
Description Dorsal fin: 13–16; Anal: 14–17; Pectoral: 12–14; Vertical scale rows: 45–50; Gill rakers on first arch: 18–25; Gill rakers on second arch: 15–20 [320]. Arramphus sclerolepis is commonly between 150–250 mm SL but may attain a length of 360 mm SL (about 400 mm TL) and a weight of 255 g [37, 936]. Figure: composite, drawn from photographs of adult specimens 180–220 mm SL, Bowen River, May 1991; drawn 2002.
Collette [320] initially believed these differences to be clinal on the east coast of Australia, but evidence for clinal variation was no longer apparent when specimens from other northern Australian population were considered. Significant differences between adjacent populations are evident for some meristic characters however, but the pattern of variation is not consistent across all characters except for the ratio of lower jaw length to head length [320].
Arrhamphus sclerolepis is a long slender fish (although relatively stout bodied compared with other garfishes) with a protruding lower jaw: lower jaw proportionally longer in smaller individuals, particularly in the subspecies A. s. krefftii (see Figure 114 in Merrick and Schmida [936]). Caudal fin forked with lower lobe slightly longer than the upper lobe. Colour in life: silvery-white laterally grading to an olive-green dorsally and white ventrally. A metallic midlateral stripe extends from the opeculum to the base of the caudal fin. The margins of the dorsal scales may be darkened at their dorsal and ventral extremities, thus imparting a regular spotting to the dorsal surface. The extremity of the lower jaw may be a vivid orange in colour.
Two points are of interest here. First, very few of the fish in the series upon which A. sclerolepis sclerolepis is based were collected from freshwater (possibly one individual from Rollingstone Creek in Queensland and another from the Gascoyne River in Western Australia) [320]. Second, there is a substantial overlap in meristic counts for the two subspecies. Furthermore, subspecific differences in head morphology are only evident in larger fish: both subspecific forms appear to belong to the same statistical population with respect to the rate of increase with increasing size
Significant geographical variation in meristics and morphometry led Collette [320] to erect the two 161
Freshwater Fishes of North-Eastern Australia
and distribution). No synonyms are known for the former whereas the latter was originally described as Hemirhamphus kreftii Steindachner (note incorrect spelling of species epithet) and subsequently as Hemiramphus breviceps Castelnau [1042], and incorrectly identified or listed as H. argenteus, H. sclerolepis, A. schei or A. brevis (=Melapedalion breve (Seale)) [320].
of the head to lower jaw ratio when less than 100 mm long. Importantly, approximately 85% of the Queensland sample of A. s. sclerolepis examined by Collette [320] were below this length. The larger size classes (>100 mm SL) for the A. s. sclerolepis series were dominated by fish from east of the Great Dividing Range (80%). It would be instructive to apply modern genetic techniques such as DNA sequencing to examine geographic variation in this species. It would also be instructive to determine the extent to which variations in water temperature or salinity during the early larval phase affect body meristics and morphology (i.e. spatial variation may be phenotypic and developmental rather than genetic).
Distribution and abundance Arramphus sclerolepis is widely but patchily distributed across southern New Guinea, and northern and northeastern Australia. The subspecies A. s. sclerolepis is said to occur in Australia from the Gascoyne River in Western Australia to the Pioneer River in Queensland [52]. Within this range, it has been infrequently collected from freshwaters however: occurring predominantly in near-shore marine or estuarine habitats. This species was not collected from freshwater reaches of 13 rivers in the Kimberley region [45, 620] nor were any of the Northern Territory specimens examined by Collette from freshwaters [320]. Many other studies undertaken in freshwaters of the Northern Territory, some very intensive, and collectively covering an area extending from the Daly River to Arnhem Land, have also failed to collect this species from freshwater [193, 262, 772, 944, 946, 1197, 1304].
Systematics Hemiramphidae (halfbeaks or garfishes) is a moderately large family with a circumglobal distribution, inhabiting marine, estuarine and, to a lesser extent, freshwaters. It is composed of 12 genera containing 85 species [254]. A large number of species (34) are contained with a single genus, Hyporhamphus. Cladistic relationships of the genera and species of halfbeaks have not been fully resolved [254] although the family is known to be the sister group of the Exocoetidae (flying fishes) [322]. Approximately 18 species of Hemiramphidae in seven genera are known from Australian waters: Arramphus (1 sp.), Euleptorhamphus (1 sp.), Oxyporhamphus (1 sp.), Rhyncorhampus (1 sp.), Hemirhamphus (2 spp.), Zenarchopterus (5 spp.) and Hyporhamphus (7 spp.) [1042]. Of these genera, only two (Arrhamphus and Zenarchopterus) contain species that are occasionally or principally freshwater in habit.
Arramphus s. sclerolepis occurs in the near-shore environment and estuaries of the Gulf of Carpentaria [197, 320, 356, 1349]. Cyrus and Blaber [356] found it relatively common but restricted to the lower reaches of the Embley Estuary during the wet season (28th most abundant of >100 species, CPUE = 1.5 x 10–4 fish.m.hr–1). It was more abundant (8th, CPUE = 10.8 x 10–4 fish.m.hr–1) by the start of the following dry season but still restricted to the lower estuary. By the late dry A. s. sclerolepis was still common (15th, CPUE = 2 x 10–4 fish.m.hr–1) in the lower estuary but also abundant (8th, CPUE = 5.3 x 10–4 fish.m.hr–1) in the middle reaches of the estuary. The extent of upstream movement was claimed to be limited by low salinity and high turbidity during the wet season [356].
The halfbeaks are, in general, characterised by an elongate lower jaw and short upper jaw. Arramphus however, differs from all other Australian halfbeaks in that the lower jaw is shortened also. In addition, it differs from Zenarchopterus in having a non-elongated nasal papilla, forked caudal fin (as opposed to rounded) and unmodified anal fin rays; characters it shares with all other Australian half beaks [320]. Two other halfbeak genera also share the greatly reduced lower jaw condition with Arramphus: Melapedalion (Seale) in the Philippines and Chriodorus Goode and Bean in the western Atlantic.
Freshwater populations have been recorded in the lower Mitchell River, but not its upper reaches [1186], and in the Mitchell River tributary systems, the Walsh (2602), Palmer [569] and Lynd [1349] rivers. Other rivers of western Cape York Peninsula in which this species has been recorded include the Wenlock [571], Norman [320] and Watson [1349] rivers .
The genus Arramphus was first described by Günther in 1866 with A. sclerolepis as the type species (by monotypy). The lectotype, held in the British Museum of Natural History, was incorrectly listed as coming from ‘? New Zealand’. Collette [320] believed it came from the Northern Territory or Western Australia as this species does not occur in New Zealand.
No freshwater populations of A. s. sclerolepis in rivers of the east coast of Cape York Peninsula are known despite substantial survey work. The most northern samples included in the analysis of Collette [320] were from marine near-shore habitats in the Cooktown area. The
Two subspecies are known; the nominal subspecies A. s. sclerolepis, and A. s. krefftii (but see sections on description
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Arrhamphus sclerolepis
most northern freshwater populations on the east coast appear to be those in Saltwater Creek north of Cairns [583] and the Barron River [1085, 1087, 1187]. Other rivers in the Wet Tropics region in which A. s. sclerolepis has been recorded include the Mulgrave/Russell [1184], Moresby [1183] and Herbert rivers [584]. In all cases, A. s. sclerolepis is restricted to the very lower reaches of these rivers and in some cases, the subspecific status is assumed. It has been translocated into Lake Tinaroo on the Atherton Tablelands [593].
the Burnett River barrage. Arramphus s. krefftii has been recorded from the Mary River [660, 1234] and the Noosa River (at Trewontin and in Lake Cooroibah) [320]. This species has also been recorded from the Brisbane [320, 593, 907, 1349] and the Albert/Logan rivers [1349]. This species occurs naturally in the Wivenhoe Dam approximately 150 km upstream of the river mouth and has been translocated into Somerset Dam on the Stanley River. It is apparently abundant in Wivenhoe Dam and dominates recreational angling catches [593]. Although historically present in the lower reaches of the Brisbane River [320], it was not amongst those species shown to be able to negotiate the fishway located at the Mt Crosby Weir [1238].
Further south, this species has been collected from freshwater reaches of the Ross River [1349] and the Burdekin River [586, 940, 1098, 1349]. Within the Burdekin River, it has been recorded from as far upstream as the Gorge Weir (approximately 128 km upstream from the delta) [940] and the lower reaches of the Bowen River (approximately 140 km from the delta) [1098]. Most texts put the distribution of A. s. sclerolepis as extending to the Bowen area. South of this supposed limit, Arramphus sclerolepis (subspecific differentiation not noted) has been recorded from freshwaters of the Pioneer River (Marsden unpubl. data cited in Pusey [1081]) and from estuarine waters of the Murray/St Helens creeks (Lunow unpubl. data cited in Pusey [1081]).
Arrhamphus sclerolepis is a common inhabitant of estuaries and the near-shore environment of south-east Queensland [968, 969, 970]. This species has been recorded from artificially created canal systems but is not as abundant as in adjacent natural systems [968]. Although its marine distribution extends to the Sydney area, there are few records of A. s. krefftii occurring in freshwaters in New South Wales. Collette’s sample included one specimen from the Clarence River [320]. Only four individuals were collected from two short coastal rivers of northern New South Wales (the Richmond and Hastings Rivers) during the New South Wales Rivers Survey [553, 554]. It has also been recorded from the Hawkesbury River [553].
Midgley [942] recorded A. sclerolepis (subspecific differentiation not noted) from three locations in the Fitzroy River catchment: the Fitzroy river itself approximately 70 km from the river mouth, the Don River approximately 200 km upstream and the Isaac River approximately 300 km upstream of the mouth. These records were later included as being within the distribution of A. s. sclerolepis [1349] but the basis for doing so is obscure. Johnson and Johnson also noted that A. sclerolepis was common and abundant in the Fitzroy River [659]. Berghuis and Long [160] state that A. sclerolepis is frequently observed in the lower reaches of the Fitzroy River also, and Stuart [1274] noted this species at the base of the fishway located on the barrage near the river mouth.
It may seem that a great deal of attention has been focussed above on establishing the distributional limits of this species and on the meristic and morphometric basis for subspecies differentiation. Our intent in doing so is to illustrate how infrequently A. sclerolepis has been recorded from freshwater habitats and further, when it has been recorded in freshwater, it has usually been from lowland reaches close to the river mouth. Exceptions to this observation include the inland populations present in the Brisbane, Boyne, Fitzroy, Burdekin and Mitchell rivers; notably, with the exception of the Boyne River, all are large river systems with relatively low average gradient (i.e. a large proportion of total length exists below 50 m elevation). Furthermore, we believe it important to point out how very few of the series used by Collette [320] were collected from freshwaters. Researchers should perhaps be more critical in allocating populations to different subspecies based solely on distribution in the future.
The Fitzroy River has traditionally been considered to be within the range of A. s. krefftii, however only two of the 27 Queensland fish included in the series upon which A. s. krefftii is based [320] were from this drainage. Further south, A. sclerolepis has been recorded from estuarine waters of the Shoalwater Bay area [1328] and from freshwaters of the Boyne River where it has established a self-sustaining population in the impounded reaches of Awonga Dam [943]. Freshwater populations have been recorded in the Burnett, Kolan and Elliott rivers but it was not common nor widely distributed in these systems [700]. Russell [1173] recorded A. sclerolepis moving downstream in small numbers through the fishway located on
Macro/meso/microhabitat use Freshwater populations of A. sclerolepis tend to be restricted to the lower reaches of rivers, although there are some reports (see above) of this species penetrating many kilometres upstream. Such examples typically occur in
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Freshwater Fishes of North-Eastern Australia
Maturation occurs by at least 215–225 mm TL (both males and females) [943]. Breeding apparently occurs only after surface water temperatures have reached 28°C [52], however the basis for this observation remains obscure. Allen et al. [52] suggest that under normal conditions this species moves to estuaries to breed and the spatio-temporal variation in abundance reported by Cyrus and Blaber [356] and detailed above, suggests that spawning occurs during the wet season.
large low gradient rivers. When located far upstream, the typical habitat is one of large waterholes or open river. No information is available on microhabitat use except that A. sclerolepis is mostly observed close to the water’s surface. Environmental tolerances Environmental tolerance data for A. sclerolepis in freshwaters is extremely scant, being restricted to water quality data for four site/sampling occasions in the Burdekin River [940, 1098] and three sites in the Fitzroy River basin [942]. Given the small number of fish collected and sites involved, we consider it prudent to list maximum and minimum values only in Table 1.
Movement biology No quantitative information is available on this aspect of the biology of A. sclerolepis in freshwaters although it is frequently implied that this species does indeed make substantial migratory movements between fresh and saline waters. The appearance of A. sclerolepis in fishways [1173, 1274] or congregated below such structures [586] supports this notion. Moreover, the observation that instream barriers such as weirs and dams result in strict discontinuities in disitribution also supports other evidence that A. sclerolepis moves extensively within the lower reaches of rivers. Cyrus and Blaber [356] included it among a group of species that moved upstream only when turbidity decreased and salinity increased. This observation implies that any movement upstream must be accompanied by some degree of physiological acclimation.
These values are not indicative of a great range in water chemistry. In the Embley Estuary, A. sclerolepis was recorded occurring in waters ranging from 17.2 to 39 ppt salinity and 1.2 to 9.2 NTU turbidity [356]. Cyrus and Blaber [356] classified A. sclerolepis as a marine species that, along with a number of other species (their Group B), was prevented from accessing the upper reaches of the estuary during the wet season by low salinity and high turbidity. This observation however does not accord well with other observations of this species in completely freshwater. Arramphus sclerolepis may be capable of slowly acclimating to low salinity although it is tempting to speculate that some freshwater populations (not including those landlocked by impoundments) rarely, if ever, come into contact with saltwater.
Trophic ecology Information on the diet of A. sclerolepis is limited to frequency of incidence data for a sample of 20 individuals (19 freshwater, 1 estuarine) collected from the Brisbane River [917], volumetric data for a sample of 23 individuals from the Burdekin River [705], and anecdotal accounts [52, 320, 936]. Collectively, these data suggest a predominantly herbivorous habit. McMahon [917] noted that filamentous algae and diatoms were each present in all of the fish examined. Fish in the Burdekin River [1093] consumed filamentous algae exclusively. Vascular plants were observed in 13 of the fish examined by McMahon [917] and Merrick and Schmida [936] detail an observation of A. sclerolepis grazing on Vallisneria fronds. Estuarine populations of A. sclerolepis are also herbivorous [194]. Insect larvae were recorded in only two of the individuals examined by McMahon [917] but 14/20 individuals contained mature insects (presumably terrestrial insects taken from the water’s surface). Zooplankton may also occur in the diet [936]. Interestingly, like many other herbivorous or omnivorous Australian fish (see Scortum parviceps or Nematalosa erebi), juveniles appear to totally microcarnivorous [1322].
Table 1. Physicochemical data for the snub-nosed garfish Arramphus sclerolepis. Minimum and maximum values only are presented. Units of measurement vary between studies; conductivity is given in either µS.cm–1 or ppm of Total Dissolved Solids* and turbidity is given in either NTU or Secchi disc depths (m)**. Parameter Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity Turbidity
Min. 24.5 5.6 7.3 198 145* 3.3 0.9**
Max. 29.0 8.3 8.2 235 770* 5.3 1.0**
Reproduction Information on this aspect of the biology of A. sclerolepis is limited except that it is evidently able to spawn in freshwaters. Midgley [943] reported that A. sclerolepis was able to reproduce successfully in Awonga Dam, an impoundment of the Boyne River. A self-sustaining population is also present in Wivenhoe Dam on the Brisbane River.
The morphology of the feeding apparati of A. sclerolepis was described by McMahon [917]. Numerous small (<0.5
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Arrhamphus sclerolepis
addition, A. sclerolepis may be directly involved in the export of aquatic production from freshwaters to estuarine systems or the indirectly involved in the export of aquatic production out of the aquatic food web completely (filamentous algae → garfish → piscivorous birds).
mm), tricuspid teeth, directed postero-medially, are present on margins of the upper and lower jaws. Similarly numerous and small, but predominantly molariform, teeth are located in patches within the pharynx forming a pharyngeal mill. Highly numerous mucous producing cells are located throughout the digestive system including the pharynx. The gut is simple in structure, lacking a stomach or pyloric caecae. It is short, being only about half as long as the body (i.e. Relative Gut Length (RGL) = 0.5) [917, 1322], but it has a large volume [1322]. In general, the gut of herbivorous fishes is long; RGL varying between 3.7 and 4.2 [1322]. The absence of a stomach is important for it means that acid hydrolysis of ingested material cannot occur and this typically results in low assimilation efficiencies (i.e. ~38%). Maceration of ingested material is achieved in A. sclerolepis by the pharyngeal mill. Tibbetts [1322] suggested that the copious mucus (AGP type – acid glyciproteins) produced by this species has three functions. First, it binds food together and acts to lubricate the occluding surfaces of the paryngeal mill. Second, it lubricates the movement of the ingesta through the gut. Third, it plays some role in the assimilation of plant nutrients. This last point may explain why high assimilation rates have been observed in other hemiramphid species (see Tibbett [1322]).
Conservation status, threats and management Arramphus sclerolepis is listed as Non-Threatened by Wager and Jackson [1353]. Potential threats to this species include barriers to movement such as sand dams (in the Burdekin River, for example) and tidal barrages and weirs. Hemiramphids have been included in fish kills associated with exposure of Potential Acid Sulphate soils and A. sclerolepis may also be intolerant of low pH [1180]. Activities which increase water turbidity may affect this species by negatively impacting on its major food source (aquatic plants). Elevated turbidity in estuaries and consequent effects on seagrass production is also likely to impact on this species as many hemiramphids are dependent on this food source [320]. Halfbeaks have traditionally been of commercial value [320] and 1990 landings approached 1000 t [678]. Although A. sclerolepis has traditionally been included within halfbeak landings [320, 936], Kailola et al. [678] do not list it as an important commercial species. It is of recreational significance however, being a fine table fish (although bony) and favoured as live bait for barramundi. Some research effort should be focused on better defining the genetic or environmental basis for subspecific differentiation in this species, particularly in view of the recent increase in interest in this species with respect to its suitability for translocation and the stocking of reservoirs.
Arramphus sclerolepis occurs in the diet of many species of piscivorous birds such as cormorants and sea eagles, and of fish such as barramundi [1093]. Thus, this species may be an important component of aquatic food webs in that they may accelerate the passage of primary production through different trophic levels (filamentous algae → garfish → top level predator such as barramundi). In
165
Strongylura krefftii (Günther, 1866) Freshwater longtom
37 235009
Family: Belonidae
Estimates of maximum size for this species vary from 750 mm [754] to 850 mm [52]. The maximum size recorded by Hortle [596] in a New Guinean sample of 75 individuals was 630 mm SL. A maximum size of 640 mm CFL from a sample of 224 individuals was recorded by Bishop et al. [193]. Taylor [1304] recorded a maximum length of 635 mm SL from lagoons in the Oenpelli region of Arnhem Land. Obviously, very large individuals approaching the maximum length cited by Allen et al. [52] are uncommonly encountered and fish of lengths below 500 mm SL are more common. The size distribution of the sample examined in Bishop et al. [193] was weakly bimodal with a strong peak at around 300 mm CFL and a second weaker peak at about 420-430 mm CFL. The mean length in this sample was 316 mm CFL. The equation: W = 0.00987 x L3.197, n = 224, r2 = 0.938, was found to best describe the relationship between length (CFL in cm) and weight (in g) for S. krefftii from the Alligator Rivers region [193].
Description First dorsal: 16–18; Anal: 19–21; Pectoral: 11–12; spines absent. Figure: composite, drawn from photographs of adult specimen, Burdekin River, November 1990; drawn 2002. Strongylura krefftii, or long tom, is distinctive and unlikely to be confused with any other species. The body is long and slender with the dorsal and anal fins set well back on the body. The head is large, comprising up to one quarter of total length, and is dominated by a set of elongated jaws (both upper and lower) armed with numerous sharp teeth. Development of the jaw apparatus commences with the lower jaw followed by the upper jaw, such that small specimens pass through a halfbeak phase and may resemble juvenile hemiramphids. The eye is large, particularly in juvenile specimens. Colour in life is typically dark green dorsally grading through silver on the flanks to white ventrally. A faint orange midlateral stripe occurs in the posterior half of the body in some specimens and faint spots occur on the opercula and the dorsal two-thirds of the body [596]. Sexual dimorphism has been reported for Papua New Guinean specimens: large males (>400 mm SL) develop a dorsal hump at about the midpoint of the body and large black blotches on the opercula and flanks [596].
Systematics The Belonidae is a circum-tropical family containing marine, estuarine and freshwater species and a number of species that may be found across, and even breed in, all three habitats [254]. The family has repeatedly invaded
166
Strongylura krefftii
Holroyd [571], Wenlock [571, 1349], Ducie [1349], Jardine [41, 771]; and it has been collected from swamps and lagoons near Weipa [571]. These records indicate a seemingly continuous distribution across northern Australia.
freshwaters, particularly rivers discharging into the western Atlantic [321, 1435]. Phylogenetic relationships among the Belonidae (excluding S. krefftii) have recently been examined by Lovejoy and Collette [1435] and Banford et al. [1429]. There are about 11–12 freshwater and 20 marine species. Collette et al. [322] demonstrated that the family is monophyletic and a sister group of the marine planktivorous Scomberesocidae (king gars). The genus Strongylura was suggested to be paraphyletic however [211]. Accordingly, there has been some debate about the number and identity of species within the genus and the family as a whole [322].
In sharp contrast, S. krefftii was not collected from a single river of the eastern portion of Cape York Peninsula [571] during the comprehensive CYPLUS surveys undertaken in the early 1990s and the only record of its presence in this region is that of Kennard [697] for the Normanby River. Other fish species more typical of western Cape York Peninsula also occur in the Normanby River (e.g. Arius midgleyi Kailola and Pierce). We could find no further reference to its presence in any river south of the Normanby until the Herbert River [643, 1349]. This range of latitude encompasses the otherwise highly diverse rivers of the Wet Tropics region. Significantly, these rivers are among the most thoroughly surveyed rivers of north-eastern Australia. Other belonids such as Tylosurus crocodiles (Péron and Lesueur), T. gavialoides (Castelnau) and T. strongylura (van Hasselt) have been recorded from the estuarine reaches of these rivers [1187]. Strongylura krefftii may have once been present in some rivers of the Wet Tropics in recent times. Long-time residents of the upper Russell River have recounted to the senior author that a species of long tom was present in this river but was extirpated by an outbreak of redspot disease in the 1970s.
Strongylura was first described by van Hasselt in 1824 based on the type species S. caudimaculata from SouthEast Asia. The genus contains both freshwater and marine representatives and is circum-tropical in distribution. Australian strongylurids include S. krefftii (Günther), S. incisa (Valenciennes), S. leiura (Bleeker), S. strongylura (van Hasselt) and S. urvillii (Valenciennes), of which only the former is found in freshwater. Other Australian belonid genera include Ablennes Jordan and Fordice, Platybelone Fowler and Tylosurus Cocco. Members of the latter genus are frequently observed in the lower estuary of Queensland’s northern rivers. Strongylura krefftii was first described as Belone krefftii by Günther in 1866. Synonyms are otherwise limited to misspellings of the species epithet and S. perornatus (first described as Stenocaulus perornatus by Whitley, 1938). Hortle [596] demonstrated that S. perornatus from the Sepik River fitted the description of male S. krefftii.
Strongylura krefftii occurs in the Ross River [1349] and in the Burdekin River [587, 591, 940, 1098], also penetrating far upstream into its tributary, the Bowen River [1098]; despite the difficulties posed by such barriers as the Clare Weir [587]. Strongylura krefftii (as Belone krefftii) was collected from Lillesmere Lagoon, a large floodplain lagoon of the Burdekin River in the late 1800s in a very intensive survey [847] but it has not been collected from floodplain habitats of the Burdekin delta (C. Perna, pers. comm.) or the wetlands of Baratta Creek [1046] in more recent times. Off-channel wetland habitats of this river can no longer be described habitats of even moderate condition: Lillesmere Lagoon, for example, is a weed-infested bog devoid of any riparian vegetation and with abysmal water quality. This species has not been collected from the Houghton River [255].
Distribution and abundance Strongylura krefftii is confined to northern Australia and New Guinea. The New Guinean distribution includes rivers of southern Papua New Guinea and of Irian Jaya [37, 42, 495] and the Sepik Ramu system of northern Papua New Guinea [46, 51, 316, 596]. Strongylura krefftii occurs in the Fitzroy, Carson and Ord rivers of the Kimberley region in Western Australia [388, 620] and is probably widespread in this region. Its range extends across the Northern Territory from the Victoria [946] and Daly rivers [945], through the Alligator Rivers region [193, 772, 1064, 1416] to drainages of Arnhem Land (Rosie Creek and the Limmen Bight River [944], and the Roper River [1304]). Rivers of the Gulf of Carpentaria region of Queensland from which it has been collected include the Leichhardt [1090, 1349], Gregory [643, 755] and Gilbert [755]. This species has been recorded from most rivers draining the western portion of Cape York Peninsula including the Embley [356], Mitchell [571, 643, 1186, 1349] (including its tributary systems the Walsh and the Palmer rivers), Coleman [571, 1349], Edward [571],
The distribution of S. krefftii extends further to the south to include the Pioneer [1081] and the Fitzroy River drainages [659, 942, 1274] and the latter’s tributary systems, the McKenzie, Don and Dawson rivers [942]. This species’ distribution includes the Boyne [1349], Kolan [1349], Burnett [661], Burrum [701] and Mary [701] rivers but does not extend south of the Mary River. Strongylura krefftii seldom achieves high levels of abundance. This species comprised less than 0.01% of seine-
167
Freshwater Fishes of North-Eastern Australia
netting catches and about 2% of the gill-netting catch in a three-year study of the fishes of the Burdekin River [1098]. It was absent from the electrofishing catch in this study. This species was similarly absent from electrofishing catches in lagoons of the Normanby River and comprised under 1% of the gill-netting catch [697]. In contrast, Bishop et al [193] found S. krefftii abundance in the Alligator Rivers region to be in the upper-middle quartile. Pollard [1064] found it similarly abundant in Magela Creek, in the Alligator River drainage.
have also been recorded moving through the fishway located on the barrage of the Fitzroy River. The use of lentic floodplain waterbodies by S. krefftii appears little reported for eastern rivers in contrast to reports for rivers of north-western Australia. The extent to which this difference reflects real differences in biology, regional differences in hydrology (i.e. flooding regime), regional differences in sampling effort in different habitats, or regional differences in the extent, accessibility and quality of off-channel habitats is not known; a knowledge gap of some significance.
Macro/meso/microhabitat use Strongylura krefftii has been recorded from a range of habitats. Pollard [1064] found this species to be widely distributed in Magela Creek in the Northern Territory. In a larger study of the freshwater fishes of the Alligator Rivers region, in which Magela Creek occurs, S. krefftii was recorded from 23/26 sites regularly sampled by Bishop et al. [193] encompassing floodplain, corridor and muddy lagoons, creeks with a sandy bed, escarpment main channel waterbodies and perennial escarpment streams. This study revealed that habitat use changed with age: small individuals (50–200 mm CFL) were recorded from floodplain lagoons and in sandy creeks and corridor lagoons; the latter two habitats were suggested to provide routes of dispersal. Fish between 200–360 mm CFL were rarely collected from floodplain lagoons and were more common in lowland muddy lagoons, as were fish larger than this size range, despite being widely distributed. Taylor [1304] reported both very small (50 mm) and large (635 mm) specimens in a lowland freshwater billabong that was occasionally tidally influenced during extreme wet seasons. It was also recorded in the main channel of the Roper River [1304]. We have recorded small numbers in the upper reaches of the Leichhardt River where the habitat was dominated by still, moderately deep (approx. 2 m) water over a gravel-cobble bottom.
Bishop et al. [193] detected an association between presence of S. krefftii and the extent of vegetated cover present in lagoons, with lagoons containing submerged macrophytes being favoured over lagoons with emergent or floating macrophytes and those without any vegetative cover. These authors suggested that aquatic macrophytes may be important spawning sites, citing Lake’s [754] assertion that the eggs of this species have tendrils which adhere to submerged vegetation. Pollard [1064] reports frequent observations of S. krefftii lurking under overhanging vegetation and amongst tree roots, particularly those of Pandanus species. This habit has been observed also in the Bowen River, where overhanging Melaleuca foliage is used as cover from which to launch ambush attacks on other fishes (BJP, pers. obs.). Just as frequently however, S. krefftii can be observed cruising open waters a few centimetres from the water’s surface. None of the accounts from which this summary is drawn suggest that S. krefftii occurs in reaches with appreciable current velocities despite the fact that this species is a powerful swimmer and able to move exceedingly quickly when alarmed. Environmental tolerances Few data are available on this aspect of the biology of S. krefftii except data describing ambient conditions in sites in which it has been collected (Table 1).
Kennard [697] recorded this species in both the main river channel and a floodplain lagoon of the Normanby River but it was not abundant in either habitat. In the Burdekin River, this species has been collected throughout the main river channel below the Burdekin Falls (now the site of a very large dam) and in the main river channel of its major lowland tributary, the Bowen River [1082, 1098] but currently appears absent from lagoonal habitats of the Burdekin River delta (C. Perna, pers. comm.). Strongylura krefftii appears limited to the lowland reaches of the Pioneer River although may have once been far more widespread in this system [1081]: three weirs along its lower length have probably impacted on this species. It has been recorded moving upstream through the fish lift on Dumbleton Weir (T. Marsden, pers. comm. cited in Pusey [1081]). Long tom
Strongylura krefftii has been collected from across a wide range of temperatures (22.9–38oC), nonetheless this range is typical of those temperatures expected for northern Australia. Although S. krefftii has been recorded most commonly from moderately well-oxygenated waters, it is evident from the conditions experienced in the Normanby River that hypoxic conditions may be tolerated. However, S. krefftii was recorded among the dead in a large fish kill in the Northern Territory for which hypoxia was implicated as the major cause. This species has been recorded from acidic and basic waters although the average conditions tend to be within one pH unit of neutrality. In all cases, S. krefftii was collected from waters of low conductivity and moderately
168
Strongylura krefftii
season. We have collected a ripe female (380 mm SL) containing ovulated eggs in the lower Burdekin River in November, an observation also consistent with a wet season spawning season [1093]. Although measurement of fecundity were not made, the eggs were about 2 mm in diameter.
Table 1. Physicochemical data for Strongylura krefftii. Summaries are derived from average site data from three studies: 1) Bishop et al. [193] in the Alligator Rivers region, n = 23 sites; 2) Pusey et al. [1098], n = 5 site/sampling occasions in the Burdekin River drainage, and 3) Kennard [894], two sites on the Normanby River and its floodplain. Note the difference in units used to describe turbidity. Temperature, dissolved oxygen and pH for the Alligator Rivers region and the Normanby River were taken at the water’s surface. Parameter Alligator Rivers region (n = 23) Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (cm)
Mean
Max.
Reproductive investment does not appear to be great as Bishop et al. [193] report mean female wet season GSI values of 2.2 ± 1.6% only. These data suggest that S. krefftii is iteroparous. The spawning location is unknown but in the Norethern Territory ripe females have been collected from escarpment streams, lowland sandy creeks and shallow lagoons, whereas small individuals are recorded from floodplain lagoons and corridor habitats. The eggs of some other belonids have numerous tendrils which allows attachment to vegetation. If this spawning mode also occurs in S. krefftii, then delivery to juvenile habitats by the current must occur after hatching. Egg development is apparently protracted (one to five weeks) in many belonids [224, 225].
Min.
30.0 6.3 6.4 – 72
38 9.1 8.6 98 1
24 3.7 4.6 6 360
Normanby River (n = 2) Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
– – – – –
23 2.8 7.4 263 7.1
22.9 2.4 6.0 252 2.0
Burdekin River (n = 5) Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
30.0 8.9 7.99 394 2.76
33 12.1 8.80 790 5.30
23 7.2 7.27 131 1.76
Movement There is little published information on this aspect of the biology of S. krefftii. Bishop et al. [193] implied that spawning occurred in lowland sandy creeks and shallow lagoons and that eggs or larvae were passively delivered to floodplain lagoons, the fish dispersing out of these habitats as they grew. Strongylura krefftii has been recorded in fishways [1274], congregated below such structures [587] or congregated below weirs lacking an effective fishway [942]. Unfortunately, the number of fish observed in these studies has been too few to draw any meaningful conclusions with respect to timing of, and conditions which stimulate, movement. Lateral movement into off-channel habitats clearly occurs in some rivers. Salinity tolerance is unknown in this species, however it has not been recorded in marine environments. It therefore appears unlikely that this species would be able to move easily between river basins: a characteristic that may be of importance if populations are catastrophically affected by drought, disease or human disturbance (see Environmental Tolerance section above).
high clarity. It is noteworthy that the range of conditions experienced across the three studies is not greatly different from that recorded within the Alligator Rivers region alone. Reproductive biology The reproductive biology of S. krefftii in Australia remains largely unstudied. Bishop et al. [193] reported that although gender could be determined at small size (133 and 195 mm CFL for females and males, respectively) and that stage III gonads were present in female fish at 317 mm and male fish at 267 mm, length at first maturity (i.e. length at which 50% of the sample is reproductively mature) was substantially greater, particularly for females: 420 mm and 290 mm for females and males, respectively. Based on estimated growth rates, Bishop et al. estimated that such fish were in the 2+ and 1+ age classes, respectively [193].
Trophic ecology The diet summary depicted in Figure 1 is drawn from two studies. The first is that by Bishop et al. [193] (n = 132) for the Alligator Rivers region, and the second is our own unpublished data for four fish collected from the Burdekin River. Mean contribution by each category has been weighted by sample size: accordingly the data provided by Bishop et al. [193] dominates the summary. Fish were the only item found in fish from the Burdekin River.
In the Alligator Rivers region, mature fish (stage V) were recorded in the mid-dry to early wet seasons whereas ripe fish (stage VI) were only collected in the late dry and early wet seasons only [193]. These observations suggest a spawning season coincident with the monsoonal wet
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Freshwater Fishes of North-Eastern Australia
contained a wide range of fish sizes. It is probable that piscivory increases in importance with increasing size such that adult fish are exclusively piscivorous. Very small individuals, particularly those in the halfbeak stage, may be planktivorous.
Strongylura krefftii is predominantly piscivorous but also consumes smaller amounts of surface dwelling invertebrates and terrestrial insects and prawns. The consumption of terrestrial vegetation and algae is probably accidental. The prey consumed by S. krefftii is diverse and includes chandids, melanotaeniids, plotosid catfishes, terapontid grunters, atherinids and clupeids. Unidentified (11.3%) Terrestrial invertebrates (1.0%) Terrestrial vegetation (3.6%) Algae (4.2%)
Aquatic insects (5.5%) Macrocrustaceans (3.0%)
Fish (71.4%)
Figure 1. The mean diet of Strongylura krefftii. Information sources upon which this figure is based are discussed in the text.
Bishop et al. [193] did not provide a breakdown of changes in diet with size but the sample examined in the study
170
Conservation status, threats and management Strongylura krefftii is listed as Non-Threatened by Wager and Jackson [1353], however the general paucity of biological information concerning this species makes it difficult to ascertain the existence and severity of potential threats. However, it is clear that S. krefftii make substantial movements within river systems and that different life history stages utilise different habitats. Consequently structures that impede movement are potentially threatening. The observation that juvenile S. krefftii in the Northern Territory use off-channel habitats suggests that the quality and availability of such habitats may impact on the viability of long tom populations. Moreover, since such habitats are frequently only accessible during periods of high flow, water resource development which reduces the frequency and duration of large flow events may also impact on this species. The absence of information on this species is of concern, particularly given that it is not uncommonly encountered in fishways. Greater research effort to elucidate the biology of this species is needed.
Craterocephalus marjoriae Whitley, 1948 Marjorie’s hardyhead
37 246025
Family: Atherinidae
upper jaw overhangs lower jaw when mouth closed [350, 635, 936]. Body scales large and dorsoventrally elongated with prominent circuli; large, irregularly-shaped scales on top of head. Opercles and preopercles scaled. First dorsal fin originating behind tips of pectoral fin rays, second dorsal fin originating above or slightly behind origin of anal fin [350, 635]. In the second dorsal, pectoral, pelvic and anal fins of this species, a single unsegmented ray sometimes separates the fin spine and the segmented rays (the unsegmented ray is counted together with the segmented rays in the meristics listed above). Caudal fin forked.
Description First dorsal fin: IV–VII; Second dorsal: I, 6–8; Anal: I, 6–9; Pectoral: 12–16; Caudal: 14–17 segmented rays; Pelvic: I, 5; Vertical scale rows: 27–30; Horizontal scale rows: 5–7; Predorsal scales: 10–14, Gill rakers on lower branch of first arch: 10–13; Vertebrae: 30–32 [34, 52, 350, 635, 1093, 1391]. Craterocephalus marjoriae is a small hardyhead known to reach 97 mm TL but more common to 50 mm [34, 635]. Of 9199 specimens collected in streams of south-eastern Queensland [699, 704, 709, 1093], the mean and maximum length of this species were 36 and 74 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 650 individuals (range 17–70 mm SL) sampled from the Mary River, south-eastern Queensland is W = 0.2 x 10–4 SL3.062, r2 = 0.980, p<0.001 [1093].
Body golden to sandy-yellow in colour, ventral surface and opercles silvery, top of head and snout darker. Fins clear or straw coloured. Prominent iridescent silver-gold midlateral stripe extending as far forward as pectoral fins. A dark, triangular blotch lateral to vent sometimes visible in populations from the Clarence River. In northern populations, rows of tiny black spots sometimes present on scales directly above mid-lateral stripe and on head [34, 350, 635, 936]. During the breeding season, pigmentation of male intensifies with gold mid-lateral stripe becoming more pronounced and the white testis becoming visible through the body wall. The single (left) ovary of the female also
Craterocephalus marjoriae is a robust species with a moderately deep, elongate body. The head is blunt and slightly flattened, sloping towards snout. The mouth is small, not reaching eye, and is oblique and protrusible. Two rows of small, sharp, inwardly pointed teeth present on medial third of upper jaws, single row in dentary. The
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Freshwater Fishes of North-Eastern Australia
becomes more apparent as the black mesovarium develops and the urinogenital papilla becomes transparent and dorsoventrally flattened. Preserved colouration darker than described above, specimens becoming light browntan with silvery or black mid-lateral stripe [34, 350, 635, 936, 949].
represent distinct species: C. helenae and C. marianae in the Northern Territory and C. munroi in the Gulf of Carpentaria [345, 350, 637]. Distribution and abundance Craterocephalus marjoriae is patchily distributed in coastal drainages between central Queensland and northern New South Wales. The central core of its range is from the Burnett River, south-eastern Queensland, south to the Nerang River. In this region it appears generally restricted to the larger river basins: the Burnett, Mary, Noosa, Pine, Brisbane, Logan, Albert, Coomera and Nerang rivers. With the exception of Hilliards Creek, it does not appear to be present in any of the smaller coastal streams of the region. There are isolated records of this species occurring further north in the Fitzroy River [658], small coastal streams near Sarina [779] and in the Burdekin River [350]. It is possible that these highly disjunct records are due to misidentification, the result of chance dispersal or translocation [350, 1093]. A disjunct population also occurs to the south in the Clarence River, northern New South Wales [635]. This species has not been recorded from the sand islands off the south-eastern Queensland coast.
Craterocephalus marjoriae is similar in general appearance to the largely sympatric congener C. stercusmuscarum fulvus, especially juveniles. Distinguishing characteristics of C. marjoriae include a more robust and deeper body, the distinctive protrusion of the upper jaw over the lower jaw when the mouth is closed, and prominent iridescent silver-gold mid-lateral stripe extending as far forward as pectoral fins [350]. Systematics The family Atherinidae contains approximately 173 species from about 25 genera worldwide, occurring mainly in marine and estuarine waters [422, 632, 637, 671, 1207]. In Australia, freshwater representatives comprise approximately 15 species from three genera [52, 637]. The genus Craterocephalus McCulloch, 1912 [876] is generally restricted to freshwaters and is present in New Guinea and Australia. The systematics of the genus have been thoroughly reviewed and revised in recent years by Ivantsoff, Crowley and Allen [343, 345, 346, 347, 348, 350, 352, 632, 633, 637, 638]. The genus is currently thought to contain 24 species, 14 of which occur in Australia [37, 52, 422, 637]. The etymology of the genus epithet is from the combination of the Greek for bowl or mixing vessel and head, possibly referring to the strong or sturdy head of species in the genus [422, 797], from which the common name hardyhead is also derived. Craterocephalus can be divided into three distinct groups or species complexes [635]. Two of these groups, the ‘eyresii’ (including C. marjoriae) and ‘stercusmuscarum’ groups, contain freshwater species while the third (‘honoriae’) contains estuarine and marine species [343, 635]. Electrophoretic evidence indicates that members of the ‘eyresii’and ‘stercusmuscarum’ groups are so dissimilar as to almost constitute separate genera [343]. Species radiation within the genus Craterocepahalus was considered by Crowley et al. [352] ‘to be a recent phenomenon’ in New Guinea (occurring from the Pliocene-Pleistocene epochs) but Crowley [343] considered ‘hardyheads at least ... are not the result of recent speciation’ in Australia.
Craterocephalus marjoriae is relatively uncommon at the northern extent of its range (e.g. north of the Burnett River). It is however, very common and widely distributed within the major rivers of south-eastern Queensland and is often locally abundant, forming schools of hundreds of individuals [1093]. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that it has been collected at 15 of 63 locations surveyed (13th most widespread species in the catchment) and formed 1.5% of the total number of fishes collected (12th most abundant). Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 16 017 individuals from 33% of all locations sampled (Table 1). Overall, it was the fifth most abundant species collected (9.8% of the total number of fishes collected) and was present in relatively high abundances at sites in which it occurred (15.3% of total abundance, third most common species). In these sites, C. marjoriae most commonly occurred with the following species (listed in decreasing order of relative abundance): P. signifer, R. semoni, M. duboulayi and G. holbrooki. In freshwaters of south-eastern Queensland, C. marjoriae co-occurs with its congener, C. s. fulvus, reasonably often. Both species occurred together at 47 of the 127 locations in which either species was sampled [1093]. Craterocephalus marjoriae was the 5th most important species in terms of biomass, forming 1.3% of the total biomass of fish collected. It was most common in the Mary and the
Craterocepahalus marjoriae, first described by Whitley in 1948 [1391], is confined to coastal rivers of south-eastern Queensland and northern New South Wales. However, it was once thought to have a wide and disjunct distribution in eastern and northern Australia. It is now recognised that populations previously identified as C. marjoriae actually
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Craterocephalus marjoriae
Table 1. Distribution, abundance and biomass data for Craterocephalus marjoriae. Data summaries for a total of 16 017 individuals collected from rivers in south-eastern Queensland over the period 1994-2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
32.6
66.0
–
15.0
29.7
39.7
5.0
9.81 (15.25)
13.20 (15.73)
–
0.44 (4.39)
3.89 (10.69)
9.22 (16.03)
0.06 (0.73)
5 (3)
2 (2)
–
16 (4)
8 (4)
4 (3)
21 (8)
1.27 (1.95)
1.60 (2.39)
–
–
0.79 (1.35)
0.73 (1.11)
–
5 (5)
4 (4)
–
–
8 (8)
8 (6)
–
Mean numerical density (fish.10m–2)
1.88 ± 0.31
2.14 ± 0.49
–
0.23 ± 0.05
1.27 ± 0.44
1.67 ± 0.28
0.05 ± 0.00
Mean biomass density (g.10m–2)
1.97 ± 0.32
2.44 ± 0.51
–
–
1.56 ± 0.63
1.11 ± 0.18
–
% biomass Rank biomass
present in a wide range of stream sizes (range = 0.7–44.2 m width) but is more common in streams of intermediate
Albert-Logan rivers where it was the second and fourth most abundant species, respectively. It was comparatively widespread throughout these catchments, being present at 66% and 42% of locations sampled in the Mary and Albert-Logan rivers, respectively. This species is comparatively rare or absent from the remaining catchments of south-eastern Queensland sampled by us. Across all rivers, average and maximum numerical densities recorded in 435 hydraulic habitat samples (i.e. riffles, runs or pools) were 1.88 individuals.10m–2 and 124.02 individuals.10m–2, respectively. Average and maximum biomass densities at 367 of these sites were 1.97 g.10m–2 and 105.0 g.10m–2, respectively. Highest numerical densities and biomass densities were recorded from the Mary River. In New South Wales, C. marjoriae has only been recorded from the Clarence River [282, 814, 1201] where it is apparently very common. For example, in a survey of 11 sites in the Clarence River in 1991, this was the most abundant species sampled, forming 37% of the total number of fish collected [282]. In a later survey of six sites in the Clarence River, only 10 individuals were collected from a single location [553].
Table 2. Macro/mesohabitat use by Craterocephalus marjoriae. Data summaries for 16 017 individuals collected from 435 mesohabitat units at 97 locations in south-eastern Queensland streams between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min. 5.6 4.0 0.5 0 0.7 0
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec–1) 0
Macro/mesohabitat use Craterocephalus marjoriae is found in a variety of lotic habitats, but generally only in the larger river systems within it range. It is usually widespread within river systems but appears to be restricted to freshwaters. In south-eastern Queensland, C. marjoriae has generally similar macro/mesohabitat use patterns as its congener, C. stercusmuscarum. This species occurs throughout the major length of rivers, ranging between 0.5 and 335 km from the river mouth and at elevations up to 400 m.a.s.l. (Table 2). It most commonly occurs within 200 km of the river mouth and at elevations around 110 m.s.a.l. It is
173
Max.
Mean
W.M.
4850.6 211.0 335.0 400 44.2 80.0
477.5 45.4 188.5 114 9.4 33.2
361.9 37.9 196.8 110 6.7 32.4
3.02 1.08 0.84
0.47 0.39 0.14
0.34 0.29 0.10
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
76.4 100.0 58.5 78.2 66.8 65.0 41.4
4.3 16.1 20.2 26.2 22.6 9.5 1.2
3.9 15.1 20.3 26.1 25.6 7.9 1.1
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
69.6 65.9 20.0 62.7 50.0 92.6 29.9 15.5 88.3 100.0
13.0 9.7 1.0 5.7 1.5 11.7 2.9 2.7 11.1 15.7
11.3 12.6 0.6 4.8 1.3 9.5 1.7 2.0 5.7 8.3
Freshwater Fishes of North-Eastern Australia
this species has been classified as a pool-dwelling species [553] and has been reported to prefer well-vegetated, clear, flowing streams with sand and gravel substrates [34, 635, 814, 936].
width (5–10 m) with low to moderate riparian cover (usually <40%). In rivers of south-eastern Queensland, this species has been recorded in a range of mesohabitat types but it most commonly occurs in runs characterised by moderate gradient (weighted mean = 0.34%), moderate depth (weighted mean = 0.39 m) and low to moderate mean water velocity (weighted mean = 0.1 m.sec–1) (Table 2). It also occurs in shallow riffles with high gradient (maximum = 3.02%) and high water velocity (maximum = 0.84 m.sec–1). This species is most abundant in mesohabitats with substrates of intermediate size (fine gravel, coarse gravel and cobbles) and particularly where submerged aquatic macrophytes, filamentous algae, leaf litter beds, undercut banks and root masses are common. Elsewhere, 50
(a) 50
40
40
30
30
20
20
10
10
0
0
30
Microhabitat use In rivers of south-eastern Queensland, C. marjoriae was most frequently collected from areas of low to moderate water velocity (usually less than 0.4 m.sec–1) (Fig. 1a and b). It has been recorded at maximum mean and focal point water velocity of 1.09 and 0.96 m.sec–1, respectively. Aggregations also often observed in slack-water eddies (e.g. behind rocks and debris) within high velocity riffle habitats [1093]. This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 1c). A pelagic schooling species, it most commonly occupies the mid water column (Fig. 1d). It is found over a wide range of substrate types but most often over fine gravel, coarse gravel and cobbles (Fig. 1e). Although often collected in areas greater than 1 m from the stream-bank (53% of individuals sampled) and in open water (Fig. 1f), the majority (90% of individuals) were collected in areas less than 0.2 m from the nearest available cover. It was frequently collected in close association with filamentous algae, aquatic macrophytes and the substrate, but was also found close to leaf-litter beds and submerged marginal vegetation (Fig. 1f). Nothing is known of larval habitat use. In the Mary River during January, large aggregations of juveniles 10–15 mm were often observed in slack-water areas among submerged marginal vegetation adjacent to areas of high water velocities (riffles and runs) [1093].
(b)
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 30
20 20 10
10
0
0
Total depth (cm) 30
Environmental tolerances Little quantitative data is available concerning environmental tolerances, although laboratory experiments revealed that adult C. marjoriae lost orientation and were unable to control lateral movement or remain upright at 5.4°C, and moved only spasmodically at 4.4°C [95]. Craterocephalus marjoriae has been collected over a relatively wide range of physicochemical conditions (Table 3) including sites with low dissolved oxygen concentrations (minimum 0.3 mg.L–1), mildly acidic to basic waters (range 6.3–9.1), and high conductivity (maximum 5380 µS.cm-1). The maximum turbidity at which this species has been recorded in south-eastern Queensland is 144 NTU. Despite the wide range of physicochemical conditions reported above, this species is not common in degraded urban streams of the Brisbane region [94, 95, 704, 707, 709], suggesting that it may be sensitive to habitat and water quality degradation. Harris and Gehrke [553] classified C. marjoriae as intolerant of poor water quality. It has been reported to thrive in impounded waters (e.g. Lake Barambah in the Burnett River) [205], possibly because of
Relative depth
(e)
(f) 20
20 10
10 0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Craterocephalus marjoriae. Data derived from capture records for 2582 individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
174
Craterocephalus marjoriae
[1093] than in the Brisbane River [949], suggesting reproduction may occur at a smaller size for fish in the Mary River. For example, the minimum and mean lengths of stage III females from the Mary River were 28.4 and 41.1 mm SL, respectively ([1093], Fig. 2), and those from the Brisbane River were 35.2 and 47.5 mm SL, respectively [949]. Gonad maturation in both sexes was commensurate with somatic growth, the mean length at each reproductive stage being different from all other stages (Fig. 2). Gravid (stage V) females were slightly larger than males of equivalent maturity (minimum 32.8 mm SL, mean 48.2 mm ± 0.6 SE for females; minimum 31.7 mm SL, mean 44.3 mm ± 0.6 SE for males). The minimum size of spawning female fish in aquaria is reported as 38 mm SL and the first fertile eggs were observed when males were 39.5 mm SL [1210].
the prevalence of shallow, clear water areas with sandy substrates and abundant aquatic vegetation in this lake [12, 205]. Table 3. Physicochemical data for Craterocephalus marjoriae. Data summaries for 15 274 individuals collected from 285 samples in south-eastern Queensland streams between 1994 and 2003 [1093]. Parameter
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
8.4 0.3 6.3 19.5 0.2
31.7 19.5 9.1 5380.0 144.0
Mean 19.8 8.0 7.8 496.8 5.1
Reproduction Quantitative information on the reproductive biology of C. marjoriae is available from two field studies [949, 1093] and one aquarium study [1210]; details are summarised in Table 4. This species spawns and completes its entire life cycle in freshwater and has been bred in captivity [1210]. Maturation commences at a relatively small size. Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, south-eastern Queensland, were 27.6 mm SL and 36.7 mm ± 1.5 SE, respectively for males and 21.3 and 34.2 mm ± 1.0 SE, respectively for females (Fig. 2). Fish of equivalent reproductive stage were slightly smaller in the Mary River
Reproductive stage I
II
III
IV
V
Males (49) (14) (8) (11) (28) (7)
(12) (56) (39 ) (7) (14)
100 80 60 40 20
50
Males 45
0
Females
Females 100
40
(44) (28) (19) (19) (43) (12)
(3 6) (82) (38) (13) (37)
80
35 60
30
40
25
20 0
20 I
II
III
IV
V
Reproductive stage Figure 2. Mean standard length (mm SL ± SE) for male and female Craterocephalus marjoriae within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland, between 1994 and 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 3.
Month Figure 3. Temporal changes in reproductive stages of Craterocephalus marjoriae in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in parentheses.
175
Freshwater Fishes of North-Eastern Australia
post-breeding months (March–May) and amongst mature fish (>45 mm SL) [949].
Craterocephalus marjoriae has an extended breeding season from late winter through to summer but spawning appears to be concentrated in late winter and spring. In the Mary River, immature and early developing fish (stages I and II) were most common between January and May (Fig. 3). Developing fish (stages III and IV) of both sexes were present year-round. Gravid males (stage V) were present from June to March and gravid females were present from June through to January, however gravid fish from both sexes were most abundant between August and November (Fig. 3). The temporal pattern in reproductive stages mirrored that observed for variation in GSI values. Peak monthly mean GSI values (8.4% ± 0.7 SE for males, 7.2% ± 0.5 SE for females) occurred in August for both sexes and remained elevated through to December (Fig. 4). The mean GSI of ripe (stage V) fish was 7.4 % ± 0.3 SE for males and 6.3% ± 0.2 SE for females [1093]. Reproductive activity for fish in the Brisbane River [949] generally matched that observed for fish from the Mary River [1093], except that peak reproductive activity occurred slightly later in the year. Ripe fish (equivalent to stage V) were present between September and January and peak monthly mean GSI values (7.0% for males, 8.5% for females) were observed in September for females and October for males, remaining elevated in both sexes until January [949]. Overall sex ratios for populations from the Brisbane River have been reported as 1.3 females for every male, and significantly more females were present during
The spawning stimulus is unknown but corresponds with increasing water temperatures and photoperiod. In aquaria, spawning occurred at water temperatures between 25 and 29°C [1210]. Milton and Arthington [949] observed that the peak spawning period for fish in the Brisbane River in September–October coincided with surface water temperatures between 19 to 23°C, and day length from 11 to 11.5 hours. The peak spawning period generally coincides with pre-flood periods of low and stable discharge in rivers of south-eastern Queensland. However, breeding may also continue through the months of elevated discharge at the commencement of the wet season in December/January. This species is thought to spawn repeatedly during the breeding season and it has been suggested that multiple spawning over an extended period is an adaptation to the relatively unpredictable timing of the onset of wet season flooding [949]. The spawning of adults and presence of larvae can occur when the likelihood of flooding is low, but the predictability of high temperatures and low flows are higher. These conditions are likely to increase the potential of larvae to encounter high densities of small prey, avoid physical flushing downstream due to high flows and thereby maximise the potential for recruitment into juvenile 25
Spring (n = 2217)
10
Males 8
20
Summer (n = 2552)
Females 15
AutumnWinter (n = 4429)
6
10 4
5
2
0
0
Month Figure 4. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Craterocephalus marjoriae males (open circles) and females (closed circles) in the Mary River, southeastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 3.
Standard length (mm) Figure 5. Seasonal variation in length-frequency distributions of Craterocephalus marjoriae, from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
176
Craterocephalus marjoriae
year-round and may not necessarily be related solely to prevailing temperature and/or discharge regime but may also involve other physical or biological factors.
stocks, as has been hypothesised for other small-bodied fish species in the Murray-Darling Basin [614, 615]. Milton and Arthington [949] reported that juvenile fish in the Brisbane River were present between October and February and these authors were able to discern a clear cohort that could be tracked through to the following breeding season. In contrast, subsequent sampling in rivers of south-eastern Queensland [1093] revealed that juvenile fish less than 20 mm SL were present year-round and no obvious seasonal peak in juvenile abundance (i.e. no clear cohort of juvenile fish) was observed (Fig. 5). The latter data support the suggestion made earlier that this species has an extended spawning period. The data further suggest that suitable conditions for recruitment of larvae through to the juvenile stage and beyond may persist
In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal vegetation. Spawning observations in aquaria suggest that pre-spawning behaviour is initiated adjacent to aquatic vegetation whereby the male swims beneath and behind the female, nudging the anterior rays of the anal fin and posterior belly region of the female with the interorbital or snout area of his head [1210]. Adhesive, demersal eggs are attached to aquatic macrophytes. The male follows within 5 cm of female and then releases milt onto the eggs when swimming adjacent to her. In aquaria, males and conspecifics have been observed to eat eggs during and following deposition
Table 4. Life history information for Craterocephalus marjoriae. Age at sexual maturity (months)
<12 months [949]
Minimum length of gravid (stage V) females (mm)
32.8 mm SL (field) [1093], 38 mm SL (aquaria) [1210]
Minimum length of gravid (stage V) males (mm)
31.7 mm SL (field) [1093], 39.5 mm SL (aquaria) [1210]
Longevity (years)
2+ [949]
Sex ratio (female to male)
1.3:1 [949]
Occurrence of ripe (stage V) fish
Late-winter, spring and summer. June–March [1093], September–January [949]
Peak spawning activity
Late-winter and spring. Elevated GSI between August and December [1093], Elevated GSI between September and January [949]
Critical temperature for spawning
? 19–23°C (field) [949]; 25–29°C (aquaria) [1210]
Inducement to spawning
? possibly temperature and day length
Mean GSI of ripe (stage V) females (%)
6.3% ± 0.2 SE (maximum mean GSI in August = 7.2% ± 0.5 SE) [1093]; (maximum mean GSI in September = 8.5%) [949];
Mean GSI of ripe (stage V) males (%)
7.4% ± 0.3 SE (maximum mean GSI in August = 8.4% ± 0.7 SE) [1093]; (maximum mean GSI in October = 7.0%) [949]
Fecundity (number of ova)
Total fecundity = 30–484, mean = 196 ± 8 SE [1093]; Batch fecundity = 48–259, mean = 137 ± 10 SE [949], In aquaria 2–15 eggs deposited in 3–5 day period [1210]
Total Fecundity (TF) and Batch Fecundity (BF)/length relationship (mm SL)
Log10 TF = 1.671 Log10 L – 0.575, r2 = 0.283, p<0.001, n = 146 [1093]. Log10 BF = Log10 (6.1 x 10–4) + 2.52 Log10 L, r2 = 0.58, p<0.001, n = 61 [949].
Egg size (diameter)
Intraovarian eggs from stage V fish = 1.02 mm ± 0.01 SE [1093]. Water-hardened eggs 1.15–1.25 mm [1210].
Frequency of spawning
Extended spawning period, probably repeat spawner [949]
Oviposition and spawning site
In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal vegetation. In aquaria, adhesive, demersal eggs are attached to aquatic macrophytes [1210]
Spawning migration
None known
Parental care
None known
Time to hatching
After fertilisation, hatching takes 6.5 to 7 days in aquaria at 25–29°C [1210]
Length at hatching (mm)
Newly hatched prolarvae 5.7 mm SL [1210]
Length at free swimming stage
Postlarvae 7.25 mm SL [1210]
Age at loss of yolk sack
?
Age at first feeding
?
Length at first feeding
Postlarvae 7.25 mm SL [1210]
Length at metamorphosis (days)
?
Duration of larval development
?
177
Freshwater Fishes of North-Eastern Australia
35–36 mm SL, 1+ fish were 46–47 mm SL and 2+ fish (females only) were greater than 56 mm SL. These data (together with stage-length and sex ratio data presented earlier) collectively suggest that sexual maturity is reached at one year of age, males appear to die after their first breeding season and females live for over two years. In aquaria, fish have been reported to live for up to 18 months [1210].
[1210]. No parental care of eggs has been reported. Total fecundity for fish from the Mary River is estimated to range from 30–484 eggs (mean 196 ± 8 SE, n = 146 fish) [1093]. Batch fecundity for fish from the Brisbane River ranges from 48–259 eggs/batch (mean 137 ± 10 SE, n = 61 fish) [949]. In the aquarium, C. marjoriae was observed to deposit 2–15 eggs in a 3–5 day period followed by a rest period of 6–9 days [1210]. Fecundity is significantly related to fish size. The relationship between length (SL in mm) and total fecundity (TF) for 146 fish from the Mary River is Log10 TF = 1.671 Log10 SL – 0.575, r2 = 0.283, p<0.001 [1093]. Fish of 40 mm SL produced about 150 eggs in total, whereas fish of 60 mm SL produced about 350 eggs [1093]. The relationship between length (SL in mm) and batch fecundity (BF) for 61 fish from the Brisbane River is Log10 BF = Log10 (6.1 x 10-4) + 2.52 Log10 SL. r2 = 0.58, p<0.001 [949]. Fish of 40 mm SL produced about 80 eggs per batch, whereas fish of 60 mm SL produced about 240 eggs [949]. Milton and Arthington [949] suggested that Craterocephalus marjoriae invests more into reproductive effort than its congener C. stercusmuscarum, with higher GSI values throughout the breeding season (particularly males) and higher mean batch fecundity, although both species have similar sized eggs (see also chapter on C. stercusmuscarum).
Movement There is no quantitative information on the movement patterns of C. marjoriae. This species has not been observed to use fishways on weirs or tidal barrages in the Burnett [658, 828, 1276, 1277], Mary [158, 159, 658] and Brisbane rivers [658], nor were large numbers of individuals found to be congregating below these structures, despite being abundant in the latter two rivers. However, it is likely that this species is able to undertake local dispersal and/or recolonisation movements. It is particularly abundant in streams that periodically become disconnected by extended periods of low flows, when surface waters recede to a series of isolated pools (e.g. in tributaries of the Mary and Brisbane rivers). In these streams, rapid recolonisation of previously dry river reaches has been observed soon after flows resumed in summer and longitudinal connectivity was re-established (i.e. within 48 hours [1093]).
Eggs are relatively large. The mean diameter of 1337 intraovarian eggs from stage V fish from the Mary River was 1.02 mm ± 0.01 SE [1093]. The diameter of waterhardened eggs has been reported to range from 1.15 to 1.25 mm [1210]. Eggs are characterised by a smooth nonadhesive chorion and 10 adhesive filaments (1 mm or longer) originating in a cluster at the animal pole of the egg [1210]. Oil droplets in the yolk were 0.01 to 0.1 mm diameter at spawning and were initially concentrated at the animal pole, later migrating in a bunch to the vegetal pole. Eggs hatch after 6.5 to 7 days at 25 to 29°C. Illustrations of larval stages can be found in Semple [1210]. The mean length of prolarvae three hours after hatching was 5.7 mm SL. At this stage the top of the head, preoperculum and lateral line were spotted and the eyes, swimbladder and surface pigments were black. Paired contour melanophores were visible on the dorsal surface and dendritic melanophores were present on the belly, caudal and ventral contours. Postlarvae were 7.25 mm SL and, by this stage, the anal and dorsal fin buds were developing, the caudal fin was rayed, rows of small punctate melanophores were visible on the caudal fin and anal finfold, and larvae had commenced swimming and feeding. Juveniles began to school once the fins were fully rayed [1210].
Trophic ecology Diet data for C. marjoriae is available for 224 individuals from studies in the Burnett and Albert rivers, south-eastern Queensland (Fig. 6). This species is a microphagic omnivore. Algae (filamentous and unicellular) comprised the largest proportion of the total mean diet (26.9%) and small amounts of aquatic macrophytes (2.0%) were also consumed. Microcrustaceans (23.6%) and aquatic insects (14.6%) were relatively important components of the diet and small amounts of fish (primarily fish eggs), molluscs and terrestrial invertebrates were also consumed. The high degree of herbivory in C. marjoriae is greater than that observed for other similarly sized and/or closely related species (e.g. C. stercusmuscarum) in south-eastern Queensland streams. A number of anatomical features make C. marjoriae well suited to benthic foraging and herbivory [917]. These characteristics include a small mouth with protrusible jaws that form an anteroventrally directed tube, potentially facilitating benthic grazing. This species also has an extra loop to the gut and the ratio of intestine length to standard length is over 2.5 times greater than that of C. stercusmuscarum and other similarly-sized sympatric species that consume less aquatic plant matter ([917] this study). In aquaria, adults will consume a range of food types including small anuran tadpoles, mosquito
Length at age data using evidence from scale annuli [949] indicate that 0+ fish (males and females) were around
178
Craterocephalus marjoriae
[95] observed that hardyheads (Craterocephalus spp.) in the Brisbane region were rarely present or abundant where the alien fish species Gambusia was present. These authors speculated that similarities in diet increased the potential for competition among these species. In contrast, our recent, more extensive sampling of rivers and streams in south-eastern Queensland [1093] indicates that C. marjoriae and G. holbrooki frequently occur together, often in large numbers. Co-occurrence data such as these provide no evidence for the impact of alien fish species such as G. holbrooki on C. marjoriae.
larvae and other common aquarium foods such as Calanus and Artemia nauplii, Tubifex worms and commercial flake foods [1210]. Even finely minced animal meats are eaten. Postlarvae will consume similar items to those listed above as well as infusoria made from lettuce [1210]. Fish (4.0%) Microcrustaceans (23.6%)
Unidentified (29.4%)
Molluscs (2.4%)
Terrestrial invertebrates (1.1%) Aquatic macrophytes (2.0%)
Aquatic insects (14.6%) Algae (26.9%)
Figure 6. The mean diet of Craterocephalus marjoriae. Data derived from stomach contents analysis of 224 individuals from the Burnett River [205] and Albert River [1421], southeastern Queensland.
Conservation status, threats and management The conservation status of Craterocephalus marjoriae is listed as Non-Threatened by Wager and Jackson [1353]. Although listed by Wager [1349] as having a restricted distribution, it is generally very common and widely distributed within the major rivers of south-eastern Queensland and in the Clarence River, northern New South Wales. It is relatively uncommon at the northern extent of its range (e.g. north of the Burnett River). Like many other native species, siltation arising from increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of C. marjoriae and may also affect aquatic invertebrate food resources. Interactions with alien fish species (e.g. competition for resources and predation on eggs, larvae and juveniles) is another other potential threat. Arthington et al.
Very little is known of movement patterns, however, limited upstream dispersal movements of young-of-theyear probably occur, suggesting that C. marjoriae is likely to be sensitive to barriers to movement caused by structures such as dams, weirs, barrages, road crossings and culverts. River regulation, independent of the imposition of barriers, may also impact on C. marjoriae populations. Changes to the natural discharge regime and hypolimnetic releases of unnaturally cool waters from large dams may interrupt possible cues for movement, or de-couple optimal temperature/discharge relationships during critical phases of spawning, larval movement and development. Unseasonal flow releases during naturally low flow periods in September and October appear likely to negatively affect reproductive success as this coincides with the period of peak spawning activity and larval development. The availability of aquatic macrophyte beds, the likely spawning habitat of C. marjoriae, may be maximised during low flow periods. Scouring actions of elevated discharges at the onset of the wet season may reduce or remove aquatic macrophyte beds. Larval development is also likely to be favoured during low flow periods, during which time phytoplankton and invertebrate abundances are also high [949]. Fish in aquaria have been reported to be susceptible to intestinal worm infestations [1210] and a species of Craterocephalus (possibly C. marjoriae) from the Brisbane catchment was infected by the digenetic trematode Opecoelus variabilis (Opecoelidae) [338, 339].
179
Craterocephalus stercusmuscarum (Günther, 1867) Fly-specked hardyhead
37 246029
Family: Atherinidae
Description First dorsal fin: IV–VIII; Second dorsal: I, 5–10; Anal: I, 7–10; Pectoral: 11–15; Caudal: 15–18 segmented rays; Pelvic: I, 5; Vertical scale rows: 32–35; Horizontal scale rows: 6–8; Predorsal scales: 11–18, Gill rakers on lower branch of first arch: 9–13; Vertebrae: 31–38 (C. s. fulvus: 31-36, C. s. stercusmuscarum: 35–38) [352, 486, 635, 637]. Figure: mature male specimen of C. s. stercusmuscarum, 51 mm SL, North Johnstone River at Malanda, September 1994; drawn 1998. Craterocephalus stercusmuscarum is a moderate-sized hardyhead commonly reaching 50–60 mm. The northern subspecies C. s. stercusmuscarum is known to grow to a larger size (maximum 108 mm LCF) [635] than C. s. fulvus (maximum 78 mm SL) [52, 635]; specimens from the Wenlock River may reach 125 mm TL [69]. Of 2555 specimens collected in streams of south-east Queensland, the mean and maximum length of this species were 34 and 73 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 306 individuals of C. s. fulvus (range 20–73 mm SL) sampled from the Mary River, south-eastern Queensland is W = 0.7 x 10–5 L3.217, r2 = 0.985, p<0.001 [1093]. The northern subspecies is known to consist of at least two
25
Upper Johnstone (n = 620)
20
Lower Johnstone (n = 165)
15
Mulgrave (n = 59)
10
5
0
Standard length (mm) Figure 1. Size frequency distributions for Craterocephalus stercusmuscarum stercusmuscarum populations in the upper Johnstone River (n = 620, open bars), lower Johnstone River (n = 165, hatched bars), and Mulgrave River (n = 59, closed bars). Specimens were collected over the period 1994–1998 [1093].
180
Craterocephalus stercusmuscarum
sides of C. s. stercusmuscarum, less evident or absent in small individuals or populations from southern and inland areas (i.e. C. s. fulvus). Minor colour variation between sexes. Running ripe females with dark blotch around vent; males with bright yellow or gold coloured ventral surface during breeding season. Colour in preservative: white to brown, with midlateral stripe as described above [486, 635, 637].
distinct lineages (see below) [899], with a lineage present on the Atherton Tablelands of the Wet Tropics region growing to larger size than that occurring in the lowland rivers of this area (Fig. 1). The population size structure of C. s. stercusmuscarum in the Burdekin River (n = 295) closely resembles that of lowland Wet Tropics populations depicted in Figure 1, with a maximum length (SL) of 70 mm, and a slightly bimodal distribution with modal peaks for the 35–40 and 50–55 mm size classes [1082]. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 288 individuals of C. s. stercusmuscarum (range 21–82 mm SL) from the Atherton Tablelands section of the Johnstone River is W = 1.6 x 10–5 L2.952, r2 = 0.969, p<0.001. The equivalent relationship for 134 individuals (range 17–63 mm SL) from the lower Johnstone River and the Mulgrave River (elevation less than 50 m.a.s.l.) is W = 0.9 x 10–5 L3.108; r2=0.968, p<0.001 [1093]. Bishop et al. [193] report a length/weight relationship of W (in g) = 0.011 L2.880; r2 = 0.949, p<0.001 where L = CFL in cm.
Larval C. s. stercusmuscarum are diffusely pigmented throughout larval development. A few punctate melanophores occur on the head behind the level of the eyes and nape. Stellate melanophores are irregularly and diffusely distributed down the mid-line of the dorsal surface. Stellate melanophores are present on the opercula and abdomen of some specimens, however they seldom extended forward through the isthmus. The peritoneum along the dorsal surface of the swim bladder is heavily pigmented. Stellate melanophores are always present along the lateral line but are unevenly distributed along its length [1093].
Craterocephalus stercusmuscarum is an elongate and slender species. The head of larger specimens often slopes towards snout and possesses an interorbital trough. The mouth is small, protrusible and bordered with thick lips; mouth not reaching anterior margin of eye. The mouth gape is restricted by fusion of lips. Teeth are small, in two or three rows in medial third of each jaw. Body scales relatively large, dorsoventrally oval, with concentric and complete circuli; scales arranged in distinct rows along body. Scales present on preopercle and opercle. First dorsal fin originating behind tips of pectoral rays; second dorsal fin originating in line with origin of anal fin. Pectoral fin inserted forward of pelvic fin. Caudal fin forked with rounded tips [486, 635, 637].
The two subspecies of C. stercusmuscarum can be separated on the basis of the following characters: Craterocephalus s. fulvus (sometimes referred to as the un-specked hardyhead or Mitchellian hardyhead) is generally less vividly coloured than C. s. stercusmuscarum, the lateral black spots are absent [637] or present but not as readily apparent [1093], and it has fewer vertebrae (31–36 in C. s. fulvus, 35–38 in C. s. stercusmuscarum) [637]. Craterocephalus s. fulvus in coastal south-eastern Queensland is similar in general appearance to the sympatric C. marjoriae, especially juveniles. Distinguishing characteristics of C. s. fulvus include a more slender, elongate body, a dark stripe running though eye and parallel rows of faint dark spots sometimes present along sides of body.
The larvae are typically elongate and narrowly fusiform in body plan. The eyes are heavily pigmented with a welldeveloped and slightly dorsoventrally compressed lens. The mouth is functional immediately after hatching and the gut is either simple or coiled but always non-striated in newly hatched larvae. A coiled and striated gut is present in flexion larvae. A yolk sac is present in early preflexion larvae but no longer so by flexion [1093]. More detail on larval morphology is presented in the section on reproduction (below).
Systematics Craterocephalus stercusmuscarum was originally described by Günther in 1867 [486] as Atherina stercus muscarum, the species epithet (and common name) referring to the pattern of black dots along the side of the body. Other synonyms of C. stercusmuscarum include Atherinichthys maculatus Macleay, 1883 [847] and C. worrelli Whitley 1948 [1391]. Ivantsoff et al. [637] showed that some populations of a species from the Murray-Darling Basin, previously recognised as C. fluviatilis McCulloch, 1913 [876], and populations of C. stercusmuscarum from south-eastern Queensland coastal rivers were morphologically indistinguishable, but differed from northern Australian populations of the latter species. Consequently, the subspecies C. stercusmuscarum fulvus and C. s. stercusmuscarum were recognised [352, 637]. Although differing in colouration and vertebral counts, their conspecific status
Colour varies between localities and subspecies. Dorsal surface green-grey, lower sides and ventral surface silvery. A dark stripe runs from snout and across eye, becoming black, gold or silver in colour and continuing to base of caudal fin. Dorsal surface of head often black; body scales stippled on edges. A single black spot at the base of each scale forms a series of longitudinal parallel rows along
181
Freshwater Fishes of North-Eastern Australia
was justified on the basis that preliminary electrophoretic analysis revealed no differences between C. s. fulvus and C. s. stercusmuscarum, and juveniles of both species could not be separated on the basis of external characteristics [352, 637]. Further information on the relationships between C. s. fulvus, C. fluviatilis and other hardyhead species can be found in Crowley and Ivantsoff [347]. Craterocephalus s. stercusmuscarum has been confused with C. randi [41, 1304], a closely related and almost indistinguishable species confined to Papua New Guinea [37, 343, 352]. Herbert and Peeters [569] speculated that there may be several undescribed species closely related to C. stercusmuscarum in rivers of north-western Cape York Peninsula on the basis that these populations have different scale patterns and usually lack black spots.
insufficient time for divergence since eastern and western flowing rivers had been separated. In contrast to the absence of morphological divergence, McGlashan and Hughes [899] detected high levels of genetic differentiation in eastern flowing rivers of the Wet Tropics region, identifying two highly divergent lineages and further divergence within one of these lineages. The first lineage was restricted to lowland sections of the Herbert, Mulgrave, Liverpool and Johnstone drainages. The second occurred in the high elevation Atherton Tableland sections of the Herbert, Johnstone and Barron rivers. Within this group, significant divergence between the Barron River (and one Johnstone River population) and the Johnstone and Herbert rivers was also detected. Additional preliminary analysis revealed that the high elevation populations of the Johnstone River were more closely related to Northern Territory populations of C. s. stercusmuscarum than they were to lowland populations within the same region. McGlashan and Hughes [899] argued that the upland population was derived from western flowing rivers. It is interesting to note that C. s. stercusmuscarum from the Northern Territory and high elevation sites from the Johnstone River are both less robust for a given length than lowland populations (see above). The Atherton Tablelands has a very complex geomorphic history with substantial recent vulcanism and drainage rearrangement [618].
Crowley [343] proposed that the phylogenetic structure of the Australasian craterocephalids (i.e. a single, highly distinct clade known as the ‘eyresii’ group and another clade separating into two subgroups, one composed of freshwater species and referred to as the ‘stercusmuscarum’ group and the other composed of marine or estuarine species referred to as the ‘honoriae’ group) could be explained by a series of separate invasions of freshwater. The initial invasion of the ancestral Craterocephalus species was postulated to be from the north or north-west and occurred during the mid-Cretaceous (95–110 m.y.b.p.) marine transgression when much of central Australia was flooded. As sea levels once more receded, peripheral populations also retreated whereas more inland populations become isolated and gave rise to the ‘eyresii’ group. Invasions associated with the later Oligocene/earlyMiocene marine transgression gave rise to the ‘stercusmuscarum’ group. Most New Guinean craterocephalids are closely related to C. stercusmuscarum and speciation within this clade appears to be relatively recent [352]. Crowley [343] suggested that the current distribution of the subspecies C. s. fulvus (see below) implied that it must have been present on the east coast prior to the uplift of the Tweed volcanic shield some 20–23 m.y.b.p. However, more recent allozyme electrophoretic data did not support this hypothesis and analysis of mtDNA sequence divergence suggested a more recent (approximately one million years) separation of these two populations [901]. McGlashan and Hughes [901] suggested that coastal populations of the two subspecies had been independently derived. Crowley [343], based on osteological evidence, noted that C. s. stercusmuscarum populations on either side of the Great Dividing Range in northern Queensland are almost identical and concluded that either this species had recently entered these rivers from both the Gulf of Carpentaria and the Coral Sea or that there had been
182
Distribution and abundance Craterocephalus stercusmuscarum is a very widespread species occurring in coastal and inland drainages of eastern and northern Australia. This species occurs in Timor Sea drainages of the Northern Territory, the Gulf of Carpentaria and western Cape York, coastal catchments throughout most of eastern Queensland and was historically present throughout much of the Murray-Darling Basin [52, 635]. In north-western Queensland, it is present in most major drainages in the Gulf of Carpentaria region [41, 571, 643, 1349]. This species is patchily distributed in north-eastern Queensland, and with the exception of the Annan River, it appears to be absent between southern Cape York Peninsula (south of the Normanby Basin) and the northern Wet Tropics region (north of the Barron River). It is present in most major drainages from the Barron River south to about the New South Wales border but appears absent from short coastal streams near Cardwell, Proserpine, Tin Can Bay and the Sunshine Coast. This species has also been recorded from Fraser Island off the coast of south-eastern Queensland. As far as we are aware, the eastern Australian distribution of C. s. fulvus extends only as far south as the Nerang River in south-eastern Queensland. However, Llewyllen [814] indicated that it was occasionally reported from the ‘extreme
Craterocephalus stercusmuscarum
north coast of New South Wales’ and Faragher and Harris [407] list this species as being present there. It is unclear whether these records are erroneous or whether the presence of this species has been confused with C. marjoriae, which occurs in the Clarence River. The distribution of the two subspecies of C. stercusmuscarum in Queensland was once thought to be separate. The southern limit of the distribution of C. s. stercusmuscarum was originally suggested to be the Dee River (Fitzroy Basin) [352] and C. s. fulvus was thought to occur only as far north as Maryborough [637]. More recently, Wager [1349] and Allen et al. [52] suggested that both subspecies were sympatric in the Mary River. Recent genetic analysis of populations of C. stercusmuscarum from eastern Queensland and the Murray-Darling Basin [899, 901] supported the notion that the two putative subspecies were genetically distinct (on the basis of mtDNA data) but indicated that C. s. fulvus is present at least as far north as the Elliott River and no populations of C. s. stercusmuscarum were present south of the Calliope River. It is unclear whether the subspecies are sympatric in the 250 km span between these rivers [901]. Craterocephalus s. stercusmuscarum is relatively common in northern Australia. It was the 4th most abundant species collected in extensive sampling of the Alligator Rivers region in the Northern Territory [193] and was also observed to be common and widespread in other studies of the region [189, 262, 1064]. In some habitats however, such as pools in sandy creek-beds, this species may by relatively rare and replaced by C. marianae [1416].
apparently absent from smaller drainages such as the Maria and Moresby rivers [583, 1183]. The absence from these drainages may be artefactual as this species has been recorded from small coastal drainages south of the Herbert River [1053]. This species was the 9th most widely distributed and the 10th most abundant species in an extensive survey of the region [1087]. In more recent sampling in the Johnstone and Mulgrave rivers, C. stercusmuscarum was the 15th most widely distributed and the 15th most abundant species but was only the 25th most abundant species by biomass (Table 1). This species is more abundant in the Johnstone River than in the Mulgrave River and occurs at greater biomass density in the former river, partly because it occurs at greater numerical density and partly because C. stercusmuscarum grow to larger size in the Johnstone River. Table 1. Distribution, abundance and biomass data for Craterocephalus s. stercusmuscarum in two rivers of the Wet Tropics region. Data summaries for a total of 461 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively, at those sites in which this species occurred. Total % locations % abundance Rank abundance % biomass Rank biomass
Johnstone Mulgrave River River
22.6
19.6
22.7
1.3 (9.5)
1.5 (11.3)
0.8 (6.6)
15 (3)
13 (3)
13 (6)
0.1 (2.2)
0.1 (2.6))
0.5 (1.4)
25 (7)
20 (6)
23 (12)
The subspecies C. s. stercusmuscarum is moderately common and widespread in some rivers of the Gulf of Carpentaria and western Cape York Peninsula including the Gregory, Gilbert, Mitchell (including the Walsh and Palmer rivers), Coleman, Edward, Archer, Holroyd, Ducie, Watson and Jardine drainages [571, 643, 1186, 1349]. In eastern Cape York Peninsula, it is widespread but patchily distributed, and often locally common [571, 697, 787, 1094]. Kennard [697] found C. s. stercusmuscarum contributed, on average, 8.2 ± 1.6% to the total electrofishing catch in aquatic habitats of the Normanby River: relative abundance was slightly greater in floodplain (9.7 ± 1.9%) than riverine (4.8 ± 2.6%) habitats. Temporal variation in abundance may be substantial. For example, we collected only seven individuals from the Pascoe, Stewart and Normanby rivers one year prior to Kennard’s study [179]. This species is present in the Annan and River.
This species is common and widely distributed in central Queensland drainages including the Black-Alice, Ross, Pioneer and Fitzroy rivers [176, 408, 586, 591, 658, 942, 1046, 1081, 1098]. In the Burdekin River, it is widely distributed in both upland and lowland portions of the river [586, 591, 1046, 1098] but is apparently absent or uncommon in the more turbid drainages of the Cape/ Campaspe and Belyando/Suttor rivers [255, 256] and is uncommon in the upper reaches of the Broken River [956]. This species contributed 1.4% and 2.1% of electrofishing and seine-netting catches, respectively in a study conducted in this river over the period 1989-1992 [1098].
Craterocephalus s. stercusmuscarum is widely distributed in the Wet Tropics region, occurring in all major drainages south of, and including, the Barron River [98, 230, 584, 585, 599, 643, 1087, 1096, 1177, 1184, 1223, 1349], but is
Craterocephalus s. stercusmuscarum is common to very common in the Pioneer River [658, 1081] and in short coastal streams near Sarina [779] and Shoalwater Bay [1328]. It is widespread and generally common in the
183
Mean numerical density (fish.10m–2) 0.37 ± 0.11
0.42 ± 0.02 0.29 ± 0.12
Mean biomass density (g.10m–2)
1.37 ± 0.99 0.37 ± 0.15
1.02 ± 0.65
Freshwater Fishes of North-Eastern Australia
Fitzroy River [160, 658, 659, 942, 1272, 1274, 1275], Calliope River [915], Baffle Creek [826] and the Kolan River [11, 232, 658] (possibly also C. s. fulvus in the latter two rivers).
and maximum numerical densities recorded in 232 hydraulic habitat samples (i.e. riffles, runs or pools) were 0.99 individuals.10m–2 and 16.40 individuals.10m–2, respectively. Average and maximum biomass densities at 184 of these sites were 0.68 g.10m–2 and 13.27 g.10m–2, respectively. Highest numerical and biomass densities were recorded from the Mary River.
Craterocephalus s. fulvus is moderately common in southeastern Queensland. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that it had been collected at 27 of 63 locations surveyed (ninth most widespread species in the catchment) and formed 2.7% of the total number of fishes collected (seventh most abundant). It is present but apparently relatively uncommon in the Elliott River [825] and rivers of the Burrum Basin [157, 736, 1305]. Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 4608 individuals and it was present at 25.8% of all locations sampled (Table 2). Overall, it was the 10th most abundant species collected (2.8% of the total number of fishes collected) and was present in moderate abundances at sites in which it occurred (7.96%). In these sites, C. s. fulvus most commonly occurred with the following species (listed in decreasing order of relative abundance): C. marjoriae, G. holbrooki, P. signifer, R.semoni and H. klunzingeri. It was the 19th most important species in terms of biomass, forming only 0.2% of the total biomass of fish collected. It was most common in the Mary River and the Brisbane River where it was the ninth and sixth most abundant species, respectively. It was comparatively widespread throughout these catchments, being present at 62% and 36% of locations sampled in the Mary and Brisbane rivers, respectively. This species is comparatively rare in the remaining catchments of southeastern Queensland sampled by us and was not collected in the Albert-Logan Basin, although it is known to occur in the Albert River [719, 1421]. Across all rivers, average
Craterocephalus stercusmuscarum was once present throughout much of the Murray-Darling Basin [635] where it was patchily distributed but historically common [778, 1200]. Recent surveys reveal that it is present but uncommon in the Queensland section of the upper Darling River (Condamine River) [643, 807, 957, 958, 1310]. In the New South Wales portion of the MurrayDarling Basin it is also very patchily distributed and uncommon [807, 1201]. It is thought to be rare and possibly absent from southern parts of the Murray-Darling Basin [635], although surveys in the last 20 years have revealed that it is patchily distributed but locally common in some parts of the lower Murray Basin in Victoria and South Australia [56, 507, 807, 817]. Macro/mesohabitat use Craterocephalus stercusmuscarum is found in a variety of habitats including large floodplain rivers and billabongs, small rainforest streams, volcanic crater lakes (Atherton Tablelands), dune lakes (Fraser Island), river impoundments (dams and weirs) and brackish river estuaries. In northern Australia, Craterocephalus s. stercusmuscarum is reportedly widely distributed in the Alligator Rivers region, occurring in 25 of 26 regularly sampled sites [193]. Habitats occupied by this species and in which it was relatively common included corridor lagoons, sandy creekbed habitats and floodplain lagoons. Other habitats used
Table 2. Distribution, abundance and biomass data for Craterocephalus s. fulvus in rivers of south-eastern Queensland. Data summaries for a total of 4608 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
25.8
62.0
3.4
15.0
36.0
—
2.82 (7.96)
3.82 (6.90)
0.04 (2.27)
1.55 (14.47)
5.05 (11.90)
—
South Coast rivers and streams 10.0 0.59 (40.39)
10 (6)
9 (7)
22 (5)
9 (2)
6 (2)
—
14 (1)
0.21 (0.69)
0.27 (0.63)
0.01 (0.03)
0.24 (0.41)
0.63 (1.24)
—
0.11 (0.43)
19 (10)
14 (10)
14 (6)
10 (7)
10 (7)
—
13 (3)
Mean numerical density (fish.10m–2)
0.99 ± 0.13
1.06 ± 0.17
0.03 ± 0.03
0.51 ± 0.16
0.88 ± 0.18
—
0.39 ± 0.37
Mean biomass density (g.10m–2)
0.68 ± 0.32
0.71 ± 0.14
0.03 ± 0.03
0.25 ± 0.03
0.58 ± 0.15
—
0.34 ± 0.34
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Craterocephalus stercusmuscarum
have moderate current velocities (i.e. exposed runs). This species is found across a wide array of substrate types. The disparity between arithmetic and weighted means reflects the greater abundance of this species in sites located on the Atherton Tablelands where the stream-bed tends to be dominated by rocks and bedrock. In-stream cover is reasonably abundant in mesohabitats in which this species occurs. The disparity between arithmetic and weighted means indicates that it tends to be slightly more abundant in mesohabitats with macrophyte beds and less abundant in areas with large amounts of leaf litter and woody debris, perhaps because such physical structures support greater numbers of piscivorous fishes (Table 3, [1093]). Reaches infested with para grass (a component of submerged vegetation in Table 3) also tend to support lower numbers of this species. It is noteworthy that the habitat use described in Table 3 for C. s. stercusmuscarum is in stark contrast to the lentic environments used by this species across its northern range and serve to illustrate the extreme adaptability of this species.
included muddy lowland lagoons and escarpment main channel waterbodies, but it was only rarely encountered in perennial escarpment streams. The use of floodplain lagoon habitats appears common for this species in northern Australia, having been reported for populations in Cape York Peninsula [571, 894], the Wet Tropics region [584, 585, 1085] and the Burdekin River drainage [1046, 1125]. This species reaches high levels of abundance in the weirs located on the Pioneer River [1081]. In rivers of the Wet Tropics region, C. s. stercusmuscarum (including individuals from both lineages described by McGlashan and Hughes [899]) occurs across a wide range of stream types, from small adventitious lowland streams close to the river mouth, through to the main river channel both at high and low elevation (Table 3). Such habitats tended on average to have a moderately open riparian canopy, a width of about 15 m, a mean depth 0.5 m, and Table 3. Macro/mesohabitat use by Craterocephalus s. stercusmuscarum in rivers of the Wet Tropics region. Data summaries for 393 individuals collected at 24 locations between 1994 and 1997 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min.
Max.
Mean
W.M.
Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
2.8 3.0 30.0 15 5.2 0
515.5 67.0 104.0 750 53.7 100.0
142.8 24.6 54.8 196 14.9 32.9
109.2 20.8 77.3 458 12.8 29.5
Gradient (%) 0 Mean depth (m) 0.22 Mean water velocity (m.sec–1) 0
2.26 0.91 0.45
0.4 0.51 0.19
The macro/mesohabitat use of C. s. fulvus in south-eastern Queensland differs to that described above for northern Queensland populations of C. s. stercusmuscarum, probably reflecting differences in river geomorphology and hydraulics between regions. Habitat use of C. s. fulvus is however, generally similar to the congener, C. marjoriae, a species with which it co-occurs throughout much of south-eastern Queensland. Craterocephalus s. fulvus occurs throughout the major length of rivers, ranging between 4 and 311 km from the river mouth and at elevations up to 240 m.a.s.l. (Table 4). It most commonly occurs within 220 km of the river mouth and at elevations less than 100 m.a.s.l. and is present in a wide range of stream sizes (range = 0.7–46.8 m width) but is more common in streams greater than 10 m width and with low riparian cover (<30%). This subspecies has been recorded in a range of mesohabitat types but it most commonly occurs in low gradient (weighted mean = 0.17%) runs and pools characterised by moderate depth (weighted mean = 0.43 m) and low mean water velocity (weighted mean = 0.09 m.sec–1) (Table 4). This is a substantially lower water velocity than that recorded for C. s. stercusmuscarum in rivers of the Wet Tropics region (Table 3), but note that C. s. fulvus also occurs in shallow riffles with high gradients (maximum = 2.86%) and high velocity (maximum = 0.85 m.sec-1) on occasions. This subspecies is most abundant in mesohabitats with fine to intermediate sized substrates (sand, fine gravel and coarse gravel) and particularly where submerged aquatic macrophytes, filamentous algae and submerged marginal vegetation are common. Elsewhere, this species has been classified as a pool-dwelling species [553] and has been reported to occur in still or slow-
0.43 0.55 0.20
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48.0 51.0 72.0 35.0 49.0 81.0 68.0
4.9 12.8 22.6 13.5 17.0 25.0 4.6
3.7 6.1 19.7 7.2 8.1 31.0 24.4
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
15.0 6.7 33.0 61.0 10.0 35.8 8.4 7.2 45.0 50.0
1.6 0.4 3.6 14.8 0.9 7.2 1.3 1.1 13.2 7.1
3.1 0.7 3.1 5.8 0.7 4.7 2.5 0.8 9.8 5.0
185
Freshwater Fishes of North-Eastern Australia
revealed however that this species will position itself very close to the substrate when negotiating sections of elevated water velocity [1093]. This species was infrequently collected over very fine substrates, and most commonly over rocks and bedrock, reflecting the distribution of substrate types in those sites in which it occurred (Table 3). This species is an open water schooling species occasionally making use of such cover elements as macrophyte beds and emergent vegetation (Fig. 2f).
flowing rivers, small streams, swamps, billabongs, lakes, ponds and reservoirs and in fast-flowing creeks [34, 52, 270]. Table 4. Macro/mesohabitat use by Craterocephalus s. fulvus in rivers of south-eastern Queensland. Data summaries for 4608 individuals collected from samples of 232 mesohabitat units at 76 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min.
Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
19.3 9.0 4.0 0 0.7 0
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec–1) 0
Max. 10211.7 270.0 311.0 240 46.8 80.0 2.86 1.08 0.85
Mean
W.M.
1540.1 73.5 193.1 83 12.3 28.9
996.0 56.1 220.8 89 11.5 24.1
0.30 0.43 0.14
60
40
20
20
0
0
Mean water velocity (m/sec) 40
0 0 0 0 0 0 0
99.6 100.0 56.7 70.9 65.8 41.1 76.0
8.4 18.4 21.9 30.1 16.8 3.0 1.4
7.5 31.8 22.6 24.7 12.1 0.9 0.4
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
64.5 65.9 26.7 65.7 43.3 43.3 31.0 15.5 50.0 58.8
19.8 11.8 1.5 8.6 2.3 9.1 3.8 3.0 8.5 12.1
23.2 15.5 0.9 15.0 3.5 6.9 2.9 2.4 3.9 6.9
60
40
0.17 0.43 0.09
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
(a)
(c)
(b)
Focal point velocity (m/sec) 40
30
30
20
20
10
10
0
0
(d)
Relative depth
Total depth (cm) 40
(e)
(f) 40
30
30
20
Microhabitat use Craterocephalus s. stercusmuscarum in the Wet Tropics region occurs over a range of water velocities up to 0.6 m.sec–1 although the great majority occur in flows less than 0.3 m.sec–1 (Fig. 2a). This preference for areas of low water velocity is also reflected in the focal point velocity (Fig. 2b); most fish collected from average water velocities greater than 0.20 m.sec–1 were either located low in the water column or associated with some form of cover (Fig. 2f) and thus experienced reduced flows. Most fish were collected from depths of 30–60 cm (Fig. 2c) and distributed throughout the water column although less commonly in the upper 20% of the water column or close to the substrate (Fig. 2d). Underwater observations have
20
10
10
0
0
Substrate composition
Microhabitat structure
Figure 2. Microhabitat use by Craterocephalus s. stercusmuscarum in the Wet Tropics region (solid bars) and C. s. fulvus in south-eastern Queensland (open bars). Summaries derived from capture records for 78 individuals from the Johnstone and Mulgrave rivers in the Wet Tropics region and for 558 individuals from the Mary River, southeastern Queensland, over the period 1994-1997 [1093].
Pusey et al. [1109] examined the habitat use of larval C. s. stercusmuscarum in the Johnstone River and found that
186
Craterocephalus stercusmuscarum
However, the data suggests that populations of this species in the Northern Territory rarely experience temperatures below 25°C, whereas temperatures below 20°C are experienced by populations occurring in rainforest streams at high elevation and by those in inland locations on the Burdekin River. It is likely that some degree of geographic variation exists, perhaps even with a genetic basis, in tolerance to temperature extremes.
larvae (pooled across all development stages) showed no preference for particular depths but were strongly restricted to water velocities less than 10 cm.sec–1. In addition, larvae were more frequently found in association with some form of cover than was predicted by the availability of cover within the study site. Pre-flexion and flexion larvae were particularly constrained by the need for low flow environments and cover, but post-flexion were found in slightly higher water velocities and more distant from cover and the stream bank. Fin development in this species is minimal until after flexion and thus pre-flexion and flexion larvae are constrained by high water velocities to remain close to the natal habitat (i.e. bank-associated root masses).
Riverine locations in which C. s. stercusmuscarum occurs appear to be moderately well-oxygenated, whereas Table 5. Physicochemical data for Craterocephalus stercusmuscarum. Data summaries are from a number of studies conducted in a range of rivers and habitats across northern and north-eastern Australia (the number of sites from each study is given in parentheses).
In rivers of south-eastern Queensland, C. s. fulvus was most frequently collected from areas of low to moderate water velocity (usually less than 0.4 m.sec–1) (Fig. 2a and b), however, it has been recorded at maximum mean and focal point water velocity of 0.87 and 0.76 m.sec–1, respectively. Aggregations also occasionally observed in slackwater eddies (e.g. behind rocks and debris) within high velocity riffle habitats [1093]. This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 2c). A pelagic schooling species, it most commonly occupies the mid-water column (Fig. 2d). It is found over a wide range of substrate types but most frequently used sand, fine gravel and coarse gravel (Fig. 2e). It was often collected in areas greater than 1 m from the stream bank (67% of individuals sampled) and in open water greater than 0.2 m from the nearest available cover (18% of individuals). It was also frequently collected in close association with aquatic macrophytes, filamentous algae and submerged marginal vegetation (Fig. 2f). Other workers have reported that C. stercusmuscarum is generally found in shallow water over mud, sand and gravel, and near aquatic vegetation [52], and it has been reported to congregate where streams flow into still water [936].
Parameter
Min.
Max.
Alligator Rivers Region (n = 25) [193] Water temperature (°C) 25 43 Dissolved oxygen (mg.L–1) 0.9 8.2 pH 4.0 8.1 Conductivity (µS.cm–1) 2 110 Turbidity (cm) 190 2 Normanby River floodplain (n = 13) [697] Water temperature (°C) 22.9 29.4 Dissolved oxygen (mg.L–1) 1.1 7.1 pH 6.0 8.2 Conductivity (µS.cm–1) 98 391 Turbidity (NTU) 2.1 8.6
Environmental tolerances Little quantitative data concerning environmental tolerances is available. Craterocephalus s. stercusmuscarum has been collected over a wide range of physicochemical conditions (Table 5). Average water temperature recorded at sites in which this species occurred ranged from 22.6°C to 30.9°C, reflecting its tropical distribution. The maximum temperature experienced was 43oC but note that this was measured at the surface and stream-bed temperatures were 7°C lower [193]. None-the-less, this species appears able to tolerate temperatures in excess of 30°C. Minimum temperatures recorded varied between studies, and depended on whether the temporal sampling regime of these studies included periods of low temperature.
187
Mean 30.9 5.7 6.1 48 25.5 3.7 7.1 212.1 5.5
Wet Tropics (n = 35) [1093] Water temperature (°C) 17.1 29.7 Dissolved oxygen (mg.L–1) 5.1 11.4 pH 6.2 8.2 Conductivity (µS.cm–1) 7.8 55.9 Turbidity (NTU) 0.2 9.3
22.6 7.8 7.4 36.6 2.2
Burdekin River (n = 25) [1093, 1098] Water temperature (°C) 15 33 Dissolved oxygen (mg.L–1) 2.6 11.9 pH 6.8 8.3 Conductivity (µS.cm–1) 50 790 Turbidity (NTU) 0.3 8.0
24.9 7.9 7.6 375.2 2.8
Fitzroy River (n = 10) [942] Water temperature (°C) 22 28 Dissolved oxygen (mg.L–1) 4.8 11.0 pH 7.3 8.2 Conductivity (µS.cm–1) Turbidity (cm) 190 5
70
South-east Queensland (n = 142) [1093] Water temperature (°C) 12.4 33.6 Dissolved oxygen (mg.L–1) 2.9 19.5 pH 6.1 9.1 Conductivity (µS.cm–1) 19.5 5380.0 Turbidity (NTU) 0.2 62.3
21.5 8.1 7.7 626.4 4.7
25.8 7.4 7.9
Freshwater Fishes of North-Eastern Australia
on reproduction and early development of C. s. stercusmuscarum is available from six studies [193, 306, 630, 1106, 1109, 1416], C. s. fulvus from three studies [949, 1093, 1412], and another report [1211] was concerned with a mix of both subspecies (hereafter reported with C. s fulvus). An additional account by Llewellyn [809, 811] on the spawning and embryology of a species of hardyhead from the MurrayDarling Basin (identified as C. fluviatilis but now considered [630, 635, 1211] to be C. s. fulvus) is not addressed here.
floodplain populations may experience periods of extreme hypoxia. In lagoons on the Tully River floodplain, C. s. stercusmuscarum was collected in waters with very low dissolved oxygen (minimum 0.2 mg.L-1) and low pH (minimum pH 5.38) [585]. With the exception of the Alligator Rivers population, this species occurs, on average, in waters of neutral to slightly basic pH but it is evident that it may tolerate moderately acidic conditions [193, 585]. The range of conductivity shown in Table 5 indicates that C. s. stercusmuscarum occurs most frequently in very dilute freshwaters. McGlashan and Hughes (1814) reported significant genetic differences between populations in the North and South Johnstone rivers separated only by a short estuarine confluence and interpreted this result as an indication of very low gene flow between drainages. Whether high conductivity in the estuary provided a chemical barrier was unknown, but if true, would be in contrast to that observed for C. s. fulvus (see below). Craterocephalus s. stercusmuscarum is most frequently found in waters of reasonable clarity, although both Midgley [942] and Bishop et al. [193] report its presence in highly turbid waters. It is notable however, that this species is widespread in the Burdekin River but is very uncommon or absent from those sub-catchments with persistent turbidity levels above 100 NTU [255, 256].
Craterocephalus stercusmuscarum spawns and completes its entire life-cycle in freshwater and has been bred in captivity [630, 797, 1211, 1412]. In the Alligator Rivers region, Bishop et al. [193] found that C. s. stercusmuscarum matured at a small size (27–29 mm CFL). In the Wet Tropics region, maturation commences at slightly greater size (stage II) and reproductive development is commensurate with increasing body size (Fig 3). The upland and lowland lineages present in the Johnstone River differ in the size at which attainment of each separate reproductive stage is attained: the upland population matures at greater size than does the lowland population. In addition, whereas lowland males were generally smaller than females across stages III to V, upland males tended to be larger than females except for those fish at maturity stage V. It is unknown whether upland fish live to a greater age than do lowland fish or whether faster growth is experienced by the upland lineage, however, the size distribution presented in Figure 1 does not suggest the presence of a pronounced 1+ cohort in either lineage.
Craterocephalus s. fulvus has been collected over a relatively wide range of physicochemical conditions also (Table 5), including sites with moderately low dissolved oxygen concentrations (minimum 2.9 mg.L–1), mildly acidic to basic waters (range 6.1–9.1), and high conductivity (maximum 5380 µS.cm–1). The maximum turbidity at which this species has been recorded in south-eastern Queensland is 62.3 NTU.
80
Males 70
44
35
Females
25
78
60
Given the marine affinities of the family Atherinidae, it is perhaps not surprising that C. stercusmuscarum is able to tolerate elevated salinities. It is frequently recorded at the base of tidal barrages (refer to section on movement) and in brackish and estuarine waters [1314]. Studies of salinity tolerances of C. s. fulvus revealed that experimental chronic LD50s have been observed as 43.7 ppt [1406]. Death occurred between 28 and 52 ppt, fish stopped feeding and showed signs of distress at salinities >30 ppt and fish were unable to swim in a coordinated fashion or maintain balance at salinities >44 ppt [1406]. In aquaria, larvae of C. s. fulvus have been exposed to temperatures between 23.5 and 36.0°C with no apparent adverse effects [1211]. Harris and Gehrke [553] classified C. s. fulvus as intolerant of poor water quality.
14
50
44 15
24
40
25
58
3 5
11
6 17
3
3
2 3
30 20 10 0
L
U
I
Reproduction The reproductive biology of both subspecies of C. stercusmuscarum is relatively well-studied (Table 6). Information
L
U
II
L
U
L
III IV Reproductive stage
U
L
U
V
Figure 3. Mean standard length (mm SL ± SE) within each reproductive stage for male and female Craterocephalus s. stercusmuscarum of the Wet Tropics region. Fish were collected from lowland (L) and upland (U) reaches of the Johnstone River over the period 1994–1998 [1093]. Sample sizes are given above each bar.
188
5
Craterocephalus stercusmuscarum
region entered a prolonged drought, conditions likely to favour larvae of this species. There was little evidence of pronounced recruitment associated with a very large flood in early 1991 as the population size distribution four months later contained very few fish less than 35 mm SL and was skewed towards fish of 45–55 mm SL [1082].
Craterocephalus s. stercusmuscarum has an extended breeding season in both the Alligator Rivers [193] and in the Wet Tropics regions [1093]. Breeding phenology is apparently variable from year to year in the former region, with Bishop et al. [193] recording peak mean GSI values in the mid-wet of one year and the mid-dry of the following year. Kennard [697] recorded very small fish of 10–15 mm SL in both early (May) and late dry season (November) samples in floodplain lagoons of the Normanby River, although the greater number of small fish collected in the late dry season suggested that spawning was concentrated in the mid-dry season. In the Burdekin River [1082], fish of 10–15 mm SL were absent from samples collected in November 1990 and May 1991 and present in November 1991 and May 1992. The latter two sampling occasions corresponded to a dramatic decrease in discharge as the
I 120 100
II
III
IV
In the Wet Tropics region, reproductively mature fish were present in all months sampled except May and July (Fig. 4) when water temperatures are at their minimum [1108]. The majority of fish collected between September and November were either fully mature or nearly so. Larvae were present throughout the year but occurred in very low numbers from May to August [1109]. The phenology depicted in Figure 4 is reflected in temporal changes in mean GSI values (Figure 5). Female GSI values were lowest during the winter months but increased rapidly to maximum levels by September or October, declining thereafter to intermediate levels over the summer wet season due to the presence of a small number of reproductively active fish in the population. Females from both upland and lowland lineages followed a similar pattern in GSI variation except that peak GSI values occurred in September in the former as opposed to October. Male maturation and gonad development was synchronised with that of females (Figs. 4 and 5). Bishop et al. [193] reported very similar mean GSI values as those presented here.
V
Males (6)
(11) (12) (16) (9)
(9)
(46)
(5)
(7) (13) (10)
80 60 40 20
10 0
Females - upland
120 Females 100
Males - upland
(12 (28) (17) (22) (9)
8 (14) (50) (28) (25) (44) (24)
)
6
Males - lowland Females - lowland
80 4
60 40
2
20
0
0
Month Month
Figure 4. Temporal changes in reproductive stages of Craterocephalus s. stercusmuscarum in the Johnstone River, Wet Tropics region during 1998 [1093]. Samples sizes for each month are given in parentheses. Data for upland and lowland lineages have been pooled.
Figure 5. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Craterocephalus s. stercusmuscarum males (open symbols) and females (closed symbols) in the Johnstone River during 1998 [1093]. The upland lineage is denoted by circles and the lowland lineage by squares. Samples sizes for each month are given in Figure 3.
189
Freshwater Fishes of North-Eastern Australia
are heavily pigmented, the top of the head is spotted in a circular patch, and the abdomen, opercle and midlateral stripes are pigmented [630]. Upon hatching, prolarvae swim independently of one another for the first 12 hours, schooling thereafter in the upper water column of aquaria [630]. At 30 days post-hatching, larvae were 8.4 mm TL on average and, by this stage, the anal and dorsal fins were well developed. The remnant of the fin fold persists at the origin of first dorsal fin, but the fin bud is visible. The ventral fin fold also persists between the anus and the anal fin [630]. The rate of larval development appears to be relatively rapid. Metamorphosis occurs at a small size (9–11 mm) [1093] and fish in aquaria were observed to approximately treble their size in the first 40 days (from 4.54 mm TL to 14.3 mm TL) [630]. After 3.5 months, these fish had approximately doubled their size, after which time the rate of growth slowed [630].
Craterocepahlus s. stercusmuscarum is a moderately fecund batch spawner, producing on average 200–400 small eggs in batches of about 70 eggs. The two lineages present in the Wet Tropics region differ in fecundity (Fig. 6). Females of the upland lineage produces more eggs by virtue of their greater size than do lowland females, however the rate of increase in fecundity with increasing weight is less, as is the number of eggs produced when females of equivalent size are compared (the regression equations for relationships between weight and total fecundity for these populations are given in Table 4). By contrast, the eggs of upland fish are slightly larger than those of lowland fishes (1.08 ± 0.02 mm versus 0.98 ± 0.04 mm; n = 117 and 37, respectively). Bishop et al. [193] report an intraovarian egg size of about 1 mm for fish from the Alligator Rivers region also.
800
Maturation of C. s. fulvus commences at a relatively small size. Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, southeastern Queensland, were 26.3 mm SL and 38.3 mm ± 1.6 SE, respectively for males, and 28.5 mm SL and 36.4 mm ± 1.6 SE, respectively for females (Fig. 7). Fish of equivalent reproductive stage were generally similar in size for populations from the Mary (Fig 7) and Brisbane rivers [949], south-eastern Queensland. Gonad maturation in both sexes was commensurate with somatic growth, the mean length at each reproductive stage being different from all other stages (Fig. 7). Gravid (stage V) females were slightly
700
600
500
400 300 200 100 0 0
1
2
3
4
5
6
7
55
Males 8
9
50
Females
Weight (gm) 45
Figure 6. The relationship between body size (weight in g) and fecundity for upland (■ ■, thick regression line) and lowland ( , coarsely dashed regression line) lineages of Craterocephalus s. stercusmuscarum in the Wet Tropics region and C. s. fulvus (▲ ▲, finely dashed regression line) in southeastern Queensland [1093]. See text for regression equations.
40 35 30
The duration of embryo development for C. s. stercusmuscarum has been reported to be 13 days (at 25–27°C) [630]. Illustrations and descriptions of larval stages of this subspecies can be found in Invantsoff et al. [630]. The larvae of C. s. stercusmuscarum hatch at small size but rapidly become mobile and feed exogenously (Table 6). The mean length of prolarvae one to three days after hatching was 4.0 mm TL [630]. At this stage the dorsal and ventral fin folds are continuous but the ventral fin buds are not apparent, the eyes and dorsal surface of the swim-bladder
25 I
II
III
IV
V
Reproductive stage Figure 7. Mean standard length (mm SL ± SE) for male and female Craterocephalus s. fulvus within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland, between 1994 and 1998 [1093]. Sample sizes can be calculated from the data presented in Figure 3.
190
Craterocephalus stercusmuscarum
were present for longer (August to April) and were relatively abundant throughout most of this period (Fig. 8). Temporal patterns in reproductive stages mirrored those observed for variation in GSI values. Peak monthly mean GSI values (5.1% ± 0.3 SE for males, 6.5% ± 0.5 SE for females) occurred in November for males and September for females (Fig. 9). GSI vales remained elevated for longer in females but were highest for both sexes between August and December (Fig. 9). The mean GSI of ripe (stage V) fish was 5.3 % ± 0.2 SE for females and 5.5 % ± 0.3 SE for males [1093]. Reproductive activity for fish in the Brisbane River [949] generally matched that observed for fish from the Mary River, although peak monthly mean GSI values for males were lower (4.3%) and peak GSI values for females were higher (8.5%) [949]. Overall sex ratios for populations from the Brisbane River have been reported as 1.2 females for every male and significantly more females were present amongst mature fish (>45 mm SL) [949].
larger on average than males of equivalent maturity (mean 53.6 mm SL ± 0.8 SE for females; mean 49.8 mm SL ± 1.4 SE for males), although the minimum recorded size for a gravid female was substantially smaller (24.3 mm SL) than that of a male (37.3 mm SL ([1093], Fig. 7). The minimum size of spawning fish in aquaria is reported as 32 mm SL (approximately five months of age) [1211]. Craterocephalus s. fulvus has an extended breeding season from late winter through to summer but spawning appears to be concentrated in late winter and spring. In the Mary River, immature and early developing fish (stages I and II) were most common between January and August (Fig. 8). Developing fish (stages III and IV) of both sexes were generally present year-round. Gravid males (stage V) were present for a relatively short period and were most abundant between September and November. Gravid females Reproductive stage I
II
III
IV
V
8
Males
Males (8) (6) (6) (9) (10) (9)
(13) (23) (10) (5) (4)
100
6
Females
80 60
4 40 20
2 0 Females 100
(36) (27) (10) (18) (18) (4)
(24) (19) (10) (7) (25)
0
80
Month
60
Figure 9. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Craterocephalus s. fulvus males (open circles) and females (closed circles) in the Mary River, southeastern Queensland, during 1998 [1093]. Sample sizes for each month are given in Figure 8.
40 20 0
The spawning stimulus is unknown but corresponds with increasing water temperatures and photoperiod. Milton and Arthington [949] observed that the peak spawning period for C. s. fulvus in the Brisbane River in SeptemberOctober coincided with surface water temperatures between 19 to 23°C, and day length from 11 to 11.5 h. In aquaria, spawning occurred at water temperatures
Month Figure 8. Temporal changes in reproductive stages of Craterocephalus s. fulvus in the Mary River, south-eastern Queensland, during 1998 [1093]. Sample sizes for each month are given in parentheses.
191
Freshwater Fishes of North-Eastern Australia
small-bodied fish in south-eastern Queensland streams (e.g. 207]) and in the Murray-Darling Basin (see Humphries et al. [614]).
between 25 and 29°C, with the majority of spawning activity occurring at 26°C [1211]. As summarised in the chapter on C. marjoriae, the extended spawning period of Craterocephalus spp., but with a peak in spring and early summer, may facilitate successful recruitment as the presence of eggs and larvae usually occurs when the likelihood of flooding is low, but the predictability of high temperatures and low flows are higher. Milton and Arthington [949] reported that juvenile fish in the Brisbane River were present between October and February and these authors were able to discern a clear cohort that could be tracked through to the following breeding season. A similar pattern is evident from more recent sampling [1093] where individuals less than 25 mm SL were most common in spring and summer (Fig. 10). 25
In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal vegetation. Spawning observations in aquaria suggest that pre-spawning behaviour is initiated adjacent to aquatic vegetation whereby the male swims beneath and behind the female, nudging and nipping the anterior rays of the anal fin, the vent and the belly of the female [1211]. Upon reaching a suitable spawning site within the bed of aquatic vegetation, the male and female simultaneously shed sperm and eggs, all the while touching constantly along their lateral lines. Adhesive, demersal eggs are attached to aquatic macrophytes, the entire batch resting within a radius of 10 cm of the release point. In aquaria, both sexes have been observed to eat eggs following deposition [1211]. No parental care of eggs has been reported.
Spring (n=451)
20
Summer (n=1285)
15
AutumnWinter (n=817)
10
5
0
Standard length (mm) Figure 10. Seasonal variation in length-frequency distributions of Craterocephalus s. fulvus, from sites in the Mary and Brisbane rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
Schiller and Harris [1200] suggested that C. s. fulvus was a member of a guild of species in the Murray-Darling Basin whose spawning success was flood-related. Although these authors cautioned that the mechanism was unclear, they postulated that floods may benefit larvae by transporting them to nursery areas (e.g. freshly inundated wetlands) or larvae may benefit from the increased productivity of main channel and backwater areas. This view is contrary to the hypothesis that low flow periods during the reproductive season facilitate successful recruitment in smallbodied species such as hardyheads as suggested earlier for
192
Total fecundity for C. s. fulvus from the Mary River has been estimated as ranging from 58–432 eggs (mean 219 ± 12 SE, n = 60 fish) [1093], slightly higher than that of lowland lineages of C. s. stercusmsucarum from the Wet Tropics region, but substantially lower than that of upland populations in this regions (Figure 6). Batch fecundity for fish from the Brisbane River ranges from 5–126 eggs/batch (mean 71 ± 5 SE, n = 70 fish) [949]. In the aquarium, fish were observed to deposit 2–85 eggs over a 5–35-second period, with spawning occurring on two to three successive days followed by a rest period of several days [1211]. Fecundity is significantly related to fish size; the regression equations for relationships between weight and fecundity are given in Table 4. Fish of 40 mm SL from the Mary River produced about 130 eggs in total, whereas fish of 60 mm SL produced about 270 eggs [1093]. Fish of 1 g from the Mary River produced about 130 eggs in total, whereas fish of 4 g produced about 340 eggs [1093]. Fish of 40 mm SL from the Brisbane River produced about 40 eggs per batch, whereas fish of 60 mm SL produced about 140 eggs [949]. The eggs are relatively large. The mean diameter of 496 intraovarian eggs from stage V fish from the Mary River was 1.17 mm ± 0.01 SE [1093]. The diameter of waterhardened eggs has been reported to range from 1.3 to 1.7 mm [1211]. Eggs are characterised by a finely sculptured chorion with 50 adhesive filaments (0.5–3.0 mm in length). Eight to thirteen oil droplets were present over the surface of the egg at spawning; these were 0.03 to 0.15 mm diameter, and were initially concentrated at the animal pole, later migrating in a bunch to the vegetal pole. The duration of embryo development has been reported to vary from 4 to 7 days (at 25 to 29°C) [1211] and from 8 to 10 days (at 29°C) [1412]. Illustrations and descriptions of
Craterocephalus stercusmuscarum
Table 6. Life history information for Craterocephalus s. fulvus (C.s.f.) and Craterocephalus s. stercusmuscarum (C.s.s.). Age at sexual maturity (months)
C.s.f. <12 months [949] C.s.s. <12 months [193, 1093]
Minimum length of gravid (stage V) females (mm)
C.s.f. 24.3 mm SL (field) [1093], 32 mm SL (aquaria) [1211] C.s.s. 46 mm SL (lowland lineage), 55 mm SL (upland lineage) in Wet Tropics region [1093], length at first maturity – 29 mm CFL in Alligator Rivers region [193]
Minimum length of ripe (stage V) males (mm) C.s.f. 37.3 mm SL (field) [1093] C.s.s. 36 mm SL (lowland lineage), 58 mm SL (upland lineage) [1093], length at first maturity – 27 mm CFL in Alligator Rivers region [193] Longevity (years)
C.s.f. 2+ [949] C.s.s. unknown but unlikely to exceed two years [1093]
Sex ratio (female to male)
C.s.f. 1.2:1 [949] C.s.s. 1:1 with females slightly in excess in dry season in Alligator Rivers region [193]
Occurrence of ripe (stage V) fish
C.s.f. Late winter, spring and summer. August - April [1093], October–January [949] C.s.s. present all year except from May to July in the Wet Tropics [1093], mid-dry season to mid-wet in Alligator Rivers region, variable across years [193]
Peak spawning activity
C.s.f. Late winter, spring and summer. Elevated GSI between August and December [1093], elevated GSI between September and February [949] C.s.s. September to November in Wet Tropics region [1093], early wet season and mid-dry season, variable across years [193]
Critical temperature for spawning
C.s.f. ? 19–23°C (field) [949]; 25–29°C (aquaria) [1211] C.s.s. no spawning observed when temperatures below 20°C [1093]
Inducement to spawning
C.s.f. ? C.s.s. ?
Mean GSI of ripe (stage V) females (%)
C.s.f. 5.3% ± 0.2 SE (maximum mean GSI in September = 6.5% ± 0.5 SE) [1093]; (maximum mean GSI in October = 8.5 %) [949] C.s.s. 7.9 to 8.1%, little difference between lineages; maximum mean GSI of 6.2% recorded in Alligator Rivers region [193]
Mean GSI of ripe (stage V) males (%)
C.s.f. 5.5 % ± 0.3 SE (maximum mean GSI in November = 5.1 % ± 0.3 SE) [1093]; (maximum mean GSI in September = 4.3%) [949] C.s.s. 4.7–5.0%, little difference between lineages; 4.2% for Alligator Rivers region [193]
Fecundity (number of ova)
C.s.f. Total fecundity = 58–432, mean = 219 ± 12 SE [1093]; Batch fecundity 5–126, mean = 71 ± 5 SE [949], In aquaria 2–85 eggs deposited in 5–35-second period, with spawning occurring on 2 to 3 successive days [1211] C.s.s. Total fecundity = 50–832, mean = 312 ± 85 for upland lineage, 45–390, mean = 240 ± 6 for lowland lineage of the Wet Tropics region; total (large eggs only) 55–90, mean = 71
Total Fecundity (TF) and Batch Fecundity (BF) / Length (mm SL) or Weight (g) relationship (mm SL)
C.s.f. Log10 TF = 0.017 L + 1.422, r2 = 0.370, P<0.001, n = 60 [1093]. Log10 BF = Log10 (7.2 x 10-3) + 3.01 Log10 L, r2 = 0.59, p<0.001, n = 70 [949]. TF = 67.65 W + 60.62, r2 = 0.454, p<0.001, n = 60 [1093] C.s.s. TF = 81.0 W – 49.8, r2 = 0.60, p<0.001, n = 87 for upland lineage; TF = 141.6 W - 33.9, r2= 0.84, p<0.001, n =19 for lowland lineage
Egg size (diameter)
C.s.f. Intraovarian eggs from stage V fish = 1.17 mm ± 0.01 SE [1093]. Waterhardened eggs 1.3–1.7 mm [1211] C.s.s. Intraovarian eggs from stage V fish = 1.08 ± 0.02 mm (SE ) for upland lineage and 0.93 ± 0.04 mm (SE) for lowland lineage of the Wet Tropics region; 1.0 mm (range = 0.9–1.0 mm)
Frequency of spawning
C.s.f. extended spawning period, probably repeat spawner [949] C.s.s. extended spawning , eggs release in batches [1093]
Oviposition and spawning site
C.s.f. In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal vegetation [1093]. In aquaria, adhesive, demersal eggs are attached to aquatic macrophytes [1211] C.s.s. Aquatic rootmasses in Wet Tropics streams [1109]
Spawning migration
C.s.f. none known C.s.s. none known
Parental care
C.s.f. none known C.s.s. none known
Time to hatching
C.s.f. After fertilisation, hatching takes 4 to 7 days in aquaria at 25–29°C [1211]. 8–10 days in aquaria at 29°C [1412] C.s.s. 13 days at 25–27°C [630]
193
Freshwater Fishes of North-Eastern Australia
Table 6 (continued). Life history information for Craterocephalus s. fulvus (C.s.f.) and Craterocephalus s. stercusmuscarum (C.s.s.). Length at hatching (mm)
C.s.f. Newly hatched prolarvae 5.0 mm SL [1211] C.s.s. 4.8–6.4 [1093]
Length at free swimming stage (mm)
C.s.f. Postlarvae 7.7 mm SL [1211] C.s.s. 6.3–7.7 mm at flexion [1093]
Length (mm) at loss of yolk sack
C.s.f. ? C.s.s. 6.3–7.7 mm [1093]
Age at first feeding
C.s.f. ? C.s.s. ?
Length at first feeding
C.s.f. Postlarvae 7.7 mm SL [1211] C.s.s. 6.3–7.7 mm [1093]
Length at metamorphosis (mm)
C.s.f. ? C.s.s. 9–11 mm [1093]
Duration of larval development
C.s.f. ? C.s.s. ?
larval stages can be found in Semple [1211]. The mean length of prolarvae at hatching was 5.0 mm SL. At this stage the top of the head, preoperculum and lateral line were spotted and the eyes, swim-bladder and surface pigments were black. Paired contour melanophores were visible on the dorsal surface and dendritic melanophores were present on the belly. Upon hatching, prolarvae swam randomly at the surface of aquaria. Postlarvae were 7.7 mm SL and, by this stage, the anal and dorsal fin buds were developing, the caudal fin was rayed, rows of small punctate melanophores were visible on the caudal fin and larvae had commenced swimming and feeding in midwater [1211]. King [718] speculated that the period of time from spawning to the juvenile phase was possibly 14 days for fish in the Murray-Darling Basin.
There are several instances where juveniles and adults of this species have been recorded using fishways on weirs and tidal barrages. Johnson [658] collected C. stercusmuscarum in pool-overfall type fishways on Bingara Weir in the Burnett River during December 1979 and in the Brisbane River catchment at Mt. Crosby Weir and Brightview Weir (timing unclear). Johnson [658] collected C. stercusmuscarum in the tidal barrage on the Kolan River during winter, spring and summer. He also observed hardyheads in that portion of the barrage subject to tidal influence and in which salinities ranged between 15–30 ppt. An experimental fish lift on the Kolan River Barrage was also used by this species [658]. Juveniles and adults have been collected from the fishway on the Mary River barrage and both age classes were recorded as being common in the fishway and outwash of the Tinana Creek Barrage. Other studies of fishways located on tidal barrages in Queensland Rivers [11, 158, 159, 232, 1173, 1272, 1274, 1275, 1276, 1277] documented relatively small numbers of fish using these structures in the Fitzroy, Kolan, Burnett and Mary river catchments. Results from a Burnett River study [1276] indicate that upstream migrations of small numbers of individuals occurred during August, December and February. Results from a Fitzroy River study [1274] indicate that the main period of migration occurred in November but upstream migrations of small numbers of individuals also occurred during July and December. The highest flow through the fishway at which this species was recorded using the fishway was 18 305 ML.day–1, this discharge being exceeded around 10% of the time in the Fitzroy River [1274]. Another study at the same location documented that fish used the fishway between November and February [739, 740]. Downstream migrations through fishways have also been observed: Russel [1173] recorded low numbers of fish descending the tidal barrage on the Fitzroy River (timing of movement not stated).
Length at age data using evidence from scale annuli [949] indicate that 0+ fish (males and females) grow to around 33 mm SL, 1+ fish to 49 mm SL and 2+ fish to 45 and 57 mm SL for males and females, respectively. These data (together with stage-length and sex ratio data presented earlier) collectively suggest that sexual maturity is reached within one year of age, and that fish live for over two years. Movement Some information is available on the movement biology of C. stercusmuscarum. Relatively large numbers of this species have been observed moving in Magela Creek in the Alligator Rivers region of the Northern Territory [190]. Bishop et al. [193] reported that C. s. stercusmuscarum dispersed widely on the floodplain of the Alligator Rivers region, moving from dry season refuges (escarpment habitats, sandy lowland creek-bed habitats) to occupy all available habitat types during the wet season. Little is known of the movement biology of this species in the Wet Tropics region but the existence of discrete lineages and of fixed allelic differences between lowland populations suggests that movement is limited in this region.
194
Craterocephalus stercusmuscarum
fulvus) has been recorded as having been transported in a ‘tornado-type cloud’ in south-western New South Wales [878, 1400].
This small-bodied species, particularly smaller individuals, apparently has difficulty ascending pool-weir type fishways, a design ill-suited to many small-bodied native fishes. Johnson [658] found that juveniles and adults were common downstream and upstream of Marian Weir in the Pioneer River, but were not actually collected in the fishway, which he regarded as inefficient. A large proportion of fish were unable to negotiate the full length of the fishway on a tidal barrage in the Fitzroy River, and those that did were comparatively larger in size [1274, 1275]. No significant difference was observed between the size distribution of fish collected at the bottom and top of the Kolan River barrage fishway, but substantially fewer small-sized individuals were present at the top of this fishway [232].
Trophic ecology Diet data for C. stercusmuscarum is available for 1639 individuals from studies in the Alligator Rivers region of the Northern Territory [193], Cape York Peninsula [697, 1099], the Wet Tropics regions of northern Queensland [599, 1097], central Queensland [1080], south-eastern Queensland [80, 205, 1421] and from a lake on the Murray River floodplain in north-western Victoria [396]. This species is a microphagic carnivore. Aquatic insects (35.6%), and microcrustaceans (29.6%) were the most important items in the total mean diet (Fig. 11). Aquatic algae (11.2%) and aquatic macrophytes (1.6%) were also consumed but contributed less to the total mean diet than observed for the congener C. marjoriae. Other food types of aquatic origin were relatively unimportant in the diet of C. stercusmuscarum and only small amounts of terrestrially derived prey were consumed.
Although C. stercusmuscarum has often been sampled downstream of tidal barrages or at the bottom of fishways on these structures (see references cited above), access to estuarine areas is not an obligatory component of the life cycle. Hence the movement pattern of this species may be classified as facultative potamodromy. The results described above collectively suggest that low numbers of fish move almost year-round but a peak in upstream migration possibly occurs in early summer. There is no quantitative data on the stimulus for movement of this species. Cotterell and Jackson [333] suggested that C. stercusmuscarum in the Fitzroy River, central Queensland, would move ‘anytime there is a flow between August and April’, although the source of this information was not given. Fish have been observed migrating in the Fitzroy River during high flows [1274] and fish downstream of Clair Weir in the Burdekin River were suggested to be migrating upstream during relatively high discharges in January and February [586].
Fish (0.1%) Other microinvertebrates (0.2%)
Unidentified (14.8%)
Terrestrial invertebrates (0.6%) Aerial aq. Invertebrates (0.8%) Terrestrial vegetation (0.2%) Detritus (0.4%) Aquatic macrophytes (1.6%)
Microcrustaceans (29.6%)
Algae (11.2%) Macrocrustaceans (0.2%) Molluscs (4.2%) Other macroinvertebrates (0.4%)
Aquatic insects (35.6%)
It is likely that this species is able to undertake local dispersal and/or recolonisation movements. It is particularly abundant in streams that periodically become disconnected by extended periods of low flow, when surface waters recede to a series of isolated pools (e.g. tributaries of the Mary and Brisbane rivers). In these streams, rapid recolonisation of previously dry river reaches has been observed soon after flows resumed in summer and longitudinal connectivity was re-established (i.e. within 48 hours [1093]). In the Burnett and Mary rivers, south-eastern Queensland, tens to hundreds of fish have been observed in pools immediately downstream of obstructions to movement (e.g. culverts and weirs) soon after a rise in discharge during late spring, suggesting that C. stercusmuscarum undergoes upstream dispersal/recolonisation movements cued by elevated flows [1093]. A similar phenomenon was observed for this species in the Fitzroy River [1351]. A species of small hardyhead (probably C. s.
Figure 11. The mean diet of Craterocephalus stercusmuscarum. Data derived from stomach contents analysis of 1639 individuals from the Alligator Rivers region of the Northern Territory [193], Cape York Peninsula [697, 1099], the Wet Tropics region of northern Queensland [599, 1097], central Queensland [1080], south-eastern Queensland [80, 205, 1421] and from a lake on the Murray River floodplain in north-western Victoria [396].
Some spatial and temporal variation in the diet of C. stercusmuscarum is evident. For example, in studies of lentic floodplain habitats (e.g. billabongs, lakes and wetlands [193, 396, 697]) fish were often observed to consume greater amounts of microcustaceans (zooplankton) than fish collected from lotic habitats (e.g. [80, 205, 1097]). In contrast, the diets of fish from riverine habitats [80, 599, 1080, 1097] were often dominated by aquatic insects.
195
Freshwater Fishes of North-Eastern Australia
Ecological Community in the lower Murray River [1005] and in the lowland catchment of the Darling River [329]. In Victoria, this species was once considered to be of restricted distribution, and/or rare [273], it was subsequently upgraded to indeterminate [731], but it was not included in a 2000 listing of threatened vertebrate fauna in Victoria [1004]. It is however, listed under the Victorian Flora and Fauna Guarantee Act 1998 [1040, 1189].
The extent of herbivory and planktivory appears to vary with age and size of the fish, and probably according to the availability of other food sources. For example, the diet of 0+, 15–20 mm SL fish (n = 32) in floodplain habitats of the Normanby River [697] contained 56% algae (diatoms and desmids), whereas the diet of fish between 21–45 mm SL (n = 69) contained 24% algae. Temporal variation in dietary composition of these fishes was also evident. Soon after the end of the wet season, herbivory and planktivory, contributed 4% and 59% of the diet, respectively. By the late dry season however, fish of equivalent size consumed less planktonic crustaceans (34%) whereas herbivory had increased in importance to 26%. Notably, fish collected from the river itself consumed no planktonic microcrustaceans [1099].
Like many other native species, siltation arising from increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of C. stercusmuscarum, and may also affect aquatic invertebrate food resources. Interactions with alien fish species (e.g. competition for resources and predation on eggs, larvae and juveniles) is another potential threat to C. stercusmuscarum [95].
No information on the trophic ecology of larvae is available, however larvae from other members of the genus Craterocephalus have been recorded feeding on rotifers and microcrustaceans.
Craterocephalus stercusmuscarum has been shown to undertake facultative movements although the purpose of these movements is unclear. Nevertheless, it is likely to be sensitive to barriers to movement caused by structures such as dams, weirs, barrages, road crossings and culverts. River regulation, independent of the imposition of barriers, may also impact on C. stercusmuscarum populations. Changes to the natural discharge regime and hypolimnetic releases of unnaturally cool waters from large dams may interrupt possible cues for movement or de-couple optimal temperature/discharge relationships during critical phases of spawning, larval movement and development. Unseasonal flow releases during naturally low flow periods in September and October are likely to negatively affect reproductive success as this coincides with the period of peak spawning activity and larval development. The availability of aquatic macrophyte beds, the likely spawning habitat of C. stercusmuscarum, may be maximised during low flow periods. Scouring actions of elevated discharges at the onset of the wet season may reduce or remove aquatic macrophyte beds. Larval development is also likely to be favoured during low flow periods, during which time phytoplankton and invertebrate abundances are also high [949]. High discharge rates were shown to reduce larval abundance in streams of the Wet Tropics region [1109]
In aquaria, adults will consume a range of food types including small anuran tadpoles, mosquito larvae and other common aquarium foods such as Calanus and Artemia nauplii, Tubifex worms and commercial flake foods [1210]. Even finely minced animal meats are eaten. Postlarvae will consume similar items to those listed above as well as infusoria made from lettuce [1211]. Conservation status, threats and management The conservation status of Craterocephalus stercusmuscarum is listed as Non-Threatened by Wager and Jackson [1353]. It is generally common throughout most of its coastal distribution in northern and eastern Australia. In the southern parts of the Murray-Darling Basin it is thought to have undergone declines in distribution and abundance [635] although recent surveys reveal that is still locally common in some areas [56, 507, 807, 817]. In 2000, Morris et al. [965] included C. s. fulvus in an assessment of threatened and near-threatened freshwater fish in New South Wales, on the basis that this species was considered rare in the southern parts of the Murray-Darling Basin and due to possible taxonomic confusion with other hardyhead species. It was recommended in this assessment that C. s. fulvus be listed as ‘Data Deficient’ under the IUCN Red List of Threatened Species to promote further investigation into its conservation status. However this species had not been listed as at December 2003. In an assessment of the status of freshwater fish in the MurrayDarling Basin in 2002, C. s. fulvus was considered to be widespread but declining in the basin [15]. This species has also been listed as a member of an Endangered
Craterocephalus stercusmuscarum is known to act as a second intermediate host to the digenetic trematode Stegodexamene callista (Lepocreadiidae) [339] and a species of Craterocephalus (possibly C. s. fulvus) from the Brisbane catchment was shown to be infected by the digenetic trematode Opecoelus variabilis (Opecoelidae) [338, 339]. Dove [1432] provided a list of parasite taxa recorded from C. s. fulvus in south-eastern Queensland.
196
Rhadinocentrus ornatus Regan, 1914 Ornate rainbowfish, Soft-spined rainbowfish
37 245022
Family: Melanotaeniidae
Description First dorsal fin: III–V; Second dorsal: I, 11–15; Anal: I, 18–22; Pectoral: 11–13; Caudal: 16 segmented rays. Pelvic: I, 5; Vertical scale rows: 31–37; Horizontal scale rows: 8–9; Predorsal scales: 14–16; Cheek scales: 2–6; Gill rakers on first arch: 11–12; Vertebrae: 31–37 [32, 34, 38, 39, 52, 631, 936]. Figure: adult specimen, 44 mm SL, Mellum Creek, November 1993; drawn 2003.
Scales large and cycloid, extending to cheek but excluding jaws and inter-pelvic region. Two dorsal fins separated by small gap, the second elongated. Origin of first dorsal fin approximately midway between snout tip and tail base, usually above fifth to sixth ray of anal fin [39, 1015]. Elongated anal fin originates in anterior half of body. Usually only last few anal and dorsal fin rays are branched. Caudal fin slightly forked. Sexually dimorphic [39]. Males exhibit more elongate rays in the second dorsal fin and anal fins than females; rear tips of the second dorsal and anal fins are pointed in males, rounded in females [39]. Males tend to be deeper-bodied and exhibit brighter body and fin colours, particularly during courtship and spawning [38, 39, 52, 517, 936]. The body is semi-transparent with dark scale margins forming a network pattern [38, 52].
Rhadinocentrus ornatus is a small species reaching a maximum size of 65 mm TL (females) and 80 mm TL (males), commonly 40 mm or less in the wild [52, 82, 84, 631, 783, 978]. Fish grown in aquaria can reach 100 mm TL [978]. No length–weight relationship is available for this species but it is generally similar in shape to small and mediumsized M. duboulayi. Rhadinocentrus ornatus is a slender, relatively elongate species with laterally compressed body, deepening with age [631]. Mouth very oblique, upper jaw protruding slightly. Conical to caniniform teeth in jaws; outer row at front of jaw enlarged but not separated from inner rows [978]; one or more rows extending outside mouth; vomer and palatines toothless [39]. Moderate-sized head and relatively large eyes; upper edge of eye located at or near upper head profile [39, 936, 978]. Open pores on head [978].
Colour and pattern vary spatially among populations and the various colour forms are a continuing source of fascination among many aquarists. Hansen [517] suggested that three general colour forms of R. ornatus exist and provided detailed descriptions of these: a widespread type form, a blue form confined to streams draining into Tin Can Bay and on Fraser Island, south-eastern Queensland, and a pink form confined to a very restricted area near Tin 197
Freshwater Fishes of North-Eastern Australia
external ramus on the maxilla and a reduced number of interdorsal pterygiophores [631]. Rhadinocentrus ornatus is distinguished from Cairnsichthys by the absence of a basisphenoid, a straight rather than curved caudilateral margin of the lateral ethmoid, a deep lateral urohyal, and a narrow supracleithrum [32]. A phylogenetic analysis of the family by Aarn and Ivantsoff [23] identified Iriatherina as being distinct from all other melanotaeniids and placed Rhadinocentrus and Cairnsichthys in a subclade within a larger group containing the two rainbowfish genera (Bedotes and Rheocles) from Madagascar.
Can Bay [517]. In the type form, the body is translucent light brown with fine reticulated scale pattern. Pigmentation on the upper and lower margins of the midlateral scale rows forms a pair of parallel dark stripes. Iridescent neon-blue spangles are scattered on the back and nape. The caudal fin is usually reddish with a central dark sector. Dorsal fin commonly has a red outer border with black rays, although margin is sometimes dark with a blue fin. Anal fin usually has a black margin. Fish from dark tannin-stained waters such as Coolum Creek and the upper Noosa River are very dark, almost black [517]. The blue form is dark brown on top fading ventrally with shades of blue increasing towards the tail. Scale margins dark, forming a reticulated pattern. Some males are reddish on the anterior third of the body. Iridescent blue spangles of varying densities are present. The blue fins vary from purple to sky-blue with a strong black margin. The blue form carries a recessive gene that yields bright red body colours to varying degrees [517]. The pink form is similar although less black and the blue is replaced by pink. Often varying amounts of bright red overlay a background of pink [517]. Details of the distribution of each colour morph can be found in Hansen [517]. A greenfinned colour form reputedly also occurs on the western side of Stradbroke Island (T. Page, pers. comm.). Further details on geographic variation in colour forms and relationships with phylogeographic patterns are given below.
Recent phylogeographic analysis of R. ornatus by Page et al. [1035] using mtDNA sequence analysis of the ATPase gene has revealed that this species is divided into four major clades: 1) central eastern Queensland (Water Park Creek to Tin Can Bay including populations on Fraser Island); 2) Searys Creek, some individuals from a single location near Tin Can Bay; 3) a highly diverse and differentiated group in south-eastern Queensland and northern New South Wales (Noosa River south to Cudgera Creek in New South Wales; and 4) a clade containing fish from the Richmond and Clarence rivers. Clades 3 and 4 were suggested to have diverged about 2.4 m.y.b.p. whereas these clades and clades 1 and 2 diverged from one another between 5.1 and 6.9 m.y.b.p. during the late Miocene at a time of increasing aridity. Divergence between the population at Water Park Creek and other populations within clade 1 (which are separated by a distance of 350 km) was suggested to be relatively recent (0.72 m.y.b.p.). Interestingly, these authors note that each Rhadinocentrus lineage is older than many species within Melanotaenia [1035]. The various colour forms described earlier are not fully congruent with the phyletic pattern described by Page et al. [1035]. However, Chris Marshall (pers. comm.) suggests that a basic split in colour form and morphology of R. ornatus populations north and south of the Noosa River is generally consistent with the major phylogeographic patterns described by Page et al. [1035]. Marshall suggests that northern type fish generally grow larger, do not have the black lateral lines and reticulations on the body, and have the iridescent blue scales along the nape and irregularly on sides of the body. The southern type has the lateral black lines and reticulations, is smaller and only has iridescent blue scales along the nape.
Systematics Melanotaeniidae (commonly known as rainbowfishes) is a relatively large family confined to northern and eastern Australia, New Guinea and surrounding islands, and Madagasgar [38, 39, 52]. At least 68 species from seven genera are currently recognised, the majority of which occur in New Guinea; 16 species and four genera occur in Australia [38, 52, 904]. The Melanotaeniidae are closely related to the Pseudomugilidae (blue-eyes) and Atherinidae (hardyheads), and were formerly included in the family Atherinidae [34, 38, 39]. Rhadinocentrus (meaning soft-spined) is a monotypic genus, although prior to Allen [32] erecting the new genus Cairnsichthys, C. rhombosomoides was also originally placed in this genus. Allen [32] considered both Rhadinocentrus and Cairnsichthys to be basal members of the family Melanotaeniidae. The genus is distinguished by a marked mandibular prognathism (protruding lower jaw) and shares with Cairnsichthys a series of osteological characters that separate them both from the remaining Australasian melanotaeniid genera (Iriatherina, Melanotaenia, Chilatherina and Glossolepis) including a reduced parasphenoid process on the vomer, a shelf (rather than a canal) on the temporal, a more elongated
Distribution and abundance Rhadinocentrus ornatus has a restricted and patchy distribution in coastal lowland wallum (Banksia heath) and rainforest ecosystems of central and south-eastern Queensland, and northern New South Wales. It also occurs in many streams, lakes and wetlands habitats on the sand dune islands (Fraser, Moreton, North Stradbroke and
198
Rhadinocentrus ornatus
common at sites in which it occurred (third most abundant species forming 18% of the total abundance at these sites). This species was also locally common in streams of the South Coast region where it formed 41% of the total abundance at sites in which it occurred. Across all streams, average and maximum numerical densities recorded in 29 hydraulic habitat samples (i.e. riffles, runs or pools) were 0.52 individuals.10m–2 and 3.75 individuals.10m–2, respectively. Average and maximum biomass densities at 94 of these sites were 0.38 g.10m–2 and 0.95 g.10m–2, respectively. Highest numerical and biomass densities were recorded from streams of the South Coast Basin. Rhadinocentrus ornatus most commonly occurred with the following species (listed in decreasing order of relative abundance with rank abundance in parentheses): G. holbrooki, H. compressa, H. gallii, and G. australis [1093]. Other studies have reported this species to also commonly co-occur with M. duboulayi, P. mellis, N. oxleyana and M. adspersa [82, 84, 517]. Around the Evans Head area of northern New South Wales, R. ornatus often occurs with N. oxleyana, H. galii, H. compressa, G. australis and G. holbrooki [726].
Bribie islands) off the south-eastern Queensland coast [34, 38, 52, 77, 82, 84, 153, 154, 517, 792, 884, 936, 1042, 1295]. This species occurs in several highly disjunct geographic locations. Populations are known from small wallum swamps and streams in the Shoalwater Bay drainage and Water Park Creek (within Byfield National Park) near Rockhampton in central Queensland [631, 862, 1328, 1349]. A record of R. ornatus in the Fitzroy River [1349] is reported to be of dubious authenticity [1338]. Approximately 300 km to the south, it has occasionally been reported in the Mary River but this species appears to be extremely rare in this basin [84, 104, 1234, 1349]. Rhadinocentrus ornatus occurs in most drainage basins from Tin Can Bay (as far north as Big Tuan Creek southeast of Maryborough, C. Marshall, pers. comm.) south to Currumbin Creek near the border with New South Wales. It is interesting that R. ornatus has not been recorded from apparently suitable wallum habitats in the area between Tin Can Bay and Water Park Creek to the north (e.g. the Woodgate-Kinkuna National Park and Deepwater Creek area). This species has not been recorded from the small coastal streams and wetlands of the Sandgate area and the Albert River. It is present but patchily distributed in coastal drainages of northern New South Wales and has been recorded as far south as the Orara River near Coffs Harbour [25, 726, 814].
Macro/mesohabitat use Rhadinocentrus ornatus is found in waterbodies situated in coastal lowland wallum (Banksia heathland) ecosystems generally characterised by dystrophic, acidic, stained waters with siliceous sand substrates and abundant submerged and emergent vegetation [84, 88]. This species occurs in a variety of lotic and lentic habitat types including tributaries and backwaters of moderate-sized rivers, small, short coastal streams, coastal and insular wetlands, and coastal dune lakes [52, 82, 84, 517, 726, 978]. It has been collected up to 50 km from the mouth of coastal rivers in south-eastern Queensland at a maximum elevation of 100 m.a.s.l. (Table 2). Reports of this species from localities in Obi Obi Creek [104, 1349] and Wide Bay
Rhadinocentrus ornatus is often locally common, although it has declined in some areas such as the Brisbane River system [94, 704]. Extensive sampling in rivers and streams of the south-eastern Queensland mainland yielded relatively few individuals, but it was most common and widespread in the Sunshine Coast area north of Brisbane. In this region it was the fifth most abundant species collected, forming 7.7% of the total catch and was present at almost half of the locations surveyed (Table 1). It was relatively
Table 1. Distribution, abundance and biomass data for Rhadinocentrus ornatus in streams of south-eastern Queensland. Data summaries for a total of 231 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance (40.98) Rank abundance
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
5.7
–
48.3
5.0
–
1.5
5.0
0.14 (10.86)
–
7.67 (18.03)
0.14 (2.03)
–
0.01 (0.58)
0.70
22 (4)
–
5 (3)
21 (4)
–
27 (5)
12 (1)
0.01 (2.31)
–
0.13
–
–
–
0.18
32 (5)
–
8
–
–
–
11
Mean numerical density (fish.10m–2)
0.52 ± 0.15
–
0.54 ± 0.19
0.24 ± 0.08
–
0.11 ± 0.07
1.19 ± 0.18
Mean biomass density (g.10m–2)
0.38 ± 0.16
–
0.17 ± 0.06
–
–
–
0.68 ± 0.27
% biomass Rank biomass
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Freshwater Fishes of North-Eastern Australia
debris composed of logs and branches and the fine rootlets of riparian vegetation [52, 82, 84, 726, 1093]. Most insular habitats support emergent sedges and rushes (Eleocharis spp., Lepironia articulata, Ghania spp. and Juncus spp.) and some aquatic macrophytes (Myriophyllum sp., Nymphaea sp., Chara spp. and Utricularia spp.) [84, 88, 517].
Creek [1234] in the Mary River basin are considerably further upstream from the river mouth. Stream widths at collection sites vary from 2–7.3 m, with generally high riparian cover (Table 2). Rhadinocentrus ornatus was most frequently collected from runs and pools with low water velocity (weighted mean 0.03 m.sec–1) and moderate depths (weighted mean 0.44 m). This species was collected in mesohabitats with predominantly fine-grained substrates (sand and coarse gravel), but was also associated with cobbles and bedrock outcrops (Table 2). With the exception of leaf litter beds, in-stream cover was not overly abundant in the mesohabitats in which this species was collected in streams of south-eastern Queensland (Table 2).
Environmental tolerances Limited quantitative data is available concerning the environmental tolerances of R. ornatus. Table 3 provides data for Queensland collection sites only; details for collection sites in New South Wales can be found in Knight [726]. This species is usually associated with dystrophic waterbodies that are acidic to circum-neutral (pH 4.0–8.0) and slightly to deeply stained with tannins and other organic acids, thus water transparency is usually very low (Table 3) [52, 82, 84, 726, 1093]. Conductivity is usually very low in streams, swamps and lakes supporting this species (usually <300 µS.cm–1, but up to 658.0 µS.cm–1). Temperatures at collection sites in Queensland and New South Wales have ranged from 12 to 32°C, and dissolved oxygen levels from 2.15–16.2 mg.L–1 [25, 52, 82, 84, 726, 1093].
Table 2. Macro/mesohabitat use by Rhadinocentrus ornatus in rivers of south-eastern Queensland. Data summaries for 231 individuals collected from samples of 29 mesohabitat units at 17 locations between 2000 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
Mean
W.M.
5.0 3.0 4.0 0 2.0 33.7
125.5 27.0 50.0 100 7.3 93.4
50.0 14.0 22.2 20 4.4 71.7
32.6 10.0 22.7 28 3.6 77.5
Mean depth (m) 0.11 Mean water velocity (m.sec–1) 0 Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0.8 0 6.8 0 0 0 0
0.99 0.44
0.48 0.07
Rhadinocentrus ornatus is sensitive to toxins in aquaria (e.g. ammonia, chlorine and copper) at concentrations that do not affect other taxa, such as species of Melanotaenia, Craterocephalus, Ambassis and Hypseleotris [517]. Aarn et al. [25] suggested that R. ornatus might be suitable as an indicator of environmental change on the basis of their relatively narrow environmental tolerances. Moloney [960] noted that R. ornatus was extremely susceptible to Mycobacterium (also called fish tuberculosis), reporting a 99% mortality rate of fish in aquaria infected with this pathogen.
0.44 0.03
8.7 100.0 11.3 51.8 40.3 13.2 47.3
3.2 38.6 3.2 19.0 18.9 3.4 13.8
4.9 19.3 5.1 17.9 20.5 4.4 27.9
3.0 19.0 0.5 2.8 33.5 27.8 13.5 26.8 25.0 46.7
0.6 3.8 0.2 1.9 8.6 19.3 4.0 7.4 5.0 9.3
0.1 0.6 0.1 1.7 5.5 21.5 1.7 3.0 1.4 2.5
Table 3. Physicochemical data for Rhadinocentrus ornatus from nine sites in Sunshine Coast streams over the period 1990 to 1994 [82, 84] and from 22 samples in South Coast streams over the period 1994 to 2003 [1093]. Parameter
Min.
Max.
Mean
Sunshine Coast rivers and streams [82, 84] (n = 9) Water temperature (°C) 16.0 32.0 18.7 Dissolved oxygen (mg.L–1) 3.0 14.6 7.2 pH 4.0 7.3 5.3 Conductivity (µS.cm–1) 68.0 300.0 103.0 Turbidity (NTU) clear 10 stained South Coast streams [1093] (n = 22) Water temperature (°C) 15.8 23.2 Dissolved oxygen (mg.L–1) 2.6 16.2 pH 4.4 8.0 Conductivity (µS.cm–1) 78.0 658.0 Turbidity (NTU) 0.3 331.4
Microhabitat use Rhadinocentrus ornatus is often found in close association with dense emergent and submerged marginal vegetation, leaf-litter beds, undercut banks and submerged woody
200
18.8 5.9 6.8 260.3 41.3
Rhadinocentrus ornatus
Reproduction The reproductive biology and early development of R. ornatus is known from field studies in Queensland [82, 84] and aquarium observations [38, 517, 783, 797] (Table 3). This species spawns and completes its entire life cycle in freshwater and is easy to breed in captivity [38, 517, 783, 797, 978]; it was first bred in captivity 70 years ago [978]. Sexual dimorphism is exhibited in the form of more elongate rays in the second dorsal and anal fins of male fish; males often fight among themselves; males also display a red nuptial stripe along the nape during courtship (C. Marshall, pers. comm.) [936].
[84]. From May to September, all fish caught were juvenile and/or inactive, with a few maturing fish present in August. Ripe females were captured from early November to mid-January, as for males. Spent females were present from early October to May, indicating the cessation of spawning activity from June/July to October, depending on water temperatures. Spawning occurs at water temperatures of around 24–28°C in Queensland localities and in aquaria [38], however, Aarn et al. [25] collected eggs and larvae of this species in the Upper Orara River near Coffs Harbour in mid-October at temperatures of 16–17°C. No increase in precipitation or water level was evident prior to the collection of eggs and larvae [25]. The relationship of fecundity to body size in Queensland (Blue Lake) populations could not be determined owing to the low numbers of ripe female R. ornatus captured and the variability of numbers of ripe oöcytes in fish of various body sizes [84]. However, Arthington and Marshall [84] recorded egg counts of 18–76 (mean 40 eggs per female, 23–33 mm SL).
Rhadinocentrus ornatus is believed to mature in 9–12 months [797] and has an extended breeding season [84]. In Blue Lake, North Stradbroke Island, running ripe male R. ornatus were first observed in early November and ripe males were captured from then until mid-January; spent males were present from early November until late April Table 4. Life history information for Rhadinocentrus ornatus. Age at sexual maturity (months)
9–12 months [797]
Minimum length of gravid (stage V) females (mm)
18 mm [1093]
Minimum length of ripe (stage V) males (mm)
22 mm [1093]
Longevity (years)
3–4 [517, 936]
Sex ratio (female to male)
?
Occurrence of ripe (stage V) fish
November–May [82, 84]
Peak spawning activity
November–January [82, 84]
Critical temperature for spawning
Around 23–28°C [38, 84]
Inducement to spawning
Increase in water temperature and day length [25, 84]
Mean GSI of ripe (stage V) females (%)
5.04 ± 1.08 [1093]
Mean GSI of ripe (stage V) males (%)
0.30 ± 0.20 [1093]
Batch fecundity (number of ova per batch)
18–76, mean = 40 per female (23–33 mm SL) [84]
Fecundity/Length (mm SL) or Weight (g) relationship (mm SL)
?
Egg size (diameter)
1.20–1.35 mm [25]
Frequency of spawning
Lays a few eggs each day over a number of days [34, 797, 936]
Oviposition and spawning site
Female deposits batches of 3–5 eggs on aquatic plants, Eleocharis sp. is preferred spawning site; eggs are relatively large and hang from adhesive filaments [25, 783]
Spawning migration
Probably none
Parental care
None
Minimum time to hatching (days)
6 [797], 7 [34, 936], or 8 [783] days at 20°C; 6–10 days at 23–24°C [84], 16 days at 20–22°C [25]
Length at hatching (mm)
4.1–4.6 [25]
Length at free swimming stage
?
Age at loss of yolk sack
?
Age at first feeding
?
Length at first feeding
?
Age at metamorphosis (days)
?
Duration of larval development (days)
?
201
Freshwater Fishes of North-Eastern Australia
aquatic insects (22.5%). This species also consumes microcrustaceans including copepods, ostracods and cladocerans (2.4%), macrocrustaceans (mostly atyid shrimps, 2.0%) and other microinvertebrates such as small arachnids and hydracarinids (0.9%). A small amount of algae (e.g. desmids) (1.4%) and fragments of terrestrial vegetation (0.7%) have been found in the guts of some individuals (Fig. 1) [82].
The mean GSI values observed for fish collected from Blue Lake during summer were 0.3% ± 0.2 SE for males and 5.0% ± 1.1 SE for females (<10 individuals of each sex) [1093]. The eggs are yellow, spherical and relatively large (diameter 1.20–1.35 mm) with a unipolar tuft of adhesive filaments [2495; 1453]. The female lays three to five eggs each day over a number of days, depositing them on submerged aquatic vegetation from which they hang by adhesive filaments [34, 783, 797, 936]. The most frequently used site for spawning of R. ornatus in the Orara River was the base and roots of the emergent sedge Eleocharis sp. [25]. The minimum time to hatching varies with temperature, as follows: six days [797], seven days [34, 936] or eight days [783] at 20°C; 6–10 days at 23–24°C [34, 797, 936]; 16 days at 20–22°C [25]. Moloney [960] reported that eggs in aquaria appeared to hatch over a period of a few days and that the first fry were observed approximately two weeks after courtship had commenced. Length at hatching is 4.1–4.6 mm [25].
Arthington and Marshall [82] observed that in Spitfire Creek on Moreton Island, R. ornatus had a more diverse diet than other species present (Nannoperca oxleyana, Hypseleotris galii, H. compressa) largely as a consequence of its consumption of terrestrial as well as aquatic taxa. Spatial variations in diet were also observed in this wetland system, and related to the tendency to forage at the water’s surface, where the array of prey of terrestrial origin may vary considerably due to such factors as source of terrestrial insects (low or high growths of riparian and bank vegetation), wind direction, and size and weight of prey [82].
Aarn et al. [25] describe and illustrate characteristics of larval R. ornatus. Characteristic features are: rounded cranium, cranial melanophore distribution forming a narrow ‘V’, lack of melanophores in the cranial parietal peritoneum, dorsal fin-fold originating at the fourth to fifth preanal myomere, urogenital funnel present (and gives rise to the genital rosette), first dorsal fin originates caudal to origin of anal fin and the anal fin originates next to the urogenital funnel, notochord flexion takes place after hatching, larvae maintains flexion during early development, mouth shows mandibular prognathism, there are 34–35 vertebrae, the tip of the notochord is elongate and the hypurals only partially fuse [25, 631].
In Blue Lake, North Stradbroke Island, R. ornatus had a more diverse diet than H. galii [92]. In this lake, R. ornatus consumed a wider variety of aquatic and terrestrial taxa than H. galii and took a greater proportion of its diet from food items associated with the water’s surface (overall >60% including chironomid pupae, adult Diptera, Hymenoptera, Lepidoptera and Araneae, flower parts and other plant tissues). Chironomid pupae were the most important dietary component in 1991 (25%) and adult Diptera in 1991 (26%). Small quantities of filamentous algae were consumed in both years but other algae (desmids and diatoms) were not eaten. Prey diversity and
In captivity, the young of R. ornatus can grow to 20 mm in three weeks given suitable food [978] and to 41 mm in 10 weeks [783].
Other microinvertebrates (0.9%) Microcrustaceans (2.4%) Macrocrustaceans (2.0%) Other macroinvertebrates (0.9%)
Movement Rhadinocentrus ornatus is an active swimmer that congregates in small pools [39] but is said not to be as active as other rainbowfishes [25, 783]. There is no published information on other aspects of the movement biology of this species.
Unidentified (9.3%)
Terrestrial invertebrates (23.3%)
Aquatic insects (36.6%)
Trophic ecology Diet data for R. ornatus is available for 508 individuals from the Blue Lake on North Stradbroke Island and Spitfire Creek on Moreton Island [82, 84, 92, 105]. This species is a microphagic carnivore (Fig. 1). The total mean diet is composed primarily of aquatic insects (36.6%), terrestrial invertebrates especially Diptera, Hymenoptera and Hemitera (23.3%) and aerial forms of
Algae (1.4%) Terrestrial vegetation (0.7%)
Aerial aq. Invertebrates (22.5%)
Figure 1. The mean diet of Rhadinocentrus ornatus. Data derived from stomach content analysis of 508 individuals from Blue Lake on North Stradbroke Island and Spitfire Creek on Moreton Island [82, 84, 92, 105].
202
Rhadinocentrus ornatus
long-term variability in precipitation levels, water depth and velocity [154]. In small streams and swamps, aquatic macrophytes serving as fish habitat and spawning sites for R. ornatus can be flooded or swept away at high water levels and destroyed by exposure at low water levels. Other melanotaeniids show a preference for habitat with high levels of macrophyte cover [52], and stream fishes in general often associate with macrophytes and other forms of in-stream cover [1095]. Areas with good riparian cover and aquatic vegetation also provide an abundant source of terrestrial and aquatic invertebrate food for surface feeding species such as R. ornatus [82, 84, 611].
evenness were higher for R. ornatus than for H. galii in both years of study and at all times of year [92]. Bayly et al. [149] reported similar variation in the diets of R. ornatus and H. galii in Fraser Island lakes. Conservation status, threats and management Rhadinocentrus ornatus was classified in 1993 as NonThreatened by Wager and Jackson [1353], and since then has not been given any special conservation designation in National or State listings [52] either in Queensland or New South Wales [965]. It is not listed under the Commonwealth Endangered Species Protection Act, 1992, the NSW Fisheries Management Act, 1994, the World Conservation Union (IUCN) ‘Red’ List, the Australian Society for Fish Biology (ASFB) ‘Conservation Status of Australian Fishes’ Listing, or the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). Nevertheless, many ecologists regard R. ornatus as a vulnerable species owing to its relatively restricted and patchy distribution along the coastline of central and south-eastern Queensland and northern New South Wales [52, 726, 965]
Disturbance of aquatic plant communities in coastal streams and lakes may have significant implications for the persistence of R. ornatus [82, 84]. Road and bridge construction have increased bank erosion and the sediment load in a number of small coastal creeks along the Sunshine Coast of Queensland [82, 1348]. Real estate development and housing construction in the vicinity of small creeks and swampy drainage lines may represent a serious threat if adequate precautions are not taken to contain sediment runoff from cleared land [82, 84]. Alien species are also regarded as a threat to R. ornatus [25, 52, 82, 84, 517, 960]. Gambusia holbrooki has established self-maintaining populations in many waterbodies of the wallum ecosystem in both Queensland and New South Wales [84, 726]. Gambusia holbrooki is a particularly threatening species [77, 78, 416]. Many studies have demonstrated its trophic flexibility (including the consumption of fish eggs and larvae) and its innate aggressiveness towards other fishes [78, 960, 983].
The primary threats to R. ornatus are the same factors threatening populations of Nannoperca oxleyana and Pseudomugil mellis in coastal wallum ecosystems [52, 82, 84, 726]. They include loss of habitat due to residential housing development [90, 1358] and road construction [1348], expansion of exotic pine plantations by forestry, and water contamination associated with urban and tourism development, mining operations and agriculture [82, 84, 90, 726, 790, 965, 1348, 1353]. Aarn et al. [25] note that R. ornatus was collected from Boambee Creek, south of Coffs Harbour, by the Australian Museum prior to urban development and degradation of this stream.
Moloney [960] reported a high level of predation on R. ornatus eggs and fry by G. holbrooki maintained in experimental aquaria. Rhadinocentrus ornatus was also observed to switch habitat use from areas of open water to refuge areas in the presence of G. holbrooki. Moloney [960] concluded that alien fish such as G. holbrooki have the capacity to significantly reduce the number of R. ornatus recruiting to later life stages by interfering with foraging activities and by direct predation. Dietary studies in Blue Lake, North Stradbroke Island, have shown that R. ornatus and G. holbrooki have very similar diet composition at all times of the year [84, 92]. Both species feed on aquatic and terrestrial invertebrates and show particularly high dependence on prey of terrestrial origin [82, 84, 92]. Arthington and Marshall [92] suggested that high similarity of diet composition could lead to interspecific competition if high population densities of G. holbrooki coincide with circumstances of food shortage. The occurrence of G. holbrooki in coastal creeks on Fraser and Moreton islands, in the Noosa River and in many mainland creeks within
Several aspects of the ecology of R. ornatus are particularly relevant to its protection and recovery in wallum ecosystems. This species is usually found where there is little or no flow and fish can shelter in beds of emergent and submerged aquatic macrophytes or near undercut banks and woody debris [82, 84, 726, 1093]. Cover is an important factor in environments where surface (i.e. avian) and aquatic predators (piscivores) are present. Cover elements may also serve to reduce the impact of short periods of high flow with the power to disrupt spawning activities, displace eggs and small individuals downstream, or carry fish into open areas with little protective cover [82]. Rainfall patterns and stream discharge are characteristically highly variable and unpredictable within and between years in south-eastern Queensland streams and rivers [1095]. Freshwater habitats within coastal wallum are particularly vulnerable to local rainfall events and
203
Freshwater Fishes of North-Eastern Australia
the geographic range of R. ornatus represents an ongoing threat that could well increase. [84]. Dispersal of alien fishes by natural processes (e.g. widespread flooding) is a possibility and G. holbrooki is a particularly hardy and adaptable species [83]. Human distribution of G. holbrooki still occurs occasionally [83].
purposes is potentially deleterious. Members of the public who are not familiar with the fauna of particular systems may inadvertently collect a restricted species such as R. ornatus, only to discard it later in the day, possibly into a different waterbody. Public education is the most effective way to combat this type of impact.
Introduced plants may also substantially modify the freshwater habitats of R. ornatus. Several small, confined waterways along the Queensland coast have been invaded by the South American ponded pasture species, Brachiaria mutica (para grass). This alien grass has a severe impact on aquatic habitat, water quality and invertebrate diversity in small streams and does not contribute carbon (i.e. energy) to aquatic food webs [95, 248, 250].
Several approaches to the conservation of rare and endangered fish species have been proposed in draft Recovery Plans for Pseudomugil mellis and Nannoperca oxleyana [82, 84]. Recovery Plans for these species would also protect R. ornatus [84]. Arthington et al. [82], Knight [726] and Morris et al. [965] recommend a range of Specific Recovery Actions to conserve individual localities and populations of N. oxleyana and P. mellis which are equally applicable to R. ornatus. These could include rehabilitation of degraded creeks, reconstruction of channel morphology and habitat characteristics, planting of riparian vegetation, and elimination of G. holbrooki [82, 84, 726, 965]. Recovery Plans for these rare species have not been implemented by the agencies responsible for environmental protection in Queensland.
Over-exploitation of R. ornatus is only an issue with respect to the collection of fish for aquarium stocks. The intensity and impact of this activity is not known. The Australia New Guinea Fishes Association (ANGFA) has issued several warnings to its membership that excessive collection of rare freshwater species for aquarium
204
Cairnsichthys rhombosomoides (Nichols & Raven, 1928) Cairns rainbowfish
37 245002
Family: Melanotaeniidae
located on the operculum. The body surface below the midlateral stripe tends to be white. Many specimens are distinguished by the presence of an iridescent pink-purple sheen, the intensity of which varies according to the incidence of light falling upon it. Colour in preservative: all iridescent structural colours are lost in preservative and the colour tends towards a uniform dull tan dorsally and white ventrally. The midlateral stripe remains visible but the lower stripe is noticeably faded.
Description First dorsal fin: V-VII; Second dorsal: I, 11–15; Anal: I, 17–21; Pectoral: 11–13; Horizontal scale rows: 10–11; Vertical scale rows: 36–38; Predorsal scales: 15–16 [23, 43, 52]. Figure: male, 58 mm SL, Polly Creek, North Johnstone River, September 1997: drawn 1999. Cairnsichthys rhombosomoides is a moderately sized rainbowfish rarely exceeding 63 mm SL [1108] but occasionally attaining a maximum size of 70 mm SL [38]. The relationship between body weight (g) and length (SL in mm) takes the form: W = 2.466 x 10–5 L2.878; r2 =0.873, n=372, p<0.001 [1108]. Body slender, rhombofusiform and laterally compressed [23]. Mouth terminal, initially horizontal becoming oblique caudally; large, reaching back to beyond anterior margin of eye. Outside margin of gape with several rows of small conical teeth. Body covered in faintly crenulate scales. Colour in life: published descriptions of this species do not do it justice, variously describing it as drab or dull yellow-green. In truth, it is a most beautiful bright tan-yellow on the dorsal half of the body. An intense black midlateral stripe and more diffuse ventral black stripe extend from the caudal area anteriorly to pectoral fin base. The fin margins of the dorsal surface are an iridescent yellow. A large iridescent yellow spot is
The larvae are distinctive and easily distinguished from the larvae of other melanotaeniids. The head is rounded and declined about 30° from horizontal and possesses a dense accumulation of melanophores on the dorsal surface between the mid-point of the eye and the posterior edge of the opercula. Melanophores on the operculum, snout and maxilla densely accumulated. Gut coiled but unstriated in newly hatched larvae. Eyes, feeding apparatus and gill filaments well developed at hatching [1093]. Systematics Cairnsichthys rhombosomoides was originally placed in the genus Rhadinocentrus in 1928, although the authors admitted that it was unlike the southern member and type species of the genus, R. ornatus [992]. Munro [975]
205
Freshwater Fishes of North-Eastern Australia
River in 1995 [1096]. The distribution was further extended to include the North Hull River [1087] in 1996 and the Liverpool and Maria drainages in 1997 [1179]. Although not collected from the Moresby River by Russell et al. [1183] it is likely to be present (or was present) in this drainage given its presence in rivers to the immediate north and south. Similarly, although not yet recorded from short creeks draining into Trinity Inlet, the historical connection of these streams with the Mulgrave River; as indicated by geomorphological evidence [1411] and the presence of Glossogobius sp. 4 [1349] (a species otherwise restricted to the Russell/Mulgrave River), suggests it would be present in this area also. If so, then streams of Trinity Inlet define the northern limit of its distribution and streams of the Hull River near Mission Beach form its southern limit. It has not been collected from the Tully River, despite extensive sampling [1087, 1093].
concurred, although further comparison was hampered by insufficient material. The species was, at the time, considered to be very rare [43]. Allen [32] erected the monotypic genus Cairnsichthys in 1980 in recognition of its distinctiveness as part of a generic revision of the family. Allen [32] was the first to propose a phylogeny for the Melanotaeniidae, and in his scheme, Pseudomugil and Popondetta were the most primitive genera, Melanotaenia, Chilatherina and Glossolepis were considered the most derived, while Iriatherina, Rhadinocentrus and Cairnsichthys were intermediate between these two groups. Of these latter six genera, all but Cairnsichthys are synapomorphic with regard to the attachment of the pelvic girdle to the third pleural rib (attached to the fourth in Cairnsichthys). Subsequently, the family Pseudomugilidae was recognised as distinct from the Melanotaeniidae [1190] and composed of the following genera: Pseudomugil, Kiunga and Scaturiginichthys (Popondetta having been subsumed within the genus Pseudomugil). This family (plus the newly erected Telmatherinidae) were then subsequently placed back within the Melanotaeniidae along with two genera, Bedotia and Rheocles from Madagasgar, by Dyer and Chernoff [395]. The most recent phylogenetic analysis of the Melanotaeniidae is that of Aarn and Ivantsoff [23]. In that analysis, the Pseudomugilidae, Telmatherinidae and the Melanotaeniidae were recognised as valid and different families. These authors accepted that on the basis of morphological synapomorphies, Bedotes and Rheocles remain within the Melanotaeniidae. The family is therefore composed of two subfamilies: the Iriatherininae (containing Iriatherina werneri) and the Melantaeniinae (containing Bedotes, Rheocles, Cairnsichthys, Rhadinocentrus, Chilatherina, Glossolepis and Melanotaenia). The first four genera are placed within a clade termed the Bedotiini. A recent phylogenetic assessment [905] of the family using DNA sequencing techniques unfortunately did not include any of the genera within the Bedotiinae. The genus Cairnsichthys is distinguished by a convex rostral margin of the vomer, caudolaterally directed vomerine condyles, elongate maxillary external ramus, enclosed mandibular sensory canal, broad supracleithrum and cranial spinous process of the pevic fin being attached ligamentously to the fourth pleural rib.
Cairnsichthys rhombosomoides is a moderately abundant species in those streams in which it occurs. It was the 14th most abundant species in the extensive Wet Tropics survey of Pusey and Kennard [1087]. A study undertaken in 12 sites within the Mulgrave River and 10 sites in the South Johnstone River found it to be the third and 14th most abundant species, respectively, contributing 5.8% of the total number of fish collect from both rivers [1096]. Estimates of relative abundance are highly dependent on whether appropriate streams are sampled. Table 1. Distribution, abundance and biomass data for Cairnsichthys rhombosomoides in two rivers of the Wet Tropics region. Data summaries for a total of 2761 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. Total % locations % abundance Rank abundance % biomass
Distribution and abundance Cairnsichthys rhombosomoides is limited to the Wet Tropics region and further restricted within this area also. Nonetheless, it is not as restricted or rare as some of the earlier texts suggest. Originally thought to be restricted to a few streams of the Russell/Mulgrave drainage, the distribution was extended to a single small tributary of the North Johnstone River in 1989 [34] and to the South Johnstone
25.3 7.9 (34.9)
Mulgrave River
Johnstone River
43.2
23.2
11.4 (38.0) 6.8 (32.5)
6 (1)
4 (1)
5 (1)
0.5 (10.0)
0.6 (9.8)
0.5 (10.2)
12 (5)
13 (5)
Rank biomass
15 (5)
Mean density (fish.10m–2)
3.50 ± 0.54
2.40 ± 0.44 4.36 ± 0.89
Mean biomass (g.10m–2)
3.67 ± 0.51
2.98 ± 0.53 4.20 ± 0.81
Cairnsichthys rhombosomoides is widespread and abundant in both the Mulgrave/Russell and Johnstone rivers (Table 1). It is apparently less widely distributed in the Johnstone River but this more properly is reflects the greater proportion of study sites located above an
206
Cairnsichthys rhombosomoides
elevation of 100 m.a.s.l. This species is numerically dominant in those sites in which it occurs and contributes about 10% to the total biomass of these sites also. Cairnsichthys rhombsomoides co-occurs with (in decreasing order of abundance) M. adspersa, H. compressa, P. signifer and M. maccullochi (all sites combined). It frequently occurs with A. reinhardtii (fourth) and O. aruensis (fifth) in the Mulgrave River, and with M. s. splendida (fifth) in the Johnstone River [1093]. The number of species with which it co-ocurrs in the Johnstone and Mulgrave rivers ranges from three to 15 per site (average = 7.8). The number and types of species with which it co-occurs is highly dependent on the location of the stream within the catchment (see below). It is frequently found in sympatry with M. splendida splendida (47.7% of all site/time combinations (n = 82) within the Johnstone and Mulgrave rivers containing C. rhombosomides also contained M. s. splendida) but it is rare that both species are abundant. Density values of these species are weakly (r2 = 0.203) but significantly (p<0.01) negatively correlated.
related to habitat structure (such as substrate composition, gradient or water velocity). Competition with the eastern rainbowfish Melanotaenia splendida splendida is likely to be important given the negative association between densities of these species reported above. Additional evidence for this interaction can be found by examining the distribution of both species within individual streams in which they co-occur. In all circumstances, Cairnsichthys is restricted to the most upstream reaches and often a very sharp zone of sympatry is delineated by rapid changes in gradient posed by cascades or waterfalls. (A similar pattern of distribution is seen for M. spl. splendida and M. utcheensis in the Johnstone River at higher elevation [1104]). As Cairnsichthys is the more plesiomorphic of the two species, it is possible that it was the original rainbowfish in rivers of the Wet tropics region and previous more widely distributed within individual drainages. Subsequent, and relatively recent, invasion [618] by M. spl. splendida may have restricted its distribution to that observed today.
Macro/meso habitat use Cairnsichthys rhombosomoides occurs in small streams with good riparian cover at, or below, 100 m.a.s.l. The average macrohabitat data presented in Table 2 does not truly reflect the distribution of this species within the catchments in which it occurs with respect to elevation and distance from the river mouth, however. Cairnsichthys rhomsomoides occurs in small adventitious lowland streams as well as upland tributary streams and many of the meso-scale habitat parameters listed in Table 2 vary considerably between these two habitats. Small lowland streams empty directly into 5th or 6th order rivers, and are usually (but not always) of low gradient with a mud, sand and fine gravel substrate and with abundant leaf litter (i.e. the type of habitat in which Mugilogobius notospilus is found). Such small streams contain speciose assemblages.
Table 2. Macro/mesohabitat use by Cairnsichthys rhombosomoides. Data derived from the mean habitat characteristics of 32 sites within the Johnstone River and Russell/Mulgrave River drainages sampled over the period 1994–1997. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min. 2
Catchment area (km ) Distance to source (km) Distance to river mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
0.13 0.5 8.1 5 2.0 0.0
Gradient (%) 0.02 Mean depth (m) 0.1 Mean water velocity (m.sec–1) 0
The upland tributaries in which Cairnsichthys occurs tend to be of higher gradient, typified as cascades, with higher water velocities, a substrate composed of large rocks and bedrock within a sand/fine gravel matrix. Such streams tend to contain few species (i.e. Anguilla reinhardtii and Mogurnda adspersa). Notwithstanding these differences, the critical macrohabitat components are a relatively intact riparian canopy and small stream size. As a consequence of the high riparian cover and resultant shade, vegetative cover elements such as macrophytes, filamentous algae, emergent and submerged vegetation are at low abundance. Given that Cairnsichthys is confined to small streams of quite divergent habitat structure, it is probable that their within-drainage distribution is due to biological constraints rather than constraints imposed by factors
207
Max. 62.6 19.0 64.0 100 14.3 90.0 7.33 0.55 0.36
Mean
W.M.
5.45 3.71 29.2 35.3 5.4 56.5
3.16 3.12 38.2 65.5 7.05 53.8
1.02 0.30 0.11
1.15 0.31 0.08
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 4.0 0 0 0 0
40.0 52.0 73.0 73.0 33.9 76.0 67.0
6.5 18.8 24.3 10.9 9.8 17.6 11.9
11.0 17.2 21.3 7.31 11.3 20.7 11.2
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
3.7 3.3 18.0 60.0 9.0 81.2 8.9 11.3 29.0 75.0
0.3 0.3 2.7 5.1 2.9 14.2 2.1 1.9 7.1 19.8
0.3 0.5 4.2 3.2 0.9 16.7 1.2 1.4 6.5 20.6
Freshwater Fishes of North-Eastern Australia
to its use of average water velocities. Although few individuals were collected from the upper water column, it is evident from the diet depicted in Figure 2, that this species does make forays to the surface to capture terrestrial invertebrate prey. This species was infrequently collected over a mud substrate, being most commonly collected from areas of diverse substrate composition dominated by larger substrate sizes.
Whatever the reasons for its bimodal pattern of distribution, the extent of present-day gene flow between upland and lowland populations is of interest. If connectivity is low, then lowland populations – those most at threat from habitat disturbance and acute and chronic water quality degredation – may be at risk in the long term. Microhabitat use Cairnsichthys rhombosomoides was most commonly collected in water between 30 and 50 cm deep (Fig. 1c) and velocities most commonly less than 0.2 m.sec–1 (Fig. 1a). As a consequence of being most commonly recorded from the lower half of the water column (Fig. 1d), the focal point velocity distribution (Fig. 1b) was almost identical
40
(a)
50
This species was infrequently collected from areas greater than 0.2 m from cover and most frequently from within 0.2 m of the substrate (as a consequence of its relative depth use) and from leaf litter. These data suggest that C. rhombosomoides spends much of its time concealed within the substrate or litter, however this is not the case. More frequently, this species occurs in small schools over such areas of potential cover, using them only when threatened.
(b)
The larvae vary in microhabitat use depending on stage of development [1109]. Preflexion larvae, characterised by minor fin development, are confined to areas of zero flow close to the natal habitat. Larvae were rarely recorded from depths greater than 50 cm in both upland (Mena Creek) and lowland (Polly Creek) sites. Larvae always stay close to some form of cover and avoided areas of bright sunlight. Very dense cover is avoided, possibly to reduce the potential for predation by cryptic piscivorous gudgeons. As larvae develop, the range of flows in which they occur also increases. Nonetheless, the larvae avoid areas of flow greater than 10 cm.sec–1.
40
30
30 20
20
10
10
0
0
Mean water velocity (m/sec)
(c)
Focal point velocity (m/sec) 20
20
(d)
15 10
10
Environmental tolerances Information on tolerance to water quality extremes is lacking and data listed below reflects the water quality of the streams in which C. rhombosomoides has been collected.
5 0
0
Total depth (cm)
The data presented in Table 3 indicates that Cairnsichthys rhombosomoides typically occurs in streams of high water quality reflecting the well-forested nature of such streams. The range in water temperatures indicated is typical of small rainforest streams. Although recorded as present in streams typified by a substantial range in dissolved oxygen levels, the mean value listed indicates that the streams in
Relative depth
(e)
(f)
20
40
15
30
10
20
5
10
0
0
Table 3. Physicochemical data for Cairnsichthys rhombosomoides. Data summaries for sites in which present over the period 1994–1997. Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by the Cairns rainbowfish Cairnsichthys rhombosomoides. Data derived from capture records for 840 fish (except focal point velocity where n = 744) from the Johnstone and Mulgrave rivers over the period 1994–1997.
208
Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
15.2 4.91 4.5 5.6 0.21
Max. 28.8 9.96 8.43 63.0 18.1
Mean 21.6 7.58 6.69 28.0 2.01
Cairnsichthys rhombosomoides
this species has low tolerance to elevated salinity, although this needs to be experimentally determined. In general, the waters in which C. rhombosomoides occurs are very clear and leached organic material contributes the bulk of what little colour is present. The maximum NTU value listed in Table 3 was recorded after a rainfall event resulted in substantial downstream transport of sediment originating from an upstream banana plantation. Allen [38] noted that, when in captivity, C. rhombosomoides is sensitive to even small changes in water chemistry
which it occurs are well-oxygenated. The standard error for the mean was small (± 0.18 mg.L–1) indicating that that the minimum value recorded (4.91 mg.L–1) was substantially different from most other readings. The minimum value was recorded in October when water temperature was 28.8°C: the highest recorded at this site. Air temperature at the time of measurement was 32°C, the fourth highest for the sites examined. Such high water temperatures and low dissolved oxygen levels are apparently not frequently experienced. The mean pH recorded was near neutral although the range in pH was substantial. Lowland coastal tributaries tended to be quite acidic (pH 4.5–5.5), whereas upland tributaries, especially those draining basaltic catchments in the Johnstone River were more basic (7.5–8.5). Conductivities were uniformly low and it is probable that
Reproduction The reproductive biology of C. rhombosomoides is similar to other stream-dwelling rainbowfishes in the Wet Tropics region. Fish commence breeding in their first year and
Table 4. Life history data for the Cairnsichthys rhombosomoides. Information on reproductive biology derived from a single study [1108] examining reproduction in one upland population and one lowland population, unless otherwise noted. Information on larval stages drawn from two studies [1093, 1109] undertaken at the same site. Age at sexual maturity (years)
<1 (probably 6–7 months)
Minimum length of ripe females (SL in mm) Gender discernible at 34 mm SL, fully mature fish as small as 36 mm SL, mean length of ripe fish = 47.6 mm SL Minimum length of ripe males (SL in mm)
Gender discernible at 28 mm SL, fully mature fish as small as 28 mm SL, mean length of ripe fish = 52.2 mm SL
Longevity (years)
Probably 2 years, Allen and Cross [43] suggest a maximum life span of 3 years in captivity
Female to male sex ratio during breeding season
Unity
Occurrence of ripe fish
Ripe females present from April to December, males from April to November
Peak spawning activity
September to October
Critical temperature for spawning
September water temperatures 20°C and 22°C for upland and lowland populations, respectively
Inducement to spawn
Given that some spawning females are present throughout most of the year, as are larvae, it does not appear that rising temperature is necessarily a cue for spawning. Peak spawning occurs at a time of stable low flows (see text)
Mean GSI of ripe female (%)
Peak mean GSI = 4.9% in October
Mean GSI or ripe males (%)
Peak mean GSI = 1.7% in September
Maximum fecundity (number of ova)
131–737 depending on size
Fecundity/length relationship
Log (egg number) = 1.88 ± 0.016 (SL in mm); r = 0.515, p<0.05, n = 17
Egg diameter (mm)
1.139 ± 0.021 mm for ovulated, but not water hardened, eggs, n = 9 Egg diameter significantly larger in upland population (~8%)
Frequency of spawning
Heterochronal-batch sizes varied from 8 to 66 eggs
Oviposition sites
Eggs located in root masses
Mating behaviour
Single pair with elaborate display by male
Parental care
None
Time to hatching
7 days in captivity (presumably at 25.5°C) [43], field data lacking
Length at hatching (mm)
Early preflexion larvae 3.46–5.46 mm
Length at free swimming stage (mm)
Late preflexion 5.38–6.85 mm
Length at first feeding
As above
Length at end of larval development (mm)
14.0–15.5 mm
Duration of larval development
? 30 days
Survivorship
Unseasonal increases in discharge cause high levels of mortality in larvae and reproduction is complete by the start of the summer wet-season
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Freshwater Fishes of North-Eastern Australia
Trophic ecology Information on the diet of this species is derived from a single study of 107 individuals collected in August 1992, predominantly from upland tributary sites. The diet is dominated (54.7%) by small terrestrial invertebrates such as ants [1097]. A small proportion was comprised of the adult forms of aquatic Diptera, presumably also taken from the water’s surface. The remainder of the identifiable fraction was composed of chironomid and trichopteran larvae and ephemeropteran nymphs. The relatively large eyes and mouth of this species are assets for a species relying on terrestrial sources of food and confined to wellshaded streams. A high dependency on terrestrial prey is consistent with the distribution of this species being confined to well-vegetated streams. It is probable that the use of terrestrial prey increases in importance with size.
spawning fish are present from April through to December (Table 4). Peak spawning activity is from August to October. Water temperatures at this time are above 20°C (usually 2°C warmer in lowland tributaries) but it is unlikely that rising water temperatures stimulate spawning given that low levels of spawning occur from April onward, at a time when temperatures are dropping. Sexual maturity and gonad development are commensurate with increasing body size. Given that fecundity increases with increasing size, it appears that spawning occurs when females achieve certain size. That GSI levels peak in September simply reflects synchronised growth rates in the maturing female cohort. The eggs are small and numerous. Egg diameter was slightly greater in the upland population where fish were also slightly heavier for a given length. The eggs are deposited in batches within rootmasses. It is probable that the eggs, like those of other melanotaeniids, possess adhesive filaments. The larvae are small at hatching but with little yolk, possess well-developed eyes, a welldeveloped feeding apparatus and gut, and commence feeding shortly after hatching. Larval development is complete at 14–15 mm SL by which time adult meristics (squamation and fin ray counts) are attained.
Conservation status, threats and management Wager and Jackson [1353] list C. rhombosomoides as Rare while the ASFB [117] listed this species as Vulnerable. Although this species has a relatively restricted distribution, many populations are within National Parks within the Wet Tropics World Heritage Area. Threats to this species include water resource development within the Mulgrave River system to supply domestic water for the Cairns region. Changes in flow regime that increase total discharge or the extent of variability of flow during the normally stable low flow period of late winter/spring are likely to negatively impact on spawning success and larval recruitment. Channelisation or infilling of lowland tributaries, unregulated abstraction of water for irrigation, clearing of lowland rainforest for cropping, and urban development may also pose a threat to this species.
Movement No data is available to suggest the extent or phenology of movement in this species. However, a 12-month study [1093] of the response of fish assemblages to experimental defaunation found that C. rhombosomoides readily recolonised such empty habitats in numbers similar to those present prior to defaunation. Movement into the experimental sites was from adjacent reaches and therefore only of limited extent in scale (probably in the order of 100–200 m). Information on the extent of gene flow between isolated populations is needed. Aerial aq. Invertebrates (3.5%)
Cairnsichthys rhombosomoides requires an intact riparian zone and measures are needed to protect the integrity of such areas. Lowland populations are most at threat as a result of increased urbanisation and intensive agriculture, land clearing and expansion of the sugar-cane industry. Upland populations in the Mulgrave River are reasonably secure given the presence of populations in streams within National Parks. However, upland populations in the Johnstone River catchment are not so protected and may face threats in the future from degraded water quality (particularly increased sedimentation and pesticide contamination from horticultural industries) and unregulated water use. While the distributions of C. rhombosomoides and M. s. splendida are not mutually exclusive, these species are probably competitors. Thus changes in flow regime or habitat structure (i.e. loss of riparian integrity) that favour M. s. splendida will probably be to the detriment of C. rhombosomoides.
Unidentified (5.5%) Aquatic insects (36.0%)
Terrestrial invertebrates (55.0%)
Figure 2. The mean diet of Cairnsichthys rhombosomoides. Summary derived from stomach content analysis of 107 fish collected from the Mulgrave River in August 1992.
210
Melanotaenia splendida splendida (Peters, 1866) Eastern rainbowfish
37 245014
Family: Melanotaeniidae
Pectoral fins slightly pointed; caudal fin moderately forked, lobes mildly pointed. Posterior margin of second dorsal fin and of anal fin elongated and pointed in males but not females. Colour variation is marked over the entire range of this subspecies. In general, the body surface is light blue/silver grading to white/silver ventrally. Dorsal surface may be quite dark. Midlateral dark blue/black stripe running from cheek to caudal extremity, but not present or well-developed in all populations. Typically, populations in the Wet Tropics region have a well-developed midlateral stripe whereas populations of eastern Cape York and of the Burdekin River and further south do not. A series of narrow black stripes forming a ‘zig-zag’ pattern is a prominent feature on the flank of fish from the upper Burdekin River. Elsewhere several orange-red stripes between each horizontal scale row may be present, predominantly on posterior half of the body. Green and orange hues also present on body. Fin colour variable ranging from red to yellow, with dark red, yellow or black flecking. Colour in preservative: brownish-grey dorsally, midlateral stripe dark, body pale ventrally; fins pale with darker margins.
Description First dorsal fin: V–VII; Second dorsal: I, 9–14; Anal: I, 17–24; Pectoral: 9–16; Horizontal scale rows: 10–13; Vertical scale rows: 33–38; Predorsal scales: 12–18; Cheek scales: 7–17 [43, 1093]. (But see below for discussion of geographic variation). This species is unlikely to be confused with most other species but it may co-occur with M. eachamensis, M. trifasciata and M. utcheensis in some drainages in the northern part of its range. Figure: adult male, 62 mm SL, South Johnstone River, July 1995; 1996. Melanotaenia splendida is a small, laterally compressed fish rarely exceeding 100 mm SL and 16 g. This species is typically between 60–80 mm SL in length although it is capable of reaching 115 mm SL in the wild [697] and 200 mm SL in captivity [936]. Males grow to a larger size than do females although the relationship between length and weight does not vary between the sexes [1108]. The relationship between length (SL in mm) and weight (g) for Johnstone River population takes the form: W = 1.73 x 10–5 L2.986; r2 = 0.962, n = 1965, p<0.001. Individuals from the upper Burdekin River population are slightly heavier for a given length: W = 2.01 x 10–5 L3.020; r2 = 0.956, n =1880, p<0.001. Mouth terminal and oblique; almost reaching back to anterior margin of eye, 11.2% of SL.
The larvae are about 4 mm at hatching, moderately welldeveloped, with functional eyes, mouth and gut, and with
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Freshwater Fishes of North-Eastern Australia
Burdekin River M. s. splendida are deeper in the body than are populations from elsewhere. The data presented in Table 1 only partly support this suggestion, with this effect being confined to smaller fishes only. However, as indicated above, the Burdekin River population is slightly heavier for a given length than populations from the Johnstone River.
little yolk deposits. Gut coiled and striated in preflexion larvae (in contrast to the larvae of M. eachamensis). Anal fin fold originates behind anal myomere. Melanophores diffusely distributed along dorsal surface. Metamorphosis occurs at 14 mm SL [609, 1093]. Body morphology in this species is highly plastic, varying between the sexes, between individuals from different drainages, between individuals from different habitats within drainages, and with size. In the latter case, the relationship between diagnostically important morphological ratios and body size is rarely linear but varies exponentially with the exponent value varying between 0.666 (for eye diameter) to 1.055 (for peduncle length). Body depth at the pelvic fin is the only parameter to vary linearly with size (exponent = 0.990) [1105]. Table 1 lists the maximum and minimum values for a range of meristic and morphological characters for 358 M. s. splendida from the Wet Tropics region (Bloomfield River to the Herbert River) and 41 individuals from the main channel of the upper Burdekin River. The Wet Tropics sample did not include any individuals from streams in which either M. eachamensis or M. utcheensis were known to occur and there is therefore a low probability that the sample contains hybrid forms.
Systematics Melanotaenia splendida is a member of a widespread and important family of freshwater fishes in Australia, New Guinea and Madagascar. Melanotaenia is a widespread and speciose genus, represented by 13 species in Australia [38, 52, 904]. Allen [32] recognised it as one of the most derived genera within the family. Recent phylogenetic analysis of mtDNA cytochrome b and tRNA control region sequence data is broadly consistent with the current taxonomy but also indicates that a clade restricted to northern New Guinea, consisting of M. affinis, M. japensis and three species of Glossolepis, is polyphyletic [905]. Melanotaenia splendida was previously recognised as being composed of a number of geographically isolated subspecies: M. splendida splendida (eastern rainbowfish), M. s. inornata (chequered rainbowfish), M. s. tatei (desert rainbowfish), M. s. rubrostriata (red-striped rainbowfish), M. s. australis (western rainbowfish) and M. s. fluviatilis (Murray-Darling rainbowfish). Melanotaenia splendida fluviatilus was removed from this group and elevated to full species status (as M. fluviatilus) by Crowley et al. [351] (in the process reinstating M. duboulayi). The recent investigations of McGuigan et al. [905] further challenge the view that the species consists of the five remaining subspecies, clearly showing that M. s. australis did not belong to this species group but was part of a separate clade consisting of M. s. australis, an undescribed species from North Queensland (now recognised as M. utcheensis), M. eachamensis, M. duboulayi and M. fluviatilus. This subspecies (M. s. australis) is now recognised as two valid and distinct species, M. australis (Castenau, 1873) and M. solata Taylor, 1964 [52]. The clade in which M. splendida was placed by McGuigan et al., contained the remaining subspecies plus M. parkinsoni, M. ogilbyi and M. sexlineata from southern New Guinea and M. maccullochi from northern Australia and southern New Guinea. This clade was poorly resolved however, suggesting that the evolution of species and subspecies within it is relatively recent [905]. In addition, substantial morphological, meristic and colour variation between geographically distant populations of M. s. splendida exists, indicative of substantial genetic diversity within the species and/or a highly variable and plastic phenotype. Hurwood and Hughes [618] demonstrated that M. s. splendida has experienced a recent (in the last 100 000–120 000 years) and rapid
Table 1. Meristic and morphological variation between geographically isolated populations of the eastern rainbowfish Melanotaenia splendida splendida [1093]. Proportions given as percentage of standard length. Character
Wet Tropics region
Burdekin River
Dorsal spines Dorsal rays Anal rays Pectoral rays
5–7 10–14 17–24 11–16
5–7 10–12 18–21 12–16
Horizontal scale rows Vertical scale rows Predorsal scales Cheek scales
10–13 33–38 12–18 7–17
10–12 34–36 14–16 9–16
25–91 23.3–44.4 22.8–38.0 24.4–35.3 6.6–9.6 7.3–12.2 9.1–15.2 13.4–21.0 43.7–51.1
29–67 29.1–35.8 27.0–32.0 25.9–30.7 7.3–8.9 8.5–11.7 10.5–12.4 14.8–19.5 45.7–50.5
Standard length (mm) Body depth – male (%) Body depth – female (%) Head length (%) Snout length (%) Eye diameter (%) Caudal peduncle depth (%) Caudal peduncle length (%) Predorsal distance (%)
These data indicate that body form and meristic characterisics are highly variable, even within a relatively small an area as the Wet Tropics region. Moreover, the extent of variation that occurs within a region can be greater than that between regions. Allen and Cross [43] suggest that
212
Melanotaenia splendida splendida
characteristic of M. s. inornata. The extent to which this character can be validly used to distinguish between subspecies is therefore questionable. In the phylogenetic relationship depicted in McGuigan et al. [905] (their Figure 3b – boot-strapped maximum parsimony phylogeny based on combined cytochrome b and tRNAPro control region sequence), it is noteworthy that one specimen of M. s. splendida from the Burdekin River grouped with a Northern Territory M. s. tatei specimen whereas another was included in an unresolved group consisting of specimens of M. s. splendida from the Atherton Tablelands, one specimen of M. s. inornata and one of M. s. rubrostriata. Moreover, in a study of genetic variation in M. s. splendida on the Atherton Tablelands by Hurwood and Hughes [618], one specimen from the Walsh River (a tributary of the Mitchell River and typically considered within the range of M. s. inornata) was identified as being a common splendida haplotype. It could be argued that the Walsh River lies on the border between the distribution of both subspecies and the presence of an eastern haplotype in this region is not particularly surprising. However, Hurwood has identified this same haplotype in the Leichhardt River, which drains to the Gulf of Carpentaria, and in the centre of what is traditionally considered the distribution of M. s. inornata (D. Hurwood, pers. comm.).
expansion of range that may have contributed to the genetic diversity observed in north-eastern Queensland. Considerably more research is required to understand the evolution of forms within the group and may be useful in understanding the recent evolutionary history of other groups also. The Australian subspecific populations of M. splendida are distinguished by a combination of differences in distribution, colour and slight differences in meristics. Melanotaenia splendida splendida is said to be restricted to rivers draining to the east of the Great Dividing Range, M. s. inornata to streams draining to the Gulf of Carpentaria and the Arafura Sea, and to the top of Cape York Peninsula, and M. s. tatei is restricted to central Australia, primarily to rivers draining into Lake Eyre [43, 52]. It can be seen from Table 2 that morphological differences between the subspecies are very slight and really only serve to define M. s. tatei as being distinctive by virtue of possessing fewer dorsal fin rays, fewer cheek scales, more predorsal scales, a longer caudal peduncle and a more slender body. Table 2. Meristic and morphological variation in the subspecific forms of Melanotaenia splendida [43]. Proportions given as percentage of standard length. (Note that ranges for some characters differ from those listed in the description above.) Character
M. s. splendida
M s. inornata
M s. tatei
Dorsal spines Dorsal rays Anal rays Pectoral rays
5–8 9–13 17–22 11–16
5–8 9–12 17–21 12–16
5–8 8–11 17–21 13–16
Horizontal scale rows Vertical scale rows Predorsal scales Cheek scales
10–12 33–36 14–18 8–15
10–12 31–35 14–19 9–16
10–12 34–37 17–22 7–12
33.7–48.8 32.7–40.8 25.7–29.9 7.3–9.7 7.1–11.2 9.9–11.8 11.4–15.0 10.9–18.6 46.2–52.9 48.0–55.7
30.5–35.5 26.4–32.1 24.0–26.9 6.9–8.1 7.2–9.2 8.2–9.9 10.8–12.2 15.3–21.0 44.3–48.0 48.2–54.0
Body depth – male (%) 29.0–40.3 Body depth – female (%) 26.9–35.2 Head length (%) 24.4–30.5 Snout length (%) 7.3–10.8 Eye diameter (%) 7.2–10.8 Interorbital width (%) 8.8–10.5 Caudal peduncle depth (%) 10.6–13.2 Caudal peduncle length (%) 14.3–20.8 Predorsal distance (%) 45.2–51.0 Preanal distance (%) 48.0–54.7
Distribution and abundance Clearly, the pattern of genetic and morphological variation within this species is very complex and, to our minds, a belief in the existence of subspecific differences in morphology, distribution and genetics between M. s. splendida and M. s. inornata is very difficult to sustain at this stage. Nonetheless, for those more disposed to recognising subspecific forms, the discussion below considers only that taxon which most authors traditionally view as the subspecific form M. s. splendida. This subspecies is very widely distributed along the east coast of Queensland [43]. Some authors suggest that the southern limit of M. s. splendida is the Burnett River [1173] or the Elliott River [825]. Kennard [700] believed such records were attributable to M. duboulayi. Both Allen [38] and Wager [1349] list the southern limit of its distribution as the Boyne River near Gladstone, although Hansen [525] reported the presence of M. s. splendida slightly further south in small coastal streams of the Baffle Creek drainage basin. The location of the northern limit of M. s. splendida is uncertain. Pusey et al. [1099] recorded M. s. splendida in the Pascoe River although Herbert et al. [571] believed this population to be the subspecies M. s. inornata.However, other authors have recorded M. s. splendida as far north as the Pascoe and Lockhart rivers [1349]. Populations of M. s. inornata do occur east of the Great Dividing Range in
According to Allen and Cross [43], M. s. splendida and M. s. inornata differ only on the basis of colour pattern and differences in body depth (deeper in the latter). However, it can be seen from Table 1 that M. s. splendida from the Wet Tropics region also approach the deep body form
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Freshwater Fishes of North-Eastern Australia
Cape York Peninsula [571]. For example, this subspecies is the dominant rainbowfish in aquatic habitats of the Cape Flattery region [1088]. Melanotaenia s. splendida is abundant wherever it occurs. It comprised 52%, 38% and 23% of the total catch in a study of the fauna of the Pascoe, Stewart and Normanby rivers, respectively [1099] and 18% of the total catch in floodplain lagoons of the Normanby River [697]. This species comprised 39% of the catch in the Annan River [599]. Further south in the Wet Tropics region, it was the most abundant species in an extensive survey of the region, comprising 28.4% of the total number of fish collected and being recorded in 62 of 93 sites and in all but one of the drainage basins studied [1087]. It was not recorded from the short streams of Cape Tribulation but is known to occur in these streams (G. Werren, pers. comm.). Table 3. Distribution, abundance and biomass data for Melanotaenia splendida splendida in two rivers of the Wet Tropics region. Data summaries for a total of 5021 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. Total % locations % abundance Rank abundance % biomass
44.9 14.3 (22.8)
Mulgrave River
Johnstone River
47.7
62.5
Macro/mesohabitat use Allen [38] suggests that the preferred habitat of eastern rainbowfish consists mainly of small streams. However, over its very wide distribution, this species occurs in a wide variety of stream sizes from small streams up to large, lowgradient lowland rivers including wetland habitats and floodplain lagoons [697, 1087, 1098]. Within the Burdekin River, it is significantly more abundant in reaches with little stream flow [1098] and this preference for habitats with sluggish currents seems to be the general requirement across all studies reviewed.
10.3 (18.9) 15.5 (26.7)
2 (2)
5 (3)
2 (1)
1.9 (6.3)
1.3 (5.8)
2.3 (4.2)
8 (6)
6 (5)
Rank biomass
6 (5)
Mean density (fish.10m–2)
1.43 ± 0.21
1.01 ± 0.22 1.62 ± 0.02
Mean biomass (g.10m–2)
3.69 ± 0.58
3.45 ± 0.75 3.80 ± 0.03
is susceptible to bias depending on collecting method used. For example, in the Burdekin River [1098], this species comprised 32% of the total in electrofishing samples but contributed 49% of the seine-netting total. Even greater disparity between methods was reported by Burrows and Tait [260]. Their study, in tributary drainages of the upper Burdekin River, found that rainbowfish contributed 1.3%, 12.4%, 24%, 37.6% and 82% of bait trap, gill-net (with 25 mm mesh panels), dip-net, electrofishing and seine-netting catches, respectively. It is our experience that single pass electrofishing nearly always underestimates the abundance of M. s. splendida because of this species’ vagility, swimming speed and preference for open water. The difficulty in collecting this species by some methods, particularly those methods favoured by some agencies (i.e. single pass electrofishing) or consultants (i.e. fish traps), highlights the need for rigorous sampling especially in studies aimed at determining environmental condition or river health. Melanotaenia splendida splendida is tolerant of environmental degradation, particularly the loss of riparian vegetation and changes in habitat due to impoundment, and may have potential as an indicator species in rapid assessments.
Melanotaenia s. splendida is both widespread and abundant in the Johnstone and Mulgrave rivers (Table 3), contributing about 14% of the total number of fish collected from these rivers. This species is dominant in those sites in which it occurs in the Johnstone River, contributing over one-quarter of the total number of fish and 4.2% of the biomass. It is less dominant in the Mulgrave River however, being only the fifth most abundant species overall and third most abundant species in those sites in which it occurs. Maximum density estimates for this species were 3.08 fish.10m–2 and 7.23 fish.10m–2 for the Mulgrave and Johnstone rivers, respectively.
The generalist nature of habitat use is evident from the data presented for drainages of the Wet Tropics region also (Table 4). Melanotaenia s. splendida occurred in a large range of streams sizes (order 1 to 6) and over a wide range of elevation (5–750 m.a.s.l.). Downstream limits to distribution and abundance are probably related more to predation than aversion to particular environmental conditions. Pusey and Kennard [1087] suggested that this species was one of the few able to negotiate large waterfalls and colonise upland habitats. Recent genetic investigations question the generality of this suggestion and upland populations may have arrived in rivers of the Tablelands by other mechanisms, such as drainage rearrangement, not involving upstream movement [618].
The relative abundance of M. s. splendida is usually high, often being the most abundant species in most environments. However, the estimation of rainbowfish abundance
Although occasionally present in high gradient streams (i.e. maximum gradient of 7.3%), the average gradient of the streams in which it occurs in the Wet Tropics region
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Melanotaenia splendida splendida
There is little indication that M. s. splendida is greatly dependent on any one type of cover element and the habitats in which it occurs contain a variety of types and amounts of cover. However, the difference between the mean and weighted mean coverage of submerged vegetation (composed entirely of the introduced para grass Brachiaria mutica), shown in Table 4, suggests that this species achieves greater abundance in habitats relatively free of this weed.
is much lower (0.5%), with a slight tendency for M. s. splendida to be more abundant in reaches with a more gentle gradient. Four other species of rainbowfish (M. maccullochi, M. eachamensis, M. utcheensis and C. rhombosomoides) also occur in the Johnstone River drainage and although syntopy does occur occasionally, there is a general tendency for distributions to be non-overlapping at the mesohabitat scale, with M. s. splendida being more abundant in the larger, less steep and more open streams. Melanotaenia maccullochi in the Johnstone River is found only in small, lowland low-gradient acidic streams.
It must be emphasised that the data presented in Table 4 concerns habitat use in perennial rainforest streams of the Wet Tropics region. Given the widespread distribution of this species and the generalised habitat use indicated by Table 4, it is probable that a much wider array of habitat conditions is used. For example, M. s. splendida is one of the few species that tolerates, and is even advantaged by,
Melanotaenia s. splendida is found in a variety of habitat types, from cascades to pools, and accordingly, this species occurs over a wide range of substrate types. The average substrate composition is very diverse, reflecting the wide range of habitat types in which it occurs. In larger, more seasonal rivers of Cape York and central Queensland, the substrate composition is much more dominated by the finer particle sizes.
50
Table 4. Macro/mesohabitat use by the eastern rainbowfish Melanotaenia splendida splendida in the Wet Tropics region. Summaries drawn from habitat data from 56 sites in the Johnstone, Mulgrave/Russell and Tully drainages and weighted means derived from macro/mesohabitat data for 2016 individuals. Parameter
Min.
0.13 Catchment area (km2) Stream order 1 Distance to source (km) 0.5 Distance to river mouth (km) 10.1 Elevation (m.a.s.l.) 5 Width (m) 2.8 Riparian cover (%) 0 Gradient (%) 0.001 Mean depth (m) 0.11 Mean water velocity (m.sec–1) 0
Max.
Mean
W.M.
515.5 6 67.0 104.0 750 35.0 99
73.6 3.7 14.4 38.7 103.2 9.7 35.2
74.9 3.8 15.9 47.1 194.0 10.2 31.5
7.33 0.91 0.56
0.50 0.40 0.16
0.40 0.46 0.13
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48 88 72 56 55 81 68
7.5 18.4 22.5 14.5 13.9 17.0 6.6
9.2 17.3 20.9 12.6 11.1 19.3 10.7
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Small woody debris (%) Large woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
23.7 6.9 33.0 63.1 10.0 81.2 12.3 10.5 35.0 75.0
1.3 0.3 2.3 9.0 0.6 10.4 2.0 2.3 5.6 13.4
1.7 0.5 2.5 6.3 0.5 8.2 1.7 2.3 5.0 12.1
(b)
(a)
50
40
40
30
30
20
20
10
10
0
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
20
20
10
10
0
0
20
(e)
Relative depth
Total depth (cm)
(f) 20
15 10
10
5 0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Melanotaenia splendida splendida. Data derived from capture records for 1234 fish from the Johnstone, Mulgrave/Russell and Tully rivers over the period 1994–1997.
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Freshwater Fishes of North-Eastern Australia
Table 5. Physicochemical data for eastern rainbowfish M. s. splendida. Data summaries derived from: 1) a study undertaken during the dry season of 1990 in the Pascoe, Stewart and Normanby rivers of Cape York Peninsula [1099]; 2) a study undertaken in six floodplain lagoons of the Normanby River over a six month period in 1993 encompassing the start and end of the dry season [697]; 3) unpublished data from a study of fish assemblages in the Johnstone and Mulgrave rivers of the Wet Tropics region over the period 1994–1997 [1093]; and 4) a study of fish assemblages at 12 sites in the Burdekin River over the period 1989–1992 [1093].
the change from lotic to lentic habitat conditions caused by impoundment. In general however, M. s. splendida is best considered as preferring larger streams with low water velocities. This species is moderately tolerant of disturbance such as reductions in riparian canopy. Microhabitat use Data shown in Figure 1 was derived from records for 1234 fish collected from rivers of the Wet Tropics region and as such the patterns therein may not apply entirely to other regions. Most individuals were collected from areas of low flow (<0.3 m.sec–1) and most commonly, from areas with no discernible flow. Focal velocities were similar to average velocities due to the generally low currents speeds overall and because the most common position in the water column of M. s. splendida was around that at which average water velocity occurs. Most individuals were found in the middle two-quarters of the water column.
Parameter
Min.
Max.
Cape York Peninsula (n = 12) Temperature (°C) 21.0 29.5 Dissolved oxygen (mg.L–1) 6.8 10.0 pH 6.09 8.35 Conductivity (µS.cm–1) 20 420 Turbidity (NTU) 0.1 3.3
Within streams of the Wet Tropics region, most rainbowfish were collected from depths of between 20–70 cm with few recorded from areas shallower than 20 cm and deeper than 80 cm. The upper limit may reflect a bias due to the absence of many sites with depths greater than 1 m in our study. In floodplain lagoons of the Normanby River, M. s. splendida frequently occurs in depths greater than 2 m, although most were collected in water less than 1.5 m [697]. In this habitat type, it was rare for rainbowfish to be collected from the bottom 70% of the water column, perhaps in response to the hypoxic conditions existing at such depths. Rainbowfish were collected over a variety of substrate types, reflecting the diversity of habitats in which it occurs (Table 4), and indicating little preference for any particular substrate composition.
Mean 25.4 8.0 7.07 127 1.46
Floodplain lagoons Normanby River (n = 11) Temperature (°C) 22.9 28.3 25.2 Dissolved oxygen (mg.L–1) 1.1 7.1 3.39 pH 6.0 7.5 6.87 Conductivity (µS.cm–1) 80.9 252.5 163.5 Turbidity (NTU) 2.1 7.7 4.9 Wet Tropics Region (n = 79) Temperature (°C) 17.1 Dissolved oxygen (mg.L–1) 4.91 pH 5.13 Conductivity (µS.cm–1) 6.0 Turbidity (NTU) 0.25 Burdekin River (n = 41) Temperature (°C) 15 Dissolved oxygen (mg.L–1) 1.1 pH 6.87 Conductivity (µS.cm–1) 49 Turbidity (NTU) 0.6
Melanotaenia s. splendida is predominantly an open-water species but is frequently found schooling in close proximity to cover, of which it makes use when threatened (Fig. 1f).
29.7 11.6 8.38 65.6 12.19
23.0 7.08 6.98 36.3 1.79
32.5 10.8 8.47 790 16.0
26.3 6.77 7.73 390 3.5
that determined experimentally and reported above. For example, 29.7°C was the maximum water temperature recorded in rainforest streams of the Wet Tropics region (over the period 1994 to 1997) and moribund fish were observed on this occasion: although depressed oxygen levels at this time may have been a contributing factor also. No data on the lower temperature tolerance limit of this species is available, although low temperatures have been suggested to be important in setting the southern distributional limit for M. s. splendida [1105] and southern distributional limits for other rainbowfishes [43]. Occasional frosts on the Atherton Tablelands may result in water temperatures approaching 10°C and captive rainbowfishes die at this temperature. The incidence of fungal infection in rainbowfish populations in the Wet Tropics region is greatest during the winter months [1093].
Environmental tolerances Melanotaenia splendida splendida is one of the few northeastern Australian fish species for which tolerance data of any kind exist. LD50 temperatures of 34.4°C and 31.4°C for adult (53–71 mm) and juvenile (24–32 mm) fish, respectively, have been determined experimentally [174]. Tolerance to elevated temperatures may be slightly higher in wild populations of some regions. For example, summer water temperatures frequently exceed 31°C in the Burdekin River (and elsewhere; i.e. Black-Alice River [176]) and yet on such occasions, we have seen little indication of heat-related mortality. Conversely, populations from some regions may exhibit a reduced tolerance to elevated water temperatures than
216
Melanotaenia splendida splendida
values listed in Table 5 occurred during a runoff event and it is not known how long such high turbidities might be tolerated. However, rainbowfish are present in the highly turbid waters occurring in the south-western portion of the Burdekin drainage (i.e. Belyando River) and water bodies in which M. s. splendida occurs in this river range in turbidity from 172 to 520 NTU [256].
Data presented in Table 5 suggest a preference for welloxygenated waters, however it is evident that low dissolved oxygen levels are experienced in some habitats. Kennard [697] was uncertain whether the lagoons of the Normanby River floodplain remained stratified throughout the day and whether the observed hypoxia persisted for an extended period. Nonetheless, this species was abundant in these habitats. Melanotaenia s. splendida has been recorded in wetlands of the Tully Murray system in which dissolved oxygen in the bottom layers had dropped to 0.2 mg.L-1 (i.e. almost complete anoxia) [583]. Fish probably avoid such anoxic conditions and stay in the upper water column. A dissolved oxygen level of 4 mg.L–1 would probably be adequate to protect eastern rainbowfish populations in most circumstances. It may not be high enough for populations in rainforest streams of the Wet Tropics region however.
It is clear that M. s. splendida tolerates a large range of water quality conditions and this probably accounts in part for its widespread distribution and varied habitat use. It would be extremely useful to know something of its tolerance to pesticides and herbicides and thus allow better examination of its potential as an indicator species.
The range in water acidity across the different regions given in Table 5 is substantial (5.13–8.47) and indicates a well-developed tolerance to a variety of pH conditions despite mean values tending to be around neutral. The range in pH recorded for the Cape York populations (range = 2.35 units) and for the Burdekin River (1.60 units) is much less than that recorded across the three regions (range = 3.34 units), suggesting that different populations may be adapted to localised water conditions and may not tolerate as wide a range of conditions as is recorded for the subspecies over its entire range. However, it is noteworthy that the range encountered within the streams of the Wet Tropics region (3.25 units) is almost as great as that over the three regions. Tolerance to elevated salinity varies between adult and juvenile fishes and according to acclimation history [174]. Juvenile rainbowfish do not survive abrupt transfer to salinities of 9‰ and adult rainbowfish are unable to tolerate abrupt transfer to salinities of 15‰, dying within 12 hours of transfer. Gradual acclimation improves survivorship but only marginally so: juvenile fish are able to tolerate 17.8‰ for 14 days, adults are able to tolerate 35.5‰ for five days [174]. Wild populations have been recorded from salinities as high as 13 500 µS.cm–1 (approx. 13‰) [1085] and 15.2‰ [176]. Given such a tolerance, M. s. splendida is likely to be able to withstand short-term exposure to seawater in tidally influence habitats and perhaps even move through brackish estuarine habitats. However, it is clear that the eastern rainbowfish is most frequently collected from freshwater and tolerates very low levels of dissolved solutes (ie. 6 µS.cm–1) as well as more elevated levels within the freshwater spectrum.
Reproduction Information concerning the reproductive biology of M. s. splendida is available for two river systems of contrasting hydrology (Table 6). The Black-Alice River near Townsville is hydrologically variable. Lowland populations in this river are reproductively active throughout the year although peak spawning occurs during the wet season [173]. This pattern is also observed in lowland populations of M. s. inornata [193]. In contrast, although a proportion of the populations present in rainforest streams of the Wet Tropics region are reproductively active year-round also, the majority of reproduction occurs in the warmer months leading up to the wet season [308]. Larval mortality is very high at the beginning of the wet season in this region, particularly in deeply incised streams [1109]. In both regions, fish mature at small size and breed in their first year. It is unlikely that many individuals live in excess of two years. There is little indication of a critical spawning temperature although little spawning has been observed in temperatures below 20°C and 21°C in the Johnstone and Black-Alice river, respectively. Beumer [173] believed lengthening photoperiod was more important as a spawning stimulus than was increasing temperature. In the Johnstone River, spawning commences after attainment of set size limits rather than in response to any environmental cue [308]. Nonetheless, the majority of larvae are produced during periods of predictably low and stable flows. Males perform elaborate courtship displays and compete for females. Melanotaenia s. splendida is a moderately fecund species, although peak mean female GSI values (4–5%) are not especially high. This species is a heterochronal spawner with the eggs being produced in batches (up to 14% of total egg number), thus instantaneous GSI values do not fully reveal the extent of maternal investment. Egg number and batch size increase with increasing female body size. It
The data presented in Table 5 indicate that eastern rainbowfish are found in waters of a range in clarity. The peak
217
Freshwater Fishes of North-Eastern Australia
Table 6. Life history data for the eastern rainbowfish Mealnotaenia splendida splendida. Data are drawn from studies undertaken in the Johnstone River (JR) [1093] and the Black-Alice River (BAR) [173], and detailed in the text. Age at sexual maturity (months)
<1 (probably 6–7 months)
Minimum length of ripe females (mm)
JR – 38 mm (mean = 55.2) BAR – 38 mm (range = 38–101)
Minimum length of ripe males (mm)
JR – 44 mm (mean = 75) BAR – 38 mm (range = 38–105)
Longevity (years)
1–2, rarely 3 years, longer in captivity
Sex ratio
BAR – 1:1 with occasional female excess in period leading up to wet season
Occurrence of ripe fish
JR – year round BAR – year round
Peak spawning activity
JR – strongly focused between August and November BAR – strongly focused between December and February
Critical temperature for spawning
JR – varies depending on position in catchment, generally 20°C BAR – temperatures above 21°C
Inducement to spawning
JR – attainment of minimum reproductive size limit, little evidence of environmental cues although spawning occurs during period of stable low flow BAR – unknown but increased photoperiod stimulates increased spawning activity
Mean GSI of ripe females (%)
JR – 3.7% BAR – 3.0%
Mean GSI of ripe males (%)
JR – 0.7% BAR – 0.4%
Fecundity (number of ova)
JR – maximum fecundity of 1655 eggs for 70 mm SL fish (yolked eggs only)
Fecundity/length relationship
JR – log (egg number) = 1.86 + 0.018 (SL in mm); r = 0.644, p<0.001, n = 185
Egg size (mm)
JR – 1.124 mm for ovulated unfertilised eggs; many size classes of eggs present in ovary BAR – size of ovulated eggs not given, largest eggs present 0.8–1.0 mm, fertilised and water-hardened eggs ranged from 0.95–1.73 mm
Frequency of spawning
JR – continuous when temperatures >20°C although majority of spawning complete before wet season. Eggs produced in batches of 2–177 eggs BAR – spawning period suggested to be 10–14 days
Oviposition and spawning site
Adhesive eggs deposited amongst aquatic vegetation or root masses
Spawning migration
BAR – upstream migration at onset of wet season
Parental care
Absent – parents will eat young
Time to hatching
BAR – 7–12 days, temperature dependent
Length at hatching (mm)
JR – early preflexion larvae range from 3.92–4.62 mm BAR – 2.96 mm (range = 2.1–3.47)
Length at free swimming (mm)
As above
Length at feeding
Between 4–5 mm (mid-preflexion)
Duration of larval development
?
Length at metamorphosis
10–14 mm
Survivorship
Very high larval mortality recorded at the onset of the first wet season flood
feeding prior to flexion of the notochord [308]. Larvae are capable of swimming almost immediately upon hatching [609] but remain in very low flow environments until metamorphosis is completed [1109]. Channel morphology, particularly the degree to which the channel is constrained by deeply incised banks, and the availability of flow refuges (eddies and backwaters) are important determinants of flow-related mortality. Reproduction in Wet Tropics streams may continue well into the wet season in those habitats offering some protection from elevated flows (i.e. backwaters and anabranch channels) [1109]. Further information on reproduction and early develop-
is probable that batches are fully voided before the next cohort develops. The eggs possess adhesive filaments, allowing them to be deposited safely amongst the leaves or water plants or amongst root masses. Egg size is apparently geographically variable, being larger in the stable streams of the Wet Tropics region. Parental care is lacking and hatching occurs after 7–12 days. Humphrey et al. [609] report more rapid embryonic development: 3–9 days, with ~60% of each batch hatching after five days at 28 ± 1°C. Larvae are small and undeveloped at hatching but possess little yolk reserves. The eyes, mouth and gut develop rapidly and it is probable that this species commences
218
Melanotaenia splendida splendida
ment of M. s. inornata can be found in Crowley and Ivantsoff [344]. Movement Limited information concerning the extent and pattern of movement in this species is available. An upstream migration at the commencement of the wet season has been recorded in the Black-Alice River near Townsville [173]. Lateral migrations in floodplain environments are reported in the Normanby River [697]. Upstream movement through a fishway on the Fitzroy River was detected over many months but most commonly occurred during the period from November to April [1274]. The total number of individuals using this fishway (88) was low, however. Upstream migrations to dry season refugia have been recorded for the closely related subspecies M. s. inornata in the Northern Territory, with migration occurring during daylight hours and at rates of between 4.8 and 5.4 km.day–1 [190]. No evidence to suggest migration in areas with perennial flow (i.e. Wet Tropics) but it may occur. Further research is required to assess the extent of movement of this species in more seasonal Queensland rivers and on its ability to ascend and descend fishways. Trophic ecology Data presented in Figure 2 were derived from gut analysis of a total of 2567 individuals drawn from four separate studies: three rivers of Cape York Peninsula (n = 445, dry season only) [1099]; floodplain lagoons of the Normanby River (n = 211, combined early and late dry seasons) [697]; Annan River (n = 6) [599], two rivers of the Wet Tropics region (n = 256, dry season only) [1097]; and the Burdekin River (n = 1681, over the period 1989–1992) [1093]. Fish (0.1%) Macrocrustaceans (0.1%) Molluscs (0.2%) Microcrustaceans (1.5%) Other macroinvertebrates (2.1%) Unidentified (12.9%)
Terrestrial invertebrates (12.3%)
Aquatic insects (19.2%)
Aerial aq. Invertebrates (2.5%) Terrestrial vegetation (1.7%) Detritus (2.3%) Aquatic macrophytes (2.6%)
Algae (42.5%)
Figure 2. The mean diet of the eastern rainbowfish Melanotaenia splendida splendida. Data derived from stomach content analysis of 2599 individuals from several northern Queensland rivers and encompassing riverine and floodplain habitats (see text for details).
219
Melanotaenia splendida splendida is an omnivorous feeder taking small aquatic invertebrates (such as chironomid larvae, ephemeropteran nymphs, trichopteran larvae) from the stream-bed, as well as aerial forms of aquatic insects and terrestrial insects (especially ants) from the water’s surface. Collectively, these two components account for 34% of the diet. The single largest component of the diet is algae, comprising almost 43% of the diet. In general, filamentous algae was the most important source of material within this category although diatoms were important in the diet of fish from the South Johnstone River (58% of dry season diet, n = 94) and in the late dry season diet of rainbowfish in floodplain lagoons of the Normanby River (19%, n = 87). Aquatic macrophytes (2.3%) were also consumed occasionally by M. s. splendida. The extent of herbivory varies with age and size, and probably according to the availability of other food sources. For example, the diet of fish between 15–30 mm SL (n = 233) in the Burdekin River contained 25% filamentous algae, whereas the diet of fish between 31–50 mm SL (n = 578) contained 41%, and that of fish >51 mm SL (n = 868) contained 68% filamentous algae. Temporal variation in the importance of herbivory was also evident in the Burdekin River. During periods of low flow, algal consumption rose to an average of 62% over all age classes but decreased to 45% when flows were elevated. In part, this effect was due to temporal changes in the size distribution of the population but also was related to an increased abundance of small invertebrate prey during the wet season. Kennard [697] also noted temporal variation in dietary composition in floodplain lagoons. At the end of the wet season, herbivory and planktivory contributed 9.4% and 22.3% of the diet, respectively. By the late dry season, however almost no planktonic crustaceans were present in the diet (0.8%) whereas herbivory had increased in importance to 30.4%. In addition to the temporal variation in diet discussed above, substantial differences between diets across the four studies (and equating primarily to habitat-related differences) were noted. For example, terrestrial invertebrates were very important to the floodplain fishes (20.5%), moderately important in the low-gradient seasonal rivers (12.3% and 10.6%, for rivers of Cape York Peninsula and the Burdekin River, respectively) but comprised only 2.2% of the diet in the higher-gradient rainforest rivers. Microcrustacea (mostly Cladocera) were all but absent from the diet of riverine populations but comprised 12.3% of the diet of the floodplain population. These data indicate that the generalism discussed above with respect to habitat use extends to feeding ecology also. Eastern rainbowfish are omnivorous and possess sufficient flexibility in feeding modes to allow them to track changes in the
Freshwater Fishes of North-Eastern Australia
fishes such as barramundi, eels, mangrove jack, sooty grunter, spangled perch, fork-tailed catfish and jungle perch. Piscivorous birds, especially kingfishers, also eat this species.
availability or abundance of different prey at different levels of the water column, in different habitats, and as food availability changes throughout the year. Furthermore, in addition to the habitat-based and ontogenetic variability in diet reported above, rainbowfish in the Burdekin River exhibit substantial phenotypic variation in prey choice. The stomachs of many individuals contain only one prey type such as ants or dragonfly eggs whereas others may contain only chironomid midge larvae for example. This suggests that this species forages on a particular food type within a patch until satiated. Bunn et al. [248] noted considerable individual variation in isotopic signatures among rainbowfishes in a lowland stream of the Wet Tropics region suggesting substantial variation in diet among individuals in this region also. Given that variation in isotopic ratios represents differences in diet integrated over a medium-term period (i.e. three months), this observation suggests that individuals remain faithful to a particular diet within the array of potential diets available to this species (within the constraints imposed by body and mouth size, and food availability) for a number of months. Differences in the content of individual stomachs, in contrast, represent variation at much shorter time scales (i.e. hours or days). The substantial phenotypic variation suggested by these observations may be one reason why M. s. splendida is such a successful species able to reach high abundance levels.
Conservation status, threats and management Melanotaenia splendida splendida is listed as NonThreatened by Wager and Jackson [1353]. This taxon is probably very secure by virtue of its widespread distribution, abundance and broad environmental tolerance. Eastern rainbowfish prefer low-flow environments, especially for reproduction and development. Care should be taken when assessing the environmental flow requirements of this species given that its reproductive biology (in particular) varies from region to region in relation to regional variation in hydrology. Changes in the seasonality of flows (i.e. through supplementation or downstream releases to satisfy dry season irrigation demands) are likely to negatively impact on this species, especially on larvae and juveniles. In those rivers in which spawning occurs during the period when flooding is most likely, floods may greatly expand the habitat available to juveniles and thus increase recruitment success. Flooding may also be necessary to allow fish to move between river channel and floodplain habitats. This species will persist and thrive in impounded habitats. This species may have considerable value as an indicator species but more information concerning its tolerance to water quality extremes and to biocide contamination is needed.
Melanotaenia splendida splendida is consumed by other
220
Melanotaenia duboulayi (Castelnau, 1878) Duboulay’s rainbowfish, Crimson-spotted rainbowfish
37 245004
Family: Melanotaeniidae
becoming deeper-bodied with age. Mouth oblique, upper jaw protruding, mouth extending back almost to below anterior margin of eye. Conical to canine-like teeth in jaws, several rows extending outside mouth; teeth on vomer and palatines. Head moderate in size, eye relatively large. Scales large, extending to cheek. Origin of first dorsal fin between origins of pelvic and anal fins; origin of second dorsal behind origin of anal fin. First and second dorsal fins separated by small gap. Caudal fin slightly forked. Sexually dimorphic. Males with higher first dorsal fin; tips of anal and dorsal fins pointed in males, rounded in females. Males with deeper bodies and brighter body colours, especially when mating. Colour patterns vary depending on locality. Dorsal surface generally olivebrown, sides silvery to greenish-blue, ventral surface white, yellow-orange towards tail. Most scales with dusky margins. Thin, reddish stripe between each row of scales (faint or missing in females); bright red spot on upper operculum. Diffuse black midlateral stripe often present. Fins clear in juveniles and females; males often with red spots on caudal, dorsal and anal fins. Courting males often with blackish margins on fins [38, 39, 52, 351].
Description First dorsal fin: V–VIII; Second dorsal: I, 8–13; Anal: I, 15–21; Pectoral: 12–15; Pelvic: 5; Caudal: 15–17 segmented rays; Vertical scale rows: 33–36; Horizontal scale rows: 11–13; Predorsal scales: 14–19; Gill rakers on first arch: 11–12; Vertebrae: 27–32 [39, 52, 351, 1093]. Figure: mature male, 51 mm SL, Mary River, September 1995; drawn 1999. Melanotaenia duboulayi is a small fish commonly less than 80 mm TL. Males may reach a maximum size of about 130 mm TL in captivity but do not exceed 90 mm TL in the wild; females usually do not exceed 75 mm TL [39, 509]. Of 12 345 specimens collected in rivers and streams of south-eastern Queensland, the mean and maximum length of this species were 36 and 90 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 1093 individuals (range 16–82 mm SL) sampled from the Mary River, south-eastern Queensland is W = 1.0 x 10–5 L3.124, r2 = 0.985, p<0.001 [1093]. The following description is derived largely from Allen [39] and Crowley et al. [351]. Melanotaenia duboulayi is a slender species with a laterally compressed body,
221
Freshwater Fishes of North-Eastern Australia
Queensland, south to the Hastings River in northern New South Wales. This species is also present on Fraser Island off the south-eastern Queensland coast [38, 39, 553, 1036, 1338]. All records of M. duboulayi north of the Baffle Creek basin [328, 1173, 1349] are referable to M. s. splendida.
Systematics Castelnau [284] originally described Melanotaenia duboulayi in 1878 as Atherinichthys duboulayi and named this species after its collector, a Mr Duboulay. There has been considerable confusion surrounding the taxonomy of this species and numerous synonyms exist (listed in Crowley et al. [351]). For many years M. duboulayi was considered synonymous with M. fluviatilis (Castelnau, 1878) [284], with various authors recognising a single species, two subspecies (M. fluviatilis fluviatilis and M. f. duboulayi) or a subspecies (M. splendida fluviatilis) within the splendida group [351]. In 1986, M. fluviatilis and M. duboulayi were recognised as separate species on the basis of genetic, morphometric and meristic characteristics; although morphologically differences may be slight, both species are distinguishable at all life history stages [39, 351]. Melanotaenia duboulayi and M. fluviatilis have disjunct distributions, M. fluviatilis occurring in inland waters of the Murray-Darling Basin and M. duboulayi occurring only in coastal areas of south-eastern Queensland and northern New South Wales (see below). Melanotaenia duboulayi is believed to be the first Australian fish species to be kept in captivity and there are records of this species being sent to Germany in 1927 and maintained in aquaria there [38]. Both M. duboulayi and M. fluviatilis are extremely popular aquarium species, but have frequently been erroneously sold as M. nigrans; this misidentification has been perpetuated throughout much of the aquarium literature [38, 929].
Melanotaenia duboulayi is reported to have been introduced into North America in the late 1920s and there are records of this species being caught in the Mississippi River in 1930 [929]. Meiklejohn [71] suggested that this may be one of the earliest accounts of the introduction of an ornamental fish into the waterways of the United States. Given the popularity of M. duboulayi as an aquarium specimen, it is likely that other introductions have been attempted within and outside Australia. Melanotaenia duboulayi is generally a very common species, widespread within river systems and often locally abundant, commonly forming schools of hundreds of individuals [1093]. It was the second most abundant species collected in a survey of Baffle Creek [826]; and was reported as generally common in the Kolan River [658]. It is very widespread and abundant in the Burnett River. In a review of existing fish sampling studies in this catchment, Kennard [1103] noted that M. duboulayi has been collected at 44 of 63 locations surveyed (second most widespread species in the catchment) and formed 4.9% of the total number of fishes collected (fifth most abundant). Small numbers were also collected in the Elliott River [825] and rivers and streams of the Burrum Basin [157, 736, 1305].
Distribution and abundance Melanotaenia duboulayi has a relatively narrow distribution in all coastal drainages from Mullet Creek (a small coastal stream in the Baffle Creek drainage basin situated just north of Baffle Creek proper) in southern-central
Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 19 103 individuals from 68% of all locations sampled (Table 1).
Table 1. Distribution, abundance and biomass data for Melanotaenia duboulayi in rivers of south-eastern Queensland. Data summaries for a total of 19 103 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
67.8
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams 84.0
11.70 (15.92) 10.40 (12.24)
Brisbane River
Logan-Albert River
South Coast rivers and streams
24.1
50.0
64.9
80.9
80.0
2.82 (12.53)
3.50 (9.73)
6.73 (13.17)
18.96 (26.68)
7.25 (9.05)
4 (1)
4 (3)
8 (3)
7 (3)
4 (2)
2 (1)
5 (5)
1.72 (2.56)
1.80 (2.84)
0.01 (0.35)
1.75 (3.04)
1.26 (1.74)
1.72 (2.25)
0.48 (0.72)
4 (4)
3 (3)
16 (9)
6 (3)
6 (4)
6 (5)
7 (5)
Mean numerical density (fish.10m–2)
1.29 ± 0.09
1.15 ± 0.12
0.17 ± 0.04
0.35 ± 0.09
0.76 ± 0.17
2.20 ± 0.25
0.27 ± 0.05
Mean biomass density (g.10m–2)
1.86 ± 0.12
1.93 ± 0.16
0.02 ± 0.00
3.65 ± 3.34
1.19 ± 0.41
1.96 ± 0.23
0.31 ± 0.12
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Melanotaenia duboulayi
substrates (sand, fine gravel and coarse gravel) and particularly where submerged aquatic macrophytes, filamentous algae, leaf litter beds, undercut banks and root masses are common.
Overall, it was the 4th most abundant species collected (11.7% of the total number of fishes collected) and was very common at sites in which it occurred (15.9% of total abundance). In these sites, M. duboulayi most commonly occurred with the following species (listed in decreasing order of relative abundance): P. signifer, R. semoni, C. marjoriae and G. holbrooki. Melanotaenia duboulayi was the 4th most important species in terms of biomass, forming 1.7% of the total biomass of fish collected. This species was most widespread and abundant in the Mary, Brisbane, Logan-Albert and South Coast basins, where it occurred in over 65% of locations sampled and comprised more than 6.7% of the total number of fish collected in each basin. It was less common or widespread in the short coastal streams of the Sunshine Coast and Moreton Bay region. Across all rivers, average and maximum numerical densities recorded in 656 hydraulic habitat samples (i.e. riffles, runs or pools) were 1.29 individuals.10m–2 and 27.27 individuals.10m–2, respectively. Average and maximum biomass densities at 464 of these sites were 1.86 g.10m–2 and 19.93 g.10m–2, respectively (Table 1) [1093].
Table 2. Macro/mesohabitat use by Melanotaenia duboulayi in rivers of south-eastern Queensland. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Data summaries for 19 103 individuals collected from samples of 656 mesohabitat units at 199 locations between 1994 and 2003 [1093]. Parameter
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
5.6 4.0 0.5 0 1.1 0
Gradient (%) 0 Mean depth (m) 0.08 Mean water velocity (m.sec–1) 0
Distributional information and recent survey data indicate that M. duboulayi is widespread and relatively common in northern New South Wales [82, 282, 553, 814, 1133]. Macro/mesohabitat use Melanotaenia duboulayi is found in a range of lotic and lentic habitats including large lowland rivers, upland rivers and streams, small coastal streams, dune lake and stream systems on Fraser Island, lakes, ponds and river impoundments (dams and weirs) [38, 39, 1093]. In New South Wales this species has been classified as a pelagic pooldwelling species [553]. Melanotaenia duboulayi can be widespread within river systems. In south-eastern Queensland freshwaters we have collected this species between 0.5–335 km upstream from the river mouth and at elevations up to 400 m.a.s.l. (Table 2), but it more commonly occurs within 140 km of the river mouth and at elevations around 100 m.a.s.l. It is present in a wide range of stream sizes (1.1–44.2 m in width) but is most common in streams around 8 m wide and with moderate riparian cover (~48%). This species has been recorded in a range of mesohabitat types but it most commonly occurs in runs and pools characterised by lowmoderate gradient (weighted mean = 0.18%), moderate depth (weighted mean = 0.43 m) and low to moderate mean water velocity (weighted mean = 0.09 m.sec–1) (Table 2). It also occasionally occurs in shallow riffles with high gradient (maximum = 3.02%) and high water velocity (maximum = 0.84 m.sec–1). This species is most abundant in mesohabitats with fine to intermediate sized
Max.
Mean
W.M.
9926.8 255.0 335.0 400 44.2 91.0
613.8 43.8 144.5 94 9.3 39.6
322.1 37.6 140.1 103 8.0 47.9
3.02 1.10 0.85
0.35 0.42 0.12
0.18 0.43 0.09
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
76.4 100.0 67.2 78.2 66.8 55.0 70.0
5.8 18.9 21.2 26.3 19.6 6.6 1.6
7.2 22.6 24.0 26.7 14.4 3.8 1.3
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
86.1 65.9 45.0 65.7 39.1 92.6 31.0 21.4 88.3 100.0
11.9 7.8 1.7 5.5 1.6 13.2 4.4 3.5 14.8 20.2
13.6 7.4 1.8 3.7 1.8 11.9 5.6 4.0 15.8 22.8
Microhabitat use In rivers of south-eastern Queensland, M. duboulayi was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b). It has been recorded at maximum mean and focal point water velocity of 1.28 and 0.82 m.sec–1, respectively. This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 1c). A pelagic schooling species, it most commonly occupies the mid- to upperwater column (Fig. 1d). It is usually found over fine to intermediate-sized substrates including mud, sand, fine gravel and coarse gravel (Fig. 1e). It was often collected in areas less than 1 m from the stream-bank (64% of individuals sampled) and in open water (16.5% of individuals
223
Freshwater Fishes of North-Eastern Australia
weed (Vallisneria spp.) in which other potentially piscivorous fish species (G. aprion, L. unicolor, A. reinhardtii and T. tandanus) were observed. These authors also suggested that changes in water temperatures caused by prevailing sunlight influenced the microhabitat use of M. duboulayi. In sunny conditions and during the middle of the day, schools of juveniles were observed foraging in the warm surface waters. Larger fish were more common in the lower water column, as were juveniles during cloudy condition [561]. In experimental aquaria, Brown [240] examined the behavioural responses to fish predators of M. duboulayi purported to originate from predatorsympatric and predator-naive populations. He reported that M. duboulayi from the predator-sympatric population avoided the fish predator (L. unicolor), whereas those from the predator-naive population did not display typical predator avoidance activities, but noted that this behaviour could be learned with experience.
sampled) (Fig. 1f). It was collected in close association with a wide range of submerged cover elements including aquatic macrophytes, filamentous algae, overhanging and submerged marginal vegetation, leaf litter beds, woody debris and root masses (Fig. 1f). Little is known of larval habitat use, although we frequently observed larval aggregations in the Mary River in similar habitats as adults, especially in areas of low water velocity among submerged marginal vegetation [1093]. (a)
(b)
60
60
40
40
20
20
0
0
25
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
30
Environmental tolerances Harris and Gehrke [553] classified M. duboulayi as intolerant of poor water quality, but we have collected this species over a relatively wide range of water quality conditions in south-eastern Queensland (Table 3). It was recorded over a wide range of water temperatures (8.4–31.7°C), dissolved oxygen concentrations (0.6–19.5 mg.L–1), water acidity (4.4–9.1), conductivity (51–4002 µS.cm–1) and turbidity (0.3–250 NTU) (Table 3).
20 20
15 10
10
5 0
0
Total depth (cm) 30
(e)
Relative depth 20
Table 3. Physicochemical data for Melanotaenia duboulayi. Data summaries for 18 271 individuals collected from 414 samples in south-eastern Queensland streams between 1994 and 2003 [1093].
(f)
15
20
10 10 0
Substrate composition
5
Parameter
Min.
Max.
0
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
8.4 0.6 4.4 51.0 0.3
31.7 19.5 9.1 4002.0 250.0
Mean 19.6 7.6 7.6 501.5 6.4
Microhabitat structure
Studies of salinity tolerances of the eggs and fry of M. duboulayi from coastal New South Wales revealed that experimental chronic (four-day) LD50s were 22 ppt and 21 ppt for eggs and fry, respectively [559, 560, 1405]. These salinity levels were somewhat higher than those tolerated by M. fluviatilis. Salinity tolerances of adult fish are not available. Melanotaenia duboulayi is used by the Sydney Water Board for real-time continuous monitoring of the open water-supply canals for contamination by toxicants [665]. This species was reported to be useful for detecting ammonia and chlorine contamination events caused by
Figure 1. Microhabitat use by Melanotaenia duboulayi. Data derived from capture records for 3086 individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
Hattori and Warburton [561] examined the microhabitat use of M. duboulayi by underwater observation in a tributary stream of the Mary River, south-eastern Queensland. Fish were reported to be more abundant in areas with aquatic macrophytes, but avoided dense beds of ribbon
224
Melanotaenia duboulayi
and aquarium studies [84, 351, 509, 770, 797, 950, 1093, 1133]. Details are summarised in Table 4. This species spawns and completes its entire life cycle in freshwater and is easily bred in captivity [38, 770, 794, 797]. Maturation commences at a relatively small size. Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, south-eastern Queensland, were 21.9 mm SL and 42.3 mm ± 0.7 SE, respectively for males and 26.1 and 38.4 mm ± 0.8 SE, respectively for females (Fig. 2). Gonad maturation in both sexes was commensurate with somatic growth, the mean length at each reproductive stage being generally different from all other stages (Fig. 2). Gravid (stage V) females were slightly smaller than males of equivalent maturity (minimum 26.8 mm SL, mean 49.0 mm ± 0.5 SE for females; minimum 36.4 mm SL, mean 54.0 mm ± 2.0 SE for males).
malfunctions of water treatment equipment, however it appears to be less suitable for detecting cyanobacterial toxins. Laboratory experiments revealed that the respiratory system of M. duboulayi is unaffected by short-term exposure to potentially toxic microcystin (up to 2.6 µg.mL–1) or other cyanobacterial compounds [665]. Melanotaenia duboulayi is also reported to be comparatively tolerant to endosulfan exposure (96-hour LC50: 0.5–11.4 µg.L–1, depending on test method) [1280]. Arthington el al. [95] conducted laboratory experiments to establish the chronic lower thermal tolerances of adult M. duboulayi using fish from south-eastern Queensland. Fish acclimated for four days at 15°C, lost orientation at 5.7°C and moved only spasmodically at 4.2°C [95]. Ham [502] reported little difference in the lower temperature tolerance of juvenile and adult M. duboulayi from south-eastern Queensland. Fish acclimated for seven days at 15°C were observed to lose orientation at temperatures of about 3.5°C, move spasmodically at 2.2°C and cease movement completely at about 1.8°C [502]. Fish acclimated for seven days at 10°C were reported to have a significantly greater tolerance of low water temperatures, losing orientation at temperatures of about 2.8°C, moving spasmodically at 1.8°C and ceasing movement completely at about 1.5°C [502]. Upper thermal tolerances for M. duboulayi are not available.
Reproductive stage I
II
III
IV
V
Males 100
(93) (34) (21) (25) (100) (7)
(56) (59) (48) (13) (37)
80 60
Reproduction Quantitative information on the reproductive biology and early development of M. duboulayi is available from field
40 20 0
55
Males
50
Females
Females 100
45
80
40
60
(82) (55) (29) (30) (137) (30)
( 51) (91) (36) (14) (16)
40
35
20
30
0 25 I
II
III
IV
V
Month
Reproductive stage Figure 2. Mean standard length (mm SL ± SE) for male and female Melanotaenia duboulayi within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland, between 1994 and 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 3.
Figure 3. Temporal changes in reproductive stages of Melanotaenia duboulayi in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in parentheses.
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Freshwater Fishes of North-Eastern Australia
South Wales [1133, 1135], was generally very similar to that observed for fish from the Mary River [1093], except that spawning appeared to be concentrated within a slightly shorter period (October to February) in each river. No consistent pattern in overall sex ratios was observed for populations from the Brisbane River [950].
Arthington and Marshall [84] reported that females in the Noosa River commenced spawning at 23 mm SL. Milton and Arthington [950] recorded minimum and mean lengths of ripe females (equivalent to stage V) from tributaries of the Brisbane River as 30.8 and 41.1 mm SL, respectively. Length at first maturity (equivalent to reproductive stage III) for fish from the Tweed River, northern New South Wales, was reported as 30 and 25 mm LCF for males and females, respectively [1133].
The spawning stimulus for M. duboulayi is unknown but corresponds with increasing water temperatures and photoperiod in late winter and early spring. In aquaria, spawning is reported to occur at water temperatures between 22 and 27°C [770, 797]. Milton and Arthington [950] observed that the peak spawning period for fish in the Brisbane River (October–December) coincided with minimum surface water temperatures of 20°C. The peak spawning period generally coincides with pre-flood periods of low and relatively stable discharge in rivers of south-eastern Queensland. However, breeding may also continue through the months of elevated discharge at the commencement of the wet season in December–January. Melanotaenia duboulayi is thought to spawn repeatedly over an extended period, perhaps as an adaptation to the relatively unpredictable timing of the onset of wet season flooding [950]. Maximum spawning activity of adults and the presence of larvae tend to occur when the likelihood of flooding is low, coinciding with predictably high water temperatures and relatively stable low flows. These conditions are likely to increase the potential of larvae to encounter high densities of small prey, avoid physical
Melanotaenia duboulayi has an extended breeding season from late winter through to summer but spawning appears to be concentrated in spring and summer. In the Mary River, immature and early developing fish (stages I and II) were most common between January and June (Fig. 3). Developing fish (stages III and IV) of both sexes were present year-round. Gravid males (stage V) were present between August and January. Gravid females were present for longer (August to March) and were relatively abundant throughout this period (Fig. 3). The temporal pattern in reproductive stages mirrored that observed for variation in GSI values. Peak monthly mean GSI values (3.0% ± 0.7 SE) occurred in August for males and remained elevated until November (Fig. 4). Peak monthly mean GSI values (7.1% ± 0.5 SE) occurred slightly later in females (October) but remained elevated for eight months of the year (Fig. 4). The phenology of reproductive activity and GSIs for fish from the Noosa River [84], tributaries of the Brisbane River [950] and the Tweed River, northern New
20
8
Spring (n = 1999)
Males 6
Females
Summer (n = 3238)
15
4
10
2
5
0
0
Month Figure 4. Temporal changes in mean Gonosomatic Index (GSI% ± SE) of Melanotaenia duboulayi males (open circles) and females (closed circles) in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 3.
AutumnWinter (n = 7016)
Standard length (mm) Figure 5. Seasonal variation in length-frequency distributions of Melanotaenia duboulayi, from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
226
Melanotaenia duboulayi
River ranges from 35–333 eggs (mean 132 ± 9 SE, n = 81 fish) [949]. Relationships between body length, body weight and total fecundity are given in Table 4. Fish of 40 mm SL produced about 120 eggs, whereas fish of 70 mm SL produced about 650 eggs [1093]. In aquaria, M. duboulayi is reported to deposit 10–40 eggs per day [794] and up to 200 eggs are laid over a period of several days [797].
flushing downstream due to high flows and thereby maximise the potential for recruitment into juvenile stocks, as has been hypothesised for other small-bodied fish species in the Murray-Darling Basin [614, 615]. Sampling in rivers of south-eastern Queensland [1093] revealed that juvenile fish less than 20 mm SL were present year-round supporting the suggestion made earlier that this species has an extended spawning period. These data further suggest that suitable conditions for recruitment of larvae through to the juvenile stage and beyond may persist year-round.
In the wild, spawning probably occurs in beds of aquatic macrophytes and submerged marginal vegetation [950, 1093] and eggs are reported to be deposited within 10 cm of the water surface [950]. No parental care of eggs has been reported. Eggs are relatively large. The mean diameter of 1793 intraovarian eggs from stage V fish from the Mary
Total fecundity for fish from the Mary River is estimated to range from 27–1125 eggs (mean 280 ± 12 SE, n = 217 fish) [1093]. Batch fecundity for fish from the Brisbane
Table 4. Life history information for Melanotaenia duboulayi. Age at sexual maturity
10–12 months [950]
Minimum length of gravid (stage V) females (mm)
23 mm TL [84]; 26.8 mm SL [1093]; 30.8 mm SL [950]
Minimum length of ripe (stage V) males (mm) 36.4 mm SL [1093] Longevity (years)
In the wild, 3–4 years [950]; in aquaria, possibly up to 8 years [39]
Sex ratio (female to male)
? Variable year-to-year [950]
Occurrence of ripe (stage V) fish
Late winter, spring and summer (August–March) [1093]; spring and summer (October–February) [950]
Peak spawning activity
Spring and early summer [950, 1093]
Critical temperature for spawning
? >20°C in the wild [950], 22–27°C in aquaria [38, 351, 770]
Inducement to spawning
? Possibly increasing temperature [950]
Mean GSI of ripe (stage V) females (%)
7.0 % ± 0.8 SE
Mean GSI of ripe (stage V) males (%)
5.6 % ± 0.2 SE
Fecundity (number of ova)
Total fecundity = 27–1125, mean = 280 ± 12 SE [1093]; batch fecundity 35–333, mean = 132 ± 9 SE [949], In aquaria 10–40 eggs deposited per day [794] and up to 200 eggs are laid over several days [797]
Total Fecundity (TF) and Batch Fecundity (BF)/ Log10 TF = 2.666 log10 L – 2.088, r2 = 0.457, n = 217 [1093]; Length (mm SL) or Weight (g) relationship Log10 TF = 1.354 log10 W + 1.703, r2 = 0.477, n = 217 [1093]; BF = 7.763 L – 154.24, r2 = 0.79, n = 22 (Noosa River) [84] Egg size (diameter)
Intraovarian eggs from stage V fish = 0.93 mm ± 0.01 SE [1093]; water-hardened eggs 0.88–0.93 mm [351], 1.0–1.5 mm [794], 1.41 mm ± 0.32 SE [950]
Frequency of spawning
Probably repeat spawner over extended spawning period [950]
Oviposition and spawning site
In the wild, spawning probably occurs in beds of aquatic and submerged marginal vegetation near the water surface [950, 1093]
Spawning migration
None known
Parental care
None known
Time to hatching
Varies with temperature. In aquaria eggs hatch after 4.5 days at 27°C [351], 6–7 days at 22–26°C, 7 days at 25–28°C [38], and 7–10 days at 25–27oC [770]
Length at hatching (mm)
Newly hatched prolarvae 3.7–4.2 mm SL [351]
Length at free swimming stage
? Capable of swimming soon after hatching [351]
Age at loss of yolk sack
?
Age at first feeding
12–24 hours [1295]
Length at first feeding
?
Age at metamorphosis (days)
? Squamation commences at 11.5–12.0 mm TL and is complete at 20 mm TL [351]
Duration of larval development
? Growth is rapid and a length of 20 mm TL may be achieved after eight weeks [38]
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Freshwater Fishes of North-Eastern Australia
[158, 159]. Although M. duboulayi appears tolerant to elevated salinities (see above), the presence of tidal barriers may impact on this species by preventing or hindering recolonisation of freshwaters if displaced by floods to brackish estuarine areas downstream of tidal barrages.
River was 0.93 mm ± 0.01 SE [1093]. Crowley et al. [351] reported that the diameter of water-hardened eggs from fish collected from the Mary River and an unnamed lagoon on the Sunshine Coast, ranged between 0.88–0.93 mm. Leggett [794] reported that water-hardened eggs were 1.0–1.5 mm diameter. Milton and Arthington [950] reported that the mean diameter of eggs (possibly water-hardened) from Brisbane River fish was 1.41 mm ± 0.32 SE.
Melanotaenia duboulayi appears to undertake movement wholly within freshwaters, however the purpose, scale or timing of these movements is unknown. Many more individuals were collected at the base of a fish lock located in the lower Burnett River than were collected at the top (252 versus five individuals) [11], perhaps indicating that these fish were attempting to move upstream. Johnson [658] collected a small number of individuals from a fish ladder located further upstream in this river. We have also observed large aggregations of adult fish below a weir on Barambah Creek, a tributary of the Burnett River. These fish were observed immediately after an increase in discharge, suggesting that upstream dispersal movements may occur when flow conditions allow [1093].
The demersal eggs are spherical with an adhesive tuft of filaments arising from a small area of the chorion above the animal pole [351, 770, 950]. The perivitelline space is relatively small and 30–35 small, dark gold oil droplets are present in the yolk [351]. Further details of egg characteristics are available in Crowley et al. [351]. Eggs are reported to hatch after 4.5 days at 27°C [351], 6–7 days at 22–26°C, 7 days at 25–28°C [38], and 7–10 days at 25–27°C [770]. Details of larval morphology are available in Crowley et al. [351]. Newly hatched larvae are small (3.7–4.2 mm TL) [351] and are capable of swimming soon after hatching [794]. Squamation commences at 11.5–12.0 mm TL and is complete at 20 mm TL [351].
Trophic ecology Diet data for M. duboulayi is available for 1237 individuals from four separate studies in south-eastern Queensland and northern New South Wales (Fig. 6). This is an omnivorous species that consumes animal and vegetable material within the water column and at the water surface. Terrestrial invertebrates (mostly ants) comprised 20.8% of the total mean diet and aerial forms of aquatic insects (mostly dipteran adults) a further 17.2%. Aquatic insects (mostly drifting immature stages of Trichoptera, Ephemeroptera and Diptera) were also important, forming 26.4% of the total diet. Aquatic vegetation in the form
Growth is reported to be rapid and a length of 20 mm TL may be achieved after eight weeks [38]. Milton and Arthington [950] reported that M. duboulayi reached sexual maturity within one year of age (estimated at 10–12 months). Length at age data using evidence from scale annuli from fish in the Brisbane River [950] indicate that 1+ fish (males and females) were around 35–38 mm SL, 2+ were 47–49 mm SL, 3+ fish were 65 mm SL and 4+ fish were greater than 73 mm SL, with males generally slightly larger than females in each age group. The dominant age class in this population was 1+ fish [950]. Fish in aquaria may live up to eight years [39]. Movement There is very little quantitative information concerning the movement biology of M. duboulayi. Small numbers of individuals have occasionally been reported to use fishways on weirs and tidal barrages in south-eastern Queensland rivers. Broadfoot et al. [232] collected 39 individuals in a tidal barrage fishway on the Kolan River and Stuart and Berghuis [1276, 1277] collected 12 individuals in a tidal barrage fishway on the Burnett River during November and December. It is possible that these fish were attempting to return to freshwaters after being displaced downstream into estuarine areas below the barrage by elevated flows. Berghuis et al. [162] suggested that this might also explain the presence of M. duboulayi downstream of a tidal barrage in the Mary River catchment between February and April. Further sampling within and downstream of tidal barrages in this catchment has yielded additional fish in these areas between November and April
Fish (0.1%) Other microinvertebrates (0.1%) Microcrustaceans (1.3%) Macrocrustaceans (0.5%) Molluscs (0.1%) Other macroinvertebrates (0.3%) Unidentified (19.3%)
Aquatic insects (26.4%)
Terrestrial invertebrates (20.8%)
Algae (10.5%) Aquatic macrophytes (2.6%) Detritus (0.2%) Terrestrial vegetation (0.6%)
Aerial aq. Invertebrates (17.2%)
Figure 6. The mean diet of Melanotaenia duboulayi. Data derived from stomach content analysis of 1237 individuals from the Burnett [205], Noosa [84] and Brisbane rivers [80] in south-eastern Queensland, and the Tweed River in northern New South Wales [1133].
228
Melanotaenia duboulayi
power to disrupt spawning substrates (i.e. native submerged macrophytes) and displace eggs, larvae and small individuals downstream [94, 950]. Patterns of rainfall and stream discharge are characteristically highly variable and unpredictable within and between years in south-eastern Queensland streams and rivers [1095, 1100]. Some brief spates cause rapid rises and falls in water level and may strand in-stream vegetation and leaf litter on stream-banks and in clumps suspended in riparian shrubs [94]. We have suggested that the seasonal timing of spawning in M. duboulayi (concentrated in spring and summer) represents an adaptation to the probability of low flow conditions and the availability of suitable spawning sites, as well as shelter and food supplies for larvae and juveniles. Flow modifications (particularly rapid fluctuations in water level or flow releases during naturally low flow periods of spawning and larval development) may have severe impacts on recruitment by damaging or exposing fish eggs attached to submerged and aquatic vegetation in shallow marginal habitats, or by flushing eggs and larvae downstream. Microscopic invertebrate prey is also likely to be reduced in abundance by flow-related habitat disturbances, or flushed downstream during spates and aseasonal flow releases [614, 615, 718].
of algae (filamentous algae, diatoms and desmids), charaphytes and macrophytes comprised a further 10.5% of the diet. Small amounts of microcrustaceans, macrocrustaceans, fish eggs, terrestrial vegetation and molluscs are also consumed (Fig. 3). Little spatial variation in diet was apparent, although individuals from the Tweed River, New South Wales, consumed a higher proportion of aquatic insects and aquatic vegetation and a lower proportion of allochthonous material. Diel variation in feeding activity and dietary composition is evident in M. duboulayi from streams in the Brisbane region [1093]. This species undertakes distinct crepuscular foraging on aquatic insects during their peak drifting period at dawn and dusk, with supplementary foraging on allochthonous material at or near the water surface occurring during daylight hours [1093]. This species is believed to be an effective mosquito control agent [39, 80]. Conservation status, threats and management The conservation status of M. duboulayi was listed as NonThreatened by Wager and Jackson [1353] in 1993 and this species remains generally common throughout most of its range in eastern Australia. Potential threats to M. duboulayi in south-eastern Queensland are similar to those identified for many other small-bodied fish species in this region, for example Atherinidae, Pseudomugilidae, Retropinnidae and Eleotridinae.
The implications of modified flows combined with instream barriers are not well understood for M. duboulayi. This species appears to undertake movement wholly within fresh water systems but they are probably not associated with reproduction [1093]. Milton and Arthington [950] suggested that juvenile melanotaeniids disperse throughout the stream network when elevated flows occur during summer months. We observed large aggregations of adult fish below a weir on Barambah Creek, a tributary of the Burnett River, immediately after an increase in discharge, suggesting that upstream dispersal movements of adults may occur when flow conditions allow [1093]. Such movements could be disrupted by dams, weirs, and culverts.
Melanotaenia duboulayi is highly dependent on energy supplies from the terrestrial environment. Inputs of allochthonous organic matter may be severely disrupted by land and riparian clearing [1092]. In addition, infestations of introduced para grass, Brachiaria mutica, may disrupt the foraging behaviour of this surface-feeding species in degraded urban streams. Long stolons and mats of this ponded pasture grass often extend into slow-flowing areas of stream channels, obliterating patches of native submerged macrophytes and invading open water areas where rainbowfish usually forage [80, 94, 1093]. Para grass, a C4 plant, does not contribute to energy flow through the aquatic food web of tropical streams [95, 248, 250] and this may also apply in subtropical streams. Food resources of aquatic origin (e.g. insects, crustaceans, molluscs and algae) are likely to be further limited in degraded systems by bank erosion and sedimentation of the stream-bed [1092].
Harris and Gehrke [553] classified M. duboulayi as intolerant of poor water quality, yet this species tolerates relatively wide-ranging water quality conditions in streams and dune lakes of south-eastern Queensland, and in aquaria. Melanotaenia duboulayi is sensitive to ammonia and chlorine contamination events caused by malfunctions of water treatment equipment, however it appears to be less suitable for detecting cyanobacterial toxins [665]. It is unaffected by short-term exposure to potentially toxic microcystin derived from cyanobacteria [665] and comparatively tolerant of endosulfan exposure [1280]. Thus the impacts of degraded water quality conditions in streams draining urban and agricultural catchments may be relatively slight when short-term exposure is the norm.
Melanotaenia duboulayi is most abundant in mesohabitats with fine to intermediate-sized substrates (sand, fine gravel and coarse gravel), submerged aquatic macrophytes, filamentous algae, leaf-litter beds, undercut banks and root masses. These structures may provide protection from surface (e.g. avian) and aquatic predators. Cover may also serve to reduce the impact of high flows with the
229
Freshwater Fishes of North-Eastern Australia
Alien species are also regarded as a threat to M. duboulayi [83, 94, 950] especially the poeciliid Gambusia holbrooki, a widespread species common in many waterbodies within the geographic range of this rainbowfish in Queensland and New South Wales [84, 726, 1093]. Gambusia holbrooki is a particularly threatening species known to consume fish eggs and larvae and to interact aggressively with native fishes [77, 78, 416, 983]. Moloney [960] reported a high level of predation by G. holbrooki on the eggs of the ornate rainbowfish, R. ornatus, when the two species were maintained in experimental aquaria. He concluded that alien fish such as G. holbrooki have the capacity to significantly reduce the number of rainbowfish recruiting to later life stages by direct predation and interfering with foraging activities [960]. Dietary studies in the Brisbane and Noosa rivers have shown that M. duboulayi and G. holbrooki have
very similar diet composition at most times of year [84, 92, 94], particularly in relation to their high dependence on prey of terrestrial origin. Arthington et al. [95] observed that M. duboulayi was rarely present or abundant where Gambusia was present in streams of the Brisbane region. These authors speculated that similarities in foraging behaviour and diet increased the potential for competition among these species. In contrast, our recent more extensive sampling of rivers and streams in south-eastern Queensland [1093] indicates that M. duboulayi and G. holbrooki frequently occur together, often in large numbers. Co-occurrence data such as these provide no evidence for the impact of alien fish species such as G. holbrooki on M. duboulayi. Dove [1432] provided a list of parasite taxa recorded from M. duboulayi in south-eastern Queensland.
230
Melanotaenia eachamensis Allen and Cross 1982 Lake Eacham rainbowfish
37 245005
Family: Melanotaeniidae
Description First dorsal fin: V–VI; Second dorsal: I, 9–13; Anal: I, 15–21; Pectoral: 11–14; Horizontal scale rows: 10–12; Vertical scale rows: 33–38; Predorsal scales: 14–18; Cheek scales: 9–15 [38, 1105]. Meristic characters overlap with those of Melanotaenia splendida splendida, although average values are significantly different [1105]. Figure: mature male, 52 mm SL, Dirran Creek, North Johnstone River, October 1996; drawn 1998.
10.8% of SL, respectively). Morphological comparisons are based on M. eachamensis from Dirran Creek and M.splendida from a variety of locations in the Johnstone River [1105]. Colour varies slightly from locality to locality but overall body tends to be silvery or bluish with dark midlateral stripe, 2–3 thinner dark bands present ventrally of midlateral stripe and extending almost to pectoral fins. Fins tend to be uniform bright red with little to no yellow pigmented blotches. Fin margins of dorsal and anal fins tend almost to black in breeding males. Sexually dimorphic: fins longer, more pointed and more brightly pigmented in males. Specimens derived from type locality (i.e. Lake Eacham) tend to be less brightly coloured. Colour in preservative: colours faded, body dull yellow/white to brown, faint to dark stripe and little fin colour [38]. Larvae distinguished from those of M. s. splendida by origin of the first dorsal fin-fold above first preanal myomere (as opposed to postanal origin), gut simple, uncoiled and never striated in all preflexion larvae, slightly denser pigmentation on dorsal and ventral midlines in most preflexion larvae [308].
Melanotaenia eachamensis is a small, laterally compressed fish rarely exceeding 65 mm SL in length and 5 g in weight, commonly about 40 mm in length. The relationship between length (SL in mm) and weight (g) is W = 1.05 x 10–5 L3.06; r2 = 0.933, n = 214, p<0.001 [1093]. No sexual dimorphism with respect to length–weight relationship [1108]. Greatest body depth (at origin of first dorsal fin) 26.5% of SL, slightly less than M. s. splendida (28.2%). First dorsal fin inserted more anteriorly than in M. s. splendida (44.5% versus 47.7% of SL). This difference observed in larval fishes also [308, 1377]. Head depth 23.1% of SL, eye diameter 9.7 % of SL, eye positioned more anteriorly than in M. s. splendida (i.e. snout length of 7.6% versus 8.2% of SL, respectively). Peduncle longer and deeper than in M. s. splendida (18.2% and 11.0% versus 17.5% and
Systematics The systematics of M. eachamensis have been studied very thoroughly in recent years. This species was originally
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Freshwater Fishes of North-Eastern Australia
total number of fishes collected but only 0.2% of the total biomass (16th most abundant). This species is the most abundant species with respect to density (63.2% of total) and the second most abundant with respect to biomass (9.1% of total) at those sites in which it occurs, with mean and maximum densities of 2.01 ± 0.62 fish.10m2 and 9.90 fish.10m2 respectively, and mean and maximum biomass of 2.11 ± 0.70 g.10m2 and 11.2 g.10m2 respectively, being estimated from a total of five sites and 16 samples. Other species with which it occurs include Mogurnda adspersa, Poecilia reticulata (alien), Anguilla reinhardtii and Craterocephalus stercusmuscarum (2nd, 3rd, 4th and 5th with respect to density, and 3rd, 4th, 1st and 5th with respect to biomass) [1093]. McGuigan [904] reports that M. eachamensis may frequently occur in sympatry with M. s. splendida but only very occasionally with M. utcheenis, but note that this conclusion is based on the presence of mixed or hybrid haplotypes and it is not known whether this admixture represents old or contemporary hybridisation. Translocated Hephaestus fuliginosus (a native species) were recorded by us in Dirran Creek toward the end of 1997 [1093]; the impact of this species on M. eachamensis is unknown.
described in 1982 from specimens collected from Lake Eacham, on the Atherton Tablelands [38]. The population present in the type locality became extinct shortly thereafter due to predation pressure from translocated native fishes, principally Glossamia aprion [132]. Captive populations were maintained however [293, 608]. The lacustrine population was subsequently shown to be ‘predator naïve’ and consequently susceptible to exploitation by translocated piscivorous fishes [241, 1377]. Initial electrophoretic examination of captive populations of M. eachamensis and wild populations of M. s. splendida from the Atherton Tablelands suggested full specific status for the former species may have been unwarranted [349, 634]. However, subsequent research utilising DNA sequencing methods demonstrated that M. eachamensis was a valid species and that extant populations were still present in the wild [1427]. Moreover, this study suggested that hybridisation between these two species may occur in the wild. Morphological evidence also indicated the presence of extant populations in the wild and seemed to indicate the presence of morphological forms intermediate between that of M. eachamensis and M. s. splendida [35, 1105, 1426]. Morphological intermediates were assumed to be hybrids [1105] but subsequent genetic examination has revealed the presence of another distinct lineage in the Johnstone River (the ‘Utchee Creek’ form, now known as M. utcheensis McGuigan) [904]. Melanotaenia eachamensis is an old lineage and evolutionarily more closely related to M. s. australis and M. duboulayi than to taxa within the ‘splendida’ subspecies complex [904, 1427].
Macro/mesohabitat use The data listed in Table 1 includes study sites on Dirran Creek only, for at the time in which the study commenced, this creek was the only system in which pure strains of M. eachamensis were known to exist. This stream is a high altitude tributary of the North Johnstone River (Table 1). It is worth noting that McGuigan [904] identified a population of M. eachamensis in the upper reaches of the South Johnstone River also. Dirran Creek is of moderately high gradient and with a relatively open riparian canopy, running predominantly through land used for dairy and cattle grazing. The riparian canopy would previously have been more extensive.
Distribution and abundance Melanotaenia eachamensis is restricted to the Wet Tropics region, and within this region is restricted to the headwaters of the Johnstone and Barron rivers [904]. Pusey et al. [1105] suggested that it may be present in the headwaters of other rivers draining the Atherton Tablelands, such as the Tully River. All known localities supporting M. eachamensis are located above 500 m.a.s.l. Populations previously identified as M. eachamensis occurring at elevations between 100 and 500 m.a.s.l. in the Johnstone River [1105], have subsequently been identified as the new distinct species M. utcheensis [904]. Efforts to reintroduce M. eachamensis back into the type locality using stock reared in captivity have proved unsuccessful.
Over the range of sites examined, Dirran Creek varies from 7.1 to 17.5 m in width. Average water depth and flow velocity varied from 0.3 to 0.67 m and 0.11 to 0.26 m.sec-1, respectively. The close similarity between arithmetic and weighted means suggests little spatial variation in abundance due to spatial variation in width, depth or water velocity, at least not over the ranges measured by us. The composition of the substratum in sites containing M. eachamensis was dominated by rocks and bedrock (Table 1). In-stream cover was generally limited in extent with the exception of bank-associated submerged vegetation (almost exclusively para grass) and root masses. The disparity between arithmetic and weighted means for these cover elements suggests that M. eachamensis is more abundant in streams with prolific South American para
Loose schooling occurs in M. eachmansis especially for fish less than 40 mm SL; larger fish tend to occur singly or in small groups. This species is moderately abundant where it occurs and the original lake population was reportedly large [132]. Melanotaenia eachamensis was the ninth most abundant species collected in the Johnstone River catchment over the period 1994–1997 contributing 3.4% of the
232
Melanotaenia eachamensis
Microhabitat use Melanotaenia eachamensis may occur across a moderate range of water velocities from still water to about 0.5 m.sec–1, although the majority of fish collected were from areas with no flow. The focal point velocity experienced by most fish was accordingly 0 m.sec–1 although it is apparent that those fish not collected from areas of still water experienced focal point velocities similar to the average velocity (Fig. 1b). This species occurred over a wide range of depths reflecting the distribution of depths across the range of sites sampled. In general, most fish were collected from the bottom half of the water column although M. eachamensis appears to make use of the entire water column on occasion.
grass (Brachiaria mutica) infestations and abundant root masses. However, it should be noted that the relationship is probably not a linear one as the maximum density recorded occurred was in a site with only 50% coverage by para grass. Both para grass and root masses may provide refuge against high water velocity or abundant spawning sites. Table 1. Macro/mesohabitat use by Melanotaenia eachamensis. Data summaries based on site data for five sites collected over the period 1994–1997. Parameter
Min.
27.8 Catchment area (km2) Stream order 4 Distance to source (km) 10.5 Distance to river mouth (km) 95 Elevation (m.a.s.l.) 720 Width (m) 7.1 Riparian cover (%) 5 Gradient (%) 0.1 Mean depth (m) 0.3 Mean water velocity (m.sec–1) 0.11 Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%) Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Small woody debris (%) Large woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 2 3 3 26 5 0 0 0 0 0 0 0 0 0 0
Max.
Mean
W.M.
57.5 4 21.5 104.5 790 17.5 40
45.6 4 17.1 98.8 748 12.0 21
45.1 4 16.9 99.0 749 12.3 24
2.6 0.67 0.26
1.1 0.5 0.19
50
1.0 0.46 0.19
8 17 11 6 23 65 63
3.0 5.2 4.4 4.4 7.8 50.2 25.4
4.6 3.8 5.7 5.0 10.8 51.6 19.6
5 0 12 91 3 3.5 0.7 1.2 5 24
1.0 0 2.6 37.2 0.8 1.3 0.2 0.3 1.0 7.0
0.9 0 4.1 55.9 1.4 1.6 0.3 0.5 0.4 10.2
The habitat described above is in distinct contrast to that of the type locality, Lake Eacham, a deep crater lake. This species has also been recorded from other crater lakes on the Atherton Tablelands, Lake Euramoo [1426] and Bromfield Swamp [904]. These waterbodies and Lake Eacham have abundant sedge habitats at their margins, or in the case of Bromfield Swamp, distributed in a patchy mosaic across its surface. Despite occurring, or having once occurred in these lakes, M. eachamensis is best considered a stream-dwelling rainbowfish [1105].
(a)
50
40
40
30
30
20
20
10
10
0
0
Focal point velocity (m/sec)
Mean water velocity (m/sec)
(c)
30
20 15
(b)
(d)
20
10 10 5 0
0
Total depth (cm)
Relative depth
(e)
(f)
30 60 20 40 10
20
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Melanotaenia eachamensis in Dirran Creek, North Johnstone River. Summaries are derived from capture records for 62 individuals collected over the period 1994–1997.
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Freshwater Fishes of North-Eastern Australia
unknown, as are tolerances to pesticides and herbicides. Most streams of the Atherton Tablelands in which M. eachamensis is likely to occur, are in forested areas, or areas devoted to cattle grazing. Such streams are unlikely to receive contaminants other than sediment, however given the expansion of the sugar-cane industry on the Tablelands, this situation may not persist.
This species was recorded most frequently over coarse substrate types (Fig. 1e) reflecting the average substrate composition of the sites in which it is found (see above). However, M. eachamensis frequently occurs over areas of fine gravel and gravel also, reflecting its preference for areas of lower flow than the average water velocity occurring within the stream. The great majority of M. eachamensis were collected in association with submerged para grass (Fig. 1f), however, this species was rarely found deep within the para grass stands but was most frequently outside of, but within 20 cm of the outer margin of the stand. The majority of the remaining fish were either distant from cover or were within 20 cm of the stream-bed and thus associated with the stream-bed. Larval M. eachamensis prefer marginal habitats with low water velocities (<0.1 m/sec) but of variable depth (but <100 cm). Larvae are always associated with access to cover and may be more abundant in areas of deep shade [1109].
Reproduction Details of the life history of M. eachamensis are summarised in Table 3. Spawning occurs over an extended period from August to April but peak gonadosomatic values occur during August to November. Spawning does not appear to occur when water temperatures are below 17°C. Spawning may continue during periods of high flow but is concentrated during periods of stable low flows. Larval survival decreases during periods of high flow [1109]. The eggs are demersal and adhesive; field investigations have found eggs most commonly attached to fine root masses downstream in well oxygenated areas. Females produce batches of 40–50 eggs in captivity [277] but much higher batch sizes have been observed in wild populations. Eggs are small (1.28 mm diameter) and fecundity is significantly positively related to fish size. Maturity is reached at an early age and size, and females mature at a smaller size than do males. This species is unlikely to live for more than two years in the wild. The time to hatching is reported to be 10 days at 26°C, however such a high temperature rarely occurs in the natural habitat. Larvae are small at hatching and lack a well-developed yolk sac, exogenous feeding commences shortly after hatching. Larval development is complete at between 11 and 14 mm in length.
Environmental tolerances No quantitative information is available on environmental tolerances of M. eachamensis. Data presented in Table 2 were derived from routine sampling at five sites at which M. eachamensis was present. A minimum temperature of 13.2°C was recorded over the period 1994–1997 although winter frosts are not uncommon on the Atherton Tablelands and minimum values may be less than that recorded here. The incidence of fungal infection is highest during periods of low temperature. The maximum water temperature (25.7°C) listed in Table 2 was recorded in January during a period of low flow but it is notably lower than that seen for other small streams located at lower altitude. This species has only been recorded from moderate to well-oxygenated conditions and occurs in near neutral waters.
Movement No information available on the extent or pattern of movement.
Table 2. Physicochemical data for M. eachamensis. Data summaries for fish collected from five sites and 16 sampling occasions within Dirran Creek over the period 1994–1997. Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
13.2 5.1 6.7 18.9 0.5
Max. 25.7 8.1 7.8 52.6 8.5
Trophic ecology Melanotaenia eachamensis is omnivorous, but more than 50% of the diet is composed of aquatic invertebrates (principally comprised of ephemeropteran nymphs and trichopteran and pyralid larvae) (Fig. 2). Terrestrial invertebrates and adult forms of aquatic insect larvae collectively comprise 12.7% of the diet, indicating that feeding at the water’s surface is important. Plant matter in the form of filamentous algae, diatoms and desmids are important also (10.4%). Elsewhere plant material may form a larger part of the diet. Many rainbowfish specimens from the upper South Johnstone River included in a previous description of the diet M. s. splendida [1097] were in all likelihood M. eachamensis; plant material, especially diatoms and desmids, were an important component of the diet (>50%) of fish from this area. The diet of M.
Mean 19.8 6.9 7.3 33.7 4.1
Dirran Creek has extremely low conductivity levels (Table 2). Melanotaenia eachamensis appears to be able to tolerate moderately elevated turbidity for short periods: the maximum value in Table 2 was recorded during a storm-associated runoff event. Average turbidity values indicate conditions of good water clarity. Larval tolerances are
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Melanotaenia eachamensis
eachamensis is not greatly dissimilar to that of M. s. splendida from Wet Tropics streams [1097].
Conservation status, threats and management Melanotaenia eachamensis was initially thought to be the first Australian freshwater fish to have become extinct in the wild [1353]; this species is now listed as Vulnerable [117]. Its distribution on the Atherton Tablelands is limited [904]. Potential threats include the destruction of habitat, flow regulation, hybridisation with other rainbowfishes and interactions with introduced species. The removal of riparian vegetation and subsequent changes to in-stream channel morphology and the presence of invasive grasses is likely to result in reductions in abundance. Although para grass is used as a microhabitat by M. eachamensis, it is unlikely, for a number of reasons, that reaches with very prolific infestations will continue to support large populations of M. eachamensis. First, M. eachamensis uses only the margins of para grass stands, thus para grass proliferation to the point where it dominates the in-stream habitat is likely to reduce the overall habitat availability and suitability. Second, macroinvertebrate and microalgal production are likely to be depressed
Other (6.4) Unidentified (17.4%) Algae (10.4%) Detritus (2.4%)
Terrestrial invertebrates (7.7%)
Aerial aq. invertebrates (5.0%) Macrocrustaceans (2.0)
Aquatic insects (59.1%)
Figure 2. Mean diet of Melantaenia eachamensis. Data for 148 individuals collected from Dirran Creek, Johnstone River drainage, over the period 1994–1997.
Table 3. Life history data for Melanotaenia eachamensis. Data are summarised from three studies conducted within the Johnstone River catchment over the period 1994–1997 [308, 1108, 1109]. Age at sexual maturity (years)
<1 (probably 6 to 7 months)
Minimum length of ripe females (mm)
37 mm
Minimum length of ripe males (mm)
49 mm
Age at death (years)
Probably not greater than 2 years in wild populations
Female to male sex ratio during breeding season ? Occurrence of ripe fish
August through to April
Peak spawning activity
August through to November
Critical temperature for spawning (°C)
Reproductive activity absent in Dirran Creek when water temperatures less than 17°C, larvae absent until temperatures greater than 20°C
Inducement to spawning
? Spawning period corresponds to period of stable low flows
Mean GSI of ripe females % (± SE)
8.47 ± 0.49
Mean GSI of ripe males % (± SE)
1.99 ± 0.20
Maximum fecundity (number of ova)
2126, fecundity related to size
Fecundity/length relationship
egg number = 51.6(SL) – 1273; n = 39, r = 0.65, p<0.001
Egg diameter – mm (± SE)
1.238 ± 0.022 (from ripe fish)
Frequency of spawning
Continuous while temperatures above 17°C, eggs produced in batches of between 4 and 452. Batch size varies with female size and varies between 7 and 23% of the total number of eggs
Oviposition
Adhesive eggs found in root masses in well oxygenated areas such as below riffles and rapids
Parental care
Absent – adults will eat larvae
Time to hatching (days)
?
Length at hatching (mm)
4.00–4.15 mm
Length at free swimming stage (mm)
As above
Length at first feeding (mm)
4.65–5.92 mm, little indication of large yolk deposit visible in much smaller fish
End of larval development (mm)
11–14 mm
Duration of larval development
?
Survivorship
Larvae experience high mortality with onset of wet season flooding
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Freshwater Fishes of North-Eastern Australia
Fluctuating flows during the spawning period may result in desiccation of eggs, stranding of larvae in marginal habitats or physical removal of larvae during peak flows. Given its short life-span, interference to the flow regime may impact on population levels over a relatively short time period. Reintroduction of M. eachamensis into Lake Eacham is unlikely to succeed whilst introduced predators are still present in this system. Translocation of native fishes into Tablelands streams in which they were previously absent, for the purposes of enhancing recreational fisheries, is likely to impact on populations in streams. For example, H. fuliginosus has been stocked in the upper Johnstone River and its sudden appearance in Dirran Creek suggests that this species is expanding its range on the Tablelands. It would be tragic if stream populations suffered the same fate as the lacustrine population of Lake Eacham. Impacts associated with the presence of the introduced guppy (Poecilia reticulata) are unknown in type and severity but are probably minor, providing habitat degradation does not occur in the future.
in sites dominated by para grass. A more extensive inventory of the distribution of M. eachamensis on the Atherton Tablelands, accompanied by thorough habitat mapping is needed to discern the relationship between abundance and para grass. In addition, such a program could be used to determine the conditions under which M. s. splendida is favoured and whether this is to the detriment of M. eachamensis. Hybridisation between these species was seen by McGuigan [904] as a serious threat to the continued existence of the genetic distinctiveness of M. eachamensis. Stream regulation and reductions in flow are likely to reduce habitat availability and suitability. This species prefers habitats with moderate flow and accessible marginal areas. A pronounced reliance on the larvae of aquatic invertebrates may necessitate adequate flows that allow production of this faunal component and to ensure the removal of fine sediments. Periods of stable flow are apparently necessary for spawning and successful larval recruitment, but flows must be sufficiently high to result in access to bank-side structures such as root masses for oviposition and marginal areas for larval habitat.
236
Melanotaenia utcheensis McGuigan, 2001 Utchee Creek rainbowfish
37 245025
Family: Melanotaeniidae
SL (6.6–8.9%)); caudal peduncle length 17.8% of SL (14.6–22.9%); caudal peduncle depth 11.5% of SL (14.6–22.9%). Males and females do not differ significantly with respect to these parameters, the only major differences being in colour (see below) and in fin length. The pelvic, second dorsal and anal fins are longer in males: a common sexual dimorphism observed in rainbowfishes. Melanotaenia utcheensis is deeper in the body than M. splendida (28.2%) and M. eachamensis (26.5%). Note that, in contrast, McGuigan [904] reported that M. eachamensis is deeper in the body than M. s. splendida. The first dorsal fin is inserted slightly more anteriorly in M. utcheensis than in M. splendida (47.7%) but slightly more posteriorly than M. eachamensis (44.5%). Differences in fin ray and vertical and horizontal scale row counts may also be used to distinguish between these three species (see accompanying chapters) but as is evidenced in the ranges in morphometric and meristic features given here, there is often substantial overlap between species. We have noted that the first spine of the second dorsal fin is somewhat thickened and pungent but its value as a diagnostic character remains to be demonstrated.
Description First dorsal fin: V–VII; Second dorsal: I, 10–12; Anal fin: I, 16–20; Pectoral: 11–15; Horizontal scale rows: 9–11; Vertical scale rows: 32–35; Predorsal scales: 13–16 [904, 1093]. Figure: large mature male specimen, 60 mm SL, Utchee Creek, March 1995; drawn 2003. Melanotaeia utcheensis is a moderate-sized rainbowfish rarely exceeding 60 mm SL, more commonly between 45 to 50 mm SL [1093]. The mean (± SE) and maximum length observed by us over the period 1994–1997 was 39.7 ± 0.25 mm SL and 85 mm SL, respectively [1093]. The relationship between weight (g) and length (SL in mm) is: W = 1.223 x 10–5 L3.09; r2 = 0.975, n = 56. Information concerning morphometric variation given in the original description of M. utcheensis [904] contains some apparent errors and is difficult to interpret. For this reason, we have reanalysed data in Pusey et al. [1104], using only material from sites located in the upper reaches of Utchee Creek (the exact type locality) (n = 56), to describe the morphometrics of this species. Greatest body depth, at first dorsal fin, 30.3% of SL (27.2–34.2%); head length 28.3% of SL (25.9–30.9%); predorsal length 46.5% of SL (44.1–49.3%); eye large 9.8% of SL (8.8–11.5%), particularly in smaller specimens and set forward on head (snout length 8% of
Melanotaenia utcheensis has a distinctive colour pattern. The body is silver/blue in colour with a dark blue midlateral
237
Freshwater Fishes of North-Eastern Australia
utcheensis there are two mtDNA lineages, one occurring primarily on the Atherton Tablelands and the other in streams in the coastal uplands [905]. McGuigan [904] states that the two lineages are morphologically distinct but conservatively retained them within the single species.
stripe extending from the caudal fin across the operculum to the snout. Two, sometimes three, thin, bright orange stripes extend on the dorsolateral surface from the caudal fin to about the base of the first dorsal fin. A similar orange stripe extends from the caudal fin forward to about the base of the pectoral fin, below the midlateral stripe. Ventrally of this stripe, there is diffuse thick black stripe extending forward from the insertion of the last anal ray. This stripe may be discontinuous and is most intensely pigmented in reproductively active males. The two scale rows immediately below the midlateral stripe are frequently more silver than scales above the stripe. The scales have a light purple iridescence, the intensity of which depends on the incidence of light falling upon them. A large orange spot is present on the operculum. The dorsal and anal fins have a thin black margin, as does the pelvic fin, but are otherwise a dusky brown with reddish blotches, except when males are in breeding condition these fins may be an intense red. Female colouration is similar but never as intense. Colour in preservative: most colours fade greatly, less so in alcohol than formalin, and the body tends towards a dull tan. The midlateral stripe remains prominent but the orange stripes fade to a dark brown [904, 1177].
Distribution and abundance Melanotaenia utcheensis is endemic to the Wet Tropics region and further restricted within this region to the Johnstone River Basin [904]. This lineage occurs in a small number of tributary streams of the North Johnstone River on the Atherton Tablelands (Short Creek, Ithaca River, Gillies Creek and an unnamed tributary) and in Bromfield Swamp at the head of the North Johnstone River. We have used the term lineage here rather than species because, with the exception of the population in Short Creek and the unnamed tributary, these populations are admixed to varying degrees with M. eachamensis or M. s. splendida mtDNA lineages. Pure populations of M. utcheensis are present in Utchee Creek in the South Johnstone River drainage, and Fisher and Rankin creeks of the lower North Johnstone River. An admixed lineage (with M. s. splendida) was also detected in Tregothanana Creek in the lower Johnstone River [904]. We recorded M. utcheensis in 11 locations (from a total of 52) over the period 1994–1997 [1093], all located in creeks listed by McGuigan [904] but not including any located on the Atherton Tablelands. This species was the 13th most widely distributed species, the most abundant (contributing 18.8% of the total of 27 164 fish) and the ninth most abundant with respect to total biomass (1.3% of a total of 525.1 kg). This species was the most abundant species at those sites in which it occurred and contributed 54.9% of the total number of fish from such sites. A mean density of 1.06 ± 0.13 fish.10m–2 was estimated. A mean biomass density of 1.26 ± 0.13 g.10m–2 was estimated, accounting for 9.5% of the total biomass: the fourth most significant species. Melanotaenia utcheensis commonly occurred with (in decreasing order of abundance) Pseudomugil signifer, Mogurnda adspersa, Hephaestus tulliensis and Anguilla reinhardtii [1093].
Systematics Melanotaenia utcheensis has been long recognised as a distinct colour variety of either M. s. splendida or M. trifasciata [43, 797], and has been sold in the aquarium trade as a distinct form, the Utchee Creek type [904]. Allen and Cross [43] include this type within M. s. splendida but suggest that it may be an undescribed species. In an analysis of the morphometry and distribution of M. eachamensis, Pusey et al. [1104] identified populations of the Utchee Creek type as intermediate in morphology between M. eachamensis and M. s. splendida but were forced to assign them to M. eachamensis. Schmida [1202] in an analysis based largely on colour variation, and McGuigan et al. [905] in a genetic analysis, placed the Utchee Creek type in a group containing M. eachamensis, M. duboulayi, M. fluviatilus and M. s. australis (now M. solata Taylor). This taxon was formally described in 2001 [904]. Further genetic analysis (based on mtDNA sequence data) demonstrated that M. utcheensis is more closely related to M. duboulayi than it is to M. eachamensis [904]. These species belong to an old lineage, whereas M. s. splendida is a much younger species that has colonised the Wet Tropics region only recently (see M. splendida chapter). There is some evidence of admixture of mtDNA lineages of M. utcheensis and M. s. splendida when the two species occur in sympatry, but it is unknown whether this is due to historical or contemporary hybridisation [904]. Within M.
Macro/mesohabitat use Melanotaenia utcheensis occurs in small, third or fourth order streams located above about 50 m.a.s.l. (note however that a distinct lineage of M. utcheensis occurs on the Atherton Tablelands at elevations above 500 m.a.s.l.). Such streams have a moderate gradient of about 1%, are about 12 m in width and have an intact riparian canopy covering about 40% of the stream surface (Table 1). Although M. utcheensis occurs in reaches with a gradients ranging from 0.05% (pools) to 4.1% (rapids), this species
238
Melanotaenia utcheensis
is most abundant in shallow riffles or runs (<0.4 m) with a gradient of about 0.4% and water velocities less than 20 cm.sec–1.
(a)
Table 1. Macro/mesohabitat use by Melanotaenia utcheensis. Data summaries based on site data for 11 sites collected over the period 1994–1997. Parameter
Min. 2
Max.
Mean
50
30
40
20
30
(b)
20 10
10 0
0
W.M.
1.9 Catchment area (km ) Stream order 3 Distance to source (km) 3 Distance to river mouth (km) 33 Elevation (m.a.s.l.) 55 Width (m) 0.52 Riparian cover (%) 5
34.4 4 15 41.5 80 4.07 70
16.9 3.9 10.4 35.1 62.5 1.17 37.5
14.9 3.9 11.3 34.6 64.3 0.45 42.1
Gradient (%) 6.9 Mean depth (m) 0.2 Mean water velocity (m.sec–1) 0.04
23.5 0.56 0.23
11.9 0.35 0.16
12.0 0.39 0.15
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 2 0
9 5 15 42 39 51 98
1.6 1.9 8.5 16.5 19.9 18.6 22.75
1.5 2.3 9.3 20.7 19.5 31.9 13.7
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Small woody debris (%) Large woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
0.8 0 2.0 4.0 0 31.3 1.8 3.0 26.0 44.0
0.1 0 0.6 1.4 0 5.7 0.5 0.6 4.0 7.9
0.3 0 0.5 1.7 0 5.2 0.6 0.3 2.3 8.7
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
30
25 20
20
15 10
10
5 0
0
(e)
Total depth (cm)
(f)
25
80
20
60
Relative depth
15 40 10 20
5 0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Melanotaenia utcheensis in the Johnstone River. Summaries are derived from capture records for 66 fish collected from Utchee, Fishers and Rankin creeks over the period 1994–1997.
Although M. utcheensis may occur in reaches dominated by bedrock, this species most frequently occurs, and is most abundant, in reaches with a diverse substratum dominated by cobbles and rocks (Table 1). Cover is very limited in the streams in which M. utcheensis occurs, with the exception of root masses and beds of leaf litter. It is noteworthy that macrophytes, filamentous algae and submerged vegetation (para grass Brachiaria mutica) are very limited in abundance due to the presence of an intact canopy.
most fish occur in localised areas of no or low flow(<0.1 m.sec–1). This species occurs over a range of depths but is most common in depths of 20–40 cm (Fig. 1c) and is similarly widely distributed in the water column (Fig. 1d). It tends to occur infrequently in the upper one third of the water column. There appears to be little direct substrate preference as the distribution of particle sizes evident in Figure 1e closely approximates that seen in reaches in which this species occurs (Table 1). About 20% of the 66 fish upon which Figure 1 is based were collected more than 20 cm from cover (i.e. in open water), the remainder were most frequently in association with the substrate, although not necessarily in contact with the stream-bed. In deeper water (>30 cm), M. utcheensis often congregates in small groups
Microhabitat use Melanotaenia utcheensis occurs in a range of water velocities up to about 0.7 m.sec–1 but most commonly occurs in low to moderate flows up to 0.2 m.sec–1 (Fig. 1a). Focal point velocities are much reduced however (Fig. 1b) and
239
Freshwater Fishes of North-Eastern Australia
eachamensis), some larval production occurs throughout the year as evidenced by the presence of fish in the 10–15 mm size interval on all occasions. However, the only indication of a distinct larval/juvenile cohort is in October (the smallest individual (8 mm SL) was also collected at this time) and the large numbers of fish between 20 and 35 mm SL in the wet season sample suggests greatest larval production prior to the onset of the wet season.
of two to three individuals downstream of large rocks where the current is much reduced. In shallower waters, this species tends to occur lower in the water column amongst the cobbles and rocks. These factors are the principal reasons for the reduction in focal point velocity, relative to average water velocity, experienced by M. utcheensis (Figure 1b). Environmental tolerances Melanotaenia utcheensis occurs in streams of good water quality. The range in water temperature given in Table 2 is indicative of conditions experienced in well-shaded rainforest streams. The maximum temperature recorded over the period 1994–1997 was 32.7°C and occurred at a very open site with a dominant substrate of basaltic bedrock: M. utcheensis numbers at this time were depressed relative to previous occasions suggesting either some mortality or a retreat downstream to cooler waters.
200
Feb., March; n = 1066 160
May, July; n = 667 October; n = 418
120
80
40
Table 2. Physicochemical data for Melanotaenia utcheensis. Data summarties for 5098 individuals collected from 53 samples in the Wet Tropics region over the period 1994–1997 [1093]. Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
18.2 5.7 6.4 8.3 1.7
Max. 32.7 9.2 8.1 67.6 29.7
Mean
0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Standard Length (mm) Figure 2. Temporal variation in population size distribution of Melanotaenia utcheensis in the Johnstone River.
24.5 7.1 7.2 35.7 8.6
These data also indicate a gradual increase in mean size through the year and the unimodal size distribution of fish greater than 30 mm SL suggests that few fish live longer than one or two years. It is probable, given the close relatedness of M. utcheensis and M. eachamensis, that many aspects of their life history, such as fecundity, egg size and reproductive investment, are similar. In all likelihood, M. utcheensis spawns in the late dry season prior to the onset of summer rains, is short-lived and is a moderately fecund batch spawner, producing small, adhesive eggs that are deposited amongst root masses and bank-side vegetation.
Streams in which M. utcheensis occurred tended to be of neutral pH and of very low conductivity. In general, water clarity was moderately high but high levels of suspended solids during runoff events can contribute to transient high turbidity. That part of the Johnstone River catchment in which M. utcheensis occur tends to be dominated by sugar-cane farming, and banana and tea plantations and these activities may at times contribute high levels of sediment. Generally however, the relatively high discharge in these streams removes sediment quickly and it does not settle out to any great extent (i.e. see low proportion of mud in the sediment given in Table 1).
Movement There is little information on the movement biology of this species except that provided by a defaunation experiment in which mesoscale habitats were recolonised by M. utcheensis in numbers approximately equal to that observed prior the commencement of the experiment [1093]. McQuigan [904] interpreted the presence of distinct lineages (i.e. one present on the Tablelands and the other in lowland creeks) as indicative of restricted gene flow and long-term isolation. However, the lack of any distinction between M. utcheensis lowland populations in the North and South Johnstone rivers may indicate contempory gene flow.
Reproduction The reproductive biology of M. utcheensis has not been studied in detail. Examination of the length–frequency distribution (Fig. 2) of samples collected in Utchee and Fishers creeks during the wet season (February and March), early dry season (May and July) and the late dry season (October) suggests that, in common with other rainbowfishes in the Johnstone River (see accompanying chapters for M. splendida, C. rhombosomoides and M.
240
Melanotaenia utcheensis
least, this species should be listed as Restricted, given that it endemic to the Johnstone River basin.
Trophic ecology The diet of M. utcheensis has not been studied in detail. It is probable that its diet is similar to M. eachamensis, given their close relatedness and the general similarity in habitats used, and as such would be dominated by aquatic insect larvae with significant contributions by terrestrial invertebrates and microalgae. This species co-occurs with Anguilla reinhardtii and Hephaestus tulliensis, both of which may be piscivorous, and predation may be an important influence on the behaviour and ecology of this species.
Populations of M. utcheensis appear secure: we saw no evidence of population declines over the period 1994–1997. However, streams in which M. utcheensis occurs are located in areas of intense agriculture and are occasionally subjected to high levels of suspended sediment. No information is available on the types and amounts of biocides that this species may be exposed to during periods of heavy runoff nor on their tolerance to such toxicants. We have observed low frequencies of developmental abnormalities (lordosis and asymmetric jaw development) in populations receiving runoff from banana plantations [1093]. In addition, riparian extraction of water during the dry season in order to irrigate tea and banana plantations, may impact on this species if water levels are greatly reduced.
Conservation status, threats and management Melanotaenia utcheensis does not have an official conservation status but McGuigan [904] believed it should be ranked as Vulnerable. This high listing was due to the potential for genetic introgression by M. s. splendida to dilute the genetic distinctiveness of this species. At the
241
Melanotaenia maccullochi Ogilby, 1915 MacCulloch’s rainbowfish
37 245009
Family: Melanotaeniidae
Description First dorsal fin: IV–VII; Second dorsal: I, 7–12; Anal: III, 13–19; Pectoral: 11–14; Horizontal scale rows: 9–10; Vertical scale rows: 31–35; Predorsal scales: 14–18; Cheek scales: 9–14. Meristics highly variable across range. Figure: mature male, 48 mm SL, unnamed lowland tributary of the North Johnstone River, September 1995; drawn 2000.
Colour in life varies across the entire range. The basic colour pattern is one in which the body is a silver base colour, overlain with a series of fine horizontal black lines (one per scale row), head and nape dark brown/black, dorsal and anal fins pale to bright red and variously marked with black lines and diffuse dark submarginal band. Allen and Cross [43] suggest that populations in the southern most portion of its range lack strongly defined horizontal lines on the body and often lack lines and bands on the fins. They are however, distinguished by very bright red fins [38]. This colour form was suggested to occur from the McIvor River, north of Cooktown, south to its southern range limit. However, well-defined horizontal lines and bands on the fins are both present in the populations within the dune fields of Cape Flattery only 30 km north of the McIvor River, and in populations in the Johnstone River basin [1093]. Populations further to the north (Papua New Guinea and the Jardine River) frequently show yellow hues on the fins and body as well as bold black stripes on the dorsal and anal fins. An additional difference described by Allen and Cross [43], but not described in Allen [38], is that northern populations lack the bright neon nuptial stripe on the forehead present in southern populations. Further study is needed to determine whether colour
Melanotaenia maccullochi is one of the smallest of the rainbowfishes. Allen [43] states that the maximum size attained (for both sexes) is 60 mm SL but that specimens in excess of 45–50 mm SL are rare. Of 445 specimens collected from the floodplain of the Johnstone River, 82% were less than 35 mm SL and the maximum length was 53 mm SL [1093]. No specimens greater than 40 mm SL were collected from aquatic habitats of the dune fields of Cape Flattery [1093, 1101], and most specimens were less than 25 mm SL. Body slender, greatest body depth (at first dorsal) 30.3–37.8% of SL (males) and 28.1–32.3% (females); head length 25.3–31.0%; snout length 7.0–9.3; eye diameter 9.0–12.5%; interorbital width 8.5–11.4%; caudal peduncle depth 10.0–13.1%; caudal peduncle length 16.7–19.5%; predorsal distance 43.0–56.3%; preanal distance 49.9–58.4% [43].
242
Melanotaenia maccullochi
differences indicate genetically different populations, whether observed differences are clinal across the species’ range or whether observed differences are in some way related to the optical properties of the water in which this species occurs (i.e. extent of tannin staining). Colour in preservative: very little red colouration retained, horizontal lines prominent.
distinct group of M. maccullochi although the distance to the next population is only approximately 100 km to the south. However the barrier between these two populations is significant, consisting of steep mountains abutting the coastline with very little floodplain development (the Cape Tribulation area typifies this barrier well). This next population, the Wet Tropics subgroup, extends from the floodplain on the northern bank of the Daintree River [38, 1185, 1349] south to the Cardwell area [38]. Within this area M. maccullochi has been recorded from the following drainage basins (in addition to the Daintree River catchment): the Barron (the type locality), Mulgrave (specifically Behana Creek) [1093, 1349], Johnstone [1093, 1349] and Moresby rivers [1183], Maria Creek [1179], the Hull River [1179] and the Murray/Tully River wetland systems [1085, 1349]. This species is not common in the Wet Tropics region despite its presence in the drainages listed above. For example, it was recorded by us from only three sites in each of the Johnstone and Mulgrave/Russell drainages (from a total of 56 and 47 sites, respectively). It should also be emphasised that, within each drainage, these sites were adjacent to one another (i.e. within 200 m) and it is therefore even more uncommon than these data initially suggest. It is unlikely, and disappointing, that M. maccullochi still persists in the Barron River system given the extent of floodplain reclamation that has occurred in this drainage. However, a number of small wetlands still persist on the Barron delta [229] and it would be prudent to survey and protect these valuable habitat remnants. It is our experience that M. maccullochi is very frequently syntopic with Pseudomugil gertrudae. The latter species was collected in Eubanangee Swamp by Pusey and Kennard [1085] and it seems likely that M. maccullochi occurs there also. Similarly, we predict that populations of both should exist in the extensive swamp systems located to the east of the Malbon Thompson Range to the north of the mouth of the Mulgrave/Russell systems, and the Graham Range to the south. These habitats have not been surveyed.
Systematics Melanotaenia maccullochi was originally described by Ogilby in 1915 from material collected in the Barron River drainage [1021]. This population no longer exists. No synonyms exist [1042]. McGuigan et al. [905] placed it in a clade consisting of several of the subspecific forms of M. s. splendida plus three New Guinean species: M. sexlineata, M. parkinsoni and M. ogilbyi. The distribution of the species is highly fragmented and some populations are phenotypically unique, but unfortunately the extent of genetic variation among Queensland populations is unknown. Distribution and abundance Melanotaenia maccullochi occurs as a number of isolated populations in south-western Papua New Guinea and northern Australia. The Papua New Guinean distribution extends from the lower and middle sections of the Fly River west to at least the Bensbach River near the Irian Jayan border [38]. This species is apparently absent from the main channel of the Fly River itself but occurs in small tributary creeks and floodplain swamps. In Australia, several isolated populations are known to exist in Queensland and recent surveys have detected this species in the Northern Territory [38, 1349]. McGuigan et al. [905] included two specimens from the Finnis River in their phylogenetic analysis, and importantly, specimens from the Fly and Jardine rivers were more closely related than either was to the Northern Territory specimens. Further collecting will probably extend the distribution in the Northern Territory. The distribution in Queensland includes Cape York Peninsula (predominantly eastern Cape York Peninsula) and the Wet Tropics region. Aquatic habitats in Cape York in which it has been recorded include the Jardine River [43], perched dune lakes and Harmer Creek of the Shellburne Bay area [571], and Scrubby Creek (100 km south of Cape Weymouth) [571]. This group of populations is significantly isolated from the next nearest known population, which occurs in the Jeannie River [1349]. Further south there exists a very large population in a range of aquatic habitats of the dune fields of Cape Flattery [1101]. Populations also exist in the McIvor River [43] and Black Creek at Hopevale [571]. This group of populations may possibly represent another
Macro/mesohabitat use Allen [38] described the habitat of M. maccullochi in Papua New Guinea as floodplain swamps and small adventitious tributaries. This description also fits the habitat in the Wet Tropics region well. The data listed in Table 1 summarises the description of the types of streams in which this species been recorded in the Johnstone and Mulgrave/Russell drainages. In general they are found in a range of small streams but highest abundances are recorded in small, low-gradient, sandy streams located on the coastal floodplain.
243
Freshwater Fishes of North-Eastern Australia
abundant in habitats in which the larger M. s. inornata were common.
Table 1. Macro/mesohabitat use by MacCulloch’s rainbowfish Melanotaenia maccullochi. Data summaries derived from habitat data for six sites and a total of 280 individuals. Parameter
Min.
Max.
Mean
W.M.
42.6 7.8 20.2 13.3 3.5 5.9 57.5
1.9 1.2 14.2 10.2 2.0 4.2 17.8
50
(a)
(b) 50
40
Catchment area (km2) Distance to source (km) Distance to river mouth (km) Elevation (m.a.s.l.) Stream order Width (m) Riparian cover (%)
0.1 0.5 14.0 10 2 2.01 15
Gradient (%) 0 Mean Depth (m) 0.12 Mean water velocity (m.sec–1) 0
85.0 15.0 26.0 15 5 15.0 90 0.57 0.72 0.43
0.19 0.37 0.14
0.22 0.22 0.07
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
35 88 27 73 8 5 3
8.0 54.7 15.8 18.5 1.3 0.8 0.5
10.7 85.2 1.6 2.0 0.2 0.1 0
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Small woody debris (%) Large woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 2.2 0 0 0 0
23.7 6.9 18.0 31.0 7.0 81.2 7.0 7.0 11.0 53.0
4.3 2.3 6.0 7.5 1.2 21.9 3.3 3.3 2.5 25.5
22.6 6.6 0.5 29.6 6.7 7.1 0.2 0.1 0.3 1.0
40
30
30
20
20
10
10
0
0
30
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 30
20 20 10
10
0
0
Relative depth (%)
Total depth (cm)
Unlike similar streams in which species such as M. notospilus, C. rhombosomoides, Eleotris spp. and O. aporos occur, M. maccullochi tends to be more abundant where the riparian vegetation is sparse. This characteristic really reflects the fact that the streams in which it is most abundant tend to be channels cutting through swamps and Melaleuca wetlands rather than streams cutting through rainforest. It is also evident from Table 1 that M. maccullochi prefers habitat with abundant cover. Allen and Cross [43] also note that ample cover in the form of woody debris or aquatic vegetation was a feature of the habitat in which this species occurred.
(f)
(e) 30 30 20 20 10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by MacCulloch’s rainbowfish Melanotaenia maccullochi. Data derived from capture records for 81 individuals from a lowland adventitious tributary of the Johnstone River over the period 1994–1997.
Microhabitat use Melanotaenia maccullochi is most frequently collected from areas of low velocity (<0.2 m.sec-1) (Fig. 1a) in a range of depths up to 80 cm (Fig. 1c). It is most frequently collected from the lower half of the water column but infrequently in contact with the substratum (Fig. 1d) and consequently the focal point velocity (Fig. 1b) experienced is similar to the mean water velocity. The substrate distribution shown in Figure 1e suggests that it is frequently collected over coarse substrates, however this greatly reflects the anomalous substrate composition at the site from which these data were derived. Elsewhere M. maccullochi is much more frequently collected over a sand s 28
In the sand dune country of the McIvor River and Cape Flattery area, M. maccullochi occurs in a range of habitats from large lakes to swamps, isolated pools and streams. Some of the streams are extremely shallow (<3 cm) during the dry season but contain large numbers of M. maccullochi [1093]. In the surveys of Pusey et al. [1101], this rainbowfish was more abundant in shallow swampy habitats than it was in the larger lakes and also tended to be less
244
Melanotaenia maccullochi
indicate that M. maccullochi occurs in very fresh water. The low water transparencies recorded for the Cape Flattery region were due to high concentrations of dissolved organic acids, not suspended sediment or biogenic turbidity.
substratum as suggested by Table 1. It is frequently associated with aquatic and emergent vegetation (Fig. 1f). Environmental tolerances Experimental data are lacking and inferences on water quality requirements must be drawn from field studies. Data listed in Table 2 for the Wet Tropics region are drawn from a study conducted over the period 1994–1997 [1093] in small lowland rainforest streams, whereas the data from Cape Flattery concern water quality in blackwater swamps and streams in a large sand dunefield surveyed in November 1996 [1101].
Overall, the available data indicate that M. maccullochi occurs in waters of low conductivity and very high water clarity, albeit often highly stained and acidic. Reproduction No field data is available for this species. Merrick and Schmida [936] suggest that spawning occurs over several days during which 150–200 eggs with short, adhesive filaments may be laid. Hatching occurs after 7–10 days at 25°C. Allen [38] reports that in aquaria, M. maccullochi spawn over several days and that the eggs hatch after 8–9 days at 27–28°C. Larvae achieve a length of 12 mm in 60 days and 30–35 mm in five months. Both Allen [38] and Merrick and Schmida [936] suggest that sexual maturity is reached between 25 and 35 mm SL. Given the small range in body size seen in some populations, sexual maturity may be reached at even smaller sizes. It is probable that M. maccullochi spawns during the wet season.
Water temperature values given for the Wet Tropics region are typical of those recorded in lowland aquatic habitats but substantially higher values were recorded in the aquatic habitats of Cape Flattery. On another occasion (January 2000), we collected M. maccullochi from a very shallow (2–5 cm) blackwater stream in which water temperature was as high as 36°C (air temperature was in the low 40s) [1093]. Allen [38] recommends a temperature range of 24–28°C for captive specimens and Allen and Cross [43] list field temperatures as ranging from 24–30°C.
Movement No information is available on this aspect of the biology of M. maccullochi. However, it is highly likely that dispersal from dry season refuges occurs with flooding of swampy habitats at the resumption of the wet season.
Table 2. Physicochemical data for Melanotaenia maccullochi. Note that water clarity is given as NTU for the Wet Tropics region but as Secchi disc depths for Cape Flattery. Parameter
Min.
Wet Tropics (n = 11) Temperature (°C) 19.9 Dissolved oxygen (mg.L–1) 5.79 pH 5.92 Conductivity (µS.cm–1) 6.0 Turbidity (NTU) 0.81
Max. 27.3 8.36 7.92 63.8 5.61
Mean
Trophic ecology Information on feeding ecology is very limited. Data shown in Figure 2 is derived from a sample of 20 individuals between 18 and 28 mm SL collected from a shallow,
23.1 7.22 6.57 39.1 2.01
Microcrustaceans (3.0%)
Cape Flattery (n = 7) Temperature (°C) 25 Dissolved oxygen (mg.L–1) 6.4 pH 3.6 Conductivity (µS.cm–1) 89 Secchi disc depth (cm) 20
32 7.73 5.01 385 300
28.7 7.32 4.16 163 85.7
Unidentified (3.0%)
Aquatic insects (27.0%)
Dissolved oxygen values listed in Table 2 indicate that it occurs in well-oxygenated waters but it is difficult to estimate what the lower tolerance limits might be. A conservative value of 4.0 mg.L–1 would in all likelihood, be adequate. The pH values recorded from the Wet Tropics region are typical of lowland creeks, however, the values listed for Cape Flattery are very acidic and this area represents one of the most naturally acidic freshwater fish habitats in Australia [1084]. Conductivity values listed in Table 2
Algae (67.0%)
Figure 2. The mean diet of Melanotaenia maccullochi. Data derived from stomach content analysis of 20 fish from a shallow sand dune stream in the Cape Flattery area.
245
Freshwater Fishes of North-Eastern Australia
open sandy stream in the dune fields of Cape Flattery in January 2000. The dominant item (67%) was aquatic vegetation comprising entirely of a single species of highly pigmented (red) diatom. Aquatic invertebrates comprised a further 27% of the average diet and this fraction contained chironomid and ceratopogonid larvae only. A small contribution by microcrustaceans was also noted (copepods and Cladocera). Conservation status, threats and management Melanotaenia maccullochi is listed as Non-Threatened by Wager and Jackson [1353] and not listed by ASFB [117]. These listings do not take into account the particular threats faced by isolated populations however. The Wet Tropics population has probably experienced an enormous reduction in habitat in the last century. For example, wetlands in the Johnstone, Moresby and Mulgrave/Russell River drainages have been reduced by 65%, 60% and 54%, respectively in the period 1951–1992 [1177, 1183, 1184]. Further destruction of wetland communities in the Wet Tropics region continues almost unabated as agricultural land use continues to expand. The continued survival of the Wet Tropics population is far from assured. Further north, the association between M. maccullochi and aquatic
246
habitats typical of silica sand dune country results in the potential for conflict between conservation and extractive sand mining. However, to our mind, this potential conflict is being addressed and mitigated far more effectively and honestly than are the problems associated with wetland clearing further to the south. Given that this species is more properly considered a swamp and wetland inhabitant, in-stream flows are probably not critical for the maintenance of habitat or the provision of spawning cues. However, periodic flooding of wetland habitats may be necessary for maintenance of floodplain habitats and to allow fish to disperse between isolated localities. The continued survival of this species, especially in the Wet Tropics region where it faces its greatest threat, can only be assured if greater emphasis is placed on the protection, maintenance and enhancement of floodplain and wetland habitats. Re-establishment of this species into its type locality, whilst not critical to the survival of the species, would be ecologically valuable (as it would necessitate rehabilitation and enhanced protection of the wetlands in the Cairns area) and prove a useful exercise in public education.
Pseudomugil mellis Allen & Ivantsoff, 1982 Honey blue-eye
37 245019
Family: Pseudomugilidae
first dorsal. Caudal fin forked, with rounded tips. A single dark midlateral line extending along midlateral scale row from pectoral tip to base of caudal fin. Top of head dusky, with fine grainy melanophores. Eyes blue; cheeks iridescent blue. Sexual dimorphism and dichromatism pronounced. Males have elongated dorsal, anal and pelvic fin rays; colours of body and fins in males more distinct than in females. Males generally honey or bronze coloured with first dorsal fin mainly black except anterior border white; anal and second dorsal fins honey coloured in central portion with broad black submarginal band and white outer edge; caudal fin honey coloured with dorsal and ventral edges with black submarginal band and white border. Females plain amber colour with clear fins. Nonbreeding fish of both sexes greyish. Colour in preservative: pale tan to whitish with numerous small dark spots on scales and head. Dark line running along sides of body. In males first dorsal fin black and caudal whitish or with black submarginal stripe. Pectoral and all other fins in female whitish or translucent. Body scale margins outlined with black spots [44, 52, 629, 1190, 1216].
Description First dorsal fin: IV–VI (rays); Second dorsal: 6–9; Anal: 10–13; Pectoral: 9–12; Pelvic: 5; Caudal: 13–14 segmented rays; Vertical scale rows: 26–29; Horizontal scale rows: 5–6; Predorsal scales: 8–12, Gill rakers on first arch: 10–13; Vertebrae: 28–31 [44, 629, 1190]. Figure: mature male specimen, 23 mm SL, Mellum Creek, August 1989; drawn 1992. Pseudomugil mellis is a small fish commonly reaching 25–30 mm TL; males are reported to reach a maximum size of 38 mm TL [629]. No length–weight equation is available for this species but it is generally similar in size and shape to P. signifer. The following description is taken largely from Allen and Ivantsoff [44], Saeed et al. [1190] and Ivantsoff and Crowley [629]. This species has a moderately compressed and elongate body. The mouth is subvertical and small; small villiform teeth present on jaws, posterior premaxillary teeth not exposed when mouth closed. A few small pores are present on the head but mandibular pores are absent. Eye relatively large. Scales relatively large. First dorsal fin originating before pectoral fin tip about mid way along body; second dorsal fin originates well behind anal fin origin which is in line with or just behind last ray of the
Pseudomugil mellis occasionally occurs with P. signifer, a species of similar general appearance. Major distinguishing characteristics of P. mellis include smaller scales on the
247
Freshwater Fishes of North-Eastern Australia
This species is very patchily distributed but can be locally common in south-eastern Queensland. Arthington and Marshall [84] reported that it was present at just 18 localities on the mainland and on Fraser Island despite multiple surveys by several workers (listed in Arthington and Marshall [84]) at 269 localities considered likely to support populations of P. mellis (where a ‘locality’ referred to one aquatic system, irrespective of how many sites within the system supported this species). It has been recorded from most of the major creeks draining into Tin Can Bay, where it was moderately common (6–20 individuals per standardised seine-net haul) [84]. It is relatively common in the Noosa River (<20 to over 100 individuals per seine-net haul) [84, 861]. It was relatively uncommon in swamps and creeks at Marcus Beach (6–10 individuals per seine-net haul) [84]. Further south in Mellum, Coochin and Tibrogargan Creeks it was relatively uncommon (0–10 individuals per seine-net haul) [84]. It is occasionally common (five to over 100 individuals per seine-net haul) in several creeks and lakes on Fraser Island [84]. The sustainability of populations in many of these localities is now in doubt because of a range of anthropogenic impacts (see section on Conservation status, threats and management requirements).
nape, much smaller cephalic sensory pores, and darkercoloured submarginal band on first two rays of second dorsal and anal fins, with the distal half of remaining rays whitish [52, 1190]. Systematics The family Pseudomugilidae contains at least 16 species from three genera confined to Australia, New Guinea and eastern Indonesia. Two genera are present in Australia; Pseudomugil (total of 14 species, six of which are present in Australia) and Scaturiginichthys (one species present only in Australia) [38, 52, 53, 422, 635, 639, 1190]. Kner [724] established the genus Pseudomugil in 1865 to contain Pseudomugil signifer. He placed this genus in a separate family, Pseudomugilidae, but many subsequent researchers have considered it to be a member of the Atherinidae or the Melanotaeniidae. The family Pseudomugilidae shares many anatomical characters with members of the Atherinidae and is thought to have evolved from an ancestor of this largely marine family [32, 43, 1190]. However, Saeed et al. [1190] reinstated the family Pseudomugilidae in their comprehensive taxonomic revision. The etymology of the genus Pseudomugil is from the combination of the Greek for false and the Latin for grey mullet, probably referring to the resemblance of the body to a mullet [406]. The common name blue-eye refers to the conspicuous electric-blue coloured iris. Pseudomugil mellis was described by Allen and Ivantsoff [44] in 1982. It is closely related to P. signifer [1190] and was once considered to be just a variety of this species [38, 629].
Substantial temporal fluctuations in population sizes of P. mellis have been reported. Reductions in abundances of this species during winter and increases in abundance in warmer months have been reported for populations in Tin Can Bay streams [798] and the Noosa River [84]. Semple [1216] attributed fluctuations in abundances in these streams to floods flushing large numbers of fish into intertidal areas below natural barriers and to recruitment through reproduction. Arthington and Marshall [84] reported large increases in P. mellis populations in spring that also coincided with spawning and recruitment in this species.
Distribution and abundance Pseudomugil mellis has a very restricted and patchy distribution in coastal lowland wallum (Banksia heath) ecosystems of central and south-eastern Queensland. It occurs in two highly disjunct geographic locations. A single, isolated population is known from Dismal Swamp in the Water Park Creek drainage basin (approximately 70 km northnorth-east of Rockhampton) [1328]. Approximately 390 km to the south, it occurs in streams, lakes and coastal dune wetlands from Tin Can Bay (as far north as Big Tuan Creek, 15 km south-east of Maryborough) south to Tibrogargan Creek (45 km north of Brisbane). Pseudomugil mellis is also present on Fraser Island but does not occur on Moreton, Stradbroke or Bribie island off the south-eastern Queensland coast [38, 82, 84, 88, 104, 797, 1190, 1294]. A record of this species from Little Yabba Creek in the Mary River basin [1190] is almost certainly in error. It is perhaps surprising that P. mellis has not been recorded from apparently suitable wallum habitats in the area between Tin Can Bay and Water Park Creek to the north (e.g. the Woodgate-Kinkuna National Park and Deepwater Creek area).
Arthington and Marshall [84] reported that P. mellis populations in the 18 localities described above, most commonly occurred with R. ornatus, H. galii/klunzingeri, M. duboulayi and H. compressa. The Oxleyan pygmy perch, N. oxleyana, is occasionally present at sites with P. mellis. Pseudomugil mellis is known to co-occur with its congener P. signifer at relatively few geographical locations including Lake Wabby, and Bool Creek on Fraser Island and Big Tuan Creek on the mainland [62, 84]. Macro/mesohabitat use Pseudomugil mellis is found in coastal lowland wallum ecosystems generally characterised by dystrophic, acidic, darkly stained waters with siliceous sand substrates and abundant submerged and emergent vegetation [84, 88]. This species occurs in a variety of lotic and lentic habitat
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growing on the egg chorion have been reported to cause total mortality at temperatures 23°C or less [1216].
types including moderate-sized rivers, small coastal streams, coastal and insular dune wetlands and lakes. It has also been reported in lower tidal reaches of coastal streams [84, 88, 1216]. In riverine systems it occurs in the main channel and smaller tributary streams. It is generally found in areas where there is little or no flow, and where emergent sedges and rushes (Eleocharis spp., Lepironia articulata, Ghania spp. and Juncus spp.) and aquatic macrophytes (Nymphaea spp., Chara spp. and Utricularia spp.) are abundant [84, 88]
Table 1. Physicochemical data for Pseudomugil mellis. Data summaries for fish collected from 18 insular and mainland locations in south-eastern Queensland [84].
Microhabitat use Pseudomugil mellis is a loosely schooling species. We have observed loose groups of up to five individuals swimming in very shallow water (<10 cm) over fine sand and mud substrates, in the shallow sunlit margins of a pool in Mellum Creek. These fish were observed foraging on periphyton visible on the substrate [1093]. Arthington and Marshall [84] reported that fish were commonly observed swimming among or adjacent to beds of emergent vegetation (Eleocharis ochrostachys) and Lepironia articulata) in water depths up to two to three metres. On the basis of extensive behavioural observations, it was surmised that this microhabitat was used for feeding, pre-spawning displays and territorial defence by male P. mellis, as a site for spawning and deposition of eggs, and for the early stages of feeding and growth by larvae and small juveniles [84]. Leiper [798] reported that hundreds of small juveniles (1 cm long) occur in shallow warm waters among sedges in streams of Tin Can Bay.
Parameter
Min.
Max.
Water temperature (°C ) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
14 6.8 4.4 17 2.3
29 8.7 6.8 896 17.0
Reproduction The reproductive biology and early development of P. mellis is comparatively well-studied (Table 2). This species spawns and completes its entire life cycle in freshwater and has been bred in captivity [219, 600, 603, 797, 1216]. Fish mature at a relatively small size. Minimum and mean lengths of ripe (reproductive stage V) females from the Noosa River, south-eastern Queensland, were 15.6 mm SL and 19.1 mm SL [84, 1093]. The minimum size of spawning fish in aquaria is reported as 20 mm SL for both males and females [1216]. Pseudomugil mellis breeds during spring and summer; spawning in the Noosa River occurred between September and February [84]. Immature and early developing fish of both sexes (equivalent to reproductive stages I and II) were present year-round, but most common between February and August [84]. Developing fish of both sexes (stages III and IV) were common for a shorter period of time (September to November). Gravid males (stage V) were present between November and January; gravid females were present for slightly longer (September to January). Spent fish were present between November and April and were most common in January [84]. Semple [1216] noted that populations in Schnapper Creek, Kangaroo Creek and the Noosa River were comprised almost entirely of 9–15 mm fry during late winter/early spring.
Environmental tolerances Little quantitative data concerning environmental tolerances is available, but it has been suggested that P. mellis can tolerate ‘unfavourable conditions’ [1216]. In the wild, P. mellis occurs in a variety of physicochemical conditions (Table 1) but usually characterised by dystrophic, soft, acidic waters (pH range 4.4–6.8) often darkly stained by high concentrations of organic acids. However, it also occurs in some clear water lakes on Fraser Island. Suspended sediment levels are usually very low (maximum turbidity 17 NTU). This species generally occurs in dilute waters with conductivities less than 300 µS.cm–1, although populations in lower tidal reaches of streams have been recorded at conductivities up to 896 µS.cm–1. Field observations suggest it cannot tolerate low dissolved oxygen concentrations (minimum 6.8 mg.L–1). It has been collected from streams and small off-channel pools where temperatures ranged between 14 and 38°C and similar temperature tolerances have been observed in aquaria [1216]. Fish have been bred successfully in aquaria with water chemistry quite dissimilar to conditions in habitats of wild populations (e.g. pH up to 8.4) [1294]. Algae
The spawning stimulus for P. mellis is unknown but the peak spawning period in spring and early summer coincides with increasing water temperatures, increasing day length and a reduced likelihood of elevated discharges in south-eastern Queensland streams. Like other smallbodied atheriniformes, these environmental conditions are most likely to be favourable for egg and larval development and hence, successful recruitment [84]. Semple [1216] suggested that temperature was of critical importance for spawning in aquaria. In the Noosa River, spawning occurred at temperatures between 26.5°C and 28°C [84]. Successful spawning has been observed in aquaria
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apart [1216], or 0.025–0.1 mm apart [603]. These adhesive filaments range from 0.5–5.5 mm long [600, 603, 1216] and form rope-like attachments to aquatic vegetation [1216]. Additional details on embryonic morphology and development are given in Howe [600], Howe et al. [603] and Semple [1216]. The duration of embryo development is relatively long, but shorter than observed for P. signifer [600]. Incubation periods have been reported to range from 4.5–8 days (at 25–27°C ) [1216] and 12–13.5 days (at 24–26°C ) [600].
maintained at 24–26°C [600]; spawning has been reported to commence when water temperatures reached 28°C [1216], and breeding of this species has been recommended in aquaria maintained at 25–30°C [797]. Detailed accounts of the elaborate colouration and behaviour of spawning fish in aquaria is available for fish collected from Tin Can Bay and Fraser Island [600, 1216]. In aquaria, males can be very aggressive and are territorial when in breeding condition, usually remaining near a suitable site for spawning [1216]. Territorial and courtship behaviour has been reported in wild fish, with males in the Noosa River observed defending territories and exhibiting courting behaviour within beds of emergent sedges (E. ochrostachys) in water depths of around 15 cm [84]. In the Noosa River, spawning occurred in these beds of emergent sedges [84]. Eggs are deposited on submerged vegetation and are attached by adhesive filaments. Spawning in aquaria has been observed to occur amongst aquatic vegetation, with the site of spawning varying from near the substrate at the outside fringe of java moss [600], to within the roots of floating plants or in suspended fibres of spawning mops [797]. Pseudomugil mellis is a batch spawner and, in aquaria, pairs have been observed to spawn several times a day, females producing between 1 and 15 eggs in a 24-hour period [1216]. These fish were reported to release 42–125 eggs in 7–9 days followed by a rest period of 4–9 days. This species has also been reported to release 1–4 eggs [600] and 6–15 eggs [797] per day. Following spawning, males in aquaria continue displaying and defend their territories and thus the fertilised eggs [1216]. In aquaria, females may spawn only once, usually within the first year, rarely living to spawn a second season [1216]. Batch fecundity for P. mellis collected from the Noosa River has been estimated as ranging from 11–41 eggs (mean 28, n = 23) [84]. Fecundity is significantly related to fish size. The relationship between length (SL in mm) and batch fecundity (BF) for 23 fish from the Noosa River is BF = 3.696 SL – 42.72, r2 = 0.84. Fish of 18 mm SL produced about 25 eggs in total, whereas fish of 22 mm SL produced about 38 eggs [84].
Illustrations and descriptions of larval stages are available for fish reared in aquaria [1216]. Larvae are comparatively poorly developed at hatching. The length at hatching of prolarvae reared in aquaria ranged from 3.6–5.0 mm SL and a single oil droplet remained on the anterior ventral surface of the yolk [1216]. Early-hatching larvae 4.0 mm SL were especially poorly developed and unable to swim, whereas yolk-sac larvae 4.5 mm SL showed coordinated movement [1216]. The top of the head was spotted from the interorbital area back and postorbitally, with few spots anterior to the eye. The eyes and upper surface of the swim bladder were black, small melanophores were present on the preoperculum, and punctate melanophores were intermittently spaced along the lateral line. Paired punctate contour melanophores were present on the dorsal and ventral surfaces, and medial spots were sometimes present on the belly, the size and number of melanophores increasing with protracted exposure to high-intensity light [1216]. Once the yolk and oil droplet had been absorbed, the larvae moved to the water surface, resting alongside emergent objects and began feeding within 20 mm of the water surface. At this stage the caudal fin was rayed and the second dorsal fin and anal fin buds were developing. By 6.5 mm SL, the second dorsal fin and anal fins had developed rays and the pelvic fin buds were developing. All fins were rayed at 9.0 mm SL and, by this stage, larvae were feeding in the mid-water column and from benthic structures, they also formed tight aggregations when disturbed [1216]. Semple [1216] noted that P. mellis fry feed on the surface of submerged objects, behaviour suggestive of feeding on periphyton and/or microcrustaceans.
Eggs are large relative to body size. The diameter of waterhardened eggs has been reported to range from 1.26 to 1.31 mm [600] and 1.29 to 1.64 mm [1216]. Differences in reported egg sizes between studies may be related to variation in the sizes of females studied, as bigger fish often have larger eggs [1216]. The demersal eggs are spherical and the chorion is smooth [1216]. The eggs are covered by multiple filaments that vary in number, placement and size, depending on the study consulted. Estimates of numbers range from 60–80 filaments [1216] and from 96–104 [603, 1216]. Filaments (up to 0.04 mm thick [1216]) may be spaced over the egg surface 0.2–0.3 mm
At 100 days post-hatching, fish in aquaria ranged from 15.7–21.5 mm SL, at 245 days were 21.0–23.0 mm SL, and 22.0–24.0 mm SL at 17 months [1216]. Fish first spawned at 95 days post-hatching when they were 20 mm SL [1216]. Fish have also been reported to mature at 10–12 months [797]. The life-span of P. mellis in the wild is unknown but may be one to two years. Males reared in aquaria rarely lived to two years, and some females lived longer than two years [1216].
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Table 2. Life history information for Pseudomugil mellis. Age at sexual maturity (months)
Approximately 3 months [1216]
Minimum length of gravid (stage V) females (mm)
15.6 mm SL [84]; spawning fish in aquaria 20 mm SL [1216]
Minimum length of ripe (stage V) males (mm)
Spawning fish in aquaria 20 mm SL [1216]
Longevity (years)
In the wild, 1–2 years [84]; In aquaria, males up to 2 years, females 2+ years [1216]
Sex ratio (female to male)
?
Occurrence of ripe (stage V) fish
Spring and summer (September–January) [84]
Peak spawning activity
Spring and early summer [84]
Critical temperature for spawning (°C)
? 26.5–28°C in the wild [84], 24–30 in aquaria [600, 797, 1216]
Inducement to spawning
? Probably increasing temperature [1216]
Mean GSI of ripe (stage V) females (%)
?
Mean GSI of ripe (stage V) males (%)
?
Fecundity (number of ova)
Total fecundity = 11–41, mean = 28 [84]; In aquaria, may spawn several times per day with 1 to 15 eggs in a 24 hr period [1216]; 1–4 eggs per day [600]; 6–15 eggs per day [797]; 42–125 eggs in 7–9 day period followed by rest period of 4–9 days [1216]
Total Fecundity (TF) and Batch Fecundity (BF)/ BF = 3.696 L – 42.72, r2 = 0.84, n = 23 [84] length relationship (mm SL) Egg size (diameter)
Water-hardened eggs up to 1.64 mm [1216].
Frequency of spawning Batch spawner [1216]. In aquaria, females may spawn only once, usually within the first year, rarely living to spawn a second season [1216] Oviposition and spawning site
In the wild, spawning probably occurs in beds of emergent vegetation [84]. In aquaria, adhesive, demersal eggs are deposited in aquatic vegetation, with the site of spawning varying from near the substrate at the outside fringe of java moss [600], to within the roots of floating plants or in suspended fibres of spawning mops [797]
Spawning migration
none known
Parental care
Following spawning, males in aquaria have been reported to continue displaying and defending their territories and thus the fertilised eggs [1216]
Time to hatching
Varies with temperature. In aquaria 4.5 to 8 days (at 25–27°C) [1216]; 12–13.5 days at (24–26oC) [600]
Length at hatching (mm)
Newly hatched prolarvae 3.6–5.0 mm SL [1216]
Length at free swimming stage
Postlarvae 6.5 mm SL [1216]
Age at loss of yolk sack
?
Age at first feeding
12 days
Length at first feeding (mm)
Postlarvae 6.5 mm SL [1216]
Age at metamorphosis (days)
?
Duration of larval development
? Other microinvertebrates (2.3%) Microcrustaceans (3.4%)
Movement No information available on movement, however it is unlikely that P. mellis undertakes large-scale movements.
Unidentified (17.5%)
Aquatic insects (8.7%)
Terrestrial invertebrates (6.4%)
Trophic ecology Diet data for P. mellis is available for 227 individuals from the Noosa River [84]. This species is a microphagic omnivore foraging mostly on aquatic prey, which may be planktonic or associated with aquatic macrophytes. Algae (mostly diatoms, desmids and smaller amounts of filamentous algae) comprised the largest proportion of the total mean diet (55.8%) (Fig. 1). Aquatic insects (8.7%), microcrustaceans (Copepoda and Cladocera – 3.4%) and other microinvertebrates (2.3%) were also consumed. This species evidently also forages at the water surface
Aerial aq. Invertebrates (5.8%) Terrestrial vegetation (0.2%)
Algae (55.8%)
Figure 1. The mean diet of Pseudomugil mellis. Data derived from stomach content analysis of 227 individuals from the Noosa River, south-eastern Queensland [84].
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Freshwater Fishes of North-Eastern Australia
area of this type of habitat (C. Catterall, pers. comm.) and may have disturbed or eliminated populations of P. mellis by processes such as sediment intrusion into streams and wetlands, loss of riparian shade and associated habitat elements (woody debris, leaf litter), and loss of terrestrial inputs into aquatic food webs [1092]. Sand intrusion into aquatic habitats has been well documented in the case of Lake Wabby on Fraser Island, where shallow littoral habitat has been submerged under sand derived from a large, unvegetated sand blow [62].
consuming terrestrial invertebrates (6.4%) and aerial forms of aquatic insects (mostly adult Diptera and Trichoptera – 5.8%). There was a low degree of dietary overlap between P. mellis and all other species collected in the Noosa River study site, primarily due to the large amount of algae consumed. The high degree of herbivory in P. mellis is greater than that observed for P. signifer. In aquaria, juveniles greater than 9.0 mm SL and adults have been observed to eat the eggs of conspecifics [1216]. Conservation status, threats and management The conservation status of Pseudomugil mellis was listed as Vulnerable by Wager and Jackson [1353] in 1993. This category includes taxa not thought to be endangered but deemed to be at risk by having ‘small populations’ and/or ‘populations which are declining at a rate that would render them endangered in the near future’. In 1996, the IUCN Red List of Threatened Species [17] upgraded the conservation status of this species to Endangered. The most recent assessment of the conservation status of Australian fishes by the Australia Society for Fish Biology [117] also lists P. mellis as Endangered.
Over-exploitation of P. mellis is an issue with respect to excessive collection for private aquarium stocks and commercial purposes [88, 1210]. Both may have contributed to population decline in recent years [84, 1353], however, the intensity and impact of this activity is not known. The Australia New Guinea Fishes Association (ANGFA) has issued several warnings to its membership that excessive collection of rare species for aquarium purposes is potentially deleterious. Leiper [798] suggested that populations of P. mellis in mainland creeks that are reduced to very low abundance by the collection of fish for commercial purposes might not be able to recover from other disturbances, such as flood spates, drought, pollution events or the establishment of a small population of Gambusia holbrooki. Bowman [215] commented that P. mellis should be bred in captivity to meet the requirements of aquarists, with limited collection of wild stock for breeding purposes. He further advised that the commercial collection of P. mellis, if allowed, should be carefully monitored.
Freshwater habitats within coastal wallum are particularly vulnerable to local rainfall events and long-term variability in precipitation levels. Drought conditions affect both perched and window lake water levels as well as creek discharge, either directly or by altering local and regional groundwater tables [154, 780], with the possibility that the aquatic macrophytes which serve as fish habitat are drowned at high water levels or destroyed by exposure at low water levels. Various features of the reproductive strategy and population ecology of P. mellis are similar to those documented in several closely related, small-bodied atheriniformes inhabiting unpredictable stream environments in south-eastern Queensland [949, 950]. These attributes may be presumed to confer upon P. mellis a capacity for high recruitment when environmental conditions become favourable following periods of stress and high mortality under adverse conditions [84].
The impact of water pollution is also difficult to estimate over a relatively wide area where many different toxic chemicals are used in agriculture, and nutrient enrichment may result from land use, sewage disposal and recreational activities. Eutrophication may be a more serious issue on Fraser Island, where two of the lakes (Ocean and Wabby) supporting P. mellis are already affected by recreational use [97]. The very low natural levels of nitrogen and phosphorus in the water of dystrophic systems renders them particularly vulnerable to even minor increases in nutrient concentrations [1033].
Rare fish are threatened worldwide by habitat fragmentation and loss, over-exploitation, introduction of alien species and pollution. The general nature of factors and processes threatening populations of P. mellis a decade ago were documented by Arthington and Marshall [84]. Habitat fragmentation and loss have probably had the most serious impact on this species, given its close association with coastal wallum vegetation, its habitat specificity and the history of human impacts on the wallum ecosystem via development for forestry and agriculture, urban expansion, resort development and recreation/tourism [88, 861, 1353]. The extent of clearing of wallum heathlands and shrublands has seriously reduced the available
Trampling and/or boat disturbance of beds of aquatic macrophytes (e.g. Eleocharis ochrostachys) used as habitat and spawning sites in shallow littoral areas may be a further impact of recreation in dune lakes and the Noosa River. Alien species are regarded as perhaps the most insidious and unpredictable threat to rare fish species and may be the most difficult to counter and manage. At least three alien fish species (G. holbrooki, Xiphophorus helleri and X. maculatus) are thought to have established self-maintaining populations in the freshwaters of the wallum ecosystem in
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Pseudomugil mellis
meta-population of this species are known, but quantitative details of population level impacts are generally not documented. However, Tappin [1296] suggested in 1996 that populations in Tibrogargan Creek had suffered a ‘drastic reduction’ in numbers and Chris Marshall (pers. comm.) now considers this population to most probably be extinct.
south-eastern Queensland. Several authors have suggested that P. mellis may be affected by G. holbrooki [82, 84, 1353]. Studies in the Noosa River and Blue Lake [84, 92], and many others [78, 83], have demonstrated the trophic flexibility of G. holbrooki (which may also include piscivory and the consumption of fish eggs), and its innate aggressiveness towards other fishes is well known [983]. Gambusia holbrooki is established in several localities supporting P. mellis (Noosa River, Mellum Creek, Coochin Creek and Tibrogargan Creek [84, 1093]. In Tibrogargan Creek, the possible extinction of a local population of P. mellis has coincided with an increase in the abundance of G. holbrooki as well as with disturbance in the surrounding catchment [84]. It is quite common for disturbance and the presence of G. holbrooki to act synergistically (see Arthington et al. [94]).
Arthington and Marshall [84] recommended a range of specific activities to conserve 18 individual localities and populations of P. mellis in Queensland, and also commented on the initiatives needed to protect the wallum ecosystems of south-eastern Queensland. Three phases of activity were recommended: 1) further research on topics which would provide information essential to the development of a Recovery Plan; 2) the establishment of a Recovery Team and the development of a Recovery Plan proposal for P. mellis, to be submitted to the Endangered Species Program in 1994; and 3) the conduct of a workshop involving Queensland management agencies, relevant scientists, other parties and community interests to underpin the development of a Recovery Plan for the wallum ecosystems of south-eastern Queensland. None of these recommendations have been taken up by the agencies responsible for environmental protection in Queensland.
The occurrence of G. holbrooki in many other mainland creeks within the geographic range of P. mellis and in a few coastal creeks on Fraser Island may perhaps represent a general threat given that spread by natural processes is possible and G. holbrooki is a particularly hardy and adaptable species [83]. Human distribution of G. holbrooki is still occurring in the largely misguided belief that this species is particularly beneficial for mosquito eradication. In summary, the factors and processes that presently threaten most individual populations of P. mellis and the
253
Pseudomugil signifer Kner, 1865 Pacific blue-eye
37 245020
Family: Pseudomugilidae
This species has a moderately compressed and elongate body. The mouth is subvertical, protrusible, with thick lips; mandibular pores present. Sensory pores present on dorsal surface of head. Eye relatively large. Lateral scales relatively large, dorsoventrally elongated in 5–6 even rows. First dorsal fin originates level with or just behind longest pectoral fin ray; second dorsal fin originates behind anal fin origin. Caudal fin forked, with rounded tips. Sexually dimorphic. Males with extended filaments on dorsal, anal and pelvic fins; fins of males may become brilliantly coloured yellow-orange, especially during the breeding season. Body semi-transparent, pale olive or yellowish; operculum and ventral surface silver. Iris blue. Iridescent midlateral spots or ‘sheen’ often present. Fins clear to yellow-orange; males with black blotches at base of anterior rays of anal and second dorsal fins; these fins may also have a white anterior edge and dusky posterior edge. Caudal fin white along dorsal and ventral margins, other caudal rays darker. Pectoral fins clear and possessing white tips with black submarginal band along uppermost edge. Scales with dusky margins, forming reticulated (networklike) pattern over body. Preserved colouration tan or yellowish, black margins on fins (as described above) retained in fixed specimens [34, 38, 493, 600, 629, 1190].
Description First dorsal fin: III–VI (rays); Second dorsal fin: 7–11; Anal: 10–13; Pectoral: 9–14; Pelvic: 5; Caudal: 15 segmented rays; Vertical scale rows: 25–31; Horizontal scale rows: 5–6; Predorsal scales: 9–12; Gill rakers on first arch: 9–12; Vertebrae: 27–32 [34, 493, 629, 1190]. Figure: mature male, 31 mm SL, Mulgrave River, September 1995; drawn 1999. Pseudomugil signifer is a small fish commonly reaching 30–35 mm TL. Males are known to reach a maximum size of 88 mm TL and females to 63 mm TL [629]. Of 4485 specimens collected from streams of the Wet Tropics region over the period 1994–1997 [1093], the mean and maximum length of this species was 24.1 and 56 mm SL, respectively. Of 11 093 specimens collected in streams of south-eastern Queensland [1093], the mean and maximum length of this species were 23 and 43 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 291 individuals of P. signifer from the Wet Tropics region (range 15–56 mm SL) is W = 1.4 x 10–5 L3.104, r2 = 0.931, p<0.001; and that for 366 individuals of P. signifer (range 17–31 mm SL) sampled from the Mary River, south-eastern Queensland, is W = 2.0 x 10–5 L3.065, r2 = 0.924, p<0.001 [1093].
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Pseudomugil signifer
Trinity Inlet; 4) Daintree and Mossman rivers; and 5) Low Isles and Cape Melville. The southern clade could be divided into four distinct subclades: 1) the Don, Calliope, Pioneer and Kolan rivers; 2) Burnett and Mary rivers; 3) the Pine River; and finally 4) the Clarence River south. [902, 1414]. Several points are worth noting here. First, the distinction between subclades often occurs over very small geographic distances. For example, the Mulgrave/Russell River is only approximately 50 km from the Barron River mouth. Trinity Inlet is even closer. The grouping of the Trinity Inlet and Mulgrave/Russell River populations provides further evidence of the likely historical connection between these drainages discussed in the chapter dealing with Glossogobius sp. 4. The separation of populations from the Pine River and Mary River is another such example of profound genetic differences occurring over small distances. Such distinction suggests that gene flow between adjacent catchments is negligible despite the fact that P. signifer can tolerate elevated salinities [902] (see also section on environmental tolerances). Second, despite the extensive coverage included in these studies, several major drainages such as the Burdekin, Fitzroy, Brisbane and Albert rivers or rivers of northern New South Wales such as the Hunter River were not included. Although their inclusion is unlikely to alter conclusions concerning genetic distinction between northern and southern populations it may result in the recognition of more subclades. Although not ruling it out, McGlashan and Hughes [902] could find little support for a hypothesis in which gene flow between rivers in the Wet Tropics region was facilitated by floods. In contrast, Wong et al. [1414] suggested that flood-assisted dispersal may explain the reduced extent of between basin differences observed in the southern portion of its distribution. Wong et al. [1414] believed that the identification of genetic differences between northern and southern populations of P. signifer warranted re-examination of the debate as to whether this taxon should be considered composed of two separate species. In support, they cite breeding experiments by Semple [1214] suggesting that females preferentially prefer males of the same major clade, and that fish from opposite ends of the species range will not interbreed (i.e. conditions of reproductive isolation) [1414].
Considerable spatial variation in colour and morphology with at least 15 geographical varieties recognised [38, 493]. Populations from northern populations (e.g. the Ross River near Townsville) are especially distinctive, being larger in size with exaggerated dorsal and anal fins [38]. Fish from acid wallum habitats in south-eastern Queensland often show deep orange on dorsal and anal fins [793]. This colouration is also present in populations from acidic, tannin-stained streams of the Wet Tropics region. Fin length and the intensity of colouration varies according to position in the catchment in the Mulgrave River. Male fish in small high gradient tributaries from which larger piscivorous fishes are excluded, tend to be more colourful with longer fins [1093]. Systematics Pseudomugil signifer is the most widespread member of the genus in Australia [34] and it is morphologically variable across its range, perhaps leading to the past taxonomic confusion with this species (reviewed in Hadfield et al. [493] and Saeed et al. [1190]). The type specimen used by Kner [724] to describe this species in 1865, was collected from Sydney. Specimens from Cape York were described as Atherina signata Gunther, 1867 [486], but were later synonymised with P. signifer [487]. However, Jordan and Hubbs [671] continued to recognise the Cape York specimens as a distinct species, P. signatus. Specimens of P. signifer from the Bremer River (a tributary of the Brisbane River) have also been described as Atherinosoma jamesonii Macleay 1884 [849]. In 1925, McCulloch and Whitely [881] recognised all regional forms as P. signifer, but these were subsequently redivided by Whitley [1383] into the northern species, P. signatus, and the southern species P. signifer. Whitely [1384] further suggested specimens from the Low Isles off the North Queensland Coast were a new subspecies P. signatus affinis. Electrophoretic and morphological analysis of populations of P. signifer and the two other nominal taxa P. signatus and P. signatus affinis, suggest that the populations studied represent a single species P. signifer and that variation between northern and southern populations were clinal [493, 1190]. Recent examination of the differences between northern and southern populations of P. signifer using DNA sequencing techniques has supported the notion of a major distinction between populations north of and including the Ross River, and those from the Calliope River south [902, 1414]. Separation of these clades corresponds to a region of terrestrial and aquatic biogeographic significance known as the Burdekin Gap [902, 1414]. Within the northern clade, five distinct subclades were noted: 1) Ross River and Herbert River; 2) Johnstone, Barron and Tully rivers; 3) Mulgrave/Russell River and
McGlashan et al. [903] detected significant genetic differences between populations of P. signifer within two rivers of the Wet Tropics region. Notably, genetic variation was greater among locations within a catchment than it was between subcatchments (i.e. Russell River versus Mulgrave River or North versus South Johnstone River). The estuarine confluence of each subcatchment in both rivers was not considered a barrier to movement but distance was important in determining the extent and distribution of
255
Freshwater Fishes of North-Eastern Australia
sites in which it occurred in this river, frequently occurring with (in decreasing order of relative abundance) M. splendida, H. compressa, R. bikolanus and M. notospilus. This species was similarly abundant in the Mulgrave River (Table 1), frequently co-occurring with H. compressa, C. rhombosomoides, A. reinhardtii and M. splendida. Although abundant, this species contributes little to total biomass.
genetic diversity. Thus, although P. signifer may move across an estuarine barrier to colonise an adjacent subcatchment [903], it does not appear to move out of a catchment and into another [902]. Significant amongpopulation genetic variation implied that populations in these rivers are not panmictic and that gene flow between locations is restricted. However, movement between subcatchments may occur at times of flooding.
Table 1. Distribution, abundance and biomass data for Pseudomugil signifer in the Wet Tropics region. Data summaries for a total of 4485 individuals collected from rivers in the Wet Tropics region over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred.
Distribution and abundance Pseudomugil signifer is a relatively widespread species occurring in coastal drainages of eastern Australia from the Rocky River (35 km north of the Stewart River, eastern Cape York Peninsula) [569, 571], south to around Narooma (280 km south of Sydney) in southern New South Wales [629]. There is also a single record of this species in western Cape York Peninsula (the Mission River near Weipa [1190]). It is present in marine and brackish habitats on Lizard Island, Dunk Island, Hinchinbrook Island and Low Isles off the north Queensland coast [493, 782, 851, 1349, 1383, 1384], and in lakes and streams of the dune islands of south-eastern Queensland.
Total % locations % abundance Rank abundance % biomass
Pseudomugil signifer is relatively uncommon and patchily distributed in rivers of eastern Cape York Peninsula. The northern-most populations occur in the Rocky River [571] and possibly Massey Creek [569], it is apparently absent from the Stewart River and the Normanby Basin (some 140 km of coastline) but it reappears at Cape Melville and in Alex Creek (Jeannie Basin) [571] and is present in the McIvor and Annan rivers [571, 1223]. This species was the 11th most abundant species in a survey of the Annan River but comprised 2% of the catch only [1223]. It has not been collected from lakes and streams of Cape Flattery and Cape Bedford dunefields.
Rank biomass
55.6 13.8 (26.5)
Johnstone River
Mulgrave River
48.2
88.6
10.4(26.3) 25.1(26.7)
3 (1)
1 (1)
1 (2)
0.3 (2.3)
0.2 (1.7)
0.5 (1.4)
17 (14)
13 (14)
17(14)
Mean numerical density 1.38 ± 0.11 (fish.10m–2)
1.13 ± 0.10 1.68 ± 0.16
Mean biomass density (g.10m–2)
0.42 ± 0.04 0.86 ± 0.08
0.62 ± 0.05
This species is also common and widespread in most major rivers and streams of coastal central Queensland, although it may be absent from some of the smaller catchments of the region (e.g. Leichhardt’s and St Margaret’s creeks) [1053]. Beumer [176] found it to be the second most abundant species in the Black-Alice River (M. s. splendida was the most abundant), however abundance levels varied seasonally (most abundant from August to December) and spatially (most abundant at downstream sites). This species is abundant in the Ross River also [408]. It is less abundant in the Burdekin River [1098]. Pusey et al. [1098] recorded nine individuals only from an electrofishing total of 3360 fish. Its distribution in the lower Burdekin River is limited to the Bowen and Broken rivers [1082] and adjacent catchments (Haughton River and Baratta Creek). Pseudomugil signifer occurs in the Proserpine and Pioneer rivers [658, 1081, 1093]. In the former river, it was abundant at a single site only and in which Gambusia holbrooki was absent [1093]. In the Pioneer River, P. signifer was usually the second or third most abundant species at riverine sites but was either absent or occurred at very low abundance in impounded reaches. It is reasonably common in short coastal streams near Sarina [779] and is widespread and generally
In a survey of rivers of the Wet Tropics region, north Queensland, P. signifer was the second most abundant species collected, occurring in over 56% of the 93 sites surveyed and present in all of the 10 major drainage basins sampled [1085, 1087]. This species occurs in all major drainages of the region from the Bloomfield River south to, and including, the Herbert River [98, 584, 585, 643, 1085, 1096, 1177, 1183, 1184, 1349]. It is also present in small systems such as the short creeks of the Cape Tribulation area [1085], Maria Creek and the Hull River, some short creeks of the Cardwell region [1085] and streams of Hinchinbrook Island [851]. Pseudomugil signifer is widespread and achieves very high levels of abundance in streams of the Wet Tropics region (Table 1). This species occurred at an estimated density of 1.38 ± 0.11 fish.10m2 and was the third most abundant species collected over the period 1994–1997 in the Johnstone River [1093]. It was the most abundant species at those
256
Pseudomugil signifer
common in the mid- to lower Fitzroy River [160, 404, 405, 658, 659, 942], Calliope River [915] and Baffle Creek [826]. In the Kolan River it is listed as present but not common [658].
relatively uncommon in the smaller rivers and streams of the Sunshine Coast, Moreton Coast and the South Coast sampled by us. Across all rivers, average and maximum numerical densities recorded in 481 hydraulic habitat unit samples (i.e. riffles, runs or pools) was 2.33 fish.10m–2 and 73.30 fish.10m–2, respectively. Average and maximum biomass densities at 402 of these sites were 0.67 g.10m–2 and 27.39 g.10m–2, respectively. Highest numerical densities and biomass densities were recorded from the Mary River. In south-eastern Queensland, it appears to be absent from many streams draining into Tin Can Bay and from the Noosa River (the habitat of P. mellis).
This species is very common in the Mary River but less common elsewhere in south-eastern Queensland. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that it had been collected at only six of 63 locations surveyed (19th most widespread species in the catchment) and formed 0.5% of the total number of fishes collected (14th most abundant). It is present but apparently relatively uncommon in the Elliott River [825] and rivers of the Burrum Basin [157, 736, 1305]. Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 22 394 individuals and it was present at 36.6% of all locations sampled (Table 2). Overall, it was the second most abundant species collected (13.7% of the total number of fishes collected) and was present in high abundances at sites in which it occurred (most abundant species forming 22.4% of the total number of fish collected at these sites). In these sites, P. signifer most commonly occurred with the following species (listed in decreasing order of relative abundance): C. marjoriae, M. duboulayi, R. semoni and H. klunzingeri. It was the 10th most important species in terms of biomass, forming only 0.4% of the total biomass of fish collected. It was most common and widespread in the Mary River where it occurred at 80% of locations surveyed and formed 24% of the total number of fishes collected. It was moderately common in the Brisbane River and the Logan-Albert River where formed over 3% of the total number of fishes collected in each river and was present at 31.5% and 38.2% of all locations surveyed, respectively. This species was
Pseudomugil signifer is widespread and often relatively common in coastal rivers and estuaries of New South Wales [25, 151, 438, 440, 441, 446, 553, 554, 601, 602, 604, 814, 1067, 1133]. Pseudomugil signifer is a loosely schooling species often present in very high local abundances. For example, we often observed loose schools of hundreds of individuals in shallow stream margins in rivers of south-east Queensland [1093]. In upper estuarine sections of the Ross River north-eastern Queensland, schools of fish numbering in the thousands have been observed [467]. In the Johnstone River, larvae frequently occur in aggregations of tens to hundreds of individuals, usually comprising a single developmental stage [1109]. It was usually the most abundant larval fish collected in this river [1109]. Macro/mesohabitat use Pseudomugil signifer is found in a variety of lotic and lentic habitats including small coastal streams, rainforest streams, large rivers and in dune lake and stream systems. It is also common in coastal lagoons, wetlands, salt marshes, estuaries and inshore marine areas (e.g. [151, 209, 428, 446, 602, 806, 968, 972, 1148, 1149, 1309, 1314]).
Table 2. Distribution, abundance and biomass data for Pseudomugil signifer. Data summaries for a total of 22 394 individuals collected from rivers in south-eastern Queensland over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
36.6
80.0
13.8
15.0
31.5
38.2
5.0
13.71 (22.44)
24.04 (25.36
2.03 (9.46)
0.23 (2.79)
3.18 (9.39)
3.44 (13.50)
0.14 (10.00)
2 (1)
1 (1)
9 (2)
17 (6)
10 (2)
8 (2)
17 (5)
0.41 (0.61)
0.59 (0.67)
0.01 (0.11)
–
0.14 (0.34)
0.10 (0.34)
0.01 (0.03)
10 (8)
7 (7)
17 (6)
–
18 (15)
16 (8)
16 (7)
Mean numerical density (fish.10m–2)
2.33 ± 0.24
2.96 ± 0.33
0.22 ± 0.09
0.05 ± 0.02
0.80 ± 0.17
0.61 ± 0.13
0.28 ± 0.00
Mean biomass density (g.10m–2)
0.67 ± 0.08
0.80 ± 0.11
0.02 ± 0.00
–
0.25 ± 0.06
0.19 ± 0.04
0.02 ± 0.00
257
Freshwater Fishes of North-Eastern Australia
abundant due to the elevated water velocity and moderately closed canopy. In nearly all cases, there is little difference between mean habitat characteristics and those weighted by abundance, suggesting that, across the range of habitats in which it occurs, variation in habitat structure does not greatly influence local population size.
In the Mulgrave and Johnstone river systems, P. signifer occurs across a wide array of stream types below an elevation of 70 m.a.s.l. (Table 3) from very small adventitious streams to large main channel rivers. Drainages of this region tend to rise very steeply from the coastal plain and consequently, this species does not penetrate very far upstream (maximum ~70 km). Although not usually considered to penetrate long distances inland [936], this species has been recorded over 200 km upstream from the river mouth in the Burdekin River [1082], over 300 km upstream in the Dawson River (Fitzroy Basin) [823] and up to 303 km upstream in the Mary River [1093] (see below). This species is widely distributed in the Wet Tropics region but is most common in shallow (0.34 m) streams, about 10 m in width, of moderate gradient (0.7%), and moderate water velocities (0.18 m.sec–1). Such habitats are best described as riffle/runs. Although found over a wide range of substrate types, the average substrate composition tends to be diverse (Table 3). Cover is typically not
Pseudomugil signifer occurs throughout the major length of the larger rivers of south-eastern Queensland, ranging between 8 and 303 km from the river mouth and at elevations up to 400 m.a.s.l. (Table 4). It most commonly occurs within 190 km of the river mouth and at elevations less than around 75 m.a.s.l. It is present in a wide range of stream sizes (range = 0.7–47.0 m width) but is more common streams of intermediate width (6–10 m) and with low to moderate riparian cover (<50%). In rivers and streams of south-eastern Queensland, this species has been recorded in a range of mesohabitat types but it most commonly occurs in runs characterised by moderate to
Table 3. Macro/mesohabitat use by Pseudomugil signifer in the Wet Tropics region. Data summaries for 1944 individuals collected from 78 locations in the Johnstone and Mulgrave rivers between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
0.2 1.5 8.1 5 2.4 0
Gradient (%) 0 Mean depth (m) 0.1 Mean water velocity (m.sec–1) 0
Max.
Mean
W.M.
515.5 67 69.5 70 39.1 99
73.1 14.3 36.8 32.4 10.7 41.7
65.0 13.6 37.1 34.1 9.4 39.9
4.5 0.87 0.51
0.7 0.37 0.17
Table 4. Macro/mesohabitat use by Pseudomugil signifer in rivers of south-eastern Queensland. Data summaries for 22 394 individuals collected from samples of 481 mesohabitat units at 108 locations in south-eastern Queensland streams undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
0.7 0.34 0.18
Max.
15.7 10 211.7 5.0 270.0 8.0 303.0 0 400 0.7 47.0 0 91.1
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec–1) 0
3.02 1.08 0.87
Mean
W.M.
1397.1 1174.7 67.6 56.9 162.8 189.0 73 75 10.4 6.0 38.2 46.1 0.42 0.40 0.15
0.67 0.25 0.11
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48 60 73 56 55 76 67
4.8 14.1 23.7 13.9 14.4 22.5 6.6
5.6 17.6 26.8 12.6 12.7 17.6 7.1
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
76.4 100.0 58.5 78.2 65.8 53.9 76.0
4.5 18.9 20.6 27.3 20.6 6.8 1.3
2.7 10.0 20.5 31.8 27.7 6.9 0.5
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
15.0 6.8 10.0 63.0 10.0 60.3 12.5 12.3 35.0 67.0
0.5 0.2 1.1 6.1 0.2 9.9 2.0 1.6 6.7 14.2
0.4 0.4 1.1 6.5 0.2 9.7 2.0 1.8 4.7 13.1
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
69.6 82.5 26.7 65.7 43.3 92.6 37.6 22.5 96.3 100.0
11.8 8.5 1.1 5.1 1.5 14.2 4.2 3.5 13.8 18.9
8.4 8.9 0.9 3.6 0.9 19.2 2.8 3.3 9.0 13.5
258
Pseudomugil signifer
high gradient (weighted mean = 0.67%), shallow depth (weighted mean = 0.25 m) and low to moderate mean water velocity (weighted mean = 0.11 m.sec–1) (Table 4). It is particularly common in slow-flowing marginal areas within shallow main channel riffles where stream gradients and water velocities are high (maximum gradient = 3.02%, maximum velocity = 0.87 m.sec–1). This species is most abundant in mesohabitats with substrates of intermediate size (fine gravel, coarse gravel and cobbles) and particularly where leaf litter beds, root masses, undercut banks, submerged aquatic macrophytes and filamentous algae are common. Elsewhere, this species has been classified as a pool-dwelling species [553] and has been reported to be common in clear forested streams but usually within 15–20 km of the sea [38, 52]. Microhabitat use In streams of the Wet Tropics region, P. signifer is frequently found in velocities up to 0.3 m.sec–1 and occasionally in flows up to 0.9 m.sec–1 (Fig. 1a). Focal point velocities experienced tend to be substantially less than average water velocities however, and most fish were collected from areas of low flow (<0.2 m.sec–1) (Fig. 1b). The majority of fish were collected from depths of 30 cm or less, although some individuals were collected from depths of greater than 50 cm (Fig. 1c). Although recorded from a range of positions in the water column, most P. signifer in streams of the Wet Tropics region are usually collected from the lower half of the water column, many in close proximity to the substrate (Fig. 1d) which they use as a refuge from high current velocities. This species may be found over a wide range of substrate types (Fig. 1e) similar to that observed in the reaches in which it occurs (Table 3), however more fish were collected over coarse substrates than would be suggested by average substrate composition, suggesting a preference for coarse gravel cobbles and rocks. It is not unusual in riffle habitats to observe P. signifer positioned downstream of large rocks in the lee of the current. Male fish in particular, establish small territories in such microhabitats and aggressively defend them against conspecific intruders. Such microhabitats are also used as stages for sexual display providing they are well illuminated. In reaches with a finer substrate and elevated current velocities, P. signifer is often associated with leaf litter and other bank-associated cover elements (Fig. 1f). This small species is frequently predated upon by a range of other fishes and close proximity to cover probably reflects some element of predator avoidance as well as in response to high current velocities.
(a)
(b)
60
60
40
40
20
20
0
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
40
40
30
30
20
20
10
10
0
0
Total depth (cm) 30
(e)
Relative depth 40
(f)
30
20
20 10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Pseudomugil signifer in the Wet Tropics region (solid bars) and in south-eastern Queensland (open bars). Summaries derived from capture records for 1533 individuals from the Johnstone and Mulgrave rivers in the Wet Tropics region and for 6255 individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
recorded at maximum mean and focal point water velocity of 1.28 and 0.92 m.sec–1, respectively. In riffle habitats where average water velocities are high, it is particularly common in the slow-flowing shallow stream margins among submerged riparian vegetation [1093]. This species was collected over a wide range of depths, but most often less than 40 cm (Fig. 1c). A pelagic loosely schooling species, it most commonly occupies the mid to upper water column (Fig. 1d). It is found over a wide range of substrate types but most often over fine gravel, coarse gravel and cobbles (Fig. 1e). This species was usually
In rivers of south-eastern Queensland, P. signifer was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b). It has been
259
Freshwater Fishes of North-Eastern Australia
ant of a relatively wide range of temperatures (8.4–31.7°C), whereas those of rainforest streams of the Wet Tropics have been collected over a smaller range (15.2 –29.7°C). In aquarium conditions however, populations from central New South Wales were intolerant of elevated temperatures: temperatures over 30°C, killed some individuals and prolonged exposure to temperatures above 36°C killed all fish [1214]. Aarn et al. [25] cautioned that although the wide geographical distribution and range of habitats in which this species occurs (from pristine freshwaters to polluted estuaries) may be indicative of wide environmental tolerances, populations from either very stable or physiologically stressful habitats may not be especially hardy. They cited the fact that P. signifer from Lake Wabby (a dune lake on Fraser Island) die rapidly when removed from their environment [25]. Harris and Gehrke [553] classified P. signifer as intolerant of poor water quality.
collected within 1 m of the stream-bank (75% of 6255 fish collected), and almost always was always found in close association with some form of submerged cover (Fig. 1f). Like fish from the Wet Tropics region, it was frequently collected near leaf-litter beds and the substrate in southeastern Queensland, but was also often found close to filamentous algae, submerged marginal vegetation, aquatic macrophytes and small woody debris (Fig. 1f). Some information is available on larval habitat use. In the Johnstone River, northern Queensland, larvae generally show strong preference for the upper third of the water column, shallow waters (10-30 cm) with low mean water velocities (<0.1 m.sec–1) and abundant in-stream cover [1109]. The larvae of P. signifer tend to occur in areas of greater depth, more distant from the stream bank and in areas of higher flow (albeit still greatly reduced) than the larvae of other co-occurring species such as M. s. splendida, C. rhombosomoides and M. adspersa, possibly because they hatch at a more advanced state of fin and muscle development (i.e. postflexion) [1093]. In the Mary River, south-eastern Queensland, larval aggregations have also been observed during January in pools in shallow water (<10 cm), over sandy substrates, close to the bank (<30 cm) where water temperatures were elevated (up to 33°C) [1093].
Table 5. Physicochemical data for Pseudomugil signifer in the Wet Tropics region and south-eastern Queensland over the period 1994 to 2003 [1093]. Parameter
Min.
Max.
Wet Tropics region (n = 133) Water temperature (°C) 15.2 Dissolved oxygen (mg.L–1) 5.1 pH 4.5 Conductivity (µS.cm–1) 5.6 Turbidity (NTU) 0.2
Pseudomugil signifer has been collected among mangroves and seagrass beds in near-shore habitats in northern Queensland. In central New South Wales, large numbers were collected from seagrass beds (Zostera capricorni) in a coastal brackish lagoon and from open mud banks and among mangrove pneumatophores in an open estuarine habitat [602]. Environmental tolerances Little quantitative data concerning the environmental tolerances of P. signifer is available (Table 5). It has been collected over a relatively wide range of physicochemical conditions but appears to prefer well-oxygenated (minimum recorded dissolved oxygen level in south-eastern Queensland is 3.6 mg.L–1) and acidic to basic (pH range 4.5–9.1) conditions in both the Wet Tropics region and south-eastern Queensland (Table 3). The maximum turbidity at which this species has been recorded in southeastern Queensland is 144 NTU, but it appears to prefer less turbid waters (mean 5.6 NTU). Similarly, streams of the Wet Tropics region in which this species occurs tend to have low levels of suspended sediment (Table 5). We have collected this species in freshwaters up to 1898 µS.cm–1 conductivity, however it is euryhaline and can tolerate salinites from 0 to 60 ppt, and can maintain buoyancy over this salinity range by altering swim-bladder volume [428]. Populations from south-eastern Queensland appear toler-
Mean
29.7 10.0 8.4 65.6 22.1
22.7 7.1 6.9 32.5 2.5
South-eastern Queensland (n = 274) Water temperature (°C) 8.4 31.7 Dissolved oxygen (mg.L–1) 3.6 12.3 pH 6.0 9.1 Conductivity (µS.cm–1) 72.0 1897.5 Turbidity (NTU) 0.3 144.0
20.3 8.0 7.7 512.7 5.6
Reproduction The reproductive biology and early development of P. signifer is comparatively well-studied (Table 6). This species can breed naturally in fresh and saltwater [600] and has been bred in captivity [227, 600, 604, 797, 1214, 1291, 1294]. In rainforest streams of the Wet Tropics region, P. signifer commences maturity (stage II) at approximately 28 mm SL in males and 23 mm in females (Fig. 2). Growth is commensurate with reproductive development in both sexes until stage IV development is attained, thereafter little additional growth occurs. Males grow to much larger size than do females. In contrast to the pattern observed for female fish in streams of the Wet Tropics region, in which stage V fish were present in all months except January (when peak flooding occurred), reproductively active male P. signifer
260
Pseudomugil signifer
36
Reproductive stage males
I
34 120
females 32
100
II
III
IV
V
Males (7) (6) (26) (8)
(4) (27) (3) (6) (13) (7)
Females (1) (19) (12) (27) (7)
(14) (35) (9) (35) (17) (15)
30 80
28 60
26 40
24
20
22 I
II
III
IV
0 120
V
Reproductive Stage 100
Figure 2. Mean standard length (mm SL ± SE) for male and female Pseudomugil signifer within each reproductive stage. Fish were collected from the Johnstone and Mulgrave rivers over the period 1994 to 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 4.
were detected in the period July to September only (Fig. 3). Obviously a small number of reproductively active male fish are present for much of the year, as larval P. signifer are present from July to April [1109]. The sexual differences in size at which sexual maturity is attained (Fig. 2) suggests that delayed maturation in males is balanced against some fitness gain conferred by greater size, possibly the acquisition and defence of suitable display and spawning sites. Wong [1446] concluded that traits such as body size and fighting ability were unimportant in influencing female mate choice in experimental trials with fish from the Ross River. Instead, females preferred males that engaged in longer courtship behaviours (possibly thereby communicating their paternal competance) and this conferred greater hatching success [1446]. Male fish sourced from the Johnstone River were shown experimentally to prefer larger females, possibly because they are also more fecund [1447].
80 60 40 20 0
Month Figure 3. Temporal changes in reproductive stages of Pseudomugil signifer in the Johnstone River, Wet Tropics region during 1998 [1093]. Samples sizes for each month are given in parentheses.
January that elevated current velocities over the entire site, whereas larval production continued until at least April in an adjacent anabranch site despite a similarly abrupt reduction in larval abundance in January [1109]. Maturation commences at a relatively small size in fish from the Mary River, south-eastern Queensland also. Minimum and mean lengths of early developing (reproductive stage II) fish were 18.6 mm SL and 25.7 mm ± 0.3 SE, respectively for males and 19.0 mm SL and 23.5 mm ± 0.4 SE, respectively for females (Fig. 5). At 17 mm SL, the sexes of fish in aquaria could be distinguished on the basis of the external features (elongated anal and dorsal fins in males) [1214]. Females of equivalent reproductive stage were generally much smaller in size than males for populations from the Mary River, south-eastern Queensland (Fig 5). Gonad maturation in males was commensurate with somatic growth, the mean length at each reproductive stage being different from all other stages; this was not
Although reproductively active fish are present for many months, a clear seasonal increase in mean female GSI levels and a similar but far less pronounced increase in male GSI levels is evident in Figure 4. The majority of spawning occurs from July to October in an extended spawning season. Larval abundances also peak over this period [1109]. However, it is worth noting that the interaction between stream geometry and flow regime greatly influences the length of the spawning season. For example, larval abundance at a main channel site in the South Johnstone River decreased abruptly from 120 larvae per sample to zero with the onset of the summer flood in
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Freshwater Fishes of North-Eastern Australia
Fig. 5). The minimum size of spawning fish in aquaria is reported as 32 and 28 mm SL for males and females, respectively [1214].
10 Males 8
Females
Pseudomugil signifer has an extended breeding season in south-eastern Queensland, from late winter through to late summer but spawning appears to be concentrated between late winter and early summer (August to December). In the Mary River, immature and early developing males (reproductive stages I and II) were common year-round; females of equivalent reproductive stages were most common between February and June (Fig. 6). Developing males (stages III and IV) were present for a shorter period of time (August to December) than females, which were present almost year-round (except for mid-winter). Gravid males (stage V) were present only in September and October; gravid females were present for longer (August to March) but were most abundant between September and October (Fig. 6). This pattern is
6
4
2
0
Month Figure 4. Temporal changes in mean Gonadosomatic Index (GSI% ± SE) of Pseudomugil signifer males (open circles) and females (closed circles) in the Johnstone River during 1998 [1093]. Samples sizes for each month are given in Figure 3.
Reproductive stage I
II
III
IV
V
Males 100
Males 28
(12) (11) (5)
(9) (12) (7)
(24) (25) (16) (6)
(8)
80
Females
60
26
40 20 0
24
Females 100
22
(20) (16) (11 ) (13) (15) (8)
(47) (38) (32) (13) (8)
80
I
II
III
IV
V 60
Reproductive stage Figure 5. Mean standard length (mm SL ± SE) for male and female Pseudomugil signifer within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland, between 1994 and 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 7.
so apparent in females (Fig. 5). Fully mature (stage V) males were larger on average than females of equivalent maturity (mean 28.3 mm SL ± 0.1 SE for males; mean 24.9 mm SL ± 0.3 SE for females), although the minimum recorded size for a gravid female was substantially smaller (16.9 mm SL) than that of a male (23.8 mm SL) ([1093],
40 20 0
Month Figure 6. Temporal changes in reproductive stages of Pseudomugil signifer in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in parentheses.
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Pseudomugil signifer
Females are similarly in excess in the Wet Tropics region (Table 4).
similar to that observed in the Wet Tropics region except fully mature female fish are not present year round and the greatest abundance of such fish occurs slightly later in the year.
The spawning stimulus for P. signifer is unknown but the information presented above suggest the onset and duration of spawning is controlled by water temperature. The peak spawning period from late winter through to early summer coincides with increasing water temperatures, increasing day length and a reduced likelihood of elevated discharges throughout most of its range in Queensland [602, 1093, 1294]. These environmental conditions are most likely to be favourable for egg and larval development and hence, successful recruitment. Length–frequency data indicate that juvenile fish (less than 16 mm SL) were most common in streams of southeastern Queensland during summer, further suggesting that the development of a larval cohort occurred during low-flow conditions experienced during spring and early summer (Fig. 8) [1093].
Temporal patterns in reproductive stages mirrored that observed for variation in GSI values. Peak monthly mean GSI values (2.8% ± 0.4 SE for males, 11.9% ± 0.7 SE for females) occurred in September for males and November for females (Fig. 7). Females GSI vales were always higher than those of males and remained elevated during the breeding season for longer (Fig. 7). The mean GSI of ripe (stage V) fish was 12.4 % ± 0.3 SE for females and 2.9 % ± 0.4 SE for males [1093].
12
Males
10
Females
8 6
40
Spring (n = 3336)
30
Summer (n = 3197)
4 2 0
AutumnWinter (n = 4191)
20
Month
10
Figure 7. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Pseudomugil signifer males (open circles) and females (closed circles) in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 3.
0
Standard length (mm)
The spawning season in P. signifer in south-eastern Queensland appears shorter in duration than observed in the Wet Tropics region and reproductive investment (as indicated by mean GSI values) appears greater. These data suggest that a shorter spawning season is compensated for by an increase in instantaneous reproductive output.
Figure 8. Seasonal variation in length-frequency distributions of Pseudomugil signifer from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
Sexually mature fish were observed in the Black-Alice River near Townsville in May and were observed spawning in June [172]. In the Tweed River, northern New South Wales, spawning was reported to occur in October and November [1133, 1135]. Fish from saline and brackish estuarine habitats in New South Wales showed peak reproductive activity between September and February [602]. Overall sex ratios for populations from the Sydney region have been reported as 1.8 females for every male [601].
Peak spawning in the Johnstone River occurs when dry season temperatures exceed 22°C. In aquaria, successful spawning has been reported at water temperatures between 22–27°C [1214] and 25–30°C [1294], with fry surviving within this range of temperatures. Howe and Howe [602] suggested an increase in water temperatures could be one of the major factors influencing spermatogenesis and oogenesis. They further suggested that the onset of bright fin colouration in males (see below) precedes
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Freshwater Fishes of North-Eastern Australia
also been reported to reach a maximum diameter of 1.8 mm [1214]. Egg diameters (possibly intraovarian) from fish in the Black-Alice River in northern Queensland, varied from 0.1–2.0 mm, this wide range of egg sizes being considered typical of a protracted spawner [172].
spermatogenesis and may trigger the final stage of oogenesis in females [602]. Detailed accounts of the elaborate colouration and behaviour of spawning fish in aquaria are available for fish obtained from northern Queensland and central New South Wales [600, 1214]. In aquaria, males (particularly those from northern Queensland populations) can be very aggressive and are territorial when in breeding condition, usually remaining near a suitable site for spawning [1214] except when activity courting passing females [1447]. Spawning in aquaria has been observed to occur at or near the base of aquatic plants among the roots and gravel, and in Java moss or floating mops [38, 600, 1214]. In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal vegetation, although fish have also been observed in slow-flowing river margins depositing eggs on the substrate in areas with few aquatic plants [793, 1329]. Fish in the Black-Alice River near Townsville, were observed spawning among mats of filamentous algae (Spirogyra) [172]. In aquaria, pairs were observed to spawn several times a day [1214]. The number of eggs spawned per day has been reported to vary from 2–8 [600], 4–9 [43], up to 10 [1214], 10–12 [38] and 0–18 [1291]. Eggs are laid singularly or, occasionally, in groups of two or three [1291]. Five to six eggs may be found within each of several spawning sites [43]. Spawning in aquaria continued for several days, followed by a period of inactivity [600]. In the wild, females may spawn only once (albeit producing several batches in a single season), usually within the first year, rarely living to spawn a second season [1294]. Total fecundity for P. signifer collected from the Mary River has been estimated as ranging from 2–91 eggs (mean 34 ± 2 SE, n = 73 fish) and 2–104 eggs (mean 33 ± 4 SE, n = 59) for fish from the Wet Tropics region [1093].
The demersal eggs are spherical with chorionic filaments (up to 13 mm in length) distributed evenly over the entire egg surface. These filaments are strongly adhesive and probably facilitate attachment of the eggs to aquatic plants [600, 603] or rocks [1093]. Eggs from northern Queensland populations have shorter filaments and more complex sculpturing of the chorion (surface blebs) than those from New South Wales, the latter feature possibly important in promoting oxygen uptake in warmer waters where dissolved oxygen saturation levels may be lower [603]. The embryos of P. signifer differ from those of P. mellis and other congeneric species in that they do not develop melanophores on the yolk sac [600]. Additional details on embryonic morphology and development are given in Howe [600], Howe et al. [603] and Semple [1214]. The duration of embryonic development is relatively long. Eggs of fish from central New South Wales hatched in 14 to 16 days (at 24°C), whereas fish from northern Queensland took longer (16.5 to 19 days at 24°C), although rates of early development were comparable among populations [600]. Higher temperatures are probably required for optimum development of eggs from northern populations compared with southern populations [600]. Incubation periods have also been reported to range from 12–14 days (at 28–30°C) [1291], 14–17 days (at 27°C) and 18–21 days (at 22–24°C) [1214]. Illustrations and descriptions of larval stages are available for fish reared in aquaria [1214] and for fish collected from the wild [25]. Larvae are comparatively well developed at hatching. Flexion of the notochord occurs prior to hatching in aquaria [25] and the larvae of P. signifer in the Johnstone River also hatch at the postflexion stage [1093]. The length at hatching of prolarvae reared in aquaria was 5.5 mm SL [1214]. At this stage the caudal fin, second dorsal fin and anal fin buds were developing. The top of the head, preoperculum and lateral line was spotted and the eyes, swim bladder and surface pigments were black. Paired contour melanophores were visible on the dorsal surface and several melanophores were present on the belly. Postlarvae were 6.5 mm SL and, by this stage, the anal and dorsal fin buds were developing, and larvae had commenced swimming and feeding in midwater [1214]. Wild-caught fish were 4.4–4.9 mm TL at hatching [25]. Aarn et al. [25] list the following post-hatching larval characteristics as useful for distinguishing P. signifer from sympatric Melanotaeniids (Melanotaenia duboulayi and Rhadinocentrus ornatus): larger size, caudal origin (caudal
Fecundity is significantly related to fish size; the regression equations for relationships between length and weight and fecundity are given in Table 6. Fish of 22 mm SL from the Mary River produced about 24 eggs in total, whereas fish of 28 mm SL produced about 55 eggs [1093]. Fish of 0.25 g from the Mary River produced about 30 eggs in total, whereas fish of 0.50 g produced about 50 eggs [1093]. No parental care of eggs has been reported. Eggs are relatively large relative to body size. The mean diameter of 472 intraovarian eggs from stage V fish from the Mary River was 1.49 mm ± 0.01 SE and that of 300 intraovarian eggs from stage V fish from the Wet Tropics was 1.30 mm ± 0.04 SE [1093]. The diameter of water-hardened eggs has been reported to range from 1.13 to 1.65 mm [600]. Fish obtained from central New South Wales had larger eggs than those from northern Queensland, and eggs sourced from aquarium-bred fish were smallest [600]. Eggs have
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Table 6. Life history information for Pseudomugil signifer. Where available, reference is given to data from populations collected from south-eastern Queensland (SEQ) and northern Queensland (NQ)[1093]. Age at sexual maturity (months)
6 months [1214]
Minimum length of gravid (stage V) females (mm)
SEQ: 16.9 mm SL [1093]
NQ: 22.5 mm SL [1093] Minimum length of ripe (stage V) males (mm) SEQ: 23.8 mm SL [1093] NQ: 25 mm SL [1093] Longevity (years)
In the wild, 1–2 years [602, 1294]; In aquaria, 2–3 years [793], but males may live up to 4 years [1294]
Sex ratio (female to male)
1.8:1 [601], 1.77:1 [1093]
Occurrence of ripe (stage V) fish
SEQ: late winter, spring and late summer (August–March) [1093] NQ: year round [1093]
Peak spawning activity
SEQ: Elevated GSI between August and December [1093] NQ: Elevated GSI between May and November [1093]
Critical temperature for spawning
? 22°C (minimum recorded in aquaria) [1214]
Inducement to spawning
? Probably increasing temperature and day length
Mean GSI of ripe (stage V) females (%)
SEQ: 12.4% ± 0.3 SE (maximum mean GSI in November = 11.9% ± 0.7 SE) [1093] NQ: 7.7% ± 0.3 SE (maximum GSI in August = 9.0% ± 0.4 SE) [1093]
Mean GSI of ripe (stage V) males (%)
SEQ: 2.9% ± 0.4 SE (maximum mean GSI in September = 2.8% ± 0.4 SE) [1093] NQ: 1.8% ± 0.6 SE (maximum mean GSI in September = 1.7% ± 0.7 SE) [1093]
Fecundity (number of ova)
SEQ: Total fecundity = 2–91, mean = 34 ± 2 SE [1093] NQ: Total fecundity = 2–104, mean = 33 ± 4 SE [1093]; Batch fecundity = 1–60, mean 15.2 ± 1.4 SE [1093] In aquaria, may spawn several times per day with up to 18 eggs deposited; spawning may continue for several days, followed by a period of inactivity [38, 43, 600, 1214, 1291]
Total Fecundity (TF) and Batch Fecundity (BF)/ SEQ: TF = 2.160 Log10 L – 2.151, r2 = 0.336, p<0.001, n = 73; Log10 TF = 2.979 Log10 Length (mm SL) or Weight (g) relationship W + 1.116, r2 = 0.175, p<0.01, n = 73 [1093] (mm SL) NQ: TF = 88.1 W1.293, r2 = 0.413, n =59, p<0.001 [1093] Egg size (mm) (diameter)
SEQ: Intraovarian eggs from stage V fish = 1.49 mm ± 0.01 SE [1093] NQ: Intraovarian eggs from stage V fish = 1.30 mm ± 0.04 SE [1093] Eggs (possibly intraovarian) up to 2.0 mm [172]. Water-hardened eggs up to 1.8 mm [1214]
Frequency of spawning
Proctracted spawning period [172]. Probably batch spawner [1093]. In the wild, females may spawn only once, usually within the first year, rarely living to spawn a second season [1294]
Oviposition and spawning site
Can breed in fresh and saltwater. In the wild, spawning probably occurs in aquatic macrophytes, submerged marginal vegetation and in substrate at river margins [1093, 1329] or amongst rocks [1093]. In aquaria, adhesive, demersal eggs are deposited among aquatic plants, at or near the base, and in gravel [1211]
Spawning migration
none known
Parental care
none known
Time to hatching
Varies among populations and with temperature. Southern populations: 14 to 16 days (at 24°C), northern Queensland populations 16.5 to 19 days at (24°C) [600] Incubation periods also reported to range from 12–14 days (at 28–30°C) [1291], 14–17 days (at 27°C) and 18–21 days (at 22–24°C) [1214]
Length at hatching (mm)
Newly hatched prolarvae 5.5 mm SL [1214]
Length at free swimming stage
Postlarvae 6.5 mm SL [1214]
Age at loss of yolk sack
?
Age at first feeding
?
Length at first feeding
Postlarvae 6.5 mm SL [1214]
Age at metamorphosis (days)
Flexion of the notochord occurs prior to hatching [25]. Northern Queensland [1214]: 9.9–12.4 mm SL (at 27 days), 12.1–16.2 mm SL (at 41 days), 14.2–19.4 mm SL (at 67 days); Central New South Wales [1214]: 7.2–12.4 mm SL (at 27 days), 8.4–15.6 mm SL (at 41 days), 12.9–18.6 mm SL (at 67 days)
Duration of larval development
?
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Freshwater Fishes of North-Eastern Australia
Trophic ecology Diet data for P. signifer is available for 393 individuals sampled from rivers and streams in the Wet Tropics region of northern Queensland [1097], central Queensland [1080], south-eastern Queensland [80, 205] and northern New South Wales [1133]. Data is also available for 105 fish from a salt marsh in south-eastern Queensland [972] and a tidal creek in central New South Wales [209]. This species is a microphagic carnivore. The diet of fish in freshwater habitats (Fig. 9) is dominated by aquatic insects (62.6%), terrestrial insects (8.3%) and aerial forms of aquatic insects (6.9% – mostly dipterans adults). Small amounts of algae (mostly diatoms and desmids) and microcrustaceans are also consumed (Fig. 9). Little spatial variation in diet was apparent, despite the wide geographic range and variety of habitats for which diet data was available.
to the anus) of the dorsal fin-fold, diffuse melanophore distribution on cranium, melanophores in the cranial parietal peritoneum externally visible, melanophores absent from the caudal abdomen, urogenital funnel absent, and flexion of the notochord (pre-hatching). At 8.2 mm SL, developing larvae are characterised by a dorsoventrally attenuated body profile and early metamorphosis of the fin-fold to form narrow, tall second dorsal and anal fins [25]. Further osteological variation between P. signifer and other Melanotaeniids is evident with P. signifer having fewer vertebrae, truncated notochord at caudal tip, and fused hypurals [25]. At 27 days post-hatching, fish in aquaria ranged from 7.2–12.4 mm SL and at 67 days were 12.9–19.4 mm SL. Fish reached approximate breeding size (>28 mm SL) at around 6 months of age [1214]. The lifespan of P. signifer in the wild is unknown but may be one to two years [602, 1294]. Life-span in aquaria have been estimated at two to three years [793], but males may live up to four years [1294]. Movement There is very little information on the movement patterns of P. signifer. It is rarely collected in river fishways, and then only in low numbers [158], suggesting that P. signifer does not migrate or make mass large-scale movements. In south-eastern Queensland it is common upstream of large dams [704, 1093], indicating that access to estuarine or marine areas is not an obligatory component of the life cycle of this species. It is likely that this species is able to undertake local dispersal and/or recolonisation movements. It is particularly abundant in streams that periodically become disconnected by extended periods of low flows and where surface waters recede to a series of isolated pools (e.g. in tributaries of the Mary and Brisbane rivers). In these streams, rapid recolonisation of previously dry river reaches has been observed soon after flows resumed in summer and longitudinal connectivity was re-established (i.e. within 48 hours [1093]). There is no quantitative evidence on the stimulus for movement of this species. Cotterell and Jackson [333] suggested that P. signifer in the Fitzroy River, central Queensland, would move for habitat/dispersal or feeding ‘anytime there is a flow between August and April’, although the source of this information was not given. A study of local foraging movements by this species in a shallow, brackish creek in central New South Wales, revealed that tagged fish moved parallel to the shoreline within 1 m of the bank and remained within a small area (65 m2) over the course of observations (varying from one to three hours) [209]. A discussion of the potential for movement within and between catchments based on inferences from genetic data is given in the section on systematics (above).
Microcrustaceans (3.3%) Macrocrustaceans (0.3%) Molluscs (0.2%)
Unidentified (12.3%)
Terrestrial invertebrates (8.3%)
Aerial aq. Invertebrates (6.9%)
Detritus (0.3%) Algae (5.7%)
Aquatic insects (62.6%)
Figure 9. The mean diet of Pseudomugil signifer from freshwater habitats. Data derived from stomach contents analysis of 393 individuals from the Wet Tropics region of northern Queensland [1097], central Queensland [1080], south-eastern Queensland [80, 205] and northern New South Wales [1133].
Fish from brackish creeks and salt marshes showed a stronger reliance on terrestrially-derived prey (8.6%) and other foods available at the water surface (aerial aquatic insects 35.3% – mostly dipterans adults) than fish from freshwaters (Fig. 10). Other macroinvertebrates such as polychaete worms were also an important component of the diet (19.9%) for fish in the tidal creek system [209]. These fish were observed foraging at the water surface and in the soft benthic mud [209]. Insects taken at the water surface were ingested in proportion to the rate with which they were encountered, provided they were below a maximum size dictated by the mouth gape of the fish. Experimental investigations revealed that prey encounter rates were affected by prey body size and water turbidity,
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Pseudomugil signifer
observed that P. signifer in the Brisbane region was rarely present or abundant where the alien fish species Gambusia holbrooki (a small-bodied poeciliid) was present. These authors speculated that similarities in the mode of foraging and diet increased the potential for competition among these species. Recent distribution and abundance data for south-eastern Queensland streams [1093] showed that P. signifer was the seventh most abundant species (6.3 % of total abundance) present at 510 hydraulic habitat units in which G. holbrooki occurred (27.7% of total abundance). Conversely, at those sites in which P. signifer occurred (n = 481 HUs), G. holbrooki was the 6th most abundant species (6.8%). At those subset of sites in which both species co-occurred (n = 201 HUs), G. holbrooki was the most abundant species (20.6%) and P. signifer was the second most abundant species (12.0%). These co-occurrence data provide little evidence for the impact of alien fish species such as G. holbrooki on P. signifer. Nevertheless, experimental evidence suggests that the presence of alien fish species can have severe deleterious effects on the growth and successful reproduction of P. signifer [604]. In the presence of G. holbrooki, the growth (as measured by weight and length) of P. signifer in open-air tanks was severely retarded, the ovaries were morphologically undeveloped and ovarian weight and fecundity was greatly reduced. Furthermore, no eggs of P. signifer were observed in tanks also containing G. holbrooki [604]. The mechanisms for these impacts were unclear, however the caudal fins of P. signifier were observed to be damaged, suggesting interspecific aggression (fin-nipping) by G. holbrooki. The physiological stress caused by these aggressive interactions was concluded to result in the regression of ovarian function in P. signifer. Direct predation by G. holbrooki on eggs or larvae was not an important influence on the reproductive capacity of P. signifer, although this was observed to be the case in aquaria [604] and wild-caught G. holbrooki have been found to ingest native fish larvae, possibly including P. signifer [636].
but not by the hunger level of the fish. The handling time of prey below the maximum ingestible size was relatively rapid (<10 seconds), as was the rate of foregut evacuation (up to 80% of the stomach contents may be evacuated after two hours) [209]. Microcrustaceans (2.8%) Other macroinvertebrates (19.9%)
Unidentified (5.5%) Terrestrial invertebrates (8.6%)
Aquatic insects (26.1%)
Aerial aq. Invertebrates (35.3%) Algae (1.2%) Detritus (0.7%)
Figure 10. The mean diet of Pseudomugil signifer from brackish habitats. Data derived from stomach content analysis of 105 individuals from a salt marsh in south-eastern Queensland [972] and a tidal creek in central New South Wales [209].
No information on the trophic ecology of larvae is available, however they are likely to feed on microscopic items such as algae, rotifers and microcrustaceans. In aquaria, adults will consume a range of food types including small anuran tadpoles, mosquito larvae and other common aquarium foods such as brine shrimp, Calanus and Artemia nauplii, Tubifex worms, finely minced animal meats and commercial flake foods. Postlarvae will consume similar items to those listed above as well as infusoria made from lettuce [797, 1214, 1291]. Conservation status, threats and management The conservation status of P. signifer is listed as NonThreatened by Wager and Jackson [1353] and it is generally common throughout most of its range in eastern Australia.
Although little is known of the movement patterns of this species, it does not appear to make extensive dispersal movements, suggesting that P. signifer is unlikely to be sensitive to barriers caused by weirs and impoundments. However, low dispersal abilities, as suggested by the apparently low gene flow between populations [902, 903] suggests that repopulation after extirpation, for whatever reason, may take a very long time.
Like many other native species, siltation arising from increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of P. signifer and affect aquatic invertebrate food resources. Instream habitat modification due to aquatic and terrestrial weed invasion has been implicated in the decline of P. signifier in urban streams of the Brisbane region [94, 95]. Interactions with alien fish species (e.g. competition for resources and predation on eggs, larvae and juveniles) is another other potential threat. Arthington et al. [95]
Changes to the natural discharge regime and hypolimnetic releases of unnaturally cool waters from large dams may interrupt possible cues for reproduction or de-couple optimal temperature/discharge relationships during critical phases of spawning, and larval development. Unseasonal flow releases during naturally low flow periods
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Freshwater Fishes of North-Eastern Australia
in a small number of fish from northern Queensland [172]. The cause of this condition could not be accurately established.
in September and October are likely to negatively affect reproductive success as these coincide with periods of peak spawning activity and larval development. Rapid fluctuations in water levels resulting from unseasonal flow releases has the potential to expose and desiccate the eggs of P. signifer as this species is thought to spawn among submerged and aquatic vegetation in shallow marginal areas. The availability of aquatic macrophyte beds may also be maximised during low flow periods. Larval development is also likely to be favoured during low flow periods, during which time phytoplankton and invertebrate abundances are also higher [949].
Pseudomugil signifer is reported to be capable of being experimentally infected by the strigeate trematode Diplostomum spathaceum [669]. It is also known to act as a definitive host to the digenetic trematode Prototransversotrema steeri (Transversotrematidae) and second intermediate host to Stegodexamene callista (Lepocreadiidae) [339]. Sixteen parasite species (listed in Dove [1432]) were recorded from nine individuals collected from south-eastern Queensland and fish contained an average of 3.9 parasite species each [391].
A spinal abnormality known as lordosis (curvature of the spine, giving a hump-back appearance) has been reported
268
Pseudomugil gertrudae Weber, 1911 Spotted blue-eye, Delicate blue-eye
37 245001
Family: Pseudomugilidae
confuse this species with any other except when small or when sample contains large numbers of juvenile rainbowfish, which it superficially resembles.
Description First dorsal fin: II–V; Second dorsal fin: I, 6–7; Anal: I, 8–10; Pectoral: 8–11; Vertical scale rows: 27–28; Horizontal scale rows: 6–7; Predorsal scales: 9–12; Cheek scales: 3–5. Figure: adult male specimen, 26 mm SL, Cape Flattery dunefields, January 2000; drawn 2000.
Bowman [217] described morphological and colour variations in twelve populations of spotted blue-eye, noting differences in body depth, caudal fin shape, length of the pelvic, dorsal and anal fins, in addition to differences in body and fin colouration and the size and number of black spots on the fins. However, little geographic phenotypic consistency is evident in the excellent figures shown by Bowman except that the dorsal and anal fins of populations in Queensland are shorter than those of the Northern Territory. Given that spotted blue-eye populations tend to be isolated from one another, it is probable that the observed variation in phenotype is related either to a founder effect or to random genetic drift in small populations. Either way, there is little suggestion of substantial gene flow between populations and the genetic basis of the observed phenotypic variation would prove an interesting study.
Pseudomugil gertrudae is a small species, occasionally reaching 30 mm SL but usually less than 25 mm SL. Maximum body depth 21.9–25.5% of SL; head length 24.2–28.1%; snout length 4.0–5.4%; eye diameter 8.5–10.3%; interorbital width 10.8–13.0%; caudal peduncle depth 9.9–12.9%; caudal peduncle length 21.8–28.4 mm; predorsal distance 49.8–55.7 mm; preanal distance 51.6–61.4 mm [43]. Colour in life: body colour varies from silver-white, through almost transparent to almost pale tan/yellow; three horizontal black lines present on posterior half of body, continue anteriorly as spots; fin margins dark. Dorsal, caudal and anal fins pale yellow with numerous black spots, spots coalesce to form black band on first dorsal, caudal with dark marginal band, dorsal and anal with diffuse white marginal band. Pelvic and pectoral fins iridescent white or bright yellow on leading edge. Colour in preservative: white and yellow pigments lost, body dull tan, black spots and stripes retained. It is difficult to
Systematics Pseudomugil gertrudae was originally described by Weber in 1911 from material collected in the Aru Islands, off the
269
Freshwater Fishes of North-Eastern Australia
certainly a result of translocation. The degree of concordance between the distributions of P. gertrudae and M. maccullochi (and to a lesser extent D. bandata) is noteworthy, suggesting that these species have very similar habitat and water quality requirements and share a common biogeographic history.
southern coast of Irian Jaya. No synonyms exist. This species occurs as a number of isolated populations in southern New Guinea, northern Australia and associated islands of both land masses, and substantial genetic diversity may be present and responsible for the considerable phenotypic variation (principally in colouration and fin length) depicted in various texts [34, 38, 217, 936].
Macro/meso/microhabitat use Spotted blue-eye are restricted to lowland, low elevation habitats typically of floodplain environments. It may be found in the main channel of large rivers (such as the Jardine or Tully/Murray rivers) but is restricted to marginal habitat in such circumstances. Lotic populations are more likely to occur in small, low-gradient adventitious streams. More typical habitat includes Pandanus and Melaleuca swamps and sedgelands (such as that depicted on page 57 of Allen [38]). In the Cape Flattery region, P. gertrudae was collected from isolated pools, swamps, streams and lakes (i.e. the full range of habitats available). Allen [38] notes that it may be found in turbid water or water with high loads of suspended algae.
Distribution and abundance Spotted blue-eye occur in southern New Guinea, the Aru Islands and northern Australia. In the Northern Territory, this species has been collected from the Finnis River [38], Burton and Scrubby creeks north of the Daly River [217], the Charlotte and Howard rivers near Darwin [217], eastern Arnhem Land [38, 217] and Bathurst Island [217], Melville Island [38, 217] and Groote Eylandt [38]. The distribution on the west coast of Cape York Peninsula in Queensland includes the Embley River (south of Weipa) [197], swamps in the vicinity of Weipa [571], Cockatoo and Pole creeks of the Ducie basin [1349], the Wenlock River [571], creeks and swamps associated with the Jardine River [41, 217, 571, 785] and numerous creeks in the vicinity of Bamaga [1349]. On the east coast of Cape York Peninsula, its distribution includes Jacky Jacky Creek and Conical Hill Lake (within the Jacky Jacky basin) [1349], Sachs Waterhole, an acidic dune lake 50 km south of Bamaga, Harmer Creek (130 km south of the tip of Cape York and discharging into Shellburne Bay) [571], the Olive River and associated coastal tributaries [571], Scrubby Creek (south of Cape Weymouth) [571] and swamps, lakes and streams (6 of 8 sites) of the Cape Flattery area [1088]. It was not abundant in the Cape Flattery area, and contributed only 5.1% of the total number of fish collected from these habitats. Pusey and Kennard [1085] collected only seven specimens (from a total of 7325) in their survey of the Wet Tropics region. It was recorded from Eubanangee Swamp (Russell/Mulgrave drainage), a floodplain lagoon of the Tully River and from both a riverine and a swamp site in the Murray River drainage. Subsequent intensive sampling within stream habitats of the Johnstone, Mulgrave/Russell and Tully drainages over the period 1994–1997 has resulted in the collection of an additional seven specimens. It is rarely collected in stream habitats. The extensive habitat inventory surveys of rivers of the Wet Tropics region by Russell and co-workers [1177, 1179, 1183, 1184, 1185] have failed to collect a single specimen. Hogan and Graham [583] collected it from a lagoon on the Tully/Murray floodplain but failed to detect it in wetland habitats of the Herbert River floodplain [584]. It has been recorded from the Cairns area and from the Hull River by Bowman [217]. There is a small population in Kenny Creek, a tributary of the Barron River, on the Tablelands (B. Herbert, pers. comm.) but it is almost
It is our experience that P. gertrudae tends to be most common in waters less than 60 cm deep although it may also occur in deep blackwater lakes. It may occur in creeks with a gentle flow but is more common in standing waters [1093]. It is most common over a mud and sand substrate and is frequently associated with cover elements such as emergent vegetation, log debris and leaf litter [38]. Environmental tolerances Experimental data are lacking, as are, to a large degree, field data. Only seven individuals (from six occasions) have been collected by us from streams of the Mulgrave/Russell and Johnstone drainages over the period 1994–1997. The water quality in the habitats in which they were collected was uniformly good with pH ranging from 4.5 to 7.8, dissolved oxygen ranging from 5.62 to 7.94 mg.L–1, temperature from 21.2 to 27.3°C and conductivity ranging from 33.8 to 63.8 µS.cm–1. In the dunefields of Cape Flattery, water temperatures were higher (and on subsequent occasions temperatures as high as 36°C have been measured) and pH was much lower, but water quality was otherwise good. (Table 1). Semple [1212] reports that laboratory-held individuals sourced from Jabiru in the Northern Territory became distressed when temperatures fell to 22°C and died en masse when water temperatures fell below 20°C. Allen and Cross [43] list the range in temperature and pH of Australian waters in which spotted blue-eye occur as 23 to 30°C and 5.2 to 6.7, respectively, and Allen [38] notes that water acidity for New Guinean populations ranges from 5.5 to 6.5.
270
Pseudomugil gertrudae
Trophic ecology No published information available on this aspect of its biology. The stomach contents of six individuals collected from a very shallow stream in the Cape Flattery region in January 2000 contained unidentified material (25%), a single species of highly pigmented diatom (45%), chironomid and ceratopogonid larvae (16%) and cyclopoid copepods (14%) (Fig. 1). Such a diet is very similar to that observed for M. maccullochi from the same habitat [1093]. Fish in aquaria may be cannibalistic [799].
Table 1. Physicochemical data for Pseudomugil gertrudae collected from aquatic habitats of the Cape Flattery area (n = 6 sites, 48 individuals). Parameter
Min.
Max.
Temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Water clarity (cm)
27 7.12 3.93 89 20
32 7.75 5.01 385 100
Mean 29.3 7.49 4.25 159.2 55.8
Microcrustaceans (14.0%)
Semple [1212] suggest that P. gertrudae is very acid-tolerant. These data, plus that shown in Table 1, strongly suggest that P. gertrudae is most frequently found in acidic waters and often in very acidic waters. In addition, these data suggest a preference for well-oxygenated waters. Hogan and Graham [583] did not collect this species from any of the deoxygenated lagoons they investigated on the Tully River floodplain and the only location in which they recorded it present (the Tully River itself) was characterised by high levels of dissolved oxygen (7.92 mg.L–1). In summary, this species tolerates highly acidic, warm, darkly stained waters but is probably intolerant of low dissolved oxygen levels and low water temperatures. Reproduction Nothing is known of this aspect of its biology for populations in the wild, but some aquarium observations are available [38, 797, 799, 1212]. Allen [38] reports that it is easily spawned in captivity. Males vigorously court females, flashing the dorsal and anal fins [1212]. The eggs (one or two per day [799]) are deposited amongst vegetation within 10 cm of the substrate [1212]. The eggs are small and hatching is protracted: 7–12 days at 22–29°C [797], 10–12 days at 27°C [1212]. The larvae are small at hatching: 3.8–4.0 mm SL [1212]. The eyes and swim bladder are well-developed at hatching and the body is wellpigmented. Fry commence feeding after a few days [799]. Allen reports that P. gertrudae take about three months to reach 2 cm in length [38]. A similar growth rate was reported by Semple [1212]. Sexual maturity occurs early in life – 91 days [1212]. It is probable that in the wild, this species spawns continuously once it has achieved maturity but recruitment is probably highest during the wet season.
Unidentified (25.0%)
Aquatic insects (16.0%)
Algae (45.0%)
Figure 1. The mean diet of Pseudomugil gertrudae. Data derived from stomach content analysis of six fish from a shallow sand dune stream in the Cape Flattery area.
Conservation status, threats and management Pseudomugil gertrudae is listed as Non-Threatened by Wager and Jackson [1353] and this listing is appropriate for the species over its entire geographic range. Populations in the Wet Tropics region are however, at risk from habitat destruction. The comments made elsewhere concerning threats to the persistence of M. maccullochi in this region apply equally to P. gertrudae. Given that it is more an inhabitant of swamps and wetlands than it is of streams and rivers, it is unlikely to be directly impacted by water resource development except in the cases where water abstraction has the potential to lower the water table sufficiently to impact on water levels in floodplain habitats, or water resource development that decreases the extent and frequency of contact between the main river and its floodplain.
Movement Nothing is known of the movement biology of P. gertrudae.
271
Ophisternon gutturale (Richardson, 1845) Ophisternon spp.? One-gilled swamp eels
37 285004
Family: Synbranchidae
Description Synbranchidae is a family of elongate eel-like fishes. The family history is long (dating back to the late 1700s) and obscure, perhaps due to the fact that synbranchids have a virtually featureless external anatomy and are variable in those external characters that can be measured or described accurately [1157]. Nomenclatural and diagnostic difficulties apply to the Australian synbranchids also. Four species, Ophisternon gutturale (Richardson), O. bengalense McClelland, Anommatophasma candidum Mees (= O. candidum) and Monopterus albus (Zuiew), are said to occur in Australia [52, 1042]. The specific identity of the Australian synbranchid eels, their status as indigenous fauna and the exact number of taxa involved has not been fully resolved however (see below). Anommatophasma candidum is a subterranean species restricted to a small area of north-western Western Australia [52], and is not considered here.
middle of the upper lip, upper lip thick and distinctive; six or seven branchiostegals, well-ossified to their tips at all sizes and extending backward beyond ventral tip of cleithrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Ophisternon
Ophisternon may be distinguished from Monopterus by the following combination of characters [1157]:
Ophisternon gutturale – eel-like body, may reach a maximum length of 600 mm [52] but more commonly less than 200 mm. Eye located at or just in posterior half of the distance from snout tip to end of mouth [37]. Caudal vertebrae 38–53 (T. Roberts, pers. comm.). Colour variable, ranging from reddish-brown to green, pale ventrally.
Gill opening triangular or crescentic, internally attached to isthmus; upper lip jowl-like, without a separate or swollen fold; eye on or posterior to vertical through the middle of the upper lip; branchiostegals not reaching back to cleithrum and poorly well-ossified; shoulder poorly connected to skull . . . . . . . . . . . . . . . . . . . . . . .Monopterus From the point of view of identification in the field, the most useful characters to distinguish Ophisternon from Monopterus are the presence of a distinctive upper lip in the former species and attachment of the gill opening to the isthmus by a frenum in the latter. Note however, that the shape of the lip is only useful as a diagnostic feature in larger specimens.
Gill opening a simple crescentic, transverse fold free from the isthmus, occupying one-half to one-third of ventral surface of head; eye on or anterior to vertical through the
272
Ophisternon gutturale
south and north, respectively, and either river may be the source of the type material. However, the distribution of this species as defined by Allen et al. [52] does not extend to this region, its westward limit being around the Darwin area. The type locality is probably in error [34].
Colour in preservative: dull tan/brown. Figure: 189 mm, unnamed tributary of the lower Johnstone River draining extensive Lepironia swamp, September 1994; 2003. Ophisternon bengalense – eel-like body, may reach a maximum length of 550 mm [52] but most commonly less than 200 mm. Eye located forward of middle of distance from snout to end of mouth. Caudal vertebrae 49–61 [37]. Colour variable, deep reddish-brown to brown, often mottled with small dark brown spots. Colour in preservative: dull brown.
Ophisternon bengalense was first described by McClelland in 1845 from the Bengal region of India as Ophisternon bengalensis, the type species for the genus [875]. The trivial name was subsequently altered to bengalense to make it gender-consistent with the genus name [1157]. Synonyms include Ophisternon hepaticus McClelland 1845 (possibly) and Tetrabranchus micropthalma Bleeker 1851. This species has frequently been referred to as Synbranchus bengalense [1157]. Munro [977] refers to this species as Symbranchus bengalensis, Family Symbranchidae, Suborder Symbranchoidei, Order Symbranchiformes.
Monopterus albus – eel-like body, more robust than Ophisternon species, may reach a maximum length of 900 mm but more commonly to 400 mm; head broad and thick [52]; upper lip jowl-like. Colour: brown to greyish, pale yellow or white ventrally. It has been reported that juvenile M. albus may have a dark horizontal band from the snout to the eye [936] but this character is unique to South American synbranchid eels (T. Roberts, pers. comm.).
Many references to O. bengalense in Australia are believed attributable to O. gutturale [1157] and there is considerable doubt as to whether the former species occurs in Australia. Rosen and Greenwood [1157] list O. bengalense as being confined to the Indo-Malaysian region and the Philippine Islands but examined no Australian material in their study, other than five specimens of O. gutturale. Allen et al. [52] cautioned that the Queensland population of O. bengalense requires further study and may represent a new endemic species. Tyson Roberts (pers. comm.) believes that O. bengalense does not occur in Australia although there are at least two Ophisternon species in north-eastern Australia, one of which is O. gutturale.
Systematics One-gilled swamp eels are widely distributed in fresh and estuarine waters of tropical and subtropical regions and are especially well represented in Asia and Australasia [1157]. The family is characterised by a lack of paired fins (except in larval stages), united gill membranes, a reduction of the long dorsal and anal fins to low rayless skin folds generally confluent with a reduced caudal fin, an absence or great reduction in squamation, and a trend towards eye reduction in several taxa, especially those with a burrowing habit. Even when fully developed, the eyes are small and covered with thickened skin. Many species possess suprapharyngeal diverticula and are capable of aerial respiration. Rosen and Greenwood [1157] suggest that there are four genera in the family (Ophisternon McClelland, Synbranchus Bloch, Monopterus Lacépède and Macrotrema Regan) containing 15 species in total and place A. candidum within Ophisternon. All synbranchid eels, with the exception of those within Monopterus, have cojoined branchiostegal membranes free from the overlying isthmus [1157]. The family is currently under revision by Dr Tyson Roberts and may be more speciose than is indicated here (T. Roberts, pers. comm.). The evolutionary relationships of the family currently remain unresolved.
We recognise that there are concerns about the identity of the taxon referred to as O. bengalense in Australia and for the purposes of this discussion we have referred to this species as Ophisternon sp. Monopterus albus was first described as Muraena alba by Ziuew in 1793 based on material apparently collected from Asiatic Russia, although the exact type location is not known [1042, 1157]. The taxonomy of this species is extremely confused. There are numerous synonyms (at least 13), most of which list the type locality as in China. Moreover, it is suspected that two additional taxa, one from China and the other from Java, may be represented among the material assigned to M. albus [1157]. This species is uncommon in Australia and it not clear whether it is native to the region or its presence is due to translocation [52, 936, 1157]. This species is an important food species in Asia, is easily translocated due to its ability to survive out of water for very extended periods, and has been identified as an invasive taxon [326]. Techniques for the transport and introduction of M. albus into areas outside of its natural range were developed in the 1800s
Ophisternon gutturale was first described as Synbranchus gutturalis (note change of trivial name [1157]) by Richardson in 1845 based on material supposedly collected from the Dampier Archipelago, Western Australia, during the voyage of discovery by H.M.S. Erebus and Terror (1839–1843) [1042]. Freshwater streams are very limited on islands of the Archipelago; however, the Maitland and Harding rivers discharge to the immediate
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Freshwater Fishes of North-Eastern Australia
records of O. bengalense in Australia are highly likely to be misidentifications of O. gutterale or some other as yet undescribed synbranchid. Swamp eels, while reasonably widespread in rivers of the Wet Tropics region, rarely achieve high levels of abundance or biomass in streams of the Wet Tropics region (Table 1).
(see [326]) and it is not inconceivable that this species was imported into Australia by the Chinese during the goldrushes that gripped northern Queensland in the late 1800s. Verifiable records of the presence of M. albus in Queensland are few. Pusey and Kennard [1087] list this species among the fauna of the Wet Tropics region: in retrospect, we are not confident of our assignation for at the time, we were unaware of the presence of another synbranchid within Ophisternon in addition to O. gutturale. It is very clear that an increased effort to retain swamp eels specimens for inclusion in museum collections is needed so that they are available for study.
Table 1. Distribution, abundance and biomass data for Ophisternon spp. Data summaries for a total of 43 individuals collected in two rivers of the Wet Tropics region over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred.
Distribution and abundance The distribution limits of Ophisternon gutturale are obscure. Allen et al. [52] list the Australian distribution as extending from the Darwin area eastward to the tip of Cape York Peninsula. A single record exists from the Bensbach River in southern New Guinea also [37]. A swamp eel identified as O. gutturale has been recorded from the Norman River of the Gulf region, and the Coleman, Edward, Holroyd, Wenlock, Archer and Jardine rivers of western Cape York Peninsula [41, 571, 789, 1146]. In the Wet Tropics region, O. gutturale has been recorded from the Daintree, Mossman, Barron, Russell, Murray and Herbert rivers, Liverpool Creek and streams draining into Trinity Inlet [52, 584, 643, 1146, 1179, 1187, 1349]. This species has been recorded from the Black-Alice River near Townsville [176] and from as far south as the Noosa and Mary rivers [1349].
Total
% locations % abundance
Johnstone River
Mulgrave Russell River
25.6
19.6
27.3
0.2 (1.7)
0.2 (1.6)
0.2(1.9)
Rank abundance
26 (12)
24 (11)
22 (11)
% biomass
0.1 (3.1)
0.1 (2.5)
0.1 (4.1)
Rank biomass
22 (6)
20 (6)
Mean numerical 0.21 ± 0.04 density (fish.10m–2)
21 (7)
0.25 ± 0.06
0.13 ± 0.06
Mean biomass density (g.10m–2)
2.36 ± 0.97
2.49 ± 0.97
2.39 ± 0.69
A swamp eel, identified as Ophisternon sp. has been recorded from the Mary, Noosa and Maroochy rivers [1093, 1349], from Mellum Creek and North Stradbroke Island [1093] in south-eastern Queensland. This taxon is very rare in south-eastern Queensland: we have only collected eight individuals over the period 1994 to 2003 [1093].
Ophisternon bengalense is much more widely distributed, occurring in India and Sri Lanka, to Indonesia, the Philippines, New Guinea and northern Australia [52]. A swamp eel identified as O. bengalense has been recorded from the Coleman, Edward, Holroyd, Archer, Wenlock, and Jardine rivers [41, 571, 789] and from swamps in the vicinity of Weipa [571] on the western side of Cape York Peninsula. On the eastern side of Cape York Peninsula, O. bengalense has been recorded from dune lakes near Point Usher [571] and Cape Flattery [1101] and from the Olive River [571]. This taxon is widespread in the Wet Tropics region, having been recorded from the Daintree, Mossman, Barron, Mulgrave, Johnston, Moresby, Tully and Herbert rivers [52, 584, 1085, 1177, 1184, 1185, 1187] and Saltwater, Liverpool and Maria creeks [1179, 1185]. It is worth noting that Russell et al. [1187] collected O. gutterale, O. bengalense (as Ophisternon cf. bengalense) and a third taxon identified as Ophisternon sp. from the Barron River. A swamp eel referred to O. bengalense has also been recorded from small streams near Cardwell [1085] and from the Fitzroy River [659]. We reiterate here that all
Allen et al. [52] list Monopterus albus as occurring in the vicinity of Townsville and in the Daintree and Mossman Rivers. Other records for this species also include the Barron and Mossman Rivers [1085], the Russell River [1085], and Harmer Creek and the Olive River of Cape York Peninsula [571]. These records need to be confirmed. In most of the studies cited above, swamp eels have been uncommon and recorded in a few sites in each river only. They are not common, and in most cases we have seen, the individuals are usually small (<400 mm TL). Macro/mesohabitat use In the Wet Tropics region and south-eastern Queensland, Ophisternon swamp eels were mainly collected from small, low-gradient streams located on the coastal plain (Table 2 and 3). Such streams tended to be narrow and shallow with low water velocities and well-vegetated stream-banks. The
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Ophisternon gutturale
Table 2. Macro/mesohabitat use by Ophisternon spp. Data summaries for 46 individuals collected from 20 locations in the Mulgrave and Johnstone rivers of the Wet Tropics region over the period 1994–1997. W.M. refers to the mean weighted by abundance. Parameter
Min. 2
0.1 Catchment area (km ) Distance to source (km) 0.5 Distance to river mouth (km) 10.1 Elevation (m.a.s.l.) 5 Stream width (m) 2.0 Riparian cover (%) 0
Max. 85.0 21.0 48.5 60 22 90 2.47 0.69 0.45
Mean
W.M.
22.8 6.8 22.6 25.4 6.6 60.8
23.3 6.9 21.8 24.1 6.5 65.0
Gradient (%) Mean site depth (m) Mean site velocity (m.sec–1)
0.02 0.12 0
0.43 0.35 0.13
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
38 52 60 73 33 73 17
6.6 23.0 26.5 15.8 9.5 14.3 4.5
8.9 24.0 26.5 16.3 9.4 11.8 3.9
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (%) Root masses (%)
0 0 0 0 0 0 0 0 0 0
7.0 6.7 18.0 6.0 0 81.2 11.9 11.4 35.0 65.0
0.8 0.4 3.3 6.7 9 15.6 2.7 2.7 8.5 19.8
0.8 0.5 4.2 5.5 9 19.9 2.5 2.3 8.5 22.0
Table 3. Macro/mesohabitat use by Ophisternon spp. in the Mary River, Noosa River and Mellum Creek, south-eastern Queensland. Data summaries for eight individuals collected from samples of five mesohabitat units at three locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min. 2
58.1 Catchment area (km ) Distance to source (km) 15.0 Distance to river mouth (km) 7.0 Elevation (m.a.s.l.) 4 Stream width (m) 1.3 Riparian cover (%) 33.7
0.39 0.37 0.12
Gradient (%) Mean site depth (m) Mean site velocity (m.sec–1) Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
substrate composition in such streams tends to be dominated by smaller particles, although not particularly muddy. In-stream cover, particularly leaf litter, is abundant in streams in which Ophisternon occurs. There is little difference in arithmetic and weighted means displayed in Table 1 because catches of Ophisternon rarely exceeded one or two individuals per site.
0.02 0.45 0
Max.
Mean
W.M.
697.2 54.0 100.0 20 30.0 87.9
293.6 32.0 52.3 10 7.8 55.2
214.5 27.3 41.5 9 6.3 55.0
0.04 0.99 0.20
0.03 0.70 0.04
0.03 0.74 0.03
0 59.8 0 0 0 0 0
11.0 100.0 23.3 11.9 0.0 0.0 3.3
5.1 76.2 11.4 6.1 0.0 0.0 1.1
5.1 81.1 8.8 4.3 0.0 0.0 0.6
Aquatic macrophytes (%) 0 Filamentous algae (%) 0 Overhanging vegetation (%) 0 Submerged vegetation (%) 0 Emergent vegetation (%) 0.3 Leaf litter (%) 19.9 Large woody debris (%) 3.6 Small woody debris (%) 6.7 Undercut banks (%) 0 Root masses (%) 0
0.0 0.8 0.5 2.7 33.5 64.3 13.5 26.8 50.0 53.8
0.0 0.2 0.1 1.1 8.4 32.3 8.4 14.8 29.8 35.7
0.0 0.1 0.1 1.0 12.3 29.4 8.9 14.7 24.6 31.1
species) was determined from capture records for a total of 35 individuals (all less than 250 mm in length). This species prefers shallow (<30 cm) stream margins with little stream flow (Fig. 1c and a, respectively). By virtue of their benthic habit (Fig. 1d) and preference for cover, particularly beds of leaf litter and fine substrate (Fig. 1f), the focal point velocity experienced by most specimens was usually 0 m.sec–1. Most specimens were collected over fine substrates and the elevated proportion of mud in Figure 1e relative to that seen in the environment (Table 1) suggest a preference for fine substrates. Herbert et al. [571] suggested that muddy substrates were essential for swamp eels. We have never observed Ophisternon in burrows but this feature of habitat use may be exclusive to large adult males (see below).
Allen et al. [52] list the habitat of O. gutturale and O. bengalense as soft-bottomed sediments in quiet, well-vegetated backwaters in brackish estuaries and nearby swamps. Herbert et al. [571] also identified muddy habitats, particularly those with thick leaf litter, as important for Ophisternon. Ophisternon species are not limited to reaches close to estuaries as they have been collected up to 120 km upstream from the river mouth in some studies [659, 1093]. Microhabitat use Microhabitat use by Ophisternon spp. (pooled across
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Freshwater Fishes of North-Eastern Australia
(a) 80
50 40
Table 4. Physiochemical data for Ophisternon spp. from streams of the Wet Tropics region and the Mary River, southeastern Queensland (the number of sites from each study is given in parentheses).
(b)
60
30
40
20 10
20
0
0
Mean water velocity (m/sec) 30
Parameter
Max.
Wet Tropics (n = 32) [1093] Water temperature (°C) 20.0 27.8 Dissolved oxygen (mg.L–1) 5.3 8.4 pH 4.5 7.34 Conductivity (µS.cm–1) 19 65.6 Turbidity 0.4 18.1
Focal point velocity (m/sec)
(c)
Min.
(d)
Mean 23.4 7.0 6.26 39.0 2.7
60
South-eastern Queensland (n = 4) [1093] Water temperature (°C) 16.2 24.9 Dissolved oxygen (mg.L–1) 5.5 7.2 pH 4.4 6.9 Conductivity (µS.cm–1) 100.0 563.6 Turbidity 5.4 8.8
20 40 10
20
0
0
(e) 30
30
20
20
10
10
0
0
Substrate composition
must be emphasised that these conditions are possibly unlike those experienced across the entire range. For example, Herbert et al. [571] collected O. bengalense and M. albus from a lagoon in the Olive River drainage in which dissolved oxygen concentration was a low as 1.5 mg.L–1. Some species of synbranchid eels are known to be able to tolerate very low levels of dissolved oxygen and can breathe air at the water surface [804, 936, 1093, 1156]. We have also observed captive Ophisternon gulp air at the water’s surface. A tolerance of low pH levels is indicated by the data in Table 4; not surprising, given that species of Ophisternon have been recorded from acidic dune lakes and coastal wallum ecosystems [571, 1093, 1101]. The streams of the Wet Tropics region in which Ophisternon species occur are notable for their very low conductivity but the salinity tolerance of this taxon must be well developed given that it also occurs in brackish estuaries [52].
Relative depth
Total depth (cm)
21.1 6.4 5.8 342.4 7.3
(f)
Microhabitat structure
Figure 1. Microhabitat use by Ophisternon spp. in the Wet Tropics region. Summaries derived from capture records for 35 individuals collected from the Mulgrave and Johnstone rivers over the period 1994–1997.
Reproduction Little is known of the reproductive biology of Australian swamp eels. Sex reversal has been reported for Monopterus albus: all fish start their reproductive life as functional females, changing to functional males with age [803]. Ovotestes are present in fish between 280 and 460 mm TL in length whereas fish larger than this are exclusively males. Transition commences at about two years of age and is complete by three years of age. Liem [803] also reports some observations on the eggs of this species. The eggs are large (3.4–3.6 mm in diameter) and lain in a foamy egg mass at the entrance to the male’s burrow. The male guards the eggs. Herbert et al. [571] reported that all O. bengalense in a sample collected from swamps in the vicinity of Weipa in March (i.e. end of the wet season) were gravid. The absence of non-gravid fish suggests that
Environmental tolerances Information on the water quality experienced by Ophisternon species in north-eastern Australian waters is scarce and is here limited to a summary based on the ambient water quality conditions existing in sites in the Wet Tropics region and south-eastern Queensland in which it has been collected (Table 4). In rivers of the Wet Tropics region, Ophisternon spp. occur in water quality conditions typical of small, low-gradient streams: very low conductivity, well-oxygenated, highly acidic, moderately warm and generally clear. It was collected from generally similar water quality conditions in south-eastern Queensland, except that water conductivities were much higher (maximum of 563.6 µS.cm–1). It
276
Ophisternon gutturale
male fish were not collected and sex reversal may occur in this species also. They also noted that swamp eels were absent from collections made in 1992 but were present in every river sampled in 1993, suggestive of substantial temporal variation in abundance. The wet season of 1992 was comparatively poor and recruitment may be related to rainfall in some manner or adult survival may be low in years with little rain.
morning when temperatures are below 18°C [804] but the scale, stimulus and purpose of these migrations is unknown.
Movement biology Little is known of this aspect of the biology of Australian swamp eels. Herbert et al. [571] report the presence of O. bengalense in a small fishway below a road crossing near Weipa but does not state whether they were ascending or descending. Monopterus albus is reported to migrate overland from one waterhole to another at night or early
Conservation status, threats and management Ophisternon gutturale and Monopterus albus are both listed as Non-Threatened by Wagner and Jackson while O. bengalense is not listed [1353]. Until a better picture of the taxonomic identity, indigenous status, distribution and biology of these species is assembled, it is difficult to determine what threats may exist.
Trophic ecology There is no published information on the diet of Ophisternon spp. in Australia. Items in the diet of M. albus include insects, crayfish, prawns and fishes [34].
277
Notesthes robusta (Günther 1860) Bullrout
37 287058
Family: Scorpaenidae
coalesce to form two to three thick vertical bars that may extend across body and fins. Colour pattern ensures highly effective crypsis. Extent of barring varied and related to habitat structure (especially substrate composition), time of day, microhabitat use and age. Colour in preservative little changed from that in life except less vivid. This species emits a croaking sound when handled or annoyed. All dorsal, anal and pelvic spines bear paired poison glands [540, 716, 936] therefore this species must be handled with extreme care. If stung, localised swelling is pronounced, the pain extreme and the afflicted subject may lose consciousness [540, 1093]. In our experience, hospitalisation and treatment with strong painkillers may be warranted. Immediate first aid entails placing afflicted portion in very hot water to denature toxin; further details on treatment can be found in Harris and Pearn [540].
Description Dorsal fin: XV–XVI, 9–10; Anal: III, 5; Pectoral: 11–12; Vertical scale rows: 85. Figure: mature adult 138 mm SL, Mulgrave River, October 1994; drawn 1996. A moderately sized fish, Notesthes robusta is known to attain 350 mm total length but individuals of between 150–200 mm are most commonly encountered [34, 936]. The relationship between weight (in g) and length (SL in mm) for specimens from the Wet Tropics region is: W = 6.7 x 10–6 L3.378; r2 = 0.968, n = 23, p<0.001. A deep-bodied species, with a broad head and large mouth extending to below the eye. Eyes positioned high on the head. Head armed with many sharp spines, seven on the opercula. Scales small, lateral line scales prominent and forming row parallel to dorsal profile. Dorsal fin originating forward of the pectoral fin and terminating level with posterior margin of anal fin. Pectoral fins large and rounded. Pelvic fins originating posteriorly to pectoral fin base. Anal fin small and square. Caudal fin slightly rounded and large (27% of SL).
Systematics The Scorpaenidae is a large, mostly marine family inhabiting both temperate and tropical oceans. Worldwide, there are about 300 species [1321] but only about 80 species from 33 genera occur in Australian waters [1042]. The genus Notesthes is monotypic [1042]. Prior to the erection of the genus by Ogilby in 1903, several synonomous taxa
Colour in life is variable over its range but always tending to be mottled. Base colour yellow to dark brown, mottled with green, reddish-brown, grey to black. Dark areas often
278
Notesthes robusta
from different localities were placed within the genus Centropogon [1014]. These include: Centropogon robustus Günther, C. hawkesburyensis Klunzinger, C. troschellii Steindachner and C. nitens De Vis. No other scorpaenid is reported to occur in Australian freshwaters [1042] but two New Guinean species (one of which occurs in Australian marine waters) have been recorded from either freshwater or from muddy river mouths [977].
alent numerical density (0.066 ± 0.01 fish.m–2) but greater biomass (11.60 ± 2.65 g.m–2) because few juvenile fish were collected from these streams. Macro/mesohabitat use Lake [755] reported collecting N. robusta 290 km upriver in the Burnett River. This species has been recorded 92 km upstream in the Mary River (Table 2) but is generally found much closer to the coast. For example, in both the Wet Tropics region and south-east Queensland, the average distance from the river mouth was less than 40 and 50 km, respectively. As a consequence it is rarely found at elevations greater than 100 m or in streams of high gradient. Notesthes robusta may be found in a variety of habitats ranging from second to eighth order streams but is most common in streams of order four to six.
Distribution and abundance Notesthes robusta is very widely distributed on the east coast of Australia from the Annan River [1223] south to the Broga River in southern New South Wales [1201]. It apparently occurs in Irian Jaya [977] but N. robusta is not listed in Allen’s checklist of Papua New Guinean freshwater fishes [36]. This species has not been recorded from any rivers of Cape York Peninsula [571], except the Annan River [1223]. Notesthes robusta is moderately widely distributed in those rivers in which it occurs (Table 1). It occurs in a reduced proportion of locations in the Johnstone River compared to the Mulgrave River because more sites in the former river were located at elevations greater than 100 m.a.s.l. and N. robusta is restricted to elevations less than 60 m.a.s.l. (Table 2). It was the 27th most abundant species and the 13th most important by biomass over all sites but was relatively more abundant in those sites in which it occurred and contributed 8% of the biomass in these sites. Similar numerical and biomass densities were estimated for the Mulgrave and Johnstone rivers (Table 1). This species was infrequently collected in rivers of south-east Queensland and occurred in only 6% of the locations in this region [1093] and occured at equiv-
Table 2. Macro/mesohabitat use by Notesthes robusta. Data derived from the mean habitat characteristics of 34 sites in rivers of the Wet Tropics region and 18 sites in south-east Queensland sampled over the period 1994–1997 [1093]. W.M. refers to mean weighted by fish abundance to reflect any potential preference for particular conditions. Parameter
% locations % abundance
Mulgrave River
Gradient (%) 0 Mean depth (m) 0.22 Mean water velocity (m.sec–1) 0.01
Johnstone River
16.3
25.0
10.7
0.2 (2.4)
0.4 (2.9)
0.1 (1.9)
Rank abundance
27 (11)
19 (8)
26 (11)
% biomass
0.7 (8.0)
1.4 (9.3)
0.4 (6.6)
7 (4)
14 (10)
Rank biomass
13 (5)
Mean density (fish.10m–2)
0.07± 0.01
0.07 ± 0.02 0.06 ± 0.01
Mean biomass (g.10m–2)
4.86 ± 0.95
5.48 ± 1.23 4.15 ± 1.49
Max.
Wet Tropics Catchment area (km2) 1.4 334.8 Distance to source (km) 2.6 67.0 Distance to river mouth (km) 10.1 64.0 Elevation (m.a.s.l.) 5.0 60.0 Order 2.0 5.0 Stream width (m) 5.3 39.1 Riparian cover (%) 0 100.0
Table 1. Distribution, abundance and biomass data for Notesthes robusta in two rivers of the Wet Tropics region. Data summaries for a total of 67 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. Total
Min.
279
1.9 0.87 0.54
Mean
W.M.
172.8 33.7 38.2 29.7 4.7 13.1 36.0
195.4 38.2 37.7 29.9 4.8 13.1 36.0
0.5 0.44 0.23
0.6 0.46 0.25
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
8.0 63.0 72.0 56.0 44.0 75.0 67.0
1.3 17.2 17.1 17.1 19.3 25.3 2.9
1.4 16.1 14.9 16.5 21.4 27.4 2.6
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (%) Root masses (%)
0 0 0 0 0 0 0 0 0 0
7.0 2.4 19.0 63.0 10.0 35.0 12.5 8.2 48.0 60.0
1.0 0.1 1.5 10.3 0.6 5.9 2.7 1.8 6.8 6.9
1.1 0.1 1.6 12.1 0.6 5.5 2.3 1.6 7.6 7.6
Freshwater Fishes of North-Eastern Australia
between regions. However, substrate composition does differ, tending to be coarser in the northern streams, reflecting the generally coarser substrates of the high gradient rivers of the region. Notwithstanding this difference, the data presented in Table 2 indicate a preference for habitats with a gravel/cobble substrate. In streams of south-eastern Queensland, N. robusta tends to occur in habitats with more abundant in-stream cover than observed in equivalent habitats in north-eastern Queensland. Nonetheless, stream reaches in which N. robusta occurs tend to have abundant cover.
Table 2. (cont.) Macro/mesohabitat use by Notesthes robusta. Data derived from the mean habitat characteristics of 34 sites in rivers of the Wet Tropics region and 18 sites in south-east Queensland sampled over the period 1994–1997 [1093]. W.M. refers to mean weighted by fish abundance to reflect any potential preference for particular conditions.
Parameter
Min.
Max.
South-east Queensland Catchment area (km2) 22.8 9734 Distance to source (km) 15.0 260.1 Distance to river mouth (km) 28.0 92.0 Elevation (m.a.s.l.) 0 100.0 Order 4 8 Stream width (m) 5.3 30.0 Riparian cover (%) 0 84.9 Gradient (%) 0 Mean depth (m) 0.22 Mean water velocity (m.sec–1) 0
0.83 1.05 0.55
Mean
W.M.
1057 87.7 46.5 20.6 5.8 14.0 47.9
906 90.9 39.7 11.6 5.9 11.7 52.1
0.29 0.58 0.16
Microhabitat use Summaries of microhabitat use shown in Figure 1 are derived from capture records for 51 individuals, the majority of which were collected in the Mulgrave and Johnstone rivers (41 of 51 sites). Use data indicates that
0.50 0.49 0.23
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
16.0 73.0 49.0 38.0 45.0 6.0 76.0
6.0 29.0 18.0 22.0 14.0 1.0 10.0
4.1 25.2 18.4 25.9 15.7 1.1 9.9
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (%) Root masses (%)
0 0 0 0 0 0 0 0. 0 0
35.0 13.0 4.0 7.0 4.0 19.0 30.0 12.0 67.0 71.0
4.0 3.0 1.0 3.0 1.0 6.0 11.0 6.0 18.0 25.0
2.7 2.4 0.6 2.3 0.5 5.3 15.1 5.6 14.1 21.8
30
40
(b)
30
20
20 10
10 0
0
Focal point velocity (m/sec)
Mean water velocity (m/sec) 30
(c)
100
(d)
80 20
60 40
10
20 0
Macrohabitat use by N. robusta in the Wet Tropics region does not vary greatly from that observed in south-east Queensland except that it tends to be found in larger streams (i.e. larger catchment area and greater distance from the source) in the south-east, a difference simply reflecting the combined influences of regional differences in stream size and topography (e.g. shorter, steeper rivers in the Wet Tropics region) and the life history need for egress to marine or estuarine habits which limits the extent of upstream habitat use. Notesthes robusta is found in reaches of a variety of depths and water velocities but was most commonly collected from riffle/run habitats with an average depth of about 0.5 m and flows of about 0.25 m.sec–1. Such habitats tend to have a diverse substrate composition (Table 2). It is noteworthy that average depth and water velocity differ little
(a)
30
0
(e)
Total depth (cm)
(f)
Relative depth
30 20 20 10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Notesthes robusta. Based on capture data for 51 individuals collected in August 1991 and between 1994–1997 from streams in the Mulgrave, Johnstone, Mary and Albert rivers.
280
Notesthes robusta
disease, parasites, lesions) in fish collected from NSW rivers [554] suggests that N. robusta may be quite hardy (although the authors note the potential bias due to difficulty in handling). Data presented in Table 3 indicate that N. robusta is found in well-oxygenated waters with a nearneutral pH. It must be emphasised that the data in Table 3 give no real indication of upper and lower tolerance levels and represent water quality in streams in which it has been collected. No information is available concerning the environmental tolerances of eggs or larvae.
although N. robusta is most frequently found in riffle/run habitats and consequently may be found in a variety of flows, this species occurs most frequently in flows less than 0.3 m.sec–1 (Fig. 1a). Focal point velocities experienced by N. robusta are similar to average velocity but slightly lower (Fig. 1b). This species occurs most frequently in depths less than 50 cm, although it does use deeper areas (Fig. 1c). (Note that determination of maximum depth is constrained by sampling methodology – backpack electrofishing). Notesthes robusta is a benthic species, being nearly always recorded from the stream-bed, however a small number of fish may be found higher in the water column but still associated with some cover element (woody debris or root masses) (Fig. 1d). It most frequently occurs over large particle-sized substrates but rarely occurs over mud or bedrock (Fig. 1e). Use data is skewed towards larger particles when compared to the average substrate composition of sites in which it occurs, indicating preference. This species is most frequently collected from within the interstices of the substrate (but not buried) (Fig. 1f), or associated with in-stream cover such as woody debris, undercut banks or root masses. Ontogenetic variation in microhabitat use is substantial in N. robusta. Small individuals (<100 mm SL) appear more commonly associated with the substrate whereas larger fish are more commonly associated with other cover elements such as woody debris or undercut banks. The prominent barring and saddling pattern described above may be more prominent in smaller specimens, thus increasing crypsis against a background of mixed substrate particle sizes.
Table 3. Physicochemical data for N. robusta. Data summaries for fish collected from 52 sites in north-eastern and southeastern Queensland. Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
11.7 4.77 6.27 6.0 0.25
Max. 27.1 10.0 8.95 1035.0 16.0
Mean 21.0 7.44 7.61 158.2 3.48
Reproduction Breeding biology remains effectively unstudied and no quantitative data is available. Notesthes robusta is believed capable of breeding in freshwater [755, 1068, 1133], however records of downstream movement of reproductively active individuals suggests a catadromous life cycle with a dependence on estuarine areas. Gravid stage IV females have been recorded from the estuarine reaches of the Barron River in July (D. J. Russell pers. comm.). Similarly, ripe females have been recorded in September and very small juvenile (12–20 mm) in October or November in estuarine waters of the Elliot River [825]. The apparent presence of juveniles upstream of an impoundment [755] suggests that the entire life cycle may be completed in freshwater. The source of this observation is obscure, however.
Environmental tolerances Quantitative data are very limited and data presented in Table 3 are derived from field data for streams in the Wet Tropics region and south-eastern Queensland in which N. robusta has been collected. On average, N. robusta is found in streams with very good water quality. The phylogeny of N. robusta (i.e. marine ancestry) and probable estuarine phase during spawning (see below) suggests a well-developed tolerance to high salinity. Notesthes robusta has been recorded from marine and estuarine waters [825, 828, 1068] and from Lake Macquarie, New South Wales [1315], in which chemical composition at the time was similar to seawater [136]. Thus, N. robusta appears able to tolerate sustained high salinity levels. The minimum water temperature in which this species has been recorded in Queensland was 11.7°C but it can probably withstand cooler temperatures than this given that its distribution extends to southern New South Wales. However, although it is found as far south as 36° 39’ S, its abundance within rivers south of the Sydney area is lower than rivers to the north [1201], suggesting that low water temperatures may limit distribution. The absence of abnormalities (e.g.
Spawning appears to take place in winter and spring, at least over the latitudinal range from the Barron River to the Tweed River (i.e. tropical to subtropical). Reproductive phenology is unknown for temperate areas of its range. Richardson records peak gonad development in Tweed River bullrout from April to June when water temperatures were at the lowest (14–16°C) [1133]. The relationship between breeding phenology and flow regime is uncertain. Richardson noted that peak GSI values in 1979 (8.5%) occurred in June, corresponding to a small winter peak in flow [1133]. However, in 1980, peak GSI values (13%) were detected in April prior to a large flood and GSI values were very low following this flood. Other scorpaenid species are known to be either ovoviviparous or oviparous [225]. Males of ovoviviparous forms
281
Freshwater Fishes of North-Eastern Australia
occurred predominantly from July to November in the Fitzroy River [1274], July to September in the Burnett River [1276] and August to September in the Kolan River [232]. Fish migrating upstream ranged in length from 80–323 mm in these studies [232, 1274, 1276]. Small fish (<200 mm) appeared to move up the fishway less effectively than did larger fish [1274, 1276]. Rates of passage were found to be greatest at night [1274]. These studies suggest that upstream movements, presumably occurring after spawning in estuarine areas, occur most frequently in winter and spring at times of low flow and low temperatures.
generally have a well-developed copulatory organ to facilitate sperm transfer [1321]. No such organ has been described for N. robusta and examination of ripe females has thus far revealed the presence of eggs only, thus it is probable that it is an oviparous species. Other oviparous scorpaenids may release many (up to 3000), small (<1 mm) ovoid eggs encased in a thick buoyant agglutinated mass [225, 1321]. We have observed partial gonad maturation in male fish as small as 71 mm and female fish as small as 78 mm for fish collected in August from the Mulgrave and South Johnstone rivers [1093]. Fish of indeterminate sex as large as 126 mm were also present at this time also. Richardson believed that sexual maturity was not gained until male fishes had reached 186 mm in length and female fishes 226 mm [1133]. Nothing is known of larval ecology.
Notesthes robusta is capable of short bursts of speed when alarmed but typically, movement is slow and languid. It relies more on crypsis than speed to capture prey.
Movement Quantitative data on the patterns of movement in this species are limited although it is generally believed to be diadromous [544, 825, 828, 890, 1173]. Harris [544] believed that impoundments limited distribution and caused downstream congregation of fish. Several studies have examined the movement of N. robusta in Queensland as part of larger studies examining fish movement through fishways. Russell [1173] recorded both up- and downstream movement of bullrout through a fishway on the Burnett River. Many more fish moved downstream than were observed to move upstream (383 versus 50) and peak downstream movements occurred in May. No significant corresponding upstream movement was observed. The size range of descending fish was smaller (80–160 mm) than that of ascending fish (60–320 mm) but it is unknown whether this is biologically relevant. Fish collected in May contained well-developed gonads (Russell, pers. comm.). Peak movement occurred at a time of relatively low flow immediately following a short period of zero flow. Water temperatures were between 21 and 24°C. Stuart [1274] noted that more N. robusta moved up a fishway on the Fitzroy River when water temperatures were <20°C although some movement was observed at higher temperatures also. A similar pattern was observed in the Burnett River [1276]. Most migration in the Fitzroy River occurred when flows were less than 1000 ML.day–1 (40% exceedence flow) although some upstream movement was observed at flows as high as 6937 ML.day–1 (15% exceedence) [1274]. Over 80% of migrating N. robusta recorded moving through a fishway on the Kolan River did so at periods of low flow [232] and most migrating N. robusta moved up the Ben Anderson fishway on the Burnett River during periods of low flow also [1276]. These studies examined upstream movement only. Upstream movement
Trophic ecology Notesthes robusta is a sit-and-wait predator capable of short bursts of rapid swimming to capture prey that come within range [936]. Aquatic insects, principally ephemeropteran and odonate nymphs and dipteran larvae, comprise about one-quarter of the diet. Macrocrustacea (Macrobrachium and Paratya) are the dominant food class. Aquatic macrophytes (2.0%)
Unidentified (4.6%)
Aquatic insects (25.8%)
Detritus (1.7%) Fish (5.7%)
Macrocrustaceans (60.2%)
Figure 2. Mean diet of the bullrout Notesthes robusta. Data presented are derived from two studies; one undertaken in the Mulgrave and South Johnstone rivers (17 individuals) [1097] and the other in the Tweed River (65 individuals) [1133].
Fish are a minor component in the diet. The average length of fish from which data from the Wet Tropics were derived was 107 mm only (52–183 mm) and the Tweed River sample spanned an even greater size range (22–277 mm) [1133]. It is likely that fish are a more important component in large fish (i.e. >200 mm). Plant matter comprised 2% of the diet only. Crustaceans and polychaete worms have been reported as the major items in the diet of N.
282
Notesthes robusta
fishways effectively. Changes to the seasonal pattern of flow in regulated rivers may interfere with detection of cues initiating migration. Changes in flow through regulation that impact on habitat structure, specifically substrate composition and an associated change in invertebrate composition and abundance, are expected to result in declines in abundance. Similarly, poor land use practices that result in increased inputs of fine sediments are also expected to affect habitat suitability. De-snagging is likely to effect the adult population through removal of this important microhabitat component. Reductions in discharge that result in denial of access to bank structures are similarly likely to impact on adult fishes. More information is required on aspects of reproduction, especially in the southern part of its range, to determine whether breeding is associated with periods of low flow or low temperatures. For example, it is unknown whether temperate populations of N. robusta spawn in winter when water temperature is low or in summer when discharge is reduced.
robusta from estuarine habitats [1315]. Data included in Figure 2 from the Wet Tropics were from fish collected during daylight hours. The mean gut fullness of 24 fish was low (28%), suggesting that the majority of feeding may take place at night. A nocturnal habit was also suggested by movement data [1274]. Conservation status, threats and management Notesthes robusta is listed as Non-Threatened by Wager and Jackson [1353]. Potential threats are likely to be specific to, and localised within, individual river basins. A diadromous habit indicates that N. robusta is potentially at risk from the effects of impoundments that prevent fish movement. The risk of population extirpation is likely to increase with the number of impoundments within a river and when barriers to fish movement are close to the river mouth (i.e. tidal barrages). Notesthes robusta has been shown to use fish-ways but such structures need to allow for both the upstream and downstream migration of both adults and juveniles. Small fish may be less able to use
283
Ambassis agrammus Günther, 1867 Sailfin glassfish, Sailfin perchlet
37 310008
Family: Chandidae
weakly developed serrae. Description drawn entirely from Allen and Burgess [47]. Colour in life: almost transparent over much of body surface tending to be darker tan/yellow and more opaque dorsally. A pinkish-purple sheen is also present on the flanks, thin irridescent silver stripe along side from edge of operculum to caudal base. Fins tend to be translucent with slight duskiness at base. Colour in preservative: transparency lost and replaced with an overall tan/yellow colour. Irridescent sheen lost, stripe replaced by thin dark brown line. It should be noted that variation in serrae development does occur in Ambassis and is usually associated with age. Moreover, lateral differences within individuals may also occur, even to the extent where a nasal spine may be present on one side but not the other.
Description First dorsal fin: VII, I, 7–10 (usually 8-9); Anal: III, 7–10; Pectoral: 11–14; Vertical scale rows: 28–34, lateral line incomplete usually ending prior to spinous dorsal or being interrupted in middle portion by series of tubeless scales; Horizontal scale rows (from anal origin to dorsal base): 12–14; Cheek scales: 2 rows, very occasionally 3; Predorsal scales: 12–15; Gill rakers: 16–20 on lower limb of first arch. Figure: mature specimen, 39 mm SL, Polly Creek, North Johnstone River, July 1995; drawn 1996. Ambassis agrammus is small species rarely exceeding 50 mm SL. The mean length of 185 specimens collected from the Johnstone River over the period 1994–1998 was 38.1 ± 0.7 (SE) mm SL [1093]. The maximum length in this sample was 67 mm SL. Interestingly, only three individuals within this sample were less than 25 mm SL (see comments in Movement section).
Systematics The family Chandidae contains about 41 species from eight genera distributed throughout the Indo-West Pacific [52]. Two-thirds of the species are freshwater forms and occur in India, South-East Asia and the Indo-Australian Archipelago. The remainder are inhabitants of shallow marine and brackish estuarine environments from eastern Africa, the Arabian Peninsula, coastal southern Asia, Japan, Samoa and the Ponape and Caroline islands of the
Ambassis agrammus possesses a single supraorbital spine; nasal spine absent; preorbital ridge smooth or with 1–4 small serrae; suborbital usually with 2–17 small serrae but occasionally smooth or weakly crenulate; preorbital edge with 3–10 serrae; preopercular ridge with 7–12 serrae mainly on lower limb; hind margin with additional 3–12 serrae or weak crenulations; interoperculum with 3–10 284
Ambassis agrammus
northern Pacific [47]. The family has been previously recognised as a subfamily within the Centropomidae (see section on barramundi). The name Chandidae has chronological priority over the name Ambassidae [47]. The origin and relationships of the family are obscure [47] but it is noteworthy that the distribution of species within the family closely parallels that of species within the Terapontidae, which Vari [1346] believed to originally inhabit the shallow, tropical zones of Gondwana. The Chandidae of Australia and New Guinea contains four genera: Ambassis Cuvier, Parambassis Bleeker, Denariusa Whitley and Tetracentrum Macleay. The genus Gymnochanda occurs in Malaysia. The genera Pseudambassis Macleay, Austrochanda Whitley, Negambassis Whitley, Priopidichthys Whitley and Velambassis Whitley have been shown to be invalid and synonomous with Ambassis [47]. Similarly, the genera Synechopterus Norman and Xenambassis Schultz are considered synonyms of Tetracentrum [47]. Ambassis is distinguished from Tetracentrum by the presence of a deep notch in the dorsal fin and by the last spine being twice the length of the penultimate spine; from Parambassis by the possession of larger and fewer vertical scale rows (24–36 versus 36–52); and from Denariusa by the possession of well-developed gill rakers.
Distribution and abundance The distribution of A. agrammus is extensive and comprised of a number of disjunct populations. This species occurs widely in southern New Guinea and on some coastal islands [47]. Some of the older texts published before the systematic review by Allen and Burgess [47] list the distribution of A. agrammus as extending from the Kimberley region to the Burnett River on the east coast of Australia. However records of its presence in the Kimberley region (i.e. Allen [33], Allen and Leggett [45], Hutchins [620]) appear to be based on misidentification of Ambassis sp. (as A. muelleri) [47]. Ambassis agrammus is common and widely distributed in the Northern Territory [774] and occurs from the Victoria River in the west to the McArthur River in eastern Arnhem Land, and on Groote Eylandt [47]. Bishop et al. [193] recorded A. agrammus in 29 of 45 sites within the Alligator Rivers region where it comprised 25.4% of the total number of fishes collected. Ambassis agrammus has been recorded from the Gilbert and Leichhardt rivers draining into the southern portion of the Gulf of Carpentaria [643, 979] but is generally absent from this region, being replaced here by Ambassis sp., A. elongatus and A. macleayi. This species occurs in the following westerly flowing rivers of Cape York Peninsula: Edward, Holroyd, Archer, Wenlock and Jardine rivers and swamps around the Weipa area [571]. It is also widespread on the east coast of Cape York Peninsula, being recorded from the Claudie, Olive, Pascoe, Lockhart, Stewart, Normanby, Jeannie, Howick, McIvor, Endeavour and Annan drainages [571, 599, 1099, 1349]. Pusey et al. [1099] recorded it in three of four sites in the Stewart River (absent from isolated temporary pools) where it comprised 3.2% of the total number of fishes collected, and from five of seven sites in the Normanby River where it comprised 13.9% of the total number of fishes collected. Interestingly, this species was absent from floodplain lagoons of the Normanby River where A. macleayi and D. bandata were common [697]. Ambassis agrammus was very common (present in 7 of 8 sites) in acidic aquatic habitats of the dune fields of Cape Flattery, where it comprised 21.5% of the total number of fish collected [1101].
Seven species of Ambassis are restricted to Australia, six are shared with New Guinea, and two species (A. macracanthus and A. nalua) occur in New Guinea (and elsewhere) but not in Australia [47]. A further nine species, more widely distributed throughout the Indo-Pacific, are placed within the genus. The name A. muelleri was formerly used to cover a wide-ranging species of northern and central Australia, but is now recognised as a junior synonym of A. agassizii. This taxon is now referred to as Ambassis sp. and central Australian populations of this taxon may represent another additional species [52]. Synonyms of A. agrammus include A. reticulatus Weber [42] and A. interruptus var. reticulatus Weber, both from southern New Guinea [47]. Allen and Burgess [47] noted that Australian and New Guinean material differed in modal dorsal and anal fin ray counts and that further differences occurred within New Guinean populations also. The meristics of the population from the Daru and the Bensbach River, geographically close to Cape York Peninsula, are more similar to those of Australian material than are other more distant populations [47]. Russell and coworkers, in their research on the fisheries values of rivers of the Wet Tropics region (e.g. [1177, 1183, 1184]) recognise the presence of an additional ambassid species morphologically similar to A. agrammus. Clearly, the systematics of this species needs review.
The distribution of A. agrammus in the Wet Tropics region is patchy. Pusey and Kennard [1085, 1087] recorded it from five drainage systems; the Daintree, Johnstone, Tully and Murray rivers and coastal streams of the Cardwell region; where it comprised 2.5% of the total number of fish collected in that survey. It was much more abundant in floodplain wetland systems of the region (14% of the total collected from such habitats) than it was in lotic sites. This species has also been recorded from the downstream
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Freshwater Fishes of North-Eastern Australia
creekbed habitats (0.3 and 6.4% of the total, respectively) and highest in the billabong habitats (28.1, 27.7 and 54.7% of total for lowland backflow billabongs, corridor billabongs and floodplain billabongs, respectively). These data suggest that A. agrammus prefers lentic habitats. Bishop et al. [193] found that the abundance of this species was greatest in habitats with abundant aquatic and emergent vegetation. A similar relationship between aquatic vegetation and ambassid abundance has been reported elsewhere [1095, 1098].
reaches of the Barron River [229]. The investigations of John Russell and co-workers [1177, 1179, 1183, 1184] have detected A. agrammus (often referred to as A. c.f. agrammus) in the Mulgrave/Russell River (3/46 sites), Johnstone River (1/83 sites), Moresby River (2/20 sites), Liverpool Creek (1/29 sites) and Maria Creek 1/16). They did not record it from the Hull River immediately to the south or from the Daintree, Saltwater, Mowbray and Mossman drainages to the north [1185]. Recent intensive sampling in the Johnstone and Mulgrave/Russell rivers over the period 1994–1997 has recorded A. agrammus at nine of 56 and three of 48 locations, respectively, making this species the 18th and 27th most widely distributed species, respectively. Ambassis agrammus comprised 0.7% and 0.08% of the total number of fishes collected from the Johnstone and Mulgrave/ Russell drainages, respectively, making this species the 18th and 28th most abundant species in each river, respectively. This species is relatively more abundant in those sites in which it occurs. An average density of 0.453 ± 0.177 fish.10m2 (n = 31) (sixth most abundant) and average biomass density of 0.83 ± 0.20 g.10m2 (12th most abundant) was estimated for sites pooled across both rivers. This species commonly occurs with (in decreasing order of abundance) H. compressa, M. s. splendida, P. signifer, M. notospilus and R. bikolanus [1093].
In marked contrast, A. agrammus was not recorded from floodplain lagoons of the Normanby River but was found to be moderately abundant in the main channel of the river itself. Floodplain lagoons contained A. macleayi and Denariusa bandata [697]. D. bandata was also abundant in the one Cape Flattery site sampled by Pusey et al. [1088] in which A. agrammus was absent. Elsewhere on the Cape Table 1. Macro/mesohabitat use by sailfin glassfish Ambassis agrammus in the Wet Tropics region. Data represent the minimum, maximum and mean habitat characteristics of the sites within the Russell/Mulgrave, Johnstone and Tully rivers in which A. agrammus was present. The weighted mean (W.M.) refers to the mean linearly weighted by the abundance of sailfin glassfish in each site. Parameter
Ambassis agrammus has been recorded from wetlands of the Burdekin River delta (C. Perna, pers. comm.) and this river appears to be the southern limit for this species. Merrick and Schmida [936] list the Burnett River as the southern limit of A. agrammus, apparently based on an claim by Lake [754]. The comprehensive review of fishes of the Burnett River by Kennard [700] failed to find any record of this species in this or nearby drainages. Ambassis agrammus appears to be replaced by A. agassizii in streams south of, and including, the Herbert River (notwithstanding the presence of A. agrammus in wetlands of the Burdekin River delta). It should be noted however, that Jebreen et al. [643] recorded the presence of a number of relatively uncommon unidentified taxa, collectively labelled as Ambassis spp., in addition to A. agassizii, in the Herbert River. Ambassis agrammus may be among this group of unidentified species.
Min.
0.6 Catchment area (km2) Stream order 2 Distance to source (km) 1 Distance to river mouth (km) 10 Elevation (m.a.s.l.) 5 Width (m) 2.9 Riparian cover (%) 0 Gradient (%) 0 Mean Depth (m) 0.16 Mean water velocity (m.sec–1) 0
Macro/mesohabitat use Bishop et al. [193] recorded A. agrammus from a variety of different habitat types in the Alligator Rivers region, including escarpment habitats (3/9 sites), lowland sandy creekbed pools (5/6 sites), lowland backflow billabongs (11/11 sites), corridor billabongs (3/3) and upper floodplain billabongs (4/4). Abundances varied between these habitat types, being lowest in escarpment and sandy
286
Max. 85.0 5 15 39 50 9.5 99 0.45 0.65 0.37
Mean
W.M.
17.7 3 5.3 17.3 13.2 4.9 61.0
6.84 2.45 3.4 13.9 13.7 5.5 62.6
0.14 0.32 0.08
0.09 0.32 0.04
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 2 1 0 0 0 0
38 88 55 52 24 6 14
12.0 40.1 30.3 11.0 3.1 1.0 2.6
20.1 36.5 34.2 5.8 1.5 0.6 1.5
Aquatic macrophytes (%) Filamentous alga (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Small woody debris (%) Large woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
23.7 6.0 8.0 31.0 7.0 60.3 12.3 9.0 17.0 39.0
2.5 0.7 0.9 3.4 0.5 20.7 4.4 4.0 4.3 15.9
3.7 0.5 3.2 3.0 0.5 35.1 5.4 4.4 7.5 11.6
Ambassis agrammus
Microhabitat use The microhabitat use of A. agrammus in streams of the Johnstone and Mulgrave/Russell drainages estimated from capture records of 45 individuals collected over the period 1994–1998 is shown in Figure 1. This species was collected only from areas in which the average water velocity was low (<0.2 m.sec–1) and the majority of specimens were collected from areas of no flow (Fig. 1a). The focal point velocity mirrored that of average water velocities (Fig. 1b). It was rarely collected from areas greater than 60 cm deep and was collected from the lower half of the water column (Fig. 1c and d, respectively). As would be expected from the mesohabitat conditions depicted in Table 1, A. agrammus was most frequently collected over fine substrates (Fig. 1e) and close to cover elements such as macrophytes, leaf litter and woody debris (Fig. 1f).
Flattery dunefields A. agrammus occurred in isolated pools, creeks, swamps and lakes. The survey of the Wet Tropics region by Pusey and Kennard [1085] indicated that this species was more abundant in wetland habitats than in riverine habitats. Overall and with the exception of the Normanby River, these studies indicate a preference for lentic habitats. However, A. agrammus does occur in riverine habitats and may be numerically important in those reaches in which it occurs. Table 1 lists habitat data for the Mulgrave/Russell and Johnstone rivers of the Wet Tropics region. Whilst this species occurs in a range of stream sizes from second to fifth order, it was most abundant and most commonly collected in smaller streams at low elevation and close to the river mouth. This type of adventitious stream is also characterised by a low gradient and dense riparian canopy.
100
Although A. agrammus was occasionally collected from shallow stream reaches with moderately fast current speeds, it was most commonly collected from, and most abundant in, reaches with very little flow. As expected, such stream reaches are characterised by fine substrates and there was a strong tendency for abundance levels to be greatest in reaches with a mud/sand bed. The small, coastal adventitious streams described above are also characterised by their high levels of cover, particularly of leaf litter. As a consequence of the generally high riparian cover characteristic of these streams, aquatic macrophytes are not overly abundant, however the disparity between the arithmetic mean and the weighted mean suggests fish abundance levels are greater in reaches with proportionally more macrophyte cover. In fact, most cover elements listed show greater values for the weighted mean, indicating that A. agrammus is more abundant in reaches with abundant cover. These lowland adventitious streams tend to be more swamp-like than stream-like and with speciose assemblages (mean species richness of the sites in which A. agrammus was recorded = 15 and 9 for the Johnstone and Mulgrave/Russell drainages respectively). The only parameter for which the weighted mean was greatly smaller than the arithmetic mean was bank-associated root masses. Such a microhabitat is the favoured haunt of Giurus margaritacea, Eleotris spp. and Bunaka gyrinoides. In summary, the lotic habitat in which A. agrammus occurs in the Wet Tropics region consists of complex, low gradient, low-flow stream reaches on the coastal lowlands. In many respects such habitats closely resemble the lentic habitats in which it occurs in this region and elsewhere in northern Australia.
(a)
100
80
80
60
60
40
40
20
20
0
0
Mean water velocity (m/sec) 30
(c)
(b)
Focal point velocity (m/sec) 30
20
20
10
10
0
0
(d)
Total depth (cm) 40
Relative depth
(f)
(e) 30
30 20
20
10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Ambassis agrammus in the Johnstone and Mulgrave/Russell drainages. Usage based on capture data from 45 individuals.
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Freshwater Fishes of North-Eastern Australia
Generally, A. agrammus occurs in well-oxygenated waters although it occurs in poorly oxygenated lagoons in the Alligator Rivers region also, and thus appears tolerant of low dissolved oxygen levels. However, Bishop [187] noted it was among the least hypoxia-tolerant of those species found in billabongs, being amongst the first species to suffer elevated mortality as dissolved oxygen levels declined. Similarly, Brown et al. [243] noted that A. agrammus was intolerant of the combined effects of low pH and elevated aluminium levels and the resultant gill hyperplasia which inhibited oxygen uptake. Lotic populations may be even less tolerant of low dissolved oxygen levels on the basis of the data shown in Table 2. An intolerance to hypoxia may be one reason for the apparent absence of A. agrammus from floodplain lagoons of the Normanby River despite their presence in the river itself. Oxygen levels in these lagoons often approached hypoxia, in contrast to that seen in the river itself [697, 1099]
Environmental tolerances Data listed in Table 2 are drawn from field studies in four separate regions: 1. Alligator Rivers region [193] (n = 29 sites over several seasons); 2. Cape York Peninsula (n = 8 sites in August 1990) [1099]; 3. Cape Flattery dunefields (n = 7 sites in November 1996) [1088]; and 4. Wet Tropics region (12 sites over the period 1994–1998) [1093]. Experimental data on environmental tolerances are lacking for this species. Ambassis agrammus is capable of withstanding temperatures in the 30–40°C range. However, it is probable that populations are adapted to each region’s thermal regime and the upper limits applicable to one region may be much higher than for another. For example, spot temperature records for Polly Creek, a lowland tributary of the Johnstone River, in which A. agrammus is relatively abundant, never exceeded 30°C over the period 1994–1998. It is unlikely that fish from this region could withstand temperatures as high as that experienced in the Alligator River (38°C). Similarly, fish from the Alligator River may not tolerate temperatures as low as 17°C.
The great range in pH tolerated (3.8–8.4 units) is especially noteworthy but the range within each region is much smaller (1.04 to 2.2 units). These data again suggest that regional acclimation or adaptation is important and that care should be taken in extrapolating results from one region to another. In general, these data indicate that A. agrammus prefers acidic water conditions and may be found in very acidic conditions (i.e. dune lakes). In addition, data in Table 2 indicate that A. agrammus is found in waters of low conductivity but across a range of turbidity.
Table 2. Physicochemical data for Ambassis agrammus. Turbidity values given are as NTU except for the Alligator Rivers region where they are listed as Secchi disc depths. Data listed for the Alligator Rivers region always from bottom of water body. See text for source of data. Parameter
Min.
Max.
Mean
Alligator Rivers region (n = 29) Temperature (°C) 24 38 Dissolved oxygen (mg.L–1) 2.5 6.8 pH 4.5 6.7 Conductivity (µS.cm–1) 4 220 Turbidity (cm) 1 360
29.7 4.4 5.9 32
Cape York Peninsula (n = 8) Temperature (°C) 21 28 Dissolved oxygen (mg.L–1) 8.0 11.0 pH 6.48 7.52 Conductivity (µS.cm–1) 72 200 Turbidity (NTU) 0.71 3.30
24.5 8.7 7.12 114.5 1.53
Cape Flattery dunefields (n = 7) Temperature (°C) 23 31 Dissolved oxygen (mg.L–1) 6.40 7.73 pH 3.8 5.1 Conductivity (µS.cm–1) 89 192 Turbidity (NTU) highly stained Wet Tropics region (n = 12) Temperature (°C) 17.5 27.2 Dissolved oxygen (mg.L–1) 5.62 8.40 pH 5.13 7.00 Conductivity (µS.cm–1) 26.0 65.6 Turbidity (NTU) 0.33 22.1
Merrick and Schmida [936] suggest that A. agrammus is sensitive to deterioration in water quality. Reproduction Information on the reproductive biology of A. agrammus presented in Table 3 is drawn entirely from the field observations of Bishop et al. [193] in the Alligator Rivers region and from a laboratory study of larval development by Semple [1215]. Sexual maturity is reached within the first year of life (probably after eight to nine months) and at small size. Bishop et al. [193] record a length at first maturity (that length at which 50% of the sample is mature) of 26 and 27 mm CFL for female and male fish, respectively. Semple [1215] included data from fully mature spawning females of only 25 mm SL. Given that lengths of 37–57 mm SL are achieved after 380 days growth in the laboratory and that few specimens larger than 60 mm have been collected, it is probable that most adult individuals do not live longer than one year and almost certainly very few would live to two years. A sex ratio of unity predominates although Bishop et al. [193] did record significant transient departures from unity that they believed to be artefactual. Spawning occurs between 28–32°C in the field but at slightly lower temperatures in the laboratory. The
27.4 7.20 4.17 126.3
23.0 6.71 6.15 39.7 2.4
288
Ambassis agrammus
into food-rich habitats prior to spawning.
actual spawning stimulus is unknown but given the observed spawning phenology it may be related to temperature, flooding or both. Reproductive investment is moderate (mean GSI levels of 7 and 4.2% for female and male fish, respectively) although the fact that more than one spawning may occur (i.e. each event separated by recovery period), lifetime reproductive investment is probably higher than that indicated by instantaneous GSI values. Spawning apparently occurs over a number of consecutive nights with batches of five to 250 eggs, depending on female size, being laid at one time. Spawning most likely occurs amongst aquatic vegetation, to which the small, spherical, adhesive eggs become attached. Although adult fish are reported to move downstream to the lentic habitats in which spawning occurs, such movement precedes spawning and is thus not strictly a spawning migration but more likely the result of fish moving
Larval development is rapid, with hatching occurring in less than one day and exogenous feeding occurring after four days [1215]. The larvae are small and metamorphose into the juvenile form at small size also (see Table 3). Movement biology Information on the movement behaviour of this species is limited to that gathered in the Alligator Rivers region by Bishop et al. [190]. While these authors report only on the movements of a number of species collectively identified as Ambassis spp., it is not inappropriate to consider that the patterns described therein apply mostly to A. agrammus given its numerical dominance in that system. Ambassis agrammus is considered a nocturnal species [47], yet Bishop et al. [190] found it did not move at night but
Table 3. Life history data for Ambassis agrammus. Information drawn from two studies: one undertaken in the field in the Alligator Rivers region by Bishop et al [193], and the other in the laboratory by Semple [1215]. Information on larval development drawn entirely from Semple [1215]. Age at sexual maturity (months)
<12 months
Minimum length of ripe females (mm)
Field – length at first maturity = 26 mm CFL, mature specimens present at smaller lengths Laboratory – 25 mm SL spawning
Minimum length of ripe males (mm)
Field – length at first maturity = 27 mm CFL
Longevity (years)
Unknown but probably very few survive longer than 2 years
Sex ratio
Field – 1:1 but occasional dominance by males observed during the breeding season
Peak spawning activity
Field – early wet season: December–January
Critical temperature for spawning
Field – 28–32°C Laboratory – 25–29°C
Inducement to spawning
temperature? flooding?
Mean GSI of ripe females (%)
Field – 7.0%
Mean GSI of ripe males (%)
Field – 4.2%
Fecundity (number of ova)
Field – 312–2905, mean = 1614
Fecundity/length relationship
NA
Egg size (mm)
Field – 0.24 to 0.40 mm intraovarian Laboratory – 0.6 mm water-hardened
Frequency of spawning
Laboratory – spawning occurs at night, batch sizes of 5–20 eggs for small fish (25 mm SL), 200–250 in larger fish (45 mm SL), up to four consecutive nights with 4–6 week hiatus
Oviposition and spawning site
Field – spawning occurs in lowland lentic habitats Laboratory – adhesive, spherical eggs attached to vegetation
Spawning migration
Field – downstream migrations from dry season refugia into lowland lentic habitats
Parental care
None, but apparently adults do not eat own eggs
Time to hatching
21–22 hours at 28°C
Length at hatching (mm)
1.55 ± 0.03 mm
Length at feeding (mm)
2.23 ± 0.04 mm
Age at first feeding
4 days
Age at loss of yolk sac
?
Duration of larval development
22–25 days
Length at metamorphosis
7.0 ± 0.2 mm
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Freshwater Fishes of North-Eastern Australia
concentrated its mass migrations in the dusk and dawn hours. Such a strategy may help to lessen the intensity of predation. Upstream migration from ephemeral floodplain habitats to dry season refugia occurs in the late wet season (March to May) prior to a marked reduction in habitat availability. A great many of these fish, which are the product of spawning during the wet season, were suggested to fall prey to predators during this period of movement. Presumably, downstream migrations are made by adult fishes at the start of the wet season also but were not measured in this study. Bishop et al. [190] characterised Ambassis spp. as a slow mover, capable of 4.8–5.4 km.day–1.
Trophic ecology The diet summary depicted in Figure 2 is based on data drawn from Bishop et al. [193] for floodplain lagoon habitats of the Alligator Rivers region, and from Pusey et al. [1099] for lotic habitats in the Stewart and Normanby rivers of eastern Cape York. The dominant item of the average diet is microcrustacea (44.4%). This source of prey were almost entirely lacking in the Cape York sample (2.0% contribution by ostracods) but comprised 50% of the diet of the Alligator Rivers sample. The most important microcrustacean taxon in this latter region was Cladocera (30%) followed by copepods (10%) and ostracods (3.9%).
There is no information on the movement patterns of this species in comparable Queensland rivers. The near absence of small fish below 25 mm SL in our collections from the Wet Tropics region suggests that adult and juvenile habitats are separate. Plankton trawls at the confluence of small tributary streams of the Johnstone River (in which A. agrammus are known to occur) have collected large numbers of juvenile Ambassis spp. [1093]. This observation, coupled with the knowledge that the eggs of A. agrammus are adhesive and attached to aquatic plants or similar structures, suggests that either larvae are transported downstream to develop and later migrate back upstream or that adults may make short downstream movements to the main channel to spawn (analogous to those observed in the Alligator Rivers region but occurring over a much smaller spatial scale).
Aquatic insects comprised 25.4% of the diet of the floodplain fish sample and this component was dominated by the contribution of Diptera (18.3%) (almost entirely chironomid larvae and pupae). Aquatic insects were the dominant prey class in the diet of the Cape York sample, collectively accounting for 67.6% of the total. Of this fraction, chironomid larvae contributed 20.8%, trichopteran larvae 15.5% and ephemeropteran nymphs a further 27%.
Macrocrustaceans (1.2%) Algae (1.5%)
The differences in diet noted above, reflect the different habitats in which the studies were undertaken but do serve to illustrate that A. agrammus has reasonably flexible foraging abilities. The importance of small invertebrates simply reflects the constraint of small size on prey choice and illustrates the importance of this species within lotic and lentic food webs. It is preyed upon by a number of species including barramundi and spangled perch. Conservation status, threats and management Ambassis agrammus is listed as Non-Threatened by Wager and Jackson [1353] and not listed by ASFB [117]. This species is probably secure given its wide distribution but some populations may face threats in the future.
Unidentified (3.4%)
Detritus (18.6%)
It is evident from the data presented here that many aspects of the biology of A. agrammus vary according to the habitat utilised and the region in which it occurs. In general, this species should be considered a still-water species that achieves greatest abundance in floodplain wetlands, billabongs and lagoons. As such, maintenance of the integrity of these habitats is probably the single greatest requirement for its continued survival. In the Wet Tropics region, such habitats are increasingly under threat from expansion of the sugar-cane industry. Microcrustaceans (44.4%)
Some elements of the riverine flow regime of nearby rivers need to be considered also. In the case where floodplain and wetland habitats connect with the river proper during the wet season, the continued maintenance of this connectivity is vital. Flood capture should not lessen the extent, frequency or duration of the flooding and connectivity of
Aquatic insects (30.9%)
Figure 2. Mean diet of Ambassis agrammus. Data for 777 individuals from two regions; the Alligator Rivers region (n = 679) [193] and the Stewart and Normanby Rivers of eastern Cape York Peninsula (n = 98) [1099].
290
Ambassis agrammus
A. agrammus in the Wet Tropics region are patchily distributed but contribute to the diversity of the region and of individual basins. Of greatest threat to these populations is continued vegetation clearing and unrestricted water abstraction. Aquatic vegetation is important for shelter, spawning habitat and foraging for microcrustaceans. Changes in flow regime that impact on the abundance and distribution of aquatic plants are likely to also impact upon A. agrammus populations.
these habitats. The last requirement is a critical one, especially if floodplain and wetland habitats are seasonally ephemeral. There is little value in allowing fish access to such habitats at the beginning of the wet season but not also allowing these same fish and their progeny some route of travel back into the river proper. The design and construction of levee banks and of drainage channels intended to rapidly remove flood waters from floodplains must be carefully considered. Lotic populations of
291
Ambassis agassizii Steindachner, 1867 Agassiz’s glassfish, Olive perchlet
37 310009
Family: Chandidae
ridge, 1–7 serrae, sometimes smooth; suborbital, 3–14, sometimes smooth; preorbital edge 4–7; preopercular ridge, 3–13 on lower limb; interoperculum, 1–6; preoperculum, 7–13 on lower edge, 1–10 on hind margin (occasionally smooth). Single spine (sometimes zero or two) present on supraorbital ridge. Large cycloid scales on body; opercula with scales and two rows of scales on cheeks below eyes. Lateral line occasionally absent, but usually 1–15 tubed scales terminating anterior to, or below spinous dorsal fin, occasionally continued to the middle of caudal peduncle as an incomplete row of weakly tubed or pitted scales. Dorsal fin divided by deep notch separating spinous and soft-rayed parts; first dorsal spine small, procumbent. Anal fin located opposite soft rays of dorsal fin; anal and dorsal fins with scaly basal sheath. Pectoral fins of moderate size, originating before pelvic fins; pelvic fins large. Caudal fin forked with rounded tips [34, 40, 47, 270]. Sexually dimorphic: males reputed to have proportionally larger fins [524]; reproductively mature females have broader urinogenital papilla (remaining narrow and pointed in males) [951].
Description First dorsal fin: VII; Second dorsal: I, 7–9; Anal: III, 7–9; Pectoral: 11–13; Pelvic: I, 5; Caudal: 14–15 segmented rays; Vertical scale rows: 24–27; Horizontal scale rows: 10–12; Predorsal scales: 11–14; Gill rakers (lower limb of first arch): 15–18; [40, 47]. Figure: mature male, 51 mm SL, Mary River, drawn September 1995; 1999. Ambassis agassizii is a small fish commonly less than 60 mm TL but reaching up to about 70–80 mm TL [40, 784]. Of 3098 specimens collected in rivers and streams of south-eastern Queensland, the mean and maximum length of this species were 31 and 62 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 927 individuals (range 13–54 mm SL) sampled from the Mary River, south-eastern Queensland is W = 2.0 x 10–5 SL3.119, r2 = 0.956, p<0.001 [1093]. The following description is derived largely from Allen and Burgess [47]. Ambassis agassizii has a laterally compressed, elongate-oval shaped body. Mouth large, oblique, reaching to anterior margin of eye; teeth conical located in jaws and on vomer and palatines. Eye large. Head with serrae (small spines) as follows: preorbital
Colour in life: often semi-transparent, or with yellowish dorsal surface becoming lighter or silvery on lower sides; ventral surface white or silvery. Scales with dark margins,
292
Ambassis agassizii
common in northern New South Wales [82, 282, 553, 814].
creating reticulated pattern, especially on dorsal surface and upper sides. Fins generally clear or colourless, pelvic and anal fins often with broad, dark band on margins. Adult individuals in south-eastern Queensland, frequently with iridescent light purple colouration on ventral surface of head. Preserved colouration as above, except body colour yellow to tan [34, 40, 47, 270, 1093].
The true northern limit of A. agassizii in Queensland is uncertain. Allen and Burgess [47] list this species as occurring as far north as the Mowbray River in the Wet Tropics region. It is possible that records further north from the Stewart River [571], McIvor River [216] and Annan River [571] in eastern Cape York Peninsula are in error.
Ambassis agassizii occurs sympatrically with several other species of Ambassis throughout its range in north-eastern Australia. It may therefore potentially be confused with other morphologically similar Ambassis species, especially toward the northern end of its range. In south-eastern Queensland A. agassizii may be confused with A. marianus, a species occurring in fresh and brackish waters.
Ambassis agassizii is generally widespread but uncommon toward the northern end of its distribution in the Wet Tropics region [643, 1085, 1087, 1177, 1183, 1184, 1349]. It is generally widespread in central Queensland and sometimes locally common in rivers of this region [160, 825, 915, 1098, 1349]. This species is widely distributed in south-eastern Queensland and is present in most major rivers and streams from the Burnett River south to the border with New South Wales. It is generally common in this region and often locally abundant, forming schools of hundreds of individuals [1093]. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that A. agassizii has been collected at 33 of 63 locations surveyed (fourth most widespread species in the catchment) and formed 2.6% of the total number of fishes collected (ninth most abundant). It is present and occasionally locally abundant in the Elliott River [825] and is relatively common in the rivers of the Burrum Basin [157, 701, 736].
Systmatics In their recent revision of the Australian and New Guinea Chandidae, Allen and Burgess [47] recognised the following (regional) synonyms of A. agassizii: Pseudambassis nigripinnis De Vis, 1884 [378], P. pallidus De Vis 1884 [378] and Priopis olivaceus Ogilby 1911 [1019] for eastern coastal populations; and P. castelnaui Macleay 1881 [845] for inland Murray-Darling populations. It is possible that inland and coastal populations of A. agassizii are genetically distinct, but there are no published studies that have examined the population genetics of this species. Allen et al. [52] reported that A. muelleri Klunzinger 1879 [723] (also as A. mulleri) originally described from the Murray River, is synonymous with A. agassizii. Populations formally known as A. muelleri (= mulleri) from central desert drainages and north-western Australia are thought to represent one or possibly more undescribed species [52], as do records of A. castelnaui from central Australia [1336].
Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 5330 individuals from 29.5% of all locations sampled (Table 1). Overall, A. agassizii was the ninth most abundant species collected (3.3% of the total number of fishes collected) and was moderately common at sites in which it occurred (7.8% of total abundance). In these sites, A. agassizii most commonly occurred with the following species (listed in decreasing order of relative abundance): P. signifer, C. marjoriae, G. holbrooki and M. duboulayi. Ambassis agassizii was the 15th most important species in terms of biomass, forming 0.3% of the total biomass of fish collected. This species was particularly widespread and abundant in the Mary and Brisbane rivers, where it occurred in 64% and 30% of locations, respectively, and formed more than 4% of the total number of fish collected in these rivers. It was less common or widespread in the Logan-Albert Basin and short coastal streams of the Sunshine Coast, Moreton Coast and South Coast. We suggest that the relative abundance of A. agassizii in the Mary and Brisbane rivers, compared with elsewhere in south-eastern Queensland, may be related to the presence of extensive aquatic macrophyte beds (the preferred microhabitat type of this species – see below) which are
Distribution and abundance Ambassis agassizii is a relatively widespread species occurring in coastal and inland drainages of eastern Australia. This species is present in coastal drainages of northern Queensland south to Lake Hiawatha (between the Clarence and Bellinger rivers) in central New South Wales [40, 47]. It is also present on Fraser Island and North Stradbroke Island off the coast of south-eastern Queensland. It was previously widespread, although patchily distributed, throughout much of the MurrayDarling Basin but is now thought to be extinct in Victoria and South Australia [507, 965]. It is generally patchily distributed and uncommon in the New South Wales and Queensland portions of the Murray-Darling, except for northern tributaries such as the Condamine River [965, 1338, 1349]. Distributional information and recent survey data indicate that A. agassizii is widespread and relatively
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Freshwater Fishes of North-Eastern Australia
Table 1. Distribution, abundance and biomass data for Ambassis agassizii in rivers of south-eastern Queensland. Data summaries for a total of 5330 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
29.5
64.0
3.4
20.0
35.1
13.2
15.0
3.26 (7.76)
4.88 (7.63)
0.20 (5.05)
1.07 (5.93)
4.28 (10.53)
0.11 (1.41)
1.04 (9.00)
9 (5)
7 (5)
16 (5)
11 (4)
7 (2)
18 (10)
10 (4)
0.32 (1.21)
0.43 (1.34)
0.08 (0.21)
–
0.67 (1.37)
0.01 (0.09)
0.01 (0.22)
15 (8)
10 (8)
10 (4)
–
9 (6)
24 (16)
15 (6)
Mean numerical density (fish.10m–2)
0.81 ± 0.10
1.03 ± 0.14
0.17 ± 0.15
0.23 ± 0.07
0.50 ± 0.10
0.11 ± 0.02
0.36 ± 0.29
Mean biomass density (g.10m–2)
0.86 ± 0.14
0.99 ± 0.17
0.25 ± 0.20
–
0.63 ± 0.19
0.06 ± 0.02
0.10 ± 0.00
the process of moving upstream, and were not residents of this atypical mesohabitat type. This species is most abundant in mesohabitats with fine substrates (mostly sand,
more widespread and abundant in the mid to lower portion of these rivers than in the smaller coastal basins we have sampled in south-eastern Queensland. Across all rivers, average and maximum numerical densities recorded in 276 hydraulic habitat samples (i.e. riffles, runs or pools) were 0.81 individuals.10m–2 and 15.73 individuals.10m–2, respectively [1093]. Average and maximum biomass densities at 203 of these sites were 0.86 g.10m–2 and 17.43 g.10m–2, respectively.
Table 2. Macro/mesohabitat use by Ambassis agassizii in rivers of south-eastern Queensland. Data summaries for 5330 individuals collected from samples of 276 mesohabitat units at 87 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
Macro/mesohabitat use Ambassis agassizii is found in a variety of freshwater habitats including still or slow-flowing parts of large lowland rivers, upland rivers and streams and small coastal streams. It also occurs in dune systems (Fraser and North Stradbroke islands), lakes, ponds, swamps and river impoundments (dams and weirs) [40, 47, 1093]. In New South Wales this species has been classified as a pooldwelling species [553, 1200].
Parameter 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
Mean
W.M.
19.6 7.0 10.0 0 1.8 0
9734.3 260.5 311.0 250 40.8 91.0
770.6 53.4 179.9 85 10.5 34.0
761.2 50.6 210.9 90 13.5 35.0
Gradient (%) 0 Mean depth (m) 0.08 Mean water velocity (m.sec–1) 0
This species occurs throughout the major length of rivers, ranging between 10 and 311 km from the river mouth and at elevations up to 250 m.a.s.l. (Table 2). It most commonly occurs in the mid to upper catchment and at elevations around 90 m.s.a.l. It is present in a wide range of stream sizes (range = 1.8–40.8 m width) but is more common in larger streams (weighted mean = 13.5 m) with low to moderate riparian cover (usually <40%). In rivers of south-eastern Queensland, A. agassizii has been recorded in a range of mesohabitat types but most commonly occurs in pools characterised by low gradient (weighted mean = 0.09%), moderate depth (weighted mean = 0.50 m) and low mean water velocity (weighted mean = 0.05 m.sec–1) (Table 2). On one occasion however, we collected a small number of adult individuals from a shallow, fast-flowing riffle; we presume these fish were in
294
2.48 1.08 0.84
0.22 0.46 0.09
0.09 0.50 0.05
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
99.6 100.0 58.5 78.2 65.8 40.0 76.0
6.9 21.6 23.7 28.4 15.2 3.1 1.2
9.1 40.0 21.2 19.9 7.6 1.1 1.1
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
69.6 65.9 45.0 65.7 39.1 46.2 28.9 15.5 83.3 83.3
19.0 10.9 1.7 8.3 2.0 12.2 4.2 3.3 13.2 15.9
24.9 13.5 0.8 12.0 3.0 9.5 3.7 2.5 8.4 9.2
Ambassis agassizii
and fine gravel (Fig. 1e). This species showed no particular affinity for areas close to the stream-banks (51% of individuals sampled were within 1 m of the bank), but the majority (91% of individuals) were collected in areas less than 0.2 m from the nearest available cover. It was frequently collected in close association with aquatic macrophytes and filamentous algae, and occasionally in open water and among submerged marginal vegetation, root masses and near leaf-litter beds (Fig. 1f).
fine gravel and coarse gravel). It is particularly common in areas with abundant and extensive beds of submerged aquatic macrophytes, filamentous algae and submerged bankside vegetation. Leaf-litter beds, undercut banks and root masses are less common in such areas. Microhabitat use In rivers of south-eastern Queensland, A. agassizii was almost always collected from areas of low water velocity (less than 0.1 m.sec–1) (Fig. 1a and b). It has been recorded at maximum mean and focal point water velocities of 0.44 and 0.42 m.sec–1, respectively. This species was collected over a wide range of depths, but most often between 20 and 70 cm (Fig. 1c). A pelagic species, it most commonly occupies the mid- to lower water column (Fig. 1d). It is usually found over fine substrates including mud, sand (a)
(b)
80
80
60
60
40
40
20
20
0
0
30
Milton and Arthington [951] reported that larvae up to 40 days old formed schools near the water surface in tributaries of the Brisbane River. Upon reaching approximately 8–12 mm in length, larvae dispersed amongst aquatic vegetation [951]. In south-eastern Queensland rivers and streams we have observed aggregations of small juveniles in similar microhabitats as described above for larger fish [1093]. Large fish are sometimes observed in loose schools, especially when undertaking upstream movements. Allen and Burgess [47] reported that some species of Ambassis disperse during darkness while foraging nocturnally and congregate amongst suitable shelter during daylight.
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
Environmental tolerances There is no quantitative data available concerning the environmental tolerances of A. agassizii. However, ambient water quality data collected at sites in which this species occurred in south-eastern Queensland indicate that A. agassizii may be tolerant of a relatively wide range of physicochemical conditions (Table 3). Temperatures ranged between 11.0 and 33.6°C, but the distribution of this species in tropical and temperate regions of eastern Australia suggests that maximum and minimum absolute thermal tolerances of this species may be greater. Dissolved oxygen concentrations ranged from hypoxic to supersaturated, possibly as a result of high rates of photosynthesis and respiration by aquatic macrophytes and algae; A. agassizii commonly occurs in close association with extensive beds of these aquatic plants. It occurred in mildly acidic to basic waters (range 6.3–9.9). The maximum turbidity at
30 20 20 10
10
0
0
Total depth (cm)
Relative depth
(e)
(f) 25
30
20 20
15 10
10
5 0
0
Table 3. Physicochemical data for Ambassis agassizii. Data summaries for 5330 individuals collected from 181 samples in south-eastern Queensland streams between 1994 and 2003 [1093] Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Ambassis agassizii. Data derived from capture records for 481 individuals collected in the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
295
Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
11.0 0.3 6.3 19.5 0.2
Max. 33.6 19.5 9.9 15102.0 144.0
Mean 20.5 7.7 7.7 741.9 5.6
Freshwater Fishes of North-Eastern Australia
size of spawning fish in aquaria is reported as 32 mm TL for males and 30 mm TL for females [797].
which this species has been recorded in south-eastern Queensland is 144.0 NTU but it usually occurs in waters of much lower turbidity. Salinity tolerances appear reasonably high, possibly reflecting the marine affinities of the Chandidae: we collected this species at a maximum conductivity of 15 102 µS.cm–1.
Ambassis agassizii has an extended breeding season from spring through to autumn but spawning appears to be concentrated in spring and early summer. In the Mary River, immature and early developing fish (stages I and II) were most common between April and August (Fig. 3). Developing fish (stages III and IV) of both sexes were present year-round. Gravid fish (stage V) were present between September and May but both sexes were most abundant between September and December (Fig. 3). The temporal pattern in reproductive stages mirrored that observed for variation in GSI values, with peak GSI values observed during spring (Fig. 4). The phenology of reproductive activity and GSIs for fish from tributaries of the Brisbane River [950] were generally similar to the pattern observed
Reproduction Quantitative information on the reproductive biology of A. agassizii is available from field and aquarium studies [524, 784, 797, 951, 1093]. Details are summarised in Table 4. This species spawns and completes its entire life cycle in freshwater. Maturation commences at a relatively small size. Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, southeastern Queensland, were 22.5 mm SL and 31.7 mm ± 0.4 SE, respectively for males and 22.0 and 30.8 mm ± 0.6 SE, respectively for females (Fig. 2). Gonad maturation in both sexes was commensurate with somatic growth, the mean length at each reproductive stage being different from all other stages. Males and females of equivalent reproductive stages were similar in size (Fig. 2). The minimum and mean size of gravid (stage V) males was 28.1 mm SL and 37.5 mm ± 0.5 SE, respectively; the minimum and mean size of gravid females was 25.6 mm SL and 37.6 mm ± 0.5 SE, respectively. Milton and Arthington [950] recorded minimum and mean lengths of ripe females (equivalent to stage V) from tributaries of the Brisbane River as 32.0 and 37.2 mm SL, respectively. The minimum
Reproductive stage I
II
III
IV
V
Males 100
(80) (40) (15) (38) (52) (16)
(68) (90) (22) (18) (48)
80 60 40 20
40
Males
0
Females
Females
35
100
(92) (30) (17) (38) (71) (15)
(25) (56) (33) (22) (25)
80 30
60 40
25
20 20
0 I
II
III
IV
V
Reproductive stage Figure 2. Mean standard length (mm SL ± SE) for male and female Ambassis agassizii within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland, between 1994 and 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 3.
Month Figure 3. Temporal changes in reproductive stages of Ambassis agassizii in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in parentheses.
296
Ambassis agassizii
but the predictability of high temperatures and low flows are higher. These conditions are likely to: reduce the potential for high flows to disturb beds of aquatic macrophytes that are used for spawning sites (see below); decrease the likelihood that falling water levels will expose eggs; increase the potential of larvae to encounter high densities of small prey, avoid physical flushing downstream due to high flows and thereby maximise the potential for recruitment into juvenile stocks [951, 1093]. A similar scenario has been hypothesised for other smallbodied fish species in the Murray-Darling Basin [614, 615]. Sampling in rivers of south-eastern Queensland [1093] revealed that juvenile fish less than 15 mm SL were present year-round supporting the suggestion made earlier that this species has an extended spawning period. These data further suggest that suitable conditions for recruitment of larvae through to the juvenile stage and beyond may persist year-round and may not necessarily be limited by prevailing temperature and/or discharge regime.
for fish from the Mary River [1093], except that spawning appeared to be concentrated within a slightly shorter period (October and November). No consistent pattern in overall sex ratios was observed for populations from the Brisbane River, although females dominated the larger length classes [951].
8
Males Females
6
4
2
0 Spring (n = 581)
40
Month Figure 4. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Ambassis agassizii males (open circles) and females (closed circles) in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 3.
30
Summer (n = 1061)
20
AutumnWinter (n = 1456)
The spawning stimulus for A. agassizii is unknown but corresponds with increasing water temperatures and photoperiod in late winter and early spring. In aquaria, spawning is reported to occur at water temperatures between 22 and 25°C [797]. Spawning cues are probably not associated with rising water levels or flooding, although fish have been observed to spawn in artificial ponds soon after a rise in water level [813]. Milton and Arthington [951] observed that the peak spawning period for fish in the Brisbane River in October and November coincided with minimum surface water temperatures of 22°C. The peak spawning period generally coincides with pre-flood periods of low and relatively stable discharge in rivers of south-eastern Queensland. However, in the Mary River, breeding may also continue through the months of elevated discharge at the commencement of the wet season in December–January. The ability of this species to spawn repeatedly over an extended period may be an adaptation to the relatively unpredictable timing of the onset of wet season flooding. The spawning of adults and presence of larvae can occur when the likelihood of flooding is low,
10
0
Standard length (mm) Figure 5. Seasonal variation in length-frequency distributions of Ambassis agassizii, from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
In the wild, spawning may occur in aquatic macrophytes, the substrate, and possibly submerged marginal vegetation [951, 1093]. In the Brisbane River, eggs have been observed attached to aquatic plants (Vallisneria and Nymphoides spp.) and rocks on the stream-bed [951]. Spawning in aquaria is reported to occur among fine-leaved aquatic plants [524, 784, 797]. This species is
297
Freshwater Fishes of North-Eastern Australia
was 0.53 mm ± 0.01 SE [1093]. Milton and Arthington [951] reported that eggs (possibly water-hardened) from Brisbane River fish were 0.6 mm in diameter. Water-hardened eggs are about 0.7 mm diameter [40]. The demersal eggs are spherical and adhesive [524]. No parental care of eggs has been reported. Eggs are reported to hatch in as little as 24–36 hours at about 25°C [524], but Milton and Arthington [951] reported that eggs hatched after 5–7 days (at 22°C).
probably a repeat spawner during the breeding season, with eggs presumably laid in batches. Hansen [524] reported that females deposited 30–50 eggs per day for a period of several days, and then rested. Total fecundity for fish from the Mary River is estimated to range from 149–1574 eggs (mean 629 ± 24 SE, n = 133 fish) [1093]. Batch fecundity for smaller fish sampled from the Brisbane River ranged from 230–740 eggs (mean 427 ± 81 SE, n = 27 fish) [949]. Body length and weight were poor predictors of fecundity in populations from the Mary River [1093] and Brisbane River [951]. Llewellyn [813] reported that a 49 mm TL female contained 2350 eggs.
Few details of larval morphology are available, however larvae are reported to be relatively poorly developed at hatching, measuring about 3 mm TL [951]. Swimming and feeding commence at 4–5 days [524, 797], but may take as long as nine days [951]. Schooling of larval fishes in
Eggs are relatively small. The mean diameter of 1053 intraovarian eggs from stage V fish from the Mary River Table 4. Life history information for Ambassis agassizii. Age at sexual maturity (months)
12 months [951]
Minimum length of gravid (stage V) females (mm) 25.6 mm SL [1093]; 32.0 mm SL [951] Minimum length of ripe (stage V) males (mm)
28.1 mm SL [1093]
Longevity (years)
In the wild, 3–4 years [951]
Sex ratio (female to male)
Females dominate larger length classes [951]
Occurrence of ripe (stage V) fish
Spring to Autumn (September–May) [1093]; spring [951]
Peak spawning activity
Elevated GSI between September and December [1093]; elevated GSI in October and November [951]
Critical temperature for spawning
? 22°C [797, 951]
Inducement to spawning
? Probably increasing temperature and daylength
Mean GSI of ripe (stage V) females (%)
6.4% ± 0.2 SE (maximum mean GSI in October = 7.8% ± 0.5 SE) [951]
Mean GSI of ripe (stage V) males (%)
5.4% ± 0.2 SE (maximum mean GSI in November = 5.9% ± 0.6 SE) [1093]
Fecundity (number of ova)
Total fecundity = 149–1574, mean = 629 ± 24 SE [1093]; 2350 (49 mm TL female) [813]; batch fecundity = 230–740, mean 427 ± 81 SE [951]
Total Fecundity (TF) and Batch Fecundity (BF)/ No significant relationships reported [951, 1093] Length (mm SL) or Weight (g) relationship (mm SL) Egg size (diameter) (mm)
Intraovarian eggs from stage V fish = 0.53 mm ± 0.01 SE [1093]; eggs (possibly water-hardened eggs) 0.6 mm [951]; water hardended eggs 0.7 mm [40]
Frequency of spawning
Extended spawning period [1093]. Probably batch spawner [524, 1093]. In aquaria, females deposited 30–50 eggs per day for several days, then rested [524]
Oviposition and spawning site
In the wild, spawning may occur in aquatic macrophytes, the substrate and possibly submerged marginal vegetation [951, 1093]. In the Brisbane River, eggs observed attached to aquatic plants (Vallisneria and Nymphoides spp.) and rocks on the stream-bed [951]. Spawning in aquaria reported to occur among fineleaved aquatic plants [524, 784, 797]
Spawning migration
None known
Parental care
None known
Time to hatching
Variable. In aquaria: 1–1.5 days (at 25°C) [524]; in the wild 5–7 days (22°C) [951]
Length at hatching (mm)
Newly hatched prolarvae 3.0 mm TL [951]
Length at free swimming stage
?
Age at free swimming stage
4–5 days [524, 797]
Age at loss of yolk sack
?
Age at first feeding
4–5 days [524, 797]
Length at first feeding
?
Age at metamorphosis (days)
?
Duration of larval development
? In aquaria: 12 mm TL by 60 days [784, 797]
298
Ambassis agassizii
Stuart and Berghuis [1276] observed low numbers of this species attempting to move upstream in the lower Burnett River between August and February. Small fish appeared to have difficulty negotiating high velocities and/or turbulence within the tidal barrage fishway, as very few small individuals were collected at the top of the fishway in comparison to the large numbers collected at the bottom [1276, 1277].
surface waters of the Brisbane River was observed to continue for a period of about one month [951]. Limited data indicates that growth rates are comparatively slow; fish in aquaria reach 12 mm TL by 60 days [784, 797]. Length at age data using evidence from scale annuli from Brisbane River fish [951] indicate that fish reached ~25–27 mm SL within the first year, 1+ fish were ~37–38 mm SL, 2+ fish were 47–48 mm SL and 3+ fish were 52.6 mm SL on average, with little difference in size observed between the sexes in each age class. Milton and Arthington [951] reported that A. agassizii (as A. nigripinnis) reached sexual maturity at one year of age.
In the Burnett and Mary rivers, south-eastern Queensland, tens to hundreds of fish have been observed in pools immediately downstream of obstructions to movement (e.g. culverts and weirs) soon after a rise in discharge during late spring, suggesting that A. agassizii undergoes upstream dispersal/recolonisation movements cued by elevated flows [1093]. A similar phenomenon was observed for this species in the Fitzroy River [1351].
Movement There is little quantitative information concerning the movement biology of A. agassizii. As has been observed in other species of Ambassis (e.g. Bishop et al. [190]), it appears that mass upstream dispersal movements are undertaken by A. agassizii, sometimes cued or facilitated by elevated discharge. There are several published and anecdotal accounts supporting this hypothesis.
Although frequently documented within and downstream of tidal barrages in lowland rivers [159, 232, 658, 740, 1272, 1274, 1275, 1276, 1277], it is unknown whether A. agassizii disperses downstream to brackish estuarine areas to fulfil some necessary ecological process, or whether fish are displaced to estuarine areas by elevated flows and thereafter attempt to return to freshwaters. This species appears tolerant of elevated salinities (see above), but the presence of tidal barriers may impact on A. agassizii by preventing or hindering recolonisation of freshwaters.
In the Burdekin River upstream migration of a species of Ambassid (probably A. agassizii) was observed during flooding in January and February [586]. This species was observed moving upstream through a modified verticalslot fishway on the Fitzroy River barrage [1272, 1274, 1275]. Upstream movement was observed throughout much of the year but was concentrated during late autumn and spring. Movements occurred over a wide range of flow conditions through the fishway (between 18 and 34 440 ML.day–1 corresponding to 82% and 7% exceedence flows, respectively) [1274]. Small fish appeared to have difficulty negotiating high velocities and/or turbulent water within the fishway, as significantly fewer small individuals were collected at the top of the fishway than at the bottom [1272, 1274, 1275]. In an earlier study of the fishway on the Fitzroy River Barrage, Kowarsky and Ross [740] also collected a very small number of individuals (erroneously identified as A. agrammus) between September and February.
Trophic ecology Diet data for A. agassizii are available for 331 individuals from three separate studies in the Burdekin River [1093], Burnett River [205] and smaller tributary streams of the Brisbane River [80]. This species is a microphagic carnivore and like some species of Ambassis, may forage nocturnally [47]. Aquatic insects (45.4%) and microcrustaceans (27.9%) dominate the total mean diet of A. agassizii (Fig. 6). Small amounts of macrocrustaceans, terrestrial invertebrates and aerial forms of aquatic insects are also consumed. Other diet items form only very minor components of the total mean diet. Some spatial variation in diet was apparent, possibly reflecting spatial variation in the physical characteristics and food availability of the rivers from which the fish were collected. Individuals from the Burdekin and Burnett rivers were generally obtained from relatively deep, slow-flowing habitats, and consumed comparatively larger amounts of microcrustaceans (28.9% and 41.4%, respectively). In contrast, fish from tributary streams of the Brisbane River did not consume any microcrustaceans, probably reflecting their low availability in the shallow, lotic habitats characteristic of these streams. These habitat differences may also reflect the comparatively greater amounts of aquatic insects and terrestrial invertebrates present in the diets of fish from the Brisbane
Broadfoot et al. [232] observed upstream migrations of Ambassis spp. (including individuals of A. agassizii, but probably mostly A. marianus, a facultatively diadromous species) through a tidal barrage fishway on the Kolan River. Large numbers of these species were collected in the fishway during summer flood events, but the majority (69.5%) of fish were sampled during periods of low flow over spring and summer. Small fish appeared to have difficulty negotiating high velocities and/or turbulence within the fishway, as fewer small individuals were collected at the top of the fishway than at the bottom [232].
299
Freshwater Fishes of North-Eastern Australia
conservation status of A. agassizii: upgrade from Data Deficient to Lower Risk (least concern) in the IUCN Red List of Threatened Species; upgrade from no listing to Near Threatened under the National Environment and Protection and Biodiversity Act 1999; upgrade from no listing to Uncertain status under the Australia Society for Fish Biology listing of the conservation status of Australian fishes [117]. At the time of writing (December 2003) A. agassizii has been listed in the IUCN Red List as Data Deficient, but is not listed in the most recent (2003) listing by the ASFB.
River tributaries compared with fish from the larger rivers. No information on the trophic ecology of larvae is available, however larvae in aquaria will initially consume hard-boiled and finely particulate egg yolk, and later will consume infusorians and brine shrimp [524, 784, 797]. Fish (0.4%) Other microinvertebrates (0.1%)
Unidentified (15.5%)
Microcrustaceans (27.9%) Terrestrial invertebrates (1.6%) Aerial aq. Invertebrates (3.7%) Terrestrial vegetation (0.2%) Algae (0.1%)
Potential threats to A. agassizii in the Murray-Darling Basin are suggested to include those associated with alien fish species (particularly Gambusia and redfin perch, Perca fluviatilis), habitat degradation (particularly loss of aquatic plants and woody debris), flow regulation (particularly rapid fluctuations in water levels that may impact on reproduction and recruitment by exposing fish eggs), and degraded water quality (particularly thermal pollution) [412, 965]. Similar threats to this species probably occur throughout much of its range in Queensland coastal rivers.
Macrocrustaceans (3.5%) Molluscs (0.4%) Other macroinvertebrates (1.3%)
Aquatic insects (45.4%)
Figure 6. The mean diet of Ambassis agassizii. Data derived from stomach contents analysis of 331 individuals from the Burdekin River [1093], Burnett River [205] and tributaries of the Brisbane River [80].
Several aspects of the ecology of A. agassizii are particularly relevant to its survival and reproduction in degraded streams and impounded rivers. This species is usually found in the mid to lower water column, over fine substrates and has a very close association with aquatic macrophytes and filamentous algae. With these microhabitat preferences it is particularly vulnerable to disturbance of the stream-bed and disruption of the growth of aquatic vegetation. Disturbance of river banks and riparian vegetation, bank erosion, sedimentation and elevated turbidity may act to depress the growth of submerged aquatic macrophytes.
Conservation status, threats and management Ambassis agassizii has undergone substantial declines in distribution and abundance, throughout much of the Murray-Darling Basin. However, it is still widespread and relatively abundant in coastal drainages of eastern Australia. In 1993, Wager and Jackson [1353] listed A. agassizii as Rare, probably on the basis of declines in inland populations. This species is though to be extinct in South Australia, where it is listed as Protected by regulations under the Fisheries Act 1982. However, it was reportedly successfully reintroduced to the Murray Bridge area from a remnant population in Queensland (N. Austin (1999), cited in [965]). In Victoria, it is listed as Extinct [1004]. Prior to 2000, A. agassizii was not listed as being of conservation significance in New South Wales or Queensland, but Morris et al. [965] recently recommended that inland populations in New South Wales be upgraded to Endangered; no change of status was suggested for the populations of inland Queensland. A. agassizii is widespread and relatively common in coastal catchments of Queensland and so does not warrant a special designation of conservation status in these areas. In New South Wales, inland populations have recently been declared as Endangered under the New South Wales Fisheries Management Act 1994 [1006]. Under this Act, A. agassizii is also listed as a member of an ‘Endangered Ecological Community’ in the lower Murray River [1005] and in the lowland catchment of the Darling River [329]. Morris et al. [965] recommended the following changes to the
Vegetative cover provides habitat for small stream fishes as well as protection from avian and instream predators. It may also serve to reduce the impact of short periods of high flow with the power to disrupt spawning activities, and displace eggs deposited amongst aquatic plants and submerged marginal vegetation [951, 1093]. Areas with good riparian cover and dense aquatic vegetation also provide sources of aquatic and terrestrial invertebrates for surface and water column species such as A. agassizii The spawning stimulus for A. agassizii is unknown but corresponds with increasing water temperatures and photoperiod in late winter and early spring. The cues to spawning are probably not associated with rising water levels or flooding even though fish have been observed to spawn in artificial ponds soon after a rise in water level [813]. The peak spawning period generally coincides with pre-flood periods of low and relatively stable discharge in
300
Ambassis agassizii
rivers of south-eastern Queensland [1095]. These discharge conditions in spring and early summer are likely to reduce the potential for high flows to disturb aquatic macrophytes used for spawning, and decrease the likelihood that falling water levels will expose vegetation and fish eggs [951]. Larvae hatching during periods of stable low flows are likely to encounter high densities of small invertebrate prey and to experience elevated growth rates, factors that tend to maximise the potential for recruitment into juvenile stocks [951, 1093]. A similar scenario of spawning and recruitment has been suggested for other small-bodied fish species in the Murray-Darling Basin [614, 615]. However, conditions suitable for recruitment of larvae through to the juvenile stage and beyond may persist year-round in south-eastern Queensland, and recruitment may not necessarily be limited by prevailing temperature and/or discharge regime. These observations complicate the development of scenarios of impact associated with alterations to stream discharge regimes.
and turbulence are poorly understood but relatively low focal point velocities (maximum of 0.42 m.sec–1) suggest that this species (especially smaller individuals) may be sensitive to high velocities and turbulence in fishways. Alien fish species (particularly Gambusia holbrooki and other poeciliids) threaten many small native species with similar habitat and dietary requirements in south-eastern Queensland streams [94, 96]. Ambassis agassizii may be particularly at risk in degraded stream habitats supporting large populations of G. holbrooki, also an inhabitant of the water column and a microphagic carnivore [78, 80, 92, 94, 96]. This poeciliid has very flexible foraging behaviours [78, 983] and may compete with small native fishes when food resources are in short supply. Arthington et al. [94, 95] observed that ambassids were rarely present or abundant in the Brisbane region where Gambusia was present, and speculated that similarities in foraging and diet increased the potential for resource competition between these species [94, 95, 96]. Extensive infestations of introduced para grass, Brachiaria mutica, may also constrain the foraging behaviour of A. agassizii in degraded urban streams [94, 96].
Although little is known of movement patterns, A. agassizii appears to engage in upstream dispersal movements, suggesting that is likely to be sensitive to barriers formed by culverts, weirs and large impoundments. Fishway passage requirements in relation to water depth, velocity
Dove [1432] provided a list of parasite taxa recorded from A. agassizii in south-eastern Queensland.
301
Ambassis macleayi (Castelnau, 1878) Macleay’s glassfish
37 310013
Family: Chandidae
preopercular ridge, vertical limb smooth or with 1–9 small serrae; lower edge of preoperculum with 13–21 serrae, hind margin crenulate or with 3–28 small serrae. Lateral line scales terminate below first dorsal fin or interrupted by series of tubeless scales, then continued on caudal peduncle.
Description First dorsal fin: VII, I, 9–11; Anal: III, 9–11; Pectoral: 14–15; Vertical scale rows 27–28; Horizontal scale rows: 12–13; Predorsal scales: 12–16; Cheek scales: 2 rows; Gill rakers (lower limb of first arch): 24–29 [47]. Figure: mature specimen, 49 mm SL, Normanby River, April 1992; drawn 2002.
Body colour varies from semi-transparent, olive-green to dark green/brown or yellow/golden, tending paler ventrally [630, 1093]. The scale margins are dark and form a reticulated pattern across most of the body, being most strongly expressed on the dorsal half of the body. The nape tends to be darker than the body. The upper part of the iris is black, the remainder golden. The dorsal, anal and caudal fins are dusky; spines translucent to off-white, rays white to yellow, anal and caudal fin may have thin dark or red margin; pelvic fins white, pectoral fins transparent, base frequently with dark blotch. Colour in preservative: yellowish-tan, transparency lost, reticulate pattern retained, pelvic fin dusky [47].
Ambassis macleayi is a moderately large ambassid that may reach 77 mm SL or 90 mm TL [47, 52] but more commonly is between 35 and 45 mm SL [193, 697]. Bishop et al. [193] report a length weight relationship of 0.016L3.17; n = 2028, r2 = 0.96, p<0.001 where weight is in g and length is CFL in cm. The following description is taken entirely from Allen and Burgess [47]. The body is typically deep (47.2–49.3% SL); head large (38.2–44.8% SL); eye large (13.4–17.2% SL), set in front half of head (snout length 8.2–10.1% SL); maxilla extends back to beyond anterior margin of eye (11.7–14.5% SL); caudal penduncle length 17.7–19.0% SL, depth 16.1–19.5% SL. The first dorsal fin is tall (32.2–40.3% SL), second dorsal spine longer than third; third anal spine longer than second. Nasal spine absent; single supraorbital spine, 3–8 small serrae on preorbital ridge, suborbital smooth, crenulate or with 3–18 small serrae; 11–16 serrae on lower limb of
This species superficially resembles A. agrammus, with which it may be sympatric, but is distinguished by a higher gill raker number, a slightly higher number of rays in the dorsal and anal fins and the presence of a bar across the base of the pectoral fin [47]. 302
Ambassis macleayi
Creek catchment but adult A. macleayi were observed in these habitats in the Nourlangie Creek catchment [193]. It typically occurred in heavily vegetated habitats and was more frequently found in association with submerged macrophytes than was the sympatric congener A. agrammus [193].
Systematics Ambassis macleayi was first described as Pseudoambassis macleayi by Castelnau in 1878, based on material sourced from the Norman River in the Gulf of Carpentaria region [287], and placed in Ambassis in 1982 [33]. Distribution and abundance Ambassis macleayi occurs in northern Australia and the trans-Fly River region of southern Papua New Guinea [37, 47, 52, 1147]. It is apparently continuously distributed across northern Australia from the Carson River in the Kimberley region to the Jardine River in Cape York Peninsula [47]. Rivers in the Gulf of Carpentaria region in which it has been recorded include the Nicholson, Gregory, Leichhardt, Flinders, Staaten and Norman rivers [47, 287, 979]. Rivers of western Cape York Peninsula in which it has been recorded include the Mitchell, Coleman, Edward, Holroyd, Archer, Mission, Wenlock and Jardine rivers [41, 47, 216, 571]. The distribution on the east coast of Queensland is patchy, having been recorded from the Olive [571] and Normanby [697, 1099] Rivers of Cape York Peninsula and the Barron [1187] and Moresby [1183] Rivers of the Wet Tropics region. Additional records exist for the Black-Alice River near Townsville [176] and Plane Creek, south of Mackay [779], but they probably refer to A. agrammus.
Ambassis macleayi was equally abundant in floodplain and riverine habitats in the Normanby River [697]. Very few individuals (<10%) were collected from depths greater than 1 m and most fish were collected from the upper 50% of the water column. The use of different types of cover varied between study sites. In locations with abundant macrophyte growth (30–60% of wetted perimeter), more than 60% of the total sample was collected from macrophyte beds. In locations with little macrophyte growth, A. macleayi was collected only from leaf litter and woody debris accumulations. Kennard [697] conducted an experiment in which predator density (L. calcarifer and A. midgelyi) and woody debris densities were manipulated, and showed that small fish, such as and including A. macleayi, foraged in open waters only when predator densities were low. When predator densities were high, very few individuals foraged in open water being restricted to cover such as macrophytes, woody debris and leaf litter. Environmental tolerances The summaries presented in Table 1 are based on ambient water quality at sites in which this species has been collected and represent a wide array of different habitat types. Data were collected over a wide array of seasonal conditions.
In the Northern Territory, A. macleayi is usually abundant in those habitats in which it occurs [774]. Bishop et al. [193] found this species to be amongst the very most abundant species in the Alligator Rivers region, occurring in 19 of 26 regularly sampled sites, and Taylor [1304] reported it as abundant in freshwater lagoons of the Oenpelli area in Arnhem Land. It was abundant in both riverine and floodplain habitats of the Normanby River, where it contributed 22.3% of the total electrofishing catch and was the second most abundant species [697]. Melanotaenia s. splendida was only marginally more abundant (22.5%) in this study.
Table 1. Physicochemical data for Ambassis macleayi. Data reported for this species in the Alligator Rivers region refer to surface values. Parameter
Macro/meso/microhabit use Ambassis macleayi occurs in streams and swamps [52]. In the Alligator Rivers region, it was moderately abundant or common in corridor and muddy lowland lagoons, and floodplain and sandy creek-bed habitats and escarpment main channel waterbodies, respectively. The distribution of A. macleayi within the Alligator Rivers region varied between seasons, being restricted to muddy lowland lagoons in the late dry season, and more widely distributed in the late wet season when it occurred in corridor lagoons, lowland muddy lagoons and escarpment main channel waterbodies. This species was never observed in escarpment perennial streams in the Magela
Min.
Max.
Mean
Alligator River region [193] Temperature (°C) 23 38 Dissolved oxygen (mg.L–1) 1.0 9.1 pH 4.8 7.7 Conductivity (µS.cm–1) 2 620 Turbidity (cm secchi depth) 1 150
30.6 6.2 6.2 – 47.6
Normanby River (n = 14) [697] Temperature (°C) 22.9 33.4 Dissolved oxygen (mg.L–1) 1.1 7.1 pH 6.0 9.1 Conductivity (µS.cm–1) 98 412 Turbidity (NTU) 2.0 120.0
26.1 3.7 7.3 226.3 13.6
Ambassis macleayi may frequently occur in very warm, hypoxic conditions (Table 1), not unsurprisingly given its
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indicate that the majority of recruitment occurs during the dry season [697]. This species is moderately fecund producing up to 2360 eggs in large individuals (Table 2). The eggs are small (about 0.3 mm in diameter) but increase in size when water-hardened. A thick mucilaginous layer formed around the chorion shortly after oviposition causes the eggs to attached to vegetation as they descend through the water column. Maturation is achieved at small size, which Ivantsoff et al. [630] and Semple [1213] believed to occur at about three months of age. Bishop et al. [193] were unable to determine the age at maturity due to poorly defined temporal changes in population size structure but believed it to occur in the first year of life.
presence and abundance in floodplain habitats. The minimum dissolved oxygen levels recorded in both studies, and the persistent hypoxia recorded in lagoons of the Normanby River [697], suggest that this species is tolerant of low dissolved oxygen. Both studies indicate that it occurs in very fresh to fresh water and may occur in habitats with high levels of suspended sediment, although the mean values cited indicate that on average, sites in which it occurs are only moderately turbid. This species has been recorded over a substantial pH range (4.3 units) but average values indicate that it is most frequently recorded in mildly acidic to neutral waters. Reproduction Information on the reproductive biology of A. macleayi is available for a population in the Alligator Rivers region [193, 630, 1213], and aquarium observations [797, 1213] (Table 2).
Laboratory studies reveal that A. macleayi spawns over aquatic vegetation; a behaviour common in the chandid perches. Embryonic development is rapid, as is larval development. The larvae hatch in a poorly developed state but mature quickly and begin feeding after only three days. Metamorphosis is complete after 18 days by which time a total length of 10 mm is attained.
Ambassis macleayi breeds year-round in the Alligator Rivers region [193] although changes in length frequency distribution of populations in the Normanby River
Table 2. Life history data for Ambassis macleayi. Information drawn from two studies: one undertaken in the field in the Alligator Rivers region by Bishop et al. [193], and the other in the laboratory reported by Ivantsoff et al. [630] and Semple [1213]. Information concerning spawning behaviour and larval development are from the latter two studies. Age at sexual maturity (months)
12 months [193], 3 months [1213]
Minimum length of ripe females (mm)
Length at first maturity – 29 mm CFL
Minimum length of ripe males (mm)
Length at first maturity – 33 mm CFL
Longevity (years)
2–3 years (?)
Sex ratio
Males frequently in excess in some locations
Peak spawning activity
Mature fish present all year, small peak in mean GSI in early wet season
Critical temperature for spawning
Not reported but unlikely to need critical temperature given year-round reproduction
Inducement to spawning Mean GSI of ripe females (%)
Maximum mean GSI recorded – 3.5 ± 1.8% (SD)
Mean GSI of ripe males (%)
Maximum mean GSI recorded – 1.5 ± 1.3% (SD)
Fecundity (number of ova)
320–2360 in fish 45 and 63 mm CFL, respectively; average 1340 (n = 6)
Fecundity/length relationship Egg size (mm)
0.3 ± 0.07 mm (intraovarian), 0.45–0.55 mm water-hardened with additional mucoid covering; demersal, transparent, spherical and adhesive
Frequency of spawning
Spawns in batches of several hundred eggs each day over a 7-day period
Oviposition and spawning site
Spawns over thick aquatic plants in laboratory, field observations suggest this species spawns in flowing sandy creeks
Spawning migration
?
Parental care
none
Time to hatching
21–23 hours at 25–28°C
Length at hatching (mm)
1.5–1.6 mm
Length at feeding
2.25–2.5 mm
Age at first feeding
3 days
Age at loss of yolk sac
2 days
Duration of larval development
18 days
Length at metamorphosis
10 mm TL
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Ambassis macleayi
Aquatic insect larvae, principally chironomid larvae, accounted for 20% of the diet when averaged across the different studies but accounted for 69% of the diet of fish from the Normanby River [1099]. These data illustrate the differences in foraging strategy that may occur in different habitat types and demonstrate that this species has a flexible foraging strategy within the constraints imposed by small size. The diet shown here for A. macleayi and habitat-based differences in diet resemble very closely those observed in A. agrammus.
Movement Patterns of movement in this species are not well-defined. Bishop et al. [190] report on the movement patterns of Ambassis spp. in Magela Creek and clearly showed upstream migration in the late wet season (March to May) associated with the change in availability and quality of habitats. Ambassis agrammus and A. macleayi frequently occur in sympatry and temporal changes in habitat use by each species are similar [193]. A. macleayi probably migrates into dry season refugia also. Further research is needed to define this aspect of the biology of both species.
Conservation status, threats and management Ambassis macleayi is classified as Non-Threatened by Wager and Jackson [1353] and would currently appear secure across its range. The wide tolerance to poor water quality conditions typical of fishes inhabiting floodplain waterbodies probably ensures that, in most cases, degraded water quality does not pose a severe threat. Of concern however, is the threat posed by feral flora and fauna, particularly to populations located in northern Queensland. Exotic weeds such as Hymenachne amplexicaulus and Eichhornia crassipes (water hyacinth) have the potential to degrade the quality of aquatic floodplain habitats. Feral pigs may pose a threat because of their habit of congregating around contracted lagoons during the dry season and consuming the resting stages of aquatic plants. Aquatic plants are critical to Ambassis species. In addition, feral pigs have the potential to increase the concentration of suspended solids in lagoons and this may impact on aquatic macrophyte and phytoplankton biomass through a diminution in light availability: hence impacts on microcrustacean biomass, an important food source, may also occur. The absence of information on the ecology of this species in rivers of the Gulf of Carpentaria region is of concern in light of calls for an agricultural expansion and the attendant pressure that this may place on water resources. Changes in water regime that impact on the frequency, timing and extent of floodplain inundation have the potential to impact on this species.
Trophic ecology The diet of Ambassis macleayi closely resembles that of A. agrammus with which it is frequently sympatric (fig 1). The dominant prey item is microcrustaceans, principally Cladocera. This item formed only 10% of the diet in riverine fish of the Normanby River [1099] but accounted for 69.4% and 54.6% of the diet in wetland samples from the Normanby and Alligator rivers, respectively. Fish (0.8%) Other microinvertebrates (1.1%) Unidentified (15.4%)
Terrestrial invertebrates (0.6%) Aerial aq. Invertebrates (0.6%) Detritus (2.4%) Terrestrial vegetation (0.4%) Algae (1.1%)
Aquatic insects (19.5%)
Macrocrustaceans (0.5%) Molluscs (0.1%) Other macroinvertebrates (0.1%) Microcrustaceans (57.5%)
Figure 1. The average diet of Ambassis macleayi. Data for 642 individuals from two regions; the Alligator Rivers region (n = 485) [193] and the Normanby River in Cape York Peninsula (n = 8 [1099] and n = 149 [697]). Values presented are the means weighted by sample size.
305
Ambassis miops Günther, 1871 Flag-tailed glassfish
37 310014
Family: Chandidae
Description Dorsal fin: VIII, 9; Anal: III, 9–10; Pectoral: 13–15; Lateral line scales: 28–30, continuous or very occasionally interrupted by one tubeless scale; Vertical scale rows: 28–30 (commencing above gill opening); Horizontal scale rows: 9–10; Cheek scales: 2; Predorsal scales: 12–15 [47]. Figure: adult, 47 mm SL, lower Mulgrave River, November 1998; drawn 2002.
surfaces. Fins mainly clear, although yellow/bronze colour on caudal fin and first dorsal fin apparent on some individuals [47]. Colour in preservative: pale tan or yellowishwhite. Melanophores scattered on margins of scales. Dense melanophore accumulations on predorsal scales, interorbital, snout, lower jaw and along base of dorsal and anal fins. Thin, black midlateral stripe, mostly on posterior half of body [47].
Ambassis miops is a relatively slender species of glassfish (greatest body depth 33.4–38.6% of SL), distinguished by the presence of a single supraorbital spine and nasal spine (often subcutaneous), continuous lateral line, two rows of scales on cheek and stiff dorsal fin spines [47]. This species has a relatively large eye (12.9–15% SL), exceeding all other Australian ambassids with the exception of A. interruptus Bleeker (12.3–15.9% SL), A. urotaenia Bleeker (13.7–15.9% SL) and A. macleayi (Castelnau) (13.4–17.2% SL). This species has a relatively large mouth also; maxilla length (13.4–16.8%) is greater than all other Australian ambassids with the exception of A. nalua (Hamilton) (15.4–18.0% SL). Mouth gape increases very rapidly with increasing size [1097]. Ambassis miops is semi-transparent with a silvery/bronze midlateral stripe. Dark scale margins form a faint reticulated pattern on dorsal and lateral
Of the 107 individuals examined by Allen and Burgess [47], none was greater than 63 mm SL (approximately 80 mm TL). Systematics Ambassis miops was first described by Günther in 1871 from material collected from Rarotonga in the Cook Islands [489]. No synonyms exist [47]. It is similar to A. macracanthus but differs in having fewer predorsal scales (c.f. 17–22), fewer vertical scale rows (c.f. 12–13) and in having the third dorsal spine longer than the second (reverse condition in A. macracanthus). A. macracanthus does not occur in Australia however [47]. Distribution and abundance Ambassis miops is widespread, occurring in India, Japan,
306
Ambassis miops
probably tolerant of elevated turbidity and salinity levels but intolerant of low water temperatures. Estuarine species of glass perchlet have been shown to be intolerant of rapid declines in pH associated with runoff from potential acid sulphate soils in Trinity Inlet [1180].
Taiwan, Hong Kong, Indonesia, the Philippines, New Guinea, Samoa, New Caledonia, the Cook Islands and north-eastern Australia [47, 422]. The distribution of A. miops in Australia is somewhat more restricted and mirrors that seen for many other species with a marine larval interval (i.e. Glossogobius spp., Eleotris spp., Bunaka gyrinoides). To date, A. miops has been recorded from the Starke, Howick, McIvor and Endeavor rivers of eastern Cape York Peninsula [47, 571]. It is likely that this species occasionally occurs in other eastern Cape York rivers also, especially those with a relatively low level of interannual variation in discharge, such as the Olive and Pascoe rivers.
Reproductive biology The reproductive biology of this species remains unstudied although its wide distribution and macrohabitat led Allen [34] to suggest it has a marine larval phase. Movement No quantitative data are available on this aspect of the biology of A. miops. If a marine larval phase occurs in this species either adults make a downstream migration for spawning or eggs or larvae are passively transported downstream in the current. Some upstream colonising movement by juveniles must be made also. Such a reproductive feature makes this species vulnerable to the impacts of movement barriers if such barriers are located close to the river mouth. The observation of A. miops in floodplain wetlands indicates that this species may make small-scale colonising migrations onto the floodplain, presumably at times of high flow.
The major centre of distribution in Australia is the Wet Tropics region. Pusey and Kennard [1085, 1087] recorded A. miops from six sites in the Bloomfield, Daintree, Mossman, Barron and Russell rivers during a survey of the region. Only 14 individuals were collected, making it the 31st most abundant species. It has also been collected from the Mulgrave River [1097]. Russell and his co-workers found A. miops to be widely distributed but most commonly restricted to the very lower reaches of rivers, being collected from the Daintree River (10/46 sites) [1185], Mossman River (1/19) [1185], Barron River (estuary, Freshwater Creek and lower river) [1187], Russell/Mulgrave River (7/45) [1184], Johnstone River (4/73) [1177], Moresby River (1/18) [1183] and Liverpool Creek (4/29) [1179]. A. miops has also been recorded from floodplain wetlands of the Tully (1/16) [583] and Herbert drainages (1/11) [584]. It has not been detected south of the Herbert River despite intensive sampling in likely habitats [1081, 1328].
Small schools (5–8 individuals) of mature A. miops have been observed patrolling up and down the banks of the Mulgrave River (over a distance of about 10 m) as they searched for fish larvae prey [1093] (see below). Trophic ecology Allen [34] suggested that A. miops feed mainly on small crustaceans and juvenile fishes. A sample of 28 fish (30–50 mm SL), collected from a freshwater reach characterised by a sand and fine gravel bottom, in the lower Mulgrave River, (habitat group C in Pusey et al. [1097]), revealed a diet of greater diversity. In contrast to that observed by Allen [34], no crustaceans were found in the diet of A. miops from the Mulgrave River but this prey item may be more important in estuarine and mangrove areas. The bulk of the diet was composed of aquatic insects and dominated by ephemeropteran nymphs (34%), simulid larvae (26%) and odonate nymphs (11%) (Fig. 1). The inclusion of short tufted filamentous algae (8%) suggests that A. miops grazed/foraged over woody debris, the only solid substrate present in this part of the river.
Macro/meso/micro habitat use Allen and Burgess [47] list the habitat of A. miops as being clear, flowing creeks usually within 20 km of the sea, but it has also been collected from the main river channel, mangrove creeks, estuarine reaches and from floodplain wetlands of rivers in the Wet Tropics region (see references listed for Distribution). Notably, the types of macrohabitat used tend to be located close to the river mouth. Ambassis miops, like most ambassids, tends to be associated with some form of cover such as mangrove roots or small woody debris, where they hover in small schools. It is probable that they do not venture far from the streamor riverbank or structures that offer cover.
It is notable that in terms of dietary composition, A. miops was most similar to a range of much larger species such as N. robusta, G. aprion and juvenile A. reinhardtii and Hephaestus grunters [1097]. Much of the interspecific variation in diet in the fish fauna of the Mulgrave River can be related to a combination of differences in fish size and mouth gape [1097]. The relatively large mouth of A.
Environmental tolerances No information on this aspect of the biology of Ambassis miops is available. However, given its distribution, macrohabitat use and reproductive biology, this species is
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Freshwater Fishes of North-Eastern Australia
small schools of A. miops patrolling the riverbank in search of schools of this species. When located, the schools were shepherded into small backwaters or areas bounded by dense small woody debris, whereupon individual A. miops would repeatedly rush the corralled school and capture the small fish. This feeding behaviour was highly reminiscent of the ‘chopping’ behaviour of barramundi, or any number of other large predatory fishes, when feeding on schools of mullet, herring or other baitfish; except in miniature.
Fish (2.1%) Unidentified (14.4%)
Algae (8.3%)
Conservation status, threats and management Ambassis miops is listed as Non-Threatened by Wager and Jackson [1353]. This species occurs in the very lower reaches of rivers but may have a marine interval during its life history, and as such it is potentially vulnerable to processes which degraded lowland river and estuarine integrity such as desnagging, river regulation, exposure of potential acid sulphate soils, high nutrient and sediment inputs from activities occurring upstream in the catchment or from the imposition of barriers to movement (i.e. tidal barrages). Impacts on its major prey may have longterm implications for its survival. It is possible that abundance levels and occurrence are naturally variable from year to year depending on recruitment dynamics; therefore it may be difficult to detect real changes in abundance in the short-term. Given the widespread distribution of A. miops in the Wet Tropics region, its survival seems assured in the medium-term.
Aquatic insects (75.2%)
Figure 1. The mean diet of Ambassis miops. Data derived from stomach content analysis of 28 individuals collected from the Mulgrave River in August 1991 [1097].
miops allows it to consume large ephemeropteran and odonate nymphs (prey items 10–15 mm long). More importantly, this feature also allows it to consume small fishes. About 50% of the diet of the largest individuals within the sample (45–50 mm SL) was composed of juveniles of the empire gudgeon H. compressa. We observed
308
Denariusa bandata Whitley, 1948 Pennyfish
37 310016
Family: Chandidae
SL) and compressed; head 34.8–40.0 SL; eye large (12.3–14.6% SL); snout short (7.5–8.3% SL), mouth small, maxilla (7.0–8.0% SL) terminating before anterior margin of eye; teeth small and pointed [1304]; caudal peduncle depth 13.2–15.8% SL; caudal peduncle length 19.6–24.4% SL; height of dorsal fin 25.8–29.3% SL, second and third spines about equal in length; second and third anal spines about equal in length. Spines absent from snout and supraorbital ridge; serrae absent from preorbital and suborbital ridges; preorbital edge (overhanging maxilla) with 9–12 weak serrae, preopercular ridge usually smooth, occasionally with 1–3 weak serrae concentrated around angle; lower edge of preoperculum with 18–23 serrae, hind edge with 24–30 well-developed serrae; interoperculum with 3–14 small serrae. Head deeply pitted and grooved [1304]. Colour in life: semitransparent (although not as transparent as many Ambassis spp.), olive-green dorsally, pale to silver ventrally. Six to seven vertical dark bars present on lateral and dorsal surface of body; a dark vertical bar may pass through centre of iris; scale margins frequently dark conveying a reticulated pattern. Dorsal fin typically dusky with fine spots, dark subterminal oblique bar present between fourth and eight dorsal spines; caudal fin clear; anal fin dusky and spotted, occasionally with red tint; pelvic fin dusky, occasionally with red tint, spine
Description First dorsal fin: VII, I, 9–10; Anal: III, 7–9; Pectoral: 9–10; Vertical scale rows: 24–26, lateral line scales weakly developed or absent, tubed scales 0–4; Horizontal scale rows: 11; Cheek scale rows: 2; Predorsal scales: 12–16; Gill rakers (rudimentary only) on lower limb of first arch: 7–9 [47]. Note that Taylor [1304] lists the maximum number of vertical scale rows as 27, gill rakers as 10 and predorsal scales as 17. Specimens from Cape Flattery may have 11 rays in the dorsal fin and 10 rays in the anal fin [1093]. Figure: mature specimen, 29.5 mm SL, dune lake of Cape Flattery, January 2000; drawn 2000. Denariusa bandata is a small chandid that may reach 45 mm TL but is more commonly less than 35 mm TL [52]. The maximum size listed for Magela Creek and the Alligator Rivers region of the Northern Territory is 50 mm TL [1064] and 42 mm CFL [193], respectively; for the Arnhem Land region, 36 mm SL; the Normanby River, 25 mm SL [697]; and Cape Flattery dune lakes, 35 mm SL [1093]. Bishop et al. [193] list the relationship between length (CFL in cm) and weight (W in g) as W = 0.0244L2.75; n=1340, r2 = 0.828, p<0.001. The following description is taken largely from Allen and Burgess [47] unless stated. The body is deep (41.7–44.0% 309
Freshwater Fishes of North-Eastern Australia
Land [47, 1304] but is apparently patchily distributed in Queensland, particularly on the east coast. Records of its presence in rivers of the southern portion of the Gulf of Carpentaria region are limited to the Nicholson/Gregory River [1349] although a recent survey in this drainage failed to collect this species, possibly because off-channel wetland habitats were not included in the sampling design [643]. It has been recorded in the Georgina River [1349]. Rivers of western Cape York Peninsula in which D. bandata has been recorded include the Coleman, Edward, Holroyd, Archer, Watson, Wenlock and Jardine rivers [41, 47, 520, 571, 1349] and Burster Creek near Bamaga [520]. This species’ distribution on the eastern side of Cape York Peninsula appears limited to the Normanby River [697] and aquatic habitats of the Cape Flattery dune fields [1101, 1349].
occasionally white; pectoral fin clear, conspicuous dark spot on upper portion of axil [52, 1093]. Colour in preservative: body white to yellowish-brown; reticulated pattern retained, but somewhat diffuse; vertical bars and spot on pectoral axil retained but diffuse; fins remain dusky but red tint lost [47, 1304]. Systematics This small chandid perch was first described by Whitley from material collected in Arnhem Land, Northern Terrritory [1391]. No synonyms exist. The genus is monotypic but a second species, Denariusa australis (Steindachner), was recently suggested to occur in the Fitzroy River of Queensland [461] based on two specimens originally described as Apogon australis by Steindachner in 1867 [1262]. Paxton et al. [1042] listed A. australis as one of several apogonid taxa so poorly described as to preclude accurate identification. The types of this taxon, both in poor condition, were recently found in the Natural History Museum of Vienna, Austria by Gon and Herzig-Straschil [585] and allocated to Denariusa Whitley on the basis of the possession of a deeply notched dorsal fin, rudimentary gill rakers, nine pectoral rays, small mouth and the absence of tubed lateral line scales. The specimens differed from D. bandata in having 2–4 small serrae on the preorbital ridge (as opposed to a smooth preorbital ridge). The figure of D. australis provided in Gon and Herzig-Straschil [585] is certainly similar to D. bandata, particularly with regard to the relative length of dorsal and anal fin spines. The only other chandid commonly encountered in freshwaters of the Fitzroy River is Ambassis agassizii but D. australis as described by Herzig-Straschil [585] differs significantly from this species in many regards. Moreover, Steindachner described both species in the same publication [1262] and was therefore unlikely to have confused the two; nonetheless this raises the question of why D. australis was placed in Apogonidae rather than Ambassidae (= Chandidae) [585]. Allen (cited as pers. comm. in [585]) considered it unlikely that Denariusa occurred in the Fitzroy River and raised the possibility of a labelling error, particularly given that Steindachner never visited Australia, relying rather on commercially procuring specimens through the Natural History Museum. The possibility of a labelling error also questions the validity of the Fitzroy River as the type locality for several other taxa such as A. agassizii, Oxyeleotris lineolatus and Neosilurus hyrtlii described in the same article.
Denariusa bandata is suggested to be seasonally abundant [52]. Bishop et al. [193] found this species to be in the upper quartile of all species in the Alligator Rivers region ranked by abundance and noted temporal variation in abundance with lowest catches occurring in the early wet season in one year and the late dry season in the following year. Allen and Hoese [41] noted that D. bandata was moderately common in the Jardine River but it was uncommonly encountered in other rivers of western Cape York Peninsula [571]. Kennard [697] recorded D. bandata in only one of eight sites examined in the Normanby River, where it contributed 9.2% of the total number of fish collected. In dune lake habitats of the Cape Flattery area, D. bandata occurred in all eight sites examined and contributed 6.8% of the total number of fishes collected [1101]. This species is apparently uncommon in the Wet Tropics region. For example, it contributed only 0.15% of the total number of fishes collected in a survey of the region [1085].
Distribution and abundance Denariusa bandata occurs in northern Australia and in a few rivers of southern New Guinea (i.e. Bensbach and Fly rivers) [47, 52, 1147]. This species is widely distributed in the Northern Territory from the Daly River to Arnhem
Macro/meso/microhabitat use Bishop et al. [193] found D. bandata to be most common in floodplain lagoons (billabongs) and muddy lowland lagoons, although it was widely distributed in the Alligator Rivers region, occurring in 18 of 26 regularly sampled
Denariusa bandata was collected from a single location, Eubanangee Swamp in the Mulgrave/Russell catchment, in an extensive survey of the Wet Tropics region in 1993 [1085]. Additional records for this region are limited to Digmans Lagoon and unspecified swamps in the Tully and Murray River drainage [47, 585]. A number of wetlands in the Wet Tropics region remain to be properly surveyed and this species may be more widely distributed in this region than these data indicate. Nonetheless, the Murray River appears to be the southern limit of its distribution as it has not been collected from the Herbert River drainage, despite appropriate habitats being included in the sampling design [584, 643].
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acidic and occasionally hypoxic (Table 1). This species is evidently able to tolerate high water temperatures. We have measured water temperatures in excess of 36°C in Cape Flattery lakes [1093]. Dune lake habitats of Cape Flattery are very acidic. Water clarity in both regions is moderately low, due mainly to high levels of suspended solids in the Alligator Rivers region and high levels of tannins in the Cape Flattery area.
sites. Habitats in which it occurred were generally heavily vegetated (vegetation occurrence index – 93.2%) and dominated by submerged vegetation. A few specimens were collected from sandy creekbed habitats but were always in association with aquatic macrophytes. Allen and Burgess [47] list the habitat of D. bandata as sluggish streams and swamps with dense aquatic macrophyte growth. Denariusa bandata was collected from only those floodplain lagoons of western Cape York Peninsula with dense macrophyte growth [571]. Horseshoe Lagoon on the Normanby River floodplain, the only location in this area in which D. bandata was collected by Kennard [697], was heavily vegetated (20–40% of surface area depending on season). Eubanangee Swamp in the Wet Tropics region is notable for its prolific stands of sedges [1085].
Ambient conditions in Horseshoe Lagoon, Cape York Peninsula, are not dissimilar to those reported in Table 1 with the exception that dissolved oxygen levels were lower – 2.0 mg.L–1 [697]. Reproduction Very little is known of the reproductive biology of this species. Bishop et al. [193] report that female fish mature at 25 mm CFL and males at 31 mm CFL. Seasonal variation in population age structure suggest that fish attain maturity within 12 months but also that very few fish survive into their second year. Juvenile fish (8–20 mm CFL) appear in the population during the early wet season. Maximum mean female GSI values (5.3%) were recorded at this time also but remained relatively elevated (>3.5%) until the mid-wet season. Mean male GSI values remained low (<1%) throughout the year. Very few mature, ripe or spent fish were collected and thus no information on fecundity or egg size is available.
Denariusa bandata is widely distributed in the different habitat types present on the dune fields of Cape Flattery, occurring in large deep lakes, isolated ponds, swamps and streams [1101]. Sedges (mostly Lepironia articulata) were abundant in lake and swamp habitats but absent from isolated ponds and streams. Leaf litter and small woody debris were abundant in isolated pools and water visibility was greatly diminished (Secchi disc depth of 20 cm). Stream habitats tended to be shallow with little in-stream cover and D. bandata was restricted to patches of overhanging submerged vegetation. Denariusa bandata is predominantly a wetland-dwelling species with a high affinity for aquatic macrophytes.
Movement Little is known of this aspect of the biology of D. bandata except that Bishop et al. [190] report that it was commonly observed moving past the Ranger Uranium Mine in Magela Creek. Juvenile and adult D. bandata were recorded from similar habitat types [193] and little evidence of migrations from wetland habitats into permanent escarpment habitats at the end of the wet season, typical of many other co-occurring species, was found.
Environmental tolerances The water quality conditions in which D. bandata occurs are typical of those occurring in tropical wetlands: warm, Table 1. Physicochemical data for Denariusa bandata. Turbidity values are given as Secchi disc depths. Data listed for the Alligator Rivers region were measured at the bottom of water body [193] and those for Cape Flattery in the middle of the water column [1101]. Parameter
Min.
Alligator Rivers region Temperature (°C) 25 Dissolved oxygen (mg.L–1) 2.9 pH 4.5 Conductivity (µS.cm–1) 4 Turbidity (cm) 1
Max. 38 6.2 6.7 220 110
Cape Flattery dunefields (n = 8) Temperature (°C) 23 32 Dissolved oxygen (mg.L–1) 6.4 7.4 pH 3.6 5.1 Conductivity (µS.cm–1) 89 385 Turbidity (cm) 21 200
Trophic ecology Information on the trophic ecology of D. bandata is available for the Alligator Rivers region (n = 477) [193] and the Normanby River (n = 9) [697] (Fig. 1). Very little difference in diet between these studies was evident. Aquatic insects are the most important prey item in the diet of D. bandata and chironomid midge larvae were the overwhelmingly dominant prey (~50% of total diet) within this category in both studies. Small amounts of trichopteran larvae and ephemeropteran nymphs were consumed by D. bandata in the Alligator Rivers region also [193]. Microcrustacea are the next most important prey type, contributing 37.2% of the diet of fish from the Normanby River [697] and 20.8% of the diet of fish from
Mean 29.7 4.3 6.1 35 28 7.2 4.3 163.3 75
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Freshwater Fishes of North-Eastern Australia
Denariusa bandata is, in turn, eaten by piscivorous fishes [193] and by a number of water birds such as herons, terns and cormorants [936].
the Alligator Rivers region [193]. In both cases, Cladocera were the dominant prey item in this category. Fish (0.2%) Other microinvertebrates (0.6%)
Conservation status, threats and management Denariusa bandata is listed as Non-Threatened by Wager and Jackson [1353] and is probably secure over much of its range. However, the disjunct nature of its distribution and particularly the isolated nature of populations in eastern Cape York Peninsula and the Wet Tropics region may warrant an elevated status for these populations. Floodplain and wetland habitats of the Wet Tropics region are under increasing threat from agricultural activities and reclamation, and are greatly reduced in incidence, size and quality (see 715, 716, 1587, 2293]. Greater research effort is needed to identify other populations in this region. The Cape Flattery population is relatively large and probably secure despite sand mining in this region, however its vulnerability to impact needs to be carefully monitored in the future. This species is uncommonly encountered and is not abundant in wetlands of the Normanby River floodplain and these factors may combine to increase its vulnerability to impact. The impact of feral animals (pigs, horses and cattle) on wetland habitats in this region remains unknown. The distribution of this species in the southern Gulf of Carpentaria region is poorly defined and this may hamper effective management if crop-based agriculture expands in this region.
Unidentified (17.4%)
Microcrustaceans (21.1%)
Terrestrial invertebrates (0.1%) Detritus (0.3%) Algae (0.3%) Terrestrial vegetation (0.2%) Macrocrustaceans (0.6%)
Aquatic insects (59.4%)
Figure 1. The mean diet of Denariusa bandata. Summary derived from stomach content analysis of a total of 486 individuals from the Alligator Rivers region [193] and the Normanby River [697].
Small quantities of algae, terrestrial insects, terrestrial vegetation, detritus, shrimps and fish were consumed by D. bandata in the Alligator Rivers region. Denariusa bandata is obviously constrained in prey choice by its small mouth, however it is worth noting that the similarlysized but slightly larger-mouthed Ambassis agrammus and A. macleayi consume more microcrustaceans and less chironomid midge larvae than does D. bandata (see appropriate chapters). Thus, some additional factors influence prey choice.
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Lates calcarifer (Bloch, 1790) Barramundi
37 310006
Family: Centropomidae
pronounced in larger individuals and body depth increases relative to length.
Description Dorsal fin: XII–XIII, I, 10-11; Anal: III, 7–8; Pectoral: 17; Horizontal scale rows: 19; Lateral line scales: 52–61; Predorsal scales: 27–28 [52]. Figure: juvenile, 250 mm SL; Polly Creek, North Johnstone River, September 1996; drawn 2001.
Adult fishes are generally silver in colour, greenish-grey dorsally, fins dark, often dark brown or black. On occasions, the silver base colour may be replaced by a golden colour. Lowland river specimens frequently grey/green all over. Very small juveniles may have pronounced vertical bars on body. Older juveniles have a mottled green/brown appearance with a series of irregular white blotches on dorsal surface and up to three distinctive white stripes on head and nape.
Lates calcarifer is a distinctive fish unlikely to be confused with any other species except when small when it may be confused with the estuarine sand bass Psammoperca waigeninsis (see Systematics section below for distinguishing features). It grows to large size; up to 180 cm but more commonly to 120 cm. Bishop et al. [193] list the relationship between length (CFL in cm) and weight (g) as W = 0.0296L2.808; r2 = 0.988, p<0.001 for a freshwater population of 62 individuals from the Alligator Rivers region. Numerous other length–weight relationships have been published (e.g. Dunstan [393] lists relationships for both freshwater and estuarine populations). The body is elongate; mouth large, slightly oblique and extending beyond the eye. Lower edge of preopercle serrated with large strong spine at its angle; opercle with small spine. Body morphology changes with size. Relative length of head, size of mouth and size of eyes greatest in small individuals. The dorsal hump above the head becomes more
Systematics Greenwood [473], in his 1976 revision of the family, recognised four genera of snook: Lates, Psammoperca, Centropomus and the extinct genus Eolates. A fifth genus, Luciolates Boulenger 1914, although distinctive in some respects, was shown to be part of the genus Lates. The family has a common Tethyan origin, contains both freshwater and marine/estuarine forms and has a distribution that includes both the New and Old Worlds. The fossil record extends back to the Eocene but is restricted to Europe and Africa. The family is closely related to the marine Serranidae. In times past, the Centropomidae was
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Using electrophoretic techniques, Shaklee and Salini [1220] identified at least three different stocks of barramundi across northern Australia when comparing fish collected from the Daly River in the Northern Territory, the south-eastern portion of the Gulf of Carpentaria and Princess Charlotte Bay in Queensland. They found no difference between marine and freshwater populations. Early accounts (and even some contemporary fishing magazines) had suggested that two different body types are present in the species: a slender form from freshwaters and a deeper form from estuarine waters. These differences are age/sex related, however and not indicative of different stocks. Salini and Shaklee [1192] later broadened their study to include additional locations from the Northern Territory, the Ord River in Western Australia and three rivers discharging into the western portion of the Gulf of Carpentaria. Populations present in all locations, except those in the adjacent Daly and Finnis rivers, were significantly genetically distinct. These authors were the first to recognise the potential problems of mixing distinct populations when stocking is used to enhance fisheries, in accordance with the principle that genetically distinct populations represent the genotypes best adapted for each particular area.
used to contain the chandid perches (i.e. Ambassis and allied genera) but this was discounted by Greenwood [473]. Two synapomorphies distinguish the Centropomidae from other families: the lateral line extends far onto the caudal fin (shared with the Serranidae) and possession of an anterioposteriorly expanded neural spine on the second vertebrae. Another distinguishing character is the possession of 24 or 25 vertebrae. The genus Lates was described in 1828 by Cuvier with the Nile perch Lates niloticus as the type species. The genus is distinguished from other centropomid genera by the possession of three (rarely four) large flattened triangular spines on the horizontal limb of the opercula; the absence of a basihyoidal tooth plate; three series of lateral line scales on caudal; and two epurals and two euroneurals on caudal. Lates calcarifer may be further distinguished from Psammoperca waigensis, with which it may sometimes be confused, by the presence of a granular tongue in the latter. The genus contains nine species, seven of which (L. niloticus, L. augustifrons, L. longispinis, L. macrothalmus, L. mariae, L. steppersii (= Luciolates steppersii) and L. microlepis) are confined to freshwaters of Africa. The remaining two species L. calcarifer and L. japonicus are euryhaline South-East Asian species. Lates japonicus was described only recently by Katayama and Taki in 1984.
Shaklee et al. [1221] also examined the structure of Queensland stocks in greater detail. They identified seven distinct stocks: south-eastern Gulf, western Cape York Peninsula, Escape River to Orford Bay, Shelburne Bay to Lockhart River, Princess Charlotte Bay, Cairns to Hinchinbrook, and Mackay to Rockhampton and Bundaberg. All were distinct from stocks in the Northern Territory and, with the exception of the Gulf of Carpentaria stock, from populations in the Fly and Kikori rivers of Papua New Guinea. The authors concluded that the Torres Strait was an effective barrier to gene flow and that the observed genetic structure was indicative of longterm reproductive isolation. They supported this argument with examples of river-specific growth rates and area-specific precocious sex reversal (see below).
Lates calcarifer was first described as Holocentrus calcarifer by Bloch in 1790 from material collected in Japan [204]. The status and whereabouts of the type material are unknown [1042]. Other synonyms include Pseudolates cavifrons Alleyne and Macleay, and Lates darwiniensis Macleay. Other Australian fishes have been placed previously, and erroneously, in the genus Lates. These include the estuary perch Macquaria colonorum (as L. antarcticus, L. victoriae, L. colonorum, L. curtus and L. ramsayi) and the Australian bass (as L. similis) [1042]. Investigation of genetic differentiation in L. calcarifer over its entire range is limited to karyotypic comparison of Australian and Indian stocks. Cary and Mather [280] found that although Australian and Indian stocks shared the same number of telocentric (19) and metacentric (1) chromosomes, Australian fish had fewer submetacentric (1 versus 3) and more subtelocentric (3 versus 1) chromosomes than Indian fish. These data suggest substantial genetic differentiation within the species across its entire range. Application of modern DNA sequencing techniques to examine differentiation within the species over its range and comparison with L. japonicus has not occurred but could prove most interesting.
Further electrophoretic examination of stock structure was undertaken by Keenan [683]. Three main groups of populations were recognised: a western group ranging from the Ord River to the south-western portion of the Gulf of Carpentaria; a central group ranging from the Weipa area to Bedford Bay, north of Cairns; and an eastern group ranging from Cairns to the Mary River. Keenan concluded that the most recent development in population structure began about 115 000 y.b.p. when sea levels receded to the 75 m level and a land-bridge was formed between Australia and New Guinea. The east-west subdivision was established at this time with the isolation of ancestral populations in Joseph Bonaparte Gulf in the west
Geographic variation in population genetic structure in Australia has, in contrast, attracted considerable attention.
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and a Cairns to the Burdekin River population in the east. The central population group described above was formed by reinvasion of the Gulf region by fish from both eastern and western stocks after the Arafura Sill was once again broached as sea levels rose. Contrary to Shaklee et al. [1221], Keenan [683] suggested that contemporary gene flow between rivers was substantial and possibly involved the transport of larvae in large floodplumes. He also noted that although the genetic differences between stocks were significant, they were small.
abundance in rivers of eastern Queensland was greatest in rivers with a large discharge and low overall gradient and hence slow runoff. Essentially, these characteristics result in extensive and prolonged flooding. Both Moore [962] and Dunstan [393] suggest that overall abundance is determined by macrohabitat features. These studies imply that habitat availability for juveniles, subadults and young males is critical for determining total population size and that density dependent mortality during these life history stages determines total population size.
Chenoweth et al. [298, 299] applied DNA sequencing techniques to the problem of unravelling geographic variation in barramundi population genetic structure. The pattern revealed was essentially the same as that revealed by electrophoresis (i.e. three major regions differentiated by distinct stocks). No haplotypes were shared among regions although common haplotypes within regions were often shared among localities. These data were indicative of a major phylogenetic break (4% divergence in mtDNA control sequence) either side of the Torres Strait, reflecting approximately 335 000 years of separation [299]. Note that this period is longer than that suggested by Keenan [683] and probably relates to sea level lowering during the penultimate glacial period rather than the ultimate period. Contemporary gene flow was identified also in Chenoweth et al. Populations on the east coast were suggested to have gone through an historic genetic bottleneck, possibly due to drying of the Great Barrier Reef Lagoon and consequent forced retreat into a limited number of refugia.
One outcome of this view is that the maintenance of both the extent and integrity of floodplain habitats is critical for the maintenance of a healthy and abundant barramundi population. River systems in which water resource use limits the extent or duration of flooding are unlikely to contain a healthy and abundant barramundi population. Similarly, structures which impede both upstream and downstream movement are also likely to impact on abundance levels. This is amply demonstrated by the decline in barramundi populations in the Pioneer River due to the construction of a series of weirs that prevent or limit dispersal [1081], to the point where populations now need to be supplemented by stocking in order to satisfy recreational fishing demand. Prior to the imposition of greater control on commercial gill-netting, there was a general fear that commercial harvesting was contributing to a decline in abundance in some river systems (see below). The view that abundance levels vary between rivers according to the extent and availability of floodplain habitats, while rightfully focusing attention on the integrity of such habitats, does not sufficiently address the relationship between overall abundance and the quality of larval/postlarval habitat. Habitat for barramundi must be viewed in its broadest sense (see below).
It should be noted that Doupe et al. [390] also employed a mitochondrial DNA genealogy approach to this problem, but failed to confirm the presence of an ancestral east-west disjunction in stock structure. Distribution and abundance Barramundi are very widely distributed occurring throughout the Indo-West Pacific from the eastern edge of the Arabian Gulf east to China, Taiwan and Japan and south to Papua New Guinea and northern Australia. The latitudinal range occupied by L. calcarifer is 23°N to 26°S. In Australia, L. calcarifer is distributed widely across northern Australia extending from Shark Bay in Western Australia to about the Mary River in Queensland [52]. This species occurs in most drainages within its range. For example, of 34 river basins from Cape York Peninsula to the Mary River in south-eastern Queensland, L. calcarifer was recorded present in 33 basins. In natural systems, the abundance of L. calcarifer within individual river basins depends on river morphology and fishing pressure. Barramundi are more common in larger rivers with welldeveloped floodplains characterised by an abundance of lakes and swamps [962]. Dunstan [393] believed that
Macro/meso/microhabitat use There is surprisingly little quantitative information on the habitat use of L. calcarifer and much of the available information has been concerned with different macrohabitat use as part of the overall movement and reproductive components of its life history. It is clear, however, that the macrohabitat of barramundi is composed of a critical chain of habitats used at different phases of the life cycle. These habitats are more fully discussed in the sections covering reproduction and movement below. Environmental tolerances Larval barramundi require waters of elevated salinity and temperature in which to develop; this species cannot breed in freshwater. Larval barramundi have been routinely recorded in salinities as high as 37–38‰ [367, 370, 1174] and on occasion, in salinities approaching 50‰ [370].
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Russell and Garrett [1175] recorded larvae in salinities of 16–37‰ (mostly >30‰) and temperatures of 26.5 to 32°C in swamps of the Wet Tropics region. Temperature and salinity may routinely increase to 35–36°C and 35–45‰ respectively, during January or February but may also decline precipitously (i.e. salinity falls to 5‰) after monsoonal flushes in this region [1174]. Larval survival probably declines under such conditions of rapid change. Larval survival is optimal at temperatures of 27–28°C [683]. Hatchery based studies indicate that larval survival is optimal in the salinity range of 20–25‰ and that hatching success is optimal at salinities of about 30‰ [1415]. De [376] reports similar ranges in temperature (25–34°C) and salinity (7–28‰) as well as narrow ranges in pH (7.4–7.6) and oxygen (6.5–7.6 mg O2.L–1) for larvae in tidal swamps of Bangladesh.
mg.O2.L–1. Dissolved oxygen concentrations (near the surface) in lagoons of the Normanby River, Cape York Peninsula, in which barramundi occurred, ranged from 1.1 to 2.1 mg.O2.L–1 in the early dry season [697]. Laboratory tests have revealed that juvenile barramundi may tolerate low dissolved oxygen between 10–20% saturation for limited periods (R. Pearson, unpubl. data) but it is unlikely that tolerance extends to oxygen concentrations below 10% saturation. Barramundi have often been observed to be amongst the dead in large fish kills for which hypoxia is implicated as the primary cause [187]. Tropical fishes, especially those inhabiting floodplain environments, seem more tolerant of a greater range in water acidity than do many temperate fishes and this seems to hold true for barramundi also. Barramundi were recorded present over a pH range of 4.0 to 7.2 in the Alligator Rivers region [193] and 6.1 to 9.12 in floodplain lagoons of the Normanby River [697]. We have collected barramundi from dune lakes of the Cape Flattery region in which pH was between 5.2 and 5.6. Russell and Helmke [1180] recorded L. calcarifer in tidal creeks of Trinity Inlet near Cairns, in which pH routinely fell to between 3 and 4 units.
Adult fish are found across a range of temperatures that reflects their subtropical/tropical distribution. Dunstan [393] believed that the distribution of barramundi on the east coast of Australia was limited by winter water temperatures and cited 15.5°C (recorded in the Mary River) as the lower temperature limit. Feeding activity is greatly curtailed at water temperatures less than 24°C. There is some suggestion that susceptibility to infection by pathogens such as Saprolegnia increases at low water temperatures [185]. Maximum water temperatures recorded for adult barramundi are similar to those recorded for larvae and juveniles. Bishop et al. [193] recorded barramundi in waters with a temperature range of 26 to 35°C (recorded at surface) in the Northern Territory. Kennard [697] recorded barramundi in waters with a surface temperature as high as 33°C. A temperature range of 25–30°C is probably optimal for this species.
Lates calcarifer occurs over a wide range of water clarities and Bishop et al. [193] suggest that it is very tolerant of elevated turbidity. Reproduction Lates calcarifer is a protandrous hermaphrodite, commencing life as a male and changing into a female fish later in life after spawning. Transition is apparently rapid; Moore [961] found only six fish from a total sample of 5202 that contained either testes with developing oogonia or ovaries with remnant spermatogonia or intact sperm ducts. A further five individuals were found to be functional hermaphrodites, containing well-developed male and female tissue. Davis [364] recorded a higher proportion of transitional fishes in his study of maturation in northern Australian barramundi: 10/304 in the Northern Territory and 29/322 in the Gulf of Carpentaria region. He also identified three synchronous hermaphrodytes (810, 900, 1020 mm in length). Both authors identified female fish that had not begun life as male. Such fish were termed primary females and were much smaller than other female fish (330 and 420 mm).
Although Dunstan [393] suggested that barramundi rarely occur in waters where the salinity exceeds 30‰, the existence of entirely marine populations [1051] clearly indicates an ability to tolerate salinities approaching that of sea water. Similarly, Russell and Garrett [1174] have recorded juvenile barramundi from hypersaline waters with salinities of 94‰. The duration of tolerance to such elevated salinity is unknown however. Adult barramundi have been recorded from a very wide range of salinities (freshwater to marine) by virtue of the extreme range of habitats in which this species occurs at different times in its life history.
Males begin to mature at about one year of age when they about 300 mm in length [364]. Regional variation in growth rates and age at sexual maturity can be pronounced. For example, Davis and Kirkwood [371] developed an equation relating scale radius to length having the form L (mm) = a + bS(mm) where L = length and S = scale radius. Between-river variation was extreme.
Lates calcarifer has a moderately well-developed tolerance to low levels of dissolved oxygen, as might be expected for a species that inhabits tropical floodplain waterbodies. Bishop et al. [193] recorded barramundi in waters with a surface dissolved oxygen concentration ranging from 3.0 to 6.8 mg.O2.L–1 and bottom concentrations of 0 to 6.8
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fish. Moore [962] determined the relationship between fecundity and weight (W in kg) as F (x 106) = 1.942 W – 13.86. Similarly high fecundity estimates have been obtained by other researchers also [393]. As might be expected, GSI values for female fish are very high. Dunstan [393] records maximum GSI values for stage V (not yet fully mature) of up to 19% of total body weight. Moore [962] indicates that female GSI may attain levels in excess of 40% in Papua New Guinean stocks. Mean monthly male GSI did not exceed 4% in a total sample of 1518 fish.
For example, over a two-fold difference in magnitude of the intercept a was recorded for the East Alligator and Mary rivers, Northern Territory, (31.4 and 74.9, respectively), and the gradient b ranged from 43.6 (Mary River) to 46.8 (Norman River). These authors believed that between-river differences in growth rates reflected different environmental conditions rather than intrinsic genetic between-population differences. In general, and summarising across a number of studies [364, 371, 393, 962, 1130], barramundi attain a total length of about 350 mm in one year, 500 mm in two years, 750 mm in four years, 850 mm in six years and 1075 mm in 10 years. Barramundi commonly live for 9–10 years but occasionally live longer. Davis and Kirkwood [371] recorded one individual from the Norman River that was 14-years-old and had reached 1212 mm in length. Under experimental optimal conditions barramundi may reach 900 mm in length after four years. Growth rates of barramundi populations in impoundments are often greater than that seen in natural population (J. Russell, pers. comm.). Further information on age determination using sectioned otoliths, otolith morphometrics and fish length are available in McDougall [1436] and Stuart and McKillup [1440, 1441].
The timing of spawning is variable across the barramundi’s range. Russell and Garrett [1175] record that in eastern Queensland streams, maximal gonadal activity occurred between October and February. Maximal gonadal activity occurs from October to December in the Northern Territory [364], from October to January on the Gulf region [364] and from October to January in Papua New Guinea [962]. These data suggest that spawning precedes the wet season and the onset of monsoonal flows, despite suggestions in the literature that there is a relationship between spawning and the start of the wet season. Garrett et al. [426] suggested that spawning is initiated by coincidence of high water temperatures and high tides of the full or new moon. Spawning takes place at night. There is some debate as to whether L. calcarifer is a serial or complete spawner (heterochronal or homochronal, respectively). Moore [962] believed that small females may be serial spawners. Davis [366] could find no evidence of serial spawning (but conceded that serial spawning may occur in Papua New Guinea stocks). In the majority of Australian stocks, spawning takes place in the vicinity of river and creek mouths in areas protected from the strongest run of ebb and flood tides by sand bars and mud banks but within the path of lateral currents that transport eggs and larvae into supralittoral swamps [426].
Males are generally mature by three years of age. Davis [364] reported that 50% of a Northern Territory sample were mature when between 700–750 mm whereas fish from the Gulf region matured between 600–650 mm. Sexually precocious populations of the northern Gulf region may be fully mature at much smaller lengths (300–400 mm) [365]. Transition to the female state, a process termed inversion, occurs after spawning; ‘transitionals’ are observed mainly in December and January. Inversion occurs when fish are about 800 mm in length and very few males remain in the population once lengths of 950–1000 mm are attained. The smallest female recorded by Moore in south Papau New Guinea was 730 mm (five-years-old) and females constituted only 10% of the sample less than 895 mm. Males constituted only 31% of fish greater than 1015 mm and no males greater than 1170 mm were recorded. As detailed below, males remain in the vicinity of the spawning grounds after they have migrated downstream. Evidently they may take part, as males, in spawning for up to several years.
The eggs of L. calcarifer are small, between 0.44 and 0.55 mm in diameter and spherical. After water-hardening, the eggs are slightly larger (0.6–0.8 mm) and slightly ovoid [962]. Time to hatching is temperature dependent [1145]: hatching takes 17 to 18 hours at 25°C [426] but may occur in as little as 12 hours at higher temperatures. Moore [962] believed the eggs to be slightly heavier than 25–30‰ seawater but kept in suspension by even slight water currents. Various workers cite the work of Thai researchers Wongsomnuk and Manevonk [1415] demonstrating that the eggs are buoyant and pelagic. The larvae are small at hatching (1.5 mm), poorly pigmented and with a large yolk sac. By 2.5 mm, the mouth is well-developed and open, and the body slightly pigmented. Flexion occurs by about 3.5 mm, by which time teeth have developed, fin rays are present in the pectoral fins and the yolk sac is greatly diminished. The prominent oil globule persists for
Lates calcarifer is extremely fecund, and amongst the most fecund fish species reported in the literature. Davis [366] determined the following relationship between fecundity (F) and length (L in mm): F (x 106) = 0.3089e0.0035L; r2 = 0.822. This equation predicts a fecundity of 10 million eggs for a fish of 1000 mm and double that for a fish of 1200 mm. No differences in fecundity were found for Northern Territory or Gulf populations, or for precociously mature
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Table 1. Life history data for Lates calcarifer. References are listed in the text. Minimum age at sexual maturity (months)
Males – 36, females – 72
Minimum length of ripe females (mm)
800–900 mm, but note that substantial geographical variation exists and that precocious maturation has been reported and that primary females have also been reported
Minimum length of ripe males (mm)
600–700 mm, as above
Longevity (years)
14–20 years but possibly much longer (J. Russell, pers. comm.)
Sex ratio
Skewed towards males overall, highly skewed in smaller size classes, skewed towards females in the largest size classes
Peak spawning activity
October to February, depending on location
Critical temperature for spawning
~30°C
Inducement to spawning
Coincidence of high water temperature and salinity, high tides and new or full moon
Mean GSI of ripe females (%)
20–40%
Mean GSI of ripe males (%)
<5%
Fecundity (number of ova)
5–20 x 106
Fecundity/length relationship
See text
Egg size
0.44–0.55 mm
Frequency of spawning
Serial spawning may occur in smaller fish
Oviposition and spawning site
Eggs pelagic, spawning occurs in river mouths adjacent to supralittoral swamps
Spawning migration
Young males make downstream migration prior to spawning
Parental care
none
Time to hatching
18 hours; temperature dependent may be as short as 12 hours
Length at hatching (mm)
1.5 mm
Length at feeding (mm)
2.5–3.5 mm
Age at first feeding
1–2 days after hatching
Age at loss of yolk sac
2–4 days after hatching, oil globule still present at 140 hours after hatching
Duration of larval development
7–20 days
Length at metamorphosis
20–50 mm
pattern does occur. Barramundi in southern Papua New Guinea have a well-defined marine spawning ground and larvae are delivered by high tides to coastal swamps distant from river mouths [962]. Davis [367] reported that supralittoral swamps were uncommon in Van Diemans Gulf in the Northern Territory and that larvae relied more on floodplain and billabong systems many kilometres from the coast and were assisted in accessing these habitats by very large spring tides (7 m).
about 140 hours [1145]. Moderate pigmentation is present in larvae 4.5 mm in length. Fin ray development is complete in 8.5 mm larvae; although dorsal and anal fin ray development is complete in 5 mm larvae [1181], the head is short and deep, eyes large, scales absent and pigmentation arranged in dark transverse bars. Squamation is complete when larvae have attained 12 mm in length. The head becomes more elongated by the time larvae are 20 mm. The adult structure and form is attained in fish between 20–50 mm length. Visual feeding commences in larvae as small as 10 mm [133]. Growth is extremely rapid [376] and juveniles require a diet high in protein content [291]. Larvae attain a length of 10 mm in as little as seven days [445].
Juvenile barramundi reside in supralittoral habitats for varying amounts of time but quickly establish as the dominant predator [962, 1175]. Such habitats can be particularly harsh environments with high water temperature (up to 38°C) and salinity levels (up to 50 ppt) [370]. Moore [962] recorded juveniles (>8–9 mm) moving back into tidal waters as swamps dried out. Russell and Garrett [1176] reported that in north-eastern Queensland, juveniles remained in such supralittoral habitats for up to four months whereupon they moved into adjacent tidal creek systems [1174, 1175, 1176]. They were about 120 mm (SL) in length at this age. Juveniles remain in tidal habitats for approximately a further eight months. During this time,
Movement Pronounced movement is a dominant feature of the biology of barramundi, occurring in almost every life history stage. Typically, larvae hatch in estuarine and near-shore habitats and are passively delivered by tidal action to supralittoral swamps near the river mouth [1174, 1175, 1176]. Larvae are typically about 5 mm long and movement is largely passive. However, regional variation in this 318
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able to negotiate this velocity. Griffin [476] has observed large numbers of juvenile fish (150–500 mm TL) congregated below a road culvert. They were apparently unable to negotiate a velocity of 3 m.sec–1. Similarly, Kowarsky and Ross [740] recorded barramundi congregated below an inoperative fishway. Barriers to upstream movement (dams, weirs, sand dams, road crossings) impact heavily on young barramundi and over time may eventually depress population sizes in downstream areas by denying access to a critical link in the chain of habitats.
the scale of movement is limited but by December or January, most 0+ juveniles spawned the previous season have departed tidal creek habitats. Russell and Garrett [1176] suggested that the pattern of juvenile movement reported for northern Queensland (described above) may differ from that in Papua New Guinea or the Northern Territory. The stimulus for fish to depart tidal creek habitats is unknown but the cannibalistic habit of mature barramundi may provide a powerful incentive [1176]. Moore [962] reported that recruitment of juveniles and postlarvae into nursery swamps had ceased by February and young of the year remained in these habitats until June or July, by which time they had reached a length of 200–300 mm.
Juvenile barramundi remain in upstream, freshwater habitats for between three and five years (although a small proportion may stay longer [452]) by which time they are approximately 600 mm in length. Griffin [476] suggested, based on mark/recapture data, that the range of normal movement of fish in freshwater riverine habitats may be up to 15 km.
Extensive active movement becomes a feature of the biology of juvenile barramundi in the 1+ age class. Fish of this age are mostly immature males usually between 250–350 mm SL. Such fish may move far upstream colonising a range of freshwater habitats, including billabongs and floodplain lagoons and wetlands. The smallest barramundi recorded in floodplain habitats of the Normanby River by Kennard [697] was 350 mm SL, although much smaller individuals (212 mm SL) were recorded in the main channel of the river in August [1094]. Access to offstream habitats is largely governed by flooding regime.
Egress from upstream juvenile/young male habitats and migration downstream to spawning grounds may take place over a number of months. In the Northern Territory, young males commence downstream movements in August or September, a period corresponding to an increase in daylength and an abrupt increase in water temperature [476]. A downstream dry-season migration is typical of stocks in Papua New Guinea also [963]. Falling water levels were suggested by Moore and Reynolds [963] to stimulate barramundi to move from swamps to lake and river habitats. Such movement does not always inevitably lead to a downstream migration however, as return movements will occur if water levels rise subsequently or if fish have not commenced gonad maturation. Severe droughts stimulated greater migration in barramundi of southern Papua New Guinea [963]. Gonad maturation in these New Guinean stocks may, in itself, be insufficient to stimulate migration in the absence of water level lowering.
Upstream movement of 0+ and 1+ age class fish (100–400 mm) in the Fitzroy River occurred predominantly from October to December [740, 1274] although larger fish (up to 630 mm) were also recorded moving upstream through the fishway and smaller numbers of fish were recorded moving upstream in all except the colder months of April, July and August. No movement was recorded at temperatures below 20.5°C and only 2.5% of the sample moved at temperatures below 22°C. Movement through the fishway occurred during both the day and night. Upstream movement of barramundi in the Fitzroy River occurred over a range of flows up to about the 18% exceedance value (~8000 ML.day–1) [1274]. In contrast, Hogan et al. did not record upstream movement in the Burdekin River at low flows [587].
Davis [452] reported that a proportion of the population did not make it downstream to spawning grounds until late in the wet season and interpreted this as indicating that either these fish had migrated from far upstream or had emigrated from off-stream wetland habitats that did not connect to the main channel until late in the wet season. If true, then this is in contrast to L. calcarifer migration reported for southern Papua New Guinea, where falling water levels stimulate movement.
Mallen-Cooper [853] measured the swimming speed of juvenile barramundi in a simulated vertical slot fishway and determined a NV95 (negotiable velocity for which 95% of a fish sample pass) of 0.66 m.sec–1 at water temperatures of 22–24°C for juvenile fish of 43 mm mean length. This velocity was less than that for equivalently sized Australian bass and it was suggested that swimming performance of the test fish was less than optimal because of the low experimental temperatures. The maximum water velocity measured in the Fitzroy River vertical slot fishway was 1.4 m.sec–1 and fishes as small as 200 mm were
After spawning, males remain in estuarine reaches with mature females. A return migration does not occur. In subsequent years, these fish spawn early in the wet season because they are already resident in spawning grounds [452]. Davis [452] makes the interesting point that such fish cannot be termed catadromous given that they do not need to migrate to the spawning ground.
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A number of exceptions to this generalised migration pattern are known. In southern Papua New Guinea, spawning grounds are limited to one major coastal area near Daru as discharge from the Fly River results in dilution of coastal waters below the salinity required for larvae [963]. Mature male and female fish migrate downstream from inland habitats to the spawning grounds and subsequently return to inland habitats. Several hundred kilometres may be travelled overall and river fidelity appears to be high. A proportion of the spawning population appears not to have a freshwater interval in its life history. Pender and Griffin [1051], by comparing barium and strontium ratios in scales, identified completely marine populations of barramundi in the Northern Territory also. These populations were located in areas remote from freshwater habits with no easy access to a river mouth.
Gulf of Papua and that near-shore salinity levels are not depressed below the range suitable for larval development. Rising water levels in northern Australian, in contrast, may be necessary to combine with high tides to inundate or establish connectivity between the river and supralittoral swamps. Trophic ecology Information on the feeding ecology of Lates calcarifer presented in Figure 1 has been drawn from several different studies. Davis [368] examined the diet of 3684 specimens (of which 2292 contained food) collected from the Van Dieman Gulf region of the Northern Territory and from the Gulf of Carpentaria. These data dominate the summary presented in Figure 1. Davis noted strong ontogenetic variation in diet: fish below 80 mm (TL) consumed greatly different prey than larger size classes. Furthermore, fish between 80 mm TL and 400 mm TL consumed different prey than did fish greater than 400 mm TL. These size classes have been retained here as additional studies have, to a greater or lesser degree, reported diets for different age classes closely approximating those used by Davis [368]. For example, the sample of fish examined by Russell and Garrett [1175], collected from supralittoral swamps (n = 50) and tidal creeks (n = 41) of the Trinity Inlet and Princess Charlotte Bay areas, ranged in length from 50–250 mm TL and 200–400 mm TL, respectively, although very few fish less than 50 mm TL were included in the sample. The remaining studies were concerned primarily with adult fish and included Dunstan [393] (n = 90, fish collected from riverine and estuarine habitats in north-eastern Queensland and the Gulf of Carpentaria), Bishop et al. [193], fish collected from riverine habitats in the Alligator River region) and Arthington et al. [98] (n = 10, fish collected from Koombaloomba Dam on the Tully River).
With the exception of the examples immediately above, this discussion has focused primarily on movements within river basins. Keenan [683] believed that the transport of larvae between basins in floodplumes was significant. Adult movement may be significant also. Sawynok [1199] detailed the movement of tagged barramundi in the Fitzroy River. Of the many thousands of fish tagged in this river, a small number (55) were recaptured outside of the Fitzroy basin. Twelve fish were recaptured just out of the river mouth, 28 had migrated south and the remainder had moved north. Most movements out of the river were associated with large flow events (wet season discharge in excess of 2 x 106 ML). Two very long-range movements were detected. One fish moved north from the Fitzroy River to Cape Bowling Green, a distance of 650 km; whereas another moved a distance of 350 km south to the Hervey Bay area. It did so in an estimated time of only one month. Sawynok [1199] intimated that the Fitzroy River was an important source of colonists to rivers to the south.
Post-larval barramundi forage extensively on microcrustacean zooplankton, with copepods being the dominant prey type within this prey class. Shrimps, aquatic insect larvae and other aquatic macroinvertebrates are also consumed but these prey classes predominate in only the largest individuals of the post-larval size class. Small fish (usually the larvae of other species using supralittoral swamps as nursery areas) are also eaten. These data closely resemble the diet of very small barramundi reported from elsewhere in its extensive range. De [376] examined the diet of post-larval barramundi in low-lying tidal pools of Bangladesh. Copepods dominated (71%) the diet of postlarval (10–15 mm) fish and were still important (29%) in the diet of fish between 15 and 45 mm, although notonectid bugs were the dominant prey item (38%).
Smaller, yet still significant movement of tagged fish has been reported for barramundi in the Wet Tropics region [116]. Fish have been recorded moving from the Tully to the Herbert River (200 km), Missionary Bay to the Johnstone River (87 km) and the Murray River to the Hinchinbrook region (65 km) [116]. Davis [369] reported substantial interbasin movement of barramundi in the Northern Territory also, although it appeared that barramundi were more prone to emigrate from some rivers than others. The differences in movement biology reported for New Guinean and Australian stocks (i.e. movement out of floodplain lakes stimulated by falling water levels and movement occurring with rising water levels, respectively) warrants comment. Falling water levels in southern Papua New Guinea may signal a reduction in discharge into the
Microcrustacea feature very little in the diet of fish greater than 80 mm TL and juvenile barramundi (80–400 mm TL)
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Fish between 80–200 mm TL were more reliant on macrocrustacea and aquatic insect larvae than they were on fishes, while the reverse was true of fish between 200–400 mm TL [393, 1175]. Barramundi greater than 400 mm TL are predominantly piscivorous.
have a diet much more closely resembling that of large adult fish. More than half of the diet is composed of macrocrustaceans, predominantly species such as penaeid and paleomoneid prawns but also including various species of crabs, while a further 36% is comprised of fish. Fish (5.5%)
Ontogenetic changes in diet shown in Figure 1 reflect the influence of increasing body size and size of the feeding apparatus on the ability to capture and process larger and more mobile prey types, and the influence of ontogenetic changes in habitat use. For example, Russell and Garrett [1175] report substantial variation in the diet of fish from nursery habitats and that of fish from nearby tidal creeks. Similarly, the larger size classes of the juvenile category depicted in Figure 1 are dominated by fish collected from freshwater riverine habitats.
Aquatic insects (3.6%) Other macroinvertebrtaes (2.2%) Macrocrustaceans (5.1%)
A wide variety of fish species has been recorded in the diet of barramundi. Important prey families include the Clupeidae, Engraulidae, Gobiidae, Eleotridae, Mugilidae, Hemirhamphidae, Melanotaeniidae, Atherinidae, Chandidae, Plotosidae and Ariidae. Davis [368] noted significant relationships between fish prey length and predator length for a number of prey families, most notably for the Ariidae and Clupeidae (note that Davis grouped Nematolosa erebi within the Dorosomatidae), suggesting that as fish matured they not only foraged more on families characterised by larger size, but also consumed larger prey species within individual families. The largest prey to predator length ratio observed by Davis was 0.61 for N. erebi. Ariid catfish prey never exceeded 35% of predator length probably reflecting the constraints on ingestion imposed by the rigid pectoral and dorsal spines. Barramundi will consume other smaller barramundi (prey to predator length ratios of up to 0.50 were reported by Davis [368]), although the extent of cannibalism apparently varies from locality to locality [368]. Russell and Garrett [1176] suggested that the threat of cannibalism may be an important incentive for juvenile fishes to leave tidal creek habitats and migrate upstream at the end of the first year of life.
Microcrustaceans (83.4%)
Post larvae (n = 259) Other (1.2%)
Aqautic insects (5.6%) Other macroinvertebrates (3.0%)
Fish (36.0%)
Macrocrustaceans (54.3%)
Juvenile (n = 588) Other (1.3%) Fish (66.2%)
Macrocrustaceans (32.5%)
Barramundi are clearly an important predator and are likely to have a very important effect on the structure of freshwater communities and possibly on the transmission of organic carbon through the aquatic food web, given their predilection for eating bottom-level herbivore/detritivore species such as bony bream and mullet. Kennard [697] noted that barramundi were an important influence on fish community structure in floodplain waterbodies of the Normanby River, Cape York Peninsula. He found that associations between habitat structure and freshwater fish assemblage structure were essentially absent soon after flooding with composition being determined largely by
Adult (n = 1435) Figure 1. The average diet of postlarval (<80 mm TL), juvenile (80–400 mm TL) and adult (>400 mm TL) Lates calcarifer. Summaries are drawn from five separate studies undertaken across northern Australia (see text).
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development of tourism facilities) that result in the exposure of potential acid sulphate soils and the resulting problems of depressed pH levels and elevated concentrations of dissolved aluminium and other biotoxic metals and metalloids may impact on larval and juvenile barramundi. Although Russell and Helmke [1180] did not record barramundi in fish kills in creeks of Trinity Inlet associated with depressed pH and elevated aluminium, many of the fishes recorded in these kills were species important in the diet of juvenile barramundi. Russell and Garrett [1175] state that in developed coastal regions ‘…many of the tidal creeks and swamps occupied by juvenile barramundi have been or are threatened with various types of human disturbance’. This does not bode well for the future unless steps are taken to reduce the impact of human disturbance.
the size of the water body (i.e. a sampling phenomenon based on random distribution of fishes). Habitat associations, particularly those with woody debris, increased in strength with time. Kennard [697] hypothesised that this effect may be a result of strong predation by barramundi on other fishes mediated by spatial variation in the amount and complexity of woody debris available as refuge. He experimentally tested this hypothesis by altering predator densities and woody debris availability in a series of floodplain lagoons and the results supported the initial observations. In the absence of appreciable cover provided by woody debris, barramundi are able to regulate the abundance of prey species to the extent that overall assemblage composition is influenced by this species. Interestingly, when woody debris was sufficiently abundant to reduce the predatory efficiency of barramundi, a number of other smaller species such as spangled perch and mouth almighty, which made great use of the refuge from predation afforded by the woody debris, became important predators of a range of other smaller fishes not consumed by barramundi. The presence of barramundi significantly altered both the foraging behaviour of prey species and hence their choice of prey, but also greatly influenced microhabitat use by potential prey species. These observations invite examination of the extent to which the absence of barramundi from areas in which they would normally occur, either through overfishing or the erection of downstream barriers to movement, might impact on fish assemblage structure and the transmission of energy through the aquatic food web. Similarly, the impact of barramundi translocated into river reaches in which they were historically absent is of concern.
Water resource development, particularly the development of associated infrastructure, has significant potential to impact on L. calcarifer populations. Dams and weirs may form barriers to fish trying to move upstream and fish may be denied access to important habitats [1081]. The extent to which weirs or dams impact on the potential for movement is clearly related to the location of such barriers in the catchment. The closer to the river mouth, the greater is the extent of upstream habitat denied to migrating barramundi. For example, the barrage located on the Fitzroy River is of great significance to barramundi because it regulates access to almost the entire catchment by virtue of its position close to the river mouth [160]. Water harvesting, if sufficiently large, may limit the extent and/or duration of downstream floodplain inundation and consequently reduce opportunities for barramundi to access such habitats. Sand dams, such as those used in the lower Burdekin River, may also interfere with fish passage.
Conservation status, threats and management Lates calcarifer is listed as Non-Threatened by Wager and Jackson [1353] yet barramundi are potentially threatened by numerous human activities.
Barramundi are economically very important: commercial gill netting catches exceeded 1000 tonne in 1990 [678]. Aquaculture production is similarly large, approximately 800–900 tonne in 1998/99 [1320]. Recreational fishing catches are also substantial. For example, the recreational fishing catch in Lakefield National Park (which contains much of the Normanby River) was estimated to be between 4.4 and 9.4 tonne per annum over the period 1986–1991 and conservatively worth between $200 000 and $430 000 per annum [1178]. Recreational fishing for barramundi was estimated to contribute $8–15 million per annum to Queensland’s economy in 1990 [1188]. Current levels are probably higher. Rutledge et al. [1188] estimated that stocking of impoundments to enhance recreational fishing generated a potential economic benefit of $31 for every dollar spent in the programme. Given the economic value of barramundi, notwithstanding its ecological importance, it is important to examine the threats faced by this species. Moreover, it is worthwhile to examine what
Barramundi occupy a variety of habitats throughout their life cycle (see Movement section above). As a consequence, their persistence in a basin may be influenced by a variety of activities occurring throughout the catchment. Russell and Garrett [1174] state that larval and juvenile barramundi are dependent on sheltered shallow habitat found at the margins of northern estuaries. Changes in the integrity of such habitats or their accessibility will have negative consequences. For example, the construction of bund walls to limit lateral penetration of saline water onto the supralittoral areas of estuarine floodplains in order to enhance the production of ponded pasture grasses also limits the ability of larval and juvenile barramundi to access these areas [865]. Coastal developments (i.e. wetland reclamation, marina construction and the
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impacts harvesting (commercial, aquacultural and recreational) of barramundi has on other species. Furthermore, as no negative effects associated with barramundi stocking were considered in the cost benefit analysis of Rutledge et al. [1188], it is worthwhile to consider if such impacts exist and what their consequences might be.
and 3.0 ± 0.2 fish.net.hr–1 in the closed reach: a CPUE difference of over 50 times! Declines in abundance have resulted in the development of an extensive stock enhancement program in Queensland [1139] which commenced with the stocking of freshwater impoundments but now also includes nonimpounded reaches. Current practice limits the source of broodstock used for such programs to include only fish from the general vicinity (i.e. same evolutionary significant unit (ESU)) in recognition of the discrete genetic differences that exist between different stocks of barramundi and in accordance with the principle that genetically distinct stocks represent the genotype best adapted for each particular area [1192, 1221]. Concerns about stock enhancement, translocation and the need to preserve natural genetic heterogeneity were expressed soon after the nature of stock structure became known [681, 1192], (and continue to be expressed [389]) with the general view that this is best achieved by regulating the movement of barramundi by humans. Alternative views exist however. The argument has been made that genetic differences involve differences in the proportions of different genes, not of the genes themselves [1267], and that the observed genetic differences are extremely small, relatively recent (17 000 years) and that substantial migration between different stocks (and hence gene flow) presently exists [463]. Moreover, although geographic variation in age at sex inversion, the presence of primary females, variable sex/length ratios and the existence of fully marine life histories has been used to support inferences about the genetic basis of localised adaptation [389, 1221], a genetic basis for this variation remains to be demonstrated empirically.
Currently there are about 120 boats reporting commercial catches of barramundi on the east coast of Queensland with an annual catch of about 120 tonne [1404]. In the Gulf of Carpentaria, commercial catches are about 380 tonne per annum across 90 licences [1404]. Concerns about the effects of commercial fishing on barramundi abundance have been expressed since the 1940s [393, 1395]. Available statistics indicate that annual landings in many areas have declined [1171], necessitating the introduction of restrictions on commercial fishing such as limited licensing, vessel and gear restrictions, and the imposition of minimum and maximum size limits. On the east coast of Queensland, fishers are restricted to only three nets totalling no more than 360 m (600 m when not netting rivers), a mesh size of between 150 and 215 mm, and are prohibited from fishing between 1 November to 1 February. Fishers in the Gulf of Carpentaria region are restricted to six nets not totalling more than 360 m, a mesh size of between 162.5 m to 245 mm (although demand has resulted in most fishing being conducted with 162.5 mm and 178 mm mesh sizes) and are prohibited from fishing for a period of 3½ lunar cycles commencing seven days prior to the October full moon [501]. Commercial fishers have to observe the same size restrictions as recreational fishers: fish must be greater than 58 cm TL (east coast) or 60 cm TL (Gulf) and less than 120 cm in length. Mesh size restrictions have resulted in very low rates of bycatch capture, comparable to the lowest bycatch rates reported by the FAO [501]. Nonetheless, concerns have been expressed about the effects of barramundi netting on some species such as sawfish [777] and the rare and critically endangered Bizant River shark Glyphis sp. A. [1058]. A recent study of the effects of gill-netting has revealed that although barramundi are significantly less abundant in rivers open to commercial fishing, other secondary effects on the abundance of other species and overall biodiversity are not evident [501].
Notwithstanding the potential for genetic pollution to arise from mixing of genotypes, there still exists the potential for stocking to have negative genetic and ecological effects. Broodstock used in restocking programs are typically of low diversity because of high individual fecundity. A small effective n (size of the breeding population) may result in the production of fingerlings of unrepresentative genetic nature simply by chance, increases in the rate of genetic drift and an increased potential for inadvertent domestication [1221]. Mechanisms for brood rotation have been implemented in many hatcheries to avoid these problems (J. Russell, pers. comm.). ‘Off-shore’ cage-based aquaculture of barramundi occurs in Queensland (Hinchinbrook), the Northern Territory and Western Australia (Lake Argyle on the Ord River) and calls have been made for the expansion of this type of aquaculture in Australian inland waters [463]. The escape of hatchery bred fish from such facilities has been reported [389]. The broodstock used for such operations is typically of low
The impact of recreational fishing on barramundi has been little studied. Populations in areas that receive a large number of visitors intent on catching barramundi, such as Lakefield National Park, may experience substantial pressure. For example, in August 1990 we sampled (by gillnetting) two locations in the Normanby River open to, and heavily fished by, recreational fishermen, and one location closed to the public (unpubl. data). Barramundi catches averaged 0.06 ± 0.04 (SE) fish.net.hr–1 in the fished reaches
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residues of DDT, Heptachlor, Dieldrin and Aldrin in tissues of L. calcarifer and noted a linear correlation between residue concentration and lipid content such that residues were more concentrated in ovarian and gut tissues than in muscle or liver. Concentration of pesticide residues in eggs may have consequences for larval development and survival as well as adult fecundity. DDT, DDE, DDD, Dieldrin and Hexachlorocyclohexane residues have been recorded from barramundi in coastal streams of north-eastern Queensland [1182] and elevated mercury has been detected in New Guinean barramundi [213].
genetic diversity. For example, the Lake Argyle stock are derived from only four broodstock and one highly fecund female supplied about 75% of all progeny [389]. The potential for hatchery derived fish to transfer disease to wild populations has been generally discounted, based on the fact that wild fish are not exposed to the stresses encountered by hatchery based stock conducive to the development of infectious diseases and therefore not at risk of being affected by pathogens that may be released from aquaculture operations [850]. However, this ignores the fact that natural seasonal declines in water quality or habitat suitability may indeed stress wild fish or that natural episodic outbreaks of disease do occur in natural populations (e.g. tropical epizootic ulcerative syndrome). It is also argued that careful husbandry will eliminate the potential for inadvertent disease outbreaks and release. However, some potentially dangerous fish diseases may be carried asymptomatically by hatchery-reared barramundi [234].
The spread of the cane toad (Bufo marinus) across northern Australia and the propensity of barramundi to consume native frogs as part of their diet has led to concerns about the impact that cane toads may have on barramundi populations. Crossland [342] has recently demonstrated however that barramundi quickly learn to avoid cane toad tadpoles. The management of barramundi stocks is complex. First, the existence of distinct genetic stocks suggests that care must be exercised in the translocation of this species between basins. Importantly, genetic diversity (and integrity) of translocated stocks or stocks used in cagebased aquaculture must be maintained. Second, the complex life history of this species, involving sex reversal at large size, requires that strict size limits need to be observed. Fortunately, regulation of the recreational and commercial fishing of barramundi is well-established, as are guidelines for the translocation of this species. Although recent data suggests that commercial barramundi harvesting has little impact on other species (i.e. bycatch), there still exists the potential impact of gill netting on highly susceptible species such as sawfishes or rare taxa such as Glyphis sp. A. Illegal netting for barramundi does occur in north-eastern Australia and it is most unlikely that strict adherence to size limits or prompt release of bycatch occurs in these cases. Recreational fishing has the potential to reduce barramundi abundance in some freshwater habitats with consequences for the maintenance of other freshwater species and of assemblage structure. The imposition of rotational closures for individual reaches in some rivers may have merit.
The translocation of barramundi into impoundments is not without some ecological risk, especially if receiving waters are located above natural barriers to movement (e.g. Lake Dalrymple on the Burdekin River is located above a set of falls which historically limited the upstream colonisation of many species) or are beyond the usual limit of upstream penetration (e.g. Eungella Dam is located in the headwaters of the Broken River and these reaches of the river were not historically colonised by barramundi). In some circumstances, particularly when receiving waters are located far upstream or above barriers, the native fish community may be poorly adapted to co-exist with a large predator. The introduction of the closely related Nile perch (L. niloticus) into Queensland’s freshwaters was strongly opposed because this large predator can breed in freshwater and it was predicted to have undesirable ecological cosequences [131]. There seems little reason not to expect that barramundi, being similarly sized and similarly piscivorous, will not also have negative environmental impacts simply because it cannot breed in freshwaters. Barramundi are long-lived and there is little difference between the continual replenishment of stocks by artificial means and natural replenishment in a species in which spawning grounds are spatially distinct from juvenile and subadult habitats, with the exception that stocks may be culled (by cessation of stocking) if desired. Over 5 million barramundi have been stocked in Queensland waters.
Third, and perhaps most importantly, the complex life history of barramundi involving changes in habitat use with age requires that habitat management for this species be undertaken with a view to maintaining all of the links in the ‘critical chain of habitats’. Thus, activities such as the reclamation of supralittoral swamps or the construction of bund walls to limit saline tidal penetration into areas of ponded pasture, must be strictly controlled to maintain connectivity. Similarly, activities that impact on tidal
Concern about the extent to which barramundi may concentrate heavy metals or accumulate pesticide residues has been expressed, given that this species is a top-level predator. For example, Jabber et al. [640] recorded
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creeks and mangrove areas need to be regulated tightly. Loss of floodplain waterbodies and wetlands needs to be limited. Restoration, or even the construction of new wetland habitats as has occurred in some parts of the Tully River floodplain, may be an important step in overall management of this species. The loss of woody debris from some rivers may need to be addressed in order to restore habitat value for barramundi and refuge for prey species. Not only must the various links in this chain be maintained but the ability to move between habitats is of utmost importance. Reservoirs, weirs, barrages and sand dams all have the potential to act as barriers to passage.
Fish passage devices must be able to allow both up- and downstream movement. Flow regulation, particularly the capture of large flows that may trigger movement or the inundation of floodplain habitats, may impact severely on this species. Finally, it should be recognised that the piscivorous nature of barramundi coupled with increasing pressure to translocate this species into reservoirs and river reaches in which it was historically absent, may mean that the presence of barramundi is itself a threatening process for other fishes and crustaceans.
325
Macquaria ambigua (Richardson, 1845) Yellowbelly, Golden perch
37 311075
Macquaria sp. B (after Musyl & Keenan, 1992 [981]) Lake Eyre drainage golden perch Family: Percichthyidae
Description Dorsal fin: VIII–XI, 11–13, fourth and fifth spines longest; Anal: III, 7–10; Pectoral: 15–18; Caudal: 17; Pelvic: I, 5, first ray elongated to form filaments; Lateral line scale rows: 50–63; Vertical scale rows: 40–56, 15–18 above lateral line, 28–38 below; Gill rakers 18–24; Vertebrae: 24–28 [52, 830, 936, 989]. Figure: adult specimen, composite, drawn from photographs, 2002.
[552], with an estimated L infinity of 611 mm for M. ambigua from impoundments in the headwaters of the lower Darling, Murrumbidgee and Murray rivers [857]. This species is reported to grow as large as 27 kg [751] but whether this was in rivers, impoundments or artificial ponds was not stated. Age determination using thinsectioned otoliths (and validation of annual growth marks against fish of known age) was considered accurate to nine years of age [857], confirming earlier work by Anderson et al. [59]. In the Murrumbidgee River the oldest golden perch was estimated to be 26 years old (a male fish 533 mm total length, weight 1.8 kg) [857]. The maximum age observed in Lake Keepit and the Namoi River was 19+ years [143].
Macquaria ambigua is a moderate to large percichthyid known to reach 760 mm and 23 kg, commonly 400–500 mm and less than 5 kg [52, 815]. The relationship between length (TL in cm) and weight (kg) for 110 M. ambigua collected from the River Murray between Waikerie and Renmark is W = 3.34 x 10–6 L3.45 [670]. Anderson et al. [59] provided the following equation relating length (mm) and weight (g) for 881 (range 100–600 mm) individuals of M. ambigua collected from the Murray, Goulburn Broken, Campaspe Loddon, Edward and Wimmera rivers and several impoundments; W (g) = 3.34 x 10-7 L3.66. MallenCooper and Stuart [857] estimated maximum sizes (L infinity, total length) of 354, 418 and 502 mm total length for populations in the Darling, Murray and Murrumbidgee rivers, respectively. Fish stocked in impoundments often grow larger than those in rivers
Macquaria sp. B (the central Australian form of M. ambigua) may reach 600 mm and 5.6 kg [1354] but is commonly 1–2 kg [822]. The Fitzroy Basin subspecies M. ambigua oriens has been reported to range from 1.5–2.5 kg [1028]. Macquaria ambigua has an elongate-oval and laterally compressed body with a tapered snout; forehead with distinctive concave profile above the eyes in older specimens, the nape is strongly arched and the lower profile of the body is weakly convex. Eyes large; head deep and laterally compressed; mouth large, terminal, forming an 326
Macquaria ambigua
oblique cleft, maxilla extending to below centre of eye in adults, lower jaw protruding slightly beyond upper in larger individuals. Villiform teeth occur on palatines but not on ectopterygoids. Dorsal margin of supraoccipital crest laterally expanded to form narrow roof under skin of nape. Preoperculum finely serrate; operculum with two flat spines, the lower more prominent. Large open pores present on snout, lower jaw and lower preoperculum. Scales small to moderate size, predominantly ctenoid with fine ciliation. Snout naked, cheeks and gill covers with small ctenoid scales. Dorsal fin continuous, without a distinct notch between spiny and soft-rayed portions, caudal fin distinctly rounded, sometimes almost truncate [52, 830, 989].
waters. Based on genetic differentiation, Musyl and Keenan [981] divided ‘Macquaria ambigua’ into two different species, each comprised of two distinct subspecies. Macquaria ambigua (the Murray-Darling golden perch) is naturally confined to the Murray-Darling River system. Golden perch found in the Fitzroy River system (Dawson and Nogoa rivers) of central eastern Queensland represent a subspecies of the Murray-Darling form, named Macquaria ambigua oriens (Fitzroy River golden perch). Populations of Macquaria ambigua from the Murray-Darling Basin and the Dawson River exhibit extensive morphological divergence and can be separated with 100% confidence using 10 morphological characters [980].
Dorsal colouration of adult M. ambigua varies from dark brown to olive-green or bronze, becoming lighter to yellow and white on the lower sides and ventral surface (hence the name ‘yellowbelly’). Median fins are grey to blackish, and reddish or white borders may be present; paired fins are dusky grey to yellowish. Juveniles are silvery with scattered grey mottling on sides and dusky fins [52]. Colouration appears to be related to water colour [552]. Macquaria sp. B from the pale turbid waters of the Lake Eyre drainage are generally lighter in colour than those from the Murray-Darling river system and the Dawson River in Queensland [822].
Macquaria sp. B (Lake Eyre drainage golden perch, also known as the central Australian form of M. ambigua), is believed to be a new, as yet undescribed, species [981]. Macquaria sp. B also occurs in the Bulloo River [947] and this population has been recognised as a distinctive subspecies (the Bulloo River golden perch) based on the presence of a unique array of alleles [981]. Separation of the Murray-Darling and Lake Eyre basin forms of Macquaria ambigua is believed to have coincided with the late Tertiary dry phase in central Australia when drainage basins became isolated. Musyl and Keenan [981] describe how golden perch from the Murray-Darling Basin could have been translocated naturally into the contiguous Fitzroy drainage. Volcanism, flooding or stream capture could have translocated fish from the nearby Murray-Darling Basin into waterbodies (e.g. temporary lakes and swamps) that straddle the Great Dividing Range (GDR). Later, tectonic or volcanic activity could have tilted these waterbodies so that fish confined to them were ‘tipped’ into waterbodies on the eastern coast. An alternative mechanism may have involved stream capture brought about by ‘the slow westward migration of the GDR eroding and pirating the headwaters of westerly flowing streams, thereby translocating fish directly from western to eastern drainage basins’ [981].
Systematics Macquaria ambigua, also known as yellowbelly in New South Wales and as callop in South Australia, has been placed in two basal percoid families, the family Percichthyidae by Gosline [465], and the family Serranidae by Greenwood et al. [474]. Gosline [465] and MacDonald [830] made a case for separation of M. ambigua and other Australian percichthyids from the marine serranids, however, according to Musyl and Keenan [981], the phyletic integrity of the two families remained to be clarified. As defined by Gosline [465], Percichthyidae occurs worldwide in saline and freshwaters in subtropical and temperate areas, and is composed of about 40 species in 18 genera [888]. Johnson [656, 657] considered the Percichthyidae of Gosline [465] to be a polyphyletic group, and redefined the Percichthyidae to include only fresh and brackish-water genera found in Australia and South America. MacDonald [830] synonymised the three most generalised Australian genera (Percalates, Macquaria and Plectroplites) and assigned them to the genus Macquaria on precedence. He recognised seven species of Australian freshwater percichthyids and placed them in three genera. Musyl and Keenan [981] recognised three genera (Bostockia, Maccullochella and Macquaria) and 13 species/subspecies in Australian fresh and estuarine
Synonyms for M. ambigua include Datnia? ambigua Richardson, 1845; Dules ambiguus Günther, 1859 (redescription and re-allocation of type series of Richardson 1845); Plectroplites ambiguus Gill, 1863; Ctenolates macquariensis Günther, 1871; Dules auratus Castelnau, 1872; and Dules flavescens Castelnau 1875. This species was allocated to Macquaria ambigua by McDonald [830], although he noted that the genus was variable with respect to several key diagnostic characters. A recent phyletic analysis by Jerry et al. [654] using DNA sequencing techniques revealed that the Percichthyidae was composed of six genera (Bostockia, Nannoperca,
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from the 11 Murray region sites compared to 191 from 11 Darling region sites. This species was not collected from the North and South Coast regions even though it has been stocked into some rivers in these regions, and/or has dispersed into coastal rivers from impoundments [553].
Nannatherina, Macquaria, Maccullochella and Gadopsis) (but see relevant chapter for Guyu wujalwujalensis). Macquaria was clearly polyphyletic, with M. novemaculeata and M. colonorum grouping in a clade with the various species of Maccullochella, and M. ambigua grouping with G. wujalwujalensis and M. australasica within a subclade, within a larger group containing Bostockia and the various pygmy perches.
Macquaria ambigua oriens is widespread in the Fitzroy River having been collected from the Fitzroy River proper [659], and the Connors, Isaacs, McKenzie, Dawson, Comet and Nogoa rivers [160]. This taxon was present at 10/11 primary study sites and a further 6 of 8 secondary sites in the study of Berghuis and Long [160], but was rarely abundant (average catch <4 individuals per sampling occasion) except at one site in the upper Nogoa River (28 individuals in one sample). These authors cite unpublished data indicating that abundance levels are frequently high at this site located in the headwaters of the Nogoa River above the Fairbairn Dam, and suggest that the impounded waters of the dam may have created ideal conditions for this species. Midgley [942] found M. a. oriens to be widespread and common but expressed concern about declines in abundance in the Dawson River due to the imposition of barriers that may prevent movement, and poor landuse practices. Midgley [942] suggested that the exclusion of barramundi from the lower reaches of the Fitzroy and McKenzie rivers by the tidal barrage may benefit M. a. oriens by reducing competition for food.
Distribution and abundance West of the GDR, populations of Macquaria ambigua are found throughout the Murray-Darling Basin, except at high altitudes and above large impoundments [52, 936]. Macquaria sp. B occurs naturally throughout the Lake Eyre Basin (Georgina and Diamantina rivers, Thomson River, Cooper Creek, the Barcoo River and Lake Frome). Macquaria sp. B, new subspecies (Bulloo River subspecies of golden perch) is considered to be common in the Bulloo-Bancannia drainage [1354]. Macquaria ambigua oriens is found in the Fitzroy River system of central eastern Queensland and is the only population believed to occur naturally east of the GDR. Macquaria ambigua (Murray-Darling stock) has been widely translocated into rivers along the eastern seaboard (e.g. the Mary and Brisbane rivers in south-eastern Queensland and the Hunter River in New South Wales). Other eastern populations are believed to be escapees from the numerous farm dams and impoundments where the species has been introduced [552]. The population present in the Burdekin River is apparently the result of escapes from an aquaculture facility during an extreme flood event, but may also include fish from farm dams [1082]. It is now widespread in this system. In addition, some earlier stocks in the Burdekin River were apparently sourced from the Thompson River, within the range of Macquaria sp. B. (D. Burrows pers. comm.). Macquaria ambigua has been stocked twice in the Hay-Plenty River drainage, once in Whistleduck Creek on the Barkley Tablelands and once into Clayton Bore, which flows towards Lake Eyre [1341, 1354]. Translocated populations also occur in southern Victoria (details in Brumley [244]), Western Australia and northern Australia [989]. Hatchery bred fingerlings of Macquaria sp. have been stocked into the Thomson River catchment (e.g. Lake Dunn) [1354]. Note that these translocations include many outside of the natural range and include translocations into systems containing genetically distinct forms.
In the Lake Eyre Basin, Long and Humphery [822] recorded Macquaria sp. B at seven sites: the Broadwater (Thomson River), the Big Boomerang (Barcoo River), Currareva waterhole (Cooper Creek), and four sites on the Diamantina River. Bailey and Long [121] recorded Macquaria sp. (presumably Macquaria sp. B) at every site examined (n = 12) within the Lake Eyre drainage. This species contributed 21.7% ± 4.9 (SE) of the total number of fish collected in this study but was relatively rare in the Georgina River catchment (1.5–3% of the catch). A recent study (2001–2003) of fish assemblages in the Thomson River, Cooper Creek and Kyabra Creek (Lake Eyre drainage) recorded Macquaria sp. B in all 15 waterholes surveyed during a dry period, April 2001. Golden perch abundances (CPUE based on standardised sampling using three fyke nets per waterhole, set overnight for 19 hours) were highly variable between waterholes (CPUE 3–82) (Arthington and Balcombe, unpublished data). Macro/meso/microhabitat use Macquaria ambigua inhabits rivers, creeks, billabongs and lakes of the lower Murray-Darling river system. It prefers habitats containing relatively deep, slow-flowing water, cover, shade and shelter [143]. Radio-tracking studies in the Ovens and Murray rivers have documented strong associations of M. ambigua with woody debris [728]. In a
The NSW Rivers Survey [553] conducted in 1997 found Macquaria ambigua to be the most widespread large fish species in the State, present in all lowland sites and one slopes site in the Darling region, and at 11 sites in the Murray region [1201]. Only 37 individuals were collected
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Table 1. Physicochemical data for the Murray-Darling golden perch, Macquaria ambigua, in the Murray-Darling Basin [52, 750], Macquaria ambigua oriens in the Fitzroy River [942] and the Lake Eyre golden perch, Macquaria sp. B, in the Thomson, Barcoo, Cooper and Diamantina drainages [822]. Sample size is denoted by n. Note the different units used for conductivity and total dissolved solids (TDS). Values in parentheses represent measurements taken at depth.
lowland reach of the Broken River, Victoria, golden perch were strongly aggregated and positively associated (during both daytime and at night) with deep pools of low current velocity and sandy substrates [1050]. Strong selectivity for microhabitat features such as submerged wood, aquatic macrophytes and overhead canopy cover was also observed during the day [341]. At night, microhabitat selectivity generally decreased but the preferred macrohabitat was still deep, slow-flowing pools with canopy cover.
Parameter
In Cooper Creek, within the Lake Eyre drainage, Macquaria sp. survive in isolated, highly turbid waterholes remaining on the floodplains of the ‘channel country’ during dry periods. Most Macquaria sp. were captured from waterholes with complex basin shape (Arthington and Balcombe, unpublished data).
Min.
Max.
Mean
Macquaria ambigua (n = >100) Temperature (°C) 4 35 Dissolved oxygen (mg.L–1) 3 15 pH 7.1 7.8 Conductivity (µS.cm–1) 224 3000 Secchi disc depth (cm) 12 240
Environmental tolerances Information on tolerance to physicochemical extremes is lacking, apart from a few specific studies discussed below. The data listed in Table 1 are derived from records of the water quality of rivers, lakes and waterholes where M. ambigua and Macquaria sp. have been collected. The broad range of water quality conditions shown in Table 1 reflects the wide range of habitats in which Macquaria ambigua and the Lake Eyre species of Macquaria occur. Both species are able to tolerate a wide range of temperatures and low dissolved-oxygen levels, and generally live in neutral to slightly basic waters. Like several other percichthyids, M. ambigua can make the transition from fresh to saline waters (up to 33 g.L–1); juveniles display the same osmoregulatory capacity in salinities up to 9 g.L–1 [765]. Macquaria sp. is reported to encounter high salinities in hypersaline Lake Eyre, where the maximum conductivity recorded in a waterbody (Lake Katherine, Georgina River) supporting Macquaria sp. appears to be 2000 µS.cm–1, possibly caused by groundwater intrusion [121]. In the Cooper Creek drainage, Macquaria sp. is more often found at far lower salinities (<50 µS.cm–1) [249].
Macquaria ambigua oriens (n = 7) Temperature (°C) 24 31 Dissolved oxygen (mg.L–1) 3.6 10.0 pH 7.2 8.8 TDS (ppm) 70 160 Secchi disc depth (cm) 4 40
26.7 6.3 7.8 105 19.7
Macquaria sp. B (n = 228) Temperature (°C) at surface 25 33 Dissolved oxygen (mg.L–1) 2.2 5.8 at surface (1.4) (3.0) Conductivity (µS.cm–1) 90 144 Secchi disc depth (cm) 1.5 15
27 3.37 (2.2) 124 5.6
confinement in, or transfer to, shallow tanks which did not allow the fish to remain upright); fish showed increased plasma levels of cortisol and lactate, however glucose levels did not increase until at least 10 minutes after the stress was initiated [281]. The typical hyperglycaemic response was observed after 30 minutes of stress, suggesting that glucose was being regenerated from lactate or liberated from body stores of glycogen, lipid or protein to maintain high metabolic readiness [281]. Golden perch were considered to have the ability to recover rapidly from both acute and chronic stress. Larvae and fry of M. ambigua have been reared in ponds under the following physicochemical conditions: temperature range 17–26°C (diurnal range up to 8°C), oxygen 3–15 mg.L–1, pH 7.6–9.7, Secchi transparency 35–120 cm, nutrients (total dose of N = 4.96 g.m–2, total dose of P = 2.33 g.m–2, total dose of K = 1.75 g.m–2) [427]. High mortalities of M. ambigua larvae recorded in non-aerated experimental systems treated with litter from Eucalyptus camaldulensis were considered to be due to a combination of hypoxia and polyphenol toxicity [439]. Polyphenols precipitate protein, leading to deactivation of enzymes in the branchial epithelium and disruption of the respiratory surface ([439] and references therein). Golden perch
Macquaria ambigua is typically found in turbid lowland rivers [52]. This species is apparently common in the Belyando River within the Burdekin River basin where turbidity values are routinely above 400 NTU [256]. Habitats in which M. a. oriens occurs in the Fitzroy River are also highly turbid [942] and Macquaria sp. B also occurs in highly turbid floodplain waterbodies where Secchi disc depths as low as 5 cm are common [249]. It also occurs in river and floodplain sites with Secchi depths up to 12 cm [822]. In spite of its wide tolerance, M. ambigua held in aquaria responded rapidly (<5 min) to stressors (netting and
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model by Harris and Gehrke [550] who added a water quality component. Recent studies and a review of the primary data drawn from field observations dating back to the 1940s have led Mallen-Cooper and Stuart [857] to challenge the concept of obligate flood-cued spawning and recruitment in M. ambigua. The most relevant studies are reviewed here.
larvae and juveniles have the ability to modify their behaviour when exposed to leachates from Eucalyptus camaldulensis litter, and this response has been implicated in the avoidance of experimentally inundated floodplain habitat by larvae [433]. Inundation of areas receiving as little as 166 g.m–2 litter per annum may produce water that is not suitable for survival of M. ambigua larvae, especially very young larvae [439]. Toxic effects may be reduced if oxygen levels remain near to saturation.
Lake [750, 751] recorded spawning of golden perch (as Plectroplites ambiguus) at temperatures at or above 23.6°C, but spawning may occur at lower temperatures, possibly as low as 17°C [451]. Spawning activity was observed as follows [750]: three male fish of about 1 kg and one female fish weighing about 4.4 kg were seen near the surface in the flooded area of an experimental pond some 45 hours after inundation. The males repeatedly ‘nosed the cloacal region of the female and used their snouts to bump the female in this area and along the ventral sides of the body’ [750]. The female remained placid with her head pointing downward at an angle of about 60°, her tail occasionally breaking the surface. This behaviour continued for about four hours until dusk; spawning evidently occurred soon after dark, in relatively clear water with a Secchi depth of 63 cm and temperature >24°C. Spawning occurred most frequently within 3–5 hours after sunset, irrespective of the time of filling of the pond. Spawning did not occur even at suitable temperatures if the pond was filled and the water level kept constant, or lowered, however raising the water level and inundating the pond stimulated spawning [750].
Reproduction Quantitative information on the reproductive biology of M. ambigua from the Murray-Darling river system is available from the experimental studies of Lake [750, 751], various field and laboratory observations and a detailed analysis of age, growth and recruitment in the middle Murray River [857]. Details of these studies are given in Table 2. This species spawns and completes its entire life cycle in freshwater, although all natural stocks have at least sporadic access to more saline waters [765]. It has been bred in captivity by inundating small artificial floodplains [750, 751], and using hormone treatments to stimulate spawning [1160, 1162]. Male M. ambigua from the middle reaches of the Murray River near Torrumbarry Weir matured (i.e. reached reproductive stage II) at three years of age (occasionally at two years) at a minimum length of 32.5 cm; females reached maturity at four years or greater, at a minimum length of 39.7 cm [857]. Males in mature stages (III and IV) had GSI values >0.3% but a few spent and spawning males aged 2+ years had GSIs <0.25%. Females aged four years and older had significantly developed gonads (GSI >1.0%) and involuting or spent ovaries, with one exception, an involuting 3+ year-old fish [857]. Mackay [834] recorded a mean maximum GSI of about 15 for females from a small tributary of the Lachlan River, central southern New South Wales. Mean GSI values of 14–15 were maintained from November to early January; and fell to 3.1 in March after extensive flooding in late January to early February. This difference was considered to indicate that spawning had occurred sometime during the flood [834].
According to Cadwallader [265], J.O. Langtry reported golden perch spawning in the Murray and Murrumbidgee rivers during rises, and occasionally, falls in river levels. Flows for the dates recorded by Langtry in the 1940s varied from overbank conditions to major rises in water level that were contained within the main channel [857]. Langtry, cited in Cadwallader [265], considered that when spawning occurred in spring it coincided with the ‘first rise in the river’. Seasonal changes in the ovaries of M. ambigua from a tributary of the Lachlan River observed by Mackay [834] recorded spawning in spring and summer, mostly during a flood, but some fish evidently spawned before the flood. Mackay [834] also observed spawning in the Murrumbidgee River (at Narrandera) during a substantial rise in river level in November (1968), when flows were contained within the riverbanks. Jones [670] noted that in three of four years when spawning occurred in the Murray River between Waikerie and Renmark, river levels reached higher flood peaks (described as ‘heights above pool level’) than in years when golden perch failed to spawn [670]. He commented that the timing of flooding (late November and December) was more important than the extent
Various studies indicate that M. ambigua has an extended breeding season from September to March/April in the Murray River. The stimulus for spawning has been the subject of recent conjecture. Lake [750, 751] induced spawning in this species (as Plectroplites ambiguus) by inundating small, artificial floodplains, and from his studies proposed a flood-recruitment model for M. ambigua consistent with the contemporary ‘flood-pulse concept’ [674]. This model has been supported over the years by Mackay [834], Jones [670], Reynolds [1129, 1131] and Rowland [1160] and was elaborated into a conceptual
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mid-November 1998. They concluded that spawning of M. ambigua was not associated with river rises in the Murray River between Mulwala and Barham. Humphries et al. [614] proposed the ‘low flow recruitment hypothesis’ to explain the life history strategy of Murray-Darling fishes that spawn in association with low spring flows confined within river channels. They grouped M. ambigua in their ‘mode 2’ life-cycle style, containing species believed to use in-channel habitats such as still or slow-flowing littoral areas, backwaters and shallow embayments as nursery habitat. Humphries et al. [614] suggest that fish larvae
of flooding because elevated flows at this time of year coincided with suitable water temperatures (>23°C) whereas there was no evidence of successful spawning associated with elevated flows in September and October when water temperatures were <23°C [670]. Battaglene [139] collected spawning golden perch from the Manilla River in March 1982 during a major rise in river level that was contained within the river channel. More recently, Gilligan and Schiller [451] recorded peaks of spawning activity and golden perch eggs at stable regulated flows before, and two weeks after, a river rise of 14 000 ML in
Table 2. Life history data for Macquaria ambigua from the Murray-Darling Basin. Information on reproductive biology drawn from a number of studies undertaken under experimental and wild conditions. Age at sexual maturity (years)
Maturation of Murray River populations commences at 2–3 years in males, 4 years in females [857]
Age at spawning(years)
Spawning of Murray River populations occurs at 2–3 years in males, 4 years in females [857]
Minimum length of ripe females (mm)
397 mm [857]
Minimum length of ripe males (mm)
325 mm [857]
Longevity (years)
Oldest female (from Murray River) 11 years, 47.2 cm total length, weight 2.2 kg. Oldest male (from Murrumbidgee River) 26 years, 53.3 cm total length, weight 1.8 kg. Growth rates of males and females not significantly different [857]
Sex ratio
?
Spawning activity
September to March/April in Murray River [857]
Critical temperature for spawning
At or above 22.5°C [139, 1160, 1162]; 23.6°C [750, 751]; as low as 17°C [451]
Inducement to spawning
First rise in river level (Langtry, cited in [265]); rising water levels that inundate dry ground, at temperatures above 23°C. and ‘freshets’ in the river, at specific temperatures [750, 751]; major rise in river level within river channels [139, 834, 857]; species is not dependent on out-of-channel floods for spawning/recruitment; spawning strategy is flexible; spawning can occur during droughts, and sometimes occurs during floods [834, 857]
Minimum GSI of ripe females (%)
>1.0 [857]
Minimum GSI of ripe males (%)
>0.25–0.30 [857]
Fecundity (number of ova)
300 000–500 000 [52]
Fecundity/length relationship
At least 500 000 from a 2.5 kg female [815]
Egg size (diameter in mm)
Mature oocytes are spherical, diameter of 1.1 mm; fertilised and water-hardened eggs are 3.3–4.2 mm (mean 3.9) [751]
Frequency of spawning
Gonad maturity maintained over extended period, September–March/April; females may release only a fraction of their eggs when conditions are less than favourable [143]; fish failing to spawn resorb their gonads by involution, usually in February/March in the Murray-Darling Basin [143, 751, 1159]
Oviposition and spawning site
Spawning takes place near the surface within 3–5 hours after sunset [750]
Spawning migration
Spawning believed to be preceded by substantial upstream migration [139, 858, 1131]. Females migrate greater distances than males, with 3% of fish (mean length 41.7 cm) migrating over 1000 km [1131]
Parental care
None [834]
Time to hatching
33–34 hours at 24–25°C [751]
Length at hatching (mm)
3.1–3.4 (mean 3.2) mm [751]
Length at feeding (mm)
5.9 mm total length [751]
Age at first feeding
6 days, teeth evident at 10 days, 7 mm [751]
Age at loss of yolk sac
At 5–6 days yolk almost completely absorbed [751]
Duration of larval development
18–20 days [751]
Length at metamorphosis
9.5–11.5 mm [751]
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Freshwater Fishes of North-Eastern Australia
using these habitats are able to take advantage of high concentrations of very small benthic invertebrates and potamoplankton prey. Larvae of M. ambigua attain total lengths of 4.7–5.4 mm and mouth gapes of 0.5 mm at first feeding, enabling them to feed on small cladocerans and copepods in flooded habitats [112, 751].
[751] counted as many as 20 in a single egg. Gastrulation commences at about 6 hours and the yolk sac is fully enclosed at about 11 hours. Hatching commences after about 33–34 hours and is completed within one hour at 24–25°C; eggs kept at a temperature of 27–31°C hatch in 24 hours [751].
Mallen-Cooper and Stuart [857] concluded that M. ambigua has a much more flexible spawning strategy than is suggested by either the low flow or flood-cued recruitment hypothesis [857]. This species is definitely not an obligate flood-cued spawner as previously believed, although it has the longevity (up to 26 years) to take advantage of infrequent floods for spawning in the semiarid Murray-Darling river system [857]. In the middle reaches of the Murray River, M. ambigua has been found to spawn on the smaller and more frequent within-channel flows, showing strong recruitment in non-flood years and poor recruitment in flood years [857]. Spawning in response to within-channel flows and rises in water level that do not overtop the banks would sustain recruitment during the often lengthy spells between large overbank floods, and also allow M. ambigua to recruit successfully in areas where there is limited floodplain development. Further spawning activity during large overbank flooding events would supplement low flow spawning and recruitment by enabling larvae to access vast areas of floodplain habitat and food resources [857, 1009]. However, the use of floodplain habitats and food resources by the larvae of M. ambigua is poorly substantiated [614] and remains an unresolved aspect of the life cycle. Gherke [433] found that golden perch larvae made little use of floodplain habitats in an experimental pond-floodplain system. He suggested that adverse environmental gradients, especially low dissolved oxygen concentrations, may have constrained the use of floodplain habitat by larvae of M. ambigua. Later studies established that flooded river red gum litter produced toxic polyphenols that can cause gill tissue damage and disrupt respiration [439]. Humphries et al. [614] also pointed out the risks of dependence on floodplain habitats that occur irregularly in rivers with variable and unpredictable flooding patterns. Whilst larvae may not do so, young juveniles of M. ambigua (50 mm) make extensive use of inundated floodplain habitats [143]. Lake [751] also refers to juvenile and very small golden perch being collected from flooded backwaters.
Pelagic eggs of M. ambigua drift with the current for their short incubation period (24–46 hours). Larvae are small (average length 3.2 mm), poorly developed at hatching, with eyes still lacking pigment and the mouth unformed [751]. They are unable to swim freely and continue to drift in the current, but by 12–15 days are no longer positively buoyant. Metamorphosis takes place at 18–25 days but up to 25 days larvae still have little rheotactic behaviour (swimming against the flow) and cannot hold their position in water flowing at 5 mm.sec–1 [432]. Few larval fish studies have found the eggs and larvae of golden perch [614] even though sampling gear and regimes have been designed specifically to capture drifting larvae [451]. Drifting eggs have been collected after a flow peak in late October 2000 at a temperature of around 17°C. and a smaller number of eggs was collected following a flow peak in late November 2000 at 21°C [1273]. The reproductive biology of the Lake Eyre golden perch is poorly known. Mature Macquaria sp. B from the Lake Eyre drainage have been captured during a spawning migration in December, two weeks after a low level flood event, when males were ‘running ripe’ and females were ‘roed up’ [822]. Given the exceptional variability of river flows in the Lake Eyre Basin [1077], a flexible spawning and recruitment strategy cued to small within-channel flows, but responsive to large floods and floodplain inundation when they occur, would seem to be highly adaptive. Movement Macquaria ambigua has been classified as a potamodromous species [855]. Tagging studies of M. ambigua in the Murray River found that this species moved both up (69%) and down river (17.8%), and that nearly all the long distance movements coincided with the 1975–1976 overbank flood [1128]. During this flood golden perch moved upstream over locks along the lower Murray, and several movements through locks were recorded during nonflood periods when water movements associated with filling and draining of the chamber were thought to provide sufficient stimulus for fish passage [1128]. Several fish moved interstate (from South Australia to Victoria and New South Wales). Cadwallader [265] observed movements of M. ambigua through lock 15 on the Murray River at Euston-Robinvale in October–November and January–February and associated this seasonal migration behaviour with spawning. Reynolds [1131] found that
Eggs of M. ambigua are semi-buoyant, non-adhesive, pelagic and spherical, 3.3–4.2 mm in diameter when fertilised and water-hardened [751], with a smooth, transparent, thin but relatively tough chorion, a large perivitelline space, and usually a single large, anterior oil globule 0.76–0.84 mm. Many small oil globules (0.01–0.10 mm in diameter) may be present in some eggs, and Lake
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Macquaria ambigua
female M. ambigua migrate greater distances than males, with 3% of fish (mean length 41.7 cm) migrating over 1000 km, the maximum upstream distance moved. He proposed that golden perch migrate upstream to spawn in spring, such movements coinciding with increases in water temperature and rising river flows, followed by a downstream migration. Eggs and larvae produced in upstream spawning areas were presumed to drift downstream on high river flows and floodwaters. Reynolds [1131] estimated that unless spawning took place more than 500 km from the mouth of the Murray River, eggs and young fish would be carried to sea and die.
Fitzroy River and they did so only in spring and summer over a wide range of flow conditions (3–100% exceedence flows) [1274].
Battaglene and Callanan [143] recorded movements of sexually mature golden perch from Lake Keepit into the Namoi and Manilla rivers (Murrray-Darling Basin), predominantly in spring (at temperatures of 16–20°C). Male fish formed schools and moved into riverine habitats in advance of females. Mallen-Cooper [858] recorded significant upstream movements of juvenile M. ambigua (greater than one-year-old) through the Torrumbarry fishway, and suggested that such movements probably compensate for downstream drift of eggs and larvae. Return movements of spent golden perch have been observed in the Murray River during slack water [265]). Recent tracking studies in the Murray River have found that golden perch move long distances (>10 km) both upstream and downstream [1009] usually in association with spring/summer temperatures and rising river discharge. Many tagged fish travel up to 80 km downstream in one day, and return after approximately 15 days, indicating that a specifically timed event, possibly a spawning event, may have been involved. O’Connor et al. [1009] suggested that downstream spawning migrations at or close to the peak of high water would be likely to place larvae on the floodplain at times of maximum inundation, and maximum exposure to larval food supplies. Adult golden perch also move onto inundated floodplains [728] possibly to feed in food-rich areas [1009]. Both upstream and downstream movements of M. ambigua have been recorded at weirs. Mallen-Cooper [855] determined that adult golden perch will ascend a vertical slot fishway and that 1.83 m.s–1 (171 m head loss) is an appropriate water velocity for fishways to accommodate this species. At Kennedy’s Weir near the Barmah Forest on the River Murray, most fish passed over the weir gates rather than using the fishway, possibly because its exit represented less than 4% of the width of the wetted weir crest [1009]. Reluctance to enter openings can be due to accelerating water velocity and increasing darkness as well as decreasing wetted area [539].
Macquaria ambigua and Macquaria sp. B from the Lake Eyre drainage are generalised, opportunistic, macrophagic carnivores [130], feeding on large invertebrate prey such as macrocrustaceans (shrimps, crayfish), aquatic (and terrestrial) insects, molluscs, microcrustaceans and fish (Fig. 1). The shape and size of the mouth, dentition, gill rakers and morphology of the alimentary tract are adapted for carnivory and crushing of prey [130]. These species feed during the day and at night but are most active at dawn and dusk [143]. Feeding behaviour varies: some individuals remain in shaded areas or amongst cover and ambush prey as it passes, others move over weed beds flushing prey from cover [936]. From the patchy data available it appears that diet composition varies according to habitat type, locality and time of year. The mean diet of 15 M. ambigua from two riverine localities in the MurrayDarling was 99% macrocrustaceans, whereas populations of this species from impoundments consume fish as well as macrocrustaceans. For example, the population in Lake Keepit on the Namoi River, northern New South Wales, reportedly fed on bony bream (Nematalosa erebi) in winter and crustaceans in summer [143]. Alien fish (Carrasius
Few (17 individuals) M. a. oriens were recorded moving through a fishway located at the tidal barrage on the
Trophic ecology Information on the diet of M. ambigua is available from studies in streams, rivers and floodplain lakes in Victoria [267, 396, 607], two large urban lakes in the ACT [1152] and from the Fitzroy Basin, north-eastern Queensland [937] (Fig. 1). Diet data for Macquaria sp. is available for specimens from the Georgina and Barcoo rivers [937] and Cooper Creek [246] (Fig. 2).
Unidentified (0.2%) Terrestrial invertebrates (0.2%) Algae (0.1%)
Aquatic insects (11.4%)
Fish (13.9%) Other macroinvertebrates (0.1%) Molluscs (0.1%)
Microcrustaceans (18.6%)
Macrocrustaceans (55.8%)
Figure 1. The mean diet of Macquaria ambigua. Data derived from stomach content analysis of 268 individuals from streams, rivers and floodplain lakes in Victoria [267, 396, 607], two large urban lakes in the ACT [1152] and from the Fitzroy Basin, north-eastern Queensland [937].
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Freshwater Fishes of North-Eastern Australia
‘natural’ diet (live Carrasius or frozen bait prawns) [60]. In response to food deprivation adult M. ambigua mobilise energy from hepatic tissue, extra-hepatic lipid, and finally from muscle tissue [324, 325]. Collins and Anderson [324] concluded that golden perch are well adapted to cope with extended periods of deprivation, storing energy as perivisceral fat when food is readily available, and mobilising energy from hepatic and body reserves when food is scarce.
auratus and Cyprinus carpio) have been found to form a large part of the diet of M. ambigua from some areas of New South Wales [267]. In addition, part of the diet may be derived from allochthonous sources, especially terrestrial insects, when fresh ground is inundated by rising lake levels [143] and floodwaters. The mean diet of 69 Macquaria sp. B from the Georgina and Barcoo rivers [937] and Cooper Creek [246] was dominated by fish (63.8%) followed by micro- and macrocrustaceans (15.8% and 11.8%, respectively) and a small component (about 6%) of aerial aquatic insects (Fig. 2). In a 1985 study, Merrick and Midgley [937] found that Macquaria sp. collected from the Georgina and Barcoo rivers in winter had fed exclusively on fish (Nematalosa erebi and Neosilurus sp., respectively). They noted that Macquaria sp. continues to actively hunt at the coldest times of year (10.5–17.5°C) when temperatures are close to the lower lethal limit for N. erebi, and suggest that the sluggish reactions of this prey species may have increased predation success. Macquaria a. oriens from the Dawson River at Orange Weir also fed on small N. erebi in winter [937].
Larvae of M. ambigua begin to feed on the fifth day after the completion of hatching, consuming copepod nauplii, copepodites, copepods, cladocerans and occasionally rotifers [113, 1162]. Copepods dominate the larval diet over the first 18 days of life in aquaria stocked with zooplankton from fertilised earthen ponds. Chironomid larvae and aquatic insects (notonectids and corixids) were found in some juvenile fish after 31 and 38 days [1162]. The larvae of M. ambigua are considered to be inefficient feeders such that relatively high densities of zooplankton are required at the commencement of feeding to ensure survival. Food deprivation for two to eight days after the commencement of feeding significantly reduced larval survival and death followed when larvae were deprived of food to age 10 days [1162]. The size of food items consumed by M. ambigua larvae increases rapidly from gape limited to size dependent to large size selective predation [113]. Peak densities of the zooplankton taxa preferred at each age/size of larvae occur one to three weeks after the filling of earthen ponds [111], making 10–14 days the optimal time to stock ponds with larvae.
In dry season waterholes of Cooper Creek, Macquaria sp. B derives most of its energy from in-channel sources, especially large crustaceans (S. Balcombe, pers. comm.). These dryland waterholes are ultimately sustained by a narrow littoral ‘bathtub-ring’ of benthic algae [249]. Anderson and Braley [60] recorded a relatively lengthy total gut transfer time (96 hr ± 10.13 hr, n = 9) for a single meal, and slow digestive processes in M. ambigua compared to other fish species. Amino acids were considered to be of major nutritional importance in fish fed a Terrestrial invertebrates (0.1%) Aerial aq. Invertebrates (5.9%)
In riverine and floodplain habitats of the lower Murray River, north-western Victoria, juvenile M. ambigua were found to have fed predominantly on microcrustaceans, and aquatic and terrestrial insects (B. Ebner, pers. comm.).
Detritus (0.1%) Algae (0.1%) Aquatic insects (2.6%) Macrocrustaceans (11.8%)
Microcrustaceans (15.8%)
Fish (63.8%)
Figure 2. The mean diet of Macquaria sp. B. Data derived from stomach content analysis of 69 individuals from the Georgina and Barcoo rivers [937] and Cooper Creek [246].
Conservation status, threats and management Wager and Jackson [1353] include M. ambigua, Macquaria sp. B from the Lake Eyre basin and Macquaria ambigua oriens from the Fitzroy Basin in their list of NonThreatened species. The conservation status of Macquaria sp. B (Bulloo River subspecies) was not mentioned in their assessments. Macquaria ambigua is not listed under IUCN and ASFB categories of conservation status. This species was regarded as vulnerable in Victoria almost 20 years ago [273] but its range has been extended by releases of hatchery produced fry by angling clubs and by Fisheries Division, Victoria, between 1982 and 1985 [244]. These releases have extended the range of M. ambigua in rivers such as the Ovens and King rivers, and re-established this species in the upper reaches of the Goulburn River Basin. Many fisheries biologists have commented on the decline or disappearance of M. ambigua from large areas of the
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Macquaria ambigua
works, irrigation or tourist development was predicted to ‘exact a cost in reduced fish recruitment’.
Murray-Darling over the past 40 years, especially higher altitude reaches [244, 266, 269, 752, 1129, 1162]. The main cause of this decline is reported to be habitat degradation arising from the construction of large dams and weirs, altered natural flow and thermal regimes, and obstructions to upstream and downstream migrations. Alterations to natural flow regimes are believed to impact on these species of Macquaria by eliminating or reducing the frequency of river rises and floods that cue migration and spawning [269, 1162]. In particular, the suppression of large floods has been implicated, largely because large floods serve to inundate productive floodplain areas and the availability of these ‘nursery’ habitats has been regarded as essential for high survival of golden perch larvae and juveniles [670, 750, 751, 834, 1129, 1131, 1160]. Mallen-Cooper and Stuart [857] argue that spawning and larval recruitment within the river channel and its backwater habitats would be a more advantageous strategy in rivers with naturally variable flow regimes and unpredictable frequencies of large floods. They suggest that depressed spawning and recruitment are more likely to be caused by the regulation of the many smaller floods that remain within the river channel than by diminution or reduced frequency of large floods, as these cannot be regulated by dams. Restoring some natural variability to within-channel flows would be one way to enhance migration, spawning and recruitment of M. ambigua [857].
Natural populations have declined in upland tributaries in Victoria, such as in the Broken River where several small weirs obstruct migration of fish during all but very high flood waters [244]. The upstream movements of juvenile fish during small river rises are likely to be impeded by even low weirs as these remain effective barriers at such times [552]. Macquaria ambigua used to be common as far up the Murray River as Hume Dam (Lake Hume) but has since disappeared from the Murray above Yarrawonga Weir some 33 km downstream [269]. Cadwallader [269] suggested that Yarrawonga Weir presented a barrier to the recruitment of adults into this section of the Murray River. In addition, Lake Hume is a deep-release reservoir and follows a warm monomictic pattern of thermal stratification. The release of cold hypolimnetic water from depths of about 40 metres has reduced the temperature range in the river by about 6°C, from 7–24°C to 10–21°C, and delayed seasonal changes in river temperature by about one month, with effects diminished but still apparent up to 200 metres downstream [269]. Changes in thermal regime combined with lack of flooding cues and the barrier effects of Yarrawonga Weir have been considered the main causes of the loss of potamodromous species from this section of the river [265, 754]. However, Cadwallader [269] suggested that M. ambigua populations may have been drastically reduced when the first water releases were made from Lake Hume, noting that massive fish kills were reported at that time and attributed to large amounts of eucalyptus oil and ash in the water. The use of copper sulphate to control algae in Lake Hume also caused fish kills downstream [265].
Seasonal flow inversions and unseasonable flows (e.g. supplementary flows to the Murray River that occur for a number of weeks rather than the short-term pulse expected with a summer storm) may increase the risk of displacing both fish larvae and their food sources, and so reduce the chance of successful recruitment [269, 614]. Mature M. ambigua migrate both upstream and downstream in response to rises in river level [857] over distances of tens of kilometres to over 1000 km [1131], even 2000 km [52]. Juveniles also move in response to small rises in flow at various times of year, and larvae drift downstream (and may be carried onto floodplains) in late spring/summer. Barriers to fish movement, such as dams, weirs, culverts and road crossings, can restrict the local and long distance movements of this species duuring most life history stages, thus affecting its distribution and recruitment. Geddes and Puckridge [427] outlined the management implications in floodplain rivers, based on catches of M. ambigua (possibly Macquaria sp. B) from the northwest branch of Cooper Creek and the Coongie Lakes in South Australia. They placed emphasis on the importance of maintaining hydrological connectivity between main river channels and the more ephemeral floodplain habitats used by larval and juvenile M. ambigua [427]. Alienation of the floodplain from the main river channel by salinity
Alien fish such as trout have also been implicated in the decline of fish populations in impounded rivers such as the Murray [269]. The conversion of lentic to lotic habitat favours many alien species [247], whereas the colder water released downstream from stratified reservoirs has extended the range of trout in the Murray River system [269]. Populations of M. ambigua have persisted above some impoundments but isolation over several decades has affected their genetic diversity. The M. ambigua population from Lake Keepit on the Namoi River, New South Wales, isolated above the impoundment for about 40 years, displays much lower mean heterozygosity compared to populations from the Condamine and Murray rivers. Musyl and Keenan [981] suggested that this difference may indicate loss of low frequency alleles via genetic drift. Other impounded fish populations also exhibit low mean heterozygosity [119, 1250]. Musyl and Keenan [981]
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Freshwater Fishes of North-Eastern Australia
limits set by fisheries regulations have the potential to bias the catch towards large females, and also may not be applicable from one river to another. These challenges can be met by establishing growth relationships and minimum size regulations specific to each river system [857].
alluded to the possible effects of reduced genetic diversity on individual fitness and health. Golden perch preferentially inhabit deep sections of rivers and pools [341]. These deep areas are prone to infilling with sand, resulting in loss of hydraulic diversity and habitat homogenisation. Land clearing, river management works, removal of large pieces of submerged wood (‘desnagging’) and reduced frequencies of flows that scour sand from the stream bed are all held responsible for the accumulation of sand slugs in lowland rivers inhabited by M. ambigua [334]. De-snagging, in itself a form of habitat loss, and possibly also responsible for reduced abundance of invertebrate prey, has also been directly implicated in the decline of golden perch populations in the MurrayDarling river system [340].
Techniques are well established for large-scale artificial propagation of M. ambigua using hormone induction of spawning [1160, 1162] and rearing in earthen ponds [552]. In 1996–1997, 2.1 million fingerlings of M. ambigua were produced in aquaculture systems [1031] for stocking purposes. Between 1972 and 1988–1989, New South Wales Fisheries released over five million fingerlings into the wild to enhance recreational fisheries [627]. Macquaria ambigua (or Macquaria sp.) has been mass produced in several Queensland hatcheries with 15 000 fingerlings stocked into sites on the Barcoo River and 10 000 into Lake Dunn on the Thomson River [121]. Government controls have been placed on the translocation and introduction of hatchery reared M. ambigua into river systems where they do not occur naturally, in order to avoid the risks to genetically distinct wild populations, as well as the threat of disease transmission. Thus it is not permitted to stock M. ambigua from the Murray-Darling Basin into Lake Eyre Basin rivers and wetlands.
Macquaria ambigua is highly valued for edible and sporting qualities and forms part of both the recreational and commercial fisheries in inland rivers [1162]. A small commercial M. ambigua fishery operates in the lower Murray-Darling and although declining, contributes onethird to half of the catch from the multi-species fishery averaging 200 tonnes per annum. This species is caught with drum nets and gill nets in still waters. There is a small commercial fishery for Macquaria sp. B in the lower Cooper Creek in South Australia [1354]. Macquaria ambigua is subject to high fishing mortality when it forms large aggregations below major barriers to upstream movement [143]. Fishing mortalities of Macquaria sp. B in the dryland waterholes of the Lake Eyre drainage are not known but the overall decline of all native fishes during a five-month period of progressive drying was estimated to be 93% (Arthington and Balcombe, unpublished data).
Macquaria ambigua fingerlings are believed to be resistant to goldfish ulcer disease (Aeromonas hydrophila) which can cause darkening in color and ulceration of the skin [1164]. Various protozoan parasites are common in golden perch under culture conditions, for example, the coccidian protozoans Goussia and Eimeria observed in the gut of M. ambigua fingerlings caused chronic wasting [766]. Monogenetic and digenetic trematodes, intestinal cestodes, nematodes and the copepod Lernaea and have also been recorded in this species [1164].
Populations of M. ambigua from different areas of the Murray-Darling Basin grow at different rates and achieve quite variable maximum sizes (see above). Minimum-size
336
Macquaria novemaculeata (Steindachner, 1866) Australian bass
37 311034
Family: Percichthyidae
Description Dorsal fin: VII–IX, I, 8–11; Anal: III, 7–9; Pectoral: 12–16; Caudal: 16; Pelvic: I, 5; Lateral line scale rows: 48–55; Vertical scale rows: 25–30; Gill rakers 12–15; Vertebrae: 25 [34, 52, 270, 552, 830, 936]. Figure: adult specimen, composite, drawn from photographs, 2002.
Hawkesbury River (central New South Wales) [548]: log10 W = -4.95 + 3.091 log10 LCF; r2 = 0.971, n = 845, range = ~50–480 mm LCF. Macquaria novemaculeata has an elongate-oval and laterally compressed body [270, 552]. Dorsal head profile straight or slightly concave; snout tapered and of moderate length [270]. Mouth large, terminal, oblique, lower jaw protruding beyond upper jaw and extending to below centre of eye in adults [270]. Numerous villiform teeth in jaws, on vomer and palatines, towards front of mouth [270, 917]. Eyes are moderately large [52]. Upper arm of preoperculum serrated, lower arm with forward-pointing spines. Operculum with two spines, lower spine larger, broader and very sharp [270, 552]. Scales moderate in size, predominately ctenoid and strongly ciliated, extending onto cheeks and opercula, snout scaleless [270, 552, 830]. Single dorsal fin with moderate notch separating spinous and soft rays [552]. Pectoral fins inserted anterior to pelvic fins; anal fin located opposite soft rays of dorsal fin; caudal fin moderately forked [270, 552]. Marked morphological variation may occur between populations from different catchments [652]. This species is sexually dimorphic, with females having deeper bodies and attaining a larger size than males, although this difference may be less
Macquaria novemaculeata is a relatively large species growing to about 600 mm TL and possibly larger, and to at least 3.8 kg, but more common to 1 kg [52, 270, 552, 936]. Jerry and Cairns [652] suggested that individuals from northern populations grow to a larger size than those from more southerly localities. Equations describing the relationship between length (SL, LCF or TL in mm) and weight (W in g) are available for the following populations: Artificial ponds (south-eastern Queensland) [836]: log10 W = -5.26 + 3.23 log10 TL; r2 = 0.985, n = 536, range = 9–80 mm TL; log10 W = -4.77 + 2.93 log10 TL; r2 = 0.983, n = 262, range = 65–151 mm TL. Clarence River (northern New South Wales) [1206]: log10 W = 6.13 x 10–6 TL3.142; r2 = 0.981, n = 273, range = ~100–600 mm TL.
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Freshwater Fishes of North-Eastern Australia
placed M. novemaculeata and M. colonorum in a clade containing all members of the genus Maccullochella, although the distinction between the two genera was great.
pronounced in northern populations [552, 652]. Details on geographic variation in morphology for populations from south-eastern Queensland and New South Wales can be found in Jerry and Cairns [652].
Jerry [650] electrophoretically analysed genetic variation in bass stocks over a range of rivers from the Noosa River in south-eastern Queensland to the Mitchell River in Victoria, and detected only marginal genetic variation (~2%) attributable to site location. However, bass stocks were not behaving as a single panmictic unit, despite the detection of moderate levels of gene flow between populations. A relationship between genetic variation and geographic proximity was detected; samples from Victorian rivers were highly distinctive. A slightly higher (4.3%), although still small amount of genetic variation in stocks from the Noosa River to the Macleay River in New South Wales, was detected by Chenoweth and Hughes [297], using electrophoretic techniques. These authors detected a total of seven different haplotypes using mtDNA sequence analysis to examine these same samples, but haplotype clades were not confined to single rivers or to groups of geographically proximal rivers. The Bellinger River in northern New South Wales contained all seven haplotypes. Extension of mtDNA sequence analysis across a broader geographic range (Queensland to Victoria) by Jerry and Baverstock [653] identified a total of 19 putative haplotypes and an absence of phylogeographic structure, but also noted that rare haplotypes tended to occur in adjacent rivers. The general conclusion of these studies [297, 650, 653] was that gene flow between adjacent rivers was substantial due to the catadromous breeding habit of this species and that the observed variation in genetic structure was consistent with an isolation by distance model. In contrast, and despite evidence for gene flow between populations, Jerry and Cairns [652] identified significant and substantial clinal variation in external morphology (i.e. population specific phenotypes at different locales). They argued that because the observed morphological variation was clinally organised, it was still consistent with an isolation by distance model of gene flow, with genetic exchange limited largely to neighbouring populations. Jerry and Cairns [652] also argued that any discrepancy in the amount of geographic structuring revealed by the two different approaches (i.e. genetic and morphological) may reflect either the different time scales in which genetic and morphological variations are expressed, or that differences in morphology are primarily ecophenotypic (i.e. a consequence of local response to dissimilar environments). Clinal variation in adult morphology may occur during development and early growth in response to large-scale gradients of environmental factors such as water temperature. Interestingly, geographical differences in morphology were much more
Colour of dorsal surface is dark olive-green or grey, becoming lighter on sides, with yellow-white or silvery ventral surface and darker scale margins [34, 270]. Fins grey, colourless or translucent, bases of pectoral fins darker [270]. Anal and pelvic fins with white tips; outer ray on pelvic fin lighter in colour than inner rays. Juveniles (<120 mm TL) have 4–6 faint vertical bars along back and sides (first appearing at 85 days of age or 20 mm TL), dark spot between opercular spines and dark markings on dorsal, anal and pelvic fins [34, 270]. Colouration in preserved specimens as above [34]. Systamatics Macquaria novemaculeata was originally described as Dules novemaculeatus by Steindachner [1261] in 1866. Other synonyms include Dules reinhardti Steindachner, 1867 [1263] and Lates similis Castelnau, 1872 [285]. There has been considerable uncertainty about the taxonomy and systematics of Macquaria novemaculeata (Australian bass) and the morphologically similar estuary perch M. colonorum [830, 1407]. Historically, the Australian bass and estuary perch have been variously considered to represent a single species (often designated colonorum), two subspecies within a single species [1407], or two distinct species. As a result, a confusing synonymy has arisen and in most cases, very little justification has been given for any of the decisions made in this regard [1407]. Both species previously constituted the genus Percalates [1122]. In an ecological and taxonomic examination of the genus Percalates, the existence of two separate species, P. novemaculeata and P. colonorum was established [1407]. A revision of the Percichthyidae [830] again confirmed the Australian bass and estuary perch as separate species based on morphological and osteological dissimilarities. The genus Percalates was found to be invalid and these two species were placed in Macquaria [830]. Although an early attempt to distinguish M. novemaculeata and M. colonorum electrophoretically was inconclusive [830], recent DNA evidence irrefutably demonstrates the existence of two distinct species [654]. While the two species have been considered reproductively isolated [1407], they are now known to hybridise naturally [650]. The recent phyletic analysis of the Percichthyidae by Jerry et al. [654] placed M. novemaculeata and M. colonorum in a clade far removed from remaining members of this genus (Macquaria ambigua, Macquaria sp. B and M. australasica), thus reversing McDonald’s [830] decision to place Macquaria and Percalates in synonomy. Notably, this study
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Macquaria novemaculeata
Microhabitat use During the non-spawning period, adult M. novemaculeata preferred velocities <0.1 m.sec–1 and water depths greater than 2 m in the Tweed River, northern New South Wales [1133]. Fish were collected over a wide range of substrate types but usually in close association with abundant instream cover (especially submerged woody debris, undercut banks and overhanging vegetation) [1133]. Larvae and juveniles recruit to aquatic macrophyte beds (mostly Vallisneria gigantea and Phragmites australis) while migrating upstream from estuarine areas [547, 549].
strongly expressed in male bass (variable at 75% of all characters) than in female bass (28%) [652]. Distribution and abundance Macquaria novemaculeata is a widespread species native to coastal drainages of south-eastern Australia. It is native from streams flowing into Tin Can Bay, south-eastern Queensland, south to at least Wilsons Promontory in eastern Victoria [270, 552]. It also occurs on Fraser Island, south-eastern Queensland. Artificial propagation in fish hatcheries has facilitated the large-scale translocation of this species to rivers and impoundments within and beyond its natural range [268, 552, 593, 1031, 1266, 1342]. The natural northern limit of M. novemaculeata in Queensland is uncertain; this species is possibly native to the Mary River [701], but self-sustaining populations further north in the Burrum, Burnett and Kolan rivers, are likely to be the result of translocations to these catchments [593, 700, 701]. An attempted translocation to Fiji was unsuccessful [1407]. Historically, M. novemaculeata was a reasonably common species, often locally abundant, but natural populations have undergone reductions in abundance in recent years [52, 552]. Males may congregate in large schools (numbering several hundred) in estuaries immediately prior to spawning, but females generally do not form such large aggregations [1342]. Larvae may form schools in brackish tidal areas and juveniles may aggregate in downstream freshwater reaches.
Environmental tolerances Except for salinity requirements, surprisingly little is known of environmental tolerances, especially given the economic importance of M. novemaculeata (Table 1). In south-eastern Queensland, we have collected this species over a relatively narrow range of physicochemical conditions that most likely do not reflect the environmental tolerances of this species (Table 5). Macquaria novemaculeata is euryhaline. It spawns at salinities between 8 and 14 ppt [547] and salinities >10 ppt may be needed for fertilization of eggs and subsequent development [1343]. Salinities between 20–35 ppt are required for successful artificial propagation [146, 1342]. Eggs and sperm die in freshwater [1342]. Juvenile bass may remain in brackish waters until they develop the capability of efficient active osmoregulation against the greater ionic gradients in freshwater [765].
Macro/mesohabitat use Macquaria novemaculeata can be widespread within river systems, ranging from estuarine areas upstream to high elevation tributaries [552, 553]. In the Hawkesbury River, New South Wales, this species was formerly present at altitudes of about 600 m.a.s.l. [552]. Adults occur in a variety of lotic and lentic habitats ranging from upstream incised gorges, lowland riverine habitats, floodplain lagoons, tidal freshwater areas, and estuaries [548]. Adult fish in the Tweed River are frequently collected in deep, slow-flowing pools with abundant in-stream cover [1133]. Males tend to remain in estuarine and lowland habitats while females predominate in lagoons and upstream lotic habitats during non-reproductive periods [547, 549]. Spawning females move downstream to estuarine and brackish tidal waters [547, 548]. Larvae inhabit brackish tidal and estuarine areas and juveniles are often found in tidal and downstream river reaches [547]. Younger age classes are dominant in freshwater tidal habitats [545]. Juveniles (30–60 mm TL) have been collected in riffles and runs within tidal freshwater reaches of the Albert River, southeastern Queensland [1093].
Table 1. Physicochemical data for Macquaria novemaculeata. Data summaries for 22 individuals collected from 11 samples in south-eastern Queensland streams between 1994 and 2003 [1093]. Parameter
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
15.8 5.5 6.3 82.0 3.0
26.1 9.3 8.1 970.0 9.1
Mean 19.6 8.4 7.3 273.5 6.6
Reproduction The recreational importance of M. novemaculeata and the ability to artificially propagate this species is reflected in the considerable research effort expended on reproductive biology and early life history requirements [54, 138, 140, 141, 142, 144, 146, 147, 402, 547, 548, 765, 836, 1031, 1206, 1281, 1342, 1343, 1344, 1407]. Life history details for M. novemaculeata are summarised in Table 2. Male M. novemaculeata mature at a younger age and smaller size than females [270, 402, 547, 552, 1206, 1407].
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South Wales [1133, 1206], from May to September in the Sydney Basin, New South Wales [547, 1407], and June to December in Victorian populations [871]. Elevated autumn discharges are thought to act as a proximal factor in reproduction, stimulating the downstream spawning migration of females, oöcyte maturation and the onset of spawning in brackish tidal and estuarine waters [547]. Low water temperature and low river discharge may delay the onset of the spawning season [270, 1342] and M. novemac-
Harris [547] reported that most males examined from the Sydney Basin were mature by age 3+ years and females by 5+ or 6+ years. Gonadal development commences in autumn corresponding with decreasing temperature and photoperiod. Temperature is probably the ultimate cue for the onset of spermatogenesis [547]; spawning occurs at temperatures ranging from 11 to 24°C [146, 270, 552, 1342]. Peak spawning activity occurs from June to August in the Tweed River and Richmond River, northern New Table 2. Life history data for Macquaria novemaculeata. Age at sexual maturity
Males: 2–4 years (two fish found to be mature at 1+); Females: 5–6 years [547, 552]
Minimum length of ripe females (mm)
200–280 mm TL [270, 402, 552, 1407]
Minimum length of ripe males (mm)
180–200 mm TL [270, 402, 552, 1206, 1407]
Longevity
22+ years; fewer males reach older age-classes [545]
Sex ratio
?
Occurrence of ripe (stage V) fish
In Sydney Basin, running-ripe fish present from May–September (late winter–early spring) [547, 1407]; June–December (winter–spring/summer) in Victoria [871]
Peak spawning activity
June–August in Tweed River and Richmond River, northern New South Wales [1133, 1206]; June–September in the Sydney Basin, New South Wales [547, 1407]
Critical temperature for spawning
11–24°C [146, 270, 552, 1342]
Inducement to spawning
Gonadal development commences in autumn corresponding with decreasing temperature and photoperiod. Temperature probably the ultimate cue for the onset of spermatogenesis [547]. Elevated autumn discharges may act as the proximal factor, stimulating downstream migration of females, final oocyte maturation and onset of spawning [547]. May not reproduce during years of low flow [547]. Low water temperatures and low flows may delay onset of spawning season [270, 1342]
Mean GSI of ripe females (%)
12.7% [547]
Mean GSI of ripe males (%)
3.5% [1133]
Fecundity (number of ova)
Varies with fish size; 49 000 (270 mm LCF) –1 429 000 (446 mm LCF); fecundity may be higher in first batch than in subsequent batches [547, 552]
Total Instantaneous Fecundity (TIF)/ length (mm TL) or weight (g) relationship
TIF = 2279 L – 486 502, r2 = 0.488, n = 15, [1206]; TIF = 288 W + 108 698, r2 = 0.537, n = 15 [1206]
Frequency of spawning
May spawn repeatedly in a season, but probably only a few batches are produced due to relatively short spawning period [547]
Oviposition and spawning site
Important aquaculture species and can be bred in captivity [1342]. Females migrate downstream to spawn in brackish estuarine waters. Spawning habitat may include aquatic macrophyte beds, rocky reefs and sand bars [871]
Spawning migration
Marginally catadromous [890]
Parental care
Probably none
Time to hatching
36–91 hours (at 12–24°C) [140, 402, 1343]
Egg size (diameter in mm)
1.0–1.5 mm (water-hardened) [140, 936]. Eggs are spherical, transparent, non-adhesive and slightly demersal in spawning salinities [270, 547, 552]
Length at hatching
2.5–3.5 mm TL [140, 552, 1342]. Larvae generally poorly developed at hatching (especially at low temperatures [402])
Age at free swimming
1.5 days [140, 142, 936, 1343]
Length at first feeding
4.0 mm TL [140, 142, 936, 1343]
Age at first feeding
3–7 days (temperature dependent) [140, 142, 1343]
Duration of larval development
7 days [140]; 10–14 days [1342]; metamorphosis varies between 20–39 days [140, 146] and 90 days [146, 552]; time to swim bladder inflation varies between 6–11 days at 19°C [142]; survival and rate of larval development dependent on temperature and food density [142]
Length at metamorphosis
4.4 mm TL at 6 days, 5.4–6.2 mm TL at 19 days, 6.4–8.1mm TL at 29 days [140]; 10 mm TL at 35 days [146]; temperature dependent: 4.0–4.7 mm TL after 7 days [1343]; flexion at 6.5 mm [547]; metamorphosis at 20–30 mm [146, 552]
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Macquaria novemaculeata
the relative proportion of the adult population reaching estuarine spawning areas [547, 549]. High discharges also increase the overall area of brackish water habitat suitable for spawning [547]. Furthermore, survival and growth rates of juveniles may be influenced by elevated river discharge as the dissolution of nutrients and organic matter in flooded estuarine and inundated floodplain areas of lowland rivers increases primary and secondary production, consequently increasing food availability [546, 547, 548, 549].
uleata may not reproduce during years of comparatively low flow [547]. Ovarian involution was observed to occur when water levels in the Hawkesbury River did not rise before September [547]. Macquaria novemaculeata spawns at salinities between 8 and 14 ppt, however salinities greater than 10 ppt may be needed for fertilisation, and salinities of 20 ppt may be optimal for larval culture [547, 1343]. Immediately prior to spawning, males may congregate in large schools (numbering several hundred) but females generally do not form such large aggregations [1342]. Spawning habitat may include aquatic macrophyte beds, rocky reefs and sand bars [871]. Macquaria novemaculeata is a relatively fecund species capable of producing an average of 440 000 eggs and up to 1.5 million eggs in larger fish [552]. Schneirer [1206] estimated that fish from the Clarence River (300–452 mm TL) contained between 150 000 and 709 000 eggs and observed a strong relationship between fecundity and fish size (Table 2). Fish may spawn repeatedly in a season, but probably only a few batches are produced due to the relatively short spawning period [547]. Egg numbers may be higher in the first batch than in subsequent batches [547, 552]. Water-hardened eggs are relatively small (1.0–1.5 mm), spherical, transparent, non-adhesive and slightly demersal in spawning salinities [145, 270, 547, 552, 936]. Larvae hatch between 36–91 hours after fertilisation (at 12–24°C) and are relatively poorly developed, ranging from 2.5–3.5 mm in length [140, 402, 552, 1342]. Larvae commence swimming about 1.5 days after hatching and feed between 3 to 7 days after hatching at lengths of about 4.0 mm TL [140, 142, 936, 1343]. Larval survival and rate of development may be dependent on temperature and food density [1344]. Metamorphosis occurs at 20–39 days, at which time larvae are 20–30 mm long, but metamorphosis may take as long as 90 days [140, 146, 552]. Macquaria novemaculeata grow relatively rapidly, reaching 100 mm in the first year, 150–200 mm at two years and 250 mm at three years [552, 1342]. This species is relatively long-lived: Midgley [939] estimated that two large individuals (578 mm TL and 571 mm TL) trapped in a dam in south-eastern Queensland may have been there for as long as 15 years, and Harris [545] estimated that the oldest fish he collected in the Sydney Basin, central New South Wales, was 22+ years of age. In general, adult males have a higher mortality rate than females [549].
Movement Population-specific and clinal variations in morphological traits are evident among M. novemaculeata from different river drainages, suggesting that movement between river systems may be limited [652]. When dispersal between catchments does occur, it is likely to be confined to geographically close populations [652]. Allozyme and mtDNA evidence suggest however, that the level of population structuring is probably only slight, with substantial gene flow occurring among neighbouring populations, conforming to an isolation by distance mode of gene dispersal [296, 297, 650, 653]. Evidence from tagging return data suggests that at least limited dispersal may occur between proximate drainages [297]. A single adult fish was recaptured in Serpentine Creek (lower Logan River), approximately 80 km away from its original tagging location in an adjacent catchment, the lower Brisbane River [1198]. In addition, an anecdotal account exists of a single specimen being collected almost 5 km off-shore in central New South Wales soon after flooding [1407]. Macquaria novemaculeata is considered to be a ‘marginally’ catadromous species [890]. Adults (primarily females) undertake seasonal downstream migrations to spawn in brackish tidal and estuarine waters. Elevated discharges during autumn and winter are thought to stimulate downstream movement of spawning females [547]. Adults may not undertake downstream spawning migrations in years of low discharge [547]. Adult females in the Sydney Basin generally migrated downstream in May and June [547]. In the Tweed River, progressive downstream increases in gill-net catch rates were documented from December through to August, indicating downstream movement coinciding with the period of peak reproductive activity in autumn and winter [1133]. Tagging return data also indicated that downstream movement had occurred at some time between June and October [1133]. A similar seasonal pattern was observed for fish in rivers of central New South Wales [1407]. Tagging return data from fish in the Brisbane River also suggest downstream movements of adults during autumn and winter [1198]. Furthermore, Stuart and Berghuis [1276] recorded adults
Reproductive success of bass may be positively related to the magnitude of river discharge during the spawning season. Evidence from populations in the Sydney Basin indicates that recruitment and subsequent year-class strength of bass populations were positively related to the magnitude of river discharge during the spawning months [407, 547, 549]. High discharges are thought to influence
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Freshwater Fishes of North-Eastern Australia
water depths of only 0.5 cm at velocities less than 0.5 m.sec–1, but a minimum depth of 3 cm was considered suitable for passage of 100% of individuals [1133]. Adult fish (283–357 mm TL) could negotiate velocities as high as 2.1 m.sec–1 and depths as low as 2.5 cm, however 50% of individuals successfully negotiated velocities of 1.85 m.sec–1 and 100% negotiated depths of 20 cm. [1133]. Bishop and Bell [188] suggested that adult bass may be able to swim against water velocities as high as 2–4 m.sec–1, for at least short periods of time.
moving downstream through a tidal barrage fishway in the Burnett River, south-eastern Queensland. Following spawning, males may remain in downstream and estuarine waters while females migrate further upstream, leading to sexual segregation during the nonbreeding season [552]. The return of adults to freshwater and upstream migration is suggested to occur from August through to October/November in New South Wales but may occur later in Victoria [270, 1342]. Tagging return data from fish in the Brisbane River suggest that adult fish move upstream during spring and summer [1198]. Following spawning, adult fish appeared to return to upstream reaches of the Tweed River by December [1133]. Harris [542] suggested that following spawning, adult fish migrate upstream and may return to the same pool following. Juveniles are thought to migrate upstream during spring and summer and possibly only during periods of stable low flow [543, 544, 552]. Low numbers of juvenile fish were recorded moving upstream in the Burnett River between late spring and early autumn, but the major upstream migration occurred in late summer [1276]. Laboratory evidence suggests that larvae begin schooling at about 45 days and juveniles may commence upstream dispersal migrations at two to three months of age [402]. Development of the active osmoregulatory system of juvenile bass may stimulate and facilitate their movement into lower salinities upstream [765]. Juvenile bass have been reported to migrate during stable low flows in the Nepean River, New South Wales [542]. Subadult bass (one to two years of age) may require increase in discharge to stimulate upstream dispersal movements during late summer and autumn [483]. A radio tagging study of non-spawning adult fish indicated that movements occurred over relatively short distances (mean of 414 ± 75 m day–1 and 1571 ± 75 m month–1). These data led Gehrke et al. [442] to conclude that daily movements for most tagged fish were within a home range, except for infrequent excursions over greater distances undertaken by a small number of individuals.
On the basis of his experiments, Mallen-Cooper [853] recommended a maximum velocity through tidal barrage fishways of 1.0 m.sec–1. Further upstream, where migrating juveniles would presumably be larger, a maximum velocity of 1.4 m.sec–1 was considered appropriate [853]. Stuart and Berghuis [1276] observed that juveniles were able to ascend a vertical slot fishway on a tidal barrage in the Burnett River, in which maximum velocities reached 1.4 m.sec–1. Water depths between 30 and 40 cm were considered sufficient for passage of juveniles, but greater depths are probably required to allow passage of adult fish through fishways [853]. Harris [543] suggested that upstream-migrating juveniles may require passage during only a few months, between November and May, and for only a few hours each day [543]. Trophic ecology Diet data for M. novemaculeata juveniles (<~50 mm TL) and larger fish (>~50 mm SL, hereafter termed adults) is available for individuals sampled from rivers, streams and impoundments in south-eastern Queensland [205], northern and central New South Wales [546, 555, 1133, 1206], and Victoria [871]. Macquaria novemaculeata is a euryphagic carnivore capable of feeding on a wide variety of prey. This species possesses a number of anatomical features characteristic of carnivorous fishes, including relatively large eyes, terminal mouth, numerous teeth, large stomach, low ratio of gut length to body length, broad pectoral fins and muscular caudal peduncle [546, 917]. Juveniles generally rely on small-sized food items, switching to larger food items with growth (Fig. 1). The diet of juvenile fish is dominated by aquatic insects (40.2%), and microcrustaceans (33.5%). Small amounts of terrestrial invertebrates (10.1%) and filamentous algae (8.1%) are also consumed. Adult fish consume a wide range of food types including large crustaceans (31.5%), aquatic insects (21.7%) and fish (19.7%) (Fig. 1). Allochthonous food sources are also an important component of the diet of adults with terrestrial invertebrates comprising 17.9% of the total mean diet and aerial forms of aquatic insects and terrestrial vertebrates comprising a further 1.2% and 0.4%, respectively. Relatively small
Macquaria novemaculeata is generally not prone to jumping, indicating that this species may have restricted passage requirements in relation to water depth, velocity and turbulence through fishways [541, 544, 1133]. Experimental tests of juvenile swimming abilities in a vertical-slot fishway revealed that 95% of 40mm juveniles could negotiate velocities of 1.02 m.sec–1, 64 mm juveniles: 1.40 m.sec–1 and 93 mm juveniles: 1.84 m.sec–1 [853, 856]. Mortality of 93 mm fish was observed at velocities greater than 2.0 m.sec–1 [853]. In experimental flume trials, 10% of juveniles (27–38 mm TL) could negotiate velocities of 1.3 m.sec–1. and 50% could negotiate velocities of 1.0 m.sec–1 [1133]. Juveniles could also successfully negotiate
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Macquaria novemaculeata
[1206]. Habitat and sex-specific variation in growth rates are evident in populations from streams of the Sydney Basin [548]. Growth was faster in young female fish from floodplain lagoons and slowest in males from freshwater tidal habitats. Habitat-specific variation in growth rates has been attributed to differences in food availability and population densities between habitats [548]. In experimental feeding trials, increasing zooplankton concentrations had a significant positive effect on larval survival and growth, although larvae were susceptible to overfeeding at high zooplankton densities [147, 1344].
amounts of other aquatic invertebrates, aquatic vegetation and molluscs are also consumed (Fig. 1). A pattern of increasing prey size with ontogeny was observed for fish in the Richmond River [1206] and the Sydney Basin [546]. Spatial and temporal variations in the diets of fish from the Sydney Basin were also observed [546]. Fish from upstream lotic habitats and freshwater tidal areas consumed greater amounts of terrestrial prey relative to fish from floodplain lagoons and brackish waters. These differences were attributed to the greater extent and density of riparian vegetation in the riverine habitats and the deeper waters occupied by fish in the estuarine and lagoon areas [546]. Terrestrial insects formed a greater proportion of the diet in summer than in winter, possibly related to seasonal patterns of insect emergence and activity [546]. Temporal variation in feeding rates may occur as fish from the Richmond River, New South Wales, were observed to have higher stomach fullness values between spring and autumn than in winter, possibly because of higher metabolic demands during the warmer months
Conservation status, threats and management Macquaria novemaculeata was classified as NonThreatened in 1993 by Wagner and Jackson [1353]. However, natural populations are reported to have declined in recent years due to a combination of factors including overfishing, translocations, habitat destruction, stream acidification, flow regulation and artificial obstructions to movement [552]. Macquaria novemaculeata is a popular angling species that supports a major recreational fishery. Increased mortalities due to overfishing by recreational anglers and illicit commercial operators, together with occasionally large bycatches from commercial fishing, have probably reduced average age and size of populations in the Sydney Basin [549, 552]. In 1974, the Noosa River in south-eastern Queensland was declared a fish habitat reserve and much of Lake Cootharaba and upstream has been closed to net fishing, theoretically ensuring the protection of bass habitat and bass populations [411]. However, mortality of M. novemaculeata has been reported in Lake Cootharaba during the spawning period, due to incidental catches by commercial net fishing [411]. In Queensland, bass may not be marketed commercially, have a bag limit of two per person and a minimum legal size of 30 cm TL [411, 593].
M. novemaculeata (juveniles), n = 134 Unidentified (8.1%)
Terrestrial invertebrates (10.1%) Microcrustaceans (33.5%)
Algae (8.1%)
Aquatic insects (40.2%)
M. novemaculeata (adults), n = 848 Unidentified (1.1%) Fish (19.7%)
Other microinvertebrates (0.1%) Microcrustaceans (0.1%)
Terrestrial invertebrates (17.9%)
Aerial aq. Invertebrates (1.2%) Terrestrial vertebrates (0.4%) Detritus (0.2%) Aquatic macrophytes (1.1%) Algae (0.8%)
Aquatic insects (21.7%)
Macrocrustaceans (31.5%)
Other macroinvertebrates (3.3%) Molluscs (0.9%)
Figure 1. The mean diet of Macquaria novemaculeata juveniles (<~50 mm TL) and adults (>~50 mm TL) (sample sizes for each age class are also given). Data derived from stomach content analysis of fish from south-eastern Queensland [205], northern and central New South Wales [546, 555, 1133, 1206], and Victoria [871].
343
Artificial propagation in fish hatcheries and increases in translocations within and beyond the natural distribution of this species may have potentially serious implications for the integrity of natural populations. The potential impacts associated with translocations are yet to be fully evaluated but may include a loss of genetic diversity, swamping of local gene pools, negative biotic interactions with local populations of native species, and the introduction of new parasites and disease organisms [146, 552, 650, 652]. Numerous external and internal parasites have been reported to infect M. novemaculeata, including cyclopoid copepods, nematodes and platyhelminthes [339, 1206]. The catadromous life cycle and upstream dispersal movements of juveniles and subadults indicate that M. novemaculeata is likely to be sensitive to barriers to
Freshwater Fishes of North-Eastern Australia
movement [552, 1342]. Weirs and impoundments that form barriers to longitudinal migration have drastically reduced the amount of suitable upstream habitat and resulted in the extirpation of this species upstream of larger barriers throughout much of its natural range [270, 442, 543, 544, 551, 552, 704, 859, 860]. Marsden et al. [859, 860] suggested that in catchments such as the Shoalhaven River, southern New South Wales, where numerous barriers exist that may periodically drown out in high flows, it may still take several years for this species to penetrate even a relatively short distance upstream. As M. novemaculeata is generally not prone to jumping, it is likely to have restricted passage requirements in relation to water depth, velocity and turbulence in fishways, and be reliant on seasonally appropriate discharges to overcome barriers to fish movement [541, 544, 859, 1133].
be especially critical to the successful upstream dispersal of larvae and juveniles, particularly due to their small size and relatively weak swimming ability [551, 552]. Anthropogenic changes to interannual variations in the relative magnitude of river discharge may also be critical as this aspect of the flow regime may influence: the relative proportion of the adult population reaching estuarine spawning areas [547, 549]; the overall area of suitable brackish water spawning habitat [547]; and food availability, hence the survival and growth rates of juveniles [546, 547, 548, 549].
Flow regulation (particularly aseasonal flow releases or long periods of low flows during critical periods) is likely to negatively affect the reproductive success of M. novemaculeata. Water harvesting or capture of high flows in dams may cause loss of cues for downstream movements of reproductively active adults, or the upstream dispersal movements of subadults. Juveniles migrate upstream in the absence of floods and possibly only during periods of stable low flow in spring and summer [543, 544, 552]. Elevated discharges resulting from artificial flow releases during naturally low flow periods may therefore
344
Adult M. novemaculeata show a relatively high degree of reliance on terrestrial food sources. Alterations to the natural duration, frequency, timing and magnitude of high flow events together with destruction of riparian vegetation may therefore affect inputs of allochthonous matter and have serious implications for food availability. Habitat destruction resulting from human activities (bank slumping, increased siltation and turbidity, eutrophication, loss of in-stream cover including woody debris and aquatic macrophytes) has been a major factor associated with declining recruitment of M. novemaculeata in the Sydney Basin and elsewhere [270, 547, 549, 552]. Acidification of streams resulting from artificial drainage schemes in areas with acid sulphate soils may also affect recruitment of this species [552].
Guyu wujalwujalensis Pusey & Kennard, 2001 Bloomfield River cod
37 311183
Family: Percichthyidae
lower portion of the upper arm. Operculum with two spines. Post-temporal serrate, cleithrum not serrate. Jugal smooth. Foramina on lachrymal large and well developed. Villiform teeth on the dentary, premaxilla, vomer and ventral margin of ectopterygoid and the upper and lower pharyngeals. Pelvic fins inserted behind pectoral fin base level with third or fourth dorsal spine.
Description Dorsal fin: XI or XII, 8–9; Anal: III, 7–9; Pectoral: 13–14; Caudal: 16–18; Vertical scale rows: 37–43; Horizontal scale rows: 20–26; Gill rakers: 13–14. Figure: mature male 101 mm SL (holotype), Bloomfield River, April 1995; drawn 1996. Guyu wujalwujalensis is a small fish; the maximum length of the type series being 101 mm SL [1091]. Body sub-ovate and deep (about 31% of SL). Snout tapered, profile straight. Snout naked, cheek and operculum scaled. Lateral line complete, curved to follow dorsal profile, continued on caudal fin base. Jaws equal, forming slightly oblique cleft reaching to just beyond anterior edge of orbit. Eyes lateral and large (about 25% HL). Dorsal neurocranial surface transversely convex in the interorbital region. Continuous transverse ridge present on the posterior frontals. Prominent frontoparietal ridges. Supraoccipital crest well developed, triangular in shape, with oblique median ridge on each side. Lateral line canal foramina on the frontals large and well developed. Foramina on the dentary surface well defined and larger posteriorly. Pectoral girdle twice as long as wide with a moderately long but unforked post-pelvic process. Preoperculum serrate on upper portion of upper arm with spines on the
Colour in life varies according to time of day and site of capture. In specimens collected from open water, the daytime colour is light khaki dorsally and silver-white ventrally. Specimens collected from shaded areas or from woody debris and undercut banks are dark green dorsally and khaki-green ventrally. Specimens collected at night are dark green. The head region is a greenish-yellow except for a darker green bar running below the eye from the snout to the opercular margin. A wide oblique iridescent light green band runs from behind the eye to the opercular margin. The margins of the membranes of the spinous section of the dorsal and anal fins are darkly pigmented. Colour in alcohol: dull khaki. Colour in formalin: tan to light brown. Systematics The family Percichthyidae, as defined by Johnson [657], contains eight Australian genera (Macculluchella,
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Freshwater Fishes of North-Eastern Australia
Bloomfield Falls and downstream of Roaring Meg Falls. Despite intensive sampling throughout the rest of the catchment, it has not yet been located in downstream or upstream tributaries.
Macquaria, Bostockia, Edelia, Nannoperca, Nannatherina, Gadopsis and Guyu) and two South American genera (Percilia and Percichthys). Pusey and Kennard discovered Guyu wujalwujalensis in 1993 [1085, 1087] and published a description of this species in 2001 [1091]. The etymology of the genus is derived from the Kuku-yalangi word Kuyu meaning freshwater fish. The K sound is pronounced as a ‘g’ and the ‘oo’ sound is clipped. The species name is in reference to the Aboriginal township Wujalwujal at the mouth of the Bloomfield River, north Queensland.
Guyu wujalwujalensis is not an abundant species. For example, it was the 33rd most abundant species (out of 66 species) collected by Pusey and Kennard [1087] in a large survey of the fish fauna of the Wet Tropics region. Such a pattern is to be expected for a species with a highly restricted distribution. This species comprised only 4% of the total catch for the Bloomfield River, which included fish caught from a number of locations, the majority of which were not located within the distribution of G. wujalwujalensis. This species is reasonably abundant in those reaches in which it occurs, however [1091]. It cooccurs with Melanotaenia splendida splendida, Mogurnda adspersa, Anguilla reinhardtii and very occasionally with Sicyopterus lagocephalus: species known for either their ability to negotiate waterfalls or to be frequently found above such structures.
Recent phylogenetic analysis (Jerry et al. [654], P. Unmack, pers. comm.) using DNA sequencing techniques has revealed that the generic classification of the family requires revision and that some genera, particularly Macquaria, are polyphyletic. Jerry et al. [654] placed G. wujalwujalensis in a clade with M. australasica and grouped these two species with M. ambigua. Other members of Macquaria (e.g. M. colonorum and M. novemaculeata) were placed in a deeply branched clade with members of Maccullochella. Unmack’s initial phylogenetic analysis also placed Guyu closest to Macquaria australasica (mountain perch) in a clade quite separate from the other species within the genus Macquaria. Since M. australasica is the type species for the genus Macquaria [1042], Guyu may be found to be invalid as a genus name. However, M. australasica and G. wujalwujalensis [1091] are morphologically distinct and we prefer to retain them as separate genera until a definitive systematic analysis is completed. McDonald [830] and Musyl and Keenan [981] suggested that Macquaria arose from a marine ancestor that became trapped in the vast inland sea that divided the Australian continent about 80 m.y.b.p. Pusey and Kennard [1091] proposed a similar origin for Guyu. Guyu wujalwujalensis is the only truly tropical Australian percichthyid.
Macro/meso/microhabitat use Guyu wujalwujalensis has been collected from the main river channel of the Bloomfield River above the Bloomfield Falls only. The two locations from which the type specimens were collected were structurally similar. The river was between 30 and 40 m wide and depth varied from less than 1 m to over 4 m. The reaches examined were a complex mix of cascade sections, runs and deep pools. Water velocities ranged from greater than 1 m.sec–1 in the cascade sections to 0.03 m.sec–1 in the pools. In-stream cover was limited and consisted of boulders, some bank undercutting and associated root masses, and sparse woody debris. Specimens collected by electrofishing during the day were almost always associated with these cover elements. Specimens collected at night were often observed high in the water column in open water about 1 m from the bank. Snorkelling surveys revealed that G. wujalwujalensis was distributed over a wide range of depths. Fish were observed at depths of 4 m but were always within 0.5 m of the bottom. Such fish rapidly sought cover amongst the cracks and tumbled slabs of rock on the stream-bed. Information on the diet provided below indicates that the Bloomfield cod spends most of its time foraging on the stream-bed but occasionally forages at the water’s surface.
Distribution and abundance The Bloomfield River cod is, as the name suggests, entirely restricted to the upper reaches of the Bloomfield River just north of Cape Tribulation [1087]. Intensive sampling in the adjacent Daintree River at the same elevation and in similar habitat has failed to reveal its presence there [1093]. Hephaestus tulliensis (khaki bream) was common in the Daintree River in such reaches, however this is absent from the Bloomfield River. Pusey and Kennard [1091] suggested that distribution of these two species was mutually exclusive and that the relictual status of G. wujalwujalensis had arisen because potential competitors and predators, such as species of Hephaestus, are excluded from the upper Bloomfield River by the downstream Bloomfield Falls.
Environmental tolerances Nothing is known about the tolerances of this species. Guyu wujalwujalensis has been collected (on one occasion in April and another in September) from well-oxygenated, very clear water (Secchi disc depth >4 m) with pH values
Within the Bloomfield River, G. wujalwujalensis is restricted to the main river channel upstream of the
346
Guyu wujalwujalensis
Trophic ecology Included in the description of this species are dietary data collected for 18 specimens [1091]. Guyu wujalwujalensis is almost exclusively carnivorous; only 3% of the diet was composed of plant material (2% algae and 1% terrestrial vegetation) (Fig. 1). Given this small contribution it is probable that the plant matter was incidentally ingested. Fish (juvenile G. wujalwujalensis) comprised 6% of the diet but were present in one individual only. Terrestrial invertebrates (mostly ants) contributed 7% to the diet. The greater bulk of the diet was comprised of small aquatic invertebrates: chironomid larvae (17%), ephemeropteran nymphs (18%), pyralid larvae (13%) and trichopteran larvae (6%). Unidentified arthropod fragments made up the remainder (28%). The specimens of Guyu wujalwujalensis from which this summary was derived ranged in length from 34–79 mm SL.
between 5 and 6. Water temperature was 21°C (September) and 23°C (April) and conductivity was extremely low (28–30 µS.cm–1). Given these conditions, it is highly unlikely to tolerate degraded water quality. Reproduction Very little known about the breeding biology of G. wujalwujalensis. This species matures to the point where gender is discernible upon internal examination at small size; 42 and 43 mm SL are the minimum sizes for distinguishably male and female fish, respectively. The spawning season is unknown, however the holotype (101 mm SL), a mature male collected in April, was running ripe at the time of capture. Movement Nothing is known of the extent or phenology of movement in this species. Judging from its absence from tributary streams, it does not disperse into such habitats. Guyu wujalwujalensis may make an upstream spawning migration similar to that seen in Macquaria australasica [552].
Conservation status, threats and management The conservation status of G. wujalwujalensis is listed as Vulnerable [117]. Pusey and Kennard [1091] believed that the most significant threat facing this unique fish was the translocation of therapontid grunters (i.e. Hephaestus fuliginosus) into the catchment to satisfy recreational fishers and to stock farm dams. Much of the catchment is not vested in National Park and lies outside the Wet Tropics World Heritage Area, residing in pastoral leasehold or freehold. There has been recent conversion of the former land title to aboriginal ownership and management by the Wujalwujal Community. Pusey and Kennard [1091] recommended that a ban on the collection of this species, other than that necessary to address scientific and management concerns, be enacted to protect it from unscrupulous collectors, at least until more is known of its biology and management needs. This species is apparently restricted to waters of near-pristine quality and maintenance of water quality is a high priority. Given the distribution of Guyu wujalwujalensis, it is unlikely that it will face any threats from water resource development in the near future.
Terrestrial invertebrates (7.0%) Fish (6.0%) Algae (2.0%) Terrestrial vegetation (1.0%)
Aquatic insects (83.0%)
Figure 1. Mean diet of Guyu wujalwujalensis. Summary derived from a total of 18 specimens collected in September 1993 (five specimens) and April 1994 (13 specimens).
347
Maccullochella peelii mariensis (Mitchell, 1838) Mary River cod
37 311076
Family: Percichthyidae
peduncle, greater postorbital head length, smaller orbit, larger interorbital width, fewer scales rows below lateral line, shorter fifth–sixth dorsal spine and shorter extensions of the first anal pterygiophore [1237].
Description Dorsal fin: X–XII, 13–16 (usually XI, 15); Anal fin: III, 11–13; Pectoral: 19–20; Caudal: 16–18; Pelvic: I, 5 with relatively long tapering filament; Lateral line scale rows: 65–80; Gill rakers: 17–21; Vertebrae: 34–35, 15 precaudal [52, 552, 1237]. Figure: adult specimen, composite, drawn from photographs, 2004.
Dorsal colouration varies considerably, from goldenyellow to green to dark brown, overlaid with a black to black-green mottling which extends onto the grey or whitish ventral surface in some specimens [1237]. Dorsal, pectoral, caudal and anal fins clear to dark with grey-green mottling on bases. The soft dorsal, anal and caudal fins have thin whitish margins, and the whitish pelvic fin has white filaments [552, 1237]. Spotted markings and a blunter head profile tend to develop with age [1237].
Maccullochella peelii mariensis is an elongate, percoid fish with concave head profile above eyes, large mouth reaching behind eye level; jaws about equal, the lower sometimes protruding in large specimens. Body depth 17.8–40% of SL [52, 1237]. Maccullochella peelii mariensis is a moderate to large percichthyid known to reach 23.5 kg, possibly up to almost 40 kg, but uncommon over 5 kg and 700 mm TL [552, 936, 1237]. Murray cod, Maccullochella peelii peelii, have been recorded up to 113.5 kg and 1800 mm TL [552].
Systematics The genus Maccullochella contains Australia’s largest strictly freshwater fish, the Murray cod (M. peelii peelii). Morphological and genetic investigations by Berra and Weatherley [166] in 1972 established that two species of ‘cod’ were present in the Murray River: M. peelii and M. macquariensis, and that the latter is more restricted in distribution [52, 166]. Berra and Weatherley [166] give a full account of the nomenclatural history of these two species. Large cod-like fish were also known to occur in some rivers of northern New South Wales and southern
Maccullochella peelii mariensis can be distinguished from the nominal species M. peelii peelii by the combination of longer pelvic fins, deeper and shorter caudal peduncle, shorter extensions of first anal pterygiophore towards vertebral column, large sagittal otoliths, and distinctive colouration. M. peelii mariensis can be distinguished from Maccullochella ikei by the combination of deeper caudal 348
Maccullochella peelii mariensis
Queensland but specimens of these fish were either not included, or not recognised as sufficiently different from M. peelii to warrant special note in any systematic reviews of the genus or the family [166, 830]. Rowland [1161] described the cod present in the Clarence River as a new species (M. ikei) and the cod present in the Mary River as a subspecies (M. peelii mariensis) of the Murray River cod (M. peelii peelii). Maccullochella ikei was estimated to have diverged from ancestral M. peelii stock approximately 1.7 m.y.b.p. whereas the subspecies M. peelii mariensis was estimated to have diverged from its ancestral stock approximately 0.8 m.y.b.p. Both events were suggested to be associated with isolation of eastern and western stocks due to progressive back cutting of the eastern scarp [1161]. Maccullochella peelii peelii and M. ikei appear to be reproductively isolated as artificially induced hybrids suffer a high frequency of abnormality during development, few hatch successfully and even fewer manage to survive more than 24 hours [1161]. However, it should be noted that hybridisation between the more divergent M. peelii and M. macquariensis [654] has been reported in the wild and artificially induced hybridisation between these species results in the production of young with low levels of abnormality (<5%) and high survivorship during the initial phase of development post-hatch [387]. Significant differences in five morphometric characters (peduncle depth, peduncle length, pelvic fin length, head length and orbit diameter) and the length of the first anal pterygiophore were reported for comparisons of M. peelii peelii and M. peelii mariensis.This subspecies differed from M. ikei with regard to 10 characters [1161]. Interestingly, both M. peelii and M. ikei have longer pelvic fins than M. peelii peelii and Rowland suggested that this character was diagnostic of fish from eastern drainages. Jerry et al. [654] identified Maccullochella as a monophyletic group within Percichthyidae but suggested, based on mtDNA sequence diverge, that the two subspecies of M. peelii are, in fact, not sister taxa. Rather, M. peelii mariensis and M. ikei were shown to be more closely related than either was to M. peelii peelii. However, the distinction between these three taxa was poorly resolved, indicative of the short period of divergence suggested by Rowland [1161]. Although Jerry et al. [654] did not go so far as to say that the Mary River cod should be recognised as M. ikei, their analysis certainly demonstrates that the debate about the number and identity of species in Maccullochella is far from over.
throughout most of the larger, and many of the smaller, tributaries and throughout the length of the main river channel in the early 1990s, and up to 1950s and 1960s. The Queensland Museum holds a few records of M. peelii mariensis from the headwaters near Maleny, Six Mile Creek, Tinana Creek and Coondoo Creek [1237]. Recent surveys by Simpson in 1994 [1234] and cod captures by local anglers record this species in four main areas of the Mary River: Obi Obi Creek at Obi Obi Gorge, the Widgee/Glastonbury area, Six Mile Creek downstream from Lake Macdonald and Coondoo/Tinana Creeks upstream from Tinana Barrage [1237]. Occasional cod captures in other areas (e.g. Amamoor Creek, upper Mary River) outside of the main remnant distribution probably represent small pockets of survivors in large pools, and/or fish that have dispersed from remnant and stocked populations. Cod caught in lower Yabba Creek are believed to be escapees from the 1992 stocking of Borumba Dam with fingerlings, rather than members of a natural remnant population, however, anecdotal records suggest that this stream supported a healthy cod population in the 1930s and 1940s [1237]. Since 1998, the Queensland Fisheries Service has been re-stocking M. peelii mariensis fingerlings in key parts of the Mary River basin and other catchments in south-eastern Queensland [701, 702]. Cod (Maccullochella spp.) were present in large numbers throughout coastal rivers of south-eastern Queensland and north-eastern New South Wales in the 1800s and early 1900s, and the Brisbane and Mary rivers were particularly renown for large catches of cod [1234]. Some settlers even used them as pig feed [1237]. Rowland [1161] described cod collected from the Clarence River as a new species (Maccullochelli ikei) but the identity of cod in the Brisbane, Logan-Albert and Coomera rivers remains unknown. The belief that this eastern cod was more likely to have been Maccullochella peelii mariensis has evidently justified the translocation of M. peelii mariensis into southern rivers to provide a recreational species for anglers. Local landholders in the Albert River reported catching a species of cod in the river prior to World War 2 but occasional reports of cod being collected since that time are unsubstantiated [1349] (aside from recently stocked individuals). The known distribution of cod in the Mary River extends over about 170 km of stream length, whereas the presumed historical distribution extended over at least 700 km of stream and river length [1237]. The total population of cod from the four main areas of its remaining distribution was estimated in 1996 to be 660 individuals only [1237]. Details of cod distributions in each area can be found in Simpson and Jackson [1237]; for example, in Tinana and Coondoo creeks, the distribution extends over
Distribution and abundance Maccullochella peelii mariensis is endemic to the Mary River system in south-eastern Queensland [52, 1237, 1239]. Anecdotal accounts assembled by Simpson and Jackson [1237] suggest that the Mary River cod occurred 349
Freshwater Fishes of North-Eastern Australia
in Victoria for Murray cod; for example, the work of Cadwallader and Gooley [271]. Differences between the two subspecies have now been established. In this account reference is made to the behaviour of Murray cod for comparative purposes and to provide information that is relevant but not yet available for the Mary River cod.
approximately 70 km of stream length and was estimated to contain a population of about 250 individuals. Recent extensive sampling at numerous wadeable sites throughout in the Mary River Basin failed to detect any M. peelii mariensis [516]. Macro/meso/microhabitat use Maccullochella peelii mariensis occurs in a variety of types of habitat in the Mary River system from high-gradient rocky upland streams to large, slow-flowing pools in lowland areas [1234, 1237]. The ideal habitat appears to be deep, shaded, slow-flowing pools with mud/clay substrates, abundant woody debris and log-jams, wellshaded by overhanging vegetation [552, 1237]. Upland populations are found in habitats that generally lack instream timber and riparian cover; instead, cover is provided by undercut banks, rock ledges and boulders [1237]. Cover is considered important for concealment from potential prey and as resting sites, and woody material, especially hollow logs, also provides sites for spawning [1234]. The depth of water in which this species was caught by Simpson [1234] ranged from 0.8 to 3.4 m. All cod were caught in pools with nearly zero flow velocity; juveniles of this species were not captured [1234].
The size at which male and female Maccullochella peelii mariensis become sexually mature is not known, however mature specimens of both sexes around 300 mm in length have been caught in the wild. Spawning of M. peelii mariensis is believed to occur annually around spring, when temperatures rise above 20°C [1237]. Like the Murray cod, the Mary River cod becomes active before spawning, forming pairs [552, 1237]. The male appears to play the main role in selection and guarding of the spawning site; structures such as hollow logs are probably used in the wild, but in hatchery ponds hollow concrete pipes are commonly selected for egg deposition [1237]. Males become increasingly territorial as they select their spawning sites [1237]. Spawning may involve considerable aggression between the spawning pair such that eggs may be scattered around the spawning site and the female is frequently injured before she can escape the aggression of the guarding male [1237]. The eggs are large (3–3.5 mm in diameter), opaque, adhesive and demersal. The fecundity of M. peelii mariensis is not known but 2000 eggs per kg of mature female represents average to good fecundity in hatchery conditions [1237]. Fecundity of M. peelii peelii ranges from 10 000 to 90 000 eggs in females of 2.5–23 kg [552]. Some females of the Mary River cod may spawn more than once in a season [1237]. The eggs begin to hatch towards the end of the fourth day at 21°C; hatching is usually completed by the end of the seventh day. Newly hatched larvae vary from 5.0–7.0 mm in length. The male fish guards (and possibly fans) the eggs and the larvae until the brood begins to disperse in search of food, around 7–10 days after hatching [1237]. Larvae feed on zooplankton and aquatic insects, especially chironomid larvae [552]. Fry reared in hatchery ponds at Lake Macdonald may reach 50 mm (TL) in less than 10 weeks [1237].
Environmental tolerances The physicochemical requirements of Maccullochella peelii mariensis do not appear to be particularly specific. Water of the Tinana/Coondoo creek system tends to be acidic (pH 6.0–6.5), of relatively high conductivity (up to ~800 µS.cm–1), frequently low in dissolved oxygen (minimum 3.9 mg.L–1) due to low flows and is typically stained by tannins and other organic compounds [1093, 1237]. At the opposite end of the spectrum of habitats in the upland areas of Obi Obi Creek, water is circumneutral in pH (7.3), of low conductivity (about 100 µS.cm–1), relatively high in dissolved oxygen (maximum 9.7 mg.L–1) and of low turbidity [1093, 1234]. Stream temperatures at sites supporting this species varied from 15.7 to 29°C [1234]. Reproduction Maccullochella peelii mariensis spawns and completes its entire life cycle in freshwater. Most information on the reproductive biology and early development of M. peelii mariensis has been obtained during the development of culture techniques at the Lake Macdonald hatchery in the Mary catchment [1237]. The following account draws heavily on the work of Gerry Cook and Russell Manning from the Lake Macdonald hatchery, supplemented by the observations in the wild and interpretations of Simpson [1234, 1237]. Available information is summarised in Table 1.
Movement There is very little information on the movement or migration of Maccullochella peelii mariensis in the published literature. Simpson and Mapleston [1239] used radiotelemetry to investigate the movement behaviour of this species and its use of habitat in the Mary River. Thirteen fish varying from 420–760 mm TL and 1.3–5.5 kg were fitted with transmitters and they were tracked for over 20 months [1239]. Nine cod were located 344 times in 1997–1999; only two individuals were located less than 30 times. Fish displayed two relatively distinct types of movement: rapid, directional, long-distance movements
The earliest attempts to induce spawning in cod and to rear them in captivity were based on techniques developed 350
Maccullochella peelii mariensis
formed 72% of habitat area [1239].
indicative of abandonment of the home range; and localised, non-directional activity within the home range [1239]. In the former type, movement and the mean distance moved were positively correlated with monthly stream discharge, but the direction of movement was unpredictable. The three longest upstream distances moved were 35, 28 and 23 km (in February), and the three longest downstream distances moved were 32, 31 and 23 km (in May). Movements that exceeded 10 km were usually completed in one to three weeks [1239]. Five of the six cod that made long-distance movements later returned virtually to their original locations in the river, after three to nine months away, three cod returned to a specific, previously occupied log or log-pile. Cod established home ranges that varied for 70 to 820 m (mean 339.3 m) in length; boundaries were usually marked by a distinctive feature such as a log or riffle, and several core areas were occupied frequently within these home ranges [1239]. Most of the 344 contacts with tagged cod were made within 2 m of large fallen timber (95%), especially log-piles (44%). Very few contacts were made with fish in open water (4%) even though this
Observed patterns of movement of cod in the Mary River were considered to be unrelated to spawning behaviour, as stream depths were generally too low to allow movement in spring when spawning occurs. Large mature cod did not display increased activity or movement immediately before or after the spawning period [1239]. However, local activity of cod was relatively high in late summer, autumn and winter in the lead-up to spawning, possibly as a consequence of territorial interactions during selection of nest sites prior to spawning [1239]. The movements of juvenile cod were not studied. The larvae of M. peelii peelii drift downstream for a period of several days after leaving the natal habitat. Larvae were classified by Humphries [612] as active drifters, drifting only at night. It is probable that the larvae of M. peelii mariensis also drift downstream in the current. The limited and isolated distribution of this species suggests that larvae either drift short distances only or that mortality is high in widely dispersing larvae.
Table 1. Life history information for Maccullochella peelii mariensis. Age at sexual maturity (months)
?
Minimum length of gravid (stage V) females (mm) ? 300 mm [1237] Minimum length of ripe (stage V) males (mm)
? 300 mm [1237]
Longevity (years)
?
Sex ratio (female to male)
?
Occurrence of ripe (stage V) fish
? Spring, August to October in hatchery ponds [1237, 1239]; possibly as late as December in the wild [1239]
Peak spawning activity
? spring [1237]
Critical temperature for spawning
Above 20°C [1237]
Inducement to spawning
? Temperature rise
Mean GSI of ripe (stage V) females (%)
?
Mean GSI of ripe (stage V) males (%)
?
Fecundity (number of ova)
? 2000 eggs per kg of mature female [1237]
Fecundity.size relationship
?
Egg size (diameter in mm)
3.0–3.5
Frequency of spawning
Annually but some females may spawn more than once in a season [1237]
Oviposition and spawning site
Hollow logs, solid surfaces in wild; hollow concrete pipes in hatcheries [1237]
Spawning migration
? Probably none [1237]
Parental care
Male selects spawning site, guards (and probably fans) the eggs, and guards the young until they disperse to feed [1237]
Time to hatching
4–7 days at 21°C [1237]
Length at hatching (mm)
5–7 mm [1237]
Length at free swimming stage (mm)
? 5–7 mm [1237]
Age at loss of yolk sack
? 7–9 days after hatching [1237]
Age at first feeding
? 7–9 days after hatching [1237]
Length at first feeding
?
Age at metamorphosis (days)
?
Duration of larval development
?
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Freshwater Fishes of North-Eastern Australia
Remnant populations, habitats likely to support natural populations and restocking sites in the Mary River and its tributaries warrant special and ongoing management, protection and/or restoration, given the rarity of Mary River cod and the considerable efforts recently undertaken as part of the recovery plan for this species (see Simpson and Jackson [1237]). Specific recovery actions should include efforts to minimise the impacts of barriers to movement; appropriately designed fishways should be installed on all newly constructed stream storages in the Mary River catchment [1239]. Stream crossings should be constructed to conform to guidelines established by the Department of Primary Industries [332]. Large woody debris should be preserved or enhanced throughout the species range in the Mary River catchment. Riparian regeneration should be promoted in areas where riparian cover has been reduced or removed, to foster the production of woody debris and the consolidated structure of stream-banks.
Trophic ecology There is no published quantitative dietary information on the diet of M. peelii mariensis but adults of this species, like other percichthyids, are fully carnivorous; they consume a range of relatively large food items such as crustaceans and fish, and possibly also frogs, snakes, waterbirds and mice [552]. Conservation status, threats and management Maccullochella peelii mariensis was listed as Endangered by Wager and Jackson [1353] and is also listed as Critically Endangered in the list maintained by the Australian Society for Fish Biology [117]. It is listed as threatened under the National EPBC Act 1999. The overall status of the Mary River cod is parlous. The known distribution was estimated in 1996 to extend over only some 170 km of stream length, whereas the presumed historical distribution extended over at least 700 km of stream and river length [1237]. The total population of cod from the four main areas of remnant populations is estimated to be less than 1000 individuals [1237]. In one important focal area, Tinana and Coondoo creeks, the distribution extends over approximately 70 km of stream length and contains a population of only about 250 individuals. This sub-catchment also contains Queensland lungfish (Neoceratodus forsteri) and the only known populations of the Critically Endangered Oxleyan pygmy perch (Nannoperca oxleyana) in the Mary River Basin.
Mary River cod may not be able to breed successfully in large impoundments and recruitment in impoundment populations is likely to be very low to judge from evidence for other percichthyiid species (see [1237]). Nonetheless, Mary River cod breed successfully in large artificial ponds thus successful spawning and recruitment in large dams may potentially lead to self-sustaining populations provided suitable conditions are available [1237], especially fallen timber and woody debris as cover and spawning sites.
There has been a significant reduction in the size of cod in this river system since the early 1900s [1237]. Cod weighing 5–6 kg are now rare, probably as a result of fishing pressure, and altered habitat conditions and habitat loss, or a combination of the two [52, 552, 1234, 1237, 1239]. Loss of fish passage due to dams and weirs is also believed to have impaired the movement and homing behaviour of the cod and disrupted its access to the most suitable habitats and structural features providing cover and resting sites [1237, 1239]. The presence of tidal barriers (e.g. in the Mary River and Tinana Creek) may further impact on cod by preventing or hindering recolonisation of freshwaters if displaced by floods to brackish estuarine areas downstream of tidal barrages.
The effects on cod of large-bodied translocated species such as yellowbelly (Macquaria ambigua) are unknown, however, this ecologically similar species now occurs in several tributaries and main channel areas of Mary River Basin. It is possible that negative biotic interactions (e.g. predation and competition for food and space) may be detrimental to remnant and re-stocked cod populations. The potential impacts of changes in river flows on cod are not understood [1234], but there are increasing pressures on water resources in the Mary River Basin and elsewhere in south-eastern Queensland. Numerous water infrastructure developments (e.g. dams, weirs and interbasin transfer facilities) and plans for further development exist in the Mary River. The forthcoming Water Resource Plan for the Mary River Basin represents an opportunity to address the possible implications of altered flow regimes on the habitat of M. p. mariensis, and associated impacts of water infrastructure on key aspects of the biology and ecology of this Critically Endangered species such as movement, spawning and recruitment processes [701].
Simpson and Jackson [1237] have suggested that habitats currently occupied by remnant cod populations in the Mary River system do not represent optimal cod habitats but are simply refuges where small populations have been able to survive. Historical accounts strongly suggest that large deep pools that once occurred along the main channel of the Mary River were probably important habitats producing very large individuals, before erosion and siltation caused infilling and loss of habitat heterogeneity [1237].
352
Nannoperca oxleyana Whitley, 1940 Oxleyan pygmy perch
37 323008
Family: Percichthyidae
preorbital hidden under skin. Mouth relatively small with jaws reaching to below anterior part of pupil. Teeth in front of lower jaw enlarged. Truncate caudal fin. Body light brown to olive, darker on back, sides paler and mottled with three to four patchy dark brown bars extending from head to tail. Opercular flap has a blue iridescence. Scales with dusky outlines. Prominent round black spot with orange margin at the base of caudal fin, fins mainly clear. During breeding, dorsal and anal fins are black, caudal fin and lateral stripes turn scarlet [90, 744, 745, 936].
Description First dorsal fin: VI–VIII, 7–9; Anal: III, 7–9; Pectoral: 11–13; Pelvic: 5; Caudal: 14–15 segmented rays; Vertical scale rows: 25–28; Horizontal scale rows: 11–13; Predorsal scales: 15, Gill rakers on first arch: 9–12 [52, 744, 745, 1385]. Figure: mature specimen, 27 mm SL, Noosa River; drawn 1992. Nannoperca oxleyana is a small fish thought to reach about 75 mm TL but more commonly grows to 45 mm SL. Of 951 specimens collected in the Noosa River [84], coastal creeks and on Moreton Island [82], the mean and maximum length of this species were 22.2 mm and 51 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 951 individuals of N. oxleyana from south-eastern Queensland populations [82] (range 8–51 mm SL) is Log W = 10.045 + 2.817 log L, r2 = 0.940, p<0.001.
Systematics There has been much uncertainty about the systematics of the Australian pygmy perches. They have been variously placed within the Kuhliidae [755, 936, 1042], Nannopercidae [745], or Percichthyidae [656, 744]. Recent genetic evidence unequivocally places the pygmy perches within Percicthyidae [654]. The group comprises six species currently placed within two genera: Nannoperca and Nannatherina. A third genus, Edelia, was previously recognised but has been placed within Nannoperca [745]. This decision was fully supported by the results of a recent molecular phylogenetic analysis [654]. Only one species of pygmy perch, Nannoperca oxleyana, occurs in Queensland, and it is the most northerly distributed species within this
Knight [726] found that N. oxleyana collected from streams and lakes near Evans Head in New South Wales ranged from 15 to 55 mm TL with the majority in the 17–37 mm size range. This species has a moderately compressed body covered by ctenoid scales and without a lateral line. Rear edge of
353
Freshwater Fishes of North-Eastern Australia
North Range Lake by means of five seine-net hauls through shallow beds of a submerged sedge. Since then, further surveys in the military training reserve have been prohibited by security regulations of the Commonwealth Government.
group [34, 656, 744, 745, 755, 936, 1042]. Nannoperca oxleyana was described by Whitley [1385] 1940, based on material collected from Moreton Island. Genetic analysis of N. oxleyana populations in south-eastern Queensland revealed relatively high levels of allozyme and mitochondrial DNA variation among discrete populations, suggesting that dispersal among populations is extremely limited [606].
The earliest record of N. oxleyana in New South Wales dates from 1929 and has been traced to either the Richmond River at Coraki, or to a small lentic waterbody on private property south-west of Lismore [726]. There are no further records of N. oxleyana from this general locality, due to lack of collecting effort and/or the marginal nature of aquatic habitat for this species [726]. Llewellyn [812] reported N. oxleyana in Lake Hiawatha near Wooli, New South Wales, but this species has not been recorded in this lake in more recent surveys [726]. Nannoperca oxleyana was recorded from a dune lake near Wooli in 1995, and Australian Museum records dating from 1997 report this species from Wooli Creek and Tick Gate Swamp in Yuraygir National Park (formerly Red Rock National Park) to the south of Lake Hiawatha [965]. Knight [726] notes that the most southern record of N. oxleyana is from Tick Gate Swamp, approximately 50 km south of the Clarence River mouth.
Distribution and abundance Nannoperca oxleyana has a very restricted and patchy distribution in mainland and insular coastal lowland ecosystems of south-eastern Queensland and north-eastern New South Wales [82, 84]. In these wallum (Banksia dominated heath) ecosystems, N. oxleyana was historically known to occur as far north as Carland Creek and Searys Creek in the Tin Can Bay area until a more northerly population in Coondoo and Tinana creeks (tributaries of the Mary River) was discovered in 1994 [1093]. This species is patchily distributed in a few streams and rivers of the Noosa, Maroochy and Pine basins, as far south as Burpengary Creek [1349]. It is also present on Fraser, Moreton, and North Stradbroke islands off the south-eastern Queensland coast [82].
The most recent records of N. oxleyana in New South Wales have been provided by Knight [726] and colleagues. A 26-day survey of wallum waterbodies conducted in June and July 2000, and additional surveys of seven waterbodies conducted in August and September 2000, produced 25 new records of N. oxleyana from 13 streams and 12 lakes within and around Broadwater National Park, near Evans Head, north-eastern New South Wales [726]. This concentration of records in a relatively small area has no parallel in the Queensland distribution of N. oxleyana.
In Queensland, the distribution of N. oxleyana is often shared with P. mellis, P. signifer, R. ornatus, M. duboulayi, H. galii, H. compressa, G. australis and Gambusia holbrooki [82, 1093]. It is generally not locally abundant although N. oxleyana comprised approximately 20% or more of the fish collected by electrofishing, seine-netting and bait trapping in Spitfire, Tempest, Marcus and Coondoo creeks, south-eastern Queensland [82]. Nannoperca oxleyana is well-established in the upper Noosa River and many of its upper tributaries although it was not found in Kin Kin Creek [82]. A survey of the Noosa River system conducted in April 1994 produced higher catches of N. oxleyana in several tributaries (mean per five seine hauls = 17) compared to main river sites (mean per five seine hauls = 4) [82].
In the Evans Head area, the distribution of N. oxleyana was shared with R. ornatus, H. galii, H. compressa, G. australis and Gambusia holbrooki. In the systems surveyed (see above) N. oxleyana comprised 14% of the total number of fish collected by pocket seine and commercial fish (‘bait’) traps [726]. Similar proportions of the total catch of N. oxleyana (566 individuals) were taken from lotic (52%) and lentic (48%) systems, however one lake and one discrete site in a creek produced 71% of the total number collected [726].
Until recently, N. oxleyana was believed to have a restricted and patchy distribution in north-eastern New South Wales. It was found by us at only one of 33 coastal heathland localities surveyed in northern New South Wales in 1993, at North Range Lake situated in Bundjalung National Park immediately to the south of the township of Evans Head [82, 726]. Waterbodies in this area lie within a military training reserve where the dunes are damaged by bomb craters and extensive road development. However, public access has been very limited in the past and many areas of the park and its waterbodies are in near pristine condition. Three individuals of N. oxleyana were caught in
Macro/mesohabitat use N. oxleyana is found in lotic and lentic habitats within wallum ecosystems situated close to the coast of southeastern Queensland and north-eastern New South Wales. Lentic waterbodies along this costal strip lie over siliceous sand in dune valleys and swales. This species has been recorded from 53 discrete waterbodies in the two states:
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Nannoperca oxleyana
various extensive leaf-litter beds, emergent macrophytes (Lepironia articulata, Gahnia sp., Juncus sp.) and submerged species (Eleocharis spp., Nymphaea sp., Chara sp. and Utricularia sp.) provide in-stream cover [82].
one river (the Noosa River), 29 streams, 18 lakes, three swamps and two aquatic systems of unknown character [726]. In the Noosa River this species has been collected from the main river channel as well as five small tributaries [82]. In a more complex lake/swamp system on Moreton Island, N. oxleyana was recorded from the lake proper (Lake Jabiru) and a swampy drainage line connecting the lake to a freshwater creek swamp (Spitfire Creek) close to the east coast, and possibly opening intermittently to the sea [82]. This species is also found in perched dune lakes situated in dune depressions sealed by accumulated organic matter bonded with sand to form semipermeable ‘coffee rock’ [82].
Microhabitat use In streams of south-eastern Queensland, Nannoperca oxleyana was most frequently collected from areas of low water velocity (usually less than 0.2 m.sec–1), over mud and sand substrates, in moderate water depths (10–50 cm) and in the mid-water column (Fig. 1). In lentic environments it is reported to occur in water depths up to 1.5 m and is often observed throughout the lower two-thirds of the water column, with smaller individuals tending to be found in the upper part of this zone [82, 84, 1093]. In lotic and lentic sites N. oxleyana is often found in close association with
In rivers and streams of mainland south-eastern Queensland, this species most commonly occurs in small shallow low gradient tributaries 4–40 m.a.s.l. and 7–123 km from the coast (Table 1). Most of the creek sites have some form of riparian cover, and in streams and lakes
60
Table 1. Macro- and mesohabitat use by Nannoperca oxleyana in rivers and streams of mainland south-eastern Queensland. Data summaries for 23 individuals from samples of five mesohabitat units at four locations in south-eastern Queensland streams collected between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min.
Max.
Mean
W.M.
Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
58.1 15.0 7.0 4 3.2 33.7
697.2 54.0 123.0 40 9.4 90.0
265.0 32.0 70.0 18 6.5 63.9
149.9 24.2 52.2 17 5.4 56.5
Gradient (%) 0.01 Mean depth (m) 0.22 Mean water velocity (m.sec–1) 0 Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0.09 0.99 0.19
0.05 0.68 0.07
38.7 100.0 16.2 10.5 0.0 0.0 9.5
11.9 80.8 3.2 2.1 0.0 0.0 1.9
12.9 84.9 1.0 0.6 0.0 0.0 0.6
Aquatic macrophytes (%) 0 Filamentous algae (%) 0 Overhanging vegetation (%) 0 Submerged vegetation (%) 0 Emergent vegetation (%) 0 Leaf litter (%) 18.3 Large woody debris (%) 0 Small woody debris (%) 6.2 Undercut banks (% bank) 0 Root masses (% bank) 0
0.0 0.0 1.0 9.4 50.9 27.8 16.0 26.8 28.8 46.7
0.0 0.0 0.3 2.4 25.5 22.0 8.9 12.8 10.8 16.6
0.0 0.0 0.1 1.0 34.7 23.9 6.1 10.1 3.8 6.0
60
40
40
20
20
0
0
60
(b)
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 80
40
60 40
20 20 0
0.06 0.63 0.06
0 61.3 0 0 0 0 0
(a)
0
Total depth (cm) 60
(e)
Relative depth 30
40
20
20
10
0
0
Substrate composition
(f)
Microhabitat structure
Figure 1. Microhabitat use by Nannoperca oxleyana in Tinana Creek (Mary River), south-eastern Queensland. Summaries derived from capture records for 23 individuals collected over the period 1994–1997 [1093].
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extended to March/April, possibly occuring as late as May, but with relatively low levels of reproductive activity in the latter period [84]. For example, a few mature N. oxleyana were caught in a tributary of the Noosa River surveyed in May 1990 when the fish were still displaying breeding colours. The mean GSI (%) of ripe (stage V) females is 3.3 ± 0.002 and that of males is 0.6 ± 0.197 [82].
dense emergent and submerged marginal vegetation, leaf-litter beds, undercut banks and occasionally woody debris and the fine rootlets of riparian vegetation (Fig. 1f) [82, 965]. Knight [726] recorded very similar microhabitat use in streams of northern New South Wales. Environmental tolerances Little quantitative data is available on the environmental tolerances of this species. Table 2 provides data for Queensland collection sites only; details for collection sites in New South Wales can be found in Knight [726]. N. oxleyana is usually associated with dystrophic waterbodies that are acidic (pH 4.2–6.7) and deeply stained with tannins and other organic acids, thus water transparency is usually very low [82, 726]. Conductivity is also very low in streams, swamps and lakes supporting this species (68–300 µS.cm–1). Temperatures at collection sites in Queensland and New South Wales have ranged from 12 to 32°C, and dissolved oxygen levels from 2.15–13 mg.L–1 [82, 726].
The spawning stimulus for N. oxleyana is unknown but the peak spawning period in spring and early summer coincides with increasing water temperatures, increasing day length and low probability of elevated discharge in south-eastern Queensland streams [82]. These environmental conditions are most likely to be favourable for egg and larval development, availablity of food for larvae and successful recruitment in streams with highly variable flows that may disturb or strand aquatic vegetation or the substrates used to deposit eggs [82, 84]. Spawning may continue into the summer months when stream flows are higher and more variable but less effort is expended at this time. In the Noosa River, spawning occurred at temperatures between 26.5°C and 28°C [84]. Successful spawning has been observed in aquaria maintained at temperatures greater than 20°C [1348]. Courtship and mating involve a pair of fish casually approaching one another and as they come close, quickly shuddering and releasing eggs and milt, then continuing on past each other [1348]. Eggs are deposited onto the substrate or into aquatic vegetation. Females lay a few eggs each day throughout the spawning season, and over one to two weeks may release up to 100 eggs. The eggs have been reported to hatch in 1–3 days [797], and in 3–4 days [1348] and larvae begin feeding in another 1–2 days on rotifers and protozoans (infusoria) [1348]. Nannoperca oxleyana bred in aquaria reach maturity in four to five months [1348]. Leggett [790] observed that fish bred in aquaria were 18 mm TL 10 weeks after hatching. Analysis of length-frequency data from Queensland and New South Wales populations suggests that N. oxleyana may live up to 3–5 years [726] as do other members of the genus [611, 1050].
Table 2. Physicochemical data for Nannoperca oxleyana in south-eastern Queensland. n = numbers of sites. Parameter
Min.
Max.
Mean
Noosa River and Spitfire Creek (n = 9) [82, 84] Water temperature (°C) 16.0 32.0 18.7 Dissolved oxygen (mg.L–1) 5.0 13.0 7.2 pH 4.2 6.7 5.3 Conductivity (µS.cm–1) 68.0 300.0 103.5 Mary River, Noosa River, Marcus Creek (n = 4) [1093] Water temperature (°C) 16.4 23.2 18.7 Dissolved oxygen (mg.L–1) 5.5 7.3 6.2 pH 4.4 6.5 5.1 Conductivity (µS.cm–1) 100.0 259.4 189.8 Turbidity (NTU) 8.0 25.0 13.7
Reproduction Relatively little is known of the reproductive biology and early development of N. oxleyana, except for that obtained from two field studies in Queensland [82, 84] and a limited amount of aquarium observations [797, 1348] (Table 3). This species spawns and completes its entire life cycle in freshwater and can be bred in captivity [790, 797, 1348].
Movement Genetic analysis of N. oxleyana populations from Lake Jabiru and Spitfire Creek, Moreton Island, and the Noosa River, two extensive systems compared to the small coastal streams most often inhabited, indicates that fish move, mix and interbreed within individual drainage systems [606]. However, little or no dispersal between individual catchments has occurred in their present configurations [82, 606]. On the other hand, Knight [726] has proposed that the wide occurrence of N. oxlyeana in streams and lakes near Evans Head in New South Wales may be a consequence of fish dispersing during periods of flooding
Maturation commences at a relatively small size. Minimum lengths of gravid (reproductive stage V) females and males from the Noosa River, south-eastern Queensland, were 30 mm TL and 27 mm TL, respectively [82, 84]. The spawning season is extended and is indicated by the assumption of breeding colours. In the Noosa River, spawning commenced in September/October and
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Nannoperca oxleyana
Table 3. Life history information for Nannoperca oxleyana. Age at sexual maturity (months)
4–5 months in aquariums [745]
Minimum length of gravid (stage V) females (mm) 30 mm TL [745, 797], 19 mm SL (mature females at Spitfire Creek) [82] Minimum length of ripe (stage V) males (mm)
27 mm TL [745, 797], 19 mm SL (mature males at Spitfire Creek) [82]
Longevity (years)
Possibly up to 5 years [726]
Sex ratio (female to male)
?
Occurrence of ripe (stage V) fish
September/October–March/April [82, 84], October–May [745]
Peak spawning activity
October–December [82, 84]
Critical temperature for spawning
>20°C [745, 1348]
Inducement to spawning
When water temperature exceeds 20°C [745, 1348]
Mean GSI of ripe (stage V) females (%)
3.3 ± 0.002 [82]
Mean GSI of ripe (stage V) males (%)
0.6 ± 0.197 [82]
Fecundity (number of ova)
23–270 eggs/fish [82]
Fecundity/length relationship
?
Egg size (diameter) (mm)
?
Frequency of spawning
Spawning is protracted with a few eggs being laid daily during the spawning season [745, 797, 1348]
Oviposition and spawning site
Eggs are demersal and adhesive attaching to aquatic vegetation or substrate [90, 745, 1348]
Spawning migration
None known
Parental care
None known
Time to hatching
1–3 days [797]; 3–4 days [745, 1348]
Length at hatching (mm)
?
Length at free swimming stage
?
Age at loss of yolk sack
?
Age at first feeding
1–2 days after hatching [1348]
Length at first feeding
?
Age at metamorphosis (days)
?
Duration of larval development
?
oxleyana to be quite mobile, moving as individuals, pairs and in groups of three or four younger individuals while foraging along the stems of aquatic plants. The extent of these daily foraging movements is unknown.
and hydrological connection of waterbodies on the low lying coastal plains. Studies at Marcus Creek, Queensland, indicate that when sufficient rain occurred to allow drainage from an upstream pool, the abundance of N. oxleyana decreased in the pool while the stream below yielded higher catches than previously [82, 1093]. This type of change may represent a form of dispersal as a necessary component of the species’ life history, or may simply represent opportunistic activity. Abundances at other sites surveyed by us were often reduced, sometimes to zero, during and shortly after high flow events [82, 84, 726]. Repetitively surveyed sites in the Mary River catchment recently recorded a few N. oxleyana well downstream from their previously known location in Coondoo Creek (an upstream tributary). This new record so far downstream in Tinana Creek can probably be explained by high flow events prior to sampling flushing N. oxleyana downstream. Whether these types of dispersal events are voluntary or not is unknown. Snorkeling observations in Spitfire Creek showed N.
Trophic ecology Dietary data for N. oxlyana are available for 178 individuals from the Noosa River [84] and Spitfire Creek on Moreton Island [82]. This species is a microphagic carnivore (Fig. 2). The total mean diet was composed primarily of microcrustaceans including copepods, ostracods and cladocerans (31.3%), aquatic insects (23.5%) and macrocrustaceans (mostly atyid shrimps, 22.2%). This species also consumed small amounts of terrestrial invertebrates, especially dipterans and small spiders (2.8%), aerial forms of aquatic insects (2.0%) and other microinvertebrates such as mites (6.9%). Substantial spatial variation in fish diets was evident between the two Queensland diet studies. Fish from the Noosa River consumed far more aquatic insects than fish
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Freshwater Fishes of North-Eastern Australia
Other microinvertebrates (6.9%)
Park and World Heritage listings), Moreton Island National Park, and the Forestry Scientific Reserve near Beewah (all in Queensland), and in Broadwater National Park, Bundjalung National Park and Yuraygir National Park in New South Wales [965]. Under the New South Wales Fisheries Management Act 1994 (amended 1997), waterbodies supporting this species have been recommended as components of Critical Habitat to be legislated under Part 7a of the amended Act [726]. This is regarded as a necessary step towards the conservation and recovery of this endangered species in New South Wales [965].
Unidentified (8.4%) Terrestrial invertebrates (2.8%) Aerial aq. invertebrates (2.0%) Terrestrial vegetation (0.2%) Algae (0.2%)
Microcrustaceans (31.3%)
Aquatic insects (23.5%)
Other macroinvertebrates (2.5%)
Macrocrustaceans (22.2%)
Figure 2. The mean diet of Nannoperca oxleyana. Data derived from stomach content analysis of 178 individuals from the Noosa River [84] and Spitfire Creek (Moreton Island) [82] in south-eastern Queensland.
from Spitfire Creek on Moreton Island (28% versus 4%, respectively). Noosa River fish also consumed a smaller component of micro- and macrocrustaceans. These differences may reflect variable food resources in the two types of system, with the riverine habitat possibly supporting higher diversity and abundance of aquatic insects than the relatively confined swamp at the terminus of Spitfire Creek. Such differences may also reflect the different duration of examination (i.e. a 12-month study versus a single sample for the Noosa River and Spifire Creek, respectively) [82].
The primary and increasing threats to N. oxleyana include loss of habitat due to residential housing development [90, 1358], road construction [1348], expansion of exotic pine plantations by forestry, and water contamination associated with urban and tourism development, mining operations and agriculture [82, 84, 90, 726, 790, 965, 1348, 1353]. Several aspects of the ecology of N. oxleyana are particularly relevant to its protection and recovery in wallum heathlands. This species is usually found where there is little or no flow and fish can find shelter in beds of emergent and submerged aquatic macrophytes or near undercut banks and fine root masses. Cover is an important factor in environments where surface (i.e. avian) and aquatic predators (fish) are present. The cover provided by aquatic macrophytes may also reduce the impact of short periods of high flow with the power to disrupt spawning activities, displace eggs and small individuals some distance downstream or carry fish into open areas with little protective cover. Rainfall patterns and consequently stream discharge are characteristically highly variable and unpredictable within and between years in south-eastern Queensland streams and rivers [1095]. Freshwater habitats within coastal wallum are particularly vulnerable to local rainfall events and long-term variability in precipitation levels, water depth and velocity [154]. In small streams and swamps, the aquatic macrophytes which serve as fish habitat and spawning sites can be flooded or swept away at high water levels and destroyed by exposure at low water levels. Areas with aquatic vegetation can also provide an abundant source of invertebrate food as well as filamentous and attached algae associated with a dense and complex structural habitat [82, 611]. Beds of macrophytes present a more productive and secure foraging habitat for N. oxleyana than sedge stands or open water areas where few individuals have been captured and probably limited foraging occurs [82, 84]. Other members of the genus Nannoperca show a preference for habitat with high levels of macrophyte cover [611].
Wager [1348] observed that the ideal diet for fish in aquaria includes cladocerans, ostracods, copepods, rotifers and other invertebrates. In captivity N. oxleyana will eat ‘almost anything that moves’, including mosquito larvae and earthworms [1348]. Conservation status, threats and management Nanoperca oxleyana is currently classified as Vulnerable under the Queensland Nature Conservation Act 1994, and as endangered under numerous legislations and conservation listings including: ‘The Action Plan for Australian Freshwater Fishes’ developed by Wager and Jackson [1353]; the Commonwealth Endangered Species Protection Act 1992; the NSW Fisheries Management Act 1994; the World Conservation Union (IUCN) Red List; the Australian Society for Fish Biology (ASFB) ‘Conservation Status of Australian Fishes’ Listing; and the Australian and New Zealand Environment and Conservation Council (ANZECC) ‘Threatened Fauna List’ [726]. Nannoperca oxleyana is probably fairly secure in some parts of its range, particularly in National Parks and other protected areas. These presently include the Noosa River and waterbodies on Fraser Island (protected by National
Severe disturbance of the aquatic plant communities found in coastal streams and swamps may have significant
358
Nannoperca oxleyana
implications for the persistence of N. oxleyana at the level of local populations [82]. Any type of land use, process, or pollutant that impacts on the diversity and biomass of aquatic vegetation in heathland waterbodies is a potential threat. Road and bridge construction have increased bank erosion and the sediment load in a number of small coastal creeks along the Sunshine Coast [82, 1348]. Urban development and housing construction in the vicinity of small creeks and swampy drainage lines may represent a serious threat if adequate precautions are not taken to contain sediment runoff from cleared land.
The occurrence of G. holbrooki in a few coastal creeks on Fraser Island and Moreton Island, in the Noosa River and in Mellum Creek, and in many other mainland creeks within the geographic range of N. oxlyeana, is considered to represent a general threat. Dispersal of alien fishes by natural processes (e.g. widespread flooding) is a possibility and G. holbrooki is a particularly hardy and adaptable species [83]. Human distribution of alien fish such as G. holbrooki still occurs occasionally [83]. In several New South Wales localities N. oxleyana may be threatened by large populations of G. holbrooki [726, 965, 1358].
Genetic analysis of populations from Lake Jabiru and Spitfire Creek, and the Noosa River, two very extensive systems compared to small coastal creeks, supports the view that fish move, mix and interbreed within individual drainage systems [606]. Maintenance of hydrological connectivity within individual drainage systems should be an objective of a conservation strategy for N. oxleyana. Small weirs and other obstructions may interrupt such movements by blocking fish passage, and should be removed or modified to permit fish passage [965].
Introduced plants may also substantially modify freshwater habitats. Marcus Creek south of Noosa Heads, is a small confined waterway invaded in its lower reaches by the South American ponded pasture species, Brachiaria mutica (para grass). This invasive weed has a severe impact on aquatic habitat, water quality and biodiversity in small streams and does not contribute carbon (i.e. energy) to aquatic food webs [95, 248, 250]. Over-exploitation of N. oxleyana is only an issue with respect to the collection of fish for aquarium stocks. The intensity and impact of this activity is not known. The Australia New Guinea Fishes Association (ANGFA) has a strong commitment to the conservation of indigenous biota and has issued several warnings to its membership that excessive collection of rare freshwater species for aquarium purposes is potentially deleterious. Members of the public who are not familiar with the fauna of particular systems may inadvertently collect a rare species, only to discard it later in the day, possibly into a different waterbody. Public education is probably the most effective way to combat this type of impact.
Alien species are regarded as perhaps the most insidious and unpredictable threat to rare fish species and may be the most difficult to counter and manage [82]. Several alien fish species have been recorded in catchments where N. oxleyana also occurs in the south-eastern Queensland wallum ecosystem. These species include Gambusia holbrooki, Xiphophorus helleri, X. maculatus and Misgurnus anguilicaudatus; all except the latter species are thought to have established self-maintaining populations in many of these catchments. Gambusia holbrooki is a particularly threatening species [77, 78, 416] and many studies (see [78]) have demonstrated its trophic flexibility (including the consumption of fish eggs and larvae), and its innate aggressiveness towards other fishes is well known [983]
Relatively high levels of allozyme and mitochondrial DNA variation among discrete populations of this species suggest that dispersal among isolated populations is extremely limited and once eliminated, small populations are unlikely to be restored by natural dispersal [606]. This has implications for conservation. Any stocking activities to replenish populations at risk should use stock reared from system-specific genotypes [606].
Gambusia holbrooki is established in several Queensland localities supporting N. oxleyana (e.g. some sites in Mellum Creek, Marcus Creek and parts of the Noosa River). Dietary studies in the Noosa River indicate that the two species feed on aquatic and terrestrial invertebrates but that their diets differ due to the higher dependence of G. holbrooki on prey of terrestrial origin [84]. However, G. holbrooki is capable of feeding at all levels in the water column [78] and in Blue Lake, North Stradbroke Island, has been shown to switch to the preferred prey of native fishes at some times of year [92]. It is possible that the G. holbrooki may utilise food resources that are important to N. oxleyana. Predation upon the eggs and early developmental stages of N. oxleyana is also a possibility but has not been demonstrated.
Two fundamental approaches to the conservation of N. oxleyana in Queensland have been recommended [82]. The first would involve efforts to conserve all of the separate, genetically differentiated sub-populations of the species in order to conserve maximum genetic diversity [82, 606]. An alternative approach would be to focus on the protection of large tracts of coastal heathlands and the waterbodies therein, especially on the Queensland mainland, where the existing system of reserves offers limited protection for wallum ecosystems and their indigenous flora and fauna. Both approaches are relevant to the
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Freshwater Fishes of North-Eastern Australia
habitat characteristics, planting of riparian vegetation, and elimination of G. holbrooki [82, 84, 726, 965]. A recovery plan [82] for this Vulnerable species has not been implemented by the Government agencies responsible for environmental protection in Queensland.
conservation of N. oxleyana. Arthington et al. [82], Knight [726] and Morris et al. [965] recommended a range of specific recovery actions to conserve individual localities and populations. These could include rehabilitation of degraded creeks, restoration of channel morphology and
360
Amniataba percoides (Günther, 1864) Barred grunter, Banded grunter
37 321009
Family: Terapontidae
This species is the smallest of the therapontid grunters, occasionally reaching 200 mm SL but most often less than 120 mm SL. The relationship between length (SL in mm) and weight (g) for fish from the Burdekin River [1093] takes the form: W = 3.80 x 10–5 L2.965; r2 = 0.968, n = 560, p<0.001. The relationship between length (CFL in cm) and weight (g) for fish from the Alligator Rivers region [193] takes the form: W = 0.0185 L3.06; r2 = 0.990, n = 581, p<0.001. Note the differences in units and definition of length.
Description Dorsal fin: XIII–XIV, 8–10; Anal: III, 7–9; Pectoral: 14–16; Pelvic: I, 5; Lateral line scales: 36–43; Horizontal scale rows: 13–15 below lateral line, 5–7 above; Predorsal scales: 14–16 scales to occiput; Cheek scales: 4–5 rows; 1 row of scales in sheath at base of dorsal, sheath extending to third or fourth dorsal ray; two scale rows in anal fin base sheath, sheath extending to third or fourth ray [1346]. Note that Vari [1346] included Nichol’s paratypes (see below) in his review and the fact that the upper limit of the number of lateral line scales in the former is less than the average for A. percoides yorkensis by Nichols indicates some problems in defining exactly what are lateral line scales in this species). Figure: adult specimen, 63 mm SL, upper Burdekin River, April 1995; drawn 1999.
It is difficult to confuse this species with any other therapontid grunter due to its distinctive coloration. The top of the head is dark with the several dorsal head stripes visible in juveniles, variably masked in larger specimens. Dorsal surface dark brown, base colour of golden-tan grading to white on ventral surface. Five to seven vertical black bars present on side, each about two scales wide. Diffuse spots present on flanks. Colour in preservative: similar to that in life, except golden colour faded to dull tan.
Amniataba percoides is a medium-sized species with a moderately compressed, deep body. The dorsal profile is more pronounced than the ventral. Gape oblique, mouth small (gape (mm) = 1.226 + 0.089 (SL in mm); r2 = 0.752, n = 527, p<0.001), maxillary reaching only to vertical through posterior nostril. Teeth conic, arranged in bands, outer row enlarged. Interorbital region with distinct ridges; lachrymal serrate; preoperculum serrate; cleithrum exposed, serrate posteriorly.
Systematics The Terapontidae is a moderately speciose family of fishes inhabiting marine, estuarine and freshwaters of the Indo-West Pacific. The family has undergone most of its
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Freshwater Fishes of North-Eastern Australia
diversification in the freshwaters of northern Australia and New Guinea [1346]. Fossilised otoliths of an unidentified terapontid have been collected from the Rundle oil shale formation and tentatively aged as Oligocene [1335]. Vari [1346] believed the family to be considerably older than this and postulated that marine/estuarine terapontids may have inhabited the Australian near-shore environment as early as 150 m.y.b.p. The family is composed of 15 genera.
population variation shown by A. percoides are best disregarded in taxonomy and it appears that the only justification for the erection of the subspecies yorkensis is ‘…that it will prove advantageous to recognise a few of the major geographic variations’ (p. 5). On this basis and an inability to recognise any consistent geographic morphological differences (despite acknowledging the existence of differences between populations), Vari [1346] did not recognise any subspecific units in his revision of the species.
The genus Amniataba was first erected by Whitley [1388] in 1943 to contain a single species: A. percoides; previously placed in the genus Therapon. Whitley also proposed the monotypic genus Amphitherapon at the same time to contain Amniataba caudivittatus, a widespread, predominantly estuarine grunter. This species was later placed within Amniataba by Vari [1346]. Vari considered the genus to be one of the least derived in the family. Amniataba contains two Australian species and one New Guinean species, A. affinus, and is distinguished from other therapontids by the possession of two spines on the first proximal dorsal pterygiophore, the absence of a foramen for exit of blood vessels from the third haemal arch anterior to the parahypural vertebrae, and by its distinctive caudal mottling pattern. The two Australian species are distinguished by the presence of vertical black bars in A. percoides and an oblique black bar across each lobe of the caudal in A. caudivittatus. Both species possess body spots (despite assertions to the contrary [1346]), but they are smaller and more numerous in A. percoides.
Vari [1346] was probably justified in disregarding the subspecific status of A. percoides yorkensis, however it must be highlighted that he did not examine a single specimen from east of the Great Dividing Range. Comparison of DNA sequence divergence in populations on either side of the Great Dividing Range in northern Queensland has revealed substantial divergence (3.4%), certainly enough to warrant reconsideration of the extent of subspecific differention within the species [1083]. It is not surprising that geographic differences exist in a species that is as widely distributed as A. percoides (see below). Distribution and abundance Amniataba percoides is a very widespread species. The natural southern limit in Queensland appears to be the Gregory River north of Maryborough [700] (but see below). This species has recorded from the Elliot, Kolan and Burnett rivers also but is not overly abundant in any of these rivers [700]. This species comprised only 0.31% of total fish collected during surveys in the Burnett River but was present in 15.9% of study sites. Distribution within the Burnett River is patchy: for example, it penetrates no further than 30 km up Barker Creek (a major tributary) [101, 205]. Amniataba percoides has been recorded from the Boyne and Baffle rivers near Gladstone [1349]. The distribution within the Fitzroy River extends from the downstream barrage [1274] to headwater streams [155, 160, 942]. This species has been recorded from Planes Creek and Rocky Dam Creek near Sarina [779]. It is present but not widespread in the Pioneer River and Proserpine River [1081] but has not been recorded from the Don River near Bowen [590].
This species was originally described from material from the Fitzroy River near Rockhampton [1042]. Several synonyms (in addition to T. percoides) exist and include T. fasciatus Castelnau, 1875 (west coast of Australia); Datnia fasciata Steindachner, 1877 (?Queensland); T. terrae-reginae Castelnau, 1877 (?Fitzroy River) and T. spinosior DeVis, 1884 (Queensland). Two subspecies have been erected: A. percoides burnettensis Whitley, 1943 from the Burnett River, and A. percoides yorkensis Nichols, 1943 from the Archer and Coen rivers of Cape York Peninsula [1346]. The erection of A. percoides burnettensis by Whitley [1388] was based solely on the inclusion in Ogilby and McCulloch [1024] of a key distinguishing populations in the Burnett River from ‘typical’ A. percoides in the Fitzroy River. Nichols [990] provides a very comprehensive description of A. percoides yorkensis yet does not also provide a set of characters that might reliably distinguish this subspecies from any other forms. The only substantive difference is that A. percoides yorkensis has marginally more lateral line scales (41–47) than that of the series examined by Vari [1346] (36–43) (n = 372, 17 of which were paratypes of A. percoides yorkensis). Nichols agreed with Ogilby and McCulloch’s assertion that minor
Amniataba percoides is common and widely distributed in the Burdekin River [1098] where it comprised 6.0%, 8.9% and <0.1% of electrofishing, seine- and gil-netting catches, respectively, in a study conducted over the period 1989–1992. This species is present upstream and downstream of the Burdekin Falls and in upstream tributary streams. Surveys undertaken in tributary streams of the Dotswood area (Keelbottom Creek, Star River, Fanning River) reveal that barred grunter made up 1.55%, 3.4%, 2.66% and 6.19% of electrofishing, seine-netting, bait trap and gill-netting catches, respectively, but was absent from
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Amniataba percoides
1350], Watson [1349], Archer [571, 990, 1349], Holroyd [571, 1349], Coleman [571, 1349], Edward [571], Mitchell [571, 785] rivers. Wager [1349] states that it is present in all basins throughout the Gulf drainage division.
hand-netting catches [1408]. This species has not been recorded from the Balyando River in the south-west of the catchment [256]. The distribution of barred grunter is patchy in coastal drainage systems to the north of the Burdekin River, having been recorded from the Ross River [1349] but not the Black-Alice River [176] or shorter coastal tributaries such as Leichardt Creek, St. Margaret’s Creek, Hencamp Creek and Saltwater Creek [1053]. Pusey and Kennard [1087] did not collect a single specimen in their extensive survey of the Wet Tropics region. It has been subsequently collected in small numbers from the southern portion of the region however, being recorded from floodplain habitats of the Herbert River (4/11 sites) [584], Tully/Murray River (2/16 sites) [583], Maria Creek (1/17 sites) [1179], and the Moresby River (2/18 sites) [1183]. This species was not recorded in other surveys undertaken in the Tully River [98, 1087, 1093]. This species was not collected from the Liverpool (29 sites) or Hull (5 sites) drainages [1179] or from the Johnstone River [1093, 1096, 1177] or Mulgrave River [1093, 1096, 1184] despite an extensive sampling effort over several years. The presence of barred grunter in the upper Barron River is the result of stocking in the past [229]. Amniataba percoides has not been recorded in the Mowbray River (5 sites), Mossman River (16 sites), Saltwater Creek (20 sites) or Daintree River (40 sites) [1185].
It is probable that the distribution of A. percoides is continuous across the larger northerly flowing drainages of the Northern Territory as it has been recorded from Arnhem Land [34, 1304, 1346], the Kakadu region [193, 1346, 1416], and west to the border with northern Western Australia [774, 1346]. It was the 10th most abundant species in an intensive study of the fishes of the Alligator Rivers region [193]. Its distribution is apparently discontinuous in the Kimberley region, being absent from the Isdell, Roe and Prince Regent rivers but present in the Ord, Drysdale, Bow, Mitchell, Lawley, Carson, Meda and Fitzroy river basins [30, 45, 388, 619, 620, 1346]. Barred grunter also occur in the Pilbara region, having been recorded from the George, Maitland, Fortescue, Robe and Ashburton rivers [1346]. It seems highly likely that it is present in the DeGrey River also. The distribution of barred grunter extends also to drainage systems of central Australia. It is apparently absent from drainages within the Western Plateau drainage division but has been recorded from the Georgina and Fink rivers of the Lake Eyre drainage basin [121, 457, 1346, 1349]. It is apparently restricted to rivers and does not occur in springs.
The distribution of barred grunter across eastern Cape York Peninsula is similarly patchy; being present in the Endeavour and Annan rivers [599, 1349], apparently absent from the McIvor and Starke rivers immediately to the north [571], and once again present in the Normanby River [697, 1099, 1349] and the Hann River [990], both of which drain into Princess Charlotte Bay. It is probable that this species also occurs in the Kennedy River given that it and the Normanby and Hann rivers are connected by numerous distributaries near their respective river mouths. Pusey et al. [1099] found A. percoides to be the fourth most abundant species in combined electrofishing and gill-netting samples in the Normanby River, comprising 9.4% of the total. In another study in the Normanby River [697], barred grunter comprised 1.9% and 2.8% of electrofishing samples, and 0.9% and 1.2% of gill-netting samples in floodplain lagoon and main river channel lagoons, respectively.
This species is absent from the upper reaches of the Murray-Darling river system [264, 947] and does not naturally occur in freshwaters of New South Wales [553]. Amniataba percoides has recently been recorded from the Clarence River, outside of its natural range [1163]. It presence there is apparently due to inadvertent translocation as barred grunter have been detected in a hatchery-reared consignment of Bidyanus bidyanus. Concerns about the impact of barred grunter on native fishes in the Clarence River, particularly the endangered Eastern Cod Maccullochella ikei, have resulted in it being declared a noxious fish under the New South Wales Fisheries Management Act 1994 [1163]. Translocation has also extended the southern limit of A. percoides in Queensland to include the Brisbane River [1093]. Macro/meso/microhabitat use Amniataba percoides is widely but patchily distributed within individual river systems and may be found from relatively low-gradient lowland and upper reaches, but is rarely collected from high gradient tributary streams. Its apparent aversion to high gradient streams may be one reason for its absence from many rivers of the Wet Tropics region. In the Alligator Rivers region, this species was
Amniataba percoides has not been recorded from any other eastern Cape York rivers north of the Hann River, despite extensive survey effort [571, 785, 1099]. Amniataba percoides is very widespread on the western side of Cape York Peninsula, being thus far recorded from the Jardine [41], Ducie [1349], Wenlock [571, 785, 990,
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Freshwater Fishes of North-Eastern Australia
al. [193] with regard to environmental tolerances in general) and a lower temperature limit of 10°C is not unreasonable. The recent establishment of a self-sustaining population in the Clarence River [1163] suggests that the natural distribution of barred grunter in rivers of the east coast of Australia is not limited by water temperature. Merrick and Schmida [936] report barred grunter being collected from waters at 40°C. It is unlikely that barred grunter could survive temperatures more than a couple of degrees in excess of this temperature and it is also unlikely that high temperatures in excess of 35°C could be endured for long periods.
found in sandy corridor lagoons (and to a lesser extent muddy floodplain lagoons), sandy creek-bed pools, and escarpment pools. Larger adult specimens were more commonly collected from deeper, more permanent waters of the escarpment and floodplain [193]. Although found in floodplain lagoons of the Normanby River [697], it was more abundant in lotic habitats of the main channel [1093]. In the Burdekin River, A. percoides is very widely distributed and occurs both upstream and downstream of the Burdekin River Falls, and in main channel and tributary habitats [1098]. This species is significantly less abundant in tributary streams however [1093]. Ordination and correlation analysis indicates that A. percoides is more abundant in shallow stream reaches with flows greater than 0.3 m.sec–1 (i.e. runs) and a coarse substrate [1098]. Interestingly, barred grunter from such habitats attain significantly greater condition values (weight for a given length) than do fish from tributary streams [1093].
Barred grunter appear moderately tolerant of hypoxia given the low levels of dissolved oxygen recorded in floodplain lagoons of the Normanby River and the extremely low level recorded in the Alligator Rivers region. However, it must be emphasised that barred grunter was not an abundant species in the lagoons studied by Kennard [697] and that low dissolved-oxygen may have been one factor limiting abundance. Woodland and Ward [1416] recorded barred grunter from isolated sandy pools of Magela Creek in which dissolved oxygen fell as low as 0.8–1.3 mg.L–1.
Bishop et al. [193] found A. percoides to be most commonly collected from areas with a dominant substrate of sand. In the Burdekin River, A. percoides is far less associated with bankside structures and woody debris than are other terapontids. As a consequence, they tend to comprise a much larger fraction of seine-netting catches than electrofishing catches [1098, 1408].
Table 1. Physicochemical data for barred grunter Amniataba percoides. Turbidity values* are in cm (Secchi depth) for the Alligator Rivers region, and in NTU for the Burdekin River and the Normanby River. Data listed for the Alligator Rivers region were recorded at the bottom of the water column.
Amniataba percoides is a benthic species and rarely observed in the upper half of the water column.
Parameter
Environmental tolerances Experimental data are lacking and inferences about environmental tolerances must be drawn from field data. Data listed in Table 1 are drawn from two long-term studies, one medium-term study, and one short-term study. The first was conducted in the Alligator Rivers region over 15 months [193], the second was conducted in the Burdekin River [1098] over three years, the third was conducted in floodplain lagoons of the Normanby River over a sixmonth period (one late-wet and one late-dry season sample) [697] and fourth was conducted in the Normanby River in the mid-dry season [1099].
Min.
Max.
Mean
Alligator Rivers region Temperature (°C) 23 Dissolved oxygen (mg.L–1) 0.2 pH 4.5 Conductivity (µS.cm–1) 2 Turbidity (cm) 1
35 9.5 7.3 230 360
112
Burdekin River (n = 42) Temperature (°C) 21 Dissolved oxygen (mg.L–1) 4.6 pH 6.75 Conductivity (µS.cm–1) 48 Turbidity (NTU) 0.28
32 11.0 8.46 780 17.0
26.2 7.73 7.66 385.7 2.97
28.9 4.8 6.0
Normanby River floodplain lagoons (n = 9) Temperature (°C) 23 27.7 25.1 Dissolved oxygen (mg.L–1) 1.0 7.1 3.52 pH 6.0 7.51 6.80 Conductivity (µS.cm–1) 81 270 175.3 Turbidity (NTU) 2.1 8.1 5.17
The average temperatures listed for barred grunter (Table 1) probably reflect the average annual water temperature for most of northern Australia and as such only reflect the fact that barred grunter are naturally restricted to north of 25°S on the east coast and 23°S on the west coast. The minimum temperature recorded (21°C) is high and probably much greater than the actual lethal lower temperature. The similarity between the distribution of spangled perch and of barred grunter suggests a similar temperature tolerance (a suggestion remarked upon by Bishop et
Normanby River main channel (n = 6) Temperature (°C) 21 26 Dissolved oxygen (mg.L–1) 7.3 11.0 pH 6.45 8.2 Conductivity (µS.cm–1) 80 420 Turbidity (cm) 0.5 5.4
364
24.2 8.9 7.0 307 2.4
Amniataba percoides
Amniataba percoides reaches maturity at a small size and in its first year (Table 2). Gender is discernible at a very small size (40–50 mm) in both sexes and fully mature, stage V, adults were observed at lengths as small as 59 and 80 mm CFL for male and female fishes, respectively, in the Alligator Rivers region [193]. It is probable that the maximum lifespan is between three and four years but it must be stressed that no ageing studies have been undertaken on this species. A sex ratio approaching unity has been observed in both the Burdekin River [1082] and the Alligator Rivers region [193].
However, it should be noted that barred grunter in such environments decreased in abundance with time and these authors characterised them as a species showing high mortality. High mortality may have been associated with depressed oxygen availability. In the Burdekin River, A. percoides prefers flowing water and riffle and run habits (see above), and it is probable that it prefers welloxygenated water in this river. Barred grunter occur over a wide pH range (4.5–8.45): the pH range from each study is substantially smaller however (2.8, 1.71, 1.51 and 1.75 pH units for the Alligator Rivers region, Burdekin River, Normanby River floodplain and Normanby River main channel, respectively) suggesting that acclimation may be important. The greater range listed for the Alligator Rivers region reflects the greater diversity of study sites examined (escarpment pools to lowland floodplain lagoons). A similar range is seen for the Normanby River if floodplain and main channel sites are combined. On the basis of the data presented here, we suggest that the optimum pH range for A. percoides is 5.5–8.
The spawning season appears to be variable in occurrence across its range [931], lasting from August (the early dry season) to March (mid-wet season). In the Alligator Rivers region, ripe fish are present from the late dry (Sept/Oct) to the mid-wet season (Jan/Feb) [193]. In the Burdekin River, peak recruitment occurs during the dry season. Barred grunter are apparently able to breed in impoundments [936] and the fact that breeding can occur prior to the onset of wet season flooding indicates that rising water levels are not an important stimulus for spawning, as has been suggested for other terapontids. It is probable that increasing day length or water temperatures cue spawning but it is evident from the observed regional differences in the phenology of spawning that a single critical temperature does not exist and that a range of temperatures from 26–33°C [936] is important. Further information concerning temperatures critical for reproduction in geographically distinct stocks is needed.
Amniataba percoides has been recorded from freshwater only. It was not recorded in any of the surveys undertaken in north-eastern Queensland estuaries reviewed by Pusey [1081]. However, given its phylogeny, it is probably able to withstand, for short periods at least, high levels of salinity, similar to that observed for L. unicolor. Although the data presented in Table 1 indicates that A. percoides may be found in very turbid waters, it is most frequently found in relatively clear waters (turbidity <5 NTU). The absence of A. percoides from the south-western tributaries of the Burdekin River (i.e. Balyando River) may be a result of the persistently high turbities characterisitic of these rivers (e.g. Burrows et al. [256] recorded a mean turbidity of 414 NTU across five sites in the Belyando River during the dry season).
Amniataba percoides is relatively fecund, producing many thousands of small eggs (Table 2). Data are lacking to allow a rigorous assessment of whether spawning occurs only once a year or is more protracted. However, that the maximum GSI recorded was 6.04% only, coupled with the observation that egg size is variable within individual females (i.e. suggestive of multiple batches) strongly suggests that spawning may be protracted and that several batches of eggs are produced in one season.
The paucity of experimental data concerning the environmental tolerances of this species greatly reduces the extent to which we can predict how it might respond under various types and intensities of impact or to speculate on what factors limit its distribution. That this is the case for such a common and widely distributed species is highly regrettable.
Spawning may occur in a number of different habitats. In the Alligator Rivers region, spawning occurred in escarpment main channel water bodies, sandy lowland creekbeds, muddy lowland lagoons, and corridor and floodplain lagoons (i.e. nearly all available habitats) [193]. Spawning occurred in main channel and tributary streams of the Burdekin River [1093]. Spawning behaviour has not been observed nor is the location of the oviposition site known. However, the eggs are known to be demersal and non-adhesive and it is likely that spawning occurs over sand and mud substrates. Nothing is known of the larval development of this species.
Reproduction Information concerning the reproductive biology of this species is surprisingly scant. Bishop et al. [193] includes some information, based on a small number of adult fishes, on its reproduction in the Alligator Rivers region. Merrick [931] includes comments drawn from observations in several river systems and Pusey [1082] reports on some demographic aspects of its biology in the Burdekin River.
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Freshwater Fishes of North-Eastern Australia
Table 2. Life history data for Amniataba percoides. Data drawn from Pusey et al. [1082, 1093] for the Burdekin River (BR) and Bishop et al. [193] for the Alligator Rivers region (ARR) unless otherwise noted. Age at sexual maturity (months)
<12 months
Minimum length of ripe females (mm)
BR – Sex discernible at 50 mm SL ARR – Sex discernible at 40 mm CFL, first maturity at 50 mm, smallest stage V at 80 mm
Minimum length of ripe males (mm)
BR – Sex discernible at 50 mm SL ARR – Sex discernible at 50 mm CFL, first maturity at 70 mm, smallest stage V at 59 mm
Longevity (years)
? 3–4 years
Sex ratio (female to male)
1:1
Occurrence of ripe fish
Variable across range: August to March [936] BR – dry season ARR – late dry to early wet
Peak spawning activity
As above
Critical temperature for spawning
26–33°C [936]
Inducement to spawning
? probably temperature, flooding not obligatory
Mean GSI of ripe females (%)
ARR – 5.2 (peak 6.04%)
Mean GSI of ripe males (%)
ARR – 3.0
Fecundity (number of ova)
40 000–70 000 [936] ARR – mean fecundity of 125 000
Fecundity/length relationship
?
Egg size (diameter in mm)
0.4–0.45 mm water hardened [936], range of egg size intraovarian 0.16–0.40 mm [193]
Frequency of spawning
Unknown frequency within season, iteroparous over lifetime
Oviposition and spawning site
Varied (see text)
Spawning migration
Varied in extent and timing (see text)
Parental care
Absent
Time to hatching
?
Length at hatching (mm)
?
Length at free swimming stage
?
Length at metamorphosis (days)
?
Duration of larval development
?
Age at loss of yolk sack
?
Age at first feeding
?
Information on movement of A. percoides in Queensland rivers is limited to that derived from fishway studies. Berghuis [155] recorded barred grunter moving past the Eden Ban Weir in the Fitzroy River over a long period from April to January (i.e. mostly during the dry season). Stuart [1274] recorded upstream movement through the Fitzroy River barrage from July to November and again during February but with the greatest numbers moving between September and November. Both upstream and downstream movement through a tidal barrage in the Burnett River was noted by Russell [1173], however the total number recorded over 21 ⁄2-year period was very low (15 individuals). Kennard [700] considered that most movement was undertaken by dispersing juveniles.
Movement Bishop et al. [193] report that adult A. percoides were most frequently collected from perennial escarpment habitats whereas small fish were collected from lowland habitats especially sandy corridor habitats. Bishop et al. [193] suggest that barred grunter spawn over a range of habitats; A. percoides moved from refugial escarpment habitats to lowland floodplain habitats at the commencement of the wet season [190]. Return upstream migrations were made by juvenile and adult grunter as lowland habitats contracted with the onset of the dry season and these migrations occurred at slightly different rates consistent with differences in body size. Fish less than 50 mm SL were recorded moving upstream at 6.46–7.25 km.day–1 whereas adults moved at 8.53–9.44 km.day–1. Movement occurred during daylight hours and there was no significant change in the number of migrating fish over the course of the daylight period.
In the Burdekin River, some adults move into tributary streams to spawn but this does not appear to be an obligate part of their reproductive pattern [1093].
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Amniataba percoides
component of the average diet, reflecting the constraint imposed by a small mouth gape. Mouth gape increases with body size (see above) and macrocrustacea increase in importance in large individuals. For example, small barred grunter (<40 mm) in the Burdekin River consumed no macrocrustacea but this source of prey accounted for 4.4% of the diet in fish greater than 80 mm SL [1103]. Microcrustacea contribute almost 5% to the average diet and the importance of this component varied between studies (see below). Terrestrially derived prey were a minor component of the diet reflecting the benthic foraging style of barred grunter.
Trophic ecology Dietary information presented in Figure 1 was derived from seven separate studies undertaken in a range of regions and habitats: the Alligator Rivers region (n = 131 [1416], 479 [193]); Cape York Peninsula (n = 20 [599], 41 [697], 56 [1099]); the Burdekin River (n = 517 [1093]), and the upper Burnett River (n = 15 [205]). Amniataba percoides is omnivorous, with about 23% of the diet being comprised of aquatic vegetable matter and 5% comprised of terrestrial vegetation (Fig. 1). In the Burdekin River, the relative importance of aquatic vegetation, and the type of vegetation consumed, changes markedly with increasing size. Fish less than 40 mm SL consume only small amounts of filamentous algae (5.7%). Larger fish (40–80 mm SL) consume much more filamentous algae (19.9%) but only small amounts (1.2%) of aquatic macrophytes. The largest size class (>80 mm SL) consumed even more filamentous algae and macrophytes (28.2% and 8.6%, respectively) [1093]. Notably, these changes appear unrelated to ontogenetic changes in gut morphology as A. percoides possesses a relatively simple gut (unlike some other terapontids that develop a multicoiled gut with age) but may be associated with increasing gut length.
The seven studies included here cover a substantial geographical range and range in habitat types, and accordingly there is substantial variation in diet between the studies. For example, gastropod molluscs were prominent in the diet of fish from Barambah Creek in the Burnett River (15%), as was detritus (25%). These items rarely exceeded 4% in the other studies. Microcrustacea were very important prey for A. percoides in the isolated sandy pools of Magela Creek (25%) [1416]. Intermediate levels of microcrustacean consumption were also observed in floodplain lagoons of the Normanby River [697] (3.2%). Microcrustacea were absent from the diet of fish in the main channel of the Normanby River [1099], the Annan River [599] and the Burdekin River [1103]. These data suggest that barred grunter modify their foraging behaviour in different habitats and under conditions of different food availability.
Fish (1.8%) Other microinvertebrates (0.1%) Microcrustaceans (2.8%) Macrocrustaceans (1.4%) Molluscs (1.0%) Other macroinvertebrates (0.6%)
Unidentified (4.1%) Terrestrial invertebrates (0.6%) Aerial aq. Invertebrates (0.7%) Terrestrial vegetation (5.1%) Detritus (0.7%)
Spatial variation in the diet at finer scales has also been demonstrated. Bishop et al. [193] identified differences in the diet of fish from several different habitat types (i.e. escarpment pools, sandy creekbed pools) involving switches from filamentous algae to macrophytes, and changes in the relative contributions of aquatic insect larvae, microcrustaceans or fish. Similarly, Pusey et al. [1103] observed that dietary composition varied according to average water velocity, reflecting the types of invertebrates that occur in habitats of different current speed (i.e. simuliid larvae were important in flowing water tributary sites but absent from low gradient tributaries).
Aquatic macrophytes (6.1%)
Algae (16.4%)
Aquatic insects (58.6%)
Figure 1. The average diet of Amniataba percoides. Data presented are the mean contributions of each category derived from several studies and weighted by the number of individuals used in each study. The studies and the sample sizes used are detailed in the text.
Fish, on average, are only a minor component of the diet of barred grunter (1.4%). However, fish were a more important prey source in both studies undertaken within the Alligator Rivers region (3.7% in both) [193, 1416]. In summary, Amniataba percoides is omnivorous. The majority of the diet is composed of benthic aquatic insect larvae although it very occasionally forages at the water’s surface. Plant matter is an important component of the diet and its importance increases with increasing size. Substantial spatial variation in diet is apparent and related
The major component of the average diet of barred grunter is aquatic invertebrates (such as chironomid larvae, trichopteran larvae and ephemeropteran nymphs) as would be expected from a benthic/lower water column species with a generalised percimorph body plan. Macrocrustacea (shrimps and prawns) are a minor
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Freshwater Fishes of North-Eastern Australia
water velocity are likely to reduce population sizes. Third, although A. percoides is not dependent on floods for spawning, recruits do benefit from the increase in available resources associated with flooding. Spawning prior to the break of the wet season may give juveniles a competitive advantage over other terapontid species more reliant on flooding. Desynchronisation of flow and thermal regimes may reduce recruitment success. In the case where downstream releases of water from dams occurs, changes to the downstream temperature regime may disrupt or completely curtail spawning. Similarly, large downstream releases during the late dry period may result in significant larval mortality. Changes in flow regime that impact on primary and secondary production are likely to be the most important way in which water resource development may impact on this species. Increased primary production will not favour this species despite the fact that it is able to eat filamentous algae. Moreover, juveniles are unable consume plant matter and the negative impacts on metazoan prey availability associated with increased primary production are likely to impact heavily on juvenile barred grunter. Finally, it should be emphasised that the translocation of A. percoides, inadvertent or otherwise, may represent a threatening process to other fish species.
to differences in habitat. The generalised nature of the diet allows it to be successful in a range of different conditions that range from small flowing streams through to large rivers or lentic floodplain habitats. However, its generalised foraging style ensures that, at least in some drainage systems, barred grunter may compete with other terapontids such as spangled perch [1093]. Conservation status, threats and management Amniataba percoides is listed as Non-Threatened by Wager and Jackson [1353]. The wide distribution and varied habitat use exhibited by A. percoides suggest that it is a highly adaptable species. However, several aspects of its biology indicate its susceptibility to perturbation by flow regime manipulation and water resource development. First, infrastructure that inhibits the movement of this species is likely to impact in the long-term. Second, this species shows a preference for flowing water habitats in some drainages, and changes in flow regime that reduce average water velocities may disadvantage this species and favour competitors such as spangled perch. It must be emphasised however, that A. percoides is not usually found in swiftly flowing streams. Changes in flow regime (i.e. supplementation) that greatly increase within-channel
368
Leiopotherapon unicolor (Günther, 1859) Spangled perch
37 321018
Family: Terapontidae
Description Dorsal fin: XI–XIII, 9–12; Anal: III, 7–10; Pectoral: 15–16; Pelvic: I, 5. Vertical scale rows: 45–57; Horizontal scale rows: 23–29, 7–9 scales above lateral line, 3–6 scales on caudal; Predorsal scales: 15–20. One row of scales in dorsal fin sheath, two in anal fin sheath. Cheek scales in 6–9 rows. Sexually dimorphic only during breeding season when the female genital papillae becomes enlarged and bulbous. Figure: adult specimen, 120 mm SL, upper Burdekin River, April 1995; drawn 1999.
Burnett River [99] and relates weight (g) to SL (cm): 0.037 L2.936; r2 = 0.910, n = 277, p<0.001. The fourth was also generated from a sample collected in Barambah Creek and relates weight (g) to Standard Length (mm) [205]: W = 2.2 x 10-5 L3.06; r2 = 0.996, n = 388, p<0.001. Note the differences in unit length (cm versus mm). Given that the first relates weight to caudal fork length and the remainder to standard length, these relationships are very similar and indicate that there is little difference in the length/weight relationship over much of its range.
Leiopotherapon unicolor is a moderately sized, robust species commonly attaining 150 mm SL and occasionally larger. Maximum length recorded by us is 330 mm SL for a specimen collected from the impounded waters of the Suttor River in the Burdekin River catchment [1093]. Four equations relating length to weight are available. The first was generated from a sample collected from the Alligator Rivers region and relates weight (g) to caudal fork length (cm) [193]: W = 0.0204 L2.949, r2 = 0.980, n = 349, p<0.001. The second was generated from a large sample collected from the Burdekin River drainage and relates weight (g) to standard length (mm) [1093]: W = 2.50 x 10–5 L3.049; r2 = 0.983, n = 1067, p<0.001. The third was generated from a sample from Barker Barambah Creek, a tributary of the
The body is slender, tending to be more fusiform in small individuals. Large individuals may sometimes develop a concave dorsal head profile. Jaws equal in length with slightly oblique gape. Gape relatively large: gape in mm = 0.15(SL in mm)–0.30; r2 = 0.929, n = 246, p<0.001 [1093]. Teeth strong and conic with the outer row enlarged and the inner teeth being villiform and arranged in bands [1346]. Lachrymal weakly serrate whereas the preoperculum more strongly serrate, particularly on the posterior edge. Cleithrum exposed and serrate on the posterior margin whereas the post temporal not exposed (etymology of genus name refers to smooth shoulder). Coloration dominated by silver background overlain with numerous bronze spots. Head and dorsal surface tend to be darker.
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Pectoral and pelvic fins tend to be colourless whereas as dorsal, anal and caudal fins tend to be duskier. Juvenile fish characterised by a black mark coupled with a more dorsally oriented yellow mark along the ventral edge of the caudal fin, a pattern that diminishes at around a length of 58 mm; the approximate length at which sexual maturation is underway. Colour may be variable across locations to a moderate extent. In highly turbid waters the bronze spangling is often very subdued. Colour in alcohol not greatly different from in life except not as vibrant. Spangled perch are an extremely handsome fish and are difficult to confuse with other species, even when small.
spangled perch was limited by low water temperature, with the then known distribution being limited by the July minimum temperature isotherm of 4.4°C. Subsequent records show that the distribution extends to areas outside of this isotherm [1201], however the inference that temperature limits distribution is probably correct. Unmack [1338] considers that all eastern coastal populations south of the Mary River are introduced. Leiopotherapon unicolor is a common inhabitant of Gunpowder Creek, an upstream tributary of the Leichhardt River, which drains into the Gulf of Carpentaria (8.9% of total, three sites) [1093]. This species was relatively uncommon in a study of 39 sites within the Alligator Rivers region in the Northern Territory, accounting for only 0.2% of the total catch [193]. However, many of the sites studied were classified as billabongs and lagoons and it was infrequently collected from lowland floodplain billabongs. In contrast, this species was dominant in the sandy pools of Magela Creek [1416]. This species was considered common in rivers of Cape York Peninsula [571].
Systematics Leiopotherapon unicolor is one of four species within the genus: congenerics include L. aheneus (Mees) and L. macrolepis Vari from north-western Australia and L. plumbeus (Kner) from the Phillipines [1346]. Originally described as a member of the genus Therapon. Synonyms include T. unicola Kent, T. truttaceus Macleay, T. longulus Macleay, T. elphinstonensis De Vis, Terapon ideoneus Ogilby, T. unicolor Rendahl, T. truttaceus Waite and Madigania unicolor Whitley. Leiopotherapon was erected by Fowler in 1931 with L. plumbeus as the type species. The monotypic genus Madigania was erected in 1945 by Whitley [1390] but subsequently rejected by Vari [1346] in a revision of the family. The genus is distinguished from all others in the family by the presence of only one spine on the first proximal dorsal pterygiophore (all others possess two). Although L. unicolor is extremely widely distributed (see below) Vari did not remark upon any consistent variation in meristics or morphometrics across its range. DNA sequencing of a range of populations across northern Queensland revealed low levels of divergence [1083].
Leiopotherapon unicolor is often very abundant but abundance levels vary greatly in space and time. This species was the second, fourth and second most abundant species collected by electrofishing, seine-netting and gill-netting, respectively, in a study conducted over three years and across 12 sites within the Burdekin River, accounting for 22%, 2% and 10%, respectively of each total [1098]. Similarly high abundances have been recorded for rivers of eastern Cape York Peninsula [1099] where it contributed 11.3%, 13.8% and 15.8% of the total number of fish collected from the Pascoe River (three sites), Stewart River (three sites) and Normanby River (seven sites), respectively. It was not as abundant in floodplain lagoons of the Normanby River however (6.6%) [697]. Leiopotherapon unicolor is relatively uncommon in the higher gradient, faster flowing rivers of the Wet Tropics region, being the 25th most abundant species and contributing 0.2% only to the total catch in a survey encompassing 93 sites [1087]. Also uncommon in the Annan River of southern Cape York Peninsula, being the 13th most common species and contributing only 1% of the total collected [599].
Distribution and abundance Leiopotherapon unicolor is one of the most widely distributed Australian freshwater fishes, second only to the bony bream, Nematolosa erebi. It is distributed from the Geraldton region of Western Australia [1346] through the Pilbara [34] and Kimberley regions [45, 388], across the Northern Territory [193, 772, 1416], Gulf of Carpentaria region [1093], Cape York Peninsula [571, 697, 1099], Wet Tropics [1085, 1087], central Queensland [160, 700, 1081], south-eastern Queensland [704, 1095], north-eastern New South Wales (north of Newcastle) [1346] and inland drainages of the Murray-Darling system [1201]. This species is also present in the Bulloo-Bancannia drainage system [947], drainages emptying into Lake Eyre [121, 455], and desert streams of the Western Plateau drainage division [455], possibly as far west as Wiluna (BJP, unpubl. obs.). Llewellyn [810] suggested that the distribution of
Further south in the Black-Alice River near Townsville, spangled perch accounted for 5.6% of all fish collected from six sites [176]. The abundance of this species decreases markedly further south. In the Burnett River spangled perch accounted for 1.9% of the total number of fish collected [700]. In the Mary [1093], Brisbane [704], Logan [699] and Albert [1093] rivers, spangled perch accounted for 0.6%, 0.4%, 0.09% and 0.06%, respectively. Johnson [662] believed that spangled perch were translocated into the
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Brisbane River in the late 1930s. In a large survey of rivers of north-eastern New South Wales conducted over 1994–1995, spangled perch were not collected [1201], although they were recorded as being present in a survey 12 years previous [814]. This species was recorded as present but was very uncommon in the Murray River (only one specimen collected) and more abundant in the Darling River (0.9%) [1201].
habitats and in areas with a sand substratum. Whether a preference for a substrate composition such as that listed above merely reflects a more primary aversion to high flow environments is unknown. However, the low abundances recorded for streams of the Wet Tropics region, in which higher flow environments are the norm, suggests that water velocity may be an important determinant of abundance and habitat use.
Care must be exercised in comparing the relative abundances cited above for differences in collection methodology may seriously bias assessments of spangled perch abundance. Surveys listed above conducted by us [1093] have always included electrofishing as a major collecting method in concert with seine and gill-netting. Spangled perch appear to be very susceptible to capture by electrofishing and perhaps less so susceptible to capture by seine-netting due to their pattern of meso- and microhabitat use (see below). The apparent low abundance of spangled perch in New South Wales compared to Queensland is probably real given that similar methods were employed in the different studies used for comparison, but it is uncertain whether the differences observed between abundances in Queensland and the Alligator Rivers region are real or partly artefactual.
Despite its tolerance of elevated salinity levels (see below), spangled perch are rarely encountered in estuarine areas and it was not recorded in any of 10 recently surveyed Queensland estuaries [1081]. The presence of closely related truly estuarine terapontids such as Therapon jarbua probably prevents their use of such habitats. Leiopotherapon unicolor is frequently the dominant species in isolated pools of intermittent rivers (i.e. sandy pools in Magela Creek) [1416]. Such habitats are remnants of a much larger aquatic habitat and fish become concentrated as available habitat diminishes. In isolated spring pools, Kodric-Brown and Brown [727] found that spangled perch were absent from pools less than 707 m2 in area. These authors suggested that the lower limit of pool size was set by its carrying capacity for perch and the probability of extinction for populations of small size.
Nonetheless, the data above suggest that spangled perch are most common in sandy river reaches with low flows. This inference is supported by comparative catch data for the Burdekin River which showed spangled perch to be most abundant in slow-flowing tributary stream sites and least abundant in rocky fast-flowing sites [1098]. Abundance levels are temporally variable, with highest numbers being recorded after wet season floods. Abundances may also be high in recently isolated pools but decrease with time in such environments [1098].
Pusey et al. [1098] noted substantial variation in abundance associated with meso-scale habitat differences in the Burdekin River in addition to the macro-scale habitat differences discussed earlier. It was most abundant, and the population dominated by individuals less than 50 mm SL, in areas of some flow and available cover (undercuts and root masses). It was much less abundant in open areas distant from the stream-bank (this being the domain of the barred grunter Amniataba percoides). Large adult spangled perch were most abundant in deep areas with abundant woody debris.
Macro/meso/microhabitat use Leiopotherapon unicolor is found over a wide range of conditions including desert springs and bores, billabongs, impoundments, rivers and streams. The abundance data presented above suggests that in the tropics, L. unicolor prefers lotic conditions, yet it can achieve high abundance levels in impoundments [696] and is capable of breeding in such environments [810]. In the Burdekin River, spangled perch were more abundant in tributary streams and achieved significantly greater weight for a given size here than in other habitats [1093]. Significant spatial variation in abundance was correlated with substrate composition (being most abundant in habitats dominated by mud, sand and fine gravel) and low to moderate water velocity (being most abundant in habitats with a mean velocity of <0.3 m.sec–1) [1098]. Bishop et al. [193] also found L. unicolor to be most common in upstream escarpment
Kodric-Brown and Brown [727] characterised the microhabitat usage of L. unicolor in desert springs as very broad, as it was observed at all levels in the water column. Kennard [697], in a study of the habitat usage of fishes in billabongs of the Normanby River floodplain, recorded L. unicolor from a variety of depths but the majority of fish were collected from areas of less than 100 cm and most were collected from the middle one-third of the water column. However, an examination of the mean diet (see below) suggests that the majority of foraging occurs close to the stream-bed although fish do move to the surface to take terrestrial invertebrates. The great majority of fish in Kennard’s lagoon study were collected within 20 cm of some form of cover, predominantly woody debris, root masses and aquatic macrophytes.
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been experimentally determined for some parameters. Llewellyn [810] found that survival decreased below 7.3°C and that no fish survived temperatures less than 4.1°C. Fish in aerated conditions survived longer than did those in non-aerated conditions. Survivorship decreased above temperatures of 37.5°C with complete mortality occurring at 40°C. Beumer [174] estimated upper temperature tolerance limits for juvenile and adult fish to be 35.5 and 41.8°C, respectively (LD50 values). Glover [456] found that L. unicolor from Dalhousie Springs could tolerate temperatures of 45°C for brief periods and that these same individuals died at temperatures below 16–18°C and concluded that acclimation history was important in determining thermal tolerance. In contrast, Gerkhe and Fielder [436] observed that spangled perch can also survive rapid (1°C.hr–1) changes in temperature up to 35°C and down to 5°C. Increasing temperature is accompanied by increased ventilation, heart beat and oxygen consumption rates, although the rate of increase is greatest for heart beat and oxygen consumption rates [436]. The upper temperature limit defined by these studies (40–45°C) is similar to that of the most heat-tolerant of North American fishes, including those inhabiting thermal springs [150], and approximates the upper biokinetic limit for aquatic ectothermic vertebrates [233].
In the Mary and Albert rivers of south-eastern Queensland, spangled perch were most commonly collected from areas of little or no flow (Fig. 1) and from depths of between 30 and 60 cm [1093]. They were most frequently collected from the bottom two-thirds of the water column. Spangled perch were infrequently collected over coarse substrates or mud, and most frequently over sand, fine gravel and gravel, and infrequently collected in open water, being most commonly collected from some form of cover. (a)
(b)
50
50
40
40
30
30
20
20
10
10
0
0
Mean water velocity (m/sec) 30
(c)
Focal point velocity (m/sec) 30
20
20
10
10
0
0
(d)
The salinity tolerance of spangled perch is very broad. It has been collected from springs of low salinity (0.2‰) [455, 458] and the upper tolerance has been experimentally determined to be that of sea water (35.5‰) [174].
Total depth (cm)
(e)
Relative depth 20
Similar experimental data for oxygen, pH and turbidity tolerances are unavailable and inferences on tolerance must be drawn from studies of distribution. Spangled perch have been collected from springs with depressed dissolved oxygen (DO) concentrations (1 mg.L–1) [455, 458], from billabongs of the ARR with depressed DO (surface – 0.9 mg.L–1, bottom – 0.4 mg.L–1) [193], isolated anoxic pools of the Burdekin River (bottom – 0.8 mg.L–1) and anoxic waters (0.4 mg.L–1) of Lake Dalrymple, the impounded portion of the Burdekin River [1098]. Physiologic responses to decreasing dissolved oxygen in spangled perch are complex and related to ambient temperature. Leiopotherapon unicolor becomes bradycardic (reduced heart rate) at low oxygen levels: the heart rate begins to slow at 27% saturation at 10°C but begins to decline at 40% saturation at 35°C [436]. In the laboratory, spangled perch are a metabolic conformer (i.e. O2 consumption decreases with decreasing availability) below critical oxygen thresholds: the magnitude of which is temperature dependent. At 10°C, spangled perch are able to maintain metabolic rate until oxygen tensions fall to 12% but at 35°C, metabolic rate begins to decrease at 42% saturation [436]. Spangled perch have a large respiratory
(f)
30 15 20
10
10
5
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by the spangled perch Leiopotherapon unicolor from the Mary and Albert Rivers, south-eastern Queensland. Data derived from capture records for 145 fish sampled from 18 sites in the Mary River and two sites in the Albert River during 1994–1997.
Environmental tolerances Leiopotherapon unicolor is one of the few Australian species for which environmental tolerance limits have
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Spangled perch have been recorded as being infected with the ciliate protozoan Chilodonella hexatsticha in the Finke River in central Australia [767]. This infection of the gills leads to epithelial hyperplasia resulting in hypoxaemia and ultimately death and is commonly associated with winter fish kills. These authors hypothesised that low dry-season flows may concentrate fish and increase cross infection rates and that low winter temperatures may depress the immune capacity of fishes to withstand infection. Tropical ulcerative syndrome (red spot disease) has been recorded for spangled perch in the Burdekin River and rivers of Cape York Peninsula [1093].
surface area (569 mm2.g–1) [430] and consequently are able to extract oxygen from hypoxic waters such as those listed above. They cannot, however, survive long periods of hypoxia by anaerobiosis [436]. Anecdotal reports suggest that L. unicolor is able to aestivate [936]; laboratory investigations have not been able to induce anything other than desiccation and morbidity however [174, 810]. Several adaptations are necessary to allow a fish to successfully aestivate, including the ability to control water loss, depress its metabolic rate, store the products of protein catabolism and, most importantly, exchange respiratory gases in air. To date, these aspects of the physiology of spangled perch have not been investigated and there is little evidence to suggest that it can aestivate. It has been suggested that it may be able to survive in moist sand covered in leaf litter [810] and healthy but inactive specimens have been observed in pools containing very little water in tributaries of the Burdekin River [1093].
Overall, the water quality tolerances of this species are extremely broad as would be expected for a fish with such a wide distribution and catholic habitat requirements (see above). Reproduction Life history details of the spangled perch are summarised in Table 1. Spangled perch develop quickly and are sexually mature at a small size within their first year, with males achieving maturity at a slightly smaller size than females. The sex ratio is close to unity although the earlier maturation of males may skew the sex ratio in the early part of the breeding season. It is clear that spangled perch breed during the summer wet season when water temperatures exceed 20–26°C. Rising water temperatures are probably the most important cue for stimulating reproduction. Rising water levels were previously thought to be an important stimulus but flooding is not essential given that this species will spawn in impoundments. In the Burdekin River, successful recruitment was observed in years without flooding [1093], further suggesting that rising water levels are not essential. However, recruitment, as opposed to spawning, is much greater in years with a significant wet season flood due to the increase in habitat and food available during such events.
Bishop et al. [193] recorded spangled perch from water bodies with a pH as low as 4.0, as high as 8.6 (surface values) and with an overall mean of 6.1. These authors recorded it from waters ranging from turbid (Secchi depth of 1 cm) to very clear (Secchi of 360 cm). Average turbidity values for the Burdekin River sites studied by Pusey et al. [1098] ranged from 1.52 to 5.44 NTU. In the Burdekin River, it has been collected from floodwaters of extremely high turbidity (260 NTU) but it is unknown for how long it could tolerate such high levels of suspended sediment. Given that spangled perch are present in inland drainages that often stay turbid for long periods of time, it is probable that adult tolerance is high. Given that this species is primarily a visual predator (see below), it would be instructive to compare growth rates and life history parameters of populations in turbid and non-turbid rivers. Tolerance data for a range of other contaminants is lacking. However, the abundance of spangled perch was found to be significantly depressed in stream reaches receiving copper-enriched effluent [1093]. Whether this was a result of direct effects of copper or indirect effects mediated by changes in food base is unknown. Brown et al. [243] did not record spangled perch among those species present in a natural fish kill resulting from naturally elevated acid conditions (which leads to elevated dissolved aluminium levels and interference with oxygen transfer across the gills) and Bishop [187] found that spangled perch were present in only one of eight documented fish kills in the Northern Territory. In that one case, however, mortality was a result of desiccation, not changes in water quality. This latter observation does not lend much credence to the notion that this species is able to aestivate.
Floods may be an important stimulus for movement however. Ripe males may develop very large testes during the breeding season, and male GSI values may exceed those for female fish. Ripe females may achieve relatively high GSI values (max. = 13.7%) also, although the average is usually about one half this value. In the Alligator Rivers region, spawning probably takes place in backwaters and lagoons in addition to more riverine habitats. There is little evidence for spawning in floodplain lagoons of Cape York Peninsula however. In rivers of central and south-eastern Queensland, spawning takes place in tributaries and flooded marginal areas. Spawning apparently takes place at night and probably involves large aggregations of fish. The high male GSI
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Table 1. Life history data for Leiopotherapon unicolor. Age at sexual maturity (months)
3–6 months (Burdekin River)
Minimum length of ripe females (mm)
58 mm [173], 78 mm [810], gender discernible at small size 50–60 mm [1093]
Minimum length of ripe males (mm)
66 mm [173], 58 mm [810], gender discernible at small size 30–40 mm [1093]
Longevity (years)
Unknown but probably 2–3 years for most specimens, occasionally 4–5 years
Sex ratio (female to male)
0.8 : 1[102], skewed towards males early in breeding season due to earlier maturation of males [1093]
Occurrence of ripe fish
Alligator Rivers region – Oct–March [1264] Burnett River: Oct–Feb [102] Black-Alice River Qld – Dec–Feb [173]
Peak spawning activity
Alligator Rivers region – Summer wet season [1064] Alligator Rivers region – November [1416] Alligator Rivers region – early wet season [1264] Black-Alice River Qld – Nov–Jan [173] Burdekin River– wet season [1093] Burnett River – October–November [102]
Critical temperature for spawning
22°C – Burnett River [102] 20°C (bottom) – 26.5°C (surface) – Murray-Darling region but fish sourced from south-eastern Queensland [810]
Inducement to spawning
Rising water temperatures [810] Rising water levels previously thought to stimulate spawning [750], however, flooding not essential for spawning as this species will spawn in impoundments [810]. Flooding enhances recruitment in the Burdekin River [1093] Spawns at night [810]
Mean GSI of ripe females (%)
Mean = 8.1, max = 13.7 – Burnett River [102] Mean = 7.4, max = 10.8 – Black-Alice River [173] Mean = 4.3 – Alligator Rivers region [193]
Mean GSI of ripe males (%)
Mean = 6.0, max = 7.6 – Black-Alice [173] Mean 6.5, max = 11.5 – Burnett River [102] Mean = 5.8 – Alligator Rivers region [1264]
Fecundity (number of ova)
Size dependent – between 24 000–113 200 eggs for females ranging from 24 to 65 g, respectively [810]; Average fecundity of 48 000 recorded for Alligator Rivers region [1264]
Fecundity /length relationship
F = 0.009TL3.16; n = 21 [173]
Egg size
Means of 0.68 mm fresh and 0.71 mm water hardened [810]; 0.6 mm [173] Eggs spherical, transparent, predominantly non-adhesive and demersal. Yolk aggregated at vegetal pole [810]
Frequency of spawning
Distribution of egg diameter unimodal suggesting a single spawning per season only
Oviposition and spawning site
Spawning occurs in shallow areas over a soft substrate in backwaters and still pools of lagoons and sandy creek-bed habitats [936]. Little spawning evident in lagoons of the Normanby River system [697]
Spawning migration
Upstream spawning run in coastal north Queensland streams [173]
Parental care
None
Time to hatching
45–55 hrs at 23–26.4°C [810]
Length at hatching (mm)
1.72–2.56 mm (average = 2.18 mm) [810]
Length at free swimming stage
?
Length at metamorphosis (days)
Approximately 20 mm [810]
Duration of larval development
28–35 days [810]
Age at loss of yolk sack
?
Age at first feeding
3 days 21 hr [810]
species, producing many thousands of small spherical eggs. Eggs are non-adhesive and demersal. No parental care occurs. The eggs hatch in about 3 days and the larvae are small at hatching. Feeding commences shortly after hatching. Larval development takes between 28–35 days
values recorded and the unimodal distribution of in vivo egg size suggests a single spawning per individual although the prolonged breeding season noted in some studies suggests that spawning is not tightly synchronised within populations. Leiopotherapon unicolor is a highly fecund
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[1229] believed that the capacity of this species to move overland through very shallow surface water could account for such reports and this is probably true in many cases. However, the examples compiled by McCulloch [878] and Whitley [1400] strongly support the notion that small fish such as juvenile spangled perch may become entrained in ‘water spouts’ and transported away from aquatic habitats. Similarly, observations by a station owner in the Hughendon area and recounted to the senior author, of spangled perch appearing on dry land after a severe thunderstorm support the case for aerial dispersal. When questioned, the owner agreed that overland movement from permanent water 2 km away could account for all specimens observed except for the single individual found in the rain gauge! Whitley [1400] presented a list of 53 examples of fish rains compiled from regional newspapers, personal communications, radio programs and governmental reports. Leiopotherpon unicolor figured in several of these reports and central Queensland appeared to be a region in which such occurrences were relatively common. Whitley was led to comment drolly that ‘one man’s meteorology was another man’s poisson!’. Some small specimens of spangled perch are able to withstand transmission within pumps and pipelines for at least 500 m [1093]. An early account reports the presence of spangled perch in subterranean bores at considerable depth [1260]. Ogilby and McCulloch [1229] believed the report mistaken and that the fish were ‘aestivating’ in the area and were revived by the borewater, however Stead’s [1260] description of the condition of the fish observed is consistent with them having been brought to the surface from depth.
and metamorphosis occurs at approximately 20 mm length in laboratory studies. Smaller (12 mm) fully metamorphosed individuals have been observed in the Burdekin River [1093]. Movement Spangled perch are capable of rapid and extensive movement. Bishop et al. [190] classified this species as ‘fastmoving’, capable of speeds within the range of 8.5–9.4 km.day–1. Shipway [1229] estimated the average velocity of juvenile spangled perch dispersing from a previously isolated pool during an intense thunderstorm over a sixhour period at 2.7 km.hr–1 (i.e. a moderate walking pace). Seasonal migrations by spangled perch have been documented in the Alligator Rivers region by Bishop et al. [193]. At the commencement of the wet season, fish move out of perennial escarpment pools downstream onto the floodplain. Return migrations are made at the end of the wet season. Movement was greatest (in terms of number of individuals) in the morning, increasing as light intensity increases [190]. In the Black-Alice River of north Queensland, spangled perch move upstream at the commencement of flooding to spawn in tributary creeks [173]. Lateral movement of spangled perch into floodplain lagoons of the Normanby River during floods was documented by Kennard [697]. Studies of the passage of fish through fishways have generally been uninformative with regard to this species. Leiopotherapon unicolor was not recorded moving through the Burnett River barrage by Russell [1173] and only a few specimens were recorded moving upstream over the Fitzroy River barrage [1274]. Both barriers are tidal barrages and the low numbers recorded probably reflect more the low abundances of this species in tidal reaches than an absence of movement. Hogan et al. [586] recorded spangled perch from 34–77 mm in length trying to access the Clare Weir fishway on the Burdekin River under a range of discharges from 50 665–127 467 ML.day–1.
Trophic ecology Quantitative data on the diet of L. unicolor is available from 10 separate studies. All but two (the Alligator Rivers region) [193, 1416] were undertaken in Queensland. The average sample size was 202 individuals (range = 26–756). One study was conducted in a reservoir (South Pine Dam [103]) while the remainder included fish from natural habitats including strictly riverine habitats as well as floodplain billabongs and lagoons. Most of the studies included fish collected over a number of occasions.
These data suggest that spangled perch make two forms of movement. The first is associated with reproduction and involves adult fish moving in either a downstream (i.e. Alligator Rivers region) or upstream direction (BlackAlice River) associated with the start of the wet season. Such movements are probably coupled with a return migration. A second type of movement involves both adult and juvenile fish dispersing away from dry season refuges. This may involve lateral movements on to floodplain habitats or just a general dispersal to other riverine habitats once connectivity is established.
The average diet shown in Figure 2 demonstrates that the diet of L. unicolor is diverse despite almost half of the diet being composed of aquatic invertebrates such as chironomid, simulid and trichopteran larvae and ephemeropteran nymphs. This high diversity was a feature common to all but one of the studies (the impoundment study). Spangled perch consume very little detritus but on average, 14% of the diet is comprised of vegetable matter, principally aquatic in origin although some leaves and fruits are consumed from the water’s surface. The degree of
Anecdotal evidence has frequently implicated spangled perch in so-called ‘rains of fishes’ [878, 1400] but Shipway
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Freshwater Fishes of North-Eastern Australia
Fish contribute 10%, on average, to the total diet, although spatial variation in the importance of this component occurs. Very few fish were consumed by spangled perch in the Annan River or Barker Barambah Creek (<2%). The greatest reliance on piscivory was recorded for the impoundment sample (42%). Elsewhere, the volumetric importance of fish to the diet varied from 7% to 18%. The extent of piscivory also varies with size in the Burdekin River, being greatest (17.5%) in fish larger than 80 mm SL, completely absent in fish less than 40 mm SL and unimportant (2.2%) in fish in the intermediate size class. These data suggest an important effect of gape limitation on prey choice in smaller fishes. Predation by spangled perch on the juveniles of other species was shown to be important in structuring fish communities in lagoons of the Normanby River [697].
importance of vegetable matter varied substantially between studies. Almost no vegetable matter (0.3%) was present in the diet of 26 fish collected from the Annan River or in the fish collected from Barker Barambah Creek in the Burnett River (1.5 and 1.55% for the two studies) [99, 205]. In contrast, more vegetable matter was consumed in the Burdekin River (9.3%) [1093], Herbert River (13%) [98], rivers of Cape York Peninsula (10%) [1099], Magela Creek (11.3%) [1416] and various locations in the Alligator Rivers region (16.8%) [193]. In billabongs of the Normanby River, aquatic vegetation contributed 26% of the diet [697]. The highest contribution (27.6%) was recorded for fish from an impoundment, South Pine Dam [103]. The extent of herbivory and type of plant matter consumed varied with size in the Burdekin River [1093]. Fish less than 40 mm SL consumed little (2.6%), all of which was comprised of filamentous algae. Fish between 40 and 80 mm SL consumed more plant matter (total = 9.5%), of which, most (7.8%) was filamentous algae. Fish larger than 80 mm SL consumed even more plant matter, and macrophytes were more important than filamentous algae (8.5 versus 5.3%). This pattern of ontogenetic change in amount and type of plant material consumed parallels that observed in other terapontid grunters of the Burdekin River. Fish (10.3%)
Unidentified (6.8%) Terrestrial invertebrates (3.0%)
Other microinvertebrates (0.1%) Microcrustaceans (2.9%)
Aerial aq. Invertebrates (1.1%) Detritus (0.5%) Terrestrial vegetation (1.7%) Aquatic macrophytes (5.6%)
Macrocrustaceans (15.6%) Algae (6.1%)
Molluscs (0.8%) Other macroinvertebrates (1.1%)
Aquatic insects (44.4%)
Figure 2. The average diet of Leiopotherapon unicolor. Data presented are the mean contributions of each category derived from several studies and weighted by the number of individuals used in each study. Studies used include Arthington et al. [98]: 116 individuals from the Herbert and Tully rivers; Arthington et al. [99]: 96 individuals from Barker Barambah Creek; Bluhdorn and Arthington [205]: 92 individuals from Barker Barambah Creek; Hortle and Pearson [599]: 26 individuals from the Annan River; Woodland and Ward [1416]: 211 individuals from Magela Creek; Kennard [697]: 84 individuals primarily from floodplain lagoons of the Normanby River; Pusey et al. [1099]: 189 individuals from the Pascoe, Stewart and Normanby rivers; Pusey et al. [1093]: 756 individuals from the Burdekin River; Bishop et al. [193]: 342 individuals from the Alligator Rivers region; and Arthington et al. [103]: 114 individuals from South Pine Dam.
376
Macrocrustacea such as caradinid and penaeid shrimps and prawns are an important component of the diet of spangled perch, contributing 16% to the total diet. The contribution by this component varied between studies also. The Herbert River sample and the two Barker Barambah Creek samples contained fish which consumed large amounts of macrocrustacea (50, 95 and 32%, respectively). However, these studies share in common the fact that the majority, or at least a large proportion, of the fish examined, were collected by gill-netting and line fishing. These methods collected fish in the upper size classes and the diet determined from such a sample will reflect the feeding ecology of large fishes rather than the entire size range. In the Burdekin River, ontogenetic variation in the consumption of macrocrustacea is pronounced. Paratya and Macrobrachium are completely absent from the diet of fish less than 40 mm SL, present but relatively unimportant (4.9%) in the diet of fish between 40 and 80 mm SL, but contrastingly, constitute one of the major prey items in fish above 80 mm SL (26%). Thus, at least some of the spatial variation in the importance of macrocrustacea reported above appears related to differences in the size range of the samples used. Experimental studies have demonstrated the effect of size on the ability to handle such large and active prey in this species [1232]. Terrestrial invertebrates were, overall, a relatively minor component of the diet (3%) except in the Annan River, where terrestrial prey contributed 18.4% to the diet [599]. The consumption of terrestrially derived prey increases in importance with size in the Burdekin River and is greatest during periods of low flow [1093]. Aquatic invertebrates were the largest component in the average diet (44%). The type of taxa included within this group was diverse and included most common freshwater insect phyla. As with many of the other dietary items
Leiopotherapon unicolor
primary and secondary consumer, which when coupled with its wide environmental tolerances and pronounced ability to disperse, allow it to colonise and exploit a very wide range of aquatic habitats. The pronounced ontogenetic variation in diet discussed above may be important in allowing spangled perch to maintain high densities in isolated pools by minimising intraspecific competition.
discussed above, ontogenetic variation in the types of prey within this category exist. Small fish (<40 mm) consume mostly chironomid larvae whereas larger fish consume odonate nymphs and trichopteran larvae and invertebrates from habitats which small fish avoid (i.e. simulid larvae from fast water habitats). In the Burdekin River, substantial spatial variation in diet exists but reflects the different types and abundances of invertebrates present within habitats differing in current velocity and substrate composition.
Conservation status, threats and management Leiopotherapon unicolor is listed as Non-Threatened [1353]. This species is able to thrive in a wide variety of conditions and it has even been suggested that in some situations it is advantaged by flow regulation [205]. However, a comparison of spangled perch abundance in regulated and unregulated reaches of the Darling River clearly showed that spangled perch abundance was greatly reduced in regulated reaches [435]. Several aspects of flow regulation are likely to disadvantage this species. First, the need for relatively high water temperatures to stimulate gonad development and spawning may be compromised in situations where the thermal regime of river is disturbed (i.e. by hypolimnetic releases). Second, given the high mobility of this species, barriers to movement are highly likely to impact on population size and genetic structure. Third, flow supplementation which results in either, or both, increases in water velocity or sediment coarseness are likely to disadvantage this species. While flooding is not necessary to stimulate spawning, recruitment success is definitely related to the extent of flooding. In floodplain rivers with off-channel aquatic habitats, connectivity needs to be maintained. The natural flood regime therefore needs to be maintained in order to protect this species.
Gehrke [431] described the various feeding behaviours of spangled perch. Small invertebrates and fish are drawn into the mouth via suction due to rapid opening of the jaws and, presumably, buccal expansion involving flaring of the opercula. Large prey, such as penaeid prawns, are ingested differently. The fish positioned itself above and posteriorly to the prey prior to ingesting the prawn. Gehrke [431] suggests that this position removes the fish from reach of the prawn’s chelipeds and Short [1232] added that this position helps to prevent the backward escape flick typical of prawns. If small enough the prawn is swallowed whole, tail first, being guided down the gullet by the pharyngeal teeth. If too large, the prawn may be broken into small pieces by violent shaking. Gehrke [431] argued that spangled perch were able to feed on a large array of prey items by being able to use both suctorial and grasping techniques. Visual cues are most important in the location of prey but Gehrke also noted that olfactory and vibratory (auditory) location of prey also occurred and may be important in turbid waters. The use of visual, olfactory and auditory stimuli to locate prey and the use of different strategies to handle prey allow L. unicolor to exploit a wide range of prey types. Rather than being a simple generalist, this species is a sophisticated
Dove [1432] provided a list of parasite taxa recorded from L. unicolor in south-eastern Queensland.
377
Hephaestus fuliginosus (Macleay, 1883) Sooty grunter, Black bream
37 321014
Family: Terapontidae
Cheek scales: 6–9 rows; Gill rakers on first arch: 6–9+1+14–17.
Description Original and complete description of material collected in the Burdekin River as follows [847]: Dorsal fin: XII, 13; Anal: III, 9; Lateral line scales: 52. Height greater than 1 ⁄3 total length, head length approximately 1 ⁄4 total length. Head wide at base, rounded at snout. Profile descending in a rather concave sweep. Lips fleshy. Mouth reaches to below anterior margin of eye. Maxillary shows largely above and behind the intermaxillary. Eye is large and approximately two diameters from snout. Cheek covered by small, fixed, little imbricate scales. The preoperculum is uniformly rounded and finely serrated. Operculum has two spines, the lower one large and flat. The first dorsal spine is short, the second less short, the rest pretty uniform. Spines of the anal are of moderate thickness, the third the longest. Soft dorsal and anal fins rounded behind, caudal slightly emarginate. Colour dull black all over, the tip of the tail edged with a lighter hue.
Meristics of sooty grunter from Wet Tropics region (n=61) are as follows: Dorsal fin: X–XIII, 9–14; Anal: III, 6–10; Pectoral: 14–17; Predorsal scales: 14–17; Lateral line scales: 43–55, 8–10 scales above lateral line, 16–19 below; anal scale sheath with 2–5 rows; Cheek scales: 5–9 rows. Figure: composite, from photographs of adult specimens 250–300 mm SL, Burdekin River; drawn 1999. Hephaestus fuliginosus is a large species commonly reaching 350 mm SL but occasionally exceeding 450 mm SL. Specimens from impoundments may grow to larger size. The relationship between length (SL in mm) and weight (g) for Burdekin River population takes the form: W = 1.897 x 10–5 L 3.129; r2 = 0.982, n = 341, p<0.001. The relationship between weight (g) and length (TL in cm) for sooty grunter from the Alligator Rivers region takes the form: W = 0.0138 L3.10, r2 = 1.0, n = 54, p<0.001[193].
Data from Vari [1346] for specimens sourced predominantly from the Northern Territory as follows: Dorsal fin: IX–XII, 12–14; Anal: III, 8–10; Pectoral: 15–17; Pelvic: I, 5; Predorsal scales: 13–17; Lateral line scales: 43–51, 7–10 scales above lateral line, 14–17 below; 3–7 scales on caudal, anal scale sheath with 3–4 rows, extending to fifth last ray;
Body moderately deep and compressed. Dorsal profile more pronounced than ventral, straight in small specimens, markedly concave in large adults. Jaws moderately large, gape oblique and lips fleshy. Maxillary reaching posteriorly to anterior edge of eye in small specimens,
378
Hephaestus fuliginosus
dissimilar, with H. bancrofti being distinguished by a much broader head and shoulders.
falling short with age, reaching only to posterior nostril. Blubberlip condition present in some populations but not observed by us in the Burdekin River. Functional significance of blubberlip condition probably related to substrate particle size [1097] (see comments for H. tulliensis). Teeth conic, slightly recurved, in bands, outer row enlarged. No teeth on vomer or palatines. Lachrymal serrate; serrations larger in juveniles. Preoperculum serrate, serrations larger on angle. Lower opercular spine stronger and longer, not extending beyond edge of opercular lobe. Post-temporal exposed and serrate posteriorly. Cleithrum exposed, serrate posteriorly and scaled laterally. Supracleithrum exposed [1346]. Colour in life: highly variable. Body may be dark, almost black, dark khaki-brown or golden-bronze with a pinkish hue. Dorsal surface darker than ventral surface. Fin colour also variable, in some cases being the same as body colouration, in others being lighter, almost transparent. Second dorsal fin usually with pale margin and basal dark blotch. Vari [1346] states that pectoral fin base marked with dark bar, but this feature is not always present. Juveniles tend to have a lighter body colouration with dark blotches on second dorsal and anal fins. Colour in preservative: tending to a dark brown or grey.
Pusey et al. [1098] suggested that elements of the fauna of the upper Burdekin River, including H. fuliginosus and the precursors to Scortum parviceps and Neosilurus mollespiculum, were derived from a westerly flowing river as a result of volcanic uplift and river diversion 6–8 million years ago. Genetic comparison of populations of H. fuliginosus in the Burdekin and Gilbert Rivers reveals very large divergence (6%) consistent with the hypothesis above (Pusey and Bermingham, unpubl. data). In addition, morphometric and meristic comparison of populations on either side of the Great Dividing Range reveals substantial differences [1093]. Together, these observations suggest that H. fuliginosus from the east coast may be a different species to that from west of the Great Dividing Range. The type locality for the species is the Burdekin River and yet, material from the type location or any east coast population of H. fuliginosus has not been previously used in any comparative study. Where comparisons have used material from the east coast in the belief that the specimens were H. fuliginosus, it now appears that the material was in fact entirely composed of another species; H. tulliensis [919], or contained substantial numbers of this species in addition to H. fuliginosus [918]. The substantial morphological variability that is said to be characteristic of H. fuliginosus may be more apparent than real because comparisons have involved more than one species. Moreover, decisions made in the past concerning synonomy need to be reassessed. The systematics of this species group is in urgent need of revision, particularly in light of the current practice of translocating this species (from a variety of stocks) into other rivers to satisfy the desires of the recreational fishing community.
Systematics The genus Hephaestus was erected by DeVis in 1884 with H. tulliensis, from the Wet Tropics region, as the type species. The systematics of H. fuliginosus is confused, partly because the original description was very short and lacking in detail (see above), partly because there may be more than one species involved and partly because subsequent taxonomic work has included material attributable to species other than H. fuliginosus. This species was originally described as Therapon fuliginosus in 1883 from material collected in the upper Burdekin River [847]. Other synonyms, according to Vari [1346], include Therapon bancrofti Ogilby and McCulloch and Terapon alligatoris Rendahl (both under a variety of spellings). However, Vari did not examine the type specimens of H. bancrofti, instead confining his examination to specimens of H. fuliginosus from the Northern Territory (91 specimens) and the Wenlock River (nine) of Cape York Peninsula. The type specimens of H. bancrofti are from the Walsh River, a major tributary of the Mitchell River. Hephaestus bancrofti and H. fuliginosus were originally distinguished from one another by greater separation between the anterior and posterior nostrils in the former [918], in addition to differences in the number of scales below the lateral line [1024]. Mees [918] noted that the former character was variable and that H. bancrofti may not be a valid species but added that a comparative study based on more material remained to be done. Type material examined by one of us (BJP) suggests that the two species are morphologically
Distribution and abundance Hephaestus fuliginosus is reported to occur in freshwaters of both Australia and New Guinea. The first reference to this species in New Guinea is that of Mees and Kailola [919] and is based on only five specimens; three from the upper Fly River and two from the upper Purari River. These specimens were compared with museum specimens of H. fuliginosus from north-eastern Queensland. All specimens examined were small (112–172 mm). Mees and Kailola [919] (p. 70) stated that the specimens from the Fly River are ‘…so close to the three specimens of T. fuliginosus from the Daintree River, Queensland…that we consider it inadvisable to separate them’. However, H. fuliginosus does not occur naturally in the Daintree River (see below) and, to our knowledge, the only Hephaestus species present there is H. tulliensis. Several comments in Mees and Kailola [919] indicate that their specimens were
379
Freshwater Fishes of North-Eastern Australia
flowing rivers of Cape York Peninsula. Pusey et al. [1099] did not collect it from the Normanby, Stewart or Pascoe rivers. There are however, unconfirmed reports of it being present in the Pascoe River (Midgely cited in Herbert et al. [571] and Leggett [785]) and the Normanby River [1349]. Herbert et al. [571] did comment on the distinctive nature of the fauna of the Pascoe River and suggested that part of the basin may have been captured from a westerly flowing river. Other rivers further to the north (the Lockhardt, Olive and Claudie) contain typically western species such as H. carbo [571, 785] and this part of the Cape is a region of substantial overlap in fauna [571]. Hephaestus fuliginosus is present in the Annan River [599] as the result of translocation and its presence there suggests that there are no intrinsic environmental factors which preclude it from inhabiting streams on the east coast of Cape York Peninsula.
indeed compared with H. tulliensis not H. fuliginosus. First, they noted that the Queensland specimens had larger eyes than the New Guinean specimens. A relatively large eye is one of the diagnostic characters for H. tulliensis [49]. Second, the dorsal fin scale sheath of the New Guinean material was said to be broader and less regularly arranged than the Australian material and the condition observed in H. tulliensis is narrow and regularly arranged. [First Name?] Allen (pers. comm.) has collected what appears to be H. fuliginosus in the lower Kikori River of Papua New Guinea, and this species may indeed occur in Papua New Guinea. As discussed in the sections dealing with the systematics and description of the species, there may currently be more than one species covered by the name H. fuliginosus. As the systematics of the species remains unresolved, we shall here present information on the distribution of all Australian taxa currently covered by this species name.
Further south on the east coast, the pattern of distribution becomes somewhat obscure due to a long history of translocation and a failure by researchers to distinguish this species from H. tulliensis in the Wet Tropics region. One possible route by which H. fuliginosus colonised the east coast is via the Burdekin River by the mechanism outlined in Pusey et al. [1098] (i.e. river capture by deflection). Within the Burdekin River, this species is widely distributed, being present in the north-eastern headwaters [590, 1098] and some of the south-western tributaries such as the Cape River (but only in the downstream-most portion) [940] and Suttor River [1098]. This species was not collected from the Belyando River by either Midgley [940] or Burrows et al. [256] but it is common downstream of the Burdekin Falls (in main channel and Bowen River) [586, 1098]. This species has been stocked in the upper Running River and in the upper Broken River (D. Burrows, pers. comm.). Various texts put the southern limit of sooty grunter as the Cape Hillsborough region [34, 936], although the basis for this remains obscure. However, it is not present in the Don River, a short ephemeral river near Bowen [590] or the Proserpine River [1081] (it has been stocked in Peter Faust Dam however (D. Burrows, pers. comm.)), and its presence in the Pioneer River [1081] is due to extensive stocking. Wager [1349] lists an unconfirmed record of sooty grunter from the O’Connell River. It is our opinion that H. fuliginosus is not naturally distributed to the south of the Burdekin River and that all such records are the result of translocation. It is unclear why the distribution does not extend further south given that a self-sustaining population exists in the Pioneer River. However, the rivers listed above (Don, O’Connell, Proserpine and Pioneer) are all small, short systems with highly variable flow regimes and in some cases, prone to long periods of zero flow, often culminating
The western limit of the sooty grunter is the Daly River in the Northern Territory [1346]. Further to the west in the Ord [619], Prince Regent [30], Drysdale [619] and Fitzroy rivers [388] of the Kimberley region, H. fuliginosus is replaced by H. jenkinsi (and to a lesser extent by H. epirrhinos). An early report lists H. fuliginosus as being present in the Prince Regent River [30]; this record has since been attributed to H. jenkinsi [619]. Similarly, Mees’ [918] report of this species being present in drainages of the Kimberley region is likewise attributable to H. jenkinsi [1346]. Hephaestus fuliginosus is widely distributed throughout the Northern Territory from the Daly River, through the Kakadu region [193, 262, 772, 1346, 1416] and Arnhem Land [535]. Occasional reference to the presence of H. fuliginosus in the drainages of central Australia may be found [514] but these are based on an incorrect attribution that seems to have become established in the literature (the species upon which the record was based was first listed as Hephaestus sp. but later changed to Scortum hillii [454]). Hephaestus fuliginosus is also present in drainages emptying into the southern portion of the Gulf of Carpentaria [1090] and drainages of the western side of Cape York Peninsula. Herbert et al. [571], in the most comprehensive survey of the fishes of the region, recorded H. fuliginosus from the Mitchell, Coleman, Edward, Holroyd, Archer and Wenlock rivers. Allen and Hoese [41] recorded it in the Jardine River also. These data suggest that H. fuliginosus is distributed throughout the Gulf country and western Cape York Peninsula. The distribution of H. fuliginosus on the east coast is more fragmented, being absent from much of the eastern side of Cape York Peninsula and the northern Wet Tropics region. Herbert et al. [571] did not collect it from any easterly
380
Hephaestus fuliginosus
Burdekin River, spreading northward into the Wet Tropics region only recently. Further dispersal in a northerly direction is prevented (or slowed) by the presence of its congener H. tulliensis, a Wet Tropics endemic.
in the complete absence of surface water. Such streams are likely to have been even more ephemeral during the Pleistocene era and would have posed very extreme environments with a high potential for widespread localised extinction. Hephaestus fuliginosus has been stocked in impoundments on the Boyne and Kolan Rivers (D. Burrows, pers. comm.).
Sooty grunter are not naturally found above large waterfalls [1349] except in the Burdekin River. Current and previous translocation programs (official and otherwise) have seen this species established in many streams of the Atherton Tablelands, in the upper Tully River and the upper Herbert River where they would otherwise not occur. This is unfortunate for several reasons, not the least of which is that it has resulted in the mixing of different stocks but also because it has resulted in the introduction of a potentially large and voracious predator into systems which were essentially predator-free (except for the occasional eel). The long-term impact on populations of genetically distinct hardyheads, endemic rainbowfishes, endemic crayfishes and shrimps, and rare and threatened frogs is unknown.
To the north of the Burdekin River, H. fuliginosus is absent from the Black-Alice River [176] and short coastal tributaries such as Leichhardt, St. Margaret’s, Hencamp and Saltwater creeks [1053] in the vicinity of Townsville. Its absence from these basins may be for the same reasons as listed above for the Don and Proserpine rivers. Sooty grunter is naturally present in the lower reaches of the Herbert River [588]. Interestingly, the Wet Tropics endemic H. tulliensis is apparently uncommon in the Herbert River [643]. Hephaestus fuliginosus is present in most drainages of the Wet Tropics region [1087], being recorded from the Tully River [588, 1087] and Murray River [1087], Liverpool Creek [1179], the Johnstone River [1096, 1177], and the Russell/Mulgrave River [1096, 1184]. It has not been collected from the smaller catchments such as the Hull River [1087], Moresby River [1183] or Maria Creek [1179]. Sooty grunter is perhaps not native to the Barron River; its presence there is probably due to stocking [588]. Russell et al. [1185] did not record it in the Saltwater, Mossman and Mowbray catchments but did record it in the Daintree River. Pusey and Kennard [1087] also failed to collect it from the Mossman River but collected a small number of specimens of a Hephaestus species, which they identified at the time as H. fuliginosus, from the Daintree River. Subsequent collecting by us has failed to collect a single specimen of H. fuliginosus in this river (unpubl. data) although many individuals of H. tulliensis were collected.
As might be expected for a top level predator, sooty grunter are not an abundant species and are much less common than their congener, H. tulliensis. For example, only 278 individuals were collected over the period 1994–1997 (22nd most abundant) (Table 1), compared to 1089 specimens of H. tulliensis (eighth most abundant). This species was very infrequently collected from the Mulgrave River but was more abundant and more widespread in the Johnstone River. Hephaestus tulliensis outnumbers H. fuliginosus by 32:1, 3.4:1 and 6.7: 1 in the Mulgrave River (80 site/sampling occasions), Johnstone Table 1. Distribution, abundance and biomass data for Hephaestus fuliginosus in two rivers of the Wet Tropics region. Data summaries for a total of 278 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. These data plus density and biomass are included for all sites combined and not for individual rivers as only five individuals were collected from the Mulgrave River.
Studies of the freshwater fish fauna of the Wet Tropics region have generally not recognised more than one species of Hephaestus, grouping all under the name H. fuliginosus. We believe that H. fuliginosus is absent from the Daintree River and probably from most drainages north of the Barron River. This species is also absent from streams of the Cape Tribulation area and the Bloomfield River [1087] and from the Endeavour River [571]. Thus, its natural northern limit in the Wet Tropics region is the Russell/Mulgrave River.
Total % locations
Comparison of DNA sequence data reveals sooty grunter from the Wet Tropics region to be a further 0.5% divergent from those in the Burdekin (Pusey and Bermingham, unpubl. data). One hypothesis that accounts for the observed distribution and pattern of sequence divergence is that sooty grunter colonised the east coast via the
Johnstone River
31.5
6.8
46.4
% abundance
0.8 (6.0)
<0.1
1.0
Rank abundance
22 (11)
30
17
3.5 (23.4)
0.15
5.3
Rank biomass
5 (4)
21
4
Mean density (fish.10m–2)
0.11 ± 0.01
—
—
Mean biomass (g.10m–2)
11.21 ± 2.29
—
—
% biomass
381
Mulgrave River
Freshwater Fishes of North-Eastern Australia
composition, the difference between mean and weighted mean values indicates that abundances are highest in reaches with little mud and dominated by gravel and cobbles. Such a substrate composition is expected for riffle/run habitats.
River (190 site/sampling occasions) and Tully River (10 sites), respectively. In addition to being less common overall, H. fuliginosus occurs at lower density (average density of 0.11 + 0.01 fish.10m–2, maximum = 0.58 fish.10m–2) at those sites in which it occurs, than does H. tulliensis (see appropriate chapter) although it occurs at equivalent biomass (23.4% versus 22.3% of total for H. fuliginosus and H. tulliensis, respectively).
Table 2. Macro/mesohabitat use by sooty grunter Hephaestus fuliginosus in the Wet Tropics region. Data presented represents the minimum, maximum and mean habitat characteristics of the sites within the Russell/Mulgrave, Johnstone and Tully rivers in which H. fuliginosus was present. The weighted mean (W.M.) refers to the mean weighted by the abundance of sooty grunter in each site. High elevation sites into which sooty grunter have been translocated were not included.
In the Burdekin River system, over the period 1989–1992, H. fuliginosus was the 3rd, 10th and 10th most abundant species in electrofishing, seine-netting and gill-netting samples, respectively; contributing 8.05%, 0.06% and 1.3% of the respective totals [1098]. Abundance levels were greatest in the late wet season following flooding [1093]. Sooty grunter comprised only 0.5% of the total number of fish from a study site in Gunpowder Creek, a tributary of the Leichardt River, near Mt. Isa [1093]. Bishop et al. [193] found sooty grunter to be eighth most abundant species, comprising 2.7% of the total number of fish collected from the Alligator Rivers region of the Northern Territory.
Parameter
Min.
Catchment area (km2) Stream order Distance to source (km) Distance to river mouth (km) Elevation (m.a.s.l.) Width (m) Riparian cover (%)
Macro/mesohabitat use The data presented in Table 2 refers to the macro/mesohabitat requirements of H. fuliginosus in small streams (maximum fifth order, mean 3.8) of the Wet Tropics region. Furthermore, it relates primarily to the habitat requirements of juvenile fishes as 92.3% of the sample upon which the summaries are based were less than 150 mm in length. Care should therefore be exercised in extrapolating these data to other regions in which H. fuliginosus occurs.
1.1 1 1.5 4.0 5 2.9 0
Gradient (%) 0.1 Mean depth (m) 0.20 Mean water velocity (m.sec–1) 0
Hephaestus fuliginosus was recorded from a variety of streams ranging from small first-order tributaries of small catchment area through to fifth-order rivers with much larger catchments. The small streams included both headwater streams moderately distant from the river mouth and at elevations up to 60 m.a.s.l., as well as lowland adventitious streams located close to the river mouth. Large, adult fish are also found close to the river mouth in the Wet Tropics region (i.e. in sixth and seventh-order main river channels) [588, 1087]. The range in stream gradient listed is a function of the diversity of sites in which sooty grunter were recorded, however, the mean gradient and weighted mean indicate that sooty grunter was most common in flowing water habitats (weighted mean water velocity of 0.18 m.sec–1) of moderate depth (weighted mean depth of 0.41 m). In other words, juvenile sooty grunter were most abundant in riffles and runs and although they were collected from sites with no flow, they were not collected from sites with an average depth of less than 20 cm. Although found in sites with diverse substrate
Max.
Mean
W.M.
334.8 5 67.0 57.0 60 39.1 100
94.5 3.8 21.2 31.8 28.5 12.5 40.5
107.0 3.8 24.1 33.3 47.6 15.8 23.4
4.1 0.87 0.43
0.41 0.44 0.16
0.53 0.41 0.18
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48 61 72 52 41 76 98
8.3 18.8 24.1 16.5 10.7 11.3 10.7
0.2 16.4 22.1 19.3 12.7 9.6 12.9
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Small woody debris (%) Large woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
7.0 0.5 9.0 12.0 3.0 60.3 12.3 12.3 32.0 47.0
0.6 0.1 1.3 1.6 1.3 8.3 2.8 2.6 6.4 13.4
0.2 0.0 1.3 2.3 0.1 4.2 2.2 1.8 5.4 6.0
The sites in which H. fuliginosus occur contain a range of microhabitat cover elements and on occasions, cover was abundant: there is little evidence however to suggest that any single element is of particular importance. Bear in mind however that the samples were dominated by small individuals. Had more large adults been sampled it is possible that elements such as woody debris and the extent of bank undercutting would have been identified as being important as they were in the Burdekin River [1098].
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Hephaestus fuliginosus
infrequently in depths greater than 70 cm (Fig. 1c). Bear in mind that electrofishing sampling efficiency may decrease with increasing depth and the previous caveat concerning the size distribution of the sample upon which this summary is based.
Elsewhere in Queensland, sooty grunter are found in streams of much lower gradient (i.e. Burdekin River, western streams of Cape York Peninsula) than those typical of the Wet Tropics region. Hephaestus fuliginosus were significantly more abundant in the main channel of the Burdekin and Bowen Rivers than in upstream tributary streams of the Burdekin River [1093]. The populations present in tributary streams were also dominated by small juveniles, indicating that tributary streams provided suitable spawning habitat but not adult habitat. Sites in which juvenile sooty grunter were abundant were characterised by coarse substrates and high flows. Adult sooty grunter were more abundant in the deeper pools with abundant woody debris and extensive bank undercutting [1098]. Where such mesohabitat features exist in tributary streams, adult H. fuliginosus may be locally abundant (e.g. Keelbottom Creek in the upper Burdekin River (D. Burrows, pers. comm.). Although sooty grunter may be collected from very low gradient streams in the Burdekin River, with little or no flow, and a stream-bed dominated by sand and fine gravel, this species is most abundant in reaches with access to areas of higher flow.
(a) 30
40 30
20
20 10
10 0
0
Mean water velocity (m/sec) 25
The majority of specimens collected by Bishop et al. [193] in aquatic habitats of the Alligator Rivers region were from escarpment main channel waterbodies; habitats characterised by perennial water. During the wet season, juveniles were collected from a rapidly flowing lowland sandy creek and adults were present in deep sandy lowland creekbed pools and corridor lagoons. Bishop et al. [193] believed the perennial streams of the escarpment country provided dry-season refuge for sooty grunter. Although collected in a number of rivers of Cape York Peninsula during the CYPLUS investigations, Herbert et al. [571] present no data on the types of habitat in which sooty grunter was found. Microhabitat use Figure 1 provides a summary of the microhabitat use of H. fuliginosus in rainforest streams of the Johnstone and Mulgrave rivers of the Wet Tropics region based on capture data for 113 individuals collected between 1994 and 1997. The summary must be interpreted with caution however given that it applies to rainforest streams only (which may be considered atypical habitat when the habit requirements of this species are considered in their broadest sense) and pertains predominantly to juvenile specimens. Hephaestus fuliginosus in rainforest streams occurs most frequently in areas with currents less than 0.3 m.sec–1, but may occasionally occur in areas with current velocities twice this (Fig. 1a). This species occurs across a range of depths but rarely in depths less than 20 cm (see Table 1 in which minimum mean site depth given as 20 cm) and
(b) 50
(c)
Focal point velocity (m/sec) 25
20
20
15
15
10
10
5
5
0
0
(d)
Total depth (cm) 25
(e)
Relative depth 30
(f)
20 20
15 10
10
5 0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by the sooty grunter Hephaestus fuliginosus. Data derived from capture records for 113 individuals collected over the period 1994–1997 from the Johnstone and Mulgrave rivers.
This species occurs most frequently in the lower half of the water column (Fig. 1d) and when collected from higher in the water column, an association with some form of complex microhabitat structure such as root masses is typical. However, dietary information depicted in Figure 2 does indicate that occasional foraging sorties are made to the surface to take terrestrial prey. As a consequence of being associated with the lower half of the water column,
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Freshwater Fishes of North-Eastern Australia
Table 3. Physicochemical data for the sooty grunter Hephaestus fuliginosus. Data derived from three separate areas in northern Australia; the Wet Tropics region [1093], the Burdekin River [1098] of northern Queensland, and escarpment pools of the Alligator Rivers region of the Northern Territory [193].
focal point velocities tend to be lower than average water velocities (Fig. 1b). Nonetheless, the range of focal point velocities depicted indicates that H. fuliginosus is frequently found in swiftly flowing water. This species is frequently collected over coarse substrates: reflecting the flow environment in which it occurs as well as the stream reaches in which it occurs. It may frequently occur far removed from cover (Fig. 1e) and small juveniles are frequently seen foraging in the open in loosely organised schools. Such individuals are also able to use coarse substrates as cover. Just over one-quarter of the sample was collected within 20 cm of large woody debris although such a cover element was not abundant in the streams in which this species occurs (Table 1). Root masses and undercut banks are also important microhabitat. The importance of undercut banks and large woody debris increases greatly in adult fish.
Parameter
Min.
Max.
Wet Tropics region (n = 69) Water temperature (°C) 17 32.7 Dissolved oxygen (mg.L–1) 5.51 9.24 pH 5.13 8.00 Conductivity (µS.cm–1) 6.03 80.3 Turbidity (NTU) 0.33 29.7
Environmental tolerances Experimental data on the environmental tolerances of sooty grunter are lacking and inferences about tolerance must be drawn from studies of distribution. Concomitant water quality data and fish abundance data were available for three areas; rainforests streams of the Wet Tropics region, the Burdekin River and escarpment pools of the Alligator Rivers region (Table 3). Care needs to be taken when using this approach as some populations may be highly adapted to local conditions and upper and lower limits for some populations may be lethal for others not acclimated to similar conditions. For example, the minimum temperature recorded at a site in which H. fuliginosus was present was 17°C. Temperatures at this site (Dirran Creek on the Atherton Tablelands) fall as low as 13.3°C on occasions (and possibly lower during frosts). Hephaestus fuliginosus was very uncommon at this site (only one individual recorded over 10 sampling occasions) and their low abundance may reflect the effect of low water temperatures. Temperatures between 13–17°C may be approaching the lower limit for Wet Tropics populations and it is highly likely that Northern Territory populations exposed to this low temperature would experience substantial mortality given that such low temperatures are rarely experienced (Table 3). Maximum temperatures recorded across the three studies are very similar however (32.7–34°C). The maximum recorded in the Wet Tropics region may be close to upper limit for this population as the population density recorded at this time was substantially lower than recorded three months previous (fish may have simply emigrated, however). Whitley [1396] records sooty grunter at 38.8°C in an artesian spring in central Australia, but this record is probably attributable to a Scortum species not H. fuliginosus (see section on distribution). It is most probable that the upper temperature limit for sooty grunter is 35–36°C.
Mean 23.7 6.97 6.98 37.4 4.51
Burdekin River (n = 29) Water temperature (°C) 21 Dissolved oxygen (mg.L–1) 4.2 pH 6.7 Conductivity (µS.cm–1) 56 Turbidity (NTU) 0.25
33 11.0 8.6 790 16.0
26.3 7.72 7.73 404.0 3.08
Alligator Rivers region Water temperature (°C) 23 Dissolved oxygen (mg.L–1) 5.3 pH 4.5 Conductivity (µS.cm–1) — Turbidity (NTU) 5
34 7.4 6.5 — 80
27.7 6.3 5.7 — —
Hepahaestus fuliginosus is found in moderately to welloxygenated waters, reflecting their preference for lotic habitats. The minimum dissolved oxygen concentration in which they have been recorded over the range of sites in the three areas covered in Table 3 was 4.2 mg.L–1 (recorded when water temperature was 29°C). However, Hogan and Graham [583] recorded sooty grunter in a floodplain lagoon of the Tully River in which the daytime concentration of dissolved oxygen was only 3.7 mg.L–1. Hephaestus fuliginosus has been collected over a very wide range of water acidity (4.5–8.6), although the range for each area is considerably smaller. The average pH recorded for the Wet Tropics population was near neutral although sooty grunter was also recorded from acidic waters in this region. The minimum value recorded was for a lowland well-vegetated small creek, and although H. fuliginosus was not abundant here, it was frequently present over the period 1994–1997. The tendency for sooty grunter to be present in more basic waters of the Burdekin simply reflects the range of acidities present in the Burdekin. Similarly, Bishop et al. [193] comment that the acidic nature of waters in which sooty grunter were collected in the Alligator Rivers region simply reflects the range in acidity observed for escarpment pools. Thus, it appears that H. fuliginosus are found over a wide range of water acidity (although the range is smaller for individual populations).
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Hephaestus fuliginosus
season flooding provides enhanced and expanded larval habitat. The relatively higher gradient and more incised nature of the rivers and streams of the Wet tropics region results in little lateral expansion during flooding. Rather, streams depths increase dramatically as does mean water velocity across most of the stream channel. Such conditions are not favourable for small fish larvae.
Hephaestus fuliginosus is a freshwater species and has been collected from dilute to very dilute waters only. Hogan and Nicholson [589] experimentally determined that the sperm of H. fuliginosus was most active at salinities less than 5‰. The turbidity values listed in Table 3 indicate that sooty grunter occur in clear waters. However, the maximum values presented in Table 3 also indicate that it may, at times, occur in turbid waters also. While high levels of suspended solids are generally transitory in rainforest streams of the Wet Tropics, persistently high levels are more common in the Burdekin River. For example, we have recorded turbidity levels of 114 NTU following a minor spate in the Burdekin River, such levels are likely to persist for several weeks. This species has not yet been recorded from the extremely turbid waters of the Belyando River, but it does occur in the lower Cape River which is also highly turbid for much of the year. It is not common there however. Sooty grunter is a visual predator and high turbidity probably reduces feeding efficiency.
Spawning behaviour in the field has been observed by several investigators but all such observations pertain to populations in the Wet Tropics region. In short, sooty grunter spawn in aggregations in shallow, lateral, slackwater habitats adjacent to riffle/rapid habitats. Such habitats are very susceptible to rapid de-watering in the event of upstream regulation. There is general agreement across the studies cited that temperatures above 25°C are required for spawning. Water resource infrastructure that impacts on the natural thermal regime of tropical rivers (i.e. through hypolimnetic releases) would have a high potential to disrupt the reproduction of this species. The early spawning season of sooty grunter in the Wet Tropics compared to the Northern Territory may be related to a mismatch of the flow regime and the thermal regime. Water temperatures in this region are greatest in the early part of the wet season prior to flooding. The onset of flooding, whilst reducing mean daily temperature by as little as 1°C, may reduce the daily range in temperature by up to 10°C [1093].
Reproduction The information presented in Table 4 was derived principally from studies undertaken in the Alligator Rivers region [193], the Burdekin River [1093] or the Wet Tropics region [1093], unless otherwise indicated. The general pattern is for female sooty grunter to delay reproduction until the second or third year and until large size is attained. Accordingly this species is long-lived and it is likely that a female spawns several times in one season and over several seasons. Delayed maturation is not as apparent in males as there is probably little fitness advantage associated with large size for a species that spawns in groups. Sex ratios are skewed towards males during the breeding season, probably reflecting earlier maturation of males rather than a greater overall number of males in the population. Larger females certainly produce more eggs but whether delayed maturation results in an increased lifetime fitness compared to maturation at small size equivalent to that seen in males is unknown. It is possible that spawning compromises survival during the dryseason. Whatever the forces selecting for this aspect of the life history, they evidently apply over the species’ entire range.
Flooding or minor rises in water level are not essential cues for reproduction over its entire range. However, it is clear from correlations between temporal variation in recruitment strength and the extent of wet season flooding in the Burdekin River [1093], that flooding does enhance the production of young. This effect is probably due to the provision of an expanded habitat and the stimulation of primary and secondary production. Movement Herbert et al. [571] list some observations (e.g. reproductive fish moving into Prospect Creek, an intermittent tributary of the Palmer River, in March; p. 218) and anecdotal accounts of H. fuliginosus movements (e.g. upstream migration in the Wenlock River in November to December at the start of the first rains; p. 153) that suggest in rivers of western Cape York Peninsula, this species migrates into tributary streams for spawning. In contrast, sooty grunter in the Alligator Rivers region move downstream out of escarpment headwater refugia and onto the floodplain to spawn [193]. This occurs in the early wet season. Interestingly, although males were well developed at this time of year, females were much less so, the inference being that female maturation occurred after they had arrived on the floodplain. Upstream return migrations by juvenile
A notable difference in reproductive tactics over its range is the tendency in populations of the wet-dry tropics (Northern Territory and Cape York Peninsula) and subtropical areas (Burdekin River) for spawning to take place during the wet season and to be associated with flooding, whereas in the perennial streams and rivers of the Wet Tropics region, reproduction occurs early in the year and tends to precede wet season flooding. Clearly the differences observed here relate to the extent that wet
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Freshwater Fishes of North-Eastern Australia
Table 4. Life history data for Hephaestus fuliginosus. Age at sexual maturity (months)
Gender discernible at small size in Burdekin River: males – 50–60 mm SL, females 80–90 mm SL equating to 6–8 months old Hogan [581] estimates maturity at 12 months for males and 24–36 months for females
Minimum length of ripe females (mm)
Alligator Rivers – estimated length at maturity 250–320 mm CFL but based on small sample [193] Burdekin River – smallest stage IV female 281 mm SL but based on small sample [1093] Wet Tropics – 300 mm SL [581] Widespread sample – 265 mm [936]
Minimum length of ripe males
Alligator Rivers – estimated length at maturity of 200 mm CFL but the smallest mature male collected was 150 mm [193] Burdekin River – smallest stage IV male 144 mm SL [1093] Wet Tropics – 150 mm SL [581] Widespread sample – 190 mm SL [932, 936]
Longevity (years)
Unknown but probably in the range of 5–7 years
Sex ratio
Alligator Rivers – slightly skewed towards males [193] Burdekin River – skewed towards males [1093]
Peak spawning activity
Alligator Rivers – early to mid-wet-season, females mature later than males [193]. Cape York Peninsula – wet season: November to March [571] Burdekin – wet season: January to April [1093] Wet Tropics – reproductively active fish present from September to April but majority of spawning in spring to early summer (i.e. before wet season) [581]
Critical temperature for spawning
25–30°C [571, 588, 936]
Inducement to spawning
Rising water levels suggested to stimulate spawning [936] but not necessary in Wet Tropics region [581] nor Burdekin River [1093]. Flooding does enhance recruitment in the Burdekin River however [1093]
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
26 000–107 000 for fish ranging from 0.3 to 0.6 kg [931] 177 000 per kg [581]
Fecundity/length relationship
?
Egg size
1.8–2.3 mm, mean = 2.1 mm diameter water hardened, demersal, initially adhesive [581]
Frequency of spawning
Serial spawner [581, 931]
Oviposition and spawning site
Wet Tropics region – slack water habitats adjacent to rocky riffle/rapid habitats [581, 936] Unknown for low gradient rivers or rivers lacking perennial fast-water habitats but spawning during wet season probably ensures that eggs are laid in flowing water microhabitats Demersal eggs sink down into crevices between sediment. Initial adhesiveness may help to prevent them being swept downstream
Spawning migration
Upstream in most rivers but downstream in rivers of the Alligator Rivers region (see section on movement), extent of movement variable
Parental care
None
Time to hatching
24–48 hours at 28°C [581], 42 hours at 26°C [936]
Length at hatching (mm)
?
Length at feeding
?
Age at first feeding
3 days after hatching
Age at loss of yolk sac
?
Duration of larval development
?
Length at metamorphosis
14–15 mm [581]
upstream to spawn while the other moves downstream. However, in both systems, movement is out of the dryseason refugial habitats and into ephemeral wet-season habitats for spawning.
fish (during daylight hours) were observed by Bishop et al. [190] and juveniles were estimated to be capable of moving 6.4–7.25 km.day–1. Initially, these observations seem at odds with one another; one population moving
386
Hephaestus fuliginosus
to feed throughout the water column.
Spawning occurs in both main channel and tributary habitats in the Burdekin River and most adults return to main channel habitats after spawning [1093]. Upstream migrations probably occurred at the start of the wet season. Upstream migrations probably also occur in rivers of the Wet Tropics region but it is also probable that they are shorter and occur earlier in the year (see above) than for the populations discussed above. Merrick and Midgely [932] remarked on the absence of fish for 0.5 km downstream of a spawning aggregation, the inference being drawn that fish had migrated upstream over this distance. In the circumstance where suitable spawning sites (areas of slack water adjacent to riffle/rapids) are regularly positioned up the stream profile it is probable that adult fish make only localised movements to them. However, Hogan [588] showed that some tagged fish in the Tully River made substantial movements upstream during the breeding season. One fish moved approximately 16 km. Significantly, this individual was initially tagged in a downstream sandy reach that lacked suitable spawning habitat. Fish that had been tagged in the rocky rapid middle section of the river (i.e. spawning habitat) tended not to move far (the majority were recaptured in the same reach in which they were initially captured). Two tagged individuals made extensive downstream movements (43 and 50 km) during this study. In summary, it is probable that H. fuliginosus, over its entire range, make some form of migration associated with spawning. The extent and direction of the movement is probably dependent on the distance between, and location of, wet season spawning habitat and of dry season refugial habitat. In low gradient rivers in the wet/dry tropics of northern Australia, distances travelled may be substantial. In the perennial streams of the Wet Tropics region it is possible that the distances travelled are often less than a few kilometres. Migrations to spawning areas are necessarily followed by return migrations as conditions deteriorate with the approach of the dry season. Trophic ecology The dietary summary presented in Figure 2 is derived from studies undertaken across this species’ range and includes studies undertaken in the Tully and Herbert rivers (n = 148 from riverine habitats and 10 from Lake Koombaloomba) [98], the Mulgrave and South Johnstone rivers (n = 28) [1097], the Alligator Rivers region (n = 51) [193], the Burdekin River (n = 303) [1093], and the Annan River (n = 1). The summary pertains to both adult and juvenile fish but is skewed towards juveniles. Hephaestus fuliginosus is omnivorous and its diet is diverse in composition, containing terrestrial insects and vegetation, fish, aquatic insect larvae, macrocrustacea (shrimps and prawns) and aquatic vegetation. Such a diversity indicates sooty grunter are able
The diet of H. fuliginosus varies markedly as it grows. In the Burdekin River [1093], increasing size was accompanied by an increase in the diversity of food items consumed, an increase in the size of prey items and an increased consumption of plant material. The relative importance of chironomid larvae decreased with increasing size (from 22.4% to 3.5% in the smallest (<40 mm SL) and largest size classes (>80 mm SL), respectively). The relative importance of ephemeropteran nymphs also changed in a similar way (24.7% to 1.9% in the smallest and largest size classes, respectively). In contrast, trichopteran larvae remained important for all size classes (>25%). Macrocrustaceans and fish were important dietary items in the largest size class only, comprising 10% of the diet. Plant material was absent from the diet of fish less than 40 mm SL. Filamentous algae contributed 6.5% of the diet in fish 40–80 mm in length and increased to 18.8% in the largest size class. Aquatic macrophytes and terrestrial vegetation were absent (or at very low levels in the case of terrestrial vegetation) in fish less than 80 mm SL but collectively comprised 13% of the diet in fish greater than 80 mm SL. Mouth gape increases significantly with size (gape (mm) = 0.301 + 0.134 (SL (mm)): r = 0.989, n = 322, p<0.001) and changes in diet partly correspond to an increased ability to handle larger prey items in larger fish. However, the importance of small invertebrate prey, particularly trichopteran larvae and simulid larvae, remained high in large fish. Moreover, the increasing importance of filamentous algae and macrophytes in larger fish is probably unrelated to changes in mouth gape. Of greater importance are Other microinvertebrates (0.1%) Microcrustaceans (0.3%) Macrocrustaceans (10.9%)
Fish (3.4%) Unidentified (13.1%)
Molluscs (0.2%) Terrestrial invertebrates (3.7%)
Other macroinvertebrates (0.8%)
Aerial aq. Invertebrates (0.2%) Terrestrial vegetation (3.5%) Detritus (0.4%) Aquatic macrophytes (4.4%)
Algae (13.3%)
Aquatic insects (45.7%)
Figure 2. The mean diet of the sooty grunter Hephaestus fuliginosus. Diet summary derived from stomach content analysis of 541 individuals from several studies conducted in northern Australia. See text for list of studies. Summary includes data from a large range in size and substantial ontogenetic variation in diet is an important feature of the ecology of this species.
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Freshwater Fishes of North-Eastern Australia
Conservation status, threats and management Hephaestus fuliginosus is listed as Non-Threatened [1353]. Likely threats are related to local factors and fall into four general categories: 1. over-exploitation; 2. habitat alteration; 3. water infrastructure and flow regime manipulation associated with the water industry; and 4. dilution of genetic distinctiveness. Sooty grunter are a prized angling species and may experience heavy localised exploitation, especially during the spawning season. This species is currently protected by legal size and bag limits in Queensland. Loss of riparian vegetation and subsequent loss of undercut banks and woody debris as well as loss of allochthonous food sources may impact in the long term. Increased sedimentation may impact on in-stream secondary production and subsequently on growth rates and survivorship. Siltation is likely to adversely affect demersal eggs. Hephaestus fulinisosus is highly adapted to flowing water habitats and appears to be among the most rheophilic of all the terapontid grunters. As such, manipulation of flow regimes has a high potential to impact on this species. Hogan [588] expressed concerned that the operating conditions of hydropower plants (peaking demand) could lead to stranding of eggs and death. Impoundments may also inundate upstream riffles and races that provide critical spawning areas. Similarly, flow supplementation resulting in the ‘drowning out’ of riffles and runs, and reduction of the diversity of flow environments within reaches, is likely to reduce spawning success. Impacts may arise from changes to the thermal regime (i.e. from hypolimnetic relaeases) or to the flooding regime of a river and flow seasonality; both of which will result in desynchronisation or loss important spawning cues. The loss of medium-sized flood events which would otherwise ensure that fine sediments are mobilised and removed from riffle habitats (i.e. flushing flows) will ultimately result in the loss of suitable spawning areas. Similarly, such changes will result in a reduction in secondary production and a disruption to the aquatic food base available to sooty grunter. Interception and storage of large floods that ordinarily link up isolated dry-season refugia with other habitat patches and which allow access by reproductive fish to spawning areas, will very quickly result in reductions in population size. Sooty grunter undertake migrations associated with spawning [588] and are thus prone to impacts arising from the imposition of in-stream barriers [586]. Movement in both directions must be allowed in order to accommodate the needs of both adult and juvenile fishes. It is of little use to assume that the passage requirements of this species, or of all life history stages of this species, are met by meeting the requirements of more charismatic species such as barramundi. The translocation of sooty grunter into rivers or reaches in which they are naturally absent poses dangers for aquatic fauna (fish, amphibians
ontogenetic changes in gut length and arrangement. The gut of H. fuliginosus is long and arranged in a series of coils and loops. A long gut is characteristic of omnivores and herbivores, particularly in the Terapontidae but is a feature of larger fish only. Similar ontogentic changes in diet were observed for fish from the Mulgrave and South Johnstone rivers [1097]. Utilisation of terrestrial invertebrates also increased with size. Anecdotal accounts of the importance of terrestrial fruit and seeds to the diet of sooty grunter are common, however the average diet depicted in Figure 2 does not suggest that it is of great importance. However, it must be borne in mind that the samples upon which the summary is based were dominated by juveniles whereas frugivory appears to be more a feature of large fish. Moreover, riparian fruits tend to be highly seasonal in availability and will not appear important in dietary studies unless samples include the appropriate occasions. For example, seeds were present in the diet of sooty grunter in Magela Creek on one occasion only (late dry). In the Wet Tropics region, the fleshy fruit of the Atherton penda (Xanthostemon whitei) is consumed in large amounts by adult sooty grunter [1093], however the fruits are available for a short time only (flowering appears to be in response to flooding) and flowering and fruiting do not occur every year. Spatial variation in diet is apparent. In the Mulgrave and South Johnstone rivers, pyralid larvae and ephemeropteran larvae were more important than observed in the Burdekin River. Similarly, chironomid larvae were more important in the diet of the latter fish. These differences simply reflect the different assemblages expected to occur in high gradient rocky streams and low gradient sandy streams. Similar differences are observed within rivers. For example, on most sampling occasions, simulid larvae were important prey in two sites within the Burdekin drainage only; both were characterised by rocky substrates and high water velocities. Similarly, the diet of fish from Koombaloomba Dam was dominated by shrimps and prawns (78%) compared to the riverine population (22%). In part, this was because the impoundment sample contained much larger fish but in greater part the differences reflected the prey likely to be available in such different habitats. Mention should be made of the ‘blubber-lip’ form of sooty grunter. We have not observed this condition in the Burdekin River population but have observed it in fish from the Wet Tropics (it is much more common in H. tulliensis). The blubber-lip form may be rare in the Burdekin River because such a feeding mode would be of little benefit in habitats dominated by sandy substrates (see comments concerning this condition in the H. tulliensis chapter).
388
Hephaestus fuliginosus
of stock from east and west of the Great Dividing Range be strenuously avoided. The translocation of other species into sooty grunter habitat also needs to be assessed for potential impacts. Similarly, the ecological impact that translocated H. fuliginosus may have on other fauna, particularly the many endemic elements of the aquatic fauna of the Wet Tropics region, such as frogs, needs to be evaluated, or at least considered.
and invertebrates) and increased potential for genetic distinctiveness of nearby populations to be reduced. For example, stocking of the upper Barron River used fish from the Burdekin, Mulgrave, Johnstone, Tully, Herbert and the Mitchell rivers [229]. The translocation of sooty grunter into impoundments outside of its natural range should be opposed. If translocation continues, it is only prudent that locally derived stock are used and that mixing
389
Hephaestus tulliensis DeVis, 1884 Khaki bream, Tully grunter
37 321034
Family: Terapontidae
below 150 mm SL. Some specimens may exhibit the ‘blubber-lip’ condition in which the lips become hypertrophied to form a thick fleshy cushion. This condition is present in other species within the genus also [34, 936]. Teeth villiform in multiple rows, outer row enlarged with brown tips. Vomer and palatines without teeth. Anterior and posterior nostril narrowly separated, each surrounded by thin membranous flaps. Lachrymal smooth on lower edge, preoperculum distinctly serrate along posterior margin, lower opercula spine prominent extending to or beyond opercula lobe. Eye relatively large, 6.5–8.1% of SL. Spinous dorsal fin arched, spines increasing length to fourth or fifth spine, decreasing thereafter. Soft dorsal and anal fins rounded with elevated middle portions. Second anal spine longer and stouter than either first or third spine. Colour in life varies substantially both within and between rivers and according to age and level of stress. The most common pattern is a body colour of overall dusky grey-brown to a khaki green, scale margins narrowly whitish; fins greybrown, similar to body colour, except soft rays of pelvic and anal fins pale yellow and pectorals translucent. The iris is red or orange. A pale yellow body colour has been observed by us in the Tully River and this pattern may be associated with breeding [1093]. Populations of H. tulliensis in the
Description Dorsal fin: XI–XIII, 11 or 12; Anal: III, 8–10 (rarely 7); Pectoral: 15 or 16; Pelvic fin: I, 5; Vertical scale rows (just above lateral line): 46–52; Horizontal scale rows: 23–26 (7–8 between lateral line and base of dorsal spines); Predorsal scales: 12–18; Transverse scale rows on cheek: 7–8; Gill rakers on first arch: 7+15; Vertebrae: 10+15 [49]. Figure: adult specimen, 280 mm SL, North Johnstone River, July 1996; drawn 1997. Hephaestus tulliensis is a moderately large, robust fish that may reach 300 mm SL in length and about 1 kg in weight, but rarely exceeds 200 mm SL. It may be confused with the larger grunter H. fuliginosus, with which it is sympatric over part of its range. Body deep, laterally compressed, greatest depth 40–45% of SL (usually not as deep in juvenile specimens). Head short (31–37% SL) with a relatively sharp snout, dorsal profile relatively steep and straight, but becoming slightly concave above the eye in larger specimens; ventral profile curves gently from the snout to the pelvic fin origin becoming horizontal between pelvic and anal fins. Mouth relatively small, non-protractible; maxillary reaching back to about the level of the posterior nostril; gape slightly oblique. Mouth smaller than equivalently sized H. fuliginosus except for specimens of the latter
390
Hephaestus tulliensis
Distribution and abundance Hephaestus tulliensis is endemic to the Wet Tropics region of northern Queensland ranging from the Herbert River north to the Daintree River [643, 1087]. This species was thought to be absent from the Herbert River (A. Hogan, pers. comm., [584]) but a recent survey [643] has collected it in small numbers from this river. This species is sympatric with H. fuliginosus over its most of its range except in the Daintree River. The relative abundance of H. tulliensis with respect to that of H. fuliginosus varies from river to river with the ratio in the Tully River (11 sites), Johnstone River (190 site/sampling occasions) and Mulgrave/Russell River (80 site/sampling occasions) being 6.7, 3.4 and 34 to 1, respectively. In the past, this species has been erroneously referred to H. fuliginosus. Examination of all Hephaestus specimens from the Mulgrave River held in the Queensland Museum revealed them to be H. tulliensis exclusively [1093].
Daintree River contain many individuals with an orangered body coloration. Young individuals (<100 mm SL) are distinguished by darker dorsal and anal fins: this condition persists in many larger individuals also but tends to be restricted to the outer margins (such as in specimen figured above). Colour in preservative: overall dark brown dorsally and tan ventrally. Allen and Pusey [49] provide a comparison of H. tulliensis and H. fuliginosus (based on 32 and 19 specimens, respectively) allowing separation of the two species. Hepahaestus tulliensis is deeper in the body (43.3% versus 37.6%), possesses a larger eye (7.2% versus 5.9%), broader interorbital (10.4% versus 8.6%), smaller mouth (maxillary length: 10.2% versus 11.8%), and a deeper and shorter caudal peduncle (15.1% versus 12.8% and 14.4% versus 16.2%, respectively). There are many other significant differences also. The most useful characters for differentiating between these species in the field include differences in iris colour (reddy-orange versus dusky brown), differences in the number rows above the lateral line (7–8 versus 8–10) and length of the pelvic fins. When depressed against the body, the pelvic fins of H. tulliensis reach back to the anus whereas they usually fall well short of the anus in H. fuliginosus.
Table 1. Distribution, abundance and biomass data for Hephaestus tulliensis in rivers of the Wet Tropics region. Data summaries for a total of 1089 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred.
Systematics Hephaestus tulliensis was first described by De Vis in 1884 [378] from material collected in the Tully River and is the type species for the genus. The description is incredibly meagre, leading Vari [1346], in his revision of the family, to place it in synonomy with the more widespread H. fuliginosus. It appears that in the interval between its description and subsequent relegation to synonomy, the name H. tulliensis has never again appeared in print. Nonetheless, the existence of this species as a valid but undescribed taxon was recognised by some fisheries scientists working in the Wet Tropics region (A. Hogan, pers. comm.) and it was included as such in an analysis of the distribution of fishes of the region [1087]. The species was formally reinstated in 1999 [49].
Total % locations % abundance Rank abundance % biomass
Mulgrave River
Johnstone River
44.2
40.9
50
3.1(12.6)
2.1(9.6)
3.4 (13.7)
8 (5)
10 (3)
8 (4)
4.5 (22.3)
4.3 (26.9)
4.9 (20.5)
4 (3)
5 (4)
Rank biomass
4 (3)
Mean density (fish.10m–2)
0.28 ± 0.03
Mean biomass (g.10m–2)
10.13 ± 1.83 18.24 ±5.72 7.0 ± 1.12
0.32 ± 0.09 0.25 ± 0.03
Hephaestus tulliensis is a widespread and abundant species, being the eighth most abundant species collected over the period 1994–1997 (Table 1). It is relatively more abundant in those sites in which it occurs being either the third or fourth most abundant and among the most important of species with respect to biomass. The average numerical density and biomass of H. tulliensis recorded was 0.28 fish.10m–2 and 10.13 g.10m–2, respectively. Maximum density and biomass density values were 2.32 fish.10m–2 and 34.1 g.10m–2, respectively. Juveniles H. tulliensis are frequently observed foraging in loose schools of 10–40 individuals foraging in open areas of the stream-bed. Adults are contrastingly solitary. This species commonly occurs with (in decreasing order of abundace) P. signifer, M. s. splendida, M. utcheensis and A. reinhardtii.
Allen and Pusey [49] provide a photograph (their Figure 2) of two specimens of H. tulliensis (including one syntype) and one specimen of H. fuliginosus. It is notable that the syntype figured is atypical of the species, as were some other specimens within the series of syntypes, in that the mouth was comparatively very large and the head profile was deeply concave: characters more associated with H. fuliginosus. Other distinguishing characters (listed above) were very much within the range for the species however. The atypical nature of some of the syntypes raises the interesting possibility that H. tulliensis and H. fuliginosus may hybridise when in sympatry. 391
Freshwater Fishes of North-Eastern Australia
Microhabitat use Estimates of microhabitat use depicted in Figure 1 were derived from capture records for 196 individuals, 80% of which were less than 150 mm in length (SL). Thus, Figure 1 is primarily concerned with the microhabitat use of juvenile or subadult fish. Hephaestus tulliensis may occur over a wide range of flows (0–0.8 m.sec–1) (Fig. 1a) and depths (<10–>100 cm) (Fig. 1c) although the great majority of fish were collected from flows less than 0.3 m.sec–1 and depths between 20 and 60 cm. This species most frequently occurs in the lower one-third of the water column (Fig. 1d), within 20 cm of the substrate (Fig. 1f) and as a consequence, focal point velocities experienced by this species are much lower than the average velocity (Fig. 1b). This species most frequently occurs over coarse substrates and is often found over broad areas of bedrock
Macro/meso habitat use Hephaestus tulliensis occurs across a wide range of macrohabitat conditions being recorded from small first-order headwater tributary streams to larger lowland sixth-order rivers (Table 2). Table 2. Macro/mesohabitat use by the khaki bream Hephaestus tulliensis. Summaries derived from 47 sites within the Russell/Mulgrave, Johnstone and Tully river basins and a total of 402 individuals. Weighted means (WM) estimated by weighting sites by abundance data. Parameter
Min. 2
1.1 Catchment area (km ) Distance to source (km) 2 Distance to river mouth (km) 12 Elevation (m.a.s.l.) 10 Stream width (m) 1.9 Riparian cover (%) 0
Max.
Mean
W.M.
515.5 67 69.5 60 39.1 85
86.7 17.5 39.3 35.3 12.3 35.4
93.5 18.1 39.1 39.2 13.5 22.6
Gradient (%) Mean site depth (m) Mean site velocity (m.sec–1)
0 0.15 0
4.6 0.87 0.51
0.8 0.41 0.19
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
45 43 45 56 41 76 98
2.5 8.2 16.7 16.8 27.7 27.8 11.1
1.7 6.6 16.1 18.9 17.5 21.6 17.5
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (%) Root masses (%)
0 0 0 0 0 0 0 0 0 0
7 2.5 9 75 10 35.8 12.5 10.7 35 56
0.3 0.1 1.4 7.8 0.4 7 1.8 0.9 6.4 12
0.4 0.1 1.3 6.6 0.2 5.5 2.2 1.0 7.1 9.3
(a) 30 30 20
20
10
10
0
0
Mean water velocity (m/sec) 30
Focal point velocity (m/sec)
(c)
(d) 30
20 20 10
10
0
0
Depth (cm)
Relative depth
(f)
(e)
Although found in streams ranging in gradient from 0 to 4.6%, H. tulliensis are most common in fourth-order streams with an average gradient of about 1%. Such streams tend to be moderately wide with an intact riparian canopy covering about 20–40% of the surface, about 0.4 m deep, moderately fast average water velocities and a diverse substrate. The differences between average macro/mesohabitat conditions and average conditions weighted by the number of individuals present are minor. The habitats in which H. tulliensis tend to occur most commonly, whilst not entirely devoid of in-stream cover, do not contain large amounts of microhabitat elements such as macrophytes, leaf litter or bankside vegetation. This is expected given the macro/mesohabitat conditions described above.
(b) 40
1.0 0.41 0.20
60
30 20
40
10
20
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Hephaestus tulliensis. Summaries derived from capture records for 196 individuals collected from the Mulgrave/Russell, Johnstone and Tully rivers over the period 1994–1997.
392
Hephaestus tulliensis
Reproductive biology Details of the reproductive biology of this species are almost completely unknown. Spawning behaviour has been observed by us in the Tully River in September 1993 [1093]. Two large individuals (>200 mm SL) were observed spawning in shallow still-water adjacent to a fastflowing rapid. A number of smaller males, which were reproductively mature and producing milt, were observed to make quick sorties over the spawning area (presumably releasing sperm as they did so) and were aggressively met and chased by the larger male. The larger male and several of the smaller males were collected after spawning and all were at stage VI (running ripe). The large presumed female was not collected and it is unknown how many females were involved in this presumed spawning aggregation. Reproductively mature male fish as small as 100 mm SL have been collected from the Johnstone River from June through October. It is probable that many aspects of the reproductive biology of H. tulliensis are similar to that of H. fuliginosus but further research on this aspect of the biology of this species is urgently needed.
(Fig. 1e). Larger fish (>150 mm SL) make greater use of woody debris and undercut banks than is indicated here. Environmental tolerances The summary data listed in Table 3 is based on ambient conditions present at 101 sites in rainforest streams over the period 1994–1997. Care should therefore be exercised in interpreting these data as defining the water quality tolerance limits of this species. The range in water temperatures listed in Table 3 are typical of rainforest streams of the Wet Tropics area. The maximum temperature of 32.7°C was recorded in November at a time of low flow in a shallow site with very exposed bedrock (basalt) substrate. The number of H. tulliensis collected at this time was much reduced compared to the previous sampling occasion and it is possible that the high temperatures experienced resulted in substantial mortality. Alternatively, fish may have simply vacated this area for pools downstream although potential emigration was not reflected in elevated abundances in a run/pool site located 100 m downstream. Temperatures approaching 35°C probably represent the upper limit for this species. The range in dissolved oxygen concentrations and water acidity listed indicate well-oxygenated, neutral pH waters typical of third and fourth order rainforest streams of the area. Given the habitat requirements of this species it is unlikely to be tolerant of hypoxia. This species has been recorded (by us) across a narrow range of conductivities indicative of very freshwaters, but given that it does also occur in large lowland rivers, this species may be tolerant of more elevated conductivities. Nonetheless, it is a strictly freshwater species. Hephaestus tulliensis has been recorded over a wide turbidity range although it is most frequently recorded from fairly clear waters. The maximum turbidity value listed in Table 3 was recorded immediately after a severe rainfall event in a site immediately downstream of a banana plantation. Elevated turbidity at this site was transitory.
Movement No quantitative information is available on this aspect of the biology of H. tulliensis. Anecdotal evidence suggests that an upstream spawning migration may occur but details or veracity are unknown.
Table 3. Physicochemical data for the khaki bream Hephaestus tulliensis. Summaries derived from 101 site/sampling occasions in four rivers of the Wet Tropics region over the period 1994–1997. Parameter
Min.
Max.
Wet Tropics region (n = 101) Water temperature (°C) 18.2 Dissolved oxygen (mg.L–1) 5.13 pH 6.41 Conductivity (µS.cm–1) 7.8 Turbidity (NTU) 0.25
32.7 9.24 8.43 67.6 29.7
Mean 23.4 6.99 7.36 34.6 4.87
Trophic ecology The average diet of Hephaestus tulliensis is depicted in Figure 2 and is derived from data for 16 adult (>150 mm SL) and 40 juvenile fish from the Mulgrave River collected in during the dry season. (Data listed here for H. tulliensis were originally and erroneously published as for H. fuliginosus from the Mulgrave River [1097]). Figure 2 indicates that the average dry-season diet of H. tulliensis is dominated by aquatic insects (chironomid, trichopteran and pyralid larvae, and ephemeropteran and plecopteran nymphs) and aquatic plant material. Ontogenetic variation in diet is substantial. Larger fish consumed less aquatic invertebrates than did small individuals (31% versus 74%, respectively) and consumed more plant material (38% versus 12%, respectively). Moreover, the aquatic plant material in the diet of larger fishes was comprised of both filamentous alga and macrophytes in equal proportion whereas filamentous alga alone was present in small individuals. Material taken from the water’s surface was more important in larger fish also. These differences parallel those ontogenetic differences described for other terapontid grunters, particularly H. fuliginosus (this volume). Although not included here, Pusey et al. [1097] list dietary data for the ‘blubber lip’ form and showed that they
393
Freshwater Fishes of North-Eastern Australia
Fish (2.2%) Macrocrustaceans (6.5%)
‘suck’ out otherwise unattainable prey. They predicted that this form would only occur in stream reaches with coarse substrates as no adaptive advantage would be conveyed by this morphological structure in reaches with a sandy substrate. This prediction remains to be tested.
Unidentified (4.6%) Terrestrial invertebrates (2.0%) Detritus (1.5%) Terrestrial vegetation (1.5%) Aquatic macrophytes (4.9%)
Algae (13.7%)
Conservation status, threats and management Hephaestus tulliensis is currently without an official conservation status. Although restricted to the Wet Tropics region, it is locally abundant and probably secure and should therefore be listed as Non-Threatened. The apparent preference for flowing water habitats and indications of a dry-season spawning phenology suggest that this species may be sensitive to impacts wrought by water abstraction. If shallow lateral habitats adjacent to riffles and rapids are required for spawning, then changes to the flow regime due to from hydroelectric power generation (i.e. pulsing flows which periodically inundate and then strand spawning areas) or over abstraction (i.e. denying access to spawning areas) may impact on this species. Very little is known of the biology of this species and greater research effort is needed.
Aquatic insects (63.0%)
Figure 2. The mean diet of the khaki bream Hephaestus tulliensis. Summary derived from data from 56 individuals (16 adults and 40 juveniles) from the Mulgrave River [1097].
consumed much smaller prey than was predicted on the basis of their size. They suggested that the hypertrophied lips acted as a gasket when the snout was pressed into the interstices of coarse substrates and allowed the fish to
394
Scortum parviceps (Macleay 1884) Small-headed grunter
37 321027
Family: Terapontidae
Nonetheless, mouth gape is significantly linearly related to body size, with the relationship taking the form: gape (mm) = 4.61 + 0.057 (SL in mm); r2 = 0.811, n = 132, p<0.001 [1082]. Snout elongate and becoming more obviously so with increasing size. Vomerine teeth present in small specimens but absent in adults, as are palatine teeth. Lachrymal serrate in small specimens, less so in larger specimens. Preoperculum serrate, particularly on angle. Cleithrum exposed, serrate posteriorly. Supracleithrum and post-temporal exposed, with the latter being serrate along posterior edge. The gut is highly elongated and multicoiled, with six loops between stomach and anus. Small specimens have a relatively shorter gut with the number of loops increasing from two to six as the fish matures; the exact age or size at which the gut changes in form is unknown.
Description Dorsal fin: XIII, 10–11; Anal: III, 9; Pectoral: 15–16; Vertical scale rows: 51–61; Lateral line scales: 49–51, 3–4 scales on caudal, 3–4 rows of small scales on sheath of anal fin base which extends across all rays, two rows of small scales on dorsal sheath which extends to seventh or eighth ray; Horizontal scales rows: 28–32, 8–10 above lateral line. Figure: adult specimen, 156 mm SL, upper Burdekin River, April 1995; drawn 1999. Scortum parviceps is a moderate to large-sized grunter routinely growing to 300 mm SL and about 1 kg. Maximum size recorded 360 mm SL [1082]. The relationship between length (SL in mm) and weight (in g) takes the form W = 1.4 x 10–5 L3.19; r2 = 0.968, n = 560, p<0.001 [1093]. Body moderately deep and laterally compressed. Profile straight to slightly convex on dorsal surface, ventral surface straight to isthmus and thereafter slightly convex to insertion of pelvic fins. Jaws equal, gape horizontal, lower jaw slightly flattened, dentary rotated outwards and teeth, which are flattened and slightly depressible, pointing outward also [1346]. Vari [1346] suggests that the maxillary reaches posteriorly to the anterior margin of the eye in small specimens but falls short with age, reaching only to the posterior nostril in larger specimens.
Colour in life varies from golden-green to olive-green. Irregular blotching is common, and very pronounced in stressed specimens shortly after capture. Fins tend to be a dusky green-grey, often very dark in small individuals. An iridescent green-gold band runs from the snout underneath the eye. Similarly coloured blotches also present on operculum. Colour in preservative: khaki green to tan, blotches retained but iridescent blotches fade to a light green [1093].
395
Freshwater Fishes of North-Eastern Australia
drainage and within this drainage is further restricted also. Midgley [940] recorded a Scortum species from four of eight locations within the catchment. Three locations (Cape River, 2 in the Burdekin River proper) were located upstream of the Burdekin Falls whilst the fourth was located downstream. Sites in which Scortum were absent included the Belyando River and Fletcher Creek, both upstream tributaries, and the Broken River, a downstream tributary. Interestingly, Midgley identified both S. hillii (as hilli) and S. parviceps (with the former being the most widely distributed) as present in the Burdekin River drainage. Wager [1349] also lists S. hillii as being present in the Burdekin based on personal communications and data independently provided by H. Midgley and R. Leggett. Comprehensive sampling by a variety of methods over a three-year period collected 361 specimens of S. parviceps, all but 25 of which were collected from the main channel of the upper Burdekin River [1098]. None were located downstream of the Burdekin Falls in that study but subsequent sampling by us has yielded a single individual from the Bowen River near Collinsville. Hogan et al. [586] did not record this species as present in a study of the Clare Weir fishway although they did note that three specimens were tagged by the local angling association. Subsequent sampling by Hogan et al. [591] did record this species present in a small number of locations in the Bowen River. From these data, it appears that although S. parviceps is present downstream of the Burdekin Falls, it is not common in this section of the river.
Systematics Scortum parviceps was originally described as Therapon parviceps by Macleay in 1884 [847]. Genus Scortum erected by Whitley in 1943 with S. parviceps as the type species [1388]. The genus is distinguished from most other terapontid genera by having slightly flattened depressible teeth and a moderately rotated dentary, characters it shares to varying extent with Pingalla and Syncomistes. These latter genera are distinguished by a more pronounced rotation of the dentary and fully depressible flattened teeth. In addition, the gut in both genera is further elongated and coiled (11 loops compared to six seen in Hephaestus and Scortum) [1346]. Scortum contains five species: S. barcoo McCulloch and Waite, 1917, which is restricted to central Australian drainages, (although this species was recently collected in the lower Mary River in south-eastern Queensland (M. Hutchison, pers. comm.), undoubtedly as a result of translocation); S. parviceps, endemic to the Burdekin River; S. nieli Allen, Larson and Midgley (1993), endemic to the East Baines and Angalarri rivers, tributaries of the Victoria River, Northern Territory; S. ogilbyi, confined to drainages of the Gulf of Carpentaria region; and S. hillii (Castelnau, 1878), previously thought to be endemic to the Fitzroy River but recorded from the Burdekin River also [940]. This latter species is frequently said to occur in drainages of the Gulf region (e.g. [1042]) but such records are based upon Vari’s [1346] synonomy of S. ogilbyi Whitley 1951 with S. hillii. Vari did not believe the differences in lateral line counts, body depth and relative lengths of the second and third anal spines to be sufficiently great to warrant recognition of two species. Two taxa: S. cf. hillii and S. cf. barcoo were collected from westerly flowing rivers of Cape York Peninsula (Coleman, Holroyd and Edward) [571]. These authors commented that meristic differences (i.e. lateral line counts) between the specimens collected and the nominal forms warranted further examination and raise the possibility that one of these forms is S. ogilbyi. Allen et al. [52] include S. ogilbyi as a valid species in a recent treatment of the Australian fish fauna. Confirmation of the presence of S. hillii in the Burdekin River is needed and the systematics of the genus warrants formal re-examination.
As mentioned above, few specimens were collected from upstream tributary streams by Pusey et al. [1098]. Wager [1349] recorded it being collected from Fletcher Creek (not detected there by Pusey et al. [1098]). Williams et al. [1408] found this species to be absent from a number of left-bank tributaries of the upper Burdekin River (e.g. Star, Little Star, Keelbottom, Fanning and Reid drainages). This species has been recorded from two (of five) sites on the Belyando River by Burrows et al. [256] but was not abundant, being the sixth or eighth most abundant species (out of eight and 10 spp., respectively) and contributing only 6.5 and 2.3%, respectively, of the total number of fish collected. This species has been recorded by us from the impounded reaches of the Suttor River [1093]. Scortum parviceps was uncommon in the surveys of Pusey et al. [1098] contributing only 0.5, 0.2 and 4.7% of electrofishing, seine-netting and gill-netting catches, respectively. Overall, these data indicate that S. parviceps, although patchily distributed throughout much of the Burdekin catchment, is most abundant in the main channel of the Burdekin River and its larger south-western tributaries, upstream of the Burdekin Falls. Abundance never attains high levels however.
Vari [1346] believed the genus name Scortum (Latin for leather or hide) referred to the leathery texture of the flesh. Scortum parviceps is indeed culinarily unrewarding but the name more likely refers to the thickness and strength of the skin. For example, its congener S. hillii from the Fitzroy River (and more rarely the Burdekin River also) is known by the vernacular names green-hide jack or leathery grunter. Distribution and abundance Scortum parviceps is endemic to the Burdekin River
396
Scortum parviceps
Table 1. Physicochemical data for Scortum parviceps. Data derived from average site data from 24 separate site/sampling occasion combination over the period 1989–1992 [1093].
Macro/meso/microhabitat use The information discussed above suggests that this species is most commonly found in riverine reaches and rarely in tributaries. Scortum parviceps was recorded in reaches with a mean width of 33 to 84 m, (depending on the time of year) by Pusey et al. [1098]. The substrate was a mix of sand, fine gravel and occasional outcrops of bedrock. Such sites also varied in depth, within and between sampling locations. For example, the area sampled at Valley of Lagoons, in which S. parviceps is moderately abundant, was characterised by shallow (<0.5 m) riffles, deeper (~ 1 m) runs and very deep pools; S. parviceps was collected from all such mesohabitats. Merrick and Schmida [936] suggest that this species may prefer clear fast-flowing water based on the fact that most specimens considered by them had been collected from rapids or immediately downstream of a race. Such habitats are neither common in the Burdekin River, nor available year-round (due to the episodic nature of the river’s flow regime [1089]). They may be important spawning habitats however. Moreover, comparison of the catch data for different sampling methods in Pusey et al. [1098] reveals that S. parviceps was relatively uncommon in electrofishing samples which were concentrated in shallow areas where flow was elevated (i.e. riffles and runs). Greater numbers were collected by seinenetting in moderately deep (<1 m) areas with a sand, fine gravel substrate and little or no flow. Gill-netting in areas greater than 2 m deep and with abundant woody debris also yielded relatively large numbers of fish. It must be emphasised however that no juvenile fish less than 40 mm SL were collected in this study and it is likely that such small fish show a preference for faster flowing areas with abundant woody debris, undercut banks and root masses for cover (as observed for juveniles of the other terapontids in this system). The specimens collected by Midgley and by Burrows et al. came from large and turbid, isolated pools sampled during the dry season. Microhabitat data is lacking but it is probable that S. parviceps forages predominantly in the lower one-third of the water column in most circumstances. Exceptions may occur in deep anoxic pools. Very large individuals of this species have been observed foraging in thick macrophyte beds (especially Vallisneria sp.) in areas of moderate flow. Given the herbivorous nature of its diet (see below), it is surprising that S. parviceps is not more abundant in tributary streams of the upper Burdekin River as macrophytes are generally more abundant here than in the main channel.
Parameter
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS/cm) Turbidity (NTU)
23.0 4.0 6.66 55 0.3
32.9 10.0 8.47 610 20.8
Mean 26.3 6.9 7.76 375 5.3
The data provided in Table 1 were derived from average water quality readings for sites in the upper Burdekin in which S. parviceps was present. As such, they represent the average water quality conditions in which this species is found, not tolerances per se. The data indicate that small headed grunter occur in warm waters as would be expected for a species limited to a subtropical river. The maximum value (32.9°C) was recorded in November 1990 when air temperatures were above 40°C and flow very reduced. It is probable that temperatures up to at least 35°C could be tolerated. The minimum temperature was recorded in May 1991. Subsequent visits to the region have measured water temperatures as low as 17°C at 8 am after night-time air temperatures dropped to below 5°C. It is unlikely that temperatures less than 15°C are experienced for long periods. Midgley [940] recorded pronounced temperature stratification in pools within the Valley of Lagoons in the headwaters of the Burdekin River with temperatures of between 17–15°C being recorded at depths of 5 m or more. Scortum parviceps is moderately common in such pools. It should be noted that total anoxia was recorded at 10 m depth by Midgley, and hypoxia (0.4 mg/L) was recorded at a depth of 4 m, and it may therefore be that small-headed grunters at this locality avoid waters of low temperature and dissolved oxygen. The minimum dissolved oxygen concentration measured by us was 4.0 mg/L. Scortum parviceps were recorded in waters ranging from slightly acidic (6.66) to moderately basic (8.47) with the mean being slightly basic and reflecting the underlying geology of the region (olivaceous basalt). This species has been recorded from freshwaters only, within a considerable range of conductivities (55–610 µS/cm). Given its limited distribution and phylogeny, it is probable that S. parviceps does not tolerate elevated salinities well and an upper tolerance limit of 1500–2000 µS/cm seems plausible. Scortum parviceps has been collected from very clear to relatively turbid waters. Burrows et al. [256] recorded it present in the Belyando River at much higher turbidity levels (368 and 581 NTU) than that recorded in the upper Burdekin and displayed in Table 1. Tributaries
Environmental tolerances Quantitative data on tolerance to degraded water quality is completely lacking and inferences about such tolerance must be drawn from data collected during surveys.
397
Freshwater Fishes of North-Eastern Australia
Table 2. Life history information for Scortum parviceps. Summaries derived from Merrick and Schmida [936] and Pusey [1082]. Age at sexual maturity (months)
Unknown but probably after 1 year, possibly longer
Minimum length of ripe females (mm)
Gender discernible at 70–80 mm SL in a few individuals, generally at 100 mm SL [1082]. Fully mature at 170 mm SL [936]
Minimum length of ripe males (mm)
Gender discernible at 60–70 mm SL [1082]. Fully mature at 230 mm SL. Fish of indeterminate sex present up to 150 mm SL [1082]
Longevity (years)
? possibly 6–7 years.
Sex ratio (female to male)
Sample collected by Pusey et al. [1082] skewed towards males (1:1.94)
Occurrence of ripe fish
?
Peak spawning activity
? October–November [936], December–March [1082]
Critical temperature for spawning
? >24°C [936]
Inducement to spawning
? Small increases in water levels [936]
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
Up to 115 000 [936]
Fecundity /length relationship
?
Egg size
4.2–4.3 mm diameter [936]
Frequency of spawning
?
Oviposition and spawning site
? possibly rapids and riffles
Spawning migration
? probably upstream
Parental care
? not present in any other therapontid
Time to hatching
36 hours [936]
Length at hatching (mm)
?
Length at free swimming stage
?
Length at metamorphosis (days)
?
Duration of larval development
?
Age at loss of yolk sack
?
Age at first feeding
?
listed by Merrick and Schmida [936]. These authors suggest that spawning occurs in October or November and is stimulated by rising water levels, even minor level changes. It is unknown whether the sampling regime upon which this inference is based included sampling occasions other than October or November. However, Pusey [1082] found very few individuals were fully mature (stage VI) at this time (only one individual in November 1989) and furthermore, also found a ripe female (stage VI) present in May 1992. Many stage V fish of both sexes were present in the November samples however. Temporal changes in population size structure [1082] suggest that spawning occurrs sometime over the summer wet season and that recruitment is greatest (although still not pronounced) in years when the summer flood occurred. It was also noted that the population was dominated by larger, older individuals (no juveniles less than 40 mm SL were collected), in contrast to that observed for L. unicolor, A. percoides and H. fuliginosus. Although Merrick and Schmida [936] state that a female can produce up to 115 000 eggs, the failure by Pusey et al. [1082] to observe a well defined young-ofthe-year cohort over the period of their study (three years)
in the south-western portion of the catchment are typified by such elevated turbidity values and the presence of S. parviceps in the Belyando [256] and Cape [940] Rivers suggests it is tolerant of such high sediment loads. Symptoms consistent with tropical epizootic ulcerative syndrome (‘red spot disease’) have been observed on one specimen collected in November. An ectoparasitic isopod (‘fish doctors’), are not uncommonly observed in the buccal cavity of large specimens [1093]. Beumer et al. [185] do not record such parasites for any other freshwater fish species, although they are common in a range of marine species. Reproduction Information on the reproduction of this species is very limited and that listed in Table 2 is based upon a series of personal communications between J.R. Merrick and S. H. Midgley and M. MacKinnon [936] and more recent sampling undertaken by the authors [1082]. Scortum parviceps matures at a greater size than do other grunters found in the Burdekin River [1082], but it is likely that the minimum size at maturation is somewhat less than that
398
Scortum parviceps
Aquatic invertebrates contributed a meagre 6.3%, while macrocrustacea contributed a further 3.9% to the average diet. A small proportion of the diet was comprised of fish and the presence of surface invertebrates (gerrids) and terrestrial vegetation (Melaleuca blossoms) indicates that this species makes occasional foraging sorties to the water’s surface.
suggests that it is not as fecund as the other grunters with which it occurs. The large size of the pelagic egg given by Merrick and Schmida [936] also raises some doubts about the fecundity of this species also and it is probable that the number of eggs produced per female is considerably less than 100 000. Further research on the reproduction of this species is warranted as the limited available evidence suggests that this species has a life history strategy quite dissimilar from other terapontids for which data exists. Moreover, the low abundances of this species coupled with late maturation and possibly a reduced fecundity compared with other sympatric grunters may suggest high potential for populations to be easily and severely impacted in a short time with little prospect for rapid recovery.
The extent of ontogenetic variation in diet is not as pronounced in S. parviceps as it is in other therapontids, although it must be stressed that no fish less than 40 mm SL have been examined. Filamentous algae comprised 69% of the diet in fish between 40–80 mm SL (n = 15), 42% of the diet in fish between 80 and 160 mm SL (n = 40), and 73% of the diet in fish greater than 160 mm SL (n = 77). Aqautic macrophytes contributed 0%, 20% and 18% in these size classes, respectively. Detritus was absent in the diet of the largest size class, contributed 2% in the intermediate size class and 10% in the smallest size class. Thus, plant matter comprised 79%, 64% and 91% of the diet in the smallest to largest size classes, respectively. The reduction in importance of plant matter in the diet of fish in the second age class occurred because many of the fish within this size class were collected in May 1991 when discharge and secondary production were elevated. Simulid larvae contributed 45.8% of the diet in this age class on this occasion, but were completely absent from the diet on all other occasions. It is probable that fish less than 40 mm SL have a diet similar to that of similarly sized spangled perch, barred grunter and sooty grunter (e.g. chironomid larvae, simulid larvae and ephemeropteran nymphs).
Movement Nothing is known of the extent or phenology of movement in this species. It is possible that upstream migrations prior to spawning occur as has been documented for S. hillii [936]. Limited information suggests that the eggs are pelagic [936] which also suggests a compensatory upstream migration prior to spawning. The general absence of S. parviceps from tributary streams or downstream of the Burdekin Falls does not suggest that juveniles disperse widely. Trophic ecology The presence of a long, coiled gut, depressible flattened teeth and a rotated dentary were suggested by Vari [1346] to be adaptations for herbivory and although Scortum parviceps is omnivorous, the bulk of the diet is indeed made up of plant material (algae – 64% and aquatic macrophytes – 16%) (Fig. 1). Fish (0.9%) Microcrustaceans (0.1%) Macrocrustaceans (3.9%) Molluscs (0.7%) Other macroinvertebrates (0.1%)
Conservation status, threats and management Scortum parviceps is listed as Restricted by Wager [1349] and as Data Deficient by the ASFB [117]. Scortum hillii is listed as a Poorly Known Species by Wager [1349] and as Data Deficient by the ASFB [117]. Potential and existing threats to both species include flow regulation and the introduction of translocated native species. It is clear that the restricted distribution of S. parviceps and S. hillii rightfully accords both species elevated conservation significance, as neither species is common or widely distributed, and populations are highly fragmented (especially in the case of S. hillii).
Unidentified (1.6%) Terrestrial invertebrates (0.7%) Aerial aq. Invertebrates (1.0%) Terrestrial vegetation (3.0%) Detritus (1.8%)
Aquatic insects (6.3%)
Aquatic macrophytes (16.4%)
The limited information available about the reproductive biology of S. parviceps suggests that although it may be long lived, it is not particularly fecund nor does it mature at an early age. These factors, when coupled with an apparently limited ability to disperse, ensure that any impacted populations may take considerable time to recover, if at all. Flow events that may be of significance to this species include high wet-season flows that greatly increase secondary production and food availability for juveniles.
Algae (63.6%)
Figure 1. The diet of small-headed grunter Scortum parviceps. Based on stomach content analysis of 134 individuals collected on five occasions over the period November 1989 to May 1992 [1082].
399
Freshwater Fishes of North-Eastern Australia
production. It would be instructive to know the diet of small-headed grunter from rivers such as the Cape and Belyando but it is probable that they rely heavily on diatoms and filamentous algae growing in the narrow photic zone along the stream edge. Such areas are highly susceptible to impact by rapidly fluctuating water levels.
However, artificially elevated flows which disturb the accumulation of detritus and/or the attachment of filamentous algae and macrophytes have great potential to impact on this species given its reliance on these food sources. It is probable that this species undertakes some form of spawning migration especially given the suggestion that the eggs are pelagic. Barriers to movement posed by weirs etc. are therefore likely to impact on this species. If the suggestion that even small rises in water levels stimulate spawning in this species is true, then impoundments that trap all but the largest floods are likely to depress recruitment significantly by removing important trigger stimuli. Despite the presence of S. parviceps in habitats of very high turbidity, it is probable that water resource developments that increase and maintain high levels of turbidity may impact on populations via a negative effect on in-stream primary
Recent massive increases in the distribution and abundance of the sleepy cod Oxyeleotris lineolatus subsequent to its translocation into the upper Burdekin River (where it does not naturally occur) may pose a threat to S. parviceps in the long-term given the piscivorous habit of sleepy cod. Other piscivorous fishes, such as barramundi and yellowbelly, have been translocated into the upper Burdekin River. The potential for either species to impact on S. parviceps is unknown, nor has it ever been assessed.
400
Kuhlia rupestris (Lacépède, 1802) Jungle perch, Rock flagtail
37 323004
Family: Kuhliidae
This species may be confused with an occasionally syntopic species, K. marginata, but is easily distinguished by differences in the shape of caudal fin (deeply emarginate almost forked, with pointed lobes in K. marginata), mouth size (maxilla not reaching vertical through middle of eye in K. marginata), fewer branched rays in anal fin (11–12 in K. marginata) and coloration. Red coloration on anal and caudal fins distinctive in K. marginata and lateral spotting may coalesce to form horizontal lines in anterior half of body in K. marginata [37, 1123].
Description Dorsal fin: X, 10–11; Anal: III, 10–11; Pectoral: 13–14; Lateral line scales: 39–41; Horizontal scale rows: 13–16; Predorsal scales: 14–16; Gill rakers: 7–9 + 17–19 [37, 1123]. Figure: adult specimen, 254 mm SL, un-named lowland tributary of the North Johnstone River, November 1998; drawn 2002. Kuhlia rupestris is a moderately large species, reaching 450 mm in total length and 2.7–3.0 kg in weight [936, 1123] although fish less than 250 mm SL are most common [800]. Body relatively deep, 33–38% of SL; mouth large, maxillae reaching to below posterior half of eye. Caudal fin emarginate, lobes somewhat rounded. Brown/olive dorsally grading through silver laterally and white ventrally. Scale margins darkened on dorsal surface, those on sides with black spot. In juvenile fish, each lobe of the caudal fin is distinguished by a large white-margined black spot that expands and fuses in larger fish such that almost all of the fin except the margins is black. A large black spot is also present in the front half of the second dorsal fin. Anal fin generally clear except for one or two rows of black spots located near fin base [37, 936, 1123]. Dark spots present on cheeks and operculum. Colour in preservative: generally similar to that described above for live specimens except brown/olive colour greatly faded.
The relationship between length (SL in mm) and weight (g) for a small sample (n = 14), dominated by fish less than 150 mm SL, collected from the Mulgrave and Johnstone rivers, was determined by us to be W = 0.372 x 10–5 L3.388: r2 0.987, p<0.001. A different relationship was reported by Lewis and Hogan [800] for a larger sample (n = 332) collected from Saltwater Creek, near Mossman, northern Queensland: W = 3.627 x 10–5 SL2.9628. Although these authors suggest that female fish are significantly heavier than males (and provide separate regression equations for each sex) [800], the regression equation for male fish predicts weights in excess of that predicted for females. The differences are minor however; 2 g for fish of 100 mm SL, 4 g for fish of 200 mm SL and 13 g for fish of 400 mm SL. Female fish do grow to larger size than do male fish however [800]. 401
Freshwater Fishes of North-Eastern Australia
salelea Schultz. Of these latter two species, the former is known only from the Society Islands and the latter from American and Western Samoa. The tail of the fish identified as K. marginata in Herbert and Peeters is forked rather than emarginate; the condition in K. rupestris [1123]. Herbert and Peeters note that this species is distinguished from K. rupestris by the presence of a distinct red margin on the anal fin. A red margin on the anal fin, and the upper and lower lobes of the caudal fin, are clearly evident in the figure of K. marginata presented in Allen [37] (Plate I, 18). Randall and Randall [1123] make no mention of this distinctive colouration, presumably because all specimens examined were preserved material. Thus, there seems little doubt that K. marginata occurs in northern Queensland.
Systematics The Kuhliidae is composed of a single genus (Kuhlia) containing 14 species of moderately deep-bodied and compressed fish characterised by the possession of two opercula spines, a deeply notched dorsal fin of 10 spines and 9–13 rays, a scaly sheath at the base of the dorsal and anal fins, and a relatively large eye. Both marine and freshwater species occur within the family and many species may move between both habitats on occasions. The family occurs in tropical and subtropical waters of the IndoPacific region but is most speciose in the central Pacific region (i.e. the islands of Oceania) [1123]. In Australia, the Kuhliidae has traditionally been used to contain a number of small freshwater fishes collectively known as pygmy perches of the genera Edelia Castelnau, Nannoperca Günther and Nannatherina Regan [745, 1042]. These latter genera are now placed within the Percichthyidae [656]. In general, the Kuhliidae do not exceed 250 mm SL [1123].
Synonyms of K. rupestris include Centropomus rupestris Lacépède, Perca ciliata Cuvier (ex Kuhl & van Hasselt), Dules fuscus Cuvier, Dules guamensis Valenciennes, Dules vanicolensis Valenciennes, Dules haswellii Macleay, Kuhlia rupestris hedleyi Ogilby, Kuhlia caerulescens Regan and Kuhlia sauvagii Regan [406, 1123]. This latter species, K. sauvagii, was not considered a synonym of K. rupestris by Randall and Randall [1123].
Four species of Kuhlia are known from Australian waters: K. rupestris (Lacépède), K. munda (De Vis), K. mugil (Forster) (= K. taeniurus (Cuvier) in Paxton et al. [1042]) [1123] and K. marginata (Cuvier). Kuhlia mugil ranges from the Red Sea and the east coast of Africa to Baja, California and Columbia and extends from southern Japan south to Lord Howe Island. It apparently never enters freshwater [1123]. Kuhlia munda is less widespread, being recorded from northern Queensland (the type specimens were collected from near Cardwell at the southern limit of their Australian distribution [1042]), New Caledonia and Fiji. This species may be found in fresh or brackish waters [1123]. Literature accounts suggest that K. marginata occurs in freshwaters of northern Queensland [569, 571, 1087], yet Australia was not considered to be within its range in a recent and comprehensive review of the flagtails of the central Pacific region [1123]. The name Kuhlia marginata has erroneously been applied to at least five other kuhliid species, including K. munda, and Randall and Randall [1123] believed that because of these misidentifications some literature records of this species may be suspect. Nonetheless, K. marginata has a very wide distribution ranging from Taiwan, through the Philippines, Indonesia, the Solomon Islands, New Caledonia, a number of small central Pacific islands and including New Guinea [37, 1123]. It is not unreasonable to consider that its distribution also extends into northern Queensland. Herbert and Peeters [569] include a photograph (Plate 25) and description of a fish they believed to be K. marginata. The only discernible meristic character is the number of lateral line scales, which number about 40. The only other kuhliids with a lateral line scale count less than 42 are K. rupestris, K. malo (Valenciennes) and K.
Distribution and abundance Kuhlia rupestris has an enormous distribution ranging from the east coast of Africa, east to American Samoa, and from Japan south to eastern Australia [37, 1123]. An unsuccessful attempt was made to introduce this species into Hawaii [1357]. Kuhlia rupestris occurs only in easterly flowing drainages of north-eastern Australia. It is widely distributed across eastern Cape York Peninsula having been recorded from the following drainages: Harmer Creek, Olive River, Claudie River, Lockhart River, Stewart River, Starke River, Howick River, McIvor River, Endeavour River, Annan River, Massey Creek and Rocky River [571, 599]. Although listed as present in the Normanby River [1099], this listing is in error; the specimens were from the Pascoe and Stewart rivers. This species has not yet been recorded from the Normanby River but probably occurs in this system. Kuhlia rupestris has been recorded from every major easterly flowing drainage system in the Wet Tropics region from the Bloomfield River to the Herbert River [583, 584, 800, 1085, 1087, 1096, 1177, 1179, 1183, 1184, 1185, 1187]. It is both common and moderately abundant in the region. For example, K. rupestris was the 11th most abundant species and occurred in 34 of 93 sites surveyed during a survey of the freshwater fish biodiversity of the region [1085, 1087]. Other surveys have also shown it to be widely distributed. For example, Russell et al. recorded this species from 23/45 sites, 16/19 sites and 6/10 sites in the
402
Kuhlia rupestris
A recent review of the southern distribution of K. rupestris using literature accounts, museum records and angler records has been conducted by Hutchison et al. [621] and the following account of this portion of the distribution of K. rupestris is drawn largely from this work. Although historically present in the Pioneer River [1081], recent sightings of this species are rare. Hutchison et al. [621] report that anecdotal accounts list it as widely distributed in the river as far upstream as Silver and McGregor creeks prior to the construction of the Marion Weir. Thereafter it was present up to the weir until the construction of the Dumbleton Rocks Weir. Kuhlia rupestris have been recorded in the fish lock located on this weir only very recently [621].
Daintree River, Saltwater Creek and Mossman River, respectively [1185], and 25/45 sites in the Russell/ Mulgrave drainage [1184]. This species may be very abundant in certain habitats. For example, K. rupestris contributed over 20% of the total number of fishes collected from short rainforest streams of the Cape Tribulation area [1087]. Table 1. Distribution, abundance and biomass data for Kuhlia rupestris in two rivers of the Wet Tropics region. Data summaries for a total of 97 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. Total % locations % abundance
Mulgrave River
Barriers to passage imposed by weirs and barrages were frequently implicated in the demise of K. rupestris in the southern limits of its distribution [621]. For example, occasional specimens are still recorded in the Fitzroy River but only downstream of the barrage. Similarly, K. rupestris was once found in the Burnett River system as far upstream as the junction with Barambah Creek but is now only occasionally found downstream of, or in the fishway located on, the Ben Anderson Barrage [621]. This species has also been recorded below the barrages on the Burrum River and the Mary River. Although once common in the Maroochy River, it is only infrequently collected in this river now. Contemporary records also exist for this species in the Noosa River. Several records for this species in small streams draining into Pumicestone Passage were also reported by Hutchison et al. [621] and Fraser Island streams still provide suitable habitat for K. rupestris [77]. This species is still very occasionally collected from below the Crosby Weir on the Brisbane River and in the Albert River and Tallebudgera Creek [621]. Remarkably, the distribution of K. rupestris even extends into New South Wales, it being recently recorded from the Richmond River [621].
Johnstone River
26.0
34.1
19.6
0.3 (2.5)
0.7 (3.2)
0.7 (1.8)
Rank abundance
25 (11)
16 (10)
16 (15)
% biomass
1.0 (5.8)
2.2 (7.2)
2.2 (4.4)
6 (5)
6 (6)
Rank biomass
9 (5)
Mean density (fish.10m–2)
0.10 ± 0.02
Mean biomass (g.10m–2)
6.68 ± 1.53 10.34 ± 2.53 2.84 ± 1.31
0.16 ± 0.03 0.04 ± 0.01
Despite occasionally being abundant in some streams, the data in Table 1 indicate that this species tends to restricted in distribution in the Mulgrave and Johnstone rivers, to occur at low densities and to be among the least common of species at those sites in which it occurs. It does contribute significantly to the total biomass at these sites however. This species commonly co-occurs with (in decreasing order of abundance) P. signifer, M. s. splendida, H. compressa, A. reinhardtii and H. tulliensis [1093].
Macro/mesohabitat use The habitat of K. rupestris is generally considered to be fast-flowing rainforest streams and rivers [52] although this species has been recorded from floodplain lagoons also [255, 583]. Notwithstanding this latter observation, K. rupestris is best considered a riverine species.
Kuhlia rupestris occurs in several drainages located between the Herbert and Burdekin Rivers, including Leichhardts and St. Margaret Creek [1053] and the Black-Alice River [176]. This species has recently been collected from a floodplain lagoon of the Haughton/Burdekin Delta [255] but was formerly much more abundant in the region [1082]. Several anecdotal records of the presence of this species in the Burdekin River exist [1082] and at one time it penetrated as far upstream as the Broken River in the headwaters of the Bowen River [940]. It no longer occurs in this location and its absence is most certainly due to the existence of downstream barriers such as the Clare and Collinsville weirs.
The data presented in Table 2 is summarised from habitat information for 87 individuals collected from 28 sites within the Mulgrave/Russell, Johnstone and Tully rivers of the Wet Tropics region. It should be borne in mind that these sites were located in wadable streams and consequently, the range of streams sampled was dominated by small streams rather than large lowland rivers. Moreover, given the relatively low density values recorded for this
The distribution of Kuhlia rupestris is said to extend south of the Burdekin River to the Maroochy River [936, 1042].
403
Freshwater Fishes of North-Eastern Australia
Johnstone rivers, small fish (<150 mm SL, a size class under represented in the study by Lewis and Hogan because of sampling constraints) tended to be most common in small streams at low elevation located close to the river mouth (Figure 1) although it should be noted that fish as small as 40 mm SL occur in a variety of streams up to 50 km from the river mouth and at elevations of 50 m.a.s.l. Thus the size/sex related segregation in distribution and habitat use noted by Lewis and Hogan [800] appears to also extend to the smallest size classes also.
species, most sites examined contain only one or two fish. Consequently, there is little difference between mean and weighted mean values. Furthermore, the sample upon which this summary is based was dominated by fish less than 100 mm SL. Given these caveats, the habitat in which we have recorded K. rupestris is very broad and ranges from small (1.9 m wide), first-order streams located relatively high in the catchment distant from the river mouth, through to large streams or rivers (order five) of low gradient, and including small low-gradient streams located close to the river mouth. Thus, K. rupestris inhabits nearly all of the available riverine environment.
It should be noted that the upper limits for elevation and distance from the river mouth listed in Table 1 reflect the distribution of study sites in the Mulgrave and Johnstone rivers examined by us, and do not reflect the true limits for this species. For example, we have observed very large populations of K. rupestris in the Daintree River at elevations of >200 m.a.s.l. [1093] and reports of this species in
Lewis and Hogan [800] showed that the lower reaches of two rivers (Saltwater Creek, a short river north of Cairns, and the Navua, Fiji’s third largest river) were dominated by male fish and the upper reaches by female fish. Because of the greater size attained by female fish, upper reaches contained fish of greater size. In the Mulgrave and
8
Table 2. Macro/mesohabitat use by jungle perch Kuhlia rupestris. Summary information derived from mean habitat characteristics of 28 sites in the Mulgrave/Russell, Johnstone and Tully rivers. W.M. referes to the mean weighted by fish abundance to reflect any potential preference for particular conditions. Parameter
Min.
0.27 Catchment area (km2) Distance from source (km) 1 Distance to river mouth (km) 8.1 Elevation (m.a.s.l.) 10 Order 1 Stream width (m) 1.9 Riparian cover (%) 0 Site gradient (%) 0.01 Mean average depth (m) 0.12 Mean water velocity (m.sec–1) 0.02
Max.
Mean
W.M.
334.8 67 69.5 60 5 23.5 90
50.2 11.4 26.6 26.6 3.4 8.0 42.3
39.8 9.3 31.0 26.0 3.4 7.2 48.3
4.071 0.68 0.38
0.83 0.37 0.18
Elevation 6
4
2
0 8
Distance to River Mouth
0.71 0.38 0.18
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
26 60 41 60 39 76 98
4.5 12.7 16.4 15.2 15.4 27.0 8.4
5.4 12.8 16.8 13.0 14.4 28.4 8.7
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% of bank) Root masses (% of bank)
0 0 0 0 0 0 0 0 0 0
7.9 0.5 10.0 75.0 10.0 35.8 12.5 13.5 45.0 65.0
0.6 0 1.1 9.7 0.4 6.4 2.5 1.9 6.1 18.1
0.7 0 0.9 10.4 0.2 5.4 1.8 1.3 8.2 16.8
(43, 44)
6
(28, 59)
4
2
0
Standard Length (mm) Figure 1. The size distribution of Kuhlia rupestris populations in streams of differing elevation and distance from the river mouth. Fish occurring at low elevation (<30 m.a.s.l.), or occurring within 20 km from the river mouth are distinguished by closed bars and the sample size is listed first.
404
Kuhlia rupestris
than 150 mm SL and that it reflects microhabitat use over the range of macro/mesohabitat conditions surveyed by us. For example, the maximum average depth of sites from which these data were recorded was 0.68 m (Table 2) and consequently it is unlikely that our sample will contain many fish caught in waters deeper than this value. In fact, a substantial proportion (>50%) of the fish upon which Figure 2 is based were collected from depths greater than the average site depth shown in Table 2. Thus it would appear that, over the range of sites examined by us¸ K. rupestris was preferentially using the deeper parts of those sites. Accordingly, if our sample had included sites with depths in excess of 1 m (which methodologically precludes backpack electrofishing), it is probable that we would have observed fish in this depth range. Finally, it must be stressed that K. rupestris is a highly mobile species and over the course of a single day probably ranges across a wide
the Broken River in the Burdekin drainage indicate it is capable of penetrating hundreds of kilometres upstream. Its distribution upstream is probably only limited by the availability of suitable habitat and the presence of natural barriers. Data in Table 2 indicate that K rupestris, although occasionally occurring in low gradient, still or slowly flowing reaches with a muddy substrate, occurs most frequently in streams of higher gradient with moderate flow velocities. The range of habitats in which K. rupestris occurs ensures that the mean substrate composition shown in Table 2 is very diverse. However, sites in which it is most common tend to be dominated by larger sized particles. Streams in which K. rupestris occur tend not to be notable for large accumulations of cover such as macrophyte beds, leaf litter or woody debris. Note that although K. rupestris occasionally occurs in streams with little or no riparian cover and dominated by invasive grasses such as para grass (classified as submerged vegetation in Table 2), it is much more likely to be found in stream reaches with an intact riparian canopy and with little submerged bank-side vegetation.
(a)
(b)
30 20 20 10
10
It is worth repeating that the sample upon which this summary of macro- and mesohabitat use is based is restricted to small streams, and further, that it is based largely on the habitat use of fish between 40 and 150 mm SL. Greater research effort is needed to properly elucidate the habitat requirements of fish outside of this size range especially given concerns expressed about a decline in abundance and distribution (see below).
0
0
Focal point velocity (m/sec)
Mean water velocity (m/sec)
(c)
25
30
20
20
15
(d)
10 10
Kuhlia rupestris apparently breeds in the lower estuarine or the near-shore marine environment (see below). Consequently, larval and metamorphosed juvenile fish must have yet another habitat distinct from that of juveniles and adult fishes. Moreover, the previously described segregation of fish of different size or sex must break down at some time of the year and the habitat of spawning fish must be extended to include the estuarine or near shore environment also. Thus, the macrohabitat of Kuhlia rupestris when considered across all age classes is comprised of the entire river, not just a subsection of it. Cappo et al. [279] referred to such a pattern of habitat use as involving a ‘critical chain of habitats’. Loss of, or damage to, any one link in this chain would seriously compromise the continued survival of K. rupestris in a river. Microhabitat use Capture records for 29 individuals were used to compile the microhabitat assessment depicted in Figure 2. Care must be taken in interpreting these data given that the sample size is small, the sample is dominated by fish less
30
5 0
0
Relative depth
Total depth (cm) 30
(f)
(e) 30
20
20
10
10
0
0
Substrate composition
Microhabitat structure
Figure 2. Microhabitat use by the jungle perch Kuhlia rupestris. Based on capture data for 29 individuals collected over the period 1994–1997 in the Mulgrave/Russell, Johnstone and Tully rivers.
405
Freshwater Fishes of North-Eastern Australia
gives some indication that water temperatures below 20°C are tolerated. This value was recorded for a small, wellforested stream in the Mulgrave River during August 1995. It can be bitterly cold (for tropically adapted ecologists!) in the Mulgrave River valley at this time of year and such low temperatures may persist for several days. It would be instructive to know whether K. rupestris leave small cold tributary streams for the relative warmth of the main river at this time of year. The Kuhliidae are a subtropical/tropical family and in all likelihood intolerant of low water temperatures, indeed the distribution and abundance of K. rupestris in southern Queensland and northern New South Wales is probably controlled by low water temperatures. However, some geographic acclimation (perhaps genetic adaptedness) to low water temperature probably occurs.
range of microhabitat conditions. Kuhlia rupestris occurs across a substantial range of water velocities but tends be infrequently collected from areas with little or no flow (Fig. 2a). Unlike other fishes such as gobies or bullrout which may occur in fast-flowing waters but which are typically located in and amongst the substate particles, the focal point velocities experienced by K. rupestris tend not be greatly different from the average water velocity (Fig. 2b) because they most typically occur in the upper half of the water column (Fig. 2d). As mentioned previously, K. rupestris appear to select the deeper areas of the sites in which they occur and avoid areas less than 30 cm deep (Fig. 2c). No preference for particular substrate types is evident with the distribution of different particle sizes seen in Figure 2e approximating the average substrate composition given in Table 2. Although many of the K. rupestris upon which Figure 2 is based were collected from open water, this species does make use of such cover elements as woody debris and bank-associated structures (Fig. 2 ).
Kuhlia rupestris has only been recorded by us from relatively well-oxygenated waters (Table 3), in keeping with its preference for flowing water habitats. Hogan and Graham [583] recorded this species from a lagoon of the Tully/Murray River floodplain in which dissolved oxygen concentration was only 3.8 mg.L–1. Such a low level must be approaching the lower limit for this species.
Environmental tolerances Information on the physicochemical tolerances of K. rupestris is lacking but greatly needed. The data presented in Table 3 represent summaries of water quality conditions at sites in which K. rupestris have been collected. As such they give limited indication of upper and lower tolerance levels. Rather they are an indication of the conditions in which K. rupestris are likely to occur.
In general, streams of northern Queensland in which K. rupestris have been collected are of neutral pH. It is clear however, that it can tolerate for some time, the period of which is unknown, lower pH (i.e. pH = 4.5). Water acidity in this range is not atypical of lowland, low gradient streams draining rainforests or swamps, and such streams are used by both adult and juvenile K. rupestris. Indeed, records of this species from streams draining the sand dune systems of the Cape Flattery region, of Fraser Island streams, and of streams draining the wallum country north of Brisbane (see above) all suggest a relatively well developed tolerance of acidic waters.
Kuhlia rupestris was recorded predominantly from warmwater streams although the minimum value listed (18.5°C) Table 3. Physicochemical data for the jungle perch Kuhlia rupestris. Data derived from unpublished data sets for three sites in two rivers in Cape York Peninsula [1099] and 38 site/sampling occasion combinations in four rivers of the Wet Tropics region [1093]. Parameter
Min.
Max.
The information presented above for water clarity suggest that this species occurs in clear-water streams. The peak value presented in Table 2 (29.7 NTU) was recorded in a small lowland stream receiving runoff from a sugar cane plantation, immediately after a very heavy rain event. Elevated turbidity was transitory with values of 2 NTU being recorded the following day. Although K. rupestris probably experience elevated turbidity during the wet season spawning migration (see below), it is unlikely that they would tolerate highly elevated levels for a significant length of time. Kuhlia rupestris is a visual predator and the ability to locate prey (in addition to direct sediment/turbidity effects on their prey) would likely compromise food intake.
Mean
Cape York Peninsula (n = 3) Water temperature (°C) 26.0 29.5 Dissolved oxygen (mg.L–1) 6.8 8.3 pH 6.09 7.58 Conductivity (µS.cm–1) 94 102 Turbidity (NTU) 0.3 2.2
27.5 7.5 7.06 98.7 1.1
Wet Tropics region (n = 38) Water temperature (°C) 18.2 32.7 Dissolved oxygen (mg.L–1) 5.13 8.81 pH 4.50 8.43 Conductivity (µS.cm–1) 6.1 67.6 Turbidity (NTU) 0.2 29.7
23.4 7.09 7.12 32.9 3.6
Conductivity values listed in Table 3 all indicate that K. rupestris occurs in waters of low conductivity and
406
Kuhlia rupestris
relationship between the stimulus to move upstream and sexual maturity. Lewis and Hogan [800] tentatively suggest that males mature at smaller size than do females. If upstream movement continues until sexual maturity occurs and if there are no differences between the growth rates of male and female fish, then females will be distributed further upstream than males.
sometimes in waters of extremely low conductivity (e.g. 6.1 µS.cm–1 recorded in a small stream high in the catchment of the Mulgrave River). However, Hogan and Nicholson [589] showed that sperm motility in K. rupestris was optimal at salinities approaching 20 ppt and completely absent in freshwaters; spawning was postulated to take place in brackish estuarine/near-shore habitats. Lewis and Hogan [800] list several examples of adult K. rupestris occurring in estuarine habitats also. These data suggest a very well-developed ability to osmoregulate over a large range of water salinities although this remains to be empirically demonstrated like so many other aspects of this species’ biology.
At a smaller scale, we have observed that K. rupestris rarely remains stationary and are most commonly observed in small loose schools patrolling up and down along stream banks. Trophic ecology A quantitative summary of the diet ecology of K. rupestris is shown in Figure 3 and based on a total of 50 individuals drawn from three studies undertaken in: the Stewart and Pascoe rivers, Cape York Peninsula (n = 5) [1099]; the Mulgrave and Johnstone rivers, Wet Tropics region (n = 10) [1097]; Liverpool Creek, Wet Tropics region (n = 4), Hen Camp Creek, north of Townsville (n = 10) and 16 individuals from the Annan River [598].
Reproduction Little is known of the reproductive biology of this species. Lewis and Hogan [800] report that the minimum size of ‘running ripe’ males in their study was 17 cm SL and that of a ‘nearly ripe’ female was 24.5 cm SL. Spawning is believed to take place in estuarine or near-shore marine habitats although spawning aggregations have never been observed. Hogan and Nicholson [589] showed that K. rupestris sperm was immotile in freshwater and most active in salinities approaching that seen in estuaries or the near-shore marine environment during the wet season. Spawning probably occurs during the wet season as males in spawning condition have been observed from November to April and apparently spent females from January to May.
The dominant food item in the diet of K. rupestris is terrestrial invertebrates including large animals such ants, spiders, cockroaches and grasshoppers. The adult aerial forms of aquatic invertebrates such as mayflies and caddisflies are also important prey. Collectively, animal prey taken from the water’s surface comprise over half of the diet. Terrestrial vegetation, including leaves, flowers and fruits, comprise a further 9.3% of the diet. Whitley [1399] also noted that riparian fruits such as figs were important in the diet of K. rupestris. It is probable that the consumption of large amounts of terrestrial material is a feature of the diet of adults or larger size classes as it is in many other northern Australian fishes that use this source of food.
Hutchison et al. [621] report that K. rupestris may be a serial spawner based on the observation of three distinct egg size classes. If so, then it is likely that female fish would remain in the spawning grounds for some time before returning upstream. The largest eggs released during a hormone induced spawning event were 0.75 mm in diameter. Obviously much needs to be learnt about the reproductive biology of jungle perch.
Aquatic invertebrates, principally ephemeropteran nymps and trichopteran larvae, are also important in the diet of K. rupestris, particularly in the smaller size classes. Large shrimps and prawns figure prominently in the diet also. Fish are a minor component but may be more important in some locations than in others. For example, fish comprised 10% of the diet of fish from Cape York Peninsula [1099] but were absent from the diet of fish from the Wet Tropics region [610, 1097]. It is likely that K. rupestris would occasionally consume frogs and small terrestrial vertebrates that might through circumstances find themselves in the aquatic environment. This species has been reported to consume the larvae of the cane toad Bufo marinus [336]. The long-term effect of consumption of toad larvae is unknown.
Movement Quantitative information on the movement biology of K. rupestris is lacking but studies on the efficacy of fishways within its range should, in the future, provide much useful information. It is clear that the life history of K. rupestris is characterised by extensive movement. Adult fish must move downstream to spawn in estuarine or near-shore marine environments [800]. It is unknown whether fish migrate back upstream after spawning. Juvenile fish must migrate from the spawning grounds into freshwater habitats and it probable that upstream movement continues as they grow. The factors that govern the extent to which the different sexes migrate upstream is unknown but may involve a
407
Freshwater Fishes of North-Eastern Australia
Fish (2.3%) Other microinvertebrates (0.2%)
needed to determine the conditions under which K. rupestris will successfully negotiate fishways. Despite having a very large geographical range, movement between individual river basins seems limited, for once a population has been impacted by a barrier, it apparently does not recover, or does so very slowly once steps are taken to ensure that passage past such barriers occurs [621]. For this reason, Hutchison et al. [621] recommend that stocking programs are necessary to restore this species in many rivers. Careful examination of any geographical variation in genetic structure is required if widespread restocking does occur to ensure that this remedial process does not in itself become a threatening process.
Unidentified (0.6%)
Macrocrustaceans (18.3%)
Terrestrial invertebrates (44.9%)
Aquatic insects (17.5%)
Algae (0.4%) Detritus (0.1%) Terrestrial vegetation (9.3%)
Aerial aq. Invertebrates (6.4%)
Figure 3. The mean diet of the jungle perch Kuhlia rupestris. Data for 50 individuals from three studies undertaken in northern Queensland.
Other potential threats facing K. rupestris include the continued destruction of riparian forests, either through deliberate clearing, by weed invasion and inappropriate fire regime management, or by flow regime manipulation. Kuhlia rupestris consumes large amounts of terrestrial invertebrates derived from the riparian zone and also eats the fruits of such trees. Continued reclamation of lowland streams and wetlands, channelisation of small streams and desnagging in larger water courses to speed water removal during the wet season, and changes to lowland floodplain hydrology all pose a threat to K. rupestris. These threats are most intense in the Wet Tropics region where the lowland reaches of the rivers of this region are poorly protected despite the fact that the upper reaches may be vested in National Park or World Heritage Area and consequently afforded a high degree of protection. The life cycle of K. rupestris involves substantial segregation between the sexes and age classes. Failure to protect any one of the links in this ‘critical chain of habitats’ will result in population declines.
Conservation status, threats and management Over its entire range, K. rupestris is not considered of special conservation significance (i.e. not listed by the IUCN) [17] nor are Australian populations considered of special significance (i.e. classified as Non–Threatened) [1353]. Whilst northern populations (Cape York Peninsula and the Wet Tropics region) are currently secure, populations from the Burdekin River south are less so secure and have undergone dramatic reductions in size and distribution. Other species (e.g. M. adspersa) for which only some populations are at risk, have an elevated conservation status despite the fact that other populations are not threatened [117, 1353]. This distinction needs to be made for K. rupestris also. The greatest threat to K. rupestris; the imposition of barriers to movement imposed by water resource infrastructure, is clearly evident from the changes in its distribution and abundance discussed above. Fishway studies have great potential to provide information on unresolved aspects of the biology of this species and greater effort should be made towards this end. In addition, studies are
The impact of recreational fishing on this species is unknown although the imposition of strict bag limits (one per day) and a size limit of 35 cm to protect female fish, suggest that it may be considerable, particularly in populations facing threat from other processes.
408
Glossamia aprion (Richardson, 1842)
37 327103
Mouth almighty Family: Apogonidae
Description First dorsal fin: VI; Second dorsal: I, 9–11; Anal: II, 8–9 (rarely 10); Pectoral: 11 or 12 plus 2 unbranched rays; Caudal: 15 segmented rays; Lateral line scales: 25–43 (varies between populations – see below), lateral line complete; Gill rakers on first arch: 6–8, plus 8–10 very low rudiments [52, 936]. Figure: 72 mm SL, Cooper Creek, Cape Tribulation, September 1993; drawn 2002.
(g) is W = 0.0109. L3.167; r2 = 0.994, n = 1020, p<0.001 for the Alligator Rivers region. For the Wet Tropics region, the relationship between length (SL in mm) and weight (g) is W = 9.02 x 10–6.L3.292; r2=0.989, n=12, p<0.001 [1093]. Body deep and compressed; head similarly compressed, large, exceeding 33% of SL, snout pointed. Mouth large, extending back below middle of eye, lower jaw slightly protruding. Preopercle, preorbital and suborbital bones entire, or a few poorly developed serrae on edge of preopercle at angle. Eye large, particularly in small individuals. First and second dorsal fins tall, origins positioned roughly level with origin of pelvic and anal fins, respectively; caudal fin rounded or may be slightly emarginate in southern populations. Scales large, mostly ctenoid [52, 1093]. External sexual dimorphism in apogonids is slight or nonexistent, except females may be larger [1321].
Glossamia aprion is usually a small to moderate-sized fish reaching a maximum size of about 180 mm SL [34] but usually less than 80 mm SL. Translocated populations in lakes and impoundments may exceed 250 mm SL [1093] and are a surprisingly fine table fish. Mean length for a sample of 45 fish from the Johnstone and Mulgrave rivers was 62 mm (range = 25–130 mm SL) [1093]. Approximately 60% of 210 individuals from floodplain habitats of the Normanby River were less than 50 mm SL (range = 10–170 mm SL) [1093]. Of 642 specimens collected in streams of south-east Queensland [699, 704, 709, 1093], the mean and maximum length of this species were 49 and 128 mm SL, respectively. Bishop et al. [193] report a mean length of 52 mm CFL (n = 1020; range = 11–175, mode = 30–35 mm). The equation best describing the relationship between length (CFL in cm) and weight
Colour in life highly variable according to habitat, breeding condition and level of stress. Base colour is generally greenish-yellow to tan, overlaid with a dark brown to reddish-brown mottling, frequently forming a series of three to four thick irregular bars on the dorsal and midlateral surfaces, interspersed with similarly coloured spots. The ventral surface tends to be pale. Two dark brown ocelli
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Freshwater Fishes of North-Eastern Australia
This species was subsequently described as Apogonichthys gillii by Steindachner in 1866 [1262] from material collected in the Fitzroy River of Queensland. Numerous other synonyms exist [1042]: Mionorus lunatus Krefft, 1868; Gulliveria fusca Castelnau, 1878; Gulliveria fasciata Castelnau, 1878; Apogonichthys roseobrunneus Macleay, 1881; Gulliveria ramsayi Macleay, 1884; Apogonichthys longicauda De Vis, 1884; Mionorus ramsayi Fowler, 1908; and Kurandapogon blanchardi Whitley, 1939. Reference to this species as Glossamia gillii and Apogonichthys aprion may also be found in the literature [879, 881, 1304, 1398].
are present at the base of the caudal fin. The head tends to be darker than the body with a thick dark stripe extending from the maxilla through the eye to the junction of the operculum. This stripe may extend to the lower jaw also. A distinct dark spot is present below the eye. The cheeks tend to be pale and faintly spotted whereas the operculum is darkly pigmented, sometimes giving the impression of horizontal stripes. The first dorsal fin is darkly pigmented anteriorly of the third spine and thereafter darkly pigmented on the marginal one third only. The second dorsal and anal fins are dusky at the base grading to pale/clear near margins. The caudal fin is generally clear but dusky near base. The pelvic fin is usually darkly pigmented with a vivid white leading edge and occasionally with white margins [34, 936, 1093]. This colour pattern affords a high degree of crypsis.
Munro [976] was the first to recognise the existence of two subspecies, G. aprion aprion and G. aprion gillii within the nominal species. The subspecies differ most with respect to the number of lateral line scales (37–43 in G. aprion aprion and 25–31 in G. aprion gillii) and distribution: G. aprion aprion occurs across northern Australia south to about the Pioneer River whereas G. aprion gillii is restricted to the Fitzroy River south to the Clarence River [34]. Recognition of the validity of these subspecies continues in some recent publications on Australian freshwater fishes [34, 52] although not in the Zoological Catalogue of Australia [1042]. Temperature regime during embryonic development can markedly influence adult morphology in freshwater fishes [1286] and the geographical differences in the number of lateral line scales purportedly indicative of subspecific differentiation may be due to the effects of low average water temperatures in rivers of south-eastern Queensland.
Stressed fish (i.e. shortly after capture) may initially be very dark but quickly fade to an overall pale colour after several minutes [1093]. Sexual dichromatism associated with spawning has been reported for G. aprion [193]. Males assume a light golden colour except on the ventral surface, which become an iridescent light purple; the first dorsal and pectoral fins are black, the operculum is edged in black and the eye bar becomes very prominent. Females assume the light golden colour also but with dark spots on the body, and the fins become a dusky white. We have observed these same colour differences in fish from the Wet Tropics region in August or September and in south-eastern Queensland at around the same time of year [1093].
Distribution and abundance Glossamia aprion is widely distributed across northern Australia and southern New Guinea [37, 52]. The Australian range extends from the Kimberley region [620], across northern and eastern Australia and south to coastal northern New South Wales [1340]. In the Northern Territory, this species has been recorded from the Daly, Roper and Victoria rivers [944, 946], the Alligator Rivers region [193, 1064, 1416], the Arnhem Land region and some offshore islands (e.g. Groote Eylandt and Goulburn Islands) [1304]. Its distribution is probably continuous across this region. Glossamia aprion was characterised as common in Magela Creek [1064] but rare in isolated sandy pools [1416]. Bishop et al. [193] found this species to be abundant (in the top quartile of species ranked by abundance) and widespread (present in 22 of 26 regularly sampled locations) in the Alligator Rivers region. Midgley [945] found this species to be widely distributed in the Daly River occurring in 12 of 16 sites, ranging in abundance from rare to common.
Systematics Apogonidae is a large family of small, mainly inshore marine and occasionally estuarine fishes inhabiting all tropical and temperate seas [1042]. The family is composed of two subfamilies, the Apogoninae and Pseudaminae. The number of genera and species within the family varies between 21 and 26, and 207 and 280, respectively, depending on the authority consulted [34, 52, 989, 1042]. Approximately 16 to 18 genera and 91 to 94 species are known from Australian waters (marine and freshwater) [989, 1042], of which only three genera and 13 species occur in temperate waters. Only a single extant genus, Glossamia Gill of northern Australia and New Guinea, occurs in freshwater [34]. Glossamia contains seven species, but only G. aprion, which also occurs in New Guinea, occurs in Australia [52]. Glossamia aprion was first described as Apogon aprion by Richardson in 1842 [1138], from material collected in the King River near Port Essington (now Darwin) in the Northern Territory. It was subsequently placed within the genus Glossamia as the type species by Gill in 1863 [450].
This species has been recorded from most major rivers of the south-western portion of the Gulf of Carpentaria
410
Glossamia aprion
River Falls [1098]. Although moderately distributed in this part of the river [1046], its abundance varies with habitat structure, comprising only 0.2% of the total electrofishing catch in riverine sites [1098] but 5.6% of the catch (variety of methods) in more lentic habitats [1046]. Glossamia aprion occurs in the Pioneer River [1081].
region, except for the Flinders River, where it is probably also present. Most rivers of the western portion of Cape York Peninsula are reported to contain G. aprion [41, 356, 571, 643, 991, 1349], as are those of the eastern portion [571, 697, 991, 1099, 1349]. Within this region, this species has been recorded from swamps [571], floodplain lagoons [697] and dune lakes of the Shelburne Bay, Olive River and Cape Flattery regions [571, 781, 1101].
Glossamia aprion is widely distributed in the Fitzroy River drainage, having been recorded from the Fitzroy, Isaac, McKenzie, Dawson, Don and Connor rivers [160, 659, 942]. Although widely distributed and sometimes common, it rarely reaches high levels of abundance in this drainage [160]. This species also occurs in the streams of the Shoalwater Bay area [1328, 1349], Baffle Creek and the Kolan River.
Glossamia aprion is widely distributed, but not overly abundant, in the Wet Tropics region. It has been recorded from the Annan River [599, 1223, 1349] but it appears to be absent from the Bloomfield River and short coastal streams of the Cape Tribulation area. South of here, it is present in most drainages south to the Herbert River [643]. This species occurred in 25 of 93 sites throughout the region [1085] but comprised only 1.2% of the total collected. It comprised approximately 5% of the total in a study undertaken in the Annan River [599]. The distribution of G. aprion within individual rivers varies greatly between individual rivers in the region. For example, Russell et al. found this species at 21 of 45 sites in the Mulgrave/Russell River [1184], 16 of 44 sites, seven of 18 sites and one of nine sites in the Daintree River, Saltwater Creek and the Mossman River, respectively [1185], and only one of 29 sites in Liverpool Creek [1185] and only five of 67 sites in the Johnstone River (all sites in which it occurred were located on the Atherton Tablelands) [1177].
Glossamia aprion is moderately common and widely distributed in south-eastern Queensland. It has been recorded from the Burnett River [11, 205, 237, 565, 658, 1173, 1276], Elliot River [825], Gregory River [157], Isis River [1305], Burrum River [736] and the Mary River [158, 159, 162, 643, 658, 660, 1093, 1234]. South of here, it is very patchily distributed, having only been recorded from the Noosa, [643], Brisbane [1349] and Logan rivers [1349]. It is suspected to have been translocated into this latter basin [1338]. The natural distribution of G. aprion is believed by some [52, 814, 1065, 1349] to extend south into New South Wales to the Clarence [52] or Hunter rivers [1340] but it was not collected in recent comprehensive surveys of rivers in northern New South Wales [282, 554]. The type locality for Mionorus lunatus, Krefft and Mionorus ramsayi, Fowler is the Cox River (New South Wales) and Victoria, respectively. Both are in error. This species has not been recorded from the sand islands off the south-eastern Queensland coast [988].
We have recorded G. aprion in only four of 56 sites in the Johnstone River and six of 38 sites in the Mulgrave/Russell River sampled over the period 1994–1997 [1093]. This species was only the 26th and 23rd most abundant species in this study with average densities of 0.14 ± 0.05 (SE) and 0.138 ± 0.06 fish.10m–2 for the Johnstone and Mulgrave rivers, respectively [1093]. This species was the 8th most abundant species in those sites in which it occurred where it contributed 5.5% to the total number of fish collected. A mean biomass of 1.88 ± 0.73 g.10m–2 was recorded, being 2.7% of the total biomass at those sites in which it occurred and the 10th most important species. These estimates of abundance accord well with an earlier study of these rivers in which G. aprion was the 14th most abundant species in the Mulgrave River but was not recorded in the Johnstone River [1096]. Glossamia aprion has not been recorded from some of the smaller drainages of the Wet Tropics region although it has been reported in smaller streams north of Townsville [1053]. Glossamia aprion frequently occurs with (in decreasing order of abundance) M. s. splendida, P. signifer, C. s. stercusmuscarum, A. reinhardtii and H. compressa.
In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that G. aprion had been collected at only 7 of 63 locations surveyed (18th most widespread species in the catchment) and formed only 0.27% of the total number of fishes collected (17th most abundant). Glossamia aprion is generally uncommon and patchily distributed in south-eastern Queensland. Surveys undertaken by us between 1993 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected 888 individuals of G. aprion and it was present only in the Mary and Brisbane rivers (10% of all locations sampled) (Table 1). This species was most widespread in the Mary River, where it was present at 34% of locations sampled. Overall, it was the 18th most abundant species collected (0.54% of the total number of fishes collected), but was the 14th most abundant species collected in the Mary River (0.96%). Overall, it was relatively uncommon at sites in which it occurred (3.9% of
In the Burdekin River system, G. aprion is restricted to the lower portion of the basin downstream of the Burdekin
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Freshwater Fishes of North-Eastern Australia
Table 1. Distribution, abundance and biomass data for Glossamia aprion in rivers in south-eastern Queensland. Data summaries for a total of 888 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
10.1
34.0
–
–
11.7
–
–
0.54 (3.86)
0.96 (4.04)
–
–
0.34 (2.76)
–
–
18 (9)
14 (9)
–
–
19 (11)
–
–
0.35 (5.14)
0.56 (5.46)
–
–
0.06 (0.78)
–
–
11 (3)
8 (3)
–
–
22 (11)
–
–
Mean numerical density (fish.10m–2)
0.57 ± 0.13
0.64 ± 0.15
–
–
0.20 ± 0.07
–
–
Mean biomass density (g.10m–2)
3.86 ± 1.20
4.30 ± 1.33
–
–
0.18 ± 0.08
–
–
total abundance, ninth most common species). In these sites, G. aprion most commonly occurred with the following species (listed in decreasing order of relative abundance with rank abundance in parentheses): Pseudomugil signifer, Craterocephalus marjoriae, Gambusia holbrooki, C. s. fulvus, and Ambassis agassizii. The distribution of G. aprion in south-eastern Queensland rivers and the cooccurrence with species listed above, may reflect the presence of extensive aquatic macrophyte beds, which are very common in the Mary and Brisbane rivers (see also sections on habitat use below). Across all rivers, G. aprion was the 11th most important species in terms of biomass, forming 0.35% of the total biomass of fish collected, but a relatively high biomass of this species was recorded in the Mary River (eighth most important species). Average and maximum numerical densities recorded in 93 hydraulic habitat unit samples (i.e. riffles, runs or pools) were 0.57 fish.10m–2 and 8.33 fish.10m–2, respectively. Average and maximum biomass densities at 74 of these sites were 3.86 g.10m–2 and 63.10 g.10m–2, respectively.
Table 2. Macro/mesohabitat use by Glossamia aprion in the Wet Tropics region. Data summaries for the Wet Tropics region are based on site data for 48 individuals from 12 sites collected over the period 1994–1997. Parameter 2
Catchment area (km ) Distance from source (km) Distance to mouth (km) Elevation (m.a.s.l.) Order Stream width (m) Riparian cover (%)
Macro/mesohabitat use Glossamia aprion in the Alligator Rivers region is reported to occur in a variety of habitats although juveniles and adults showed a loose segregation [193]. Juveniles (<65 mm CFL) occurred mostly in floodplain lagoons and to a lesser extent, lowland muddy lagoons. Adults also occur in these habitats but were dispersed more widely in the landscape and occurred in sandy creeks, escarpment perennial streams and main channel waterbodies also. This species is also common in main river channel habitats of the Northern Territory and northern Queensland [945, 946, 1085, 1098]. This species is a common inhabitant of the floodplain lagoons of Cape York Peninsula [571, 697] and of the Wet Tropics region [583, 584] and has been recorded from dystrophic dune lakes in Cape York Peninsula also [571, 1101].
Min.
Max.
Mean
W.M.
1.0 1.5 10.3 10 2 3.6 0
85 21.0 104.0 722 5 33.0 100
47.6 13.0 45.4 210 4.0 11.7 48.2
49.9 15.5 65.6 402.7 4.2 12.2 32.3
Site gradient (%) Mean average depth (m) Mean velocity (m.sec–1)
0.02 0.22 0
0.78 0.69 0.41
0.25 0.45 0.20
0.33 0.48 0.24
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 4 0 0 0 0
24 55 41 28 33 76 68
3.7 21.8 22.2 10.4 10.5 21.0 10.2
2.5 13.7 17.3 8.5 13.6 22.7 21.8
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
6.7 0 33 60 4 27.4 11 12.1 30 50
1.2 0 4.0 16.1 0.5 6.2 2.8 3.1 10.7 20.7
2.4 0 3.5 20.6 1.4 4.4 1.7 1.6 7.8 10.8
In the Wet Tropics region of northern Queensland G. aprion may be found in a variety of streams ranging from small second order, high gradient streams with dense 412
Glossamia aprion
Bishop et al. [193] report that G. aprion was most commonly collected over muddy or sand substratum in areas with dense macrophyte growth
riparian cover through to larger, low gradient open fifth order streams, and may occur in riffles, runs or pools (Table 2). The apparently high mean elevation estimated for sites in which this species occurs is occurs because G. aprion is common in the section of the Johnstone River flowing through the Atherton Tablelands as well as in lowland coastal streams and rivers of the region. Its presence in streams on the Tablelands is almost certainly due to unauthorised translocation.
In rivers and streams of south-eastern Queensland G. aprion occurs at low to moderate elevations (0–175 m.a.s.l.) but most commonly at less than 50 m.a.s.l. (Table 3). This species occurs throughout the major length of streams and rivers, ranging between 87 and 271 km from the river mouth. It is present in a wide range of stream sizes (range = 2.3–47.0 m width) but is more common in larger rivers (20 m weighted mean width) and with low riparian cover (<20%). In rivers of south-eastern
Glossamia aprion may be found in reaches of a variety of substrate types ranging from sand to bedrock. The high mean proportional contribution by rocks and bedrock (especially when weighted by abundance) reflects the nature of substratum in many streams of the Atherton Tablelands section of the Johnstone River. Sites in which this species occurs are characterised by abundant instream cover, in particular submerged vegetation such as the alien weed, para grass. Glossamia aprion is one of the few native species favoured by proliferation of this weed.
80
Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
130.0 10 211.7 20.0 270.0 86.5 271.0 0 175 2.3 47.0 0 79.1
Gradient (%) 0 Mean depth (m) 0.09 Mean water velocity (m.sec–1) 0
2.33 1.08 0.84
Mean
42.4 100.0 50.5 74.2 65.8 16.3 76.0
7.9 30.6 21.4 25.2 12.7 1.1 1.0
10.8 60.6 12.5 11.8 3.8 0.3 0.3
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
64.5 65.9 21.7 65.7 39.1 64.3 21.7 15.5 50.0 46.7
21.8 10.1 1.0 10.9 2.3 7.9 4.7 3.0 8.2 11.8
27.6 7.5 0.3 16.7 3.5 5.5 3.8 2.0 2.8 4.5
20
0
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 20
10
10
0
0
Relative depth
Total depth (cm) 40
0.04 0.56 0.04
0 0 0 0 0 0 0
40
20
20
W.M.
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
60
40
30
3892.0 3523.7 132.6 117.9 171.3 195.1 44 47 17.6 20.7 23.0 17.7 0.19 0.47 0.13
(b) 80
60
Table 3. Macro/mesohabitat use by Glossamia aprion in rivers of south-eastern Queensland. Data summaries for 888 individuals collected from samples of 93 mesohabitat units at 30 locations undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
(a)
(e)
(f) 30
30 20 20 10
10 0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Glossamia aprion in the Wet Tropics region (solid bars) and in south-eastern Queensland (open bars). Summaries derived from capture records for 21 fish collected from the Mulgrave and Johnstone rivers in the Wet Tropics region and for 168 fish collected from the Mary River, south-eastern Queensland over the period 1994–1997 [1093].
413
Freshwater Fishes of North-Eastern Australia
Most specimens were collected from total depths less than 1 m but were from the upper two-thirds of the water column (perhaps in response to low dissolved oxygen levels at depth). Most specimens were collected in close association with cover, including root masses, leaf litter and especially aquatic macrophytes. Hattori and Warbuton [561] also report that G. aprion is always found in areas that are structurally complex, especially among dense weed-beds.
Queensland, G. aprion most commonly occurs in deep, slow-flowing pools and less commonly in moderately flowing runs (Table 3). This species is most abundant in mesohabitats with fine substrates (sand and gravel) and was most frequently collected where submerged aquatic macrophytes and submerged marginal vegetation were common. Elsewhere, this species has been classified as a benthic pool-dwelling species [553]. It has also been reported to occur in tidal reaches of rivers [936].
Environmental tolerances Ambient water quality information is available for several different populations and habitat types across the range of G. aprion (Table 4). These include: the Alligator Rivers region (n = 22 sites) [193] of the Northern Territory; Midgley’s surveys of the Daly, Roper and Victoria rivers (n = 27 sites), the Pascoe and Normanby rivers (n = 8 sites) [1099] and floodplain lagoons of the Normanby River (n = 15 site/sampling occasions) [697] of Cape York Peninsula; the Mulgrave and Johnstone rivers of the Wet Tropics region; and 63 samples in the Mary and Brisbane rivers, south-eastern Queensland.
Microhabitat use Glossamia aprion occurs in areas of zero to low flow in streams of the Wet Tropics region (Fig 1a). This species was very rarely collected more than 20 cm from some form of cover (Fig. 1f) and accordingly, the focal point velocities experienced are overwhelmingly dominated by zero flow (Fig. 1b). Over the range of sites examined, G. aprion occurred most frequently in areas less than 60 cm in depth and was most frequently collected in the lower two-thirds of the water column. The range of substrate types over which G. aprion was collected reflects the range present in the sites in which this species occurred, except that it was more common over mud and sand, reflecting its preference for areas of little flow and the types of particle sizes likely to occur in slack waters. Submerged vegetation, leaf litter and small woody debris were the most frequently used forms of cover used by G. aprion. It is from such structures that this species is able to launch ambush attacks on its prey.
Glossamia aprion may be found over a wide range of temperatures (14.1 to 38°C) but is most frequently encountered in waters between 21 and 30°C. Low winter water temperatures may limit the southern distribution of this species notwithstanding the fact that there is probably local acclimation to low temperatures in certain parts of the range (i.e. south-east Queensland and high elevation areas of the Wet Tropics region). Bishop et al. [193] report that larvae from the Alligator Rivers region die after a fiveday exposure to temperatures below 22–24°C.
In the Mary River, south-eastern Queensland, G. aprion was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b), closely matching that of fish from the Wet Tropics region. However, we did record this species at a maximum mean and focal point water velocity of 0.78 m.sec–1. This species was collected over a wide range of depths, but most often between 20 and 70 cm (Fig. 1c) and usually occupied the lower half of the water column (Fig. 3d). It was usually collected over fine substrates (mud, sand and gravel) (Fig. 3e). It was often collected in areas greater than 1 m from the stream-bank (67% of individuals sampled) but usually within 0.2 m from the nearest available cover (95% of individuals). It was frequently collected in close association with aquatic macrophytes, filamentous algae, submerged marginal vegetation and large woody debris (Fig. 3f). The greater use of macrophytes in the Mary River relative to that observed in the Wet Tropics region reflects the greater availability of this form of cover in the former.
Glossamia aprion appears able to tolerate a wide range of dissolved oxygen concentrations and to be moderately tolerant of hypoxia (to at least about 1 mg DO.L–1). The most hypoxic habitats in which this species occurs are floodplain lagoons and wetlands (Table 4). Hogan and Graham [583] report a minimum DO level of 1.3 mg.L–1 for wetlands of the Tully River floodplain. Glossamia aprion has been recorded among the dead in fish kills in floodplain habitats for which hypoxia was implicated as the primary cause [187]. Over the range of studies included in Table 1, this species has been recorded over a wide range of pH (4.9–9.1), but with a tendency to occur on average, in neutral to slightly acid waters, except in south-eastern Queensland waters where it is more common in slightly basic waters. The pH range within individual studies was often small with the exception of the Alligator Rivers sample [193] where G. aprion were collected from habitats spanning a range of 3.2 pH units.
Microhabitat use by G. aprion in floodplain lagoons of the Normanby River is similar to that reported above [697].
Glossamia aprion is clearly a freshwater species and is able
414
Glossamia aprion
Reproduction Glossamia aprion is a buccal incubator; males exhibit parental care. Buccal incubation is a feature of the apogonid subfamily Apogoninae but not the Pseudaminae [1321]. Many of the life history traits of this species are in general accord with that expected for species exhibiting parental care (Table 5): the eggs are relatively large but not numerous and the young hatch at a relatively advanced stage. However, this species matures at a relatively small size.
to tolerate very dilute waters. The upper tolerance level for this species is unknown but given its recent marine ancestry it is probably well developed. In estuarine areas of northern Queensland, this species is replaced by a range of other apogonids, particularly Apogon hyalosoma. Table 4. Physicochemical data for Glossamia aprion from several different localities across northern and eastern Australia. See text for explanation. Parameter
Min.
Max.
Alligator Rivers Region (n = 22) [193] Temperature (°C) 25 38 Dissolved oxygen (mg.L–1) 1.3 9.7 pH 4.9 8.1 Conductivity (µS.cm–1) 2 620 Turbidity (cm) 1 200
Mean
Spawning occurs in the late dry and early wet seasons in the Alligator Rivers region [193]. Differences in size structure in different habitats led Bishop et al. [193] to suggest that adults migrated into muddy lowland and floodplain lagoons to spawn and incubate but also noted that dispersal by young-of-the-year from such areas occurred shortly after incubation had ceased. These authors also suggested that still water conditions were necessary for the transfer of the egg mass to the male. Kennard [697] noted that although a few very small free-swimming juveniles (<10 mm SL) were present in floodplain lagoons of the Normanby River in June, many such small fish (10–30 mm SL) were present by November (late dry season). These observations suggest a dry season spawning. In addition, we have observed buccal incubating male fish in the Normanby River and fish in presumed nuptial colours in lowland streams of the Wet Tropics region in August [1093]. The production of young prior to the wet season
30.6 6.2 6.3 41
Daly, Roper and Victoria rivers (n = 27) [944, 945, 946] Temperature (°C) 21.5 37 26.9 Dissolved oxygen (mg.L–1) 3.4 9.2 6.9 pH 6.4 8.5 7.9 Conductivity (µS.cm–1) Turbidity (cm) 50 500 260 Cape York Peninsula (n = 6) [1094] Temperature (°C) 23 26 Dissolved oxygen (mg.L–1) 7.2 11.2 pH 6.2 8.4 Conductivity (µS.cm–1) 92 420 Turbidity (NTU) 0.1 5.4
24.3 8.4 7.0 180.6 1.7
Normanby River floodplain lagoons (n = 15) [697] Temperature (°C) 22.9 29.4 25.4 Dissolved oxygen (mg.L–1) 1.1 7.1 3.6 pH 6.0 8.2 7.12 Conductivity (µS.cm–1) 81 391 197.1 Turbidity (NTU) 2.1 8.6 5.3 Wet Tropics region (n = 12) [1093] Temperature (°C) 17.1 27.1 Dissolved oxygen (mg.L–1) 6.4 11.6 pH 5.8 7.3 Conductivity (µS.cm–1) 19 66 Turbidity (NTU) 0.4 3.1 South-eastern Queensland (n = 63) [1093] Temperature (°C) 14.1 31.0 Dissolved oxygen (mg.L–1) 4.2 11.9 pH 6.8 9.1 Conductivity (µS.cm–1) 203.7 1429.0 Turbidity (NTU) 0.5 62.3
40
Spring (n=97) Summer (n=299)
30 Autumn-Winter (n=246)
21.4 7.84 6.7 30.7 1.3
20
10 22.5 8.3 7.9 555.3 5.2
Glossaamia aprion has been recorded over a wide range of water clarity. This species is a visual feeder and low visibility is likely to impact on this species in the long term. Moderate levels of suspended solids may confer some foraging advantage to this species however by reducing the ability of prey species to detect its presence and avoid it.
0
Standard length (mm) Figure 2. Seasonal variation in length-frequency distributions of Glossamia aprion, from sites in the Mary and Brisbane rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
415
Freshwater Fishes of North-Eastern Australia
gone unstudied. Thresher [1321] provides descriptions of spawning behaviour in several species of marine apogonids. The egg mass is extruded and then quickly inhaled en masse by the male (in contrast to the singular ingestion described in Breder and Rosen [225]) and the females of some species guard the male during incubation. In none of the accounts was there a significant interval between egg mass extrusion and inhalation/ingestion and little direct evidence of how fertilisation is achieved. However, spawning behaviour in three species of Apogon (inerbis, maculatus and cyanosoma) involves a courtship dance in which the bodies are pressed closely together and the male anal fin is wrapped around the female covering the urinogenital opening, followed by simultaneous trembling and then by egg extrusion. It is probable that sperm are transferred into the urinogenital open of the female during this behaviour. In A. notatus and Phaeoptyx sp., courtship culminates in a short period when the vents of both the males and female are pressed tightly together during after which the eggs are engulfed by the male. In yet another marine species, Cheilodipterus lineatus, courtship is
may ensure that they are sufficiently large to take advantage of the increased production of small fishes during the wet season. In south-eastern Queensland, lengthfrequency data (Fig. 2) suggests that spawning probably occurs in spring and early summer as juveniles between 10 and 30 mm SL were most common in summer samples, but small numbers of fish this size were present through to Autumn/Winter [1093]. It is possible that spawning takes place at night for this species is generally nocturnal. Spawning has been observed once only [225]: a female G. aprion extruded a single egg mass measuring approximately 20 x 10 mm in size and contained within a fine membrane, in a single effort after a short courtship. The male was observed to swim around the female, with the head inclined downwards, coupled with a trembling motion, prior to eggmass extrusion. The male then tore open the sac and ingested each egg individually. This description did not contain any details about how fertilisation was achieved and this aspect of the biology of apogonids appears to have
Table 5. Life history data for Glossamia aprion. Summary based on Bishop et al. [193] unless otherwise noted. Age at sexual maturity (months)
<12 months
Minimum length of ripe females (mm)
Length at first maturity 70 mm CFL
Minimum length of ripe males (mm)
Length at first maturity 60 mm CFL
Longevity (years)
? probably <5 years
Sex ratio
1:1, males more abundant in wet season samples however
Peak spawning activity
Late dry season, early wet, incubating males and spent females present in early wet and mid-dry seasons, mature fish present throughout the year
Critical temperature for spawning
>22 [755]
Inducement to spawning
?
Mean GSI of ripe females (%)
4.0–7.6%
Mean GSI of ripe males (%)
<1%
Fecundity (number of ova) Fecundity/length relationship
136–430, mean 250; incubating males 188–416
Egg size
0.8–1.78, mode 1.5, eggs laid in bundle, apparently surrounded by fine membrane, intrabuccal eggs 3 mm [755]
Frequency of spawning
?, probably more than once given range of egg sizes present
Oviposition and spawning site
? lentic conditions suggested necessary for egg transfer to male
Spawning migration
? not documented
Parental care
Males brood eggs and young in mouth, incubation suggested to be about 2 weeks in duration [755]
Time to hatching
?
Length at hatching (mm)
7 mm, 10 mm in 8 days.
Length at feeding
Mouth structures well developed at hatching, likely that exogenous feeding possible shortly after thereafter
Age at first feeding
? see above
Age at loss of yolk sac
Unknown but newly hatched larvae possess moderately large yolk sac
Duration of larval development
?
Length at metamorphosis
?
416
Glossamia aprion
of this species in the wild. Second, between-study variation in dietary composition, and hence regional variation in diet, was minimal (but see below); and as a consequence there was little difference between the mean diet weighted by sample size and that estimated without weighting. For example, fish, aquatic insects and macrocrustacea collectively comprised 77.3% of the diet when weighted by sample size and 85.7% of the diet without weighting.
followed by the male swimming over a clear patch on the seafloor, trembling slightly in doing so, whereupon the female expels a small egg mass onto the same spot, and it is then ingested by the male. It is unknown at what point the juveniles disperse from the brooding parent. Movement Glossamia aprion is not frequently recorded in fishway studies in Queensland and by inference probably does not move widely. Russell [1173] recorded only 51 individuals (roughly equal numbers moving up- and downstream) through the fishway on the Burnett River barrage. This species was commonly observed moving through Magela Creek in the Northern Territory however, but further details of phenology were not reported [190]. Spatial variation in habitat use by different size classes in the Alligator Rivers region led Bishop et al. [193] to suggest that G. aprion moved into lowland lagoons to spawn and that juveniles dispersed widely throughout the riverine landscape shortly after the end of the incubation period.
Aquatic insects (principally chironomid midge larvae and ephemeropteran and trichopteran nymphs) are the most important item in the diet of G. aprion. Macrocrustacea and fish are also important. The large mouth of G. aprion enables it to ingest these larger prey even at small size. As a consequence, this species is trophically more similar to large fish such as the therapontid grunters [697, 1097]. The importance of fish and macrocrustacaea in the diet increases with increasing body size. This change is probably accompanied by a change in foraging mode from one of active searching to that of highly cryptic, sit and wait ambush predator. Microcrustacea were important in the diet of fish collected from wetland habitats, comprising 11% and 4.4% of the diet of fish from the Normanby River floodplain and the Alligator Rivers region, respectively [193, 697]. This species, particularly larger fish, will occasionally rise to the surface to consume terrestrial prey [697, 1099].
Trophic ecology Information on the diet of G. aprion summarised in Figure 3 was drawn from eight studies undertaken in the Northern Territory or Queensland and a total of 655 individuals. These studies included: Bishop et al. [193], Alligator Rivers region (n = 425); Kennard [697], floodplain lagoons of the Normanby River (n = 160); Pusey et al. [1099], rivers of Cape York Peninsula (n = 30); Pusey et al. [1093]; Hortle and Pearson [599], Annan River (n = 8); Burdekin River, (n = 6); Pusey et al. [1097], rivers of the Wet Tropics region (n = 7); Bluhdorn and Arthington [205], Burnett River (n = 3); and Arthington [80], urban streams of Brisbane (n = 16).
Although fish contribute about one-sixth of the average diet, predation by G. aprion has been suggested to be an important factor in the structure of freshwater fish communities and in influencing prey behaviour. For example, unofficial translocation of G. aprion into Lake Eacham on the Atherton Tablelands was suggested to be the primary cause of extinction of Melanotaenia eachamensis in this lake [132]. Microhabitat use by rainbowfishes has been shown to be modified by the presence of a model Glossamia predator [240].
It should be noted that the total sample from which this summary is based was overwhelmingly dominated by fish less than 70 mm in length, reflecting the size distribution Fish (16.3%)
Microcrustaceans (5.5%)
Conservation status, threats and management Glossamia aprion is classified as Non-Threatened by Wager and Jackson [1353]. Given its wide distribution it is likely to be secure over most of its range. The southern limit of its range appears to have contracted northward in recent years and some concern is expressed for residual populations in rivers of northern New South Wales, if they ever did or still do naturally occur there.
Unidentified (13.7%)
Terrestrial invertebrates (1.2%) Aerial aq. Invertebrates (0.4%) Terrestrial vegetation (0.8%) Detritus (0.4%) Aquatic macrophytes (0.3%) Algae (0.4%)
Macrocrustaceans (18.8%)
This species has been translocated widely and has the ability to impact strongly on native fishes in some circumstances [132, 240, 241, 242] and some concern about its impact on native fishes is here expressed. Predator-naive populations (i.e. those for which piscivorous predators are
Molluscs (0.1%) Other macroinvertebrates (0.1%) Aquatic insects (42.3%)
Figure 3. Mean diet of Glossamia aprion. Summary based on 655 individuals from eight studies in northern Australia.
417
Freshwater Fishes of North-Eastern Australia
on native species as a result of changes in habitat structure fish without the additional stress due to elevated predation pressure.
evolutionarily novel) are particularly at risk. Glossamia aprion may be favoured by the changes in habitat structure wrought by proliferation of ponded pasture grasses and by riparian clearing which may lead to increased proliferation of aquatic macrophytes and submerged marginal weeds, habitats favoured by this species. Such changes place stress
Dove [1432] provided a list of parasite taxa recorded from G. aprion in south-eastern Queensland.
418
Toxotes chatareus (Hamilton 1822) Seven-spot archerfish
37 359001
Family: Toxotidae
pigmentation [936] whereas startled fish or fish stressed by poor holding conditions may be very darkly pigmented on body. Fish collected from very turbid waters are often completely lacking in pigmentation. Colour in preservative: essentially the same as in life except that white base colour may be replaced by dusky or tan colour. Some preserved specimens may be extremely dusky over the entire body, apparently in response to the ultimate stress of death [31].
Description Dorsal fin: IV–VI (usually V), 12–14; Anal: III, 15–17; Pectoral: 11–14; Lateral line scales: 29–37 (usually 29–32); Horizontal scale rows: 12–16; Gill rakers on lower limb of first arch: 5–7 [31]. Figure: composite, drawn from photographs of adult specimens, upper Burdekin River; drawn 2002. Toxotes chatareus is a highly distinctive, laterally compressed fish of moderate size: usually less than 250 mm in length but occasionally up to 400 mm and 700 g in weight [31, 755]. Bishop et al. [193] list the relationship between length (CFL in cm) and weight (in g) as: W = 0.0021L2.971; n=290, r2=0.992, p<0.001. Body deep, 42–53% of SL; head large, 25–33% of SL; eye large, 20–28% of head length. Relative eye size greatest in smaller individuals. Dorsal profile from snout to first dorsal fin usually straight, may be convex in small specimens. Colour in life: white overall with six to seven irregular dark blotches, sometimes forming vertical bars, along dorsal surface. Dark blotch present on base of caudal fin. Pectoral fins usually clear or dusky. Pelvic fins may be darkly pigmented. Dorsal and anal fins usually clear or dusky at base but distinguished by dark margin. Colour may be variable depending on time of day, environmental conditions and degree of stress. Fish observed or collected at night may have little or no dark
Body morphology and meristics vary considerably across this species’ range, depending on growth, locality and environmental conditions. Specimens from freshwater tend to less deep in profile and to have shorter dorsal spines than specimens from brackish waters. Allen [31] speculated that differences in dorsal spine length may be related to reduced calcium intake in freshwater. These environmental differences have, in the past, led to the description of different species for these forms, with dorsalis being the slender freshwater form and chatareus the deeper-bodied brackish water form. Systematics The Toxotidae is a small perciform family of fishes containing a single genus comprised of six described species [31] (but see below), collectively known as 419
Freshwater Fishes of North-Eastern Australia
archerfishes or riflefishes. Of the six described species, Toxotes chatareus (Hamilton), T. lorentzi Weber, T. jaculatrix (Pallas) and T. oligolepis Bleeker, are said to occur in Australia, and the remaining two species, T. blythi Boulenger and T. microlepis Günther, occur in South-East Asia. Allen [31], in his 1978 review of the family, remarked that Western Australian populations of T. oligolepis differed from Irian Jayan populations in having a deeper body and a greater lateral line count and suggested that they could possibly represent a distinct species or subspecies. Allen et al. [52] are more emphatic and list the archerfish from the Kimberley region as an undescribed form distinct from T. oligolepis. Thus the family contains seven species, three of which do not occur in Australia.
restricted to the upper reaches of the estuary at this time [356]. Abundance levels declined ten-fold by the late dry season. Slightly higher abundance levels were recorded during the wet season (CPUE of 2.1–2.7) at which time T. chatereus was distributed throughout the estuary [356]. Toxotes chatareus is more patchily distributed on the east coast of Australia. It has been recorded from Jacky Jacky Creek [1349], and the Olive [571, 1349], Stewart [571], Normanby [697, 1099, 1349], Howick [571] and Endeavor [1349] rivers. In the Normanby River, this species occurs approximately 350 km upstream in the river’s headwaters but it is not abundant in this part of the river. This species comprised 6.8% of the total gill-netting catch in a twoyear study of the fishes of the Normanby River but comprised less than 1% of the electrofishing catch [697].
The genus was first described by Cuvier in 1817 with the type species being T. jaculator (based on Sciaena jaculatrix Pallas, a junior synonym of Labrus jaculator Shaw). A replacement name for the genus, Trompe, was erected by Gistel in 1848 but not generally accepted [31]. Toxotes chatareus was first described as Coius chatareus by Hamilton in 1822 based on material from the Ganges River, India. Other synonyms include T. carpentariensis Castelnau, T. dorsalis Whitley and T. ulysses Whitley [31].
Within the Wet Tropics region, T. chatareus has been recorded from the Daintree [1185, 1349], Saltwater [1185], Mossman [1349], Barron [1187, 1349], Mulgrave/Russell [1085, 1349] and Johnstone [1349] drainage systems. Other rivers in the region in which T. chatareus has not been recorded despite survey attention include the Mowbray [1185], Moresby [1183], Liverpool, Maria and Hull [1179], Tully [583] and Herbert [584] river systems. Pusey and Kennard [1085] collected five specimens from only two sites in a single drainage (the Russell River) during their extensive survey of the region. This species has not been collected by us from stream sites in the Johnstone and Mulgrave rivers over the period 1994–1997 despite intensive effort and extensive site coverage. These data suggest that T. chatareus is either very patchily distributed, occurs in habitats not easily sampled by backpack electrofishing (the principal sampling method used in the studies cited above), or is very difficult to collect (see below). In all likelihood it is a combination of the last two factors and T. chatareus is probably more widely distributed in the region than these data suggest. However, it should be noted that T. jaculatrix occurs in brackish/estuarine habitats in the region [1185]. It is possible that the higher gradient freshwater reaches of drainages systems of the Wet Tropics region do not provide suitable habitat for T. chatareus and the patchy distribution described above may be real. Whatever the case, T. chatareus is not abundant in the region.
Distribution and abundance Toxotes chatareus is widely distributed, occurring in India, Burma, South-East Asia, Indonesia, New Guinea and northern Australia [31]. Its distribution in northern Australia is similarly widespread. This species has been recorded from many rivers of the Kimberley region [31, 388, 620], and of the Northern Territory [31, 774], including the Kakadu region [193] and Arnhem Land [535]. In the Gulf of Carpentaria region of north-eastern Australia, T. chaterus has been recorded from the Gregory [31, 754] Nicholson [1349], Leichhardt [1090, 1349], Flinders [31, 1349], Saxby [31], Norman [1349] and Staaten [1349] River drainages. Lake [754] recorded it approximately 200 km upstream in the Gregory River. Further north, this species has been recorded from the Mitchell River [229, 1349] and its tributary systems the Palmer River [571] and the Walsh River [1186]. Its distribution in the Mitchell River extends upstream to its headwaters near the western boundary of the Wet Tropics region [1186]. Other rivers of western Cape York Peninsula in which T. chatareus occurs include the Coleman, Edward, Holroyd, Archer, Watson, Wenlock and Jardine rivers [31, 571, 1349]. This species has also been recorded from the Embley River estuary near Weipa [197, 1349] and was relatively abundant in this system. Both the abundance and distribution of this species within the estuary varied seasonally, being most abundant during the early dry season (CPUE = 16.3 x 10–4 fish.m–1.h–1) but
Toxotes chatareus has been recorded from the Ross, Burdekin and Proserpine river systems [1349] and its presence in the Pioneer River (T. Marsden, cited in Pusey [1081]) represents its southern limit. It has not been collected in rivers further south, such as the Fitzroy River, despite intensive sampling effort [160, 659]. Toxotes chatareus is widely distributed and common in the Burdekin River system occurring in most tributary
420
Toxotes chatareus
amount of its food. Wetlands systems in which riparian systems are greatly degraded and dominated by invasive grasses (i.e. such as many of those wetlands of the lower Burdekin River) contain very few T. chatareus, although it is probable that they historically supported large numbers of this species.
systems of this basin, both upstream and down of the former Burdekin Falls (and present day site of the Burdekin Falls Dam) [256, 586, 940, 1045, 1098]. It has in the past been recorded from wetland systems on the floodplain of the river (i.e. the Barratta wetlands) [1046] but is now uncommon in, or absent from, many such floodplain wetland systems, the majority of which are degraded by weed invasion, poor water quality and loss of riparian forests (C. Perna, pers. comm.). This species was the 10th most abundant species in seine-netting samples and third most abundant species in gill-netting samples in a threeyear study undertaken in the Burdekin River yet it was very uncommon in electrofishing samples (21st most abundant). The vagility and visual acuity of this species make it very difficult to collect by backpack electrofishing and a failure to detect this species, as discussed above for rivers of the Wet Tropics region, may be largely attributed to sampling difficulty. Although present in faster-flowing habitats in the Bowen River, this species is more abundant in the lower gradient reaches of the upper Burdekin and its tributaries [1098]. It is noteworthy that Midgely [940] recorded T. chatareus from the Belyando River but it is now apparently absent from this highly turbid river system [256]. It is also uncommon in the Cape River [258], another highly turbid tributary system of the Burdekin River.
Small juvenile fishes are most frequently observed in the vicinity of dense beds of macrophytes. Toxotes chatareus is most frequently observed within the top one-third of the water column and often within a centimetre or two of the water’s surface. However, the composition of the diet (see below) also suggests that this species often forages close to the stream-bed. Environmental tolerances Experimental data on environmental tolerances of this species are lacking and inferences on this aspect of its biology must be drawn from water quality data for sites in which occurs. The data presented in Table 1 are drawn from several sources. The data presented for the Alligator Rivers region is drawn from summaries in Bishop et al. [193] and that for the Burdekin River from surveys undertaken over the period 1989–1992 [1093]. The summaries Table 1. Physicochemical data for Toxotes chatareus. See text for source of summaries. Note that turbidity values given for the Alligator Rivers region refer to water clarity as determined by Secchi disc depths in cm.
Macro/meso/microhabitat use Quantitative information on habitat use is lacking for this species. Toxotes chatareus is more typically an inhabitant of large, low gradient rivers and is able to penetrate many hundreds of kilometres upstream, as well occurring in estuarine habitats. The presence of T. chatareus in the upper reaches of the Burdekin River is noteworthy, for the Burdekin Falls has historically been a major barrier to colonisation of the upper reaches by many species. This species is not frequently observed in fast- flowing streams, or streams with a gradient in excess of 1%.
Parameter
Min.
Alligator Rivers region Water temperature (°C) 26 Dissolved oxygen (mg.L–1) 4.3 pH 4.6 Conductivity (µS.cm–1) 2 Water clarity (cm) 1
Toxotes chatareus has been recorded from floodplain lagoons in northern Australia [193, 697, 1046]. In the Alligator Rivers region, T. chatareus was recorded from most floodplain and lowland muddy lagoons, in sandy creek-bed habitats, corridor lagoons and escarpment main channel waterbodies but only occasionally in escarpment perennial streams [193]. Habitat use varied seasonally in this system (see below) [193]. This species does well in lakes and impoundments into which it has been translocated. For example, it is conspicuously abundant in crater lakes of the Atherton Tablelands, north Queensland. A common feature of the habitats in which T. chatareus is found, and one which we believe is critical, is the presence of an intact riparian zone; the source of a significant
421
Max. 36 9.7 7.2 420 360
Mean 30.8 6.3 6.1 – 83
Normanby River (n = 8) Water temperature (°C) 22.9 29.4 Dissolved oxygen (mg.L–1) 2.4 9.0 pH 6.43 8.20 Conductivity (µS.cm–1) 130 391 Turbidity (NTU) 3.3 8.6
25.2 6.4 7.19 200.3 4.7
Normanby River floodplain (n = 6) Water temperature (°C) 22.9 27.7 Dissolved oxygen (mg.L–1) 1.1 6.3 pH 6.02 7.50 Conductivity (µS.cm–1) 80.9 204.0 Turbidity (NTU) 2.1 8.1
24.9 3.3 6.79 257.4 4.8
Burdekin River (n = 22) Water temperature (°C) 20.5 Dissolved oxygen (mg.L–1) 4.2 pH 6.68 Conductivity (µS.cm–1) 56 Turbidity (NTU) 0.6
26.5 7.29 7.69 389.2 4.55
33.0 9.6 8.40 790 20.8
Freshwater Fishes of North-Eastern Australia
for the Normanby River of Cape York Peninsula are partitioned into summaries for the river itself based on data collected in August 1990, June 1991 and December 1991 [697, 1099], and for six floodplain lagoons sampled in June and December 1991 [697].
salinity. Catch per unit effort declined from 4.56 x 10–4 fish.m-1.hr–1 in waters of between 20 and 33 ppt salinity, to only 0.34 x 10–4 fish.m–1.hr–1 in salinities above this range.
The range of temperatures over which T. chatareus has been recorded (20.5–36°C) (Table 1) reflects the tropical distribution of this species. It is likely that the upper limit of 36°C recorded in the Alligator Rivers region is approaching the upper tolerance limit for this species, although some geographical variation due to local acclimation probably occurs. The lower limit of 20.5°C recorded in the Burdekin River is probably approaching the lower limit for this species. The southern distribution of T. chatareus is probably limited by water temperature. For example, Mackay [839] reports August water temperatures in the Pioneer River of 17.5°C and water temperatures in May or June are likely to be a few degrees colder. Berghuis and Long [160] report winter water temperatures in the Fitzroy Basin as being as low as 14.1 to 16°C. Toxotes chatareus does not occur in the Fitzroy River and the Pioneer River is at the southern limit of its historical distribution.
Toxotes chatareus occurs over a relatively wide range of water clarity/turbidity (Table 1) but is most frequently collected from reaches in which turbidity is relatively low. This species relies on its ability to visually locate prey and high levels of suspended sediment are likely to impair this capacity. The relatively high turbidity value of 20.8 NTU in the Burdekin River was recorded immediately after an intense rainfall event and was transitory. Cyrus and Blaber [356] report that the abundance of T. chatareus in the Embley Estuary declined with increasing turbidity. Average CPUE values of 5.68, 1.39 and 0.92 x 10–4 fish.m–1.hr–1 were estimated for the turbidity classes <2, 2–10 and >10 NTU, respectively. These data suggest that even slight increases in turbidity are associated with a reduction in abundance, although it should be noted that abundance levels may vary in response to many factors, many of which are not themselves directly related to turbidity. A conservative upper tolerance level of 10 NTU is here suggested although the validity of this needs to be determined experimentally.
Toxotes chatareus has been recorded over a wide range of dissolved oxygen concentrations although the mean values presented in Table 1 suggest it is most frequently collected from waters of relatively high levels of dissolved oxygen. The very low levels (<2.5 mg.L–1) recorded in floodplain lagoons of the Normanby River and in the river itself are notable and must be close to the lower tolerance level for this species. The fact that T. chatareus occurs most frequently at the water’s surface may ensure that this species has access to relatively more oxygenated water than is found at depth. Nonetheless, T. chatareus populations in some of the lagoons studied by Kennard [697] experienced massive declines in abundance over the period of study and the cause of which may have been related to long-term exposure to hypoxia.
Reproduction The information presented in Table 2 is drawn largely from the work of Bishop et al. [193] in the Alligator Rivers region of the Northern Territory. Data preceded by a ‘?’ represent our best estimate. Toxotes chatareus is a relatively long-lived, highly fecund, wet season spawner. It is likely that spawning is homochronal (i.e. each female produces only one batch of eggs per season) and fish are iteroparous (i.e. spawn more than once over the life-span). Bishop et al. [193] cited a personal communication from H. Midgley that the eggs of T. chatareus are buoyant and pelagic. The observation that large numbers of larval T. chatareus are swept downstream in the current suggests that the larvae are pelagic also.
With the exception of that for the Alligator Rivers region, data in Table 1 suggest a preference for waters of a neutral pH of between 6 and 8.5. Geographical variation in response to local acclimation is apparent given the more acid conditions encountered in the Alligator Rivers region.
The limited information available concerning larval development suggests that it is rapid and that exogenous feeding occurs at small size. Bishop et al. [193] note that the characteristic feeding mode of archerfish (i.e. spitting) is assumed by fish as small as 20 mm CFL.
The conductivity values listed in Table 1 reflect the fact that all of the studies cited were undertaken in freshwaters. Allen [31] examined many specimens collected from brackish waters, indicating a well-developed tolerance of elevated salinity. Similarly, Cyrus and Blaber [356] recorded this species over a salinity range of 0–36 ppt, however they list this fish as an essentially freshwater species and note that abundance varied according to
No information on the breeding biology of this species in other Australian river systems is available and thus some care must be taken in translating the results obtained by Bishop et al. [193] for a large floodplain system of the Northern Territory to other river systems, particularly those without extensive floodplain wetlands or those with irregular flow regimes. For example, Kennard [697] collected small juvenile T. chatareus (<20 mm SL) in
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Toxotes chatareus
Table 2. Life history data for Toxotes chatareus. See text for source. Age at sexual maturity (months)
24 months
Minimum length of ripe females (mm)
Estimated length at maturity 190 mm although gender discernible at smaller sizes (minimum = 82 mm CFL)
Minimum length of ripe males (mm)
Estimated length at maturity 180 mm although gender discernible at smaller sizes (minimum = 80 mm CFL)
Longevity (years)
? 3–5 years
Sex ratio
Males frequently in excess
Peak spawning activity
Early wet season although aseasonal spawning reported for New Guinean populations [1147]
Critical temperature for spawning
Unknown but unlikely that attainment of set temperature induces spawning but may be involved in maturation process in males
Inducement to spawning
Unknown but males running ripe prior to full female maturation
Mean GSI of ripe females (%)
5.3 ± 2.4%
Mean GSI of ripe males (%)
1.9 ± 1.4%
Fecundity (number of ova)
20 000–150 000
Fecundity/length relationship
?
Egg size
0.4 mm intraovarian, not water-hardened
Frequency of spawning
Probably only once given variation around mean egg size relatively small: 12–16%
Oviposition and spawning site
Spawning occurs throughout preferred range, particularly in shallow, muddy lowland lagoons
Spawning migration
None
Parental care
None
Time to hatching
?
Length at hatching (mm)
Unknown but <4 mm
Length at first feeding (mm)
Larvae at 5 mm have well developed mouth parts
Age at first feeding
?
Age at loss of yolk sac
Unknown but yolk sac absent in even small larvae of 5–8 mm
Duration of larval development
?
Length at metamorphosis (mm)
?
isolated lagoons on the Normanby River flooplain during the late dry season (November). We have observed very small juvenile T. chatareus in the upper Burdekin River in only two locations: the Valley of Lagoons and Fletcher Creek. Thus, this species may spawn in a limited number of habitats throughout its range in this river. If so, then some form of spawning-associated migration occurs. It is noteworthy that the two reaches discussed above have very abundant and extensive beds of aquatic macrophytes. We find it surprising that so little is known about the reproductive biology of a species otherwise famous for its foraging strategy.
dispersed widely during the wet season to colonise a much wider array of habitats (see above). Cyrus and Blaber [356] and Kennard [697] also report widespread dispersal during the wet season. Bishop et al. [193] cite an unpublished report by Hamar Midgley describing the downstream, presumably passive, transport of juveniles less than 15 mm CFL early in the wet season followed by a return active upstream migration by fish between 20 and 35 mm CFL one month later.
Movement Quantitative data on this aspect of the biology of this species is lacking and it has not been recorded in fishway studies with the exception of being collected at the base of the inoperative fishway at the Clare Weir on the Burdekin River [586]. Bishop et al. [193] recorded this species from only six sites during the late dry season (mainly escarpment main channel and corridor lagoons) but found it had
Trophic ecology Toxotidae are renowned for their ability to spit jets of water into riparian foliage to dislodge terrestrial insects, which then fall onto the water’s surface and are devoured. Even a small wren (Malurus sp.) has been found in the stomach of one large individual (270 mm SL) from the Normanby River [697], although it seems unlikely that T. chatareus could capture such large and mobile prey
Movement over a smaller scale is a feature of this species’ biology and it may frequently be seen patrolling up and down streambanks in search of food.
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Freshwater Fishes of North-Eastern Australia
Terrestrial invertebrates are the most important source of food for T. chatareus, accounting for 41.3% of the total diet. A further 16.7% of the diet was based on the adult forms of otherwise aquatic invertebrates. This component included surface-dwelling forms such as pond skimmers (Gerriidae) and aerial insects such as dragonflies and mayflies. A small contribution by terrestrial vegetation was also observed. Together, food sourced from outside the aquatic environment contributed almost 60% to the diet. (Note that this is a very similar proportion to that observed for jungle perch Kuhlia rupestris (60.9%) and the Cairns rainbowfish (58.5%) in the Wet Tropics region).
spitting a jet of water – it most probably fell from a nest and was consumed at the water surface. The palate contains a long groove that is converted to a tube when the tongue is depressed to the roof of the mouth. Forceful compression of the opercula directs water under pressure from the pharanx through the palatine canal past the tip of the tongue, which acts as a valve [31]. Water may thus be ejected with accuracy over distance of up to 3 m [193]. Even small fishes of only 30 mm CFL may spit to a distance of 0.95 m [193]. The eyes of T. chatareus are relatively large, a feature that appears common to many fish species that rely heavily on terrestrial prey (e.g. Kuhlia rupestris and Cairnsichhtys rhombosomoides or Nannatherina balstoni of south-western Australia). Toxotes chatareus is able to accommodate for the refractive differences of air and water [383] and thus spit with great accuracy [193, 754, 1367].
Fish and macrocrustacea (prawns and shrimps) contributed only a minor proportion of the diet. Aquatic invertebrates, mostly trichopteran and chironomid larvae and ephemeroptern nymphs, contributed 33% of the mean diet.
The diet summary provided in Figure 1 is based on four separate studies undertaken across northern Australia. The first, undertaken by Bishop et al. [193] in the Alligator Rivers region was based on a total of 236 individuals collected from a variety of habitats over a period extending from the late dry season of 1978 to the late dry season of the following year. The second source of information was two studies undertaken in the Normanby River drainage of Cape York Peninsula. A total of 32 individuals collected from several locations in the main river in August 1990 [1099] and a total of 71 individuals collected from floodplain lagoons of the Normanby River in early and late dry season of 1991 [697] were included in this data set. Finally, dietary information from a total of 90 individuals from the Burdekin River collected on five occasions, including wet and dry seasons, over the period 1989 to 1992, was used.
The extent to which terrestrial invertebrates dominated the diet of this species varied between studies. In lagoons of the Normanby River, terrestrial invertebrates contribute 77% to the diet and the adult forms of aquatic insects comprised a further 3% [697]. However, these two sources comprised only 20% of the diet of T. chatareus from the main channel [1099]. Fish from the main channel consumed large amounts of corixid and notonectid bugs (47.7%). These organisms were abundant at the time of sampling and many other fish species consumed this prey also. Terrestrial invertebrates comprised 39% and 34.4% of the diet of T. chatareus from the Burdekin River and the Alligator Rivers region, respectively. The adult form of aquatic insects comprised 9% and 26% of the diet of these fish, respectively. It is evident that substantial spatial variation in diet may occur and the extent of this variation may vary more between habitats in the same location, than between geographically distant areas. Nonetheless, terrestrial prey are the most important food items for this species.
Fish (1.1%) Other microinvertebrates (0.1%) Microcrustaceans (0.3%) Macrocrustaceans (1.3%) Molluscs (0.3%) Other macroinvertebrates (0.5%)
Bishop et al. also noted spatial variation in dietary composition within the Alligator Rivers region [193]. Fish from escarpment waterbodies fed more on terrestrial prey (particularly ants) than did fish in shallow muddy lowland lagoons. They speculated that increased turbidity in the latter habitat type may have made it difficult to detect terrestrial prey but also noted that lowland lagoons did not have a very thick riparian zone. These authors also noted that terrestrial prey were most dominant in the diet during the wet season but declined greatly in importance during the dry season.
Unidentified (3.9%) Terrestrial invertebrates (41.3%)
Aquatic insects (32.8%)
Aquatic macrophytes (0.1%) Algae (0.1%) Terrestrial vertebrates (0.3%) Terrestrial vegetation (1.2%) Aerial aq. Invertebrates (16.7%)
Kennard [697] reported only minor temporal variation in the extent of reliance on terrestrial material in T. chatareus from lagoons of the Normanby River. This food source
Figure 1. Mean diet of the archerfish Toxotes chatareus. See text for details.
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Toxotes chatareus
contributed 77.5% in the early wet season (n = 43) and 72.7% in the late dry season. However, the types of organisms within the food class varied between sampling occasions. Grasshoppers were important in the early dry season (28.9%) but almost absent in the late dry season (2%), whereas ants increased in importance from 9% to 31.6% over the same period. The size distribution of fish within each sample did not differ greatly [697] and thus the observed differences are probably related more to differences in available food than to ontogenetic differences in prey choice.
pressure from a variety of impacts. If, as is likely, movement is a very important component of the biology of T. chatareus, in-stream barriers such as weirs and tidal barrages may impact on the integrity of metapopulations within individual rivers, despite the fact that this species does not need to migrate downstream to breed. The extent to which fish produced in one habitat move into or are dependent on the other is unknown however. The extent to which different breeding populations represent segregated stocks is also unknown. In view of these uncertainties, it would be prudent to ensure that connectivity between these habitats is maintained. Important in this regard is the maintenance of connectivity between the habitat of pelagic larvae and of juveniles and adults. Wet season dispersal has been noted for this species [193, 356] and may be critical for the long-term sustainability of some populations. The importance of riparian forests as a source of food for T. chatareus suggests that any degradation of riparian systems will in turn have negative consequences for this species also. Inappropriate landuse and extensive catchment clearing leading to an inevitable decrease in water clarity are likely to decrease the foraging efficiency of this species and lead to population declines in the long-term. Translocation of this species into impoundments or lakes may itself pose a threat to other fish species as it will consume other fish.
In summary, Toxotes chatareus is primarily a predator of insects and other invertebrates occurring in vegetation adjacent to, or overhanging, watercourses. However, a wider array of prey is also consumed, with many aquatic invertebrates featuring in the diet also. This species is apparently able to track seasonal changes in food availability and to change foraging strategies in order to maintain food intake. It is not solely reliant on terrestrially derived food. Conservation status, threats and management Toxotes chatareus is listed as Non-Threatened by Wager and Jackson [1353]. This species is secure over its entire range, however populations in some rivers may be facing
425
Mugil cephalus Linnaeus, 1758 Sea mullet
37 381002
Family: Mugilidae
below lower margin of orbit, posterior above or level with margin. Prominent adipose eyelid present in older specimens. Pectoral and pelvic fins with prominent axillary scale [1311].
Description First dorsal fin: IV; Second dorsal fin: I, 8; Anal: III, 8; Pectoral: 16–17, with distinct axillary scale; Vertical scale rows: 38–42; Horizontal scale rows: 14–15; Predorsal scales: 24–26; Cheek scales: 3–4 rows [52, 470]. Figure: composite, drawn from photographs of adult specimens; 2002.
Colour in life varies according to habitat. Ocean-going specimens are olive-green dorsally with bright silvery sides, grading into off-white ventrally. Freshwater sea mullet are often very dark dorsally and less vividly silver laterally. A series of six or seven faint median lateral bands may be present and for this reason sea mullet may be called striped mullet in some Australian states (e.g. New South Wales) and elsewhere in the world. The fins have a dusky appearance, except for the pelvic fins, which are usually a pale yellow in colour. A dark blue or violet spot is present at the base of the pectoral fins. Colour in preservative not greatly different from that in life except lacking in vitality, with silver body colour tending to a dull uniform grey. The pectoral spot becomes black upon preservation.
Mugil cephalus is a moderately large schooling species that may attain a length of 900 mm and weight of 10 kg [755]; such large sizes are rarely attained however. Females tend to be deeper in the body and heavier for a given weight [469]. Length (cm) weight (g) relationships reported in the literature vary substantially between studies with median values for a and b being 0.0085 and 3.0, respectively [422]. The body is robust and elongate; the head markedly broad, its length greater than body depth; snout length greater than diameter of eye, its anterior profile sharply curved. Mouth terminal with oblique cleft; lips thin, symphysal knob weakly developed; both lips with a single row of setiform teeth, second row sometimes present but always composed of only a few scattered teeth, teeth lost or embedded in lip tissue in older specimens; no teeth on palate; maxillae concealed when mouth closed. Nostrils equidistant from one another, anterior nostril
Systematics Mugilidae is a large family, occurring throughout the world’s tropical and temperate seas. It contains between 15 and 17 genera and 68 and 75 species, depending on the authority consulted [37, 52, 406]. Six genera: Mugil, Liza,
426
Mugil cephalus
tropical waters. It is apparently absent from the Great Australian Bight but there is no evidence for differentiation of eastern and western stock based on morphology or physiology [678].
Valamugil, Myxus, Rhinomugil and Aldrichetta occur in Australian waters. Worldwide, Mugil and Liza are the most speciose genera (19 and 24 species, respectively) whereas Valamugil contains six species and Myxus, Rhinomugil and Aldrichetta each contain two species only. The Mugilidae is distinguished from other fishes of the Mugiloidea by the possession of 24–26 vertebrae (usually 24) and by having the pelvic bones connected to the post-cleithra by a ligament [1311]. The Mugilidae is apparently closely related to the Sphyraenidae (barracuda) and the Polynemidae (threadfins) [254]. In the most recent phylogenetic analysis of the family, the genus Mugil was included in a polychotomy with several other genera near the top of the family tree [557].
Although various texts list the distribution of Mugil cephalus as encompassing the entire Australian continent, this species is either absent or rarely encountered in many rivers of northern Australia. Doupe and Lenanton do not list it present in the Fitzroy River [388], nor was it detected in subsequent survey work in this river (D. Morgan, pers. comm.). This species is not listed as occurring in the large range of Kimberley rivers examined by Hutchins [620] or Allen and Leggett [45] and it was not collected during extensive survey work of the Northern Territory by researchers from Murdoch University (D. Thorburn and A. Rowland, pers. comm.). This species was not collected by Bishop et al. [193] during the extensive examination of the fish fauna of the Alligator Rivers region nor was it listed for the Northern Territory by Larson and Martin [774]. It was included, however (as M. dobula), in a collection of fishes from the Port Darwin area made in the 1870s [842].
Linnaeus first formally described M. cephalus in 1758 although it had been described or named in many earlier writings, notably those of Aristotle in his Historia Animalium and Guillaume Rondelet in his 1558 treatise entitled Histoire entière des poissons [354]. Many characters used to define mugilid genera have been found to vary with age and size; including the presence or absence of an adipose eyelid, change from cycloid to ctenoid squamation, loss or embeddedness of teeth on the lips, and change in the angle of the maxillary. Recent systematic work has resulted in a reduction of the number of genera within the family and recognition of many synonyms for M. cephalus. For example, Thompson’s [1311] treatment of the Australian mullets identified a total of 38 extant genera, of which only 13 were found to be valid. The list of junior synonyms for Mugil cephalus is extensive and includes Mugil albula Linnaeus 1766, M. crenilabrus our Forsskål 1775, M. our Forsskål 1775, M. provensalis Risso 1810, M. linneatus Valenciennes 1836, M. cephalotus Valenciennes 1836, M. japonicus Temminck & Schlegel 1845, M. vulpinus Nardo 1847, M. dobula Günther 1861, M. ashanteensis Bleeker 1863, M. gelatinosus Klunzinger 1872, M. occidentalis Castelnau 1873, M. mexicanus Steindachner 1876, M. grandis Castelnau 1879, M. muelleri (or mulleri) Klunzinger 1880, M. hypselosoma Ogilby 1897 and M. pacificus Steindachner 1900 as well as Myxus superficialis Klunzingeri 1870, My. caecutiens Günther 1876 and My. barnardi Gilchrist and Thompson 1914. Much early Australian research on the ecology of M. cephalus was reported under the name M. dobula.
Mugil cephalus is included in a checklist of the freshwater fish fauna of Papua New Guinea [36] and both Allen [37] and Munro [977] state that is present in Papua New Guinean waters. Localities or rivers in which this species occurs were not given and the latter author suggested it is little known in Papua New Guinea. It was not listed as present in the Sepik Ramu or the Fly River by Coates [316]. There are few records of sea mullet in rivers of northern Queensland. de Castelnau [287] recorded it (as M. dobula) from the Norman River in 1878, otherwise it is apparently absent from the Gulf of Carpentaria region [197, 356]. It has not been recorded from rivers of the western side of Cape York Peninsula [571]. A single record exists for the Starke River north of Cooktown on the eastern side of Cape York Peninsula [571], otherwise it appears absent from this region also [599, 697, 1099, 1223]. Other mullet species such as Liza vaigiensis (diamond scale mullet) and Valamugil buchanani (blue-tail mullet) are much more common in far northern Australian rivers. Mugil cephalus does occur in the Wet Tropics region, although again, it is uncommon and appears restricted to the southern portion of this region. It was not collected in the Daintree, Mowbray, Mossman or Saltwater drainages by Russell et al. [1185]. A single specimen was collected from the Barron River by Pusey and Kennard [1087] and its presence here was confirmed by Russell et al. [1187] who recorded it in the estuary and in Freshwater Creek. To the south of the Barron River, this species has been
Distribution and abundance Mugil cephalus is a cosmopolitan species inhabiting the coastal waters of all seas of the tropical, subtropical and temperate zones [1430]. The Australian distribution includes all mainland states with occasional recordings from Tasmania [678]. Allen et al. [52] suggest that it is more common in temperate Australian waters than in
427
Freshwater Fishes of North-Eastern Australia
within this region. This species was only the 11th most abundant species (100/6020) in the South Coast region despite being collected from all rivers except the Georges River. Despite being apparently sensitive to flow regulation [435], the decreased abundance of M. cephalus in the southern region did not appear to be due to a greater extent of flow regulation.
collected from the Mulgrave/Russell River [1184], Liverpool and Maria drainages [1179], the Johnstone River [1177], the Moresby River [1183], the Tully/Murray drainage [583] and the Herbert River [584]. This species was not abundant or widely distributed in any of these river systems. Contemporary surveys [940, 1098] have not collected Mugil cephalus from the Burdekin River although it was collected from Lillesmere Lagoon in the late 19th century [847] and it is present in marine waters of the area [468].
Macro/meso/microhabitat use Habitat use in sea mullet is very much a function of age as M. cephalus moves extensively throughout its life (see below). Juvenile fish less than one-year-old are typically confined to estuaries although some movement upstream into freshwaters may occur during this period [1313]. During this time they are most frequently encountered in shallow waters over a sandy mud bottom. Older fish (1+ and older) may penetrate many hundreds of kilometers upstream but typically do not enter small, fast-flowing tributaries. They will ascend rapids but tend not to persist long in fast-flowing habitats perhaps because suitable food resources are at low abundance. A more complete description of macro- and mesohabitat use is included in the movement section below.
These data support the observation by Allen et al. [52] that Mugil cephalus is more common in temperate Australian waters and suggest that while present in northern Queensland, it is not common there. It may seem odd that we have concentrated on those rivers in which sea mullet rarely, if ever, occur. However, in light of the common inference that the distribution of this species tends towards ubiquity, this focus seems necessary for two reasons. First, the apparent absence of east-west stock differentiation warrants re-examination given the evident disjunction in distribution in both northern and southern Australia. Second, information on the factors that limit the northern distribution may prove useful in managing southern stocks. Temperature may play an important role in determining the distribution of M. cephalus (see below).
Sea mullet may be found in a variety of water depths. They forage most extensively on the bottom although in some circumstances they may be observed feeding at the surface, presumably on the rich film that may occasionally form on the water’s surface, particularly downstream of sewage treatment plants.
Sea mullet are commonly encountered in the Fitzroy River system [659, 740, 942, 1349] although the present-day distribution appears greatly reduced from that observed prior to the construction of impoundments along its length. Impoundments impact on the distribution of this species in the Pioneer and Burnett rivers also [700, 1081, 1276]. Mugil cephalus can be assumed to occur in most, if not all, major Queensland drainages south of the Fitzroy River. It has been recorded in the Burnett [700, 828, 1349], Mary [1095, 1349], Noosa [1349], Maroochy [1349], Brisbane [704, 907], Albert/Logan [1093, 1100], Nerang [968], Tallebudgera [970] drainages and drainages of Frazer [1349], Moreton [969] and Stradbroke islands [1349].
Environmental tolerances The salinity tolerance of M. cephalus, particularly that of fry and small juveniles, has been extensively studied. Developing eggs are intolerant of salinities less than that of seawater, whereas newly hatched larvae are intolerant of salinities less than 28‰ [995]. Nordlie et al. [995] found that fish between 20 and 69 mm in length could tolerate abrupt transfer to a range of lowered salinities except that of freshwater and suggested that the osmoregulatory response was fully developed (i.e. same as adults) after a size of 40–69 mm. Cicotti et al. [305], in contrast, found that even small juveniles (mean length 28 + 3.5 mm) could tolerate slow acclimation to freshwater: morphological and biochemical aspects of the gills and oesophagus in juveniles were similar to adults suggesting that osmoregulatory ability was precociously developed. Osmoregulatory ability in small mullet is temperature dependent [953]. Sea mullet are able to tolerate salinities as high as 80‰.
Morton [968, 970] found that sea mullet were an important component of the fish fauna occurring in residential canal developments in the Nerang River and Tallebudgera Creek and often achieved higher abundances than in the adjacent river proper. He hypothesised that higher abundances were supported by a greater accumulation of organic matter in the bottom sediments of canals. Mugil cephalus is common in the Tweed River [1133] and was commonly encountered during the New South Wales Rivers Survey [553], being the second most abundant species (657 collected out of a total of 10 017) in rivers of the North Coast region, and present in all rivers sampled
The widespread distribution of sea mullet ensures that they experience a wide range of water temperatures. Thompson [1311] suggests that growth ceased at temperatures below 16–18°C in a Western Australian population
428
Mugil cephalus
and Nash and Kuo [984] report an optimum temperature range for growth of 20–24°C. This latter study did not examine Australian stocks of sea mullet and there is potential for substantial geographical variation in temperature preferenda; it is noteworthy that this upper temperature range is less than that frequently found in, and perhaps even typical of, tropical Australian rivers. For example, Grant and Spain [468] recorded water temperatures of 21–32°C in the Townsville area. Water temperature may play a role in determining the distribution of sea mullet in Australia.
Brisbane River and in river sediments themselves led Connel [330] to suggest that it was accumulated during feeding. Gas chromatography revealed the compound to be very similar to commercial kerosene and its source was probably sewerage effluent.
Red-spot disease or tropical epizootic ulcerative syndrome has been reported for M. cephalus. [883, 1154]. Infection rates can be high (>25%) and rates of incidence appear greatest in post migratory/spawning adults when water temperatures and salinity are low (<5.5 ‰). Dieldrin and DDT residues have been detected in sea mullet from the Clarence, Richmond and Tweeds rivers [883]. Although the average concentrations recorded were below the maximum recommended levels, some fish exhibited very high levels of dieldrin accumulation. Sea mullet have also been recorded as having a kerosene-like taint. The presence of this taint in sediments within the gut of mullet from the
Reproduction Growth is rapid in juvenile sea mullet. A length of 150 mm is reached after one year, 240 mm after two years and 330 mm after three years [678, 715]. Growth may be slightly faster in tropical stocks [468]. Sexual maturity is reached at sizes between 300 and 350 mm when fish are three years old. Fish in excess of 550–600 m are at least eight years old [468] and the maximum recorded life-span for an Australian sea mullet is nine years [678] (Table 1).
Sea mullet fry apparently avoid areas of high light intensity and are attracted to areas of high turbidity. Blaber [195] suggested that positive orientation to elevated turbidity provided the mechanism by which small fish located and entered rivers.
A deviation away from a sex ratio of unity has been reported in two studies, with females dominating (3.4:1)
Table 1. Life history information for Mugil cephalus. Age at sexual maturity (months)
24 [715]
Minimum length of ripe females (mm)
300–350 [678, 715]
Minimum length of ripe males (mm)
?
Longevity (years)
9 years
Sex ratio (female to male)
Varies according to habitat, female dominance in freshwater [1230], males in marine [715]
Occurrence of ripe fish
Varies according to latitude, usually in autumn to winter
Peak spawning activity
Autumn to winter
Critical temperature for spawning
?
Inducement to spawning
Possibly lowered water temperatures
Mean GSI of ripe females (%)
9–24% [468, 715]
Mean GSI of ripe males (%)
5–6% [715]
Fecundity (number of ova)
1.57–4.77 x 106 [468]
Fecundity/length relationship
F = 0.009 L3.16 – fork length in mm [468]
Egg size
0.63 mm [468]
Frequency of spawning
Homochronal [1230], females spawn repeatedly over life span
Oviposition and spawning site
Broadcast spawning?, surf zone
Spawning migration
Extensive, from freshwater/estuarine to distant on-shore marine
Parental care
None
Time to hatching
36–50 hours at 22–24°C [746]
Length at hatching (mm)
2.0–3.4 mm [746]
Length at free swimming stage (mm)
~6 [195]
Length at metamorphosis (mm)
11–18 [195, 746]
Duration of larval development
Metamorphosis completed by 28–42 days [195, 746]
Age at loss of yolk sack
?
Age at first feeding
3 days [195]
429
Freshwater Fishes of North-Eastern Australia
column, also causes them to congregate in areas of high turbidity. Blaber [195] presented a model in which juvenile mullet use elevated turbidity and depressed salinity as cues by which they orientate movement into estuaries and rivers. Recruitment into estuaries includes both passive and active movement involving post-larvae of between 10–15 mm in length corresponding to about 28–42 days of age. Such fish commonly enter estuaries on the flood tide and do so by passively drifting in on the flood tide and then settling to the benthos during the ebb tide. Once inside the estuary, postlarval mullet disperse actively in vast numbers in shallow waters adjacent to the riverbank. Thompson [993] examined the movement of mullet within the Albert/Logan River. By early to late September, vast numbers of postlarvae and fry had dispersed into small schools of a few hundred at the mouth of the river. By mid-October, such schools were encountered approximately 10 km upstream of the mouth where the water was still brackish. By mid-November, schools of juveniles were encountered at the head of the tidal zone. Thompson suggested that fry prefer reduced salinities but cautioned that not all of the fish that enter an estuary migrate upstream to freshwater. These 0+ fish move about extensively, particularly in the hours around dawn and dusk and quickly become powerful swimmers. Juvenile mullet (2.5–6.5 cm) are recorded as having sustained swimming speeds of 5–6 body lengths.sec–1, sustained maximum swimming speeds of 12.7 body lengths.sec–1 for 30 seconds and burst speeds of 20–30 body lengths.sec–1 for up to 2 seconds [1168, 1401]. Swimming speeds increase with size: a maximum burst speed of 1.45 m.sec–1 was estimated for fish less than 40 mm, whereas fish of between 86–130 mm could sustain a two-second burst speed of 1.6 m.sec–1 [1401]. Kowarsky and Ross [740] report young mullet negotiating average velocities of 1.2 m.sec–1 in the fishway ascending the Fitzroy River barrage.
in riverine environments [1230] and males dominating (2:1) market landings of fish taken during the spawning season [715]. Shireman [1230] postulated that male fish did not enter riverine environments in as large numbers as females and Kesteven [715] suggested that males may spend longer on or around spawning grounds and were hence more susceptible to capture. The spawning season is protracted but confined to autumn and winter. There is some evidence that stocks in the northern part of the distribution spawn later in the year (about August) [468] than do southern stocks [715, 1311, 1313]. An autumn to early winter spawning season is typical of sea mullet throughout the temperate part of their distribution [195]. Although the exact location of spawning is unknown, all evidence suggests it is marine and more than likely it is just seaward of the surf zone near the mouths of rivers [195, 468, 715]. Although migration appears to be stimulated by decreasing water temperatures, the cue(s) responsible for initiating spawning remains unknown. However gonad maturation commences (up to stage IV) in freshwater/estuarine habitats prior to migration [304]. Mugil cephalus is a highly fecund species producing millions of small eggs. Fecundity increases with body size [468] (Table 1). The relative size of the developing gonads increases slightly, but significantly, with size also [715]. The eggs are non-buoyant, will sink unless held in suspension by water turbulence and must stay in suspension in order to develop [195]. Intraovarian eggs vary little in size and are probably shed in a single spawning bout [1230]. Individual females probably spawn several times over their life span. Hatching occurs 36–50 hours after fertilisation at temperatures between 22–24°C [746]. The larvae are initially small (2.0–3.4 mm) and poorly developed. However, development is rapid, with feeding first commencing at about three days after hatching, fin development being largely completed by six days and squamation completed by 28–30 days.
The majority of 1+ mullet remain in the one river system, moving extensively between freshwater and estuarine habitats. Thompson suggested that there was no pattern in this movement [1313]. However, Russell recorded that nearly all of the juvenile mullet (150–300 mm) moving upstream through a fishway on the Burnett River did so in the months of May and June, whereas the majority of small mullet (95% <150 mm FL) trying to move upstream through the Fitzroy River barrage did so in November [1274]. Kowarsky and Ross [740] found that juvenile migration through this fishway peaked in December or January. Significantly more juvenile mullet tried to ascend the fishway during the day than at night [1274].
Movement Movement at a variety of scales is a pronounced feature of the biology of M. cephalus throughout its life history. Larvae, which hatch at sea, are initially pelagic and passively drift in currents (generally southward, see below). At about 10 mm in length, mullet fry migrate down into the water column where they remain until they enter an estuary. This movement corresponds to a welldocumented change in dietary habit from that of pelagic planktivore to one of feeding on benthic plankton and meiobenthos (see below). Blaber [195] suggests that such small fish are negatively phototactic and that this behaviour, in addition to driving larvae down in the water
Many 1+ and 2+ fish may move out of freshwater and estuarine habitats and re-enter the marine environment in what are known as ‘hard-gut’ or ‘wash-out’ runs [715,
430
Mugil cephalus
are filtered from the water and sediment. The mouth is protrusible [1312] and when opened, the palatine, stenohyoid, and opercular muscles, combined with the muscles of the branchial arches, create a sucking action by enlarging the buccal cavity. Particles are filtered through a series of minute teeth located on the dorsal pad of the pharyngeal series of pads [459]. A series of pharyngeal taste buds helps to identify organic-rich sediments [1010]. The oesophagus is straight and tubular but becomes progressively more folded near the stomach, which is divided into a thick-walled, gizzard-like structure anteriorly and a thinwalled saccular portion posteriorly [1312]. The intestine is thin-walled and long (5.5–5.7 x body length) and looped within the body cavity.
1313]. These migrations do not occur every year but when they do occur, they occur most frequently in early summer and are associated with flooding (hence the term ‘washout’). Although Chubb et al. [304] suggest that a ‘hard-gut’ run occurs in the Swan-Avon system of Western Australia, the phenomenon appears to be more a feature of eastern stocks. Fish involved in such runs typically do not feed and it has been suggested that the ‘hard-gut’ run occurs in response to flood-induced removal of detrital food sources. Fish involved in such runs usually re-enter the river system from whence they came or move to adjacent rivers, usually to the north [715, 1313]. Spawning runs, in contrast, may be very extensive, involving distances of greater than 300 kms and frequently in excess of 600–700 kms. Such runs are nearly always northward [712]. Kesteven [712] suggested that only 30–50% of the resident mullet population moved out of a river each year and that such migrations may occur several times over a fish’s life-span. Gonad maturation commences in freshwater prior to migration. Maturing fish commence to move downstream to congregate near the river mouth and form large schools [712, 1313]. Although the stimulus for fish to leave rivers and commence the northward journey is unknown, Thompson [1313] suggests that a prolonged period of offshore westerly winds is required. Such winds do not stimulate mass exodus if they occur in January or February prior to gonad maturation, however. Spawning migrations generally commence in April in the southern portions of the mullet distribution [1313], about May to June in the central portions [712] and as late as July in the most northern portion of the eastern Australian distribution [468]. This latitudinal gradient in migration phenology suggests that migration is stimulated by a decrease in water temperatures. That a period of sustained westerly winds is implicated may be due to such winds increasing turbulence in rivers with an east-west orientation sufficiently to cause mixing of deep, cold water with warmer surface water. This would result in an abrupt lowering of water temperature. An autumn to winter spawning run is typical of mullet throughout their distribution [195].
Although much has been written about the diet of mullet, frequently information is anecdotal or qualitative at best. For example, Thompson [1312] examined a total of 130 individuals and stated that the diet consisted of fine detrital material, plant fibres, sand, grit, diatoms and filamentous algae: he did not reveal the proportions of each. Thompson [1312] cites several other studies which list the diet as consisting of: diatoms, foraminifera, mud and detritus; diatoms, desmids and blue-green algae; protozoa, rotifera, cladocera and sand; or filamentous algae and diatoms. Two studies, Richardson [1133] (n = 75, Tweed River) and Arthington et al. [99] (n = 31, Barker-Barambah Creek, Burnett River) have described diet quantitatively and a summary is presented in Figure 1. Detritus and algae (desmids and diatoms) make up the bulk of the mullet diets in these studies. The question of what comprises ‘detritus’ (i.e. living or dead plant cells) or its source (i.e. terrestrial or aquatic) is not clear however. Thompson [1312] states that plentiful protozoa, bacteria and algal flora must be ingested along with sediment and form a not inconsiderable proportion of the food. Nonetheless, very fine organic material form a large proportion of the diet of adult sea mullet [1010]. The pharygeal apparatus is very efficient at selecting for very small particles of organic matter. Odum [1010] reports that the organic content of material in the gut may be up to 25 times greater than the organic content of the sediments upon which mullet feed and, furthermore, may contain up to three times more small particles (<10 µm). Particles of this size collect, by adsorption and absortion, proportionally more organic material (plus nitrogen and phosphorus) than do larger sediment particles. In addition, up to 99% of all bacteria and flagellates in the sediment are adsorbed on these small particles [1010].
Spawning runs typically do not last longer than four to eight weeks, although Kesteven [715] suggested that males remain at large for longer periods than do females. A generally northward spawning run requires either an active adult return migration or that eggs and larvae are passively moved southward in the prevailing currents. In fact, both mechanisms are involved. Trophic ecology Mugil cephalus has been classified as a filter-feeding detritivore [459] although it is able to graze on submerged hard surfaces also [1010]. Detritus and other organic particles
This ileophagous habit is expressed early in life [195]. Larvae are initially pelagic and planktivorous, feeding first
431
Freshwater Fishes of North-Eastern Australia
are actively targeted by gill-netting in a fishery involving about 400 fishers. The monthly total catch is about 8 tonne, the majority (~90%) of which is taken from Bundaberg south to the New South Wales border. Gill mesh size varies from 75 to 87 or 102 mm, as fishers actively select for larger fish, particularly roe-bearing females. Mullet roe can fetch up to about 30 times the value of fresh fish at market [678]. Sea mullet comprise almost 87% of the fishes netted in this fishery and bycatch rates were considered low (5.6%) [501]. Yellowfin bream (Acanthopagrus australis) was the second most commonly netted species, comprising 3.7% of the total catch (logbook data), of which 52% were discarded with apparently high levels of survival. The fishery is regulated with restrictions on length of net used, mesh sizes, size limits and numerous spatial and temporal closures. Sea mullet is a good table fish when consumed fresh and is targeted by recreational fishers. Mullet fillets, or whole live or dead fish, are highly prized as bait for larger predatory species such as jacks, trevally and barramundi.
on surface-dwelling plankters and then switching to a diet dominated by vertically migrating plankters at about 10–15 mm in size when they themselves start to become benthic in habit. Selection for benthic zooplankters changes to that of meiobenthos by about 20 mm in length. A gradual change to the fully ileophagous habitat occurs by the time a length of 45 mm is attained, corresponding to movement from the marine to the estuarine environment. Blaber [195] cites studies showing that the energy value of benthos and sediments is up to 100 times greater than that of zooplankton in South African estuaries. Aquatic insects (0.8%)
Molluscs (0.4%) Unidentified (19.2%)
Algae (39.3%)
Commercial harvesting of sea mullet currently appears sustainable, despite early concerns about over-exploitation. Bycatch issues associated with the fishery appear minimal. However, the fact that mullet migrate extensively means that the continued persistence of populations in some rivers or localities may be dependent on activities occurring in catchments many kilometres to the south, potentially in different state jurisdictions. Thus, inappropriate land use, pest management strategies, waste disposal etc. in one catchment may impact on populations in that river as well as another river hundreds of kilometres to the north.
Detritus (41%)
Figure 1. The diet of Mugil cephalus. Summary based on quantitative information for a total of 106 individuals from two studies (see text).
Mugil cephalus is consumed by an enormous array of other organisms including flathead, tailor, barracuda, trevally, sharks, barramundi, mulloway, cormorants, egrets, pelicans, fish eagles, dolphins and crocodiles [195, 678].
Mugil cephalus is highly dependent on estuaries and the continued maintenance of estuarine integrity is essential for this species’ maintenance. Given the extent that sea mullet are consumed by other fishes, many of which are of commercial or recreational significance, and the fact that they are trophically located low in aquatic food webs, sea mullet appear to be very important in the nutrient and energy dynamics of estuarine systems. In addition, the movement of millions of juvenile mullet across marine/estuarine/freshwater ecosystem boundaries represents an enormous transfer of marine-derived carbon between ecosystems, the significance of which is unknown but potentially high. The migration of mullet out of freshwaters and estuaries represents a similarly large transfer of energy across ecosystem boundaries.
Conservation status, threats and management Mugil cephalus is listed as Non-Threatened by Wager and Jackson [1353]. Sea mullet have long been an important fisheries species, being commercially harvested throughout the 20th century [715]. Serious concern about a decline in stocks due to over-exploitation was expressed by 1942 [715], necessitating the introduction of size limits and gear restrictions. More recently, the total annual Australian catch has varied from about 3500 tonne to about 6000 tonne over the period 1964–1990 [678] and although annual catches have fluctuated markedly over this period, there is no evidence for further declines in stocks. Sea mullet are harvested by gill-netting in mixed-species fisheries located in estuaries, bays and inlets, and by targeted beach seine-netting. Halliday et al. [501] provide a recent account of the mullet fishery in Queensland. Sea mullet
The imposition of barriers to movement by structures such as weirs and barrages represents the single largest threat to the persistence of sea mullet in many river systems. The ability to ascend fishways or overcome
432
Mugil cephalus
impact on sea mullet populations in rivers of New South Wales [435]. Although the mechanism involved remains obscure, mullet populations in unregulated rivers of the North Coast region contained a greater proportion of fish below 100 mm. Water harvesting may reduce the extent of recruitment of postlarval fishes.
barriers imposed by weirs and barrages is a major determinant of the distribution of sea mullet within a river system [700, 907, 942, 1081]. Road crossings and culverts may also restrict upstream movement although such structures are most likely to be located on smaller streams not often frequented by sea mullet. River regulation, independent of the imposition of barriers, has been shown to
433
Glossogobius sp. 1 (after Allen et al. 2002) False Celebes goby, Mountain goby
37 428029
Family: Gobiidae
six dark brown saddles may be present on the dorsal surface and the extent of expression of these saddle-like markings depends substantially on substrate composition. These markings are poorly expressed when this species is found over uniformly fine particle substrates, but strongly expressed when it occurs over a more complex substrate containing gravel, cobble and rocks. This saddle-like pattern is observed across a wide range of unrelated benthic stream-dwelling fishes and provides obliterative countershading affording a high degree of crypsis when expressed [67]. Five to six dark midlateral blotches present, tending to be flanked by up to nine, but more commonly five to six thin, dark horizontal lines. The head is distinguished by several dark blotches, particularly on the cheek and opercula that frequently coalesce to form distinct lines running from the jaws to the opercula edge. The jaws are frequently pigmented, usually more so on the upper jaws. The anal and pelvic fins tend to be clear or occasionally the pelvic fins may be white. Although the pelvic fins are fused, they do not form a particularly noticeable cup-like structure. The pectoral fins tend to be transparent or light dusky tan striated by four light vertical brown lines. A dark blotch is present on the base of the pectoral fin and extends a short way on to the fin itself.
Description First dorsal fin: VI; Second dorsal: I, 8–9; Anal: I, 7–8; Pectoral: 20–21; Horizontal scale rows: 8–9; Vertical scale rows (in midlateral series): 28–31; Predorsal scales: 12–15; Gill rakers on first arch: 8–9; Head scales mainly absent except on nape; uniserate lines of papilla on head. Figure: 100 mm SL, Fishers Creek, North Johnstone River, July 1996; drawn 1998. Glossogobius sp. 1 is a moderate-sized goby able to reach 140 mm but more frequently less than 100 mm SL. The relationship between length (mm SL) and weight (g) for a sample of 42 individuals from the Mulgrave and Johnstone rivers is W = 1.503 x 10–5. L3.043; r2 = 0.983, n = 42, p<0.001 [1093]. The head is large and depressed. Head scales, when present, are cycloid, as are the scales on the breast; elsewhere, the scales are ctenoid. Mouth large, extending obliquely back to anterior margin of eye, lower jaw prominent protruding forward of the upper jaw. Teeth welldeveloped and tongue bilobed. Body cyclindrical in cross-section between pectoral and second dorsal fin, becoming compressed posteriorly. The colour of Glossogobius sp. 1 varies according to habitat. In general, the base colour of the body is a yellow/tan on the dorsal surface grading to white or dusky white ventrally. Five to
434
Glossogobius sp. 1
restricted to the east coast and is said to extend from Princess Charlotte Bay south to the Townsville region [52] and it has been recorded from the Howick and Starke rivers [571]. This species has however been recorded from the Lockhart River of Cape York Peninsula to the north of Princess Charlotte Bay [571] and apparently occurs in the Embley River of western Cape York Perninsula also [197]. Glossogobius sp. 1 is most commonly encountered in the Wet Tropics region, having been recorded from every major drainage, with the exception of the Hull and Moresby rivers, from the Annan River south to at least the Tully River [599, 1087, 1177, 1179, 1184, 1185, 1223]. Further sampling effort would probably reveal the distribution to be continuous. The distribution probably extends south to at least the Cardwell region as this species has been recorded from Hinchinbrook Island [851]. Jebreen et al. [643] did not record Glossogobius sp. 1 from the Herbert River in two surveys undertaken in 2000 and 2001. They did however record G. giurus, Glossogobius spp. and Glossogobius sp. 2 (listed as Glossogobius sp. C – the square blotch goby). The distribution of G. giurus certainly extends to this region, whereas previous descriptions of the distribution of Glossogobius sp. 2 do not include any rivers draining the eastern seaboard. In all likelihood, the identification of Glossogobius sp. 2 is in error and possibly a result of confusion with Glossogobius sp. 1. Given that the Hinchinbrook Channel and Hinchinbrook Island were historically part of the Herbert River drainage and the unresolved identification of Glossogobius species therein, it is reasonably safe to assume that Glossobgobius sp. 1 occurs in the Herbert River also. Glossogobius sp. 1 is moderately abundant in drainages within the core of its distribution (i.e. the Wet Tropics region). Pusey and Kennard [1087]
The dorsal fins are also transparent or a light dusky tan and marked by a fine barring pattern. Caudal fin clear to dusky brown with five to six thin, irregular vertical bars. Colour in preservative similar to that of live specimens except yellow/tan colour greatly subdued. The extent of sexual dimorphism, which may be great in some gobies, has not been examined. No information on the appearance of larvae is available. Systematics The Gobiidae is one of the most speciose and widespread families of teleost fishes, containing marine, estuarine and freshwater representatives [52, 1041]. Many freshwater species still retain a marine larval phase. The relationships of the Gobiidae and other members of the suborder Gobioidei (eg. Eleotridae) are highly complex and the subject of ongoing phylogenetic analysis [e.g. 579, 1362, 1428, 1442]. The Gobiidae contains at least 1900 species from about 212 genera, but new species continue to be discovered each year [52, 1041]. Most members of the Gobiidae can be distinguished from other gobioids by the fused pelvic fins, which form a disc-like structure [52]. The genus Glossogobius was first erected by Gill in 1862 and currently contains about 40 species, many of which are undescribed [37]. Species of Glossogobius may be found throughout the tropical Indo-Pacific in freshwater streams and brackish estuaries [36]. Species radiation within the genus has occurred more extensively in Papua New Guinea (25 spp.) than in Australia (seven freshwater species.). The genus Glossogobius is easily distinguished from other gobies by the presence of 8–12 rays in the in the second dorsal fin [52]. Three species (G. giuris, G. aureus and Glossogobius sp. 2) are widespread across northern Australia whereas the remainder are more restricted in range [52]. Glossogobius species tend not to be found in marine environments but are most commonly restricted to freshwaters and estuaries. The widespread distribution of some species is associated with the presence of marine larval phase. Species of more restricted distribution may complete their life histories in freshwater.
Table 1. Distribution, abundance and biomass data for Glossogobius sp. 1 in two rivers of the Wet Tropics region. Data summaries for a total of 314 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred.
Glossogobius sp. 1 in Australia has previously been attributed to G. celebius (Valenciennes, 1837). This latter species does not occur in Australia and is restricted to the islands of central Indonesia [52].
Total % locations % abundance
Distribution and abundance The distribution of this species is widespread, ranging around the Western Pacific rim from Japan to New Guinea and northern Australian, east to the Solomon Islands [52]. However, given the unresolved systematics of this species, the distribution is best considered ill-defined. In Australia, the distribution of Glossogobius sp. 1 is reported to be
Rank abundance % biomass Rank biomass
435
Mulgrave River
Johnstone River
31.5
43.2
17.9
0.9 (4.5)
1.7 (4.8)
0.7 (4.1)
19 (7)
11 (7)
21 (6)
0.3 (3.0)
0.4 (3.3)
0.2 (2.7)
19 (11)
14 (10)
18 (9)
Mean density (fish.10m–2)
0.212 ± 0.038 0.279 ± 0.061
0.157 ± 0.047
Mean biomass (g.10m–2)
1.139 ± 0.203 1.699 ± 0.390
0.670 ± 0.136
Freshwater Fishes of North-Eastern Australia
Table 2. Macro/mesohabitat use by Glossogobius sp. 1. Summaries derived from 33 sites within the Russell/Mulgrave, Johnstone and Tully drainages and a total of 92 individuals.
found it to be the eighth most abundant species collected in an extensive survey of the region]. Glossogobius sp. 1 is moderately widespread in the lowland reaches of the Mulgrave and Johnstone rivers, occurring in 43.2% and 17.9% of study locations, respectively (Table 1). The lower proportion reported for the Johnstone River reflects the greater number of sites at elevations >60 m.a.s.l. and this species is restricted to reaches below this altitude (Table 2). This species is not highly abundant contributing less than 1% of the total number of fish and biomass collected over the period 1994–1997. Moreover, this species is usually not highly abundant, with respect to density or biomass, in those sites in which it occurs (Table 1). Maximum densities of 1.7 fish.10m–2, and maximum biomass densities of 0.11 and 10.4 g.10m–2 have been recorded however [1093].
Parameter
Min. 2
1.04 Catchment area (km ) Distance to source (km) 2.5 Distance to river mouth (km) 8.1 Stream order 2 Elevation (m.a.s.l.) 10.0 Stream width (m) 2.9 Riparian cover (%) 0
Macro/mesohabitat use Allen [34] suggested that the preferred habitat of Glossogobius sp. 1 is clear streams close to the sea. This description fits the distribution of this species in the Wet Tropics region well (Table 2). We have recorded this species from a variety of streams below an elevation of 50 m.a.s.l. and at distances of 8.1 km to 68.8 km from the river mouth. Maximum abundances were recorded in sites located at about 31 m.a.s.l. and 31.5 km from the river mouth. Streams in which this species have been collected range from very small second order streams of about 3 m in width up to sixth order streams (i.e. the main river channel) where channel width approaches 25 m; however a comparison of the disparity between mean and weighted mean values indicate that Glossogobius sp. 1 is most commonly encountered in fourth order streams, moderately close to the river mouth and below an elevation of 25 m.a.s.l. Such streams tend to be of moderate gradient (approaching 1%).
Max.
Mean
W.M.
515.2 67.0 68.8 6 50.0 24.3 80.0
90.1 17.3 32.1 4.0 23.9 9.2 27.0
68.4 15.2 31.5 3.6 24.8 10.2 21.9
Gradient (%) Mean site depth (m) Mean site velocity (m.sec–1)
0.01 0.11 0
4.55 0.76 0.51
0.77 0.36 0.21
0.85 0.37 0.28
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
26 51 59 56 55 75 64
4.4 16.1 21.5 14.7 15.8 21.0 6.0
6.0 13.1 15.0 13.7 19.8 21.9 8.9
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (%) Root masses (%)
0 0 0 0 0 0 0 0 0 0
15.1 6.7 10.0 63.0 10.0 21.6 10.5 10.7 32.0 40.0
1.1 0.3 1.1 9.6 0.4 6.8 1.6 1.6 4.3 12.0
6.1 5.7 6.4 13.9 5.7 11.1 6.3 6.5 9.0 14.1
particle size with a tendency for larger particles (cobbles, rocks and bedrock) to dominate (Table 2). The extent to which this reflects a particular preference for these types of substrate or is related more to a preference for moderately flowing waters is unclear. However, larger particle-sized substrates may provide better cover for this species or this species may be more cryptic when viewed against such diverse substrates compared to uniform sand and fine gravel substrates (see comments about saddle-like markings above). Cover provided by various in-stream elements such as macrophytes or woody debris are frequently present in the habitats in which this species occurs. Cover tends not be highly abundant however.
Glossogobius sp. 1 may be found in streams with a wide range of riparian cover. In part, this reflects the effect of increasing stream size on the extent to which the riparian canopy encloses the stream channel, but the disparity between mean and weighted mean values for riparian cover suggests that this species is slightly more abundant in streams with an open canopy. Allochthonous food plays little part in the diet of this species (see below) but wellinsolated streams may support greater levels of primary and secondary production.
Microhabitat use Data derived from measurements at the point-of-capture for 82 fish were used to estimate microhabitat use by Glossogobius sp. 1 (Figure 1).
The mesohabitat of Glossogobius sp. 1 is best described as riffles or runs of moderate depth (0.3–0.4 m) and moderate current velocities (0.2–0.3 m.sec–1), although this species may occasionally be found in high gradient cascade-type habitats or sluggish, low-gradient pools. The preferred habitat is typified by a diversity of substrate
Glossogobius sp. 1 has been recorded over range of flows but the majority of fish were collected from areas with
436
Glossogobius sp. 1
the substrate. When disturbed, this species will quickly flee four or five metres away to seek refuge in the interstices between rocks and cobbles.
average flows of 0.1–0.3 m.sec–1 (Fig. 1a). This species is found in areas of a variety of depths also, up to about 80 cm (Fig. 1c). These data approximate the distribution of average depths and current velocities observed in sites in which this species occurs. Glossogobius sp. 1 is a benthic species, only rarely being observed not in direct contact with the substrate (Fig. 1f): as a consequence, the focal point velocities experienced by this species tend to be lower, to much lower, than the average current velocity. Capture records reveal that substrate use is broad (Fig. 1e) and comparable to the mean substrate composition estimated at the mesohabitat scale, with the exception of a possible avoidance of areas containing mud and silt. Although Glossogobius sp. 1 occurs in sites with moderate amounts of in-stream cover, little use is made of these elements (Fig. 1f). Most fish collected were associated with 30
(a)
Environmental tolerances Experimentally derived tolerance data are unavailable for this species and the summary listed below is based on instantaneous water quality information at 73 sites in which Glossogobius sp. 1 has been recorded in the Wet Tropics region. As such these data are a reflection of the ambient conditions in which this species occurs, not of its tolerance to extremes. Glossogobius sp. 1 occurs over a fairly narrow range of water quality conditions. The range of temperatures shown in Table 3 is typical of the seasonal variation that may be encountered in rainforest streams of the region. Similarly, the range in dissolved oxygen concentrations listed is typical of many such streams. These data suggest that Glossogobius sp. 1 may be intolerant of hypoxia, however the absence of streams subject to hypoxia across the entire range of sites sampled by us makes this suggestion a qualitative judgement only.
(b) 30
20
20
10
10
0
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c) 80
30
Table 3. Physicochemical data for Glossogobius sp. 1. Data summaries for fish collected from rainforest streams at 73 localities in the Wet tropics region over the periuod 1994–1997.
(d)
60
20
40 10
20
Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg/L–1) pH Conductivity (µS/cm–1) Turbidity (NTU)
18.5 5.5 5.13 6.1 0.3
Max. 29.7 14.4 8.38 65.6 12.2
Mean 23.3 7.11 6.85 34.7 1.6
0
0
The range of pH values across which Glossogobius sp. 1 has been recorded is also typical of streams of the region; the mean value is close to neutral however. Conductivity and turbidity values listed in Table 3 are indicative of very clear freshwaters. The maximum turbidity value recorded occurred immediately after a heavy downpour and was associated with liberation of sediments from a nearby banana plantation. Such high levels of turbidity tend to be short lived however.
Relative depth
Total depth (m)
(e)
(f) 60
20
40 10 20 0
0
Substrate composition
It must be emphasised that Glossogobius sp. 1 probably has a marine or estuarine larval phase: accordingly larvae and small juveniles must have a well-developed tolerance to elevated salinity levels. It is unknown whether this tolerance extends to adults also.
Microhabitat structure
Figure 1. Microhabitat use by Glossogobius sp. 1. Data derived from capture records for 82 fish from four rivers of the Wet Tropics region over the period 1994–1997.
437
Reproduction No information on the reproductive biology of this species is currently available. A marine larval phase may occur and
Freshwater Fishes of North-Eastern Australia
Trophic ecology The dietary summary upon which Figure 3 is based is drawn from a single study undertaken in the mid-dry season in the Mulgrave and Johnstone rivers [1096].
this would certainly correlate with the widespread distribution of this species. Figure 2 shows the length frequency distribution of 131 fishes collected at sites below 20 m.a.s.l. elevation compared to that of 108 individuals collected from sites at or above this elevation. Although the distributions are reasonably similar and very small individual (25–35 mm SL) are present both above and below 20 m.a.s.l., the presence of relatively more individuals smaller than 40 mm in length in the downstream, low elevation is consistent with the notion of a marine or estuarine larval phase. These data also suggest that upstream migration by small juveniles is comparatively rapid in some circumstances. It is not known whether adult Glossogobius sp. 1 migrate downstream en masse to spawn in estuaries or at sea or whether downstream movement is by eggs or larvae.
Glossogobius sp. 1 is a microphagous carnivore. The diet is dominated by aquatic invertebrates, mostly medium-sized insect larvae characteristic of flowing water and rocky substrata (e.g. Ephemeroptera, Trichoptera, Plecoptera and Pyralidae). Chironomid larvae contribute little (~3%) to the diet. Mouth size increases with increasing body size in this species, consequently fish are able to consume larger prey as they grow. The presence of macrocrustacea (caradinid shrimps and Macrobrachium spp.) and of fish in the average diet shown in Figure 3 is due to the presence of these items in the diet of large individuals (>70 mm SL) only. No terrestrial prey was recorded in the diet. Overall, the diet reflects both the meso- and microhabitat use of this species, being dominated by benthic invertebrates characteristic of running waters. The diet is similar to that of juveniles of Tandanus tandanus, Anguilla reinhardtii and Hephaestus grunters and of adult Glossogobius sp. 4, with which it is frequently syntopic. Nothing is known of the diet of larval or small juvenile Glossogobius sp. 1 or of the extent of seasonal variation in prey use.
Movement Little is known of this aspect of the biology of Glossogobius sp. 1 other than that suggested in the section above. 25
20
Conservation status, threats and management Glossogobius sp. 1 is classified as Non-Threatened [1353]. However, until this species is formally described and the extent of variation within the species across its range is known, this classification should be viewed as conditional.
15
10
5 Fish (3.4%) Macrocrustaceans (7.6%)
0
Unidentified (7%)
5
10
15
20
Standard Length (mm)
Aquatic insects (82%)
Figure 2. Length frequency distributions for Glossogobius sp. 1 collected below an elevation of 20 m.a.s.l. (solid bars) compared to those collected above this elelvation (open bars).
Figure 3. Mean diet of Glossogobius sp. 1. Data dereived from stomach contents analysis of 29 individuals collected from the Johnstone and Mulgrave rivers in August 1991.
438
Glossogobius sp. 1
levels. Flow supplementation may drown out riffle habits. Impoundments, when located close to the river mouth, are likely to interfere with the passage of larvae or juveniles given the high likelihood of a marine or estuarine larval phase in the life history. Such structures may also impact on adult fishes if they need to make spawning migrations to estuarine areas. Increased sedimentation resulting from poor land use is likely to lead to a reduction in the quality of habitat for invertebrate prey and hence impact on Glossogobius sp. 1 in the long-term.
Although the biology of this species remains very poorly documented, a number of potential threats to its continued presence in north-eastern Australia can be identified. These are primarily related to water use and the construction of impoundments, although poor land use may be a threat. The preferred habitat of Glossogobius sp. 1, runs and riffles with coarse substrates, are easily modified by changes in flow regime. Uncontrolled riparian extraction and upstream regulation both have the potential to reduce the quality and extent of such habitats by reducing water
439
Glossogobius aureus Akihito and Meguro, 1975 Golden goby
37 428148
Glossogobius giuris (Hamilton, 1822) Flathead goby
37 428151
Family: Gobiidae
Head large (32–35% of SL), and depressed (width and depth at posterior margin of preopercle: 14–17% and 16–19% of SL, respectively). Body roughly tubular in section posteriorly of pectoral fins (depth at origin of pelvic fins: 14–19% of SL; width at origin of pectoral fins: 16–19% of SL). The second, third and fourth spines of the first dorsal fin may be extended to form short filaments. Anterior nostril tubular, posterior nostril a pore. Eye relatively small (4–6% of SL). Maxilla terminating just posterior to anterior margin of eye in both sexes (12–14% of SL). Tongue bilobate. Head with numerous lines of prominent papilla, arranged in uniserial rows (Fig. 1) [28].
Description Glossogobius aureus First dorsal fin: VI; Second dorsal: I, 7–10; Anal fin; I, 7–9; Pectoral fin: 16–21; Vertical scale rows (in midlateral series): 29–34; Horizontal scale rows: 9–12 (usually 10); Predorsal scales: 22–27; Head scaleless except on nape; Gill rakers on first arch 8–11 [28, 52]. Figure: mature male, 61 mm SL, Normanby River, May 1991; 2003. Glossogobius aureus is a moderate-sized goby reaching 273 mm SL [28] in length but more commonly is much smaller. The type series examined by Akihito and Meguro [28] ranged in length from 33 to 273 mm SL (n =253), of which 50% were less than 100 mm SL. Allen et al. [52] list a much smaller maximum size of about 140 mm TL. Akihito and Meguro’s series contained 35 specimens from northern Australia, the maximum size of which was 157 mm SL, and of which only six specimens exceeded 100 mm SL. The maximum size in a sample of 43 individuals from the Normanby River was 80 mm SL [697, 1099] and that in a sample of 53 individuals from the Alligator Rivers region was 125 mm TL [193]. This species may not grow to large size in Australia. Bishop et al. [193] list the relationship between length (CFL in cm) and weight (in g) as: W = 0.0547L3.192; n = 53, r2 = 0.912, p<0.001.
Glossogobius aureus is grey-brown to tan in colour grading to pale tan or white ventrally; six dark brown/black saddlelike markings are present on the dorsal surface; five dark brown/black blotches are present on the midlateral surface, a sixth blotch may be located dorsally of the pectoral fin. A series of fine midlateral stripes is also present on the dorsolateral surface. The head tends to be uniformly grey/brown, often with three dark lines radiating caudoventrally from the posterior margin of the eye. The trivial and common names refer to a golden colour observed in South-East Asian populations [28]. The pectoral and pelvic fins are generally dusky to transparent
440
Glossogobius aureus, Glossogobius giuris
in colour, as is the anal fin. The dorsal fins are also dusky but grading to transparent near the margins. A black spot may be present on the fin membrane behind the sixth spine. A fine stippling concentrated over the spines and filaments gives both fins, especially the second dorsal, a fine barring pattern. This pattern is also evident on the caudal fin but more strongly expressed, with the lower half of this fin more darkly pigmented than the upper half. Colour in preservative: essentially the same as in life except colours faded to a light brown or tan [28].
between length (LCF in cm) and weight (g) as 0.0103L2.775, n = 278, r2 = 0.954, p<0.001. Note that this relationship predicts smaller weight for a given length than does the relationship given above for G. aureus. Glossogobius giuris has a colour pattern very similar to that of G. aureus except that the dorsal fins and caudal fin of the former have three to four diffuse horizontal bars, and five to six vertical bars, respectively, as opposed to a finely striated pattern. In addition, the membrane of the first dorsal fin may have a black spot between the first and second spines.
Glossogobius giuris Fist dorsal fin: VI; Second dorsal: I, 8–9; Anal: I, 7–9 (mostly 8); Pectoral: 17–22; Vertical scale rows: 29–35 (mostly 31–34); Horizontal scale rows: 9–11 (mostly 10); Predorsal scales: 14–24 (mostly 18–21): Gill rakers on first arch: 8–12 (mostly 10–12) [28].
Glossogobius giuris is very similar to G. aureus in both morphology and colour. The two species differ in the number of predorsal scales (fewer in G. giuris – see Fig. 1) and Akihito and Meguro [28] note that the fifth from upper most outer gill raker on the lower limb of the first gill arch in G. aureus has four to nine spines but that such spines are either lacking or few in number (one or three) in G. giuris. The two species are however most easily distinguished by differences in the arrangement of cephalic papillae (pit organs) lines (Fig. 1). All papillae lines are uniseriate in G. aureus. Note that Figure 1 is stylised and the arrangement of papillae in G. giuris is more complex than that represented here [447].
Glossogobius giuris is a large goby that may exceed 350 mm in length [46, 1064, 1241] and 0.1 kg weight [1241], but most commonly is much smaller [52]. Of the 255 specimens examined by Akihito and Meguro [28], the maximum size was 229 mm SL. Fifty-three Australian specimens of G. giuris were include in that study, the maximum length of which was 132 mm SL. Bishop et al. [193] recorded a maximum length of only 110 mm TL in a sample of 278 individuals, and list the relationship
Systematics Glossogobius aureus was first described by Prince Akihito and Meguro in 1975 [28]. The holotype is from the Okinawa Prefecture of Japan and paratypes (n =10) are from Thailand, Taiwan, the Philippines, Singapore and northern Australia. Previously, this species had been considered to be within G. giuris. Glossogobius giuris was first described as Gobius giuris by Hamilton in 1822 from material collected in the Ganges River [28]. Not unexpectedly, given its large range, there are numerous synonyms, including Gobius gutum Hamilton, 1822; Gobius russeli Valenciennes, 1837; Gobius catebus, Valenciennes, 1837; Gobius spectabilis Günther, 1861; Euctenogobius striatus Day, 1868; Gobius grandidieri Playfair, 1868; Eleotris laticeps De Vis, 1884 and Glossogobius tenuiformis Fowler, 1934 [28, 406]. Reference to this species as G. giurus is not uncommon. Distribution and abundance Both G. aureus and G. giuris are very widely distributed, with the range of the former species including the rim of the tropical western Pacific (including Japan, Taiwan, Philippines, the Indo-Malay Peninsula, Indonesia and New Guinea) and that of the latter species being the IndoWest Pacific including Africa, India, Pakistan, Bangladesh, Japan, Taiwan, the Indo-Malay Peninsula, Philippines, Indonesia and New Guinea [28, 52, 890].
Figure 1. Sensory papilla arrangement in Glossogobius aureus (top) and G. giuris (bottom). Redrawn after Akihito and Meguro [28].
441
Freshwater Fishes of North-Eastern Australia
The Australian distribution of G. aureus extends from the Kimberley region, across the Northern Territory to Cape York Peninsula [45, 52, 774]. Although widely distributed, this species does not appear to occur in high abundance [193, 620]. It has been recorded from the Nicholson, Gregory, O’Shanassy, Saxby, Leichardt, Flinders/Staaten and Norman rivers in the Gulf of Carpentaria region [28, 643, 1110] and the Mitchell, Coleman, Edward, Holroyd and Archer rivers of western Cape York Peninsula [571]. Its distribution on the eastern side of Cape York Peninsula is limited to the Olive [571] and Normanby rivers [28, 697, 1099]. These rivers (and the Pascoe River) frequently contain species more typical of rivers draining to the west. Wager [1349] lists an unconfirmed report of a Glossogobius species in the Georgina River. Hoese (cited as a personal communication in Unmack [1338]) believed all reports of a Glossogobius species in this river were attributable to G. aureus.
presence in these reaches indicates either a remarkable ability to ascend waterfalls (a not uncommon facility in gobies) or the existence of a landlocked population. This species has been recorded from streams on Hinchinbrook Island [851]. Further to the south, G. giuris has been recorded from the Black-Alice, Ross and Burdekin rivers in the Townsville region [28, 176, 1304], Rocky Dam Creek near Sarina [779], the Fitzroy [739], Calliope [331] and Burnett rivers [2] and from estuarine habitats of the Shoalwater Bay area [1328]. An unidentified species of Glossogobius was collected from the Burnett River also [827]. The most southern record for this species is the Noosa River [643]. Macro/meso/microhabitat use Allen et al. [52] list the habitat of G. aureus as clear to turbid freshwater streams and rivers with mud, sand or gravel bottoms, and that of G. giuris as clear to turbid freshwater streams with a sand, gravel or rock bottom. Skelton [1241] reported that the habitat of G. giuris in south African rivers included quiet sandy zones, backwater habitats and floodplain pans and that this species may penetrate hundreds of kilometres upstream in larger rivers. Bishop et al. [193] recorded juvenile G. giuris (minimum length 15–16 mm) predominantly in sandy corridor lagoons but also in sandy creek bed pools and escarpment main channel habitats in the Alligator Rivers region. Adults were more widely distributed occurring in sandy corridor lagoons, sandy creek-bed pools, muddy lagoons, floodplain lagoons and escarpment main channel habitats [193, 1416]. Sand was clearly the most dominant substrate type in these habitats. Macrophytes were moderately common and all fish collected were from such microhabitats. Glossogobius aureus was much less widely distributed in this river system, being recorded from a single floodplain lagoon and a tidal lagoon.
The Australian distribution of G. giuris is more extensive than that of G. aureus and includes the Pilbara and Kimberley region of Western Australia [28, 45, 52, 388], and most coastal rivers of the Northern Territory [193, 774, 1416]. This species has been recorded from the Nicholson, Gregory, Leichhardt and Flinders/Staaten rivers in the Gulf of Carpentaria region [643, 1110]. Glossogobius giuris has been recorded from the Mitchell, Ducie, Edward, Holroyd, Archer and Jardine rivers of western Cape York Peninsula [1110, 1349] but appears absent from rivers of eastern Cape York Peninsula with the exception of the Normanby, Annan and Endeavour rivers [599, 1349]. The distribution and abundance of this species may be temporally variable as the extensive CYPLUS surveys of Cape York Peninsula undertaken in the early 1990s did not record it in any river examined [571]. Glossogobius giuris is widely but patchily distributed in rivers of the Wet Tropics region but never reaches high abundance. A total of five specimens only was collected (all from the Bloomfield River) during an extensive survey of the region [1085]. Museum records indicate it present in the Daintree River and Saltwater Creek [28] but it was not detected in more recent surveys in these drainages [1085, 1185]. Abundance and presence may be temporally variable in the Wet Tropics region also. Other rivers in which this species has been recorded include the Barron [1187, 1228], Johnstone and Herbert rivers [643]. We have collected a single specimen only in the Johnstone River despite intensive survey work in this drainage over the last decade [1093]. The presence of G. giuris in the Barron River is notable, for it was recorded from the estuarine portion of the river plus freshwater reaches in Flaggy Creek and the middle stretches of the river downstream of Lake Tinaroo, both located above the Barron Falls. Its
Kennard [697] recorded G. aureus, ranging in size from 10–75 mm SL, from only one of six floodplain lagoons (~2% of total abundance) and two riverine sites (5.5% of abundance) in the Normanby River. These lagoon and river sites were located approximately 100 km upstream from the river mouth. The majority of G. aureus collected in this study were from depths less than 50 cm, in the lower 20% of the water column and associated with macrophyte beds if these were available, or with leaf litter and small and large woody debris if macrophytes were absent [697]. Glossogobius giuris may also penetrate far inland. In the Mitchell River drainage, this species occurs in the Walsh River subcatchment more than 300 km upstream of the river mouth. Similarly, the Burdekin River record for this species was from the Gorge Weir, approximately 130 km
442
Glossogobius aureus, Glossogobius giuris
conditions [890, 1147] and have been recorded in estuarine environments in Australia [1328].
upstream. This species may also occur in estuarine habitats in the adult form [1328], and elsewhere in its total distribution, is frequently found in these areas [890].
Reproduction The larvae of these species has a marine interval and adults migrate to the sea to breed [225]; in some areas the landward migration by larvae and recently metamorphosed juveniles forms the basis of very large fisheries [274, 890]. This species may be able to breed in freshwater however. Bishop et al. [193] found small juveniles (15–19 mm TL) of G. giuris in freshwater pools isolated for at least four months from the sea and other larger freshwater habitats, and speculated that reproduction may have occurred in these habitats. The presence of G. giurus in the upstream reaches of the Barron River may indicate spawning in freshwater also. This species spawns in freshwater and estuaries during the summer in South Africa [1241]. Recently metamorphosed juvenile G. aureus (10 mm SL) have been recorded from a floodplain lagoon of the Normanby River approximately six months after connectivity between the lagoon and the main river had ceased. Either these juveniles had migrated 100 km upstream into this lagoon and then ceased to grow over the following six months or spawning had occurred in freshwater during the dry season. Further evidence for freshwater spawning may be provided by the presence of G. aureus in the Georgina River, an endorheic basin.
Environmental tolerances The data presented in Table 1 represent ambient water quality conditions at sites in which G. aureus and G. giuris were present. Table 1. Physicochemical data for Glossogobius aureus and Glossogobius giuris. Summaries for G. aureus are based on water quality conditions for one floodplain lagoon site and three riverine sites [697] and a further four riverine sites [1093]. Summaries for G.giuris are based on water quality conditions in a range of aquatic habitats in the Alligator Rivers region [193]. Where parameters were measured in both the surface and bottom waters, values are presented for bottom layers only. Parameter
Min.
Max.
Glossogobius aureus (n = 8) Temperature (°C) 23.5 29.4 Dissolved oxygen (mg.L–1) 2.5 9.0 pH 6.5 8.2 Conductivity (µS.cm–1) 119 391 Turbidity (NTU) 3.3 8.6 Glossogobius giuris (n = 22) Temperature (°C) 23 35 Dissolved oxygen (mg.L–1) 5.2 6.8 pH 5.1 6.7 Conductivity (µS.cm–1) 6 36 Turbidity (cm) 360 1
Mean 25.9 6.2 7.2 198.1 5.0 29.7 6.3 6.2
Spawning by G. giuris was suggested to occur during the dry season in the Northern Territory [193]. Roberts [1147] reported that G. giuris in the Fly River, Papua New Guinea, was reproductively active from October to December [1147]. In the Philipinnes, fisheries catches of G. giuris larvae peak in September [274]. Maturation is rapid in G. giuris: gender is discernible by about 35 mm TL and stage IV gonads may be present in fish as small as 40 mm TL. This species is relatively fecund, producing between 1000 and 16 000 eggs (36 and 60 mm TL, respectively); the eggs are small (1.0 x 0.3 mm). The maximum female GSI value recorded was 6.25% [193]. Equivalent data are not available for G. aureus in Australia.
76
Both Glossogobius species occur in waters typical of northern Australia: fresh, moderately turbid and warm. The pH range recorded in the Alligator Rivers region is typical for the area [193]. The range in dissolved oxygen levels recorded for G. giuris is relatively narrow [193] and possibly indicates a preference for well-oxygenated waters. Similarly, the mean dissolved oxygen level recorded for G. aureus in the Normanby basin indicates use of welloxygenated habitats. The minimum value recorded for this species occurred in the Laura River at the beginning of the dry season and at which time it was uncommon. The general absence of G. aureus from floodplain lagoons in this catchment may be due to frequent hypoxia in these habitats.
Movement As for any species with a marine larval interval, movement between environments is a pronounced feature of the biology. Migration between the marine and riverine environment is apparently rapid, occurring over only a few days [890]. Bishop et al. [193] report an abrupt change in population size distribution of G. giuris between the early dry and mid-dry seasons due to the appearance of many small individuals between 17–30 mm TL in freshwater habitats of the Alligator Rivers region. These fish distributed widely in this system, even penetrating upstream into escarpment
The data presented in Table 1 indicate that both species are found in freshwaters. The larval phase of both G. giuris and G. aureus is known to occur in the marine environment [52, 890]. Migration into freshwater is apparently rapid [890] indicating substantial osmoregulatory ability. Adult G. giuris are known to tolerate fully marine
443
Freshwater Fishes of North-Eastern Australia
Glossogobius giuris feeds predominantly on aquatic macroinvertebrates, principally insect larvae and nymphs (Fig. 2). Large prey items such as macrocrustaceans and fish contribute about 5% only to the diet. Planktonic microcrustacea (mostly Cladocera) contribute almost 14% to the average diet. Microcrustacea are less important in the diet of G. aureus, in part reflecting the differences in habitat from which these summaries are derived (i.e. lagoons versus riverine channels). For example, microcrustacea contributed 5% of the diet of fish from lagoons of the Alligator Rivers region [193] but only 1.3% of the diet in fish from riverine habitats of the Normanby River [697, 1099]. Similarly, microcrustacea were more important in diet of G. giuris from floodplain lagoons than riverine sites [193]. The two species also differ with respect to the importance of large prey items such as fish and macrocrustacea (collectively comprising 13.3% in G. aureus). Fish comprised 17% of the diet of G. aureus from the Alligator Rivers region. The majority of fish included in this analysis were less than 100 mm SL, and it is probable that the consumption of fish and macrocrustaceans increases in importance with size. In South African rivers, juvenile G. giuris feed on benthic invertebrates and larger fish prey upon fish and tadpoles [16].
habitats, but were proportionally more common in sandy corridor waterbodies approximately 80 km upstream of the river mouth. Further dispersal throughout the basin occurred as fish matured but, as for juveniles, sandy corridor habitats remained the preferred habitat. It is evident from the data presented above concerning habitat choice that G. giuris may penetrate many kilometres upstream. This species has been observed trying to negotiate fishways [2, 586]. The movement biology of G. aureus is probably similar to that of G. giuris. Trophic ecology The dietary summaries presented in Figure 2 are based on three separate studies undertaken in northern Australia. The summary for G. giuris is based on Bishop et al. [193] for the Alligator Rivers region and includes data collected over a range of seasons. The summary for G. aureus includes data from the Alligator Rivers region collected over a range of seasons (n = 24) and data from the Normanby River collected in the early and late dry season (n = 20) [697] and the mid-dry season (n = 23) [1099]. Glossogobius giuris(n=93) Fish (4.4%)
Unidentified (5.5%)
The dietary summaries presented here are not greatly dissimilar to that of Glossogobius sp. 1 or Glossogobius sp. 4, and reflect the constraints of size and microhabitat use (i.e. a benthic habit) on prey use. It is notable however, that G. giuris consumes microcrustacea.
Microcrustaceans (13.9%)
Macrocrustaceans (1.1%) Other macroinvertebrates (6.6%)
Conservation status, threats and management Both G. giuris and G. aureus are listed as Non-Threatened by Wager and Jackson [1353] and both are probably secure across their Australian ranges. The absence of data on many aspects of their biology makes it difficult to assess the types and intensity of threats that may face these species in the future. They quite clearly require unimpeded access between marine/estuarine and freshwater environments, and barriers to movement (i.e. weirs, tidal barrages, sand dams) will impact negatively on population size and persistence in individual rivers. Structures intended to allow fish passage over such barriers (i.e. fishways and fish locks) need to take into account the very small size of migrating juveniles. Catchment based activities, such as riparian clearing and sediment loading that impact on stream invertebrates, their major food source, may affect these species also. Temporal variation in population size, which may be related to the vagaries of a marine dispersal phase, may mean that long-term impacts on population size may be difficult to detect.
Aquatic insects (68.5%)
Glossogobius aureus (n=67) Fish (7.3%) Microcrustaceans (2.5%) Macrocrustaceans (6.0%)
Unidentified (10%) Detritus (1.8%) Algae (0.7%)
Other macroinvertebrates (2.0%)
Aquatic insects (69.3%)
Figure 2. The average diet of Glossogobius giuris and Glossogobius aureus.
444
Glossogobius sp. 4 (after Allen et al. [52]) Mulgrave River goby
37 428315
Family: Gobiidae
black markings. Prominent posterior black spot, often ringed by vivid yellow border, on first dorsal fin; second dorsal and anal fin dusky with dark spots and often with intense orange border. Orange colour may also be present around throat and on belly in some specimens and may be associated with reproduction, otherwise pale brown to white. Pelvic and pectoral fins dusky. Colour in preservative: similar to that in life except yellow and orange pigments only weakly retained.
Description First dorsal: VI; Second dorsal: I, 10–11; Anal: I, 8–9; Pectoral: 16–17; Vertical scale rows: 29–31; Horizontal scale rows: 10–12; Head scaleless; Predorsal scales: 3–7; Gill rakers on lower limb of first gill arch: 6–7; Midline of belly scaleless [34]. Figure: male, 46 mm SL, Little Mulgrave River, October 1995; drawn 1999. Glossogobius sp. 4 is a small goby, rarely exceeding 50 mm. Maximum size of 489 individuals collected from fresh water over the period 1994–1997 was 60 mm SL with the median length being 41 mm SL. Only 14% of sample was less than 30 mm SL, with the minimum length being 16 mm. The relationship between length (SL in mm) and weight (g) is: W = 1.31 x 10–5 L3.087; r2 = 0.882, n = 121, p<0.001. Body elongate, tubular, only slightly laterally compressed; head depressed, but not as greatly as in other species within genus; cheeks bulbous with longitudinal rows of papillae; mouth extending back to eye, lips enlarged, snout blunt and rounded [34].
Systematics Glossogobius sp. 4 remains undescribed and has previously been referred to as Glossogobius sp. B [34, 936]. Distribution and abundance Glossogobius sp. 4 is restricted to a very small area of north Queensland: the Wet Tropics region. This species has been recorded from the Mulgrave and Russell rivers [1085] and a few short tributaries that drain into Trinity Inlet [1349]. Its presence outside of the Mulgrave/Russell drainage is relictual and provides strong supportive evidence for a previous northward flow of the Mulgrave River to discharge into Trinity Inlet during parts of the Pleistocene, as suggested by Willmott and Stephensen [1411]. This
Colour in life: body dusky brown with distinct reticulated pattern formed by darkened scale margins; series of large black spots (8–9) along side of body, posterior 2 often coalescing. Head generally darker than body, with irregular
445
Freshwater Fishes of North-Eastern Australia
ranging from small tributary streams to the main river channel. This species has not been recorded at elevations greater than 70 m.a.s.l. Although this species occurs in streams on the coastal plain within about 30 km of the river mouth, it is rare in the main channel at low elevation. It is most abundant in medium-sized streams with a moderate amount of riparian cover.
species was the 24th most abundant species in an extensive survey of the Wet Tropics region [1087]: given its restricted distribution, it was unlikely to ever be ranked highly however. Glossogobius sp. 4 may be locally moderately abundant, it was the sixth most abundant species over a range of 12 Mulgrave River sites sampled in 1991 [1096]. Glossogobius sp. 4 was the sixth most abundant species over a range of 48 Mulgrave/Russell River sites sampled over the period 1994–1997, ranked 20th in terms of biomass and was present in 26 of these sites [1093]. It was the fourth most abundant species by density and ninth by biomass at those sites in which it occurred. Mean and maximum densities of 0.482 ± 0.072 (15.1% of total density) and 1.13 individuals.10m–2 and mean biomass of 0.747 ± 0.141 g.10m–2 (4.3% of toal biomass) were estimated for those sites in which it occurred over the period 1994–1997 [1093], respectively.
Glossogobius sp. 4 is found in a variety of mesohabitat types but is rare in deep pools, isolated pools or backwaters and uncommon in reaches with substantial areas of glide habitat. This species is most abundant in rapid, riffle and run habitats with an average depth of 33 cm, moderately fast current speed, a diverse substrate composition dominated by cobbles and rocks, and little available cover except that provided by large substrate particles (Table 1).
Macro/mesohabitat use Glossogobius sp. 4 is widely distributed in the Russell/Mulgrave basin and occurs in a variety of habitats
(a)
Min. 2
0.5 Catchment area (km ) Distance to source (km) 2.5 Distance to river mouth (km) 32.0 Elevation (m.a.s.l.) 20 Stream width (m) 4.0 Riparian cover (%) 0
Max.
Mean
W.M.
515.5 41.0 64.0 70 35.0 90.0
82.7 13.7 48.7 45.7 15.2 39.9
82.9 14.4 51.5 48.8 17.3 33.5
Gradient (%) Mean site depth (m) Mean site velocity (m.sec–1)
0.02 0.10 0
3.46 0.77 0.51
0.69 0.37 0.19
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
5 51 73 35 55 76 67
1 8 23 13 19 32 6
0 5 20 13 19 34 9
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (%) Root masses (%)
0 0 0 0 0 0 0 0 0 0
18 4 2 0 2 49 3 2 4 8
1 0 0 0 0 10 0 0 0 0
0 1 0 0 0 7 0 0 0 0
40
20
30
15
Table 1. Macro/mesohabitat use by Glossogobius sp. 4. Summaries derived from 28 sites within the Russell/Mulgrave basin and a total of 489 individuals. Weighted mean (W.M.) estimated by weighting sites by abundance data. Parameter
25
(b)
20
10 10
5
0
0
Focal point velocity (m/sec)
Mean water velocity (m/sec)
(c)
80
(d)
30 60 20
40
10
20
0
0.75 0.33 0.23
0
Total depth (cm) 25
(e)
(f)
Relative depth
60
20 15
40
10 20
5 0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Glossogobius sp. 4. Data derived from capture records for 140 individuals collected from the Mulgrave/Russell drainage over the period 1994–1997.
446
Glossogobius sp. 4
Microhabitat use Although Glossogobius sp. 4. occurs most commonly in riffles and rapids, within these habitats this species occurs over a wide range of water velocities (Fig. 1a) and depths (Fig. 1c), inhabiting nearly all of the available habitat within the riffle environment with the exception of the most shallow margins. Glossogobius sp. 4 is a benthic species (Fig. 1d), most frequently found around and within the interstices (Fig. 1f) of coarse substrates (Fig. 1e) and consequently experiences water velocities much lower than the average water column velocity (Fig. 1b).
Reproduction Nothing is known about this aspect of the biology of Glossogobius sp. 4 except that fully gravid females have been collected from August to November, suggesting that spawning occurs during the dry season when flows are low and relatively stable. The presence of presumed nuptial colours in males during this period suggests that they actively guard territories and possible spawning sites (nests?). If so, eggs are probably attached to the underside of stones in nests. The limited distribution suggests that the entire life history occurs in freshwater.
Environmental tolerances Information on environmental tolerances is limited. Data presented in Table 2 is derived from field collections in streams of the Russell/Mulgrave drainage. Glossogobius sp. 4 usually occurs in sites of very high water quality. Water temperatures are typical of rainforest streams of the Wet Tropics region, with the highest value recorded in November at a time of very low flow. Dissolved oxygen levels reflect preference for riffle/rapid habitats and high water clarity is typical of the rainforest streams of this basin. Streams in which Glossogobius sp. 4 occur tend to have pH values near neutral and the small range (2.2 units) probably reflects the ambient distribution of pH values in this basin rather than a preference for near neutral waters. It is found in streams of very low water conductivity.
Movement Nothing is known about this aspect of the biology of the Glossogobius sp. 4. A marine interval is unlikely. It is unknown whether larvae require estuarine areas for development but the absence of very small individuals (<16 mm SL) in our collections suggests that larvae and juveniles do not develop in the same habitats occupied by adults. This aspect of the biology of Glossogobius sp. 4 requires investigation. The imposition of barriers to movement by larvae and juveniles may impact on this species. Trophic ecology The dry-season diet of Glossogobius sp. 4 was studied by Pusey et al. [1097]. The diet of this species is comprised almost entirely (93%) of the immature stages of aquatic insects typical of riffle habitats (Figure 2). Mayfly larvae were the dominant item (47%), followed by trichopteran larvae (21%) and chironomid larvae (16%). Odonate and
Table 2. Physicochemical data for Glossogobius sp. 4. Data summaries for fish collected from 27 sites within the Russell/Mulgrave basin over the period 1994–1997. Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity
17.2 5.6 6.20 13.3 0.42
Max. 26.8 11.4 8.43 46.5 2.40
Fish (1.0%) Terrestrial invertebrates (5.0%)
Mean
Unidentified (1.0%)
21.9 8.0 7.19 23.9 0.87
It is likely, given the data presented in Table 2, that Glossogobius sp. 4 would be relatively intolerant of poor water quality. For example, the maximum values for temperature and conductivity, and minimum dissolved oxygen levels, were recorded at the end of the 1994 dry season and at a time when abundance was lower than on other sampling occasions. Similarly, the high dissolved oxygen values recorded for this species are typical of riffle/rapid habits in which it is predominantly found. It is unlikely that this species has a highly developed tolerance to hypoxia. However, nothing is known of the actual tolerance of larvae, juveniles or adults.
Aquatic insects (93.0%)
Figure 2. The mean diet of Glossogobius sp. 4. Data derived from stomach content analysis of 99 individuals collected from the Mulgrave River in August 1991.
447
Freshwater Fishes of North-Eastern Australia
that it has a well-developed dependency on running water. Infrastructural development which reduces upstream and downstream availability of riffle habitats will impact strongly on this goby. Similarly, developments that degrade water quality are also likely to impact negatively on this species. Barriers to movement may impact negatively but further research is needed to determine whether larvae undergo development in downstream reaches or remain in the general vicinity of the natal habitat. Unregulated riparian extraction, especially during the dry season, is likely to impact negatively on this species by decreasing available habitat. Poor land use leading to the input of large amounts of sediment is likely to reduce food supply and habitat suitability (i.e. by a general reduction in particle size distribution and colmation of coarse substrates). It is likely that the eggs of Glossogobius sp. 4 are attached to stones and they would therefore be susceptible to smothering by silt. Effects due to fine sediments are likely to be exacerbated by the absence or reduced frequency of flows sufficiently large to remove fine sediments.
plecopteran nymphs, and pyralid larvae comprised the remaining 9% of the aquatic insect component. Small fish (<40 mm) consumed more chironomid larvae than did larger fish. Conservation status, threats and management Glossogobius sp. 4 is listed as Rare [1353] or Lower Risk–Near Threatened [117]. This species is generally well protected given that a large part of its distribution and habitat lies within the Wet Tropics World Heritage Area and the Wooroonoora National Park. However, a growing need for water in the Cairns district may place increasing pressure on some populations (e.g. those in Behana Creek). Channelisation and drainage works are severely degrading creek habitats in the Russell River drainage. Relictual populations in tributaries of Trinity Inlet are generally without protection and probably most at threat given the extent of urban development and stream modification currently taking place around them. Tilapia are established in many of Cairns’ urban drains and pose a real threat to the continued presence of this goby in the more urbanised areas of Cairns. The conservation value and management needs of the streams within the Cairns city limits has not been adequately assessed.
Finally, the absence of information on critical aspects of the biology of this species (e.g. movement, reproduction and environmental tolerances) makes effective conservation of this species difficult. It is unwise to assume that this species is secure simply because much of its habitat resides in World Heritage areas or in National Parks.
Glossogobius sp. 4 is a Wet Tropics endemic with a distribution within the region that is highly limited. The fact that this species occurs in streams of very high water quality and most frequently in riffles and rapids suggests
448
Redigobius bikolanus (Herre, 1927) Speckled goby
37 428244
Family: Gobiidae
situated in a tube, close to edge of upper lip. This species is sexually dimorphic: the mouth is much larger, and the cheeks more bulbous in mature males than in females. Males also have longer, cylindrical urinogenital papilla, whereas the papilla of females is broad and pointed [797]. Body colour may vary from location to location, but generally the body is a light brown or tan with irregular darker brown spots and blotches, faint brown bars present on head and cheeks, two well-defined bars extend slightly obliquely forward from the eye ventrally across lips of upper and lower jaws. A faint dark brown ocellus is present at base of caudal fin, often accentuated dorsally and ventrally to give the impression of two separate dark blotches. Dorsal and caudal fins spotted, caudal spotting may give the impression of faint barring, dorsal spots may be very dark. Anal fin dusky with four to five short brown bars located immediately above base (these bars are diagnostically important); pectoral and pelvic fins clear or slightly dusky. Colour in preservative: similar to that seen in life [46, 52, 797].
Description First dorsal fin: VI; Second dorsal: I, 6 or 7; Anal: I, 6 or 7; Pectoral: 15–17; Vertical scale rows: 26–28: Horizontal scale rows: 7; Predorsal scales: 6–8; Gill rakers: short, 7 or 8 on lower limb of first arch [46]. Figure: mature female, 26 mm SL, South Johnstone River, September 1995; drawn 2002. Redigobius bikolanus is a small goby rarely exceeding 40 mm SL, more commonly being less than 30 mm SL (e.g. 82% of a total of 908 fish from the Johnstone River were 30 mm SL or less). Of 24 specimens collected in the Brisbane and Albert rivers, south-eastern Queensland [1093], the mean and maximum lengths of this species were 25 and 31 mm SL, respectively. The relationship between length (SL in mm) and weight (g) for a sample of 68 individuals from the Johnstone and Mulgrave rivers is W = 6.37 x 10–4 L2.021; r2 = 0.868, p<0.001 [516]. Body cylindrical in cross-section becoming compressed posteriorly; body depth 26–31% of SL [46]. The head is relatively large, 33–38% of SL, snout blunt, mouth terminal, rounded maxilla reaching to middle of eye in females, extending well beyond eye in males. Anterior nostril
Systematics The genus Redigobius was erected by Herre in 1927 [573] to contain Gobius sternbergi Smith 1902 from the Philippines. The genus, which contains 44 nominal species 449
Freshwater Fishes of North-Eastern Australia
In addition, this species has been recorded from the Daintree River [643, 1185] and Saltwater Creek [1185], where it was recorded from 10/49 and 2/18 study sites, respectively. It occurs in the Barron River [1187], the Mulgrave-Russell River [1096, 1184] and the Johnstone River [1096, 1177]. Russell et al. [1184] found R. bikolanus to be uncommon in the Mulgrave/Russell River, recording it from only one site (from a total of 45). In contrast it is widely distributed in the Johnstone River [1177] where it was recorded from 12 sites in freshwaters (from a total of 58, not including those located on the Atherton Tablelands). This species occurred in streams located in the coastal uplands and lowlands. Pusey et al. [1096] similarly reported R. bikolanus to be more abundant in the Johnstone River (3/10 sites, fourth most abundant species) than in the Mulgrave River (3 of 12 sites, 19th most abundant species). More recent sampling in these river systems [1177] has revealed that R. bikolanus is indeed more widely distributed, more abundant and occurs at higher average density and biomass in the Johnstone River than in the Mulgrave River (Table 1).
from both freshwater and estuarine habitats, is distributed throughout the Indo-West Pacific. The genus is currently under revision and only 11 of the 44 nominal species may be valid. Redigobius bikolanus, as currently recognised, is a species complex, and more than one species may be present in Australia (H. Larson, pers. comm.). Synonyms of R. bikolanus are numerous and include Vaimosa bikolana Herre, 1927; Gobius flavescens De Vis, 1884 (primary homonym of Gobius flavescens Fabricius); Parvigobius emeritus Whitley, 1930; Vaimosa horiae Herre, 1936; V. osgoodi Herre, 1935; V. montalbani Herre, 1936; Pseudogobius bikolanus Aurich, 1938; Gobius johnstoniensis Koumans, 1940; Mahidolia pagoensis Schultz, 1943; V. novaehebudorum Fowler, 1944; Stigmatogobius minutus Takagi, 1957; and S. versicolor Smith, 1959. In south-eastern Queensland, Redigobius bikolanus cooccurs and may be confused with R. macrostomus (Günther, 1861), a species with which it is superficially similar in appearance (the latter species being distinguished most easily by the presence of five or six oblique reddish-brown bands from below the middle of the first dorsal fin to the caudal peduncle [460, 773]).
Table 1. Distribution and abundance data for Redigobius bikolanus. Data summaries for a total of 1037 individuals collected from the Johnstone and Mulgrave rivers of the Wet Tropics region over the period 1994–1997. Data in parentheses represent summaries for per cent abundance and rank abundance based on only those sites in which this species occurred.
Distribution and abundance Redigobius bikolanus, as currently recognised, is very widely distributed, occurring along the western margin of the tropical Pacific from Japan southward to the Philippines, Indonesia, New Guinea and northern Australia [37]. In Australia, this species is reported to occur from Shark Bay in Western Australia, across northern and eastern Australia, south to the Queensland–New South Wales Border [52]. Its distribution in northern Australia is uncertain however. We can find no record of this species in Queensland drainages of the Gulf of Carpentaria and western Cape York Peninsula, despite numerous surveys in this region (see Appendix 1 and 2).
Total % locations % abundance Rank abundance % biomass
Mulgrave River
Johnstone River
25.0
15.9
33.9
2.9 (9.4)
0.7 (3.5)
2.6 (10.6)
9 (4)
17 (6)
7 (4)
0.1 (0.4)
0.1 (0.2)
0.1 (0.5)
25 (21)
23
Rank biomass
28 (17)
Mean density (fish.10m–2)
0.54 ± 0.08
0.30 ± 0.09 0.59 ± 0.09
Mean biomass (g.10m–2)
0.19 ± 0.03
0.09 ± 0.02 0.21 ± 0.03
Redigobius bikolanus is widely distributed on the eastern Australian seaboard. It has been collected as far north as the Pascoe River [1099] in eastern Cape York Peninsula and has also been recorded from the Claudie, Starke and McIvor rivers [571], and the Normanby [697, 1099, 1349], and Annan rivers [571, 599, 1223]. Kennard [697] found R. bikolanus to be moderately abundant (5.9% of total electrofishing catch) in both riverine and floodplain lagoon habitats of the Normanby River.
Other studies undertaken in the Wet Tropics region have collected R. bikolanus from Liverpool and Maria creeks [1185], and the Moresby [1183], Tully [583] and Herbert rivers [584, 643].
Pusey and Kennard [1085] found R. bikolanus to be widely distributed in the Wet Tropics region, recording it in the Bloomfield River, Oliver-Noah Creek in the Cape Tribulation area, and the Daintree, Barron, Russell and Tully rivers. It was recorded from a total of 16 of 93 sites but accounted for only 0.7% of the total catch in this study.
In central Queensland R. bikolanus appears to be patchily distributed and relatively uncommon (although this may reflect a lack of intensive sampling in many of the smaller coastal streams in this area, together with the presence of numerous dams and weirs which may affect the penetration of this species into freshwater reaches). It is reported
450
Redigobius bikolanus
is weighted by abundance suggests a preference for open sunny reaches.
to be very common in the Ross River [466], forming schools of 60–90 individuals and is present throughout the entire length of the river. It is present but uncommon in the Burdekin River [1082]. Further south it is present but uncommon in the Pioneer River [1081] and in some short coastal streams near Sarina (Plane Creek and Rocky Dam Creek) [779] and Yeppoon (Water Park Creek) [533]. It is present but uncommon in the Fitzroy [659], Calliope [915] and Boyne rivers [1349], and Baffle Creek [826].
Redigobius bikolanus may occur over a wide array of substrate types ranging from those dominated by mud to those dominated by bedrock, but it is most abundant in reaches with fine particle-sized sediment (i.e. mud, sand and fine gravel). Table 2. Macro/mesohabitat use by Redigobius bikolanus in the Johnstone and Mulgrave rivers of the Wet Tropics region. Summaries derived from a total 276 individuals from 27 locations sampled over the period 1994–1997 [1093].
This species is patchily distributed and uncommon in south-eastern Queensland. It has been recorded from the Burnett River [237], Isis River (Burrum Basin) [7] and the Mary River [1095], but in low numbers and from few sites. It is also present in the Pine River [1349]. McKay and Johnson [907] list it as common in estuarine sections of the Brisbane River, and it has been recorded from the Albert [61, 1349] and Coomera rivers [1349]. Surveys undertaken by us between 1993 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected only 28 individuals from four sites in the lower Brisbane River (downstream of Wivenhoe Dam) and two sites in the lower Albert River. This species was the 21st and 25th most abundant species in this study with average densities of 0.27 + 0.06 (SE) and 0.09 + 0.04 fish.10m–2 for the Brisbane and Albert rivers, respectively [1093].
Parameter
Min.
0.3 Catchment area (km2) Distance from source (km) 1.5 Distance to river mouth (km) 10.1 Elevation (m.a.s.l.) 5 Order 1 Stream width (m) 2.9 Riparian cover (%) 0 Site gradient (%) 0.02 Mean depth (m) 0.23 Mean water velocity (m.sec–1) 0
Redigobius bikolanus has been recorded from a number of offshore islands, including Hinchinbrook [851], Fraser [77], Moreton [2605] and Stradbroke [1349] islands. Macro/mesohabitat use It is clear from the broad geographic range described above, and from the presence of this species in both lotic and lentic habitats, that R. bikolanus exhibits a broad range of habitat use. Within the Johnstone and Mulgrave rivers, R. bikolanus occurs across a broad spectrum of macrohabitat types ranging from small, first order streams at low elevation and close to the river mouth through to larger sixth order rivers (Table 2). This species may occur in relatively high-gradient streams distant from the river mouth and may occur over a very wide spectrum of riparian cover. The average and weighted average macrohabitat conditions for this species indicate that it is most abundant in reaches within medium-sized streams located within 30 km of the river mouth at an elevation below 25 m.a.s.l. Such streams tend to be of low to moderate gradient and the disparity between the arithmetic and weighted means suggests a further preference for even lower stream gradient. Such streams tend to be 10 m or less in width, about 0.40 m deep and have low to moderate water current velocities. Such streams are moderately well-shaded but the comparatively lower riparian cover when mean cover
Max.
Mean
W.M.
515.5 67.0 43.0 60 6 39.1 99.0
98.3 18.9 25.6 22.5 3.7 9.6 45.0
117.3 24.8 26.7 24.9 3.6 8.1 30.7
1.51 0.87 0.38
0.25 0.40 0.14
0.10 0.36 0.11
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 5 0 0 0 0
48 69 55 56 41 32 64
10.2 25.9 24.1 14.4 11.8 7.7 5.8
17.1 31.7 21.3 11.4 8.9 7.3 2.2
Aquatic macrophytes (%) Filamentous alga (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% of bank) Root masses (% of bank)
0 0 0 0 0 0 0 0 0 0
4.6 0.4 9 23 3 60 10.5 12.3 30 65
0.6 0.03 0.9 3.6 0.1 11.0 3.3 3.0 7.1 17.7
0.2 0.01 1.5 5.4 0.02 8.6 3.0 3.71 3.4 11.9
In-stream cover is not a dominant feature of sites in which R. bikolanus occurs in the Mulgrave and Johnstone rivers, although on occasion this species was found in reaches with abundant leaf litter and moderate amounts of submerged, overhanging and emergent vegetation. The generally close similarity between mean and weighted mean conditions does not indicate a well-developed preference for sites with abundant cover. Rather, the disparity between these habitat estimates suggests a slight preference for reaches with reduced amounts of undercut banks and bank-associated root masses. Such cover elements are
451
Freshwater Fishes of North-Eastern Australia
Microhabitat use Redigobius bikolanus most frequently occurs in areas of little or no flow and only very occasionally in water velocities greater than 0.3 m.sec–1 (Fig. 1a). Accordingly, and because of its benthic habit (Fig. 1d), the focal point velocity is also low (Fig. 1b). Over the range of sites examined by us this species was usually collected in water depths between 10 and 60 cm (Fig. 1c). Redigobius bikolanus was collected over a wide range of substrate types similar to that observed over the range of locations in which it was recorded (Table 2). By virtue of its benthic habit, this species was most frequently collected from within, or in contact with, the substrate. A large proportion of fish were collected from other forms of cover such as leaf-litter beds (28%), large woody debris (8%) and small woody debris
often used by large-bodied species that may predate on this small goby. In the rivers and streams of south-eastern Queensland R. bikolanus occurs in generally similar habitat conditions to those described above for northern Queensland populations. We collected this species only at low elevations (maximum 20 m.a.s.l.), and from brackish freshwatertidal areas in the Albert River, but up to 149 km upstream of the mouth of the Brisbane River (Table 3). These lowland sites were generally wide (up to 30 m stream width) and had low riparian cover. The mesohabitats in which this species most commonly occurred were runs of moderate depth (around 0.5 m) and flow (weighted mean velocity 0.24 m.sec–1), with relatively coarse substrates (coarse gravel, cobbles, rocks and bedrock). This species is most abundant in mesohabitats with fine substrates (sand and gravel) and small amounts of aquatic macrophytes, root masses and undercut banks.
60
(a)
80 60
40
Table 3. Macro/mesohabitat use by Redigobius bikolanus in the Brisbane and Albert rivers, south-eastern Queensland. Data summaries for 28 individuals collected from samples of nine mesohabitat units at six locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
40 20
20 0
0
Focal point velocity (m/sec)
Mean water velocity (m/sec)
Parameter
Min.
712.6 Catchment area (km2) Distance to source (km) 95.0 Distance to river mouth (km) 28.0 Elevation (m.a.s.l.) 0 Stream width (m) 7.5 Riparian cover (%) 0 Gradient (%) 0 Mean depth (m) 0.22 Mean water velocity (m.sec–1) 0
Max. 9734.3 260.5 149.0 20 30.0 64.5 0.83 0.92 0.66
Mean
(c)
W.M.
25
5986.5 7137.1 178.3 199.8 95.1 109.2 12 14 20.3 23.9 21.7 14.8
20
80
15
60
10
40
5
20
0
0
0.11 0.58 0.17
0.05 0.49 0.24 30
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobbles (%) Rocks (%) Bedrock (%)
0 0 2.3 3.8 0 0 0
35.0 64.2 23.6 40.7 45.7 42.9 76.0
8.3 20.2 10.7 21.8 20.3 6.7 12.1
6.8 6.6 7.8 24.0 26.8 11.1 16.8
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (%) Root masses (%)
0 0 0 0 0 0 0 0 0 0
34.9 13.1 5.3 7.4 9.9 15.2 13.0 11.9 35.0 34.2
6.3 2.0 1.8 3.2 2.7 5.5 5.6 4.7 15.9 17.9
11.1 3.7 1.3 3.6 4.6 3.2 2.4 2.4 10.9 12.7
(b)
100
(e)
Total depth (cm)
(d)
(f)
Relative depth
30 20 20 10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Redigobius bikolanus in the Johnstone and Mulgrave rivers. Summaries derived from capture records of 433 individuals collected over the period 1994–1997.
452
Redigobius bikolanus
(11%); these microhabitat elements were not overly abundant in the sites in which these species occurred (Fig. 1f and Table 2), suggesting that R. bikolanus preferred these types of microhabitat.
This species may be intolerant of levels lower than this, as lagoons characterised by lower levels of dissolved oxygen did not contain R. bikolanus. However, the estimates of dissolved oxygen concentration listed in Table 4 were taken 50 cm below the water’s surface and a marked reduction in saturation was evident below this depth in most lagoons [697]. Thus, this species may be more tolerant than these data indicate. The extent to which populations from different regions or habitats are equally tolerant is unknown.
The pattern of microhabitat use depicted in Figure 1 closely resembles that described by Kennard [697] for R. bikolanus in floodplain lagoons of the Normanby River. Over 70% of all fish collected (n = 99 individuals) in these habitats were from depths less than 50 cm, all were located in the lower one third of the water column and most (~85%) were collected in the near vicinity of submerged wood, leaf litter and aquatic macrophytes.
A substantial range in the tolerated pH is evident in Table 4 (3.7 pH units). Redigobius bikolanus is, based on the data presented, clearly a freshwater species. However, this species has been recorded from estuarine and brackish waters [52, 1177] and its tolerance to elevated conductivities is undoubtedly high, like many gobies. This species is apparently able to tolerate high levels of suspended sediment for at least short periods of time (the high value recorded for the Wet Tropics region was recorded after a heavy downpour and was transitory) but appears to be found more frequently in relatively clear streams.
Environmental tolerances As for many species of Australian fishes, there are no data concerning the environmental tolerances of R. bikolanus. The data presented in Table 4 represents the ambient water quality conditions existing in sites containing this species. Accordingly, the usual caveats apply as to the extent to which these data translate into upper and lower tolerance limits. Table 4. Physicochemical data for Redigobius bikolanus. Data presented are derived from Kennard [697] for floodplain lagoons of the Normanby River (n = 7 samples), for 57 samples in the Mulgrave and Johnstone rivers of the Wet Tropics region and eight samples from the Brisbane and Albert rivers, south-eastern Queensland [1093]. Parameter
Min.
Max.
Normanby River floodplain (n = 7) Temperature (°C) 23.9 29.4 Dissolved oxygen (mg.L–1) 2.3 7.1 pH 6.1 8.2 Conductivity (µS.cm–1) 98 391 Turbidity (NTU) 2.9 8.6 Wet Tropics region (n = 57) Temperature (°C) 17.5 29.7 Dissolved oxygen (mg.L–1) 5.51 8.81 pH 4.5 7.9 Conductivity (µS.cm–1) 6.0 65.6 Turbidity (NTU) 0.33 22.1 South-eastern Queensland (n = 8) [1093] Temperature (°C) 11.7 27.0 Dissolved oxygen (mg.L–1) 4.8 9.2 pH 7.4 8.1 Conductivity (µS.cm–1) 249.2 1035.7 Turbidity (NTU) 1.5 14.5
Reproduction Very little is known of the reproductive biology of this species. Merrick and Schmida [936] citing Herre [573] state that R. bikolanus breeds in freshwater in the Philippines. The presence of this species 160 km upstream (and upstream of the barrage) in the Fitzroy River [659] also suggests it is capable of completing its life cycle in freshwater. Kennard [697] recorded a small number of juvenile R. bikolanus between 10 and 15 mm SL in offchannel floodplain lagoons of the Normanby River during the late dry season, suggesting that spawning had occurred in these freshwater habitats during the dry season. An alternative explanation for their presence other than in situ reproduction is difficult to support given that these waterbodies were isolated from the main river channel for up to nine months. Landlocked populations are reported to be present in an impoundment in the Brisbane River basin, further suggesting the ability of this species to breed in freshwater [663]. Leggett and Merrick [797] gave an account of aquaria spawning by this species [797]. Females were reported to breed at 22 mm and males at 25 mm. More than 1000 eggs were laid over a six-hour period in a patch on the upper surface of a cave. Eggs hatched in 7–12 days, with 500–800 very small larvae hatching from each egg patch. Larvae were observed to remain near the water surface and survived for only 4–5 days without correct food [797]. Fish in aquaria are also reported to establish territories but do not often fight [466].
Mean 27.2 5.3 7.4 181.7 5.6 22.9 6.95 6.66 37.6 2.46 21.3 7.8 7.7 441.2 5.1
Redigobius bikolanus has been recorded from warm-water streams and lagoons, as expected from its tropic distribution. In general, such habitats are moderately welloxygenated, the lowest level recorded being 2.3 mg.L–1.
Despite these indications of an entirely freshwater life history, the wide distribution of this goby alternatively
453
Freshwater Fishes of North-Eastern Australia
eggs or larvae is followed by a return upstream migration. A lateral movement into off-channel floodplain habitats is suggested by the work of Kennard [697]. Few R. bikolanus have been detected in studies examining the efficacy of fishway structures (three individuals collected at the bottom of the fishway on the Mary River barrage [158] and one individual at the bottom of the barrage on Tinana Creek [159]) and it is unlikely therefore that any upstream migrations involve large numbers of individuals. However, such studies have been conducted almost entirely in the southern portion of Queensland where R. bikolanus is uncommon. Moreover, the small size of this goby may make sampling difficult.
suggests an estuarine or marine larval interval, in common with many other widespread gobies. Moreover, comparison of the size distribution of R. bikolanus populations at different locations in the Johnstone River reveals that small individuals are more common in downstream sites (<12 km from the river mouth) whereas large individuals are more common in upstream sites (>26 km from the river mouth) (Fig. 2). These data strongly suggest that larvae and juveniles inhabit the lower reaches of Wet Tropics rivers after a brief marine or estuarine larval interval and migrate upstream as they mature. 160
Trophic ecology Information on the trophic ecology of R. bikolanus summarised in Figure 3 is drawn from three separate studies in northern Queensland. The first [1097] was undertaken during the mid-dry season in the Mulgrave and South Johnstone rivers (n = 43), the second [697] in floodplain lagoons of the Normanby River during the early and late dry seasons (n = 70), and the third [1099] in the Normanby and Pascoe rivers during the mid-dry season (n = 11). Note that this summary contains no dietary information for the wet season and that the total sample contains fish from both lotic and lentic samples (although in roughly equal numbers).
120
80
40
0 3
6
9 12 15 18 21 24 27 30 33 36 39 42
Standard Length (mm)
Redigobius bikolanus is a microphagous carnivore that consumes also small amounts of vegetable matter. Aquatic
Figure 2. Size distribution of Redigobius bikolanus populations located close to the river mouth (solid bars, n = 505) and distant from the river mouth (open bars, n = 402) in the Johnstone River.
Terrestrial invertebrates (0.8%) Microcrustaceans (6.9%)
Unidentified (3.7%) Detritus (1.8%) Algae (4.1%)
It should be noted that the variation in apparent reproductive mode described here may in fact be due to the presence of more than one species (see Systematics section). Helen Larson (pers. comm.) suggests that an additional, diminutive species, currently grouped within the Redigobius bikolanus species complex, may occur in northern Australia. Some of the very smallest individuals (12–18 mm) included in the downstream sample in Figure 2 were reproductively mature at the time of collection; such individuals may belong to this putative dwarf species. Resolution of the systematics of this species complex will greatly assist in understanding the reproductive biology of this species. Movement There is no quantitative information on movement for R. bikolanus although the data above suggests the movement pattern of this species may be classified as facultative amphidromy, whereby passive downstream movement by
Aquatic insects (82.4%)
Figure 3. The average diet of Redigobius bikolanus. Summary based on stomach content analysis of 125 individuals from Cape York Peninsula and the Wet Tropics region (see text for details).
454
Redigobius bikolanus
species is probably secure, however further resolution of the taxonomy and systematics of this species may reveal the presence of taxa of limited distribution that face unique threats or pressures. The absence of data on many aspects of this species’ biology makes inferences about management requirements or potential threats tenuous. For example, an understanding of movement biology is needed to predict what impact barriers to movement may have on its distribution and abundance within river systems. Similarly, absence of information on the reproductive biology of R. bikolanus precludes an assessment of the effects of changes in flow regime or the operation of water storages. The apparent preference by riverine populations for moderately shallow, low gradient streams with low to moderate water velocities may make this species sensitive to habitat changes associated with flow supplementation (i.e. drowning out of riffles and runs) and water abstraction (i.e. loss of riffle and run habitat). Processes that modify preferred in-stream cover elements such as leaf-litter beds, small to large woody debris, aquatic macrophytes, root masses and undercut banks may also impact on R. bikolanus.
insect larvae, dominated by (primarily chironomid midge larvae and trichopteran nymphs), are the dominant prey class. Vegetable matter (detritus and algae) comprises only a small proportion (5.9%) of the overall diet but made up almost 10% of the diet of R. bikolanus on the Normanby River floodplain. Microcrustacea were absent from the diet of riverine fish from the Wet Topics region, but contributed 12% to the diet of fish from floodplain lagoons of the Normanby River, and 2% to the diet of fish from the Pascoe and Normanby River proper. Despite the small size of R. bikolanus, which greatly constrains its choice of prey, this species shows substantial plasticity in diet, enabling it to consume vegetable matter and to switch between microcrustacea and insect larvae. It would be informative to know the extent of dietary change during the wet season. Also of interest is the extent to which sexual dimorphism in mouth size allows any sexual divergence in prey choice, a potentially important factor given the degree to which small size limits this species’ choice of prey. Conservation status, threats and management Redigobius bikolanus is listed as Non-Threatened by Wager and Jackson [1353]. Given its wide distribution this
455
Awaous acritosus Watson, 1994 Roman-nosed goby
37 428061
Family: Gobiidae
in males), slightly longer dorsal and anal fins, more teeth and slightly longer upper jaw in males [1365]. Colour in life generally brown to light tan/yellow, scale margins dark. A series of irregular dark brown blotches present on dorsal surface and a series of mid-lateral dark brown to black square blotches present along sides. Dorsal fins with or without a series of fine dark horizontal bars, fine vertical bars present on caudal fin. Dark blotch located at anterior base of first dorsal fin. Anal fin translucent to dark but generally with a whitish margin. Ventral surface white to pink. Two dark bars running obliquely from under eye to upper jaw and extending partially onto lip. Two horizontal bars also present on head, one running from just behind and below eye to midway along opercula, second running from below anterior margin of eye through cheek to posterior margin of opercula. Colour in preservation essentially the same as above except colours tend to be less vivid. Watson specifically notes that sexual dichromatism is not apparent, at least in preserved specimens [1365]. However, captive male specimens do develop intense bluish-black colouration of the head and aggressive encounters increase in frequency when so coloured [1093]. This species could possibly be confused with other gobies within the genus Glossogobius if observed but not collected, otherwise almost impossible to confuse identification.
Description First dorsal fin: VI; Second dorsal: I, 10–11 (the 19 specimens examined by Watson [1365] all had only 10 dorsal rays but some specimens such as the one depicted above have 11); Anal: I, 10 origin opposite that of second dorsal; Pectoral: 16–17; Vertical scale rows: 56–62; Horizontal scale rows: 14–17; Predorsal scales: 18–24 (along midline); Opercular scales: 0–8, cheek naked. Figure: 106 mm SL, Behana Creek, Mulgrave River, August 1995; drawn 1996. Awaous acritosus commonly attains 100–180 mm in length [1365, 1366] but may attain a length of 300 mm [755]. Specimens less than 60 mm in length are uncommonly collected in freshwater habitats although one 40 mm specimen included in type series was from freshwater (Cooper Creek, Daintree River) [1365]. The relationship between length (SL in mm) and weight (g) is described by W = 4.73 x 10–6 L3.317; r2 = 0.962, n= 10, p<0.001 [1093]. Scales small, may be cycloid or ctenoid depending on location. Distinct groove between upper lip and snout, snout rounded and mouth sub-terminal. Gill rakers on outer arch rudimentary. Elaborate arrangement of cephalic pores and sensory papillae on head. Eyes small and dorsally positioned. Transverse profile almost tubular. Sexual dimorphism limited to differences in shape of genital papilla (pointed 456
Awaous acritosus
with the exception of the Mowbray [1185] and Moresby [1183] drainages. In all likelihood, this species also occurs in these rivers.
Systematics Awaous acritosus is a member of the Awaous subgenus [1365] of the genus Awaous which is widely distributed throughout the Pacific and northern Indian Ocean [1364]. The Awaous species present in Australia and southern New Guinea has long been regarded as A. crassilabrus (Günther 1861). However, this name is a junior synonym for A. guamensis Valenciennes 1837 [1364]. Allen [37] was the first to recognise that the Australian species was an undescribed taxon. Watson speculated that A. acritosus was most closely related to A. personatus (Bleeker 1849) from western Indonesia, and an undescribed form from Borneo and the Phillipines [1364]. Watson [1366] considered the genus to be ancient and possibly in existence since the Cretaceous.
Although widely distributed and frequently encountered in the Mulgrave and Johnstone rivers, Awaous acritosus rarely reaches high levels of abundance or biomass (Table 1). Abundance and density may be substantially underestimated if surveys are based on a single electrofishing pass [599, 1107]. Up to four passes are often required to collect all specimens within an area due to rapid swimming ability and propensity to bury when alarmed. Stunned fish remain buried. Table 2. Macro/mesohabitat use by Awaous acritosus. Summaries derived from a total of 40 sites within the Mulgrave/Russell, Johnstone and Tully rivers sampled over the period 1994–1997, and a total of 147 individuals.
Distribution and abundance Awaous acritosus ranges from the Wet Tropics region north along the east coast of Cape York Peninsula in Australia to southern New Guinea. The southern limit in Australia appears to be the Herbert River [584], although it may have once occurred in the Pioneer River [1081], and the northern Australian limit appears to be the Pascoe River [571]. The New Guinean distribution is limited to the Laloki River drainage [167] and streams of the Port Moresby district [37]. This species has not been recorded from the western side of Cape York Peninsula [571]. Pusey and Kennard [1087] found this species to be widespread in the Wet Tropics region occurring in seven of 10 basins examined but contributing only 0.5% of the total number of fish collected. Subsequent surveys in this region have found this species to occur in all basins from the Annan River to the Herbert River [584, 1177, 1179, 1185, 1223]
Parameter 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Stream order Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
% locations % abundance Rank abundance % biomass
Mulgrave River
Johnstone River
44.1
50
26.8
0.8 (3.8)
1.6 (3.6)
0.6 (4.0)
20 (6)
12 (6)
22 (6)
0.8 (5.9)
1.3 (6.7)
0.7 (5.2)
9 (6)
10 (6)
Rank biomass
11(6)
Mean density (fish.10m–2)
0.15 ± 0.02
0.20 ± 0.04 0.09 ± 0.02
Mean biomass (g.10m–2)
2.80 ± 0.42
3.87 ± 0.73 1.75 ± 0.36
Max.
Mean
W.M.
0.8 2 12 1 10 2.9 0
515.5 67 64 6 80 35 80
73.6 15.1 34.7 3.9 32 10.1 30.9
62.1 13.8 30.2 3.8 29.6 9.6 24.1
Gradient (%) 0 Mean depth (m) 0.11 Mean water velocity (m.sec–1) 0
Table 1. Distribution, abundance and biomass data for Awaous acritosus in two rivers of the Wet Tropics region. Data summaries for a total of 284 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. Total
Min.
4 0.76 0.45
0.68 0.37 0.15
0.57 0.36 0.14
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48 52 59 52 55 53 97
6.5 17.0 22.5 13.2 15.1 17.0 8.7
9.9 19.9 22.7 12.5 12.5 13.7 8.7
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
18 5 3 22 2 30 6 9 4 6
0.9 0.3 0.2 0.9 0.1 7.2 1.3 1.3 1.3 0.6
0.3 0.1 0.1 1.8 0.1 7.1 1.5 1.3 0.7 0.1
Macro/mesohabitat use Within the Wet Tropics region, this species has been recorded from locations spanning a considerable range of macrohabitat conditions (Table 2). Awaous acritosus has been recorded from first to sixth order streams: they are, however, most commonly encountered in streams located
457
Freshwater Fishes of North-Eastern Australia
Microhabitat use Awaous acritosus most commonly occurs in areas with water velocities between 0.1 and 0.4 m.sec–1 (Fig. 1a) although its benthic habit (Fig. 1d) ensures that the water velocities that are actually experienced are generally lower (Fig. 1b). This species occurs over a wide range of depths but appears to avoid depths less than 20 cm and depths greater than 90 cm. Although mesohabitat data indicates that it may occur in stream reaches with a variety of substrate compositions, A. acritosus is most commonly collected over areas of sand and fine gravel (Fig. 1e), reflecting its feeding habit (see below). This species is occasionally collected from areas over cobble, rocks and bedrock also. Its benthic habit ensures that it is most frequently encountered associated with the substrate (Fig. 1f). The interstices of large substrate particles are used as cover when alarmed but it relies more frequently on its powerful swimming ability (which appears limited in duration) to escape. When encountered over a sand and fine gravel substrate, escape behaviour is initiated by a short swimming burst (3–10 m) ending in a rapid dive into the substrate where it remains buried. This species occasionally makes use of other cover elements.
below 80 m.a.s.l. elevation and within 40 km of the river mouth (Table 2). Such streams tend to be of moderate gradient (mean = 0.82%), but occasionally may be much steeper (maximum = 4.0%), and with an intact riparian canopy. This species is most frequently found in riffle and run habitats (19 and 49% of all sites in which A. acritosus was encountered were qualitatively classified as riffles and runs, respectively). Average depth and water velocity of sites in which present was 0.37 m and 0.15 m.sec–1. The average substrate composition of sites in which A. acritosus recorded tends to be varied although there is an evident slight preference for mesohabitat with fine sediment particle sizes. This species may also be found in high gradient areas with bedrock substrate when flows are reduced. The habitats in which this species occurs are notable for the small amounts of cover they contain. 40
(a)
40
30
30
20
20
10
10
0
0
Environmental tolerances No quantitative data is available on lethal limits for this species. The data listed in Table 3 indicate that it is found over a moderate range of water quality. Awaous acritosus has not been collected by us in streams with a water temperature of less than 18°C, suggesting that its lower tolerance limit may not extend to below about 15°C. The upper temperature tolerance is unknown: the maximum value in Table 3 was recorded in January during very low flows. Egress from this site was possible and fish were not confined; A. acritosus therefore tolerates temperatures of at least 32°C. Awaous acritosus has been recorded from the Pascoe and Stewart rivers of Cape York Peninsula during August when water temperatures were between 24.5 and 28.7°C [1093]; much higher water temperatures are to be expected for rivers of this region during summer [697]. This species appears to be generally restricted to welloxygenated streams. Hogan and Graham [583] collected it in lagoons on the Tully-Murray floodplain (16 lagoons sampled) and these habitats frequently become hypoxic. However, it was not recorded from the most hypoxic lagoons and was restricted to those with an oxygen content of 4.58 mg O2.L–1 or more. It should be noted that these data are spot records only and lower levels of dissolved oxygen may have transiently occurred in these lagoons during periods of peak plant respiration. Nonetheless, this species probably prefers well-oxygenated waters. The pH of sites in which this species occurs tends to be about neutral with a range of 2.34 units. Conductivity in streams
Focal point velocity (m/sec.)
Mean water velocity (m/sec.) 30
(b)
(d)
(c) 60
20 40 10
20
0
0
(e)
Total depth (cm)
Relative depth
(f)
40
60
30
40
20 20
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use of Awaous acritosus from the Johnstone and Mulgrave rivers. Summaries derived from capture records from 77 individuals over the period 1994–1997.
458
Awaous acritosus
time within a spawning season. Data presented in Watson [1365] for A. acritosus indicate that gender was distinguishable at a similarly small size but it is unknown whether gender was ascertained by reference to the structure of the genital papilla or by internal examination. The larvae of A. guamensis hatch in a undeveloped state and are swept out to sea where they undergo an obligate marine planktonic interval of up to 160 days duration [492]. Other Awaous species (and many other freshwater gobies) have a planktonic larval phase [1366]. Obviously, much research is needed to determine whether reproduction in A. acritosus is similar to that described above.
supporting A. acritosus is generally very low over the range of Wet Tropics streams examined. Higher conductivities have been recorded in rivers of Cape York Peninsula (93–104 µS.cm–1), nonetheless these values are also very low. Larval and juvenile tolerances are unknown but likely to be much higher than for adults. This species has been recorded from streams with very high turbidity levels, however the maximum value listed in Table 2 was recorded during runoff event and high turbidity was limited in duration. Awaous acritosus is generally found in clear streams. Table 3. Physicochemical data for Awaous acritosus. Data summaries for fish collected from 81 sites within the Wet Tropics region over the period 1994–1997. Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
18.4 5.33 5.76 6.03 0.34
Max. 32.7 11.40 8.10 67.6 21.7
Movement Little quantitative data is available concerning the movement patterns of this species. However, it is very likely that it is an amphidromous species with the larvae spending some time in marine environments. This species may make a downstream spawning migration as observed in other Awaous species. Changes in the abundance of Awaous acritosus over time at some study sites in the Johnstone River suggest that this species may move further upstream at times of low flow to feed on deposited detritus and periphyton.
Mean 23.9 7.22 7.16 33.4 5.0
Reproduction Little is known about the reproductive biology of this species but details may be speculatively surmised by comparison with other species within the genus [37], particularly A. guamensis, for which substantial data exist [492]. This species spends nearly all its adult life in fresh water and seasonally migrates downstream to the riffle closest to the river mouth (yet still in fresh water) to spawn. Migrations may be stimulated by elevated flows. This behaviour may be unique to A. guamensis as Ha and Kinzie [492] could find no other reports of adult migratory movements in this genus. Spawning occurs from August to December [492], the period during which elevated flows occur [717]. Males maintain and defend territories during this period and high mortality is experienced over the spawning season. Disparity between the number of dead fish after spawning and the number of fish on a spawning ground, combined with observations of captive spawning do not, however, support an inference of a semelparous life history. Many thousands (100 000–400 000) of small demersal eggs (about 0.3 mm) are deposited in a monolayer within a nest guarded by the female. Egg predation by Kuhlia sandvicensis (a relative of the jungle perch) is pronounced in unguarded nests. GSI values during the spawning season range from about 4 to 14.5% for females and 0.75 to 4.0% for males. Gonad maturation commenced at a small size (42 and 46 mm for females and males respectively) but most reproductive fish were above 70 mm SL. Not all females mature at the same
Trophic ecology Awaous acritosus feeds predominantly on aquatic plant matter comprised almost completely of diatoms and desmids but including some filamentous algae (Fig. 2). Detritus is an important dietary item also but it is Algae (38.0%)
Unidentified (24.2%)
Detritus (21.0%) Aquatic insects (16.8%) Figure 2. Mean diet of Awaous acritosus. Data for 50 individuals from two studies (17 individuals from the Mulgrave and Johnstone rivers [1097] and 33 individuals from the Pascoe and Stewart rivers [1099]).
459
Freshwater Fishes of North-Eastern Australia
Conservation status, threats and management Awaous acritosus is listed as Non-Threatened [1353] (but as A. crassilabrus) and is probably secure over its range. Without further information on the reproductive biology of this species, it is difficult to determine what its exact overall management requirements might be. However, two factors appear of importance. First, it is extremely likely that A. acritosus has an obligate marine larval interval and therefore any changes to flow regimes or the imposition of barriers to movement that interferes with the passage of newly hatched larvae downstream or the passage of juveniles upstream to the adult habitat will impact on population viability. Such an impact may be affected over a relatively short time span, perhaps three to four years. Juveniles moving back into freshwater environments may be small (<40 mm) and may therefore be weak swimmers. Second, processes that interfere with the development of periphytic algal growth on small substrate particles, such as sedimentation during low flow events or physical disturbance during high flows, may interfere with the ability of A. acritosus to feed effectively.
unknown whether this food source is material derived from dead plant matter or contains living algal cells also. Filamentous algae and detritus were the only food items recorded in the diet of 12 A. acritosus from the Annan River [599]. Such a diet seems typical of species of this genus [720, 1365, 1366]. Animal prey in the form of aquatic insect larvae (principally trichopteran larvae but chironomid larvae and ostracods also) comprised 16.8% of the diet of fish examined. Watson [1365] believed that the ingestion of animal prey was an accidental result of feeding on diatoms, however, the high proportional contribution recorded here suggests otherwise. Observations of wild and captive specimens reveal that feeding is accomplished by the fish ingesting large mouthfuls of sand and fine gravel, which is then expelled out through the opercula. The mechanism for retention of food material is unknown given that gill rakers are only rudimentary.
460
Mugilogobius notospilus (Günther, 1877) Pacific mangrove goby
37 428189
Family: Gobiidae
forming part of dorsal profile. Predorsal scales small, cycloid and reaching forward to behind eyes or nearly so; operculum usually with cycloid scales on upper half; cheek always naked; scales on side of body ctenoid. First dorsal fin with second to third spine longest; second dorsal fin with most posterior rays longest. Male genital papillae elongate, flattened, with rounded tip; female papilla short, rounded and bulbous or conical, with blunt tip.
Description First dorsal fin: VI; Second dorsal: I, 7–8; Anal: I, 7–9; Pectoral: 14–16; Caudal: 16–17 segmented rays; Vertical scale rows: 28–36; Circumpeduncular scales: 12. Figure: mature male, 26 mm SL, Polly Creek, North Johnstone River, September 1997; drawn 2001. The description of Mugilogobius notospilus below is summarised from Larson [773]. This species is a small goby (although moderately sized for its genus), usually not exceeding 35 mm. Maximum size recorded is 51 mm SL (the holotype) but this is unusually large: the next largest specimen, examined by Larson, was 43 mm SL. Body relatively compressed posteriorly, tubular in cross section in mid-region and depressed anteriorly. Head always wider than deep; head pores absent (as in all Mugilogobius) but elaborate pattern of papillae present. Mouth usually subterminal, slightly oblique and reaching at least to below front half of eye, slightly longer in males; several rows of teeth in upper and lower jaws, teeth rows on upper jaw consist of first row of stout curved or near conical teeth, three to four inner rows of small even sharp teeth, two rows at rear. Teeth on lower jaw all small, evenly sized and sharp, and arranged in five or six rows. Sexual dimorphism in teeth size not apparent. Eyes lateral but set high on head
Colour in life: Larson [773] based her description on a photograph of freshly killed material, which in most circumstances serves well. Head and body pale yellowish above and whitish below, scale margins brown giving cross-hatched effect to vertical bars on side of body and indistinct dark blotch at caudal base. Two round black spots present at caudal fin base and black streak along upper procurrent rays. Rest of fin translucent with dusky margin. Pectoral and pelvic fins white. Anal fin reddishorange on proximal half, dusky submarginal stripe, bluishwhite margin. Head dark with a network of yellow-orange spots, particularly on cheek and under eye. On some occasions, the body may be almost completely purple-black and the head spots are very vivid. Fish collected from heavily stained waters tend to be darker than fish from clear waters. Colour in preservative: not greatly different except
461
Freshwater Fishes of North-Eastern Australia
abundant in those sites in which it co-occurs and may be within the five most abundant species. Other species with which it co-occurs include (in decreasing order of abundace) H. compressa, P. signifer, C. rhombosomoides and M. splendida. This species contributes very little to the biomass present in stream reaches in which it occurs (<1%) by virtue of its small size. Anguilla reinhardtii, G. margaritacea, E. fusca and E. melanosoma contribute over 90% of the biomass at sites in which this species occurs. Mugilogobius notospilus occurs at a higher density and biomass in the Johnstone River than in the Mulgrave River (Table 1).
yellow-orange colours faded, especially around head region. Systematics Mugilogobius Whitley, erected in 1927, contains about 30 species distributed throughout the Indo-West Pacific. The genus has been revised by Helen Larson [773] and the material below is summarised from that work. Mugilogobius notospilus was originally described as Gobius notospilus from material collected in Fiji; other synonyms (and erroneous spellings) include Vaimosa fontinalis, V. frontinalis, V. notospila, M. notospila, M. fontinalis, Stigmatogobius duospilus, and M. duospilus. Other members of the genus Mugilogobius occurring in Australia include M. wilsoni (estuarine, northern Australia), M. mindora (freshwater to estuarine, northern Australia and elsewhere), M. filifer (freshwater to estuarine, northern Australia and the Solomon Islands), M. rivulus (estuarine, Northern Territory), M. platynotus (estuarine to marine, Queensland and New South Wales), M. mertoni (freshwater to estuarine, Northern Territory and elsewhere), M. littoralis (estuarine to marine, Northern Territory and Western Australia) and M. stigmaticus (estuarine, Queensland, New South Wales). Mugilogobius stigmaticus is widely distributed in Queensland [907, 1087, 1328] and is probably occasionally sympatric, but not syntopic, with M. notospilus. The sister genus is probably Chlamydogobius, the desert gobies.
Table 1. Distribution, abundance and biomass data for Mugilogobius notospilus in two rivers of the Wet Tropics region. Data summaries for a total of 714 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. Total % locations % abundance Rank abundance % biomass
Distribution and abundance Mugilogobius notospilus is widespread in the Pacific: Larson [773] lists its distribution as including American Samoa, New Caledonia, the Solomon Islands, Papua New Guinea and Queensland. Allen [37] includes Indonesia within its range but does not elaborate further. Within Queensland it has been collected from the Daintree River, the Mossman River, an unnamed creek draining into Trinity Inlet, an urban drain in Cairns, the Johnstone River, the Mulgrave River, Hinchinbrook Island and Waterfall Creek near Cardwell [773, 1087]. These data suggest that it is probably distributed throughout the Wet Tropics region wherever appropriate habitat conditions exist. It is also likely that it occurs along much of the eastern seaboard of Cape York Peninsula. It is not a particularly abundant species; only a single specimen was collected in the survey of Pusey and Kennard [1087]. This may reflect more its cryptic habit and its preference for habitats that researchers find unpleasant and dangerous.
Mulgrave River
Johnstone River
5.8
6.8
8.9
2.0 (13.6)
0.3 (3.8)
2.5 (16.0)
11 (4)
21 (5)
11 (3)
0.04 (1.5)
0.7 (0.3)
0.06 (1.8)
26 (9)
27 (13)
Rank biomass
32 (13)
Mean density (fish.10m–2)
1.16 ± 0.16
0.49 ± 0.10 1.24 ± 0.18
Mean biomass (g.10m–2)
0.45 ± 0.06
0.29 ± 0.06 0.48 ± 0.07
Macro/mesohabitat use Mugilogobius notospilus has a restricted macrohabitat distribution, being thus far found in very small, low-gradient streams close to the coast only (Table 2). Such streams tended to have an intact and thick riparian cover. The maximum distance from the river mouth that we have recorded this species is 14 km. Larson examined specimens collected from Barrett Creek, some 17–18 km from the mouth of the Daintree River [773] and this appears to be the maximum distance upstream that this species has been recorded. Within these small creeks, M. notospilus does not penetrate far upstream and have not been recorded elevations greater than 10 m.a.s.l. Mesohabitat conditions reflect the influence of low gradient, small catchment size and intact riparian cover. Sites in which this species were recorded were shallow (<30 cm) with very gentle current velocity. Many of the sites included in the summary below are tidally influenced (but never saline) and inflowing water from upstream may
Mugilogobius notospilus is not widely distributed in either the Mulgrave or Johnstone River (Table 1) as its macrohabitat use is restricted (Table 2), nor does it ever achieve high levels of abundance. However, it is relatively more
462
Mugilogobius notospilus
It is interesting to note that although sites in which M. notospilus were present were characterised by extensive bank undercutting and abundant submerged root masses, M. notospilus was more abundant in sites with lower levels of these two cover elements. Streams in which M. notospilus occurs also host a large number of other species of fish (species richness on any one occasion = 12–14 spp.). One site contained a total of 21 species (over all sampling occasions; n = 10) [1093]. Amongst these species were a large number of predators including Bunaka gyrinoides, Giurus margaretacea, Eleotris fusca, E. melanosoma, juvenile Lates calcarifer and Lutjanus argentimaculatus, Anguilla reinhardtii, A. obscura and Hephaestus fuluginosus. All of the above show either a preference for undercut banks or root masses, thus some of the observed variation in abundance and habitat use may reflect an avoidance of areas that harbour predators.
back up to depths of greater than 1 m. The summary data presented in Table 2 was always collected at low tide and discharge was unimpeded. The substrate was dominated by mud, sand and fine gravel and the slight differences between the arithmetic and weighted means indicates that M. notospilus is most abundant in sites with finer substrates. Table 2. Macro/mesohabitat use by Mugilogobius notospilus. Data given represents minimum, maximum and mean habitat characteristics. Summaries derived from eight sites within the Mulgrave (two sites) and Johnstone rivers (six sites), sampled in 1994 or 1995. Also shown are the means weighted by abundance (W.M.) to reflect the degree of preference. Parameter
Min. 2
Catchment area (km ) Distance from source (km) Distance to river mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
0.2 0.16 0.5 1 0.5 5.1
Max. 2.0 2.60 14.0 10 6.4 99.0
Mean 1.34 1.92 10.4 7.4 4.4 74.5
W.M. 1.36 2.22 10.8 8.4 5.1 85.8
(a)
100
80
80 60 60 40
Site gradient (%) 0.03 Mean site depth (m) 0.03 Mean water velocity (m.sec–1) 0
0.85 0.41 0.20
0.22 0.26 0.06
0.11 0.29 0.05
Mud (%) Sand (%) Fine gravel (%) Gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 1 6 0 0 0 0
30 60 60 46 33 16 5
9.8 25.9 33.9 15.0 8.6 4.4 1.6
14.2 31.5 35.9 9.5 4.4 3.1 1.0
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% of bank) Root masses (% of bank)
0 0 0 0 0 7 0 0 0 0
1 0 3 1 0 64 6 14 28 65
0.2 0 0.8 0.2 0 25.1 2.8 4.3 10.2 24.7
0.0 0 0.3 0.0 0 32.2 4.1 5.7 7.3 18.1
(b)
40
20
20
0
0
Mean water velocity (m/sec) 40
(c)
Focal point velocity (m/sec) 100
(d)
80
30
60
20
40 10
20
0
0
Total depth (cm)
(e) 50
40
(f)
Relative depth
40
30
30 20 20
Cover provided by flooded terrestrial or aquatic vegetation was at low abundance in the sites in which M. notospilus occurred, however, woody debris (both small and large) and especially leaf litter were abundant and the disparity between the arithmetic and weighted averages suggests that M. notospilus abundances were greatest in sites with more abundant leaf-litter beds. Wet season reductions in the abundance of leaf litter due to scouring by high flows is frequently accompanied by short-term reductions in the abundance of M. notospilus.
10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by the Pacific mangrove goby Mugilogobius notospilus. Data are derived from capture records for 385 fish from the Mulgrave and Johnstone rivers, Wet Tropics region over the period 1994–1997.
463
Freshwater Fishes of North-Eastern Australia
and presence on numerous Pacific islands, it is highly likely that the life history of M. notospilus has a planktonic marine interval. This inference is further supported by the close proximity of its habitat to the river mouth and the fact that very small individuals have not been collected from freshwaters: the minimum size recorded in the Johnstone and Mulgrave rivers is 17 mm SL. Breeding phenology unknown but Larson (pers. comm.) collected a ripe (stage VI) female containing an estimated 2000 eggs from freshwater in September. A stage IV female containing approximately 500 eggs, 0.3 mm in diameter, has been collected from the lower Johnstone River in February. Further research on this species is needed to reveal details of the breeding biology.
Microhabitat use The very great majority of the 385 M. notospilus for which microhabitat capture data were available were collected from areas of zero flow (Fig. 1a). The benthic habit of this goby (Fig. 1d) ensures that focal velocities are less than the average water velocity in those cases in which they were collected from areas of some flow (Fig. 1b). Mugilogobius notospilus was collected over a range of depths but rarely occurred in depths greater than 30 cm (although note that depths increase at high tide). Mud, sand and fine gravel were the dominant substrate sizes over which it was collected (Fig. 1e), reflecting its preference for areas of little flow. It was rarely collected not in association with some form of cover and was most frequently collected from leaf-litter beds (Fig. 1f). The relatively high frequency with which it was collected from small woody debris simply reflects the fact that small woody debris and leaf litter tend to accumulate in the same areas. Overall, the most important microhabitat elements for this species are low flows, fine substrates and leaf litter.
Movement No quantitative data are available for this species. Breeding adults may migrate short distances to estuaries to spawn and the eggs are probably pelagic. Juveniles would make return upstream migrations after metamorphosis. Trophic ecology Quantitative data are lacking. One specimen examined by us contained a few ceratopogonid (sandfly) larvae. Given its small size and benthic habit, it is probably restricted in prey choice to the larvae of small aquatic insects such as sandflies and chironomid midges.
Environmental tolerances Information on tolerances to extremes of water quality is unavailable and data presented in Table 3 indicate the ambient conditions occurring in sites in which M. notospilus occurs. Water quality values listed in Table 3 indicate that the streams in which M. notospilus occurs are acidic, often quite so, and of low conductivity. Temperature, dissolved oxygen and turbidity ranges given in Table 2 are all typical of the normal seasonal range in water quality expected for small lowland rainforest streams. The moderately elevated mean turbidity value listed in Table 3 was a result of high organic acid concentrations (leached from rainforest litter) not suspended inorganic sediment.
Conservation status, threats and management Mugilogobius notospilus is not listed. Mugilogobius notospilus is probably secure and threats are likely to be localised. For example, continued urban clearing and road construction in the Cairns area may pose a threat in that area in the long term. Similarly, clearing associated with coastal resort development may pose a threat to populations in the southern end of its range. The continued spread and proliferation of Tilapia (Oreochromis mossambica and Tilapia mariae) poses a potential threat in rivers of the Wet Tropics region to this and many other species. Given that this species appears limited to small coastal tributaries, it is unlikely to be impacted by water resource developments to any great extent except in the case where tidal barrages inhibit egress to the sea by eggs or larvae and impede upstream return migrations by juveniles.
Table 3. Physicochemical data for Mugilogobius notospilus. Summaries derived from data collected at eight sites in the Mulgrave and Johnstone rivers over the period 1994–1997. Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
17.0 5.62 4.50 26.0 0.33
Max. 27.0 8.40 7.11 65.0 8.40
Mean 20.4 7.89 5.76 40.5 5.53
Reproduction No quantitative data concerning this aspect of the biology of M. notospilus is available. Given its wide distribution
464
Schismatogobius sp. Scaleless goby
37 428248
Family: Gobiidae
attractive: a series of four to five dark brown-black bars are located on the dorsal surface extending about three-quarters of the way down the flanks. Interspersed between these bars in the ventral half of the profile may be a series of blotches of a similar colour. The outline of the bars and blotches is accentuated by a thin white margin. Elsewhere on the flanks, a mix of browns and oranges form swirling patterns evocative of a fine carpet. The underbelly is a pinkish-white. The head tends to be uniformly dark brown. In male specimens, the throat region is orange, as is the inside of the mouth. In some specimens, the orange colour may be extremely vivid and is presumably associated with mate attraction or nest defence. The pelvic fins of such males are almost black with a fine bright orange margin and the anal fin is similarly coloured, although not as intensely. The remaining fins are striated with browns and black pigment on the fin rays. A very distinctive dark brown cross is present on the caudal peduncle and it blends into a spectacled pattern on the anterior part of the caudal to form a pattern reminiscent of a child’s pair of scissors. Colour in preservative: the vivid oranges described above are lost in preservative and the base colour tends to be a dull tan. The white margins to the bars and blotches, which remain distinct, tend to become less distinct in preserved specimens.
Description First dorsal fin: VI; Second dorsal: I, 9–10; Anal: I, 9–10; Pectoral: 16–17; Gill rakers rudimentary, 8 on lower limb of first arch; completely scaleless [52]. Figure: mature male, 37 mm SL, South Johnstone River, July 1995; drawn 2000. Schismatogobius sp. is small goby (as are all members of the genus), rarely exceeding 35 mm SL. The maximum size collected by us was 39 mm. [1093]. Males tend to be slightly larger than females, but not greatly so (i.e. ~10% size difference). Head large, 32.3% of SL; eye small, 6.5% of SL; pelvic fin reaching almost to anus. Cylindrical in cross section, tending to be dorsoventrally compressed anteriorly and ventrally compressed dorsally. Cheeks bulbous. Mouth large, reaching well behind the eye in males, and to just behind the posterior margin of the orbit in females; gape initially oblique posterior of anterior margin of the orbit, thereafter tending towards horizontal; lower jaw projects forward of upper jaw; snout blunt and rounded. Anterior nostril tube-like and projecting over top of maxillae. Four papillae present in line between posterior and anterior nostrils. Second series of papilla (six) running posteriorly from anterior nostril. Colour in life: this small goby is quite spectacular and extremely 465
Freshwater Fishes of North-Eastern Australia
Systematics The genus Schismatogobius was erected by de Beaufort [373] in 1912. It contains five described species and one known but as yet undescribed taxon; the scaleless goby of north-eastern Australia. The genus is restricted to the western Pacific and the species within the genus are limited to freshwater as adults and tend to be restricted in distribution. Schismatogobius bruynisi, the type species, occurs in western Indonesia [373], S. ampluvinculus in Japan and Taiwan [295], S. deraniyagalai in Sri Lanka [1054], S. roxasi in the Ryukyu Islands and the Philippines [737] and S. marmoratus, the most widespread species within the genus, occurs in Japan, the Philippines and Indonesia [866].
This is perhaps the most restricted of habitat requirements, at all scales in the hierarchical habitat array, of any of the species in the region studied by us [1093]. Environmental tolerances Experimental data concerning environmental tolerances of this species are lacking, as are to a great extent, field data. Locations in which it has been collected are characterised by extremely good water quality. Data presented in Table 1 are based on capture records for six specimens only and represent the range of water quality conditions in which it has been recorded. Table 1. Physicochemical data for Schismatogobius sp. The range only is given.
Distribution and abundance Schismatogobius sp., as defined here, is endemic to the Wet Tropics region and has only been recorded from the Endeavour, Daintree, Mossman, Mulgrave, Russell, Johnstone and Liverpool drainages [34, 1087, 1097, 1185]. This species is neither abundant or frequently encountered: Pusey and Kennard [1087] recorded Schismatogobius present in only five of 93 sites surveyed across the region and it contributed only 0.4% of the total number of fishes collected (23rd most abundant species). We have collected a single individual only in the Johnstone River over the period 1994–1997, making it the rarest of species in this river [1093].
Parameter Water temperature (°C ) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
Range 20–30 6–10 7–8 10–200 0–2
The range in water temperature listed is about the annual range for most rivers of the Wet Tropics region. Schismatogobius sp. is only found in rapidly flowing waters and is probably intolerant of hypoxia. It is rare for rivers of the region to exhibit conductivities greater than 200 µS.cm–1 and for this reason we suggest that adult scaleless goby may not tolerate elevated conductivities. Larvae and juveniles may be intolerant of fresh water. Allen [34] notes that Schismatogobius sp. occur in clear streams. Higher turbidity values than is listed in Table 1 frequently occur in rivers of the Wet Tropics region during the monsoonal wet season. Such high levels tend to be transitory however.
Macro/meso/microhabitat use Schismatogobius sp. has a restricted distribution within the rivers in which it occurs. None of the specimens collected by us over the last decade (n = 40) have been from an elevation greater than 50 m.a.s.l. or more than 50 km from the river mouth. All have been collected from fourth or fifth order streams. Within such limits it is further constrained in mesohabitat use. All specimens collected by us have been from riffle/run areas with swiftly flowing water. Allen [34] also reports that it is found in fastflowing streams with a rocky or gravel bottom. Most commonly, almost exclusively, Schismatogobius sp. occurs in the transitional areas between pools and rapids where the substrate is composed of rocks and cobbles, depth averages 0.28 m (± 0.03 m) and the flow is rapid (average water velocity estimated for the six specimens for which capture data exist was 0.42 (± 0.13) m.sec–1) and flowing in an unbroken laminar fashion (i.e. flow is rapid but still sub-critical). Such habitat is very limited in extent, being confined to about 3 m at the head of the riffle or rapid. Schismatogobius sp. is a benthic species, dwelling within the interstices of the coarse substrate and as a consequence, focal point velocities experienced (0.03 ± 0.02 m.sec–1) are much lower than the average current speed.
Reproduction Quantitative data are unavailable and details can only be surmised from limited field and laboratory observations. A better understanding of the reproductive biology of this beautiful and rare Wet Tropics endemic is needed to ensure its protection. Male S. deraniyagalai from Sri Lanka [1054] construct a nest in coarse substrate and the eggs are adhered to a flat surface within the nest by the female. The observation that male Schismatogobius sp. develop an intense orange colour on the underside of the throat and inside the mouth suggests that this species may use a visual display to attract females or to defend the nest site against other males. Reproductive data were collected from two individuals collected from the Daintree River in August 1993. The first was a reproductively mature 33 mm SL female containing
466
Schismatogobius sp.
(79%). The gut contents of one of the fish described in the section on reproduction was composed of four mayfly nymphs and two trichopteran larvae. The gut of the remaining individual was empty. Thus, the small amount of information available suggests a diet composed entirely of the types of small insect larvae typical of the fast-flowing streams in which this species occurs.
well-developed bi-lobed ovaries. The GSI value of this individual was 26.8% and it contained approximately 2900 eggs. The eggs were 0.51 ± 0.02 (SE) mm along the long axis (n = 16), still intrafollicular, yolky and opaque, and tightly packed. Apart from a small proportion (10–20%) of undeveloped eggs, only one size-class of egg was present. The GSI of the second individual (a 32 mm SL stage IV/V female) was 22.1% and the ovaries contained 2300 slightly smaller eggs (0.31 ± 0.02 mm) [1093]. These limited data suggest that spawning takes place during the dry season when flows are low and stable. They also suggest that each females spawns only once and perhaps with one male only. Hatching is rapid (four days) in the related species S. deraniyagalai [1054].
Conservation status, threats and management Schismatogobius sp. is listed as Non-Threatened by Wager and Jackson [1353] and not listed by ASFB [117]. This listing (or failure to list) downplays the conservation status of this species. It is as restricted in distribution as many of the species endemic to the Wet Tropics region listed as Rare by Wager and Jackson [1353] or as Vulnerable (i.e. Cairnsichthys rhombosomoides) and Lower Risk–Near Threatened (i.e. Glossogobius sp. 4) by ASFB [117]. The conservation status of Schismatogobius sp. should be reassessed, perhaps warranting classification as Lower Risk–Near Threatened.
Movement biology Nothing is known of the movement requirements of this species except that which can be surmised from what little is known about its biology and that of its congeners. Given the very restricted range of habitats in which it has been collected, and its very small size, it is unlikely that adults move far from the habitats described above. It is likely to spawn in such habitats therefore. The larvae of Schismatogobius sp. may be transported downstream after hatching with the majority of development occurring in saline estuarine or marine waters, making this species highly vulnerable to impacts from the barrier imposed by dams, barrages and weirs; either by preventing downstream passage of larvae or upstream movement by juveniles. However, the endemic status of this species plus the fact that it occurs in a few rivers only does not suggest that it disperses widely.
The habitat requirements of this species are very restricted and changes in flow regime that impact on the availability of riffles are likely to impact on population size. Poor land management resulting in an increase in sedimentation and changes in substrate composition of the streambed may impact on Schismatogobius sp. by reducing secondary production (i.e. its food source), by smothering eggs or by reducing the three dimensional nature of the habitat provided by coarse substrates (i.e. by colmation). Such effects are likely to be exacerbated in the absence of annual flushing flows. Cold, hypoxic hypolimnetic releases from dams are, in all likelihood, highly inimical to this species. In-stream structures that might prevent the movement of larvae to the sea and return migrations by juveniles may impact on this species if it has a marine dispersal phase. The absence of life historical information on this species is of concern.
Trophic ecology Pusey et al. [1097] reported on the diet of scaleless goby in the Mulgrave River (n = 5). The diet was composed of chironomid midge larvae (20%) and trichopteran larvae
467
Eleotris fusca (Bloch & Schneider, 1801) Brown gudgeon, Dusky sleeper Eleotris melanosoma Bleeker, 1852 Ebony gudgeon, Broadhead sleeper
37 429017
37 429018
Family: Eleotridae
occasionally be a vivid crimson/black colour. Fins clear with thick transverse lines, two on first dorsal fin and three to four on second dorsal. Colour in preservative: similar but lacking any suggestion of red/crimson colour.
Description Eleotris fusca First dorsal fin: VI; Second dorsal: I, 8; Anal: I, 8; Pectoral: 17–19; Vertical scale rows: 57–65 (usually 58–62); Horizontal scale rows: 16–20; Predorsal scales: 38–50 (usually >42); Gill rakers: 10–12 [52]. Colour in life: variable ranging from a light brown/grey to a dark brown. Dorsal surface with series of dark saddle markings. Lateral surface grading from light brown dorsal (with darker saddles) to dark brown, wide midlateral stripe formed by numerous dark lines, approximately one per scale row. Ventral surface tending to be lighter again but mottled. Dorsal and anal fins with four to five thin lines over a clear background. Caudal fin with similar thin lines. Colour in preservative: similar. Figure: mature specimen of E. fusca, 87 mm SL, Polly Creek, North Johnstone River, September 1995; drawn 2001.
Species of Eleotris may be distinguished from other similar gudgeons with which they may occur (e.g. species of Bunaka or Oxyleleotris) by the presence of a downward pointing hook-like spine on the lower corner of the preoperculum. This spine may not be immediately visible as it is frequently covered by tissue but can be easily detected by running a thumbnail lightly, and carefully, along the preoperculum margin. Both species may be distinguished from E. acanthopoma by the possession of more gill rakers on the first arch (8–10 in E. acanthopoma) and more predorsal scales (usually <40 in E. acanthopoma) [52]. Eleotris acanthopoma is also distinguished by a reduced number of lines of pit organ canals along lower margin of cheek (five to six) than seen in E. fusca (8–12) or E. melanosoma (seven to nine) [52].
Eleotris melanosoma First dorsal fin: VI; Second dorsal: I, 8; Anal: I, 8; Pectoral: 17–20; Vertical scale rows: 46–56 (usually <52); Horizontal scale rows: 17–20; Predorsal scales. 35–53 (usually >40); Gill rakers: 12–13 [52]. Colour in life: pattern similar to that observed in E. fusca except browns tending to be darker, almost to a uniform black. Some individuals may
Both E. fusca and E. melanosoma are stout-bodied fish, dorsoventrally flattened anteriorly tending to lateral compression posteriorly. Allen et al. [52] suggest a maximum size of 18 cm (presumably TL) for both species. Of 242 E. fusca collected from the Mulgrave and Johnstone 468
Eleotris fusca, Eleotris melanosoma
rivers over the period 1994–1997, standard length ranged from 34–115 mm and the average size was 70.0 + 1.0 (SE) mm. Eleotris melanosoma apparently reaches a greater size in Queensland streams than does E. fusca. Of 66 specimens collected from the Mulgrave and Johnstone rivers over the period 1994–1997, standard lengths ranged from 44–203 mm with an average of 93.2 + 3.8 mm SL.
North Stradbroke Island off south-eastern Queensland, is highly disjunct and its authenticity therefore requires confirmation. Eleotris fusca has been recorded from three drainage systems of eastern Cape York Peninsula; Rocky River, Massey Creek (both of which drain the eastern flanks of the McIlwraith Ranges) and the McIvor River [571]. The distribution of E. melanosoma in Cape York Peninsula is larger and includes the Claudie, Pascoe, Stewart, Howick and Starcke rivers [571]. This species has been recorded from the Annan River also [599].
Systematics The Eleotridae is thought to contain approximately 150 species from 35 genera [52]. Recent phylogenetic analysis has indicated that the Eleotridae is a paraphyletic family within the Gobioidei composed of two subfamilies, the Eleotrinae and Butinae [579, 1362, 1428, 1442]. Gudgeons can be distinguished from most gobies by the separated pelvic fins [52].
Like many other Australian gudgeons and gobies with extensive Indo-West Pacific distributions, it is in the Wet Tropics region that E. fusca and E. melanosoma are most reliably distributed and abundant. Pusey and Kennard [1087], in their survey of the freshwater fishes of the Wet Tropics region, collected 44 individuals (out of a total of 7325) of E. fusca (20th most abundant species) from 13 of 93 sites and in seven of 10 drainages examined. Eleotris melanosoma was apparently less abundant (15 individuals collected – 29th most abundant) and widely distributed being recorded from only 4/93 sites and 4/10 drainages.
The genus Eleotris has in the past been used to contain many species of gudgeon of uncertain systematic affinity, a practice of considerable annoyance to some early ichthyologists [1012, 1013]. The two species discussed here are, however, rightfully placed within the genus. Eleotris fusca was originally described as Poecilia fusca by Bloch and Schneider in 1801. It was placed within the genus Eleotris by Quoy and Gaimard in 1824 but as E. niger. It was also placed in the genus Culius (as C. fuscus) by Cope in 1871. Other synonyms and misspellings include C. niger, E. fuscus, E. nigra, E. fornasinii Bianconi, 1855; E. cavifrons Blyth, 1860; E. soaresi Playfair, 1867; and E. klunzingerii Pfeffer, 1893. No doubt the many synonyms reflect the widespread distribution of this species (see below). The nomeclatural history of Eleotris melanosoma has been less so varied and its taxonomy has remained unchanged since its original description by Bleeker in 1852, except for an incorrect placement in the genus Culius by Cope in 1871. Another Eleotris species, E. acanthopoma (Bleeker, 1853) also occurs in Australia but is known from a single collection from Cape Tribulation in the Wet Tropics region [52].
Subsequent survey work has found both species to be more widely distributed in the Wet Tropics than these data indicate. Eleotris fusca has been recorded from the streams of the Cape Tribulation area, and the Bloomfield, Daintree, Mossman, Mowbray, Saltwater, Barron, Russell, Mulgrave, Johnstone, Liverpool, Tully, Maria and Hull drainage systems, and streams of the Cardwell area [583, 1085, 1086, 1087, 1179, 1183, 1184, 1185, 1187]. Eleotris melanosoma is apparently not so widely distributed and has been recorded from Bloomfield, Daintree, Saltwater, Mossman, Barron, Mulgrave, Johnstone, Liverpool, Tully, Maria and Herbert drainage systems [583, 908, 1086, 1087, 1093, 1179, 1183, 1184, 1185]. Eleotris fusca has recently been collected from wetland habitats of the Burdekin River delta (C. Perna, pers. comm.). It is worth noting however, that both species are frequently syntopic, and that the same or both species have not always been detected in the same system by different researchers. There is significant potential for misidentification, particularly of small individuals. Moreover, the estuarine/ marine larval phase, during which dispersal occurs, and responsible for the enormous world distribution, is unlikely to distribute colonists of either species in a greatly different way in an area as small as the Wet Tropics region. There is therefore little reason to conclude other than that both species are equally widely distributed in the Wet Tropics region. This method of larval dispersal may however lead to substantial temporal variation in abundance and potentially lead to the situation where one species is present at a location for a number of years and is
Distribution and abundance Eleotris fusca has an enormous distribution stretching from Africa (including South Africa, Kenya, Mozambique, Tanzania and Madagasgar), the Indo-Pacific (including Vietnam, China, Cambodia, India, Bangladesh, Japan, Malysia, the Philippines and Indonesia), Papua New Guinea, associated islands of Melanesia, and westward to Micronesia (Tahiti). Eleotris melanosoma has an equally extensive and almost identical distribution [37, 52]. In Australia, the distributions of both E. fusca and E. melanosoma are contrastingly restricted. Neither species has been reliably recorded from any where other than the east coast of northern Queensland. A recent Queensland Museum record of E. melanosoma from Myora Springs on
469
Freshwater Fishes of North-Eastern Australia
river mouth. As discussed above, both E. fusca and E. melanosoma also occur in estuarine habitats [52]. It is worth bearing in mind that the distribution of sites in the study from which these data are drawn did not encompass the main river stems of either the Mulgrave or Johnstone rivers close to their respective river mouths. Had there been, it is likely that a very different picture of macro/mesohabitat use might emerge. Nonetheless, over the range of sites examined by us, it is clearly evident that these species were almost restricted to these small lowland streams.
then replaced over time by the other. In such a case, changes in relative abundance at a particular site may have little to do with factors operating at the site level, but more to do with factors operating at greater spatial scales. This simply emphasises the need to consider habitat in its broadest sense. Table 1. Distribution, abundance and biomass data for Eleotris spp. in two rivers of the Wet Tropics region. Data summaries for a total of 319 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred.
% locations % abundance Rank abundance % biomass
Total
Mulgrave River
Johnstone River
16.8
20.5
8.9
0.90 (5.7)
0.8 (5.1)
0.93 (6.2)
18 (7)
14 (6)
19 (6)
0.60 (6.3)
0.71 (6.7)
0.58 (6.1)
11 (4)
11 (3)
Rank biomass
14 (4)
Mean density (fish.10m–2)
0.41 ± 0.33
Mean biomass (g.10m–2)
5.46 ± 4.32
Such lowland streams tended to be of low gradient (generally <1%), relatively shallow and with a gentle flow. As would be expected such streams are characterised by a diverse substrate composition dominated by the finer fractions. The similarity between arithmetic and weighted means in Table 1 suggests that the abundance Eleotris spp. is not strongly influenced by substrate composition. Table 2. Macro/mesohabitat use by the gudgeons Eleotris fusca and E. melanosoma. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
0.29 ± 0.06 0.50 ± 0.25
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
6.57 ± 1.50 4.70 ± 0.50
Eleotris fusca and E. melanosoma are neither widely distributed within rivers of the Wet Tropics region nor achieve high abundance. Overall, these species contributed less than 1% of the total number of fish collected over the period 1994–1997, however these species were relatively more abundant in those sites in which they occurred, contributing between 5% and 6% of the total number of fish. These species accounted for about 6% of the biomass collected at such sites (Table 1). The maximum and mean density of Eleotris spp. in the Johnstone and Mulgrave rivers (n = 42 site/sampling occasions over the period 1994–1997) was estimated by us to be 1.41 and 0. 41 individuals.10m–2, respectively. Maximum and mean biomass densities for the equivalent sample were 23.67 and 5.46 g.10m–2, respectively.
0.3 1.5 10.1 5.0 2.1 0
Gradient (%) 0.03 Mean depth (m) 0.09 Mean water velocity (m.sec–1)0
Macro/mesohabitat use The data presented in Table 2 is derived from the mean habitat characteristics of 15 sites in the Mulgrave and Johnstone rivers sampled over the period 1994–1997 and for which abundances of E. fusca and E. melanosoma have been pooled.
Max. 85.0 15.0 26.0 15.0 9.5 99.0 4.0 0.47 0.19
Mean
W.M.
7.0 3.3 13.1 9.3 5.1 63.6
2.2 2.5 11.4 8.9 5.4 71.4
0.7 0.32 0.09
0.72 0.30 0.08
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
30.0 69.0 55.0 22.0 27.0 76.0 16.0
9.1 28.9 25.6 9.4 7.0 16.1 3.3
10.0 28.6 28.1 6.6 3.8 19.1 3.1
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
4.9 0.4 8.0 60.0 0.0 60.3 9.0 13.8 28.0 65.0
0.8 0.0 0.7 6.4 0.0 18.8 3.3 3.8 7.6 21.4
0.7 0.0 1.0 3.2 0.0 24.0 4.2 4.7 4.8 15.5
The abundance of available cover, in contrast, is an important influence on the abundance of Eleotris spp. As a result of the dense riparian canopy characteristic of the small
Eleotris fusca and E. melanosoma are found predominantly in small, well-forested, lowland streams (<15 m.a.s.l.) (Table 2). Such streams are located within 26 km of the
470
Eleotris fusca, Eleotris melanosoma
no discernible flow (Fig. 1a). A very few specimens were collected from areas of flow up to 0.60 m.sec–1, but the focal point velocity for these individuals (Fig. 1b) was always much lower. These taxa were collected from a range of depths with the median depth being between 30 and 40 cm (Fig. 1c), approximating the average depth of the sites in which they were collected.
lowland streams in which these species are found, forms of aquatic vegetation such as macrophytes, algae, and emergent and submerged vegetation are at low abundance. It is notable however, that the difference in arithmetic and weighted mean submerged vegetation cover, suggests that this cover element, when at high abundance, may suppress Eleotris abundances. Submerged vegetation in the Wet Tropics regions is dominated by para grass (Urochloa mutica), an exotic ponded pasture grass. The most important microhabitat elements for Eleotris spp. are leaf litter and small and large woody debris.
Eleotris fusca and E. melanosoma are most frequently associated with the stream-bed (Fig. 1d). Substrate microhabitat use closely reflects that of the average substrate composition (Table 2) except for a slight under representation in the larger particle sizes. Although data presented in Table 2 suggests that the distribution of Eleotris spp. at the mesohabitat scale is not strongly influenced by substate composition, the data presented in Figure 1 suggests a slight avoidance of the larger particles. This probably more rightfully reflects an avoidance of high water velocities rather than substrate per se. The observation made above that leaf litter and large and small woody debris are important determinants of distribution and abundance at the mesohabitat scale is supported by the obvious high reliance on these microhabitat elements shown in Figure 1e. These species are frequently collected from bank-associated root masses also.
Microhabitat use Within the study sites examined by us, Eleotris fusca and E. melanosoma were most commonly collected from areas of 80
(a)
100
(b)
80
60
60 40
40
20
20
0
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
Environmental tolerances Experimental and, to a large degree, field data concerning the environmental tolerances of these species in Australian freshwaters are lacking. The data listed in Table 3 represent water quality conditions present in sites in the Mulgrave and Johnstone rivers over the period 1994–1997, and as such are not indicative of what upper and lower lethal limits might be.
(d)
(c) 60
20
40 10 20 0
0
Total depth (m) 30
(e)
30
20
20
10
10
0
0
Substrate composition
Table 3. Physicochemical data for Eleotris species from streams of the Wet Tropics region (n = 42 site/sampling occasion combinations, 308 individuals).
Relative depth
(f)
Microhabitat structure
Figure 1. Microhabitat use by Eleotris fusca and E. melanosoma. Data derived from capture records for 113 fish collected from the Mulgrave and Johnstone rivers over the period 1994–1997.
471
Parameter
Min.
Temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
17.5 5.62 4.50 24.1 0.3
Max. 27.2 8.81 7.11 65.6 22.1
Mean 22.7 6.94 6.22 36.0 2.1
The data presented in Table 3 suggests that E. fusca and E. melanosoma occur in streams of high water quality, albeit slightly acidic. The temperature range listed is typical of small well-forested lowland streams of the Wet Tropics region, as are dissolved oxygen, conductivity and turbidity levels. It is notable that conductivity levels shown here indicate a preference for, or at the least, usage of, streams of very low salinity and offer no indication of the
Freshwater Fishes of North-Eastern Australia
larvae, shrimps and prawns) [46]. Allen and Coates [46] noted that the stomach contents of several specimens from the Sepik River contained terrestrial insects, prawns and prosobranch molluscs.
upper tolerance levels of these species. Yet, adult fish are stated to occur in brackish estuaries [52] and larvae are found in marine waters [890]. Reproduction Little is known of the reproductive biology of these species. The information presented in the section below suggests an amphidromous/catadromous life history. It is likely that the eggs are small and numerous. Egg size in the related species E. aquadulcis, a Papua New Guinean species which reproduces during the wet season, is 0.27 mm [46].
Conservation status, threats and management Eleotris fusca and E. melanosoma do not have an official Australian conservation status [117, 1353]. Neither species is listed in the IUCN Red List. In light of the information presented above, their conservation status should be considered as Non-Threatened. However, the habitats in which these species occur include those most at threat from agricultural and urban expansion. Wetland reclamation, riparian clearing and channelisation are potentially important threats. Stream habitats in which Eleotris spp. occur are most at risk of degradation by clearing and encroachment by agriculture (particularly sugar cane farming), and invasion by noxious weeds such as para grass and Hymenachne. Such habitats are frequently close to human habitation (e.g. Cairns and Innisfail) and are thus at risk from urban encroachment. In addition, the spread and proliferation of tilapia, Oreochromis mossambicus and Tilapia mariae, may pose a serious threat to this species. Both species have different habitat requirements throughout their life history and are reliant on a critical chain of habitats. Thus, the sustained integrity of nearshore marine, estuarine and freshwater habitats is required to ensure the continued presence of either species in a river system. Moreover, the ability to move between these different habitats is absolutely critical. Water resource developments that impose barriers to movement are likely to impact on this species but only if such structures are located in the lowermost reaches of rivers (i.e. tidal barrages). It should be noted that both species (and many other similarly-shaped gudgeons) are highly susceptible to capture by electrofishing and may suffer extensive bruising and ‘dislocation’ of vertebrae at the base of the head.
Movement Little is known of the movement biology of Eleotris spp. in Australian systems. McDowall [890] suggests that the larvae and small juveniles of E. melanosoma form part of the ‘ipon’ fishery of the Philippines, in which the larvae of many amphidromous gudgeon and goby species are collected in vast seine-nets as they migrate from salt to freshwater. Similarly, E. fusca larvae form part of the enormous multi-species November–December landward migrations observed in Tahiti [890]. These observations, coupled with the wide distribution of both species, suggest a catadromous or amphidromous life history with their attendant movement patterns. Of the 319 Eleotris spp. collected from small adventitious streams of the Johnstone and Mulgrave rivers over the period 1994–1997, only 10 were less than 40 mm SL (minimum size = 34 mm SL), suggesting that movement into such habitats occurs well after the juvenile phase. Larvae and juveniles may occur in the lower estuaries and move upstream as they grow. Trophic ecology Nothing is known of this aspect of the biology of these species in Australian systems. However, it is likely that that the diet is similar to other medium-sized gudgeons with a high affinity for in-stream cover (i.e. small fish, large insect
472
Bunaka gyrinoides (Bleeker, 1853) Greenback gauvina
37 429014
Family: Eleotridae
Systematics The genus Bunaka was erected by Herre in 1927 [573] to contain the type species B. pinguis from the Philippines. Bunaka gyrinoides was originally described as Eleotris gyrinoides by Bleeker 1853 [199]. Reference to this fish as Oxyeleotris gyrinoides may be found.
Description First dorsal fin: VI; Second dorsal: I, 8; Anal: I, 8; Pectoral: 18–19; Horizontal scale rows: 16–17; Vertical scale rows: 55–60; Predorsal scales: 36–45 [37, 52]. Figure: drawn from photographs of an adult specimen, Behana Creek, Mulgrave River, September 1995; drawn 2002. Bunaka gyrinoides is a large, robust gudgeon, cylindrical in section at dorsal fin, dorsoventrally flattened at head. Mouth large, reaching back to eye. Colour variable depending on habitat and age. Juveniles typically dark brown laterally with light brown dorsal surface. Adults may be similarly coloured but more frequently an orange/brown, often very vivid, with narrow dark lines on body (one per scale row). Fins spotted or barred, caudal fin tends to be more uniformly brown. Light brown blotches forming discontinuous bars on sides of body and irregular light brown blotches present on head and lips. Juveniles may be confused with Eleotris spp. and juvenile Oxyeleotris lineolatus, adults potentially confused with adult O. lineolatus, however B. gyrinoides is a more robust fish. Colour in preservative: orange pigment greatly faded, body usually a uniform dark brown. Spotting retained on fins. Maximum size is 35 to 40 cm.
Distribution and abundance Bunaka gyrinoides has an Indo-West Pacific distribution including Christmas Island, Indonesia, Papua New Guinea, Micronesia, the Philippines and Sri Lanka [52]. Bunaka gyrinoides is superficially similar to O. lineolatus and may have been misidentified as such in the past: these species may be found in broad sympatry (i.e. river basins) but are rarely syntopic. Records of the presence of B. gyrinoides in Australia appear limited to the last decade and its distribution in Australia may be wider than is indicated below. In Australia, B. gyrinoides has been recorded from rivers draining the east coast; none were collected from rivers draining into the Gulf of Carpentaria during the extensive CYPLUS surveys of the early 1990s [571]. Herbert and Peeters [569] suggest that B. gyrinoides occurs in all streams of the east coast between Harmer Creek (Cape
473
Freshwater Fishes of North-Eastern Australia
by allochthonous inputs and contains little aquatic plant growth. Bank-associated cover (root masses and undercuts) are also common. In short, such conditions are typical of small lowland rainforest streams.
York Peninsula) and the Tully and Murray rivers. There are however, no documented records of its presence in either Harmer Creek [571] or the Tully/Murray drainage [583, 1003], nor has it been recorded from a number of other rivers within this range. Herbert et al. [571] collected B. gyrinoides from Olive, Claudie, Pascoe and McIvor rivers of Cape York Peninsula. Notably, these rivers have high runoff and are associated with patches of rainforest. Allen et al. [52] include the Endeavour River within its distribution. Bunaka gyrinoides has not been recorded from the Annan River but further surveys in the lower reaches of this river would in all likelihood find this gudgeon.
Allen [37] and Allen et al. [52] list the habitat of B. gyrinoides as rainforest streams with a mud substrate. In New Guinea, this species may penetrate upstream to an elevation of 150 m.a.s.l. Herbert and Peeters [569] suggest that in contrast to other Australian sleepy cod species, B. gyrinoides may be found in riffles and other flowing water habitats, but also state that in such cases, this species is associated with cover such as woody debris or root masses.
It is within the Wet Tropics region that B. gyrinoides is most common. Pusey and Kennard [1087] recorded this species from 17 sites in six drainages of the Wet Tropics region, where it was the 18th most commonly collected species. To date, this species has been collected from the Bloomfield River [1087], streams of the Cape Tribulation area [1087], the Daintree River [1087, 1185], Saltwater Creek [1185], Mossman River [1087, 1185], Barron River [1087, 1187], the Mulgrave/Russell River [1100, 1184], Johnstone River [1177], Liverpool Creek [1179], Maria Creek [1179], Moresby River [1183] and the floodplain and main channel of the Herbert River [584, 643]. The Herbert River drainage appears to be the southern limit of B. gyrinoides. Its apparent absence from the Tully/Murray River is curious, and surveys in its preferred habitat would probably reveal its presence there.
Table 1. Macro/mesohabitat use by Bunaka gyrinoides. Data given represents minimum, maximum and mean habitat characteristics. Derived from 12 sites within the Mulgrave (four sites) and Johnstone rivers (eight sites) sampled over the period 1994–1995. Also shown are the means weighted by abundance (W.M.) to reflect the degree of preference. Parameter
Min. 2
1.0 Catchment area (km ) Distance from source (km) 1.5 Distance to river mouth (km) 10.3 Elevation (m.a.s.l.) 10 Order 2 Stream width (m) 4.4 Riparian cover (%) 5 Site gradient (%) 0.01 Mean average depth (m) 0.22 Mean water velocity (m.sec–1) 0
Although widely distributed in the coastal lowlands of the Wet Tropics region, B. gyrinoides is uncommon. A total of only 28 individuals has been collected from the Mulgrave and Johnstone rivers over the period 1994–1997, making this species the 31st most abundant species in these rivers. Average density recorded from 12 sites in the Mulgrave and Johnstone rivers sampled over this period 1994–1997 was 0.121 ± 0.085 individuals.10m–2, density values that translate to one or two fish every 40 m of stream. It was the 13th most abundant species in these sites. It contributes substantially to the biomass in these sites however(5.4%), by virtue of its large size. The average estimated biomass was 7.19 ± 11.2 g.10m–2, making it the fourth most important species in those sites in which it occurred [1093]. Macro/mesohabitat use Macro/mesohabitat data presented in Table 1 indicate that in the Wet Tropics region Bunaka gyrinoides occurs at low elevation in small lowland rainforest streams located close to the river mouth. Such streams are typically of low gradient, relatively shallow with a moderate current (best described as run habitat), with a substrate dominated by sand, fine gravel and gravel, and usually have an intact riparian zone. In-stream cover is abundant but dominated
Max. 85.0 15 34.3 60 5 9.5 90 3.5 0.64 0.37
Mean
W.M.
18.3 5.1 15.6 15.8 3.1 5.9 57.9
11.9 3.7 13.6 13.4 2.8 5.5 63.2
0.7 0.34 0.12
0.7 0.30 0.11
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 1 1 0 0 0
32 69 39 68 36 73 7
9.0 23.8 19.7 21.6 6.8 18.3 1.0
11.1 22.1 20.6 22.1 5.5 16.8 0.7
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% of bank) Root masses (% of bank)
0 0 0 0 0 0.2 0 0 0 0
25.3 0 5.0 24.0 0 28.4 13.5 12.9 16.0 39.0
4.1 0 1.6 3.7 0 12.0 4.8 5.3 4.0 14.3
5.6 0 1.3 2.0 0 15.9 4.5 5.0 3.1 14.6
The data presented here and the statements of Allen [37] and Allen et al. [52] certainly give the impression that B. gyrinoides is restricted to small to medium-sized rainforest streams. However, this may, in part, reflect the size of
474
Bunaka gyrinoides
Bunaka gyrinoides was collected predominantly from areas of zero flow although one individual was collected from an area of very fast flow (Figure 1a). However, focal point velocity was always close to zero (Figure 1b). This pattern supports the assertion of Herbert and Peeters [569] that when located in riffle habitats, B. gyrinoides are intimately associated with some form of cover. Although B. gyrinoides may be found over a range of depths, this species apparently avoids very shallow waters and prefers the deeper areas of the sites in which it is recorded (cf. the depth distribution depicted in Figure 1 with the average site depth listed in Table 1). As suggested by Allen [37], this species may be found on the stream-bed (Figure 1d) where it hides amongst the substrate or leaf-litter beds, or it may be found higher in the water column where it hides amongst root masses and small woody debris. It was never collected by us in the open water distant from cover.
streams sampled. For example, the specimens used in Pusey et al. [1097] as part of a study examining the trophic ecology of rivers of the Wet Tropics were collected from the main channel of the Mulgrave and Johnstone rivers. Other specimens have been recently collected from the lower Mulgrave River (T. Rayner, pers. comm.). It is likely that B. gyrinoides occurs across a range of stream orders in locations close to the river mouth. The habitats in which B. gyrinoides occurs are inhabited by a wide range of other fish species also. Species diversity (including B. gyrinoides) ranged from nine to 16 species (mean = 12.9). Such stream habitats are the most biodiverse of any in the rivers of the Wet Tropics region. Microhabitat use Microhabitat use by Bunaka gyrinoides from small rainforest is depicted in Figure 1 and based on capture records for nine individuals only. (a)
80
The substrate compostion depicted in Figure 1e differs from the average composition of the sites in which it was collected in that it is dominated by sand and fine gravel and deficient in cobbles, rocks and mud. These differences suggest this species avoids areas of mud and areas of coarse substrate; the latter probably due to an aversion to high water velocities rather than coarse substrates per se.
(b)
60 60 40
40
20
20
0
0
Mean water velocity (m/sec) 50
(c)
Focal point velocity (m/sec) 50
40
40
30
30
20
20
10
10
0
0
(d)
Table 2. Physicochemical data for Bunaka gyrinoides. Data derived from 12 sites located in the Mulgrave and Johnstone rivers of the Wet Tropics region sampled over the period 1994–1997. Relative depth
Total depth (cm)
(e)
Environmental tolerances Information on the environmental tolerances of B. gyrinoides is sparse. The data presented in Table 2 represents ambient conditions at sites in which this species was present. As such they do not represent environmental limits.
40
(f)
40 30
30
20
20 10
10
0
0
Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
20.1 6.00 5.13 24.1 0.4
Max. 27.1 8.40 7.42 65.6 11.4
Mean 23.3 7.11 6.19 36.5 2.2
The data presented in Table 2 are indicative of water quality conditions typical of lowland rainforest streams of the Wet Tropics region: that is, clear, fresh, slightly acidic, warm yet well-oxygenated. Given its tropical distribution, it is unlikely that B. gyrinoides tolerates low water temperatures. Temperatures less than 15–17°C are probably deleterious. This species evidently uses waters of very low conductivity, however it is very likely that greatly elevated conductivities are experienced at some time, probably during the larval and early juvenile phase (see below).
Microhabitat structure Substrate composition
Figure 1. Microhabitat use by the greenback gauvina Bunaka gyrinoides. Data derived from a total of nine individuals collected from small streams in the lower reaches of the Mulgrave and Johnstone rivers.
475
Freshwater Fishes of North-Eastern Australia
They were entire and had not been crushed. The presence of gastropods in the gut of B. gyrinoides in the Mulgrave River was also recently observed (T. Rayner, pers. comm.). Van Zwieten [1345] noted that of three fish from the Sepik Ramu River of northern New Guinea, two contained crabs while the third contained gastropods molluscs. Given this species’ morphology and its similarity to other sleeper type gudgeons, it is also feeds on small fishes and macrocrustacea. Further research is necessary to determine the real extent of molluscivory, which is an uncommon feeding style in Australian freshwater fishes.
Reproduction Little is known of the reproductive biology of this species. The wide geographical distribution and the close association of the adult habitat with respective river mouths suggest a marine larval phase. Like many other gudgeons, it is likely that some form of parental care occurs (i.e. fanning of eggs within a nest). This aspect of its biology is in need of research. Movement Very meagre information is available on the movement biology of this species. A defaunation experiment undertaken in the lower reaches of the Johnstone River [1093] revealed that adult B. gyrinoides colonised defaunated stream reaches over the space of one year. Thus, at least some small-scale (i.e. 100 m) movements are made. Larvae and small juvenile fishes probably make the greatest movements: from the near-shore marine and estuarine habitats upstream into the adult habitat
Conservation status, threats and management Bunaka gyrinoides currently does not have an official conservation status. The available information suggests that it should be listed as Non-Threatened. Nonetheless, by virtue of its macrohabitat distribution (lowland rivers and creeks close to the sea, populations near major population centres and areas of intensive agricultural development may be impacted by urban encroachment, loss of riparian zone integrity, channelisation and by barriers to movement (i.e. barrages, road crossings). The proliferation of Tilapia in rivers of the Wet Tropics region may pose a threat in the future. These same threats are faced by many other syntopic species such as Eleotris spp., Giurus margaritacea and Mugilogobius notospilus.
Trophic ecology Very little quantitative information is available for Australian populations of this species, being limited to a total of two individuals only [1097]. The only food items present in these individuals were large elongated gastropods (?Stenomelania).
476
Oxyeleotris lineolatus (Steindachner, 1867) Sleepy cod
Oxyeleotris selheimi (Macleay, 1884) Striped sleepy cod, Giant gudgeon
37 429038
37 429040
Family: Eleotridae
back, dark lateral stripe frequently present, particularly in juveniles. Ventral surface matt brown. Indistinct horizontal stripes (one scale row wide) often present on sides. Substantial difference in fin colouration is reported by different authors. Allen [37] reports that spotting of the fins is confined to the dorsal and caudal fins whereas Allen [34] reports the anal fin is spotted also. Merrick and Schmida [936] state that all fins are spotted. Such differences probably arise from the inclusion of the closely related O. selheimi in the series upon which observations are based. In our experience, the dorsal and caudal fins only are spotted, as in Allen et al. [52]. The caudal fin is rounded. During the breeding season O. lineolatus is sexually dimorphic, with females having much larger genital papilla than males [935, 1433]. The shape of the genital papilla in both sexes appears to vary substantially between populations from the Walsh River (Gulf of Carpentaria) and the Fitzroy River (central Queensland) [935, 1433].
Description Oxyeleotris lineolatus First dorsal fin: VI; Second dorsal: I,8-9; Anal: I, 7–9; Pectoral: 17–18; Vertical scale rows 62–70; Horizontal scale rows: 18–22; Predorsal scales: 35–45 [34, 52]. Figure: 142 mm SL, Gunpowder Creek, Leichhardt River, June 1999; drawn 2001. Oxyeleotris lineolatus is a large robust species that may reach 50 cm in length and 3 kg in weight. Bishop et al. [193] list the relationship between length (CFL in cm) and weight (in g): log Wt = 7.68 x 10–3 L3.14; r2 = 1, n = 134, p <0.001. The body is elongate and the head depressed; mouth large, reaching back to below front one-third of eye; lower jaw protrudes forward of maxilla, teeth small and conical, outer row slightly enlarged (this character may be variable). Colour variable depending on age and habitat. Typically dark brown, often slightly lighter on
477
Freshwater Fishes of North-Eastern Australia
Oxyeleotris selheimi First dorsal fin: VI; Second dorsal: I, 9; Anal: I, 8–9; Pectoral: 17–19; Vertical scale rows: 62–69; Horizontal scale rows 19–20; Predorsal scale rows: 40–48 [52]. Figure: 151 mm SL, Gunpowder Creek, Leichhardt River, June 1999; drawn 2001.
to the difficulty faced by early Australian systematists in obtaining overseas taxonomic literature, many species were also placed within Eleotris up until the turn of the century. Ogilby [1012] listed a total of 51 Australian and New Guinean species placed within Eleotris up until 1897. Among these were O. lineolatus and O. selheimi. Oxyeleotris is distinguished from Eleotris by the absence of a spine on the lower rear corner of the preopercle. Allen [37] suggests that the genus currently contains about 15 species throughout the Indo-Australian archipelago but notes that the taxonomy needs study. This observation is particularly germane to the species group currently referred to as sleepy cod and which traditionally has been referred to as O. lineolatus. This species group is composed of at least two species (O. lineolatus and O. selheimi).
Oxyeleotris selheimi is also a large robust gudgeon and probably achieves the same large size as O. lineolatus. It is almost identical in body plan to O. lineolatus and differs in only a few critical morphometric and meristic features. The mouth is slightly larger, reaching back through at least the mid-point of the eye, the posterior most teeth in the outer row of the lower jaw are significantly enlarged and the caudal fin is slightly pointed. It is in terms of colour pattern and cephalic pore and papillae arrangement that the two species differ most. All fins in O. selheimi are spotted to the extent that the fins appear to be barred. The dark, wide midlateral stripe is well expressed and is distinguished by a broken white horizontal stripe running from the caudal to the mouth. Less distinct broken white lines are also present below the midlateral stripe and the ventral surface appears blotchy.
Oxyeleotris lineolatus was first described (as E. lineolatus) by Steindachner [1262] in 1867 from material collected in the Fitzroy River of central Queensland. It seems probable that the species Eleotris cresens described by DeVis [379] in 1885 from material collected in Gracemere Lagoon of the Fitzroy drainage is synonomous with O. lineolatus. Caldwell [1431] (cited in Herbert and Graham [1433]) reported that O. lineolatus from the Fitzroy River are genetically divergent from other populations in northern Australia.
The anterior nostril of O. selheimi is longer than in O. lineolatus, whereas the posterior nostril is much shorter, to the point that it no longer forms a tube. In addition, the nostril and adjacent pores in O. selheimi are surrounded by an indistinct and only moderately well organised patch of papillae. This same patch is more neatly arranged in O. lineolatus and extends between the pores and not the nostrils. The papillae below the eye are arranged in six distinct vertical lines in O. selheimi but arranged in nine indistinct vertical lines plus two anterior oblique lines in O. lineolatus. Five pores are present on the preopercle margin of O. lineolatus whereas O. selheimi possesses six. The arrangement of pores running from the eye to the dorsal attachment of the operculum also differs (the ‘E to L’ series of Figure 30 in Allen [37]) being confined to five pores in O. lineolatus and containing one additional pore in O. selheimi (in this case positioned dorsally of the second and fourth pores as similarly observed for the position of pore I between pores J and K in O. fimbriata in Allen [37]). Finally, the dorsal pair of cranial pores just posterior to the posterior margin of the eye are either fused to form a single pore or positioned very close to one another in O. lineolatus but are more widely separated in O. selheimi. Whilst these observations are based on a very limited series, they have proved useful in the field [1093].
Macleay first decribed O. selheimi as E. planiceps in 1884 from material collected in the Palmer River [846], later redescribing it as E. selheimi [849] after realising that Castelnau [287] had earlier (1878) described another gudgeon (from the Norman River) as E. planiceps. In addition, Ogilby [1012] believed that several other Eleotris species described by Macleay were attributable to E. planiceps; these included E. aporocephalus, 1884 and E. darwiniensis, 1877. However, Grant [470] listed E. darwiniensis and E. aporocephalus (but listed as ophiocephalus) as species within the genus Ophiocara and Macleay’s descriptions certainly match the appearance of the spangled gudgeon O. porocephala. Early descriptions were often very meagre in detail and make valid identification tenuous without the presence of type specimens. We have not sighted the type specimens of any of those listed above. It should be noted that Macleay also used the name E. planiceps to describe another gudgeon from the lower Burdekin River. This name has been determined to be a junior synonym of Giurus margeritacea (M. McGrouther, pers. comm.). Despite being formally described over a hundred years ago, very few workers have recognised the existence of O. selheimi until recently, although they have recognised the existence of a sleepy cod other than O. lineolatus in northern Australia. This additional species of sleepy cod in north-western Australia has been variously identified as
Systematics The genus Oxyeleotris was formally described by Bleeker in 1874 [202]. Prior to this date species within this genus were often included with the ‘catch-all’ genus Eleotris. Due
478
Oxyeleotris lineolatus, Oxyeleotris selheimi
Annan rivers [697, 1099, 1349]. Herbert et al. [571] recorded O. selheimi from the Coleman, Palmer, Holroyd, Edward, Archer and Wenlock rivers on the western Cape and also recorded it from three easterly flowing drainages: Stewart River, Massey Creek and the Annan River. Herbert et al. [571] believed that its presence in the Stewart River was evidence of long-term drainage rearrangement (i.e. river capture). We have also collected O. selheimi in the Normanby River (but listed as O. lineolatus [697]). Oxyeleotris selheimi has not been recorded from any other easterly flowing systems, except for Flaggy Creek and Lake Tinaroo in the Barron River drainage [1187] and its presence there is almost certainly the result of mindless translocation. Thus, it appears that the greater part of the range of O. selheimi lies to the west of the Great Dividing Range.
Bunaka herwerdenii [30], O. herwerdenii [936], Oxyeleotris sp. 1 [45] and Oxyeleotris sp. A [34]. Oxyeleotris herwerdinii is now known to be a junior synonym of O. selheimi [52]. Allen et al. [52] recognised five Australian species in Oxyeleotris: three small species, O. aruensis, O. fimbriatus and O. nullipora; and two larger forms, O. lineolatus and O. selheimi. A recently discovered undescribed form was also suggested to occur in north-western Australia [52]. Distribution and abundance It must be borne in mind that few workers have distinguished between these sleepy cod in the field and consequently much of the limited information concerning the distribution and biology of sleepy cod refers primarily to O. lineolatus but probably pertains to O. selheimi also. Both species are widely distributed across northern Australia and O. lineolatus reportedly occurs in southern New Guinea also [37, 42, 317]. However, Allen [36] states that ‘…there are no precise locality records from New Guinea and its occurrence there needs to be confirmed’ (p. 170) and it is not listed in Allen’s checklist of New Guinean freshwater fishes [36].
Oxyeleotris lineolatus, in contrast, occurs widely in easterly flowing rivers of Queensland. In the Wet Tropics region it has been recorded from the Daintree, Barron (translocation), Russell, Mulgrave, Tully and Herbert rivers [584, 1085, 1184, 1187]. It is, however, neither commonly encountered nor abundant in this region. For example, Pusey and Kennard [1085] collected only two individuals (from a total of 7325 individuals) from a single location in the Daintree River. Other large gudgeons are found in the freshwaters of this region, including Giurus margaritacea Valenciennes, E. fusca (Bloch and Schneider), E. melanosoma Bleeker and most importantly, the greenback guavina Bunaka gyrinoides (Bleeker) [1100]. This latter species is large and robust, very widely distributed in the Wet Tropics region and is potentially a formidable competitor to O. lineolatus. (However, it must be stated that O. lineolatus is apparently able to co-exist with its congener O. selheimi over much of their shared range.) It is noteworthy that workers in the area have only recently recognised the presence of B. gyrinoides and previously listed one species of sleepy cod only. Inexperienced collectors may have misidentified B. gyrinoides as O. lineolatus (as we did in Pusey et al. [1097]). Moreover, in those works in which both species are recognised, it is frequently the case that only B. gyrinoides is collected (as in the Daintree River [1185] despite the recorded presence of O. lineolatus by Pusey and Kennard [1085]), or O. lineolatus is much less commonly encountered. For example, Russell et al. collected O. lineolatus from only two locations in the Mulgrave Russell system whereas B. gyrinoides was recorded from 14 locations. Oxyeleotris lineolatus is not common in the Wet Tropics region.
The specific identity of the sleepy cod present in the Kimberley region is difficult to ascertain, however a sleepy cod species has been recorded from the Fitzroy, Lawley, Carson, Mitchell and Ord rivers [620]. Merrick and Schmida [936] list O. selheimi (as O. herwerdenii) as occurring in the Daly River. Allen and Leggett [45] state that the sleepy cod present in the Kimberley region and referred to O. herwerdenii by Allen [33] is O. lineolatus whereas the species referred to O. lineolatus by Allen is Oxyeleotris sp. 1 (= sp. A, = O. selheimi in the current treatment). From this, it appears that both O. lineolatus and O. selheimi are present in north-western Australia as far south as the Fitzroy River. Allen et al. [52] suggest that the range of O. selheimi extends slightly more westward than does that of O. lineolatus. Oxyeleotris lineolatus is widely distributed throughout the Northern Territory and the Gulf of Carpentaria (recorded from the Nicholson, Leichhardt, Flinders, Gilbert and Norman rivers) [1349] and O. selheimi has also been collected from a tributary of the Leichhardt River in the Gulf region also [1093]. Herbert et al. [571] were the first researchers to consistently differentiate between these two species and their distributional records reveal that both species are widespread in the Cape York region and frequently sympatric. Oxyeleotris lineolatus has been recorded from the Coleman, Palmer, Holroyd, Edward, Archer, Wenlock and Jardine rivers on the western side of Cape York Peninsula [571, 1349]. Herbert et al. [571] did not record O. lineolatus from any easterly flowing rivers of the Cape but others have recorded it present in the Stewart, Normanby and
It is tempting to speculate that the Wet Tropics region is not part of the natural range of O. lineolatus or at least, is extralimital in the sense that it holds very small and isolated populations only. The extensive translocation of
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this species throughout Queensland (see below), sadly, obscures any real examination of this question. Moreover, it obscures any real assessment of whether O. lineolatus is native to any other river on the east coast except the Fitzroy River system, its type locality.
sleepy cod have been legally translocated prior to the development of the Freshwater Management Plan include the Noosa, Kolan, Burnett, Boyne, Pioneer, Proserpine, Ross, Bowen, lower Burdekin, upper Burdekin, Russell/Mulgrave, Barron and the Johnstone rivers (QFMA, unpubl. data). They have also been stocked into the upper Leichhardt River, which drains into the Gulf of Carpentaria. Bear in mind that these are legal stockings only and note that the list of rivers includes those in the Wet Tropics region.
Oxyeleotris lineolatus has been recorded from the Herbert River [643] but not from any other river or stream systems south to the Burdekin River, other than in locations known to have been stocked. Midgley [940] asserted that O. lineolatus was present in the lower reaches of the Burdekin River prior to his 1976 survey but did not collect any. Similarly, anecdotal evidence suggests that it was present in the lower reaches of the Burdekin River from at least the 1950s (Jim Tait, pers. comm.; Damian Burrows, pers. comm.). However, fish translocations have a long history in Queensland, commencing in 1880 [1082] and certainly occurred in the Burdekin River prior to 1950 with attempts to establish yellowbelly, Murray cod and freshwater tandans into the river at Valley of Lagoons station. It is not inconceivable that sleepy cod were introduced into the Burdekin River on at least two different occasions (i.e. pre-1950 and again in 1983; see below for expanded discussion).
To a great extent, the impact of such translocations are unknown and probably, rarely even pondered. For example, there have been 54 943 fingerlings stocked into the Fitzroy River since 1989 (QFMA, unpubl. data). Of these 18 separate stocking events, seven have originated from one hatchery, two from another, one from yet another and the remaining eight are of unknown origin. From where have these fish been sourced, are they of distinct genotypes, are they the same genotype as the original sleepy cod found in the Fitzroy River and, what impact are they having on the genetic composition within the river? Critically, the Fitzroy River is the type location for this species and sleepy cod occurring naturally there are the only genetic resource available in the future to enable a careful examination of the systematics and biogeography of this species group.
Oxeleotris lineolatus is native to the Fitzroy system, being its type locality. Midgley [942] found it to be relatively widespread (5/16 sites) and ranging in abundance from rare to abundant (exact number unknown). The Fitzroy River is the southern limit of this species’ natural range. Additional localities for this species north of the Fitzroy River include Water Park Creek [1328] in the Shoalwater Bay area and Planes Creek near Sarina [779].
One river for which some information is available concerning the impact and spread of translocated sleepy cod is the Burdekin River. As mentioned above, Midgley cited anecdotal evidence for its presence in the lower Burdekin and Bowen rivers. Pusey et al. [1098] recorded it as reasonably abundant in the lower Burdekin and Bowen rivers downstream of the Burdekin Falls, where it comprised 5.6% and 0.4% of electrofishing and gillnetting catches, respectively, over the period 1989–1992. They also collected small numbers in the upper Burdekin River at the site of its 1983 introduction (Valley of Lagoons – site B1 in Pusey et al. [1098]). It here comprised 0.1% and 1% of the electrofishing and gill-netting catches, respectively, but was completely absent from tributary streams such as Running River, Keelbottom Creek and Fanning River. Midgley [940] did not collect any sleepy cod from the extremely low gradient turbid Cape or Balyando rivers which drain the south-western portion of the catchment.
Oxyeleotris lineolatus is rarely abundant (but see below). Bishop et al. [192] report that the proportional contribution of sleepy cod to the total number of fish collected during extensive research undertaken in the Alligator Rivers region of the Northern Territory ranged from 0.12% in lowland sandy pools to 1.2% in lowland backflow billabongs. In the Pascoe, Stewart and Normanby rivers of Cape York Peninsula, sleepy cod accounted for 0.7%, 0.3% and 10.6% of the electrofishing catch, respectively [1093]. Kennard [697] found that sleepy cod comprised 0.6% and 0% of gill-netting catches in floodplain lagoons and in the main channel of the Normanby River, respectively, but the proportional contribution to the electrofishing catch increased to 5.5% and 5.9%, respectively. Pusey et al. [1098] report that sleepy cod comprised 1.9% and 0.5% of electrofishing and gillnetting catches, respectively, in the Burdekin River but was absent from seine-netting catches.
Throughout the period from 1989 to 1992, the sleepy cod catch by Pusey et al. [1098] remained roughly stable at between one and three fish per sampling occasion in Valley of Lagoons and between 5–10 fish per occasion in each of the Bowen River sites examined, despite the occurrence of a very large flood (January 1991) and entry into a
Oxyeleotris lineolatus is one of the most widely translocated fishes in Queensland. Eastern rivers into which
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Oxyeleotris lineolatus, Oxyeleotris selheimi
prolonged period of drought. Annual sampling at a reduced number of sites (five) commenced in 1993 and at which time there was little change in abundance levels. By 1994, however, sleepy cod catches at Blue Range Station (site B2 in Pusey et al. [1098]) had increased from zero over the period of 1989–1993 to 16 (31% of electrofishing catch) in 1994, 39 (55%) in 1995, 29 (29%) in 1996 and 40 (39%) in 1997. These abundance figures represent the number collected in 100 m of stream in one hour of electrofishing. Further downstream at Macrossan’s Crossing (B5) abundances increased from zero over the period 1989 to 1992 to six (12%) and five (8%) in 1994 and 1995 respectively but exploded to 70 (62%) individuals by 1997 [1098]. These data support the notion that the increase in sleepy cod abundance was not synchronous over the length of the river but occurred progressively down the river and are suggestive of a colonising front slowly moving downstream.
over the period 1993–1997, always remaining less than 3% of the total electrofishing catch. The size distribution of sleepy cod in Valley of Lagoons was almost exclusively dominated by fish over 250 mm SL whereas, at recently colonised sites, the size distribution was dominated by fish less than 100 mm SL; suggesting that most colonisation and dispersal is undertaken by juvenile fish. However, the Bowen River population size structure (over the period 1989–1997) was also dominated by small fish and essentially identical to that observed in recently colonised sites; suggesting that this river has also seen an increase in abundance of sleepy cod, possibly as a result of stocking prior to the translocation event in the upper reaches of the Burdekin proper. This observation provides some support for the notion that sleepy cod are not native to the Burdekin system. Macro/mesohabitat use Bishop et al. [193] found sleepy cod to be widely distributed within the east Alligator River, being present in lowland sandy pools (three of six sites), lowland backflow billabongs (10/11 sites), corridor billabongs (3/3 sites) and upper floodplain billabongs (6/6 sites). This species was most abundant in lowland backflow billabongs. Sleepy cod were not recorded from any of the escarpment habitats sampled, suggesting that unlike many other species in this system, sleepy cod do not seasonally move between lowland wet season habitats and upland dry season regufia. Woodland and Ward [1416] recorded sleepy cod from small isolated pools in the sandy creek-bed of Magela Creek.
As mentioned above, no sleepy cod were collected from upper tributary streams by Pusey et al. over the period 1989–1992 [1098]. Similarly, other survey work undertaken in the Dotswood region (Star, Fanning and Keelbottom drainages) in 1991 also failed to detect sleepy cod [1408]. However by 1999, all three drainages had been colonised by O. lineolatus [260]. By this time sleepy cod comprised 1.6% and 4.3% of gill-netting catches in Keelbottom Creek and Fanning River, respectively and 5.9% and 7.5% of bait trap catches, respectively. Proportional contributions by sleepy cod to electrofishing catches were somewhat smaller (0.1%, 0.3% and 0.7% for the Star River, Keelbottom Creek and Fanning River, respectively). From these and our unpublished 1993–1997 data, it can be fairly safely assumed that sleepy cod have colonised almost all of the upper Burdekin River and its tributaries.
In the Normanby River of Cape York Peninsula, sleepy cod were recorded from within 60 km of the river mouth and as far upstream as 210 km, and were present in both main river habitats and floodplain habitats. Sleepy cod were not collected from the upper, more ephemeral, reaches of the Normanby River [1093].
Midgley [940] surveyed one site on the Balyando River (Mt. Douglas) in 1976 and failed to collect any sleepy cod. By 1999, O. lineolatus was present at four of five sites on this river (being absent from the most upstream site only) and comprised 7.5% of the total fish catch at five sites within this catchment (all sampling methods combined) [256]. Unpublished survey results also show that by late 2000 sleepy cod had also invaded the Cape and Campaspe rivers, being present at seven of nine sites and contributing 2.2% of the total catch (D. Burrows, pers. comm.). Thus, it appears that sleepy cod have been able to colonise all of the upper Burdekin River in 17 years and possibly in as little time as seven years.
The spread of sleepy cod throughout the Burdekin systems attests to their ability to thrive in a variety of habitats. Such habitats include deep lagoons, highly turbid pools, shallow braided open sections of the main channel and more incised deeply shaded tributaries. Burrows (pers. comm.) noted that sleepy cod were found in isolated pools in the tributaries of the Dotswood area and the only habitat not occupied by sleepy cod was that located above waterfalls. Bishop et al. [193] believed sleepy cod (listed as O. lineolatus) preferred muddy lagoon habitats with a mud substrate. Herbert et al. [571] suggest that O. selheimi prefers lagoon habitats whereas O. lineolatus preferred main channel habitats but provide no supporting evidence. If true, such habitat segregation may explain why
It is interesting to note that the abundance of sleepy cod in Valley of Lagoons, the original site of introduction, and in the two sites sampled in the Bowen River, changed little
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Environmental tolerances Information on the physicochemical tolerances of O. lineolatus (and O. selheimi) can only be drawn from field studies as no experimental examination has yet been undertaken (Table 1).
two closely related and morphological similar species are apparently able to co-exist. Microhabitat use Although found across a wide variety of mesohabitat types, sleepy cod have a definite requirement for abundant cover, either in the form of submerged macrophytes, rootmasses or woody debris. Large woody debris is also an important spawning requirement. Small sleepycod (<100 mm SL) are most frequently associated with root masses whereas larger specimens are also likely to be associated with woody debris. In the Valley of Lagoons area, large adult sleepy cod are often associated with the thick beds of Valisneria that occur in this part of the river [1098]. Bishop et al. [193] also noted that this species was typically captured in heavily vegetated lagoons. It is not uncommon to observe adult sleepy cod hanging motionless in the water column, distant from cover. However, they will always retreat to cover when disturbed.
The temperatures at which sleepy cod have been collected reflect its northern tropical distribution. The low average temperature recorded for the Belandyo River reflects the low air temperatures that may occur in inland central Queensland in early spring (when Burrows et al. [256] undertook their study). Merrick and Schimda [936] Table 1. Physicochemical data for Oxyeleotris lineolatus from several locations in northern Australia. Note that studies in Cape York Peninsula and the Alligator Rivers region may have collected both species, but not distinguished between O. lineolatus and O. selheimi. Parameter
Kennard [697] provided a quantitative analysis of microhabitat use by sleepy cod (n = 99) in the lagoons of the Normanby River system. Less than 10% of the sample was collected from open water. During the early dry season, the majority of fish were collected from root masses, followed by macrophytes and submerged branches. Similar structures were used during the late dry season but submerged branches were used more extensively than were root masses or macrophytes. These differences reflect changes in the availability of habitat elements as the lagoons decreased in volume.
Min.
Max.
Alligator Rivers region [193] Temperature (°C) 26 38 Dissolved oxygen (mg.L–1) 1.0 9.1 pH 4.80 9.1 Conductivity (µS.cm–1) 4 480 Secchi disc depth (cm) 1 100
Mean
31.1 5.8 6.4 – 26
Cape York Peninsula – riverine sites (n = 9) [1093] Temperature (°C) 22.9 29.4 25.6 Dissolved oxygen (mg.L–1) 2.4 10.2 6.7 pH 6.5 8.3 7.5 Conductivity (µS.cm–1) 98 420 229 Turbidity (NTU) 0.1 8.6 4.0
Merrick and Schmida [936] describe O. lineolatus as a benthic species whereas Bishop et al. [193] noted a preference for the surface layers (possibly in response to vertical differences in oxygen availability). In lagoons of the Normanby River [697], approximately 80% of the catch was collected from water less than 50 cm deep and 95% were in the lower part of the water column, although few were in contact with the substratum. The obvious preference for shallow water depths reflected the distribution of cover elements, these being limited to the lagoon margins. Sleepy cod use cover from which to ambush their prey and to seek refuge from other large predators such as barramundi and fork-tailed catfish. Thus, it is probable that the vertical distribution of cover and, too a lesser degree, vertical differences in dissolved oxygen, may determine the depth at which sleepy cod are found.
Cape York Peninsula – lagoons (n = 12) [697] Temperature (°C) 22.9 33.4 25.9 Dissolved oxygen (mg.L–1) 1.1 7.1 3.5 pH 6.0 9.1 7.1 Conductivity (µS.cm–1) 81 412 184 Turbidity (NTU) 2.1 120.0 14.5
Sleepy cod may be found in flowing water habitats, providing there is sufficient bank-associated or in-stream cover to provide flow refuge. It is more properly considered a still or slow-water species (<0.3 m.sec–1), given that it is not a powerful swimmer (except over short distances).
482
Burdekin River (n = 20) [1098] Temperature (°C) 20.6 32 Dissolved oxygen (mg.L–1) 4.6 11.0 pH 7.0 9.2 Conductivity (µS.cm–1) 81 650 Turbidity (NTU) 1 22
25.7 7.8 8.1 412 5.6
Belyando River (n = 4) [256] Temperature (°C) 18.3 21.5 Dissolved oxygen (mg.L–1) 4.5 7.1 pH 7.0 7.4 Conductivity (µS.cm–1) 177 184 Turbidity (NTU) 188 579
19.8 5.7 7.2 181.8 400.3
Fitzroy River (n = 5) [942] Temperature (°C) 24.0 27.5 Dissolved oxygen (mg.L–1) 4.6 8.0 pH 7.4 8.2 Secchi disc depth (cm) 5 190
25.6 6.1 7.8 81.4
Oxyeleotris lineolatus, Oxyeleotris selheimi
at which 50% of the sample are sexually mature and consequently mature fish at smaller size may be encountered. Newly expanding populations (i.e. when translocated into previously unoccupied habitat) may mature at even smaller size (200 mm SL) [1093]. It is probable that sleepy cod take two to three years to reach sexual maturity in most circumstances and probably live for a further three to four years.
believed 15°C was approaching the lower thermal limit for sleepy cod. The upper limit should conservatively be placed at 38–39°C. Sleepy cod are tolerant of hypoxia and appear able to tolerate levels as low as 1.0 mg O2.L–1 for extended periods. Woodland and Ward [1416] recorded sleepy cod in pools of Magela Creek in which dissolved oxygen had fallen to 0.8 mg O2.L–1. Brown et al. [243] listed it among the species most tolerant of low levels of dissolved oxygen in billabongs of the Magela Creek floodplain. The eggs of sleepy cod may be much less tolerant as the heart of developing embryos apparently stops beating if the eggs are not continuously aerated [1433]. From the data presented in Table 1, it is also evident that sleepy cod are also tolerant of a wide range of water acidities, with a total range of 4.6 pH units. With the exception of the Alligator Rivers data, the range in pH was generally much smaller and differences in average pH reflect differences in catchment lithology. Sleepy cod have not been detected in any of Queensland’s dystrophic highly acidic dune lakes [1101] and thus appear to avoid highly acidic habitats. A conservative pH range of 5.5 to 8.5 would be appropriate for maintenance of habitat quality.
The presence of small juvenile fishes year round and the absence of seasonal changes in gonadosomatic index led Bishop et al. [193] to suggest that sleepy cod bred throughout the year but also that the greatest activity occurred in the late dry season. They acknowledged that their sample sizes were small and that other researchers had found eggs from November to late January only. The closely related O. heterodon from Papua New Guinea has been shown to spawn throughout the year also [315]. In contrast, Herbert and Graham [1433] report unpublished observations of young sleepy cod occurring in rivers of the Gulf of Carpentaria region in December after a spawning period in October and November. Furthermore, they demonstrated that captive populations spawned over the period of late-September to mid-March only. Merrick and Schmida [936] suggest that water temperatures above 24°C are required for spawning of O. lineolatus in the Fitzroy River. Herbert and Graham [1433] report that captive populations from the Walsh River commenced spawning after water temperatures has exceeded 24°C for 3–4 days and continued until temperatures dropped to 23°C. They also noted that the number of batches of eggs laid each day during the wet season increased during periods of rainfall associated with storm events.
Sleepy cod are confined to fresh water and the data presented in Table 1 suggests that very fresh water is required. The maximum conductivity recorded across all studies was only 650 µS.cm–1. In contrast, sleepy cod are found over a wide range of water turbidity. The turbidity values recorded in the Belyando River are notable for their magnitude, however sleepy cod have established well in this system and appear untroubled by such high levels of suspended solids. Similarly, sleepy cod have been recorded from highly turbid billabongs and reservoirs [942].
Sleepy cod produce large numbers of small eggs, the number of which is size dependent. No relationship between size and fecundity is available but the figures listed in Table 2 suggest a steep increase in fecundity with size as observed for O. heterodon [315]. An average egg mass size of 43 130 eggs (range = 5000–174 000) was recorded for captive fish [1433]. A period of about 19 days between successive spawning events by an individual female was suggested by Herbert and Graham [1433]. The eggs are demersal and adhesive [935]. In the related gudgeon O. marmoratus, contact between the ovulated egg and water initiates the rapid extension of numerous adhesive filaments from the vitelline membrane nearest the animal pole [1285]. Oxyeleotris lineolatus deposits its eggs on the under surface of rocky ledges or woody debris and on the ceiling of hollow logs [935, 1433]. Merrick and Midgley [935] also make the observation that the undescribed species sympatric with O. lineolatus (which we here assume is O. selheimi) lays its eggs in locations
Sleepy cod appear susceptible to tropical epizootic ulcerative syndrome (EUS, or red spot disease), but unlike species such as bony bream in which the lesions are large in area but shallow, EUS in sleepy cod is manifested as localised, very deep ulcers (often down to the bone). Infection rates in the Burdekin River were often very high (as high as 50%) on some occasions [1093]. Coates et al. [317] noted that gudgeons in New Guinea had high EUS infection rates also. Many sleepy cod in the upper Burdekin River are also heavily infested with metacercariae of a clinostomid trematode. Infection rates are very high, as are the number of metacercariae per individual [1093]. Reproduction Bishop et al. [193] believed that sexual maturity occurred at 285 mm for female and 330 mm (CFL) for male O. lineolatus respectively (Table 2). Note that these are the lengths
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Freshwater Fishes of North-Eastern Australia
Table 2. Life history data for the sleepy cod Oxyeleotris lineolatus and striped sleepy cod O. selheimi. Information derived principally from Bishop et al. [193], Merrick and Midgley [935] and Herbert and Graham [1433]. Age at sexual maturity (months)
?
Minimum length of ripe females (mm)
285 mm CFL, 250 mm (TL?), may mature earlier when colonising rivers in which they have been newly translocated
Minimum length of ripe males (mm)
330 mm CFL, 250 mm (TL?)
Longevity (years)
Unknown but probably 5–7 years
Sex ratio
1:1
Peak spawning activity
October to February, depends on location
Critical temperature for spawning
>24°C
Inducement to spawning
Increasing temperatures, rainfall
Mean GSI of ripe females (%)
1.9 + 0.8 (s.d.) %; however no stage VI females were examined and it is therefore probable that the maximum GSI is considerably larger
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
Total fecundity = 35 000 to 170 000; average 100 000 and maximum possibly as high as 700 000 in Alligator Rivers region; much higher total fecundity levels recorded for captive populations from the Gulf of Carpentaria region
Fecundity/length relationship
Unknown but fecundity values listed above are for 310 mm female (35 000 eggs) and 390 mm female (170 000) and suggestive of a steep increase in fecundity with increasing size
Egg size
Eggs fusiform, 2–2.5 mm on long axis, 1 mm on short
Frequency of spawning
Serial spawner, Merrick and Midgley [935] suggest 5–7000 eggs laid on each occasion so potentially many separate spawnings within a season. Herbert and Graham [1433] report much higher batch sizes with an interval of about 19 days. It is probable that sleepy cod are iteroparous, commencing in third year (possibly in second year when translocated populations are expanding)
Oviposition and spawning site
Patches of eggs laid on undersurface of rock ledges, woody debris and hollow logs in O. lineolatus. O. selheimi suggested to attach eggs to all surfaces but undersurface.
Spawning migration
None reported
Parental care
Male guards nest
Time to hatching
5–7 days in artificial conditions, 3–5 days at 25–30°C
Length at hatching (mm)
?
Length at feeding
?
Age at first feeding
Within days of hatching, 7–10 days after fertilisation
Age at loss of yolk sac
8–9 days after fertilisation
Duration of larval development
?
Length at metamorphosis
?
anywhere but on the ceiling of hollow logs or the under surface of other structures. Merrick and Midgley [935] noted that artificial nests set at both the surface and at depth were used but that nests set at about 1 m below the surface were most frequently used as nest sites. They speculated that nests at this depth were insulated from temperature fluctuations as well as being unlikely to experience dissolved oxygen deficiencies. The male guards the nest (aerating the eggs with fin movement).
averaged 3.43 mm TL, possessed pectoral fins, a working mouth, a reduced yolk sac and were capable of short burst of swimming. Under conditions of controlled temperature (27°C), hatching occurred in three days and the larvae are apparently capable of exogenous feeding. A similarly short incubation period of O. lineolatus was reported by Herbert and Graham [1433], however survivorship of larvae hatching 3 days after fertilisation was poor compared to fish hatching after 5 days.
Larvae are probably small at hatching, which takes place within 3–7 days. Hatching in O. marmoratus is variable in duration and larvae hatch at different stages of development; such variability was suggested to be due to fluctuating temperature [1285]. Larvae that hatched after five days
Movement In natural circumstances it appears that sleepy cod do not make substantial migrations. Bishop et al. [190] rarely noted sleepy cod moving in Magela Creek. Whereas studies
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Oxyeleotris lineolatus, Oxyeleotris selheimi
included some individuals of O. selheimi, which were erroneously identified as O. lineolatus.
of fishways have yielded much information on the movement patterns of many species, Oxyeleotris spp. are not amongst them. Stuart [1274] recorded only five individuals moving through a fishway on the Fitzroy River. Hogan et al. [587] noted that sleepy cod between 200 and 415 mm SL were congregated downstream of the Clare Weir in the Burdekin system and inferred they were moving upstream. They did not state how many were present however, and noted that most were congregated downstream with large numbers of bony bream, rainbowfish, tarpon, catfish and barramundi. It is conceivable that the presence of sleepy cod had more to do with the abundance of prey fishes than the need to migrate. It seems probable that a slow-moving cryptic ambush predator with an obvious affinity for dense cover is unlikely to move greatly, especially when cover elements such as large woody debris are also used as nest sites (see below). However, Herbert and Graham [1433] report upstream movements by juvenile sleepy cod.
The diet of sleepy cod is diverse, when considered over all size classes, regions and habitat types (Figure 1). The majority (47%) of the diet is composed of aquatic insects with macrocrustaceans and fish contributing a further 26.2%. Molluscs (mostly gastropods) were another important item (10.9%). Material taken from the water’s surface accounted for little of the total diet (5.7%). The diet includes very little aquatic plant matter. Spatial variation in diet is, over the range of studies examined, rather slight. For example, the contribution by aquatic invertebrates to the total diet varied from 44.1% to 48.4% only. Fish were absent from the diet of sleepy cod from the Mulgrave and Johnstone rivers but molluscs comprised 33% of the diet there, in contrast to a contribution ranging from 6.4% (Alligator Rivers region) to 14.4% (Normanby lagoons) elsewhere. There remains a distinct possibility that at least some of the Wet Tropics sample contained B. gyrinoides, and this species has been observed to feed on molluscs. Fish were almost absent from the diet of sleepy cod from the Burdekin River (0.6%) although only three individuals greater than 300 mm SL were examined and fish were the only prey present in these fishes. Ontogenetic variation in sleepy cod diet is substantial. Larger fish (>150 mm SL) consumed fish exclusively whereas fish comprised only 9.1% of the diet of fish smaller than 150 mm SL. Bishop et al. [193] note that nine species of fish were present in the diet of O. lineolatus from the Alligator Rivers region.
The obvious exception is the spread of sleepy cod throughout the Burdekin River. However, in this case the majority of fish newly colonising areas were juveniles less than 100 mm SL, with the largest fish rarely exceeding 200 mm SL. Most fish of such size are not reproductively mature. Trophic ecology Information on the feeding ecology of O. lineolatus is drawn from studies undertaken in five regions; the Burdekin River (n = 35) [1098], the Mulgrave and Johnstone rivers (n = 9) [1097], rivers of Cape York Peninsula (n = 38) [1099], floodplain lagoons of the Normanby River, Cape York Peninsula (n = 68) [697] and floodplain lagoons of the Alligator Rivers region (n = 106) [193]. The samples contain both adult and juveniles and the two studies from the Normanby River [697, 1099] Fish (13.8%)
Microcrustaceans (2.6%)
Conservation status, threats and management Oxyeleotris lineolatus is listed as Non-Threatened in Wager and Jackson [1353] and is not listed by the ASFB [117]. Oxyeleotris selheimi is not listed by Wager and Jackson but Oxyeleotris sp. A is listed as Non-Threatened.
Unidentified (4.8%) Terrestrial invertebrates (1.6%) Aerial aq. Invertebrates (0.9%) Terrestrial vertebrates (2.3%) Detritus (1.2%) Terrestrial vegetation (1.9%) Aquatic macrophytes (0.1%) Algae (0.4%)
Macrocrustaceans (12.4%)
Molluscs (11.1%)
Other macroinvertebrates (0.1%) Aquatic insects (47.0%)
Figure 1. The diet of sleepy cod Oxyeleotris lineolatus. The summary below is derived from five separate studies across northern Australia and values presented for each food class are the weighted means adjusted for differences in sample size. Total n = 256.
485
In the case of O. lineolatus, these listings are probably appropriate, especially given the extent to which the distribution and abundance of this species has been artificially increased. This process may, in itself, be rightfully viewed as a threatening process, particularly in regard to the maintenance of genetic distinctiveness of different populations, especially the population in the Fitzroy River. In some circumstances, predation and competition by sleepy cod may be processes threatening the survival of other species found in catchments in which it has been translocated. For example, the increase in abundance of sleepy cod observed at Blue Range Station in the Burdekin River coincided with the decline in abundance of Mogurnda adspersa from a high of 30 fish per sample to a low of zero within two years of the appearance of sleepy cod [1093].
Freshwater Fishes of North-Eastern Australia
Juvenile sleepy cod have a diet almost identical to M. adspersa and adult sleepy cod predate upon all age classes of M. adspersa. Elsewhere, the closely related O. heterodon has been shown to prey almost exclusively on a single species of gudgeon [315]. If such a narrow and specialised foraging strategy also exists in O. lineolatus, then there is obviously a very high potential for it to impact on other species. The observation by Bishop et al. [193] that up to nine species of fish were consumed by O. lineolatus suggests that this species may be less specialised than O. heterodon however.
mechanisms exist in nature and, most importantly, whether isolating mechanisms exist under hatchery conditions. Therefore, given the failure by many to recognise the existence of more than one species and the practice of sourcing hatchery stock from a variety of locations, there is some potential for hybrid fingerlings to be produced and introduced into previously genetically unpolluted rivers. It is our opinion that no translocation of sleepy cod of any type should be allowed in rivers west of the Great Divide and that serious thought given to ceasing the practice throughout Queensland.
In addition, sleepy cod appear highly susceptible to tropical epizootic ulcerative syndrome (red spot disease) and may act as vectors for its transmission to other species and for its spread throughout the catchments into which they are introduced. This seems particularly important in the circumstance where sleepy cod are translocated into reaches above natural barriers to movement and for which an upstream pathway for transmission of EUS is unlikely.
Increased water resource development, particularly that involving the construction of large storages is likely to further increase the range of O. lineolatus unless some moratorium is placed on the process of stocking impoundments. Further research elucidating details of its reproductive biology would be useful. For example, it is unknown whether reproduction is seasonal or continuous. Similarly, it would be useful to know whether high instream flows are detrimental to larvae and small juveniles. The evident preference for lagoon-type habitats suggests that resource developments that limit or stop flooding will impact on this species. Similarly, off-stream processes such as wetland reclamation will impact negatively on sleepy cod. Sleepy cod have a high affinity for, and need of, instream cover such as woody debris, root masses and aquatic vegetation. Environmental flows need to be managed to ensure that these elements remain available. De-snagging of lowland rivers is likely to have negative impacts on these species through a reduction in available spawning sites.
Oxyeleotris selheimi is probably secure given that its range extends across nearly all of northern Australia. However, translocation of O. lineolatus may pose some a threat in the future if such activities increase in frequency and scale in this region. It is unknown whether the observed sympatry of these species is also accompanied by intense competition and consequently the extent to which the abundance of one species is regulated by the other is also unknown. Artificially increasing the population growth rate of O. lineolatus by stocking may be sufficient to result in declines in O. selheimi populations. In addition, it is unknown to what extent these two species hybridise, whether isolating
486
Oxyeleotris aruensis (Weber, 1911) Aru gudgeon
37 429036
Family: Eleotridae
Description First dorsal fin: VI; Second dorsal: I, 12–14; Anal: I, 10–12; Pectoral: 13–16; Horizontal scale rows: 16–18; Vertical scale rows (midlateral): 55–60; Predorsal scales: 35–40 [37]. Body morphology is typical of the genus: body cylindrical, dorsoventrally flattened anteriorly and laterally compressed posteriorly. Figure: mature male specimen, 46 mm SL, Mulgrave River, December 1997; 2003.
specimens. A series of chevron-like markings is frequently present on the side and is distinctive in O. aruensis, and also in O. fimbriata and O. nullipora. Two or three dark lines radiate from the eye across the cheek. A large dark ocellus is present at the base of the caudal fin. This feature is absent in O. nullipora but present in O. fimbriata. Oxyeleotris aruensis has a less well-developed cephalic pore system than O. fimbriata, lacking pores Q, H, I and J (see Figure 30 in Allen [37]), and has fewer scales (60–83 in the midlateral series). Oxyeleotris nullipora has no head pores.
Oxyeleotris aruensis is a small gudgeon: Allen [37] and Allen et al. [52] list a maximum length of 150 mm SL or 160 mm, respectively, but add that this species more commonly grows up to 100 mm in length [52]. These average and maximum lengths are greatly in excess of that recorded by us in the Wet Tropics region. For example, minimum, maximum and mean lengths (SL in mm) for a sample of 181 fish collected from the Mulgrave River over the period 1994–1997 were 18, 62 and 39 ± 0.6 (SE) mm, respectively. About 50% of the sample was between 35 and 45 mm SL, and many within this size range were sexually mature (see below).
The head, throat, ventral surface, and anal and dorsal fins (particularly the former) of O. aruensis may sometimes attain a vivid orange colour. Presumably this is associated with breeding and was observed by us in only the largest specimens (>50 mm SL). Colour in preservative: essentially the same except orange pigments greatly reduced in intensity. Systematics Oxyeleotris aruensis was originally described as Eleotris aruensis by Weber in 1911 from material collected from the Aru Islands off southern New Guinea [1371]. Some morphometric/meristic variation occurs across its range (Allen, pers. comm.) but the extent of this variation
The colouration of O. aruensis is typical of the genus, being most commonly a pale brown dorsally and chocolate brown laterally, grading to a light brown ventrally. The pale colour of dorsal surface may be absent in some 487
Freshwater Fishes of North-Eastern Australia
as G. margeritacea, B. gyrinoides, E. fusca and E. melanosoma, and suggests a distribution broadly overlapping with these species in the lowlands but which also extends into the foothills. (It also suggests some differences in reproductive biology – see below.) Although broadly sympatric with the species listed above, O. aruensis tends not to be syntopic with them, partitioning being accomplished with a slight shift upstream into reaches of slightly greater gradient and further away from the confluence with the main channel. Oxyeleotris aruensis frequently cooccurs with Cairnsichthys rhombosomoides, another species that appears restricted to tributary streams whether located in the foothills or the coastal plain.
remains to be quantified fully. In addition, the distribution of this species is highly fragmented and it is possible that more than one species is involved. Distribution and abundance Oxyeleotris aruensis occurs in both northern Queensland and New Guinea. Its distribution in New Guinea is highly fragmented, being apparently limited to the Aru Islands and the Fly and Bensbach rivers [37]. The Australian distribution is similarly fragmented and appears to be limited to the east coast, with the exception of populations in the Jardine [34, 1349] and Wenlock rivers [571]. This species was not recorded from any other river draining into the Gulf of Carpentaria during the CYPLUS surveys of Cape York Peninsula but was collected from three eastern drainages: the Olive, Lockhart and Claudie rivers [571]. Oxyeleotris aruensis has been recorded from four drainages of the Wet Tropics region: the Mulgrave, Russell, Tully and Murray rivers [1087, 1096, 1184, 1349]. This species in the Mulgrave River has been erroneously identified as O. fimbriata in the past [1096]. Given the relatively recent periodic connection between the Mulgrave River and streams draining into Trinity Inlet [1411], this species probably occurs there also. It is notable that O. aruensis has not been recorded from the Johnstone River despite many years of intensive sampling.
Allen [34] lists the habitat of O. aruensis as including rivers, lakes and creeks. Floodplain wetlands on the Murray River floodplain are also suggested to contain O. aruensis (or a closely related species) [569]. Our sampling Table 1. Macro/mesohabitat use by Oxyeleotris aruensis. Data derived from 19 sites located in the Mulgrave River, three sites in the Russell River and two sites located in the Tully River sampled in 1994 or 1995. Data given represents minimum, maximum and mean habitat characteristics. Also shown are the means weighted by abundance (W.M.) to reflect the degree of preference. Parameter
Only 14 individuals from four sites were collected by Pusey and Kennard [1087] during their extensive survey of the Wet Tropics region. More recently, maximum and mean (+ SE) density values of 1.71 and 0.36 ± 0.007 fish.10m–2 were recorded from a total of 30 site/sampling occasions in the Mulgrave (n = 25), Russell (n = 3) and Tully rivers (n = 2) over the period 1994–1997. Equivalent biomass estimates were 2.0 and 0.68 ± 0. 10 g.10m–2, respectively. This species was the fourth and 13th most abundant species, by density and biomass respectively, in these sites. Oxyeleotris aruensis most frequently occurs with (in decreasing order of abundance) C. rhombosomides, P. signifer, A. reinhardtii and H. compressa [1093].
Min.
Catchment area (km2 ) Distance from source (km) Distance to river mouth (km) Elevation (m.a.s.l.) Order Stream width (m) Riparian cover (%)
0.4 2 8.1 5 1 1.9 0
Site gradient (%) 0.02 Mean average depth (m) 0.1 Mean water velocity (m.sec–1) 0.04
Macro/mesohabitat use Oxyeleotris aruensis has a limited distribution within the Mulgrave, Russell and Tully rivers. Although found in a range of streams sizes (up to fifth order and 22 m in width, i.e. Behana Creek), it is relatively more common in smaller streams relatively close to the source (Table 1). Such streams are best typified as adventitious tributaries entering directly into the main channel and, within the Wet Tropics region, tend to host a diverse array of gudgeon and goby species. The range in elevation and distance from the river mouth is substantial compared to many other species within the family particularly other similar gudgeons such
488
Max.
Mean
W.M.
141.7 21 64.0 70 5 22.0 90
25.6 6.5 32.4 27.3 3.1 7.3 52.9
8.7 4.0 40.9 39.4 2.5 5.3 63.2
4.54 0.67 0.36
0.88 0.33 0.15
1.75 0.29 0.13
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
26 65 73 46 38 75 48
4.1 23.7 27.9 9.7 10.5 17.5 6.4
3.0 15.0 28.2 7.0 9.7 19.7 16.8
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% of bank) Root masses (% of bank)
0 0 0 0 0 0 0 0 0 0
1.4 0 0.1 75.0 10.0 33.8 8.9 11.4 35.0 53.0
0.1 0 1.4 9.5 0.5 12.4 1.8 2.1 7.8 19.7
0.1 0 0.7 7.2 0.1 11.1 1.0 1.3 4.9 15.5
Oxyeleotris aruensis
in the Wet Tropics region [1087, 1093, 1096, 1100, 1105] whilst most strongly focussed on streams, has included both large lowland rivers and floodplain wetlands (including those located on the Tully and Murray floodplain) and we have not collected O. aruensis from such habitats. The presence of O. aruensis in Australia anywhere other than the Jardine River was unknown at the time Allen [34] suggested such a wide habitat use and presumably referred to its distribution in the Jardine River or New Guinea. It is notable that subsequent publications by Allen [37, 52] do not list lentic habitats (i.e. lakes and swamps) as being used by this species.
(a)
(b)
50
80
40
60
30 40
20 10
20
0
0
Mean water velocity (m/sec)
Within the small part of the Wet Tropics region in which O. aruensis occurs, stream reaches containing this species are shallow and of low to moderate water velocity (i.e. run habitats) with a substrate dominated by sand and fine gravel but also containing a substantial amount of much coarser material. Indeed, reaches in which the substrate was dominated by fine gravel substrate and bedrock (i.e. very large boulders) were preferred (Table 1).
(d)
30
60
20
40
10
20
0
0
40
(e)
Relative depth
Total depth (cm)
(f) 30
30
Aquatic vegetation of any type (macrophytes, algae or emergent vegetation) was uncommon in stream reaches containing O. aruensis, probably because of the closed nature of the canopy. One site, with a greatly disturbed riparian canopy (0%), was notable for its prolific weed growth (Brachiaria mutica) extending into and choking the stream. However, 77% of all sites contained no such invasive grass. Leaf litter and exposed rootmasses were common in stream reaches containing O. aruensis.
20
20 10
10
0
0
Substrate composition
Microhabitat use Oxyeleotris aruensis was most frequently collected from areas with no discernible flow and in those cases where mean water velocity was greater than zero, focal point velocity was always much lower (Fig. 1 a and b). This was most often achieved by the fish being located close to the stream-bed (Fig. 1d) or by being insinuated within leaf litter or root masses (Fig. 1f). This species was very rarely collected not in association with some form of cover.
Focal point velocity (m/sec)
(c)
Microhabitat structure
Figure 1. Microhabitat use by the Aru gudgeon Oxyeleotris aruensis. Data derived from a total of 60 individuals collected from small streams in the Mulgrave River.
Environmental tolerances The summary information presented in Table 2 was derived from water quality data collected during routine sampling of fish populations at 36 site/sampling occasions in the Mulgrave (n = 31), Russell (n = 3) and Tully (n = 2) rivers over the period 1994–1997. As such they summarise ambient conditions but not environmental tolerance limits.
Oxyeleotris aruensis occurs over a range of depths but was most commonly found in water less than 40 cm deep. Depth use (Fig. 1c) closely approximates the distribution of mean depths of the sites in which this species was found. Substrate use (Fig. 1e) also closely approximates the average composition of sites in which O. aruensis was recorded, except with an apparent aversion of patches with a high proportion of bedrock. This apparent preference probably reflects the fact that root masses, one of two preferred microhabitat elements, are unlikely to develop in areas of substantial bedrock.
Oxyeleotris aruensis has been collected from waters of high quality: being slightly acidic, well-oxygenated and of very low conductivity. Except for a single sample taken immediately after a storm event, habitats in which this species was found were typified by low levels of suspended material. The temperature range given in Table 2 reflects that expected for small rainforest streams in the Wet Tropics region. Slightly higher maximum water temperatures,
489
Freshwater Fishes of North-Eastern Australia
perhaps 30–32°C, such as occur in similar streams in the Johnstone River [1108], are probably experienced during summer.
Movement No information is available on this aspect of the biology of O. aruensis.
Table 2. Physicochemical data for Oxyeleotris aruensis. Data derived from 33 site sites located in the Mulgrave and Johnstone rivers of the Wet Tropics region sampled over the period 1994–1997.
Trophic ecology No quantitative data on the diet of this species are available. Allen [34] suggests that the diet is composed of terrestrial and aquatic insects, shrimps and other crustaceans. The majority of such items tend to be relatively large and probably too large for the majority of fish examined by us. Aquatic insects such as mayfly nymphs and caddisfly and midge larvae probably constitute the major prey items of O. aruensis in rainforest streams.
Parameter
Min.
Temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
15.2 5.33 5.90 5.64 0.2
Max. 27.4 9.96 7.86 38.6 18.1
Mean 21.1 7.40 6.80 29.9 1.2
Conservation status, threats and management Oxyeleotris aruensis is listed as Non-Threatened by Wager and Jackson [1353], however its distribution is highly fragmented and it is uncommon. Some streams in which it occurs in the Wet Tropics region are exposed to a number of threatening processes such as the destruction of riparian vegetation, channelisation of small streams and spread of Tilapia (see comments for Mugilogobius notospilus, Eleotris spp.). Other inhabited streams drain small sub-catchments wholly contained within Wooroonoora National Park (formerly Bellenden Kerr National Park) and populations located therein are secure. Further investigation of the reproductive biology of this species would be desirable in order to predict how it might respond to water abstraction and/or changes in flow regime. Further investigation of the systematics of this species would also be desirable to determine whether a single species is indeed present across the fragmented distribution currently observed.
Reproduction No quantitative information on the reproductive biology of O. aruensis is available. Gravid females as small as 40 mm SL have been collected in July and August [1093]. The similarly sized O. nullipora produces about 30 large (2 mm) eggs that are attached to the ceiling of overhanging rocks or in crevices and guarded by the males for about eight days until hatching occurs [37]. A similar strategy is expected for O. aruensis. The fact that males periodically develop an intense colouration suggests that they may display to females prior to spawning. The limited and fragmented geographical range, limited macrohabitat distribution and the fact that small individuals have been collected in the same habitat as adult fish, all suggest that reproduction and larval development all occur in freshwater and that no estuarine or marine larval phase occurs.
490
Giurus margaritacea (Valenciennes, 1837) Snakehead gudgeon
37 429010
Family: Eleotridae
variance in weight is explained, and the slope of the line is low compared to other gudgeons (cf. Oxyeleotris lineolatus for example).
Description First dorsal fin: VI; Second dorsal: I, 8–9; Anal: I, 9; Pectoral: 14–15; Vertical scale rows: 30–32; Horizontal scale rows: 8–9; Predorsal scales: 17–19. The head is completely scaled. Meristics taken from Allen and Coates [46] but note that Merrick and Schmida [936] list greater variation in anal and second dorsal ray number (7–9 and 8–10, respectively) and in vertical scale rows (29–32). Figure: mature male 200 mm SL, lower Burdekin River, June 2002: drawn 2002.
The body tends to be cylindrical anteriorly and laterally compressed posteriorly. The mouth is moderately large and oblique, the maxilla reaching below the front of the eye. The eyes are dorsally oriented. This species is spectacularly coloured and most published photographs and descriptions do not adequately convey this impression. The body of adult males is rich brown dorsally, grading through a steel grey/blue on the flanks and a yellow/ochre colour ventrally. When in breeding condition, the ventral surface anterior of the anus may be a vivid yellow/gold. A series of four to five vivid red lines are present on the flanks, each line being formed by a series of large dots made up of individual scales. On occasions, these dots may be interspersed with vivid yellow or orange dots also. The dorsal fins and anal fins are red and blue with a yellow margin. The pelvic fins tend to be dark and fringed with red while the pectoral fins tend to be dusky with a feint red/orange margin. The caudal fin is large, rounded and reddish-brown with a series of reddish/gold dots running the length of the fin between each ray. The head tends to be dark dorsally, tending to blue on the opercula. Three
Giurus margaritacea is a moderate-sized species. Merrick and Schmida [936] report the maximum size attained (presumably total length) as 400 mm and a maximum weight of 1 kg. Of approximately 2000 fishes collected from the Sepik River by Allen and Coates [46], the maximum length of male and female fish was 196 and 194 mm SL, respectively. A maximum length of 300 mm SL was recorded for fish collected from the Mulgrave and Johnstone rivers over the period 1994–1997 (n = 258). The average length of this sample was 173 mm SL. The equation describing the relationship between length (SL in mm) and weight (W in g) in the Wet Tropics region is W = 6.4 x 10–4 L2.406: r2 = 0.453, p<0.01, n = 10 [1093]; but note that that the sample size is small, less than 50% of the
491
Freshwater Fishes of North-Eastern Australia
Distribution and abundance Giurus margaritacea is very widely distributed. Koumans [738] reported its distribution to be Indo-Pacific including Madagasgar, India, the Indo-Malayan Peninsula, the Philippines, Melanesia and northern Australia. Its distribution in Australia is contrastingly limited, being absent from the Northern Territory and most Queensland rivers draining into the Gulf of Carpentaria [936] with the exception of the Embley estuary near Weipa [197], the Wenlock River [571] and the Jardine River [41, 1349]. On the east coast of Cape York Peninsula, G. margaritacea has been recorded from the Claudie River, Temple Bay Creek, Alex Creek and Palm Creek (Bathurst Bay), Black Creek at Hopevale and the Endeavour River [571], and from the dune lake systems associated with the Olive River [781] and Cape Flattery [1088]. It is widely distributed in the Wet Tropics region [1096, 1100, 1349] being recorded from streams of the Cape Tribulation area, and from the Daintree River south to Herbert River [584] and including coastal streams of the Cardwell area [1096] and the Townsville area [1053]. In an extensive survey of the Wet Tropics region undertaken in 1993, G. margaritacea was recorded from 23/93 sites and 8/10 basins. Overall it was the 12th most abundant species in that survey (total collected = 103) with the greatest number (32) being collected from floodplain habitats of the Murray River.
red lines radiate out from the posterior margin of the eye to the posterior margin of the operculum. The dorsal most of these lines continues onto the base of the pectoral fin. A short red line running obliquely from the dorsoposterior margin of the eye (at the 1–2 o’clock position) may be present, as may a short oblique bar running from the eye (at the 7 – 8 o’clock position) to the mouth. Females tend to lack the vivid reds of males and are more characterised by dark brown dorsally grading to a green/yellow colour ventrally. Horizontal lines on the flanks and head are still present but are more similar in colour to that seen on the dorsal surface. Fish less than 100 mm SL are often a sky- to steel-blue and may be distinguished by a dark horizontal bar [936]. Colour in preservative: vivid colours tend to be lost in preserved specimens, to be replaced by dark brown or brick-red colour. Lines and barring are retained. On occasions, fish stored in formalin will become almost black. Systematics The snakehead gudgeon was originally described by Valenciennes in 1837 as Giurus margaritacea [355] but the species name appears not to have been used again until being reinstated in 2002 [52]. The species was later described under the more commonly used species epithet aporos and placed in the ‘catch-all’ genus Eleotris by Bleeker in 1854. Ogilby [1075] noted that this genus had been made the ‘…refuge for so many and so varied forms that it is safe to say that in no other branch of biological science would such an extraordinary agglomeration of distinct forms been permitted for so long a time’. The genus Ophieleotris was erected by Aurich in 1938 and was believed at the time to be montotypic. Synoyms of G. margaritacea are limited to Eleotris aporos (Bleeker, 1854), Eleotris hoedtii (Bleeker, 1854), Ophiocara aporos (Herre, 1936) and Ophieleotris aporos but this species has also been misidentified as E. ophicephalus (= Ophiocara porocephala) and E. tumifrons (= Ophiocara macrolepidota). Grant, in his treatise on Australian fishes [470], lists the snakehead gudgeon as Ophiocara aporos and suggests that there are three distinct colour forms; aporos Bleeker, hoedti (sic) Bleeker and guentheri Koumans. The first two species have been dealt with above. The latter putative species is actually a varietal form, O. aporos var. guentheri described by Koumans in 1937 for material from Palau [738]. Allen and Coates [46] noted the possibility that there may be more than one species of snakehead gudgeon and Larson (pers. comm.) suggests that there may indeed be several. We have here used the name Giurus margaritacea but note that the name Ophieleotris aporos will probably remain the preferred term for many years, and moreover, note that the name G. margaritacea may not in fact be the rightful name (G. Allen, pers. comm.).
Museum records indicate that G. margaritacea occurs in the Burdekin, Proserpine and Pioneer rivers [1349] and populations still exist in the Burdekin and Pioneer rivers [586, 1081]. Recent surveys of the fish of the Proserpine River did not collect any snakehead gudgeon [1093], and, if present, population size is likely to be small given the degraded nature of this river. Snakehead gudgeon have not been recorded from the Fitzroy River [161, 1274] or Shoalwater Bay area [1328]. Thus, the Pioneer River appears to be the southern limit for this species. The British Museum of Natural History contains a single specimen (BMNH 1883.11.29.71), reportedly collected from New South Wales [9]. This is, in all likelihood, in error. Giurus margaritacea is not widely distributed in the Mulgrave or Johnstone rivers (Tables 1 and 2), nor is it especially abundant at those sites in which it occurs, consequently it contributed less than 1% of the total number of fishes collected from these rivers. In contrast, G. margaritacea is the dominant species by biomass in those sites in which it occurs and consequently contributed substantially (7.11%) to the total biomass collected over the period 1994–1997, exceeded by A. reinhardtii and H. tulliensis only. This species commonly co-occurs with (in decreasing order of abundance) H. compressa, C. rhombosomoides, P. signifer, M. s. splendida and M. notospilus.
492
Giurus margaritacea
The streams in which the snakehead gudgeon occurs contain abundant amounts of in-stream cover. However, comparison of arithmetic and weighted mean values reveals that G. margaritacea were proportionally less abundant in streams with abundant submerged vegetation; which in this case is primarily para grass (Brachiara mutica), an introduced pasture grass. Para grass is limited by light availability, thus the disparity in the magnitude of the arithmetic and weighted means reflects a preference for well-forested streams (and in which para grass is expected to be uncommon) and possibly the fact that para grass is not commonly used by native fish species. Giurus margaritacea were more abundant in streams with abundant leaf litter, again reflecting the preference for wellforested streams.
Table 1. Distribution, abundance and biomass data for Giurus margaritacea in two rivers of the Wet Tropics region. Data summaries for a total of 272 individuals collected over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance, and per cent and rank biomass, respectively, at those sites in which this species occurred. Total % locations % abundance Rank abundance % biomass
Mulgrave River
Johnstone River
16.7
20.5
14.3
0.8 (4.8)
0.7 (3.9)
0.8 (4.3)
23 (8)
15 (6)
20 (11)
7.1 (54.7)
5.9 (43.3)
8.0 (61.0)
Rank biomass
3 (1)
3 (1)
3 (1)
Mean density (fish.10m–2)
0.39 ± 0.06
0.40 ± 0.14
0.38 ± 0.16
Mean biomass (g.10m–2)
66.86 ± 9.83 78.83 ± 25.78 60.26 ± 0.52
Table 2. Macro/mesohabitat use by Giurus margaritacea. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Macro/mesohabitat use The data presented in Table 2 is derived from mean habitat characteristics of 18 sites in the Mulgrave and Johnstone rivers sampled over the period 1994–1997. Although G. margaritacea occurs in a range of stream sizes from first to fifth-order streams, it was most common in streams of order two or three. Such streams tended to have a catchment area of approximately 19 km2, although it is evident that this species is most abundant in small streams with a catchment area of less than 2 km2. Sites located in such streams tend to be close to the stream source. Notably however, such sites were likely to be located on average, within 17 km of the river mouth and abundances tend to be higher in those sites located closest to the mouth. As would be expected, sites containing G. margaritacea are at low elevation and of gentle gradient. An intact riparian cover is a feature of these streams and abundances tended to be greatest in sites with greater canopy cover. In summary, the sites within the Johnstone and Mulgrave rivers containing this species were small, adventitious, low-gradient streams located close to the river mouth and with an intact riparian canopy.
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
0.13 0.5 10.1 5 2.0 0
Gradient (%) 0.02 Mean depth (m) 0.14 Mean water velocity (m.sec–1) 0
Streams from which this species was collected were on average about 6 m wide although they were recorded from both much larger streams (up to 22.6 m wide) and much smaller streams (2 m wide) also. On average, streams in which this species occurred were relatively shallow and with only minor current. As would be expected from the average gradient and water velocity, the substrate of streams in which G. margaritacea occurred tended to be dominated by the smaller-sized particles and abundances were greatest in those sites with a substrate dominated by mud, sand and fine gravel.
Max. 85.0 1.5 51.0 40 22.6 99 1.33 0.69 0.22
Mean
W.M.
19.1 4.8 16.9 11.7 5.7 59.7
1.6 1.9 11.3 10.1 4.9 69.8
0.24 0.32 0.10
0.11 0.31 0.03
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
35 88 60 73 33 58 16
8.1 34.0 27.8 14.6 6.0 6.2 3.2
13.6 35.3 37.3 10.1 0.8 1.5 1.4
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
23.7 6.8 19.0 60.0 7.0 81.2 11.0 12.3 28.0 65.0
2.1 0.4 3.6 10.4 0.3 20.6 3.3 3.4 7.1 21.3
3.0 0.6 3.0 3.5 0.6 33.1 4.6 4.2 5.6 22.1
It must be stressed that the data presented in Table 2 represent the macro/mesohabitat usage by snakehead gudgeon in streams of the Mulgrave and Johnstone rivers only and that this species is also recorded from a variety of other habitats. For example, in the section detailing the
493
Freshwater Fishes of North-Eastern Australia
Papua New Guinea and it was collected from a variety of habitats including the main river, swamps, lakes and turbid or clear tributary streams but was particularly common throughout the floodplain of the lower and middle parts of the river.
distribution of snakehead gudgeons, it was stated that the greatest number of specimens collected by Pusey and Kennard in an extensive survey of the Wet Tropics region [1087] were from lentic habitats of the Murray River floodplain, not from lotic habitats. These floodplain sites were characterised by no discernible flow, depths of between 2–3 m and very dense accumulations of floating macrophytes and emergent sedges. This species occurs in the main channel of the Mulgrave River [1096]. Elsewhere, in the Burdekin River for example, snakehead gudgeon are recorded from floodplain lagoons (C. Perna pers. comm.) and were historically present in the lower reaches of the river.
Microhabitat use Giurus margaritacea was most frequently collected from areas of very low water velocity reflecting the pattern observed in mesohabitat use (Fig. 1a and b). Most specimens were collected from areas of between 0.3 and 0.6 m deep (Fig. 1c), depths greater than indicated by the average depth of sites in which they were collected (Table 2), suggesting that they were selecting the deepest parts of the sites in which they occurred. Most individuals were collected from the upper 30% of the water column (Fig. 1d). When undisturbed, snakehead gudgeon are not uncommonly observed lying motionless at the water’s surface.
Allen and Coates [46] suggested that G. margaritacea was the most widely distributed species in the Sepik River of (a)
100
80
80
60
Snakehead gudgeon do not appear to actively select particular substrate types as the distribution depicted in Figure 1e closely resembles that suggested in Table 2. There is however, an evident disproportionate use of woody debris, indicating a strong preference for this microhabitat element. Perna [1053] also observed substantial use of woody debris (and of undercut banks and macrophytes) by snakehead gudgeon during underwater surveys in Leichhardt Creek near Townsville. Note that the use of woody debris may not be so pronounced in floodplain and wetland habitats where emergent vegetation is more abundant. However, Allen [34] notes that snakehead gudgeons are frequently observed associated with woody debris (using it as a spawning substrate) in New Guinean lakes.
60
40
40
20
20
0
0
Mean water velocity (m/sec) 30
(b)
Focal point velocity (m/sec)
(d)
(c)
40 30
20
20 10
10
0
0
Total depth (m)
Environmental tolerances Information on tolerance to water quality extremes is lacking and the data listed below reflects the water quality of streams in which G. margaritacea has been collected.
Relative depth
(e)
(f)
30
30
20
20
10
10
0
0
The data presented in Table 3 indicates that this species occurs in streams with very high quality water reflecting the well-forested nature of these streams. The range in Table 3. Physicochemical data for Giurus margaritacea. Data summaries for sites in which present over the period 1994–1997.
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by the snakehead gudgeon Giurus margaritacea. Data derived from capture date for 108 individuals from the Johnstone and Mulgrave rivers over the period 1994–1997.
494
Parameter
Min.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
17.5 5.6 4.50 7.8 0.33
Max. 27.2 8.4 8.17 65.6 22.08
Mean 22.9 6.91 6.21 36.8 2.03
Giurus margaritacea
tolerances may be higher than is here indicated. In general, the waters in which G. margaraticea occurs are very clear and leached organic acids contribute the bulk of what little colour is present. The maximum NTU value listed in Table 2 was recorded after a rainfall event resulted in substantial downstream transport of sediment. Floodplain lagoons of the Burdekin River in which snakehead gudgeons occur may be as turbid as 47.6 NTU (C. Perna, pers. comm.). It must be borne in mind that the data presented here are for small rainforest streams in the Wet Tropics region and are probably not representative of conditions over the entire range in Australia.
water temperatures indicated in Table 3 is typical of small rainforest streams. Although recorded as present in streams typified by a substantial range in dissolved oxygen levels, the mean value listed indicates that the streams in which it occurs are well-oxygenated. The standard error for the mean was small (± 0.125 mg.L–1). However, the fact that G. margaritacea is frequently found in wetland systems suggests it may be quite tolerant of low levels of dissolved oxygen and indeed, G. margaritacea has been collected from lagoons with exceptionally depressed levels of dissolved oxygen (Burdekin River floodplain; D.O. = 0.18 mg O2.L–1, C. Perna, pers. comm.). The mean pH recorded was slightly acidic although the range in pH was substantial. The presence of G. margaritacea in dunelake systems (see above) suggests it is able to tolerate greater acidity than is suggested here. Conductivities in sites in which it was present were uniformly low. However, the very wide distribution of this species strongly suggests, providing there is only one species involved, that salinity
Reproduction The data summarised in Table 4 are from a single study undertaken in the Sepik River of Papua New Guinea. Reproductive information is lacking for Australian populations and this aspect of the biology of this species is in need of study.
Table 4. Life history information for the snakehead gudgeon Giurus margaritacea. Data listed are primarily those for a population in the Sepik River of Papua New Guinea [315]. Variations from that described by Coates [315] are denoted by additional references or by * in the case of personal opinion. Age at sexual maturity (months)
? probably at around 12 months*
Minimum length of ripe females (mm)
50 mm
Minimum length of ripe males (mm)
50 mm
Longevity (years)
? probably 4–5 years*
Sex ratio (female to male)
Males in excess except at times of low water level
Occurrence of ripe fish
Year round
Peak spawning activity
Peaking during the wet season
Critical temperature for spawning
? unlikely to be a critical temperature initiating spawning given year-round spawning but there may exist a temperature below which spawning may not occur
Inducement to spawning
? probably rising water levels*
Mean GSI of ripe females (%)
9.03 ± 0.11%
Mean GSI of ripe males (%)
3.24 ± 0.76%
Fecundity (number of ova)
40 000–200 000 depending on size
Fecundity /length relationship
357 x SL1.22
Egg size
0.297 ± 0.011 mm
Frequency of spawning
?
Oviposition and spawning site
Woody debris [34]. Occurrence of larvae in marine and estuarine environments suggests a lower estuarine spawning ground in some populations
Spawning migration
Sepik River population seasonally migrate onto floodplain at times of high water. Australian populations may either move onto floodplains or to the lower portions of estuaries
Parental care
Nest guarding
Time to hatching
?
Length at hatching (mm)
?
Length at free swimming stage
?
Length at metamorphosis (days)
?
Duration of larval development
?
Age at loss of yolk sack
?
Age at first feeding
?
495
Freshwater Fishes of North-Eastern Australia
Trophic ecology There is little information concerning the diet of O. margaritacea in Australia except anecdotal accounts that suggest that grasshoppers form part of the diet [936] or that the diet consists of ‘insects, shrimps, crayfish and other fishes’ [34]. New Guinean populations consume an array of material including macrophytes and filamentous algae, detritus, microcrustacea and aquatic insects (Figure 2) but notably, terrestrial insects, macrocrustacea or fishes do not individually account for more than 1% of the diet of this sample.
Giurus margaritacea has a reproductive biology similar to that observed in many other gudgeon species. Reproductive maturity occurs at relatively small size and even small fish are highly fecund, producing many thousands of small eggs. Presumably the larvae are small and poorly developed at hatching. McDowall [316] lists several observation of the larvae of this species being collected from marine and estuarine habitats, and it is probable that some populations or some proportion of populations present in northern Australian rivers either spawn in estuaries (i.e. adults are catadromous) or larvae are passively transported to the lower portions of estuaries or the nearshore environment. The lack of small individuals in streams of the Wet Tropics region (see below) also supports the suggestion that adult and juvenile habitats are separate. Coates [315] believed many aspects of the reproductive biology of G. margaritacea were in response to heavy predation by another large gudgeon Oxyeleotris heterodon (a species similar to sleepy cod). Whilst this may be so in the Sepik River, it may not apply across its whole distribution. Movement There is little information on the movement patterns of Australian populations of Giurus margaritacea. This species has been recorded trying to negotiate the fishway on the Clare Weir on the Burdekin River [586]. Movement out of small adventitious streams to spawning grounds (which are unknown at this time) is probable in the Wet Tropics region as the smallest individual collected by us was 60 mm SL and very few were less than 100 mm SL [1093]. In the Sepik River, substantial movements are made between seasonal floodplains and permanent lakes [315]. Floodplain habitats are used during the wet season. McDowall [890] reports that larval and juvenile snakehead gudgeon are part of the near-shore marine and estuarine ‘ipon’ fishery of the Philippines. This suggests that some form of movement out of freshwater adult habitats is made by either adults or larvae. The separate and contrasting observations of spawning or larval habitat (i.e. freshwater floodplains versus estuarine/marine areas) suggests either a highly plastic reproductive strategy or the existence of more than one species. Defaunation experiments in streams of the Wet Tropics region have revealed that streams denuded of all fishes re-establish densities of snakehead gudgeons after one year [1093]. Interestingly, although the number of individuals returns to pre-experimental levels, biomass remained lower as colonising individuals tended to be smaller in size. This suggests that adults may be territorial and restrict invasion by subadult fishes.
Other (7.2%)
Aquatic insects (41.8%)
Detritus (26.4%)
Algae (13%) Aquatic macrophytes (3.6%)
Microcrustaceans (3.2%) Terrestrial vegetation (4.1%)
Figure 2. The mean diet of the snakehead gudgeon Giurus margaritacea in floodplain habitats of the Sepik River, Papua New Guinea. Data drawn from Coates [315] from a sample of 679 individuals.
It should be noted that the data upon which Figure 2 is based was drawn from samples primarily collected from floodplain habitats. The diet of this species in adventitious streams and rivers may be substantially different. For example, Bunn et al. [248] using stable isotope tracing methods to examine the structure of food webs in a lowland tropical stream system, found that the isotopic signature of snakehead gudgeons indicated a diet composed primarily of terrestrial insects (91%). The observations reported above concerning the high vegetative cover of streams in which snakehead gudgeons are found, coupled with the observation that this species is most frequently found near the water’s surface, and the dorsal orientation of its eyes and mouth also suggest a strong reliance on terrestrially derived prey. More quantitative information on this aspect of the biology is required, as it is for most aspects.
496
Giurus margaritacea
Thus, the sustained integrity of near-shore marine, estuarine and freshwater habitats is required to ensure the continued presence of this species in a river system. Moreover, the ability to move between these different habitats is absolutely critical. Weirs or barrages located close to the river mouth are highly likely to be a barrier to movement, particularly that of larvae and juveniles. Water resource development which inhibits the transfer of water and biota between the main river channel and off-stream wetland habitats is likely to lead to reductions in long-term sustainability of this species. Finally, the observation that Wet Tropics populations of snakehead gudgeon are substantially dependent on the riparian zone as a source of food necessitates protection of the riparian zone. Clarification of the systematics of this species would assist management by identifying whether the substantial plasticity in reproductive biology observed (i.e. marine or freshwater larval development) has a genetic component or is indicative of ecological and developmental plasticity.
Conservation status, threats and management Giurus margaritacea (as Ophieleotris aporos) is listed as Non-Threatened by Wager and Jackson [1353]. Although widely distributed, G. margaritacea has relatively narrow adult macrohabitat requirements, being most common in small well-forested lowland tributaries or in lowland wetland habitats. Such habitats are most at risk of reclamation, degradation by clearing and encroachment by agriculture (particularly sugar-cane farming), invasion by noxious weeds such as para grass and Hymenachne, and channelisation to improve drainage from agricultural lands. In addition, such habitats are frequently close to human habitation (e.g. Cairns and Innisfail) and are thus at risk from urban encroachment. Exotic fish species, particularly the cichlids Oreochromis mossambicus and Tilapia mariae, may pose a threat in the future as there is substantial similarity in habitat use. It is highly likely that this species has different habitat requirements throughout its life history and is reliant on a critical chain of habitats.
497
Hypseleotris compressa (Krefft, 1864) Empire gudgeon
37 429023
Family: Eleotridae
Description First dorsal fin: VI; Second dorsal: I, 8–9; Anal: I, 9–12; Pectoral: 14–17; Pelvic: I, 5; Caudal: 15 segmented rays; Vertical scale rows: 25-29; Horizontal scale rows: 9–10; Predorsal scales: 14–18; Gill rakers on first arch: 11–16; Vertebrae: 24–26 [34, 37, 578, 741, 775, 936, 1013]. Figure: mature male specimen, 57 mm SL, Polly Creek, North Johnstone River, November 1995; drawn 1999.
Johnstone rivers is W = 6.23 x 10–6 L3.281, r2 = 0.876, p<0.001 [1093]. Bishop et al. [193] report the following relationship between length (TL in cm) and weight (g) for 70 fish (range 22–69 mm TL) from the Alligator Rivers region, Northern Territory: W = 5.53 x 10–3 L3.41, r2 = 0.942. The modal length for this population was about 52 mm TL (= ~40 mm SL).
Hypseleotris compressa is a moderate-sized gudgeon suggested to reach over 140 mm TL in aquaria [569] but commonly less than 70 mm TL [1093]. Of 1512 specimens collected in streams of south-eastern Queensland over the period 1994–2000 [1093], the mean and maximum length of this species were 34 and 96 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 44 individuals (range 23–75 mm SL) from the Mary River, south-eastern Queensland, is W = 5 x 10–6 L3.350, r2 = 0.992, p<0.001 [1093]. Of 2267 specimens collected in streams of the Wet Tropics region over the period 1994–1997, the mean and maximum length of this species was 33.2 and 76 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (g) for 159 individuals (range = 21–76 mm SL) from the Mulgrave and
Hypseleotris compressa has a compressed head and slender, elongate body, deepening with growth. Mouth small and oblique, extending back almost to below anterior margin of eye. Tongue with a slightly indented tip. Gill openings broad, ending below posterior preopercular margin. Ciliated scales present on body; small cycloid scales present on cheeks, operculum and top of head forward to above middle of eyes. Ctenoid scales present between first dorsal fin base and upper edge of gill opening. No scales present on snout. Two to five pores along posterior margin of preoperculum and, in large specimens, two pores above each eye. First dorsal fin originates just behind level of pelvic fin bases. Second dorsal origin above vent. Caudal fin truncate to slightly rounded. This species is sexually dimorphic, with larger males developing a slight hump on
498
Hypseleotris compressa
Mitochondrial DNA sequencing data revealed a shallow, poorly resolved phyletic network consistent with 1) a species with a life history conducive to dispersal that occupies a range free of barriers to gene flow; or 2) a recent bottleneck or expansion, or both, with insufficient time since to allow for subsequent differentiation. These authors postulated that changes in sea level during the latter part of the Pleistocene may have played some role as mismatch analysis revealed that the phyletic structure was consistent with population contraction and subsequent expansion [900]. McGlashan and Hughes concluded that the genetic structure of Queensland populations of H. compressa was unlike that of a freshwater fish and more like that of an estuarine or marine species. Hypseleotris compressa either has some form of marine dispersal, or had such in the recent past [900].
the head and more brightly coloured fins during breeding season. Both sexes have broad urinogenital papillae; in males it is smooth-edged but in females it is fringed with small lobes at the tip. Considerable spatial, sexual and ontogenetic variation in colour exists in this species. Females and immature individuals are usually brownish or yellow-tan on dorsal surface, grading to silvery-white ventrally. Iridescent green/gold blotch sometimes present on operculum. Black or brown spot on upper part of pectoral fin base. Dark scale margins form a reticulated pattern, appearing as X-shaped marks along side; especially evident in preserved specimens. Small black spot sometimes present at base of caudal fin. Fins of juveniles and females mainly clear. Breeding males usually very colourful with golden-brown body colour and bright reddish-orange colour on ventral surface. Dorsal and anal fins with broad bluish-white marginal and black and red submarginal bands. Series of white spots on base of second dorsal and caudal fins. [34, 37, 118, 775, 936].
Distribution and abundance Hypseleotris compressa is a very widespread species occurring in coastal drainages of northern and eastern Australia and also southern central New Guinea. In Australia it occurs from the Murchison River, in the Pilbara Region of Western Australia, northward and eastward throughout the Northern Territory and Queensland, and south to the Towamba River in East Gippsland, southern New South Wales. In Queensland it has been recorded from most coastal drainages and is also present on Fraser, Moreton, Bribie and Stradbroke islands, off the coast of south-eastern Queensland [34, 52, 814, 936, 1349].
Juveniles and subadults similar in general appearance to other Hypseleotris species, especially H. klunzingeri. Hypseleotris compressa can be distinguished by the dark scale margins, which form a reticulated pattern, appearing as X-shaped marks along side (in H. klunzingeri, dark scale-bases along middle of side give barred appearance), and the absence of numerous rows of sensory papillae (present in H. klunzingeri). See also the chapters on H. klunzingeri, H galii and Hypseleotris sp. 1 for distinguishing characteristics of these species.
It is generally a very common species and is often locally abundant. Juveniles may form schools in estuarine areas [775], large numbers are often observed migrating upstream and mass spawnings of adults may occur [774].
Systematics Hypseleotris was erected by Gill [449] in 1863. The genus currently contains 17 described species, seven of which occur in Australia [52, 422]. At least three additional, as yet undescribed, species also occur in Australia [52] and some members of the genus are known to hybridise, hence leading to considerabe taxonomic uncertainty surrounding species boundaries [170]. Hypseleotris compressa was described as Eleotris compressus by Krefft [741] in 1864. The common name, Empire gudgeon, was no doubt inspired by the vivid red, blue-black and white stripes on the dorsal and anal fins of males, being somewhat reminiscent of the colours of the flag of the British Empire. Perhaps owing to its wide distribution, numerous synonyms for this species exist (listed in McCulloch [879]).
This species probably occurs throughout the Gulf of Carpentaria and western Cape York Peninsula, but has actually been sampled in relatively few drainages of this area. It has been recorded from the Leichhardt and Norman basins in the southern Gulf and from the Embley Basin, and the Archer, Wenlock and Jardine rivers [41, 216, 571, 661, 1349]. Its distribution in rivers of eastern Cape York Peninsula is widespread and seemingly continuous [571, 599, 1099, 1349]. It occurs in the dune lake systems near the eastern tip of Cape York, Shelburne Bay and further south at Cape Flattery also but does not achieve high levels of abundance in these systems [571, 1101]. Hypseleotris compressa is common and widespread in the Wet Tropics region [583, 643, 1085, 1087, 1096, 1177, 1179, 1183, 1184, 1185, 1186, 1187]. This species was the third most abundant species collected and occurred in 59 of 92 sites across the region surveyed in 1993 [1087]. This species is moderately widely distributed and abundant in
McGlashan and Hughes [900] investigated the phyletic structure of H. compressa populations of northern Australia. They found that H. compressa populations from eastern Australia were genetically distinct from those of the Northern Territory, but that Queensland populations showed no geographical structuring (i.e. panmixis) [900].
499
Freshwater Fishes of North-Eastern Australia
the Mulgrave and Johnstone rivers and is amongst the most common of species in these rivers (Table 1). It is especially common in those sites in which it occurs, being either the dominant or second most abundant species. Average densities of about 3 fish.10m–2 were estimated (about 20% of the total density at these sites) and a maximum density of 75.1 individuals.10m–2 on one occasion [1093]. Its contribution to total biomass is low (<3%) by virtue of its small size.
there is a clear need for genetics research to resolve the identity and distribution of Hypseleotris species in this river. Further to the south, H. compressa is reportedly common in the Pioneer River [658]. It is generally reported to be common to very common in short coastal streams near Sarina [779], Shoalwater Bay and Water Park Creek [1328]; and in the lower Fitzroy Basin [160, 404, 405, 740, 1274, 1275]; Calliope River [915], Baffle Creek [826] and the Kolan River [232, 658].
Table 1. Distribution, abundance and biomass data for Hypseleotris compressa in the Wet Tropics region. Data summaries for a total of 2803 individuals collected from rivers in the Wet Tropics region over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively, at those sites in which this species occurred.
This species is common and widespread in south-eastern Queensland. It was collected in high numbers in the lower Burnett River [658, 1276, 1277] and is relatively common in the Elliott River [825]. Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 3298 individuals and H. compressa was present at 22.8% of all locations sampled (Table 2). Overall, it was the 12th most abundant species collected (2% of the total number of fishes collected) but was relatively common at sites in which it occurred (second most abundant species forming 14% of the total abundance at these sites). In these sites, H. compressa most commonly occurred with the following species (listed in decreasing order of relative abundance: G. holbrooki, A. reinhardtii, H. klunzingeri, and P. signifer. Hypseleotris compressa was the 20th most important species in terms of biomass, forming only 0.2% of the total biomass of fish collected by us. This species was most widespread and abundant in the short coastal streams of the Sunshine Coast, Moreton Coast and South Coast, where it was present in over 25% of locations sampled. It is less widespread in the larger rivers of southeastern Queensland, generally occurring only in sites located in the middle and lower sections of these rivers (see section on Macro/mesohabitat use). Across all rivers, average and maximum numerical densities recorded in 161 hydraulic habitat samples (i.e. riffles, runs or pools)
Total % locations % abundance Rank abundance % biomass Rank biomass
Mulgrave River
Johnstone River
43.2
23.2
36.4 8.0 (19.2)
16.5 (19.3) 5.5 (19.1)
5 (1)
3 (1)
6 (2)
0.31 (2.5)
0.39 (2.2)
0.28 (2.8)
15 (10)
15 (10)
18 (10)
Mean numerical density 3.19 ± 1.58 (fish.10m–2)
3.71 ± 1.58 2.74 ± 0.45
Mean biomass density (g.10m–2)
2.11 ± 0.75 2.12 ± 0.32
2.17 ± 0.38
The distribution of H. compressa extends continuously south of the Wet Tropics region. This species is reportedly common in the Burdekin River [1098], however most specimens from the upper part of the river (i.e. above Burdekin Falls Dam) are probably H. klunzingeri not H. compressa. A total of six different forms of carp gudgeon have been reported from the Burdekin River [1082], and
Table 2. Distribution, abundance and biomass data for Hypseleotris compressa. Data summaries for a total of 3298 individuals collected from rivers in south-eastern Queensland over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
22.8
14.0
62.1
45.0
11.7
23.5
25.0
2.02 (13.98)
0.85 (7.93)
38.52 (50.33)
1.69 (6.95)
0.78 (7.93)
2.83 (14.98)
2.92 (11.71)
12 (2)
15 (6)
1 (1)
8 (4)
17 (5)
10 (2)
8 (5)
0.16 (0.65)
0.10 (0.32)
0.05 (0.13)
0.59 (2.65)
0.46 (5.43)
0.20 (1.80)
0.42 (3.30)
20 (6)
19 (5)
11 (6)
9 (8)
12 (3)
11 (6)
8 (4)
Mean numerical density (fish.10m–2)
1.61 ± 0.36
1.14 ± 0.63
2.06 ± 0.66
0.24 ± 0.06
0.52 ± 0.17
3.11 ± 1.10
0.29 ± 0.13
Mean biomass density (g.10m–2)
2.66 ± 0.97
1.11 ± 0.38
0.06 ± 0.04
0.31 ± 0.16
2.39 ± 0.63
4.95 ± 2.46
0.79 ± 0.71
500
Hypseleotris compressa
were 1.61 individuals.10m–2 and 34.0 individuals.10m–2, respectively. Average and maximum biomass densities at 94 of these sites were 2.66 g.10m–2 and 76.27 g.10m–2, respectively. Highest numerical densities were recorded from the Pine and Brisbane rivers and highest biomass densities were recorded from the Brisbane River.
Table 3. Macro/mesohabitat use by Hypseleotris compressa in the Wet Tropics region. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Data summaries for 769 individuals collected from 33 locations in the Johnstone and Mulgrave rivers between 1994 and 2003 [1093].
Hypseleotris compressa appears to be relatively common and widespread in coastal rivers of New South Wales [188, 437, 438, 441, 443, 484, 814, 1066, 1067, 1201]. Macro/mesohabitat use Hypseleotris compressa usually occurs in the lowland portions of river basins throughout its range and is found in a variety of lotic and lentic habitats including lowland rainforest streams, lowland sections of large rivers, floodplain wetlands, coastal streams, swamps and seepages, and in dune lake systems [774, 1085, 1087]. Juveniles and adults of this species also commonly occur in estuarine areas and in the freshwater-estuarine interface of lowland rivers [193, 370, 446, 775, 1067].
Parameter
Min.
Max.
Mean
W.M.
Catchment area (km2 ) Distance from source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
0.13 0.5 10.1 5 2.0 0
136.9 21.0 64.0 60 35.0 99.0
22.0 5.9 22.5 19.7 7.5 49.9
9.3 3.7 17.2 15.0 5.5 57.6
Gradient (%) 0.02 Mean depth (m) 0.11 Mean water velocity (m.sec–1) 0
In the Alligator Rivers region, H. compressa occurs most commonly in floodplain billabongs, corridor anabranch billabongs and lowland shallow backflow billabongs [193]. Such habitats have a dominant substrate of muddy clay and are heavily vegetated. Hyspeleotris compressa in the Wet Tropics region is restricted to streams at low elevation within 65 km of the river mouth (Table 3). Mean and weighted mean macrohabitat values indicate that it most commonly occurs in, and is most abundant in, small (<6 m), adventitious tributary streams close to the river mouth (note however that our sampling design included few lowland sites in the main river channel). Streams in which H. compressa is abundant tended to have a thick intact riparian canopy and be of low gradient. There was little difference between mean and weighted mean values for stream depth indicating little preference over the range of depths examined. It was however, more common in lower gradient streams with very low current velocities (Table 3). Such streams have a substrate dominated by mud, sand and fine gravel and substantial amounts of in-stream cover, especially leaf litter, root masses and aquatic macrophytes. This latter element is usually rare in streams of the Wet Tropics.
4.0 0.77 0.37
0.44 0.35 0.12
0.14 0.33 0.08
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
38 88 60 73 55 75 20
8.5 27.1 25.4 14.0 9.8 11.5 3.8
13.2 31.0 24.3 13.1 9.9 6.0 2.6
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
23.7 6.9 18.0 60.0 7.0 81.2 11.0 12.3 35.0 65.0
1.15 0.3 2.0 7.1 0.2 17.5 2.8 2.6 9.4 17.7
3.4 0.8 3.3 6.0 0.7 23.7 3.3 3.1 9.8 22.8
In rivers and streams of south-eastern Queensland, H. compressa occurs at low elevations (0–60 m.a.s.l.) but most commonly at less than 20 m.a.s.l. (Table 4). This species most frequently occurs in the middle to lower sections of rivers and short coastal streams (within 50 km of the river mouth), but has been recorded up to 173 km upstream from the mouth of the Mary River (Table 4). It is present in a wide range of stream sizes (range = 1.4–44.0 m width) but is more common in streams around 5 m wide and with moderate riparian cover. In south-eastern Queensland, H. compressa most commonly occurs in pools and runs characterised by low gradient (<0.2% weighted mean gradient), moderate depth (0.35 m weighted mean depth) and low mean water velocity (weighted mean = 0.05 m.sec–1) but can occur in shallow, high velocity (maximum 0.85 m.sec–1) riffle habitats (Table 2). This species is most abundant in mesohabitats with fine substrates (mud, sand and gravel) and where submerged leaf-litter beds, undercut banks and root masses are common.
Larvae and juveniles sampled in the Wet Tropics region usually occurred in low-flow environments (velocities between 0.1–0.2 m.sec–1) and at depths less than 50 cm but also showed a marked preference for habitat deeper than 60 cm [1109]. Juveniles were sampled in aggregations close to the stream margins, at or near the water surface and usually in close association with instream cover (submerged root masses and leaf litter) [1109].
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Freshwater Fishes of North-Eastern Australia
probably reflecting, in large part, the depth distribution of cover elements used by this species in the Wet Tropics region (Fig. 1d). It was most commonly collected over a mud and sand substratum (Fig. 1e) reflecting that present in the sites in which this species occurs and its preference for areas of little flow. Although occasionally collected from areas of open water, most H. compressa in streams of the Wet Tropics were associated with some form of cover, including macrophytes (which are rare), leaf litter, woody debris, undercut banks and root masses (Fig. 1f).
Table 4. Macro/mesohabitat use by Hypseleotris compressa in rivers of south-eastern Queensland. Data summaries for 3298 individuals collected from samples of 161 mesohabitat units at 64 locations in south-eastern Queensland streams undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min. 2
Catchment area (km ) Distance from source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
6.0 3.0 0.5 0 1.4 0
Gradient (%) 0 Mean depth (m) 0.10 Mean water velocity (m.sec–1) 0
Max.
Mean
W.M.
9734.3 260.5 173.0 60 44.0 91.0
728.5 44.2 49.6 20 9.8 39.5
535.2 28.3 41.5 18 4.8 41.3
2.86 1.19 0.85
0.37 0.46 0.12
In rivers of south-eastern Queensland, H. compressa was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b) reflecting the
0.17 0.35 0.05
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
100.0 100.0 82.7 66.2 62.9 44.0 76.0
8.5 30.0 18.2 22.2 13.6 4.2 3.2
15.4 47.1 12.0 13.5 8.7 1.4 1.9
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
86.1 39.7 16.8 62.7 33.5 49.5 25.9 26.8 70.0 67.0
11.2 5.4 1.3 6.0 1.9 10.9 6.5 4.3 14.2 20.8
6.7 4.7 1.6 7.1 1.0 15.7 5.4 3.7 11.1 16.6
(a) 60
60
40
40 20
20
0
30
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 60
20 40 10
20
0
0
Total depth (cm) 40
Elsewhere, this species has been classified as a pelagic pooldwelling species [553] and has been reported to occur in standing and slow-flowing waters near submerged vegetation [82, 84, 270, 814]. Microhabitat use In streams of the Wet Tropics region, H. compressa is most frequently found in still waters and only very infrequently in current velocities greater than 0.1 m.sec–1 (Fig. 1a). It may occur over a wide range of depths but is uncommon in very shallow water (<10 cm). It was frequently collected from depths greater than 80 cm; such depths are generally rare in the streams surveyed indicating some preference for deeper sections of the small creeks in which they are most common (Fig. 1c). Whether this indicates a preference for such depth or an avoidance of elevated water velocities is unknown. This species was usually collected in the lower two-thirds of the water column,
(b) 80
Relative depth
(e)
(f) 20
30
15
20
10
10
5
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Hypseleotris compressa in the Wet Tropics region (solid bars) and in south-eastern Queensland (open bars). Summaries derived from capture records for 1037 individuals from the Johnstone and Mulgrave rivers in the Wet Tropics region and for 779 individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
502
Hypseleotris compressa
from 11.7 to 31.0°C. The maximum turbidity at which this species has been recorded in south-eastern Queensland is 200 NTU, but it more commonly occurs in less turbid waters (mean 12.9 NTU). We have collected this species in freshwaters up to 2744 µS.cm–1 conductivity, and the common occurrence of this species in estuarine conditions suggests it can tolerate high salinities. Bishop et al. [193], citing earlier work, indicated that this species was collected in the lower Clarence river at salinities of at least 16 ppt.
pattern observed in mesohabitat use. This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 1c). A semi-benthic species, it occupies the lower half of the water column, most commonly in direct contact with the substrate (Fig. 1d). Although most abundant in mesohabitats with fine substrates (see above) it was collected in close association with a wide range of substrate types ranging from mud through to cobbles (Fig. 1e). This species was most frequently collected within 1 m of the stream-bank (67% of 797 fish collected), and was always found in close association with some form of submerged cover (Fig. 1f). It was most frequently collected near the substrate, and near aquatic macrophytes or filamentous algae, and less commonly near leaf-litter beds, woody debris, undercut banks and root masses (Fig. 1f). Juveniles in a dune lake on Fraser Island have been reported to swim in schools near the water’s surface with larger individuals assuming a benthic habit [508].
Table 5. Physicochemical data for Hypseleotris compressa. Data summaries are from a number of studies conducted in a range of rivers and habitats across northern and north-eastern Australia (the number of sites from each study is given in parentheses). Temperature values for the Alligator Rivers region are from readings taken in the bottom of the water column. Parameter
Environmental tolerances Very little quantitative data concerning the environmental tolerances of H. compressa is available (Table 5). Harris and Gehrke [553] classified this species as tolerant of water quality degradation. In the Alligator Rivers region, H. compressa was collected from very warm (27–33°C) freshwaters (4–160 µS.cm–1) [193]. It was collected over a wide range of pH (5.0–9.1) and water clarity. The apparently low levels of dissolved oxygen present in those water bodies of the Alligator Rivers region inhabited by H. compressa, are close to saturation given the high temperatures recorded.
Min.
Max.
Mean
Alligator Rivers region [193] Water temperature (°C) 27 33 Dissolved oxygen (mg.L–1) 3.7 7.8 pH 5.0 9.1 Conductivity (µS.cm–1) 4 160 Secchi depth (cm) 3 110
25
Wet Tropics region (n = 65) [1093] Water temperature (°C) 17.5 27.3 Dissolved oxygen (mg.L–1) 5.33 8.81 pH 4.5 7.9 Conductivity (µS.cm–1) 6.0 65.6 Turbidity (NTU) 0.33 22.1
22.9 7.0 6.4 36.2 2.2
29.9 6.1 6.9
South-eastern Queensland (n = 108) [1093] Water temperature (°C) 11.7 31.0 20.3 Dissolved oxygen (mg.L–1) 1.7 11.3 6.9 pH 4.4 9.1 7.4 Conductivity (µS.cm–1) 97.5 2744.0 586.5 Turbidity (NTU) 0.3 200.0 12.9
This species occurs in much cooler temperatures in lowland rainforest streams of the Wet Tropics region (Table 5). These streams tend to have relatively high levels of dissolved oxygen also. Hogan and Graham [584] have collected this species from hypoxic waters (0.2 mg O2.L–1) in wetlands of the Tully River. Such wetlands were moderately acidic (pH 4.6) [584] as are some rainforest streams of the Wet Tropics region (Table 5). Rainforest streams in which H. compressa occurs are usually very clear and with very low levels of conductivity (Table 5).
Reproduction The reproductive biology and early development of H. compressa is comparatively well studied (Table 6). This species spawns and can complete its entire life cycle in freshwater and has been bred in captivity [58, 118, 508, 797, 1150, 1352, 1423]. Although juveniles and adults frequently occur in estuaries, it is not known whether this species actually spawns in such habitats (although Herbert et al. [571] reported spawning aggregations in estuarine areas), or whether spawning occurs in freshwater and larvae are washed downstream to estuaries, juveniles subsequently migrating upstream to freshwaters. This aspect of the life cycle of H. compressa (i.e. a possible semiamphidromous movement pattern) is not well understood (see also section on Movement below).
In south-eastern Queensland, H. compressa has been collected over a relatively wide range of physicochemical conditions (Table 5). It appears to tolerate low dissolved oxygen concentrations (field minimum of 1.7 mg.L–1). Laboratory experiments revealed that 10%, 50% and 90% of individuals commenced aquatic surface respiration when dissolved oxygen concentrations were reduced to 1.0, 0.6 and 0.3 mg.L–1, respectively [429]. We have collected this species in acidic to basic water conditions (range 4.4–9.1) (Table 5) and at temperatures ranging 503
Freshwater Fishes of North-Eastern Australia
niles less than 10 mm SL in the period from January to April, when other larvae are virtually absent [1109]. No such small juveniles were collected during the period May to July although larger juveniles (>10 mm SL) were present in electrofishing samples. These data seem contradictory, however electrofishing is ineffective at collecting fish less than 10 mm SL.
Maturation commences at a relatively small size in fish from the Mary River, south-eastern Queensland. Minimum and mean lengths of early developing (reproductive stage II) fish were 24.5 mm SL and 26.6 mm ± 1.99 SE, respectively for males and 30.0 mm SL and 32.6 mm ± 0.5 SE, respectively for females [1093]. Bishop et al. [193] reported that fish from the Alligator Rivers region, Northern Territory, were maturing (stage III) at 38 and 43 mm TL for males and females, respectively. Merrick and Schmida [936] reported that both sexes are reproductively mature between 40 and 50 mm. Minimum and mean lengths of ripe (reproductive stage V) males from the Mary River, south-eastern Queensland, were 41.3 mm SL and 43.9 mm SL, and that of females 62.4 mm SL and 75.1 mm SL [1093].
In the Mary River, south-eastern Queensland, ripe fish (stage V) of both sexes were present in January and May [1093]. Peak monthly mean GSI values (8.6% ± 1.3 SE for males, 7.4% ± 0.4 SE for females) occurred in January for males and May for females [1093]. The mean GSI of ripe (stage V) fish was 7.5% ± 2.4 SE for males and 7.4% ± 0.4 SE for females [1093]. In the Noosa River, ripe males were present from January to April and spent fish were present between February and April, with peak spawning activity apparently occurring in January and February [84]. Length-frequency data for fish sampled from south-eastern Queensland rivers and streams indicate that very small juvenile fish (less than 15 mm SL) were present almost year-round, but fish 15–20 mm SL were most common in autumn, winter and spring, further suggesting a spawning period during summer and autumn (Fig. 3).
Hypseleotris compressa appears to have an extended breeding season between summer and autumn in northern and eastern Australia. Peak spawning activity was estimated to occur during the mid-wet season (January–March) in the Alligator Rivers region, Northern Territory [193]. Mean GSI values during this period were 8.7% ± 3.0 SD for males and 14.4% ± 10.1 SD for females. In the Wet Tropics region, recently metamorphosed juveniles were present in all sample periods, although they were not abundant (Fig. 2). Small fish (<25 mm SL) were most abundant and contributed proportionally more to the total in the period August to December. Larval sampling using dip-netting recorded the highest numbers of metamorphosed juve-
Llewellyn [814] reported that breeding of fish in New South Wales occurs from September through to March. The spawning stimulus for H. compressa is unknown but in northern and eastern Australia, the peak spawning period in summer coincides with high water temperatures
30 Aug. - Dec. (n = 1461) 20
Spring (n = 267) 30
Jan. - Apr. (n = 268)
Summer (n = 153)
May - July (n = 538)
20
Autumn-Winter (n = 617)
10 10
0 0
Standard Length (mm) Figure 2. Temporal variation in length–frequency distributions of Hypseleotris compressa from streams and rivers in the Wet Tropics region sampled between 1994 and 1997 [1093]. The number of fish from each sampling occasion is given in parentheses.
Standard length (mm) Figure 3. Seasonal variation in length-frequency distributions of Hypseleotris compressa from streams and rivers in southeastern Queensland sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
504
Hypseleotris compressa
of Hypseleotris. The mean diameter (long axis) of 120 intraovarian eggs from stage V fish from the Mary River was 0.32 mm ± 0.01 SE [1093]. The dimensions of waterhardened eggs have been reported as 0.26–0.28 mm by 0.30–0.32 mm [118]. Further details on embryonic morphology and development are given in Auty [118].
and an increased likelihood of elevated discharges. Spawning during these conditions may facilitate access to newly inundated floodplain environments and possibly result in prolarvae being washed downstream to estuarine areas [193]. Breeding behaviour has been reported to commence when water temperatures exceed 20°C [755], temperatures of 21–26°C have been recommended for breeding of this species in aquaria [797], and successful spawning has been observed in aquaria at temperatures between 23.5 and 30°C [118, 1423].
Embryonic development is relatively rapid. Incubation periods have been reported to range from 10–10.5 h (at 30°C), 12–12.5 h (at 26–28°C), 14 h (at 23.5°C) [118]. Larvae are poorly developed at hatching, being approximately 1 mm long with a relatively large ovoid yolksac and lacking a functional mouth. The prolarvae are generally unpigmented except for several melanophores on the head and single melanophores located at the anus, and posteriorly on the ventral surface. A fin-fold surrounds the caudal region extending from the dorsal surface above the middle of the egg yolk to the posterior edge of the yolk on the ventral surface [118]. Auty [118] reported that prolarvae commence swimming at hatching, and soon afterwards vigorously swim towards the water surface and then drift downwards headfirst towards the bottom. Young [1423] provided a similar account of the early swimming activities of prolarvae. Growth is rapid in the first 16–24 hours and lengths up to about 1.7 mm may be achieved by this time [118]. The yolk starts to diminish after 24 hours and is fully absorbed 7–10 days after hatching. Eye pigmentation begins at 35 hours and the eyes are fully pigmented by about 84 hours, by which time the jaw structure and digestive tract are completely developed [118]. Feeding is estimated to commence at about four days after hatching [1352]. Note however, that Young [1423] reported that the yolk sac of larvae had been almost fully absorbed 48 hours after hatching and that feeding may hence commenced soon after hatching. This species is notoriously difficult to rear in captivity, primarily due to the microscopic food requirements of prolarvae, but recommendations on rearing larvae are available [797, 1352, 1423].
Detailed accounts of the elaborate colouration of breeding males and behaviour of spawning fish in aquaria are available [118, 1150, 1423]. In aquaria, males can be very aggressive and are territorial when in breeding condition, usually remaining near a suitable site for spawning. When maintained in aquaria, the presence of a large dominant male may suppress maturation in smaller males. When the dominant fish is removed, smaller males will assume breeding colouration and commence courtship displays within a period of 10–14 days [1093]. Females are nonterritorial and may mate with multiple males [118]. Spectacular mass spawnings have been reported at Nhulunbuy in the Northern Territory [774]. Spawning in aquaria has been reported to occur amongst aquatic vegetation, sand, rocks, woody debris and aquarium glass [118, 797, 1423]. Hypseleotris compressa is a batch spawner and females in aquaria have been observed to spawn every 2–7 days for a period of several weeks; females are estimated to be capable of spawning at least 20 times per season [118]. Hypsleotris compressa is extremely fecund for its small size. Fish in aquaria were estimated to lay between 2184 to 3150 eggs per spawning session, leading Auty [118] to calculate that females are capable of producing at least 40 000 eggs per season. Total instantaneous fecundity for H. compressa collected from the Mary River has been estimated as ranging from 14 754–58 110 eggs (mean 32 786 ± 7197 SE, n = 12 fish) [1093]. Fecundity is significantly related to fish size; regression equations for relationships between fecundity and length or weight are given in Table 6. Fish of 62 mm SL from the Mary River produced about 20 000 eggs in total, whereas fish of 75 mm SL produced about 55 000 eggs [1093]. Fish of 5 g from the Mary River produced about 20 000 eggs in total, whereas fish of 9 g produced about 55 000 eggs [1093]. Following spawning, the male guards the eggs in his territory by chasing other fish away [118], but no further parental care has been reported.
Fish have been reported to attain 60–70 mm by 12 months [508]. The life-span of H. compressa in the wild is unknown. There is a second-hand anecdotal account of aquarium specimens being maintained for over 20 years [1339]. The life history of H. compressa differs in several key aspects from other Australian hypsleotrids. Unlike H. klunzingeri and H. galli, male H. compressa do not provide any parental care other than guarding the nest until hatching occurs. They do not fan the eggs during development. Embryonic development is more prolonged in H. klunzingeri and H. galli and fecundity is comparatively reduced in these species. Auty [118] noted that several aspects of the reproductive biology of H. compressa (high fecundity, lack of parental care, egg morphology and early developmental
The transparent, demersal eggs have a thin chorion and are slightly pear-shaped with a small adhesive disk at the apex [118]. The eggs are very small relative to body size, and are smaller than the eggs of all other Australian species
505
Freshwater Fishes of North-Eastern Australia
migrations entirely within freshwaters, and between estuaries and freshwater, have been recorded for a range of age classes.
characteristics) resembled those of marine pelagic spawners. Although this species may be reared successfully in freshwater, it is possible that initial larval survival and development is favoured by elevated salinities and/or the availability of microscopic food supplies in estuarine areas. Auty [118] concluded that H. compressa was less adapted to freshwater environments than other species of Hypseleotris.
Bishop et al. [193] suggested that prolarvae are probably washed downstream to estuarine areas during flood events occurring in the breeding season. Juveniles and adults of this species have often been found in very large numbers immediately downstream of tidal barrages and dams in lowland rivers (e.g. [158, 188, 442, 859, 860] and references cited above) and downstream of road crossings and culverts [584, 1093]. Cotterell [332] reported that juveniles undertake mass migrations from flooded mangrove areas. Marsden et al. [859, 860] and Gehrke et al. [442, 443]
Movement Some information is available on the movement biology of H. compressa. Like many other freshwater eleotrids, juveniles and subadults of this species may have a facultative mass dispersal phase and instances of mass upstream Table 6. Life history information for Hypseleotris compressa. Age at sexual maturity (months)
? probably <12 months [1093]
Minimum length of gravid (stage V) females (mm) 62.4 mm SL [1093] Minimum length of ripe (stage V) males (mm)
41.3 mm SL [1093]
Longevity (years)
? probably 3–5 years (possibly over 20 years in aquaria [1339])
Sex ratio (female to male)
1:1 [193]
Occurrence of ripe (stage V) fish
summer to autumn [84, 193, 1093]
Peak spawning activity
Alligator Rivers region, Northern Territory: Elevated GSI January to March [193]; South-eastern Queensland: Elevated GSI January and March [1093]
Critical temperature for spawning
? 20–30°C [118, 755, 797, 1423]
Inducement to spawning
? Possibly a combination of high water temperature and elevated discharge [1093]
Mean GSI of ripe (stage V) females (%)
SEQ: 7.4% ± 0.4 (maximum mean GSI in May = 7.4% ± 0.4) [1093]
Mean GSI of ripe (stage V) males (%)
SEQ: 7.5% ± 2.4 (maximum mean GSI in January = 8.6% ± 1.3) [1093]
Fecundity (number of ova)
Batch fecundity = 2184–3150 [118]; Total potential fecundity = estimated to be at least 40 000 [118]; Total instantaneous fecundity = 14 754–58 110, mean = 32 786 ± 7197 [1093]
Total Instantaneous Fecundity (TIF) and Batch Fecundity (BF)/Length (mm SL) or Weight (g) relationship (mm SL)
SEQ: TIF = 2751 L – 151 989, r2 = 0.932, p<0.001, n = 12; TIF = 8783 W + 23 610, r2 = 0.958, p<0.001, n = 12 [1093]
Egg size (diameter)
SEQ: Intraovarian eggs from stage V fish = 0.32 mm ± 0.01 [1093]; Water-hardened eggs pear-shaped, varying from 0.26–0.28 mm by 0.30–0.32 mm [118]
Frequency of spawning
Batch spawner over an extended breeding period. Spawns every 2–7 days over several weeks and may be capable of spawning at least 20 times in a spawning season [118]
Oviposition and spawning site
Fish in aquaria deposited eggs on aquatic vegetation, sand, rocks, woody debris and aquarium glass [118, 797, 1423]
Spawning migration
Possible upstream spawning migration from estuarine areas, but this behaviour requires confirmation (see section on movement)
Parental care
Male guards eggs until they hatch [118] but no further parental care has been reported
Time to hatching
Varies with temperature but relatively rapid. 10 to 14 hours (at 23.5–30°C) [118]
Length at hatching (mm)
Newly hatched prolarvae 1.0 mm TL [118]
Length at free swimming stage
Prolarvae commence swimming at, or soon after, hatching; >1.0 mm TL [118]
Age at loss of yolk sack
7–10 days [118]; 2 days [1352]
Age at first feeding
4 days [1352], possibly earlier [1423]
Length at first feeding
?
Age at metamorphosis (days)
?
506
Hypseleotris compressa
juveniles have been observed in August in the Wet Tropics region [1093]. Large schools of individuals 30–75 mm TL were observed moving upstream in the Burdekin River during large flood events in summer [586]. The vast majority (~98%) of individuals collected in repeated surveys of the Kolan River barrage fishway over a 1½-year period were sampled in January 2000 during a single large flow event (peak flow of 1837 ML.day–1, equalled or exceeded ~5% of the time) [232]. Although most of these fish were large adults in breeding condition, it is unclear whether these fish were undertaking a spawning migration or simply recolonising freshwaters. Broadfoot et al. [232] suggested that these fish may have been displaced from areas above the barrage by a preceding flood event but an alternative explanation may be that they were estuarine residents undertaking an upstream spawning migration into freshwaters. In the Mary River, south-eastern Queensland, hundreds of juvenile and subadult fish (15–25mm SL) have been observed aggregating in pools immediately downstream of obstructions to movement (e.g. culverts and weirs) soon after rises in discharge during late spring, suggesting that H. compressa undergoes upstream dispersal/recolonisation movements cued by elevated flows [1093]. Nevertheless, Stuart [1274] recorded fish entering the Fitzroy River barrage fishway over a wide range of flows from very low to very high flows (18–18 305 ML.day–1, these flows being equalled or exceeded approximately 82% to 8 % of the time, respectively).
interpreted the absence of this species upstream of a large dam on the lower Shoalhaven River, southern New South Wales, as evidence that upstream migration from estuarine areas is an essential component of the life cycle of this species. This species is similarly absent upstream of North Pine Dam, a large dam on the Pine River located ~20 km upstream of the river mouth and within the expected range of H. compressa within this river [1093]. Nevertheless, the ability of this species to reproduce in freshwaters (see section on Reproduction) indicates that access to estuarine areas may not be an obligatory component of the life cycle. There are several instances where juveniles and adults of this species have been recorded using riverine and tidal barrage fishways. Large numbers of H. compressa have been recorded within or immediately below fishways on tidal barrages in the Fitzroy River [739, 740, 1274, 1275], Kolan River [11, 232], Burnett River [11, 658, 1173, 1276, 1277] and Mary River [158, 159, 658], and these fish were usually considered to be making upstream movements. This small-bodied species, particularly smaller individuals, apparently has difficulty ascending some fishways. A large proportion of fish were unable to negotiate the full length of vertical-slot fishways on tidal barrages in the Fitzroy River and Kolan River, and those that did were significantly larger in size [232, 1274, 1275]. Hogan et al. [586] reported that fish could negotiate flows up to 1 m.sec-1 for short distances though Claire Weir on the Burdekin River, but required very shallow water and coarse substrates on which to ‘cling’ using their pelvic fins [586].
This species has also been recorded as having fallen to the ground in rain near Brisbane, south-eastern Queensland, possibly as a result of a whirlwind [1016, 1018, 1400].
There is no quantitative data on the stimulus for movement of H. compressa but it appears that rises in discharge may be a factor influencing mass migrations. Upstream migrations have been recorded during the early wet season (November and December) in the lower reaches of Magela Creek in the Alligator Rivers region, Northern Territory [189]. In Queensland, upstream migrations have been recorded between February and September in the Fitzroy River [1272, 1274] and Kolan River [232]. Mass movements have been observed to occur in spring and/or summer in the Burdekin River [586], Burnett River [658, 1276] and Mary River [158, 159, 658, 1093]. Russell et al. [1187] reported observing ‘probably millions’ of postlarvae moving upstream into a lowland tributary of the Barron River during the wet season. ‘Millions’ of juveniles have been observed migrating upstream after rains in the Tully River (A. Hogan, pers. comm., cited in [571]). A similar observation was reported in Gap Creek in the Annan Basin, and these fish were suggested to have been moving upstream from estuarine reaches of the creek [571]. Smaller, yet still significant, upstream migrations of
In summary, movement at various phases of the life history is a dominant feature of the biology of H. compressa and the information presented above suggests that the movement pattern of this species may be classified as facultative potamodromy and/or semi-amphidromy (see also section on reproduction). Three types of movement may be distinguished: 1) a likely passive downstream delivery of newly hatched larvae to estuarine or lowland river habitats; followed by 2) mass upstream migration by recently metamorphosed juveniles; and 3) upstream migrations by adult fish associated with either reproduction or dispersal and colonisation. The work of McGlashan and Hughes [900] strongly suggests that dispersal between drainage basins also occurs. Trophic ecology Dietary data are available for 703 individuals from large floodplain rivers in the Alligator Rivers region [193] and eastern Cape York Peninsula [1099], rainforest streams of the Wet Tropics region in northern Queensland [1097],
507
Freshwater Fishes of North-Eastern Australia
Conservation status, threats and management The conservation status of Hypseleotris compressa is listed as Non-Threatened by Wager and Jackson [1353]. It is generally common throughout most of its range, although the abundance and distribution within river basins of this migratory species may have declined in recent years. For example, this species may have been extirpated upstream of large dams in the Brisbane and Shoalhaven rivers [443, 704].
the Burdekin River in central Queensland [1093], wallum stream and lake habitats of south-eastern Queensland [82, 84], and the Tweed River in northern New South Wales [1133] (Fig. 4). Hypseleotris compressa is a microphagic omnivore consuming aquatic insects (41.7%), aquatic vegetation (mostly unicellular algae) (15.3%) and planktonic microcrustaceans (14.5%) (mostly cladocerans and copepods). Macrocrustaceans and molluscs were also consumed in small amounts and food sources of terrestrial origin or present at the water surface comprised only a small proportion of the diet. Spatial variation in the relative proportion of the major food items consumed is evident. Fish from floodplain rivers in northern Australia [193, 1099] and wallum habitats of south-eastern Queensland [82, 84] consumed greater amounts of planktonic microcrustaceans (13.1%–53.2%) than fish from more lotic environments (0–7.5%). Fish in these latter habitats tended to consume greater amounts of aquatic insects (43.3%–64.8%), than those from more lentic habitats (30.4%–35.9%). Algae formed an important component of the diet (>16.7%) of fish in all rivers except those in the Alligator Rivers region and the Burdekin River, where they formed less than 4.3% of the diet. Algae were particularly important in the diets of fish from the Tweed River, northern New South Wales, where they comprised 46.8% of the total mean diet [1133].
The capacity for facultative (and possibly obligatory) migrations by H. compressa indicates that it is likely to be sensitive to barriers to movement caused by structures such as dams, weirs, barrages, road crossings and culverts. Although the mechanisms by which barriers to movement may impact on key life-cycle processes are unclear, barriers have the potential to affect dispersal and recolonisation movements of H. compressa and the ability of most life history stages of this species to move between estuaries and freshwaters. Although movement may occur during periods of low flow and throughout the year, floods may play a role in stimulating spawning and upstream migration of juveniles. As a consequence, anthropogenic flow modifications that change the magnitude, timing and frequency of elevated flows may impact on the ability of this species to complete its life cycle. The degree to which the relative magnitude of wet season flooding influences successful recruitment is unknown but may be important.
Other microinvertebrates (0.9%) Microcrustaceans (14.5%)
Unidentified (20.8%)
Molluscs (0.4%) Macrocrustaceans (0.4%) Other macroinvertebrates (1.3%)
This species may be intolerant of riparian habitat degradation as it was found to be significantly less abundant in river reaches with disturbed riparian zones and grassy banks than in reaches with well-vegetated banks [440, 484]. Like many other native species, siltation arising from increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of H. compressa and may also affect aquatic invertebrate food resources.
Terrestrial invertebrates (0.2%) Aerial aq. Invertebrates (0.8%) Terrestrial vegetation (0.3%) Detritus (3.4%)
Algae (15.3%)
Aquatic insects (41.7%)
Figure 4. Mean diet of Hypseleotris compressa. Data derived from stomach content analysis of 703 individuals from fish populations in the Alligator Rivers region, Northern Territory [193], eastern Cape York Peninsula [1099], the Wet Tropics region of northern Queensland [1097], central Queensland [1080], south-eastern Queensland [82, 84] and northern New South Wales [1133].
This species is common in lowland streams, rivers and wetlands. Such habitats are also most at risk of reclamation, degradation by clearing and encroachment by agriculture (particularly sugar-cane farming), invasion by noxious weeds such as para grass and Hymenachne, and channelisation to improve drainage. In addition, and perhaps just as importantly, such habitats are frequently close to human population centres (e.g. Brisbane and the south-eastern Queensland coastal strip) and are thus at risk from urban encroachment. Although the importance of access to brackish and estuarine habitats for the life
This species is consumed by a range of larger fish and piscivorous birds. During their migratory phase, juvenile H. compressa are predated upon by many fish species, including melanotaeniids and ambassids [1093].
508
Hypseleotris compressa
where it acts as a definitive host [339]; it is also second intermediate host to Stemmatostoma pearsoni (Cryptogonimidae) and Tetracerasta blepta (Lepocreadiidae) [339]. Nineteen parasite species (listed in Dove [1432]) were recorded from 11 individuals collected from south-eastern Queensland and individual fish contained an average of 3.7 parasite species [391].
history of this species is not clearly understood, the prevalence of marina and canal developments in coastal and estuarine areas of south-eastern Queensland and New South Wales has potential to impact on certain populations and most life history stages of this species. Hypseleotris compressa is known to be infected naturally by the adult digenetic trematode parasite Opecoelus variabilis
509
Hypseleotris galii (Ogilby, 1898) Firetailed gudgeon
37 429025
Hypseleotris sp. 1 (after Allen et al. [52]) Midgely’s carp gudgeon
37 429049
Family: Eleotridae
Description
compressed and moderately slender body, tapering towards tail. Mouth small and oblique, extending back to below anterior margin of eye, tip of tongue truncate. Gill openings broad, ending below posterior preopercular margin. All scales imbricate; ciliated scales on body and top of head, small cycloid scales on cheeks and operculum. No head pores but may have single row of papillae below eye. Origin of first dorsal fin just behind level of pelvic fin bases; second dorsal origin above vent. Breeding males develop slight hump on head and have longer posterior rays in dorsal and anal fins. Considerable spatial, sexual and ontogenetic colour variation. Head and body may vary from pale grey, bronze to almost black. Belly lighter than body, orange-pink in breeding females. Blackish bar on upper two-thirds of pectoral fin base and extending on to body. Scales with black margins. Urinogenital papilla black in females, light brown in males. Fins clear to dusky, lighter along margins. Fin tips reddish-orange in large specimens. Caudal fin clear to reddish-orange [775, 1013, 1337, 1339].
Hypseleotris galii First dorsal fin: VI–VIII; Second dorsal: I, 10–12; Anal: I, 11–13; Pectoral: 14–15; Pelvic: I, 5; Caudal: 14–15 segmented rays; Vertical scale rows: 30–32; Predorsal scales: 8–12; Gill rakers on first arch: 9–12; Vertebrae: 29–30 (or 31) [52, 775, 1013]. Figure: mature male specimen, 26 mm SL, Albert River, November 1995; drawn 2002. Hypseleotris galii is a small gudgeon; males attain a maximum size of about 55 mm TL and females about 40 mm TL [580]. Of 5599 specimens collected in streams of south-eastern Queensland over the period 1994–2000 [1093], the mean and maximum length of this species were 28 and 53 mm SL, respectively (note that uncertainties in field identification meant that this sample probably also included individuals of Hypseleotris sp. 1 – see below). The equation best describing the relationship between length (SL in mm) and weight (W in g) for 363 individuals (identified in the laboratory as H. galii) (range 15–50 mm SL) from the Mary River, south-eastern Queensland is W = 6 x 10–6 L3.336, r2 = 0.964, p<0.001 [1093].
Hypseleotris sp. 1 First dorsal fin: VI–VIII; Second dorsal: I, 11–13; Anal: I, 11–13; Pectoral: 14–16; Pelvic: I, 5; Caudal: 15 segmented
The following description is derived largely from Larson and Hoese [775] and Ogilby [1013]. Hypseleotris galii has a
510
Hypseleotris galii, Hypseleotris sp. 1
difficult to separate as juveniles. Hypseleotris galii can be distinguished from all other hypseleotrids by the black urinogenital papilla in females (although this feature may be absent in populations from the Burnett River north [1339]) and males have elongate and pointed posterior rays on second dorsal and anal fins. Hypseleotris sp. 1 males are said to have the bluntest head [1339] and Hypseleotris sp. 2 can be distinguished by the absence of scales on the dorsal surface forward of the first dorsal fin and on the ventral surface forward of the anal fin. Unmack [1339] provides further distinguishing characteristics of hypseleotrids based on variation in body and fin colouration. See the chapters of this book on H. compressa and H. klunzingeri for distinguishing characteristics of these species.
rays; Vertical scale rows: 31–36; Predorsal scales: 13–20; Gill rakers on first arch: 11–13; Vertebrae: 29-30 [52, 775]. Hypseleotris sp. 1 is a small gudgeon, suggested to reach about 40 mm TL [52, 1339]. Although previously reported to reach up to 60 mm TL [580, 775], Unmack [1339] considers that these large individuals may have been confused with Hypseleotris sp. 3 (the Murray-Darling carp gudgeon) which grows to about this size. Of 138 specimens positively identified as Hypseleotris sp. 1, collected from the Mary River, south-eastern Queensland over the period 1994–1997 [1093], the mean and maximum length were 33 and 51 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 126 individuals (range 21–51 mm SL) from the Mary River, south-eastern Queensland is W = 5 x 10–6 L3.407, r2 = 0.958, p<0.001 [1093].
Systematics Hypseleotris galii was described as Carrassiops galii by Ogilby [741] in 1898. No other synonyms for this taxon exist. The systematics of the Hypseleotris species known as ‘carp gudgeons’ are poorly understood and several undescribed species and hybrid forms exist [170]. All carp gudgeons present in the Murray-Darling Basin were once considered to be H. klunzingeri. In 1980 however, Hoese et al. [580] recognised the existence of two undescribed hypseleotrids in this basin: ‘Midgeley’s carp gudgeon’ (as Hypseleotris sp. 4 – hereafter termed Hypseleotris sp. 1 following Allen et al. [52]) and ‘Lake’s carp gudgeon’ (as Hypseleotris sp. 5 – hereafter termed Hypseleotris sp. 2 [52]). Since then, another form known as the ‘MurrayDarling carp gudgeon’ has been recognised (Hypseleotris sp. 3 [52]) [52, 585]. It has been speculated that H. galii and Hypseleotris sp. 1 may hybridise in coastal drainages of eastern Australia [1339].
The following description is derived largely from Hoese et al. [580] and Larson and Hoese [775]. Hypseleotris sp. 1 has a compressed head and body. Ciliated scales on body. Small cycloid scales cover head to above posterior margin of eyes, also present on pectoral bases, breast and midline of belly. No scales on snout. No head pores. First dorsal fin origin just behind level of pelvic fin bases. Second dorsal fin higher than first dorsal and originating above vent. Caudal fin truncate to slightly rounded. Sexually dimorphic. Mature males develop hump on head and elongated posterior rays of dorsal and anal fins. First dorsal fin of males also less rounded, and with longer base than females, reaching back to base of second dorsal fin. Dorsal fins widely separated in females. Considerable spatial, sexual and ontogenetic colour variation. Usually pale grey to brown. Blackish spot on upper third of pectoral fin base. Scales with blackish margins, dark grey vertical bands on sides, belly silvery-white. Basal third of anal and dorsal fins clear to faint red, dark band along middle-third, outer margin usually whitish or blue, sometimes tinged with orange at the extreme edge. Basal half of caudal fin dusky yellow. Pelvic and pectoral fins clear [52, 580, 775, 1337, 1339].
Distribution and abundance Hypseleotris galii has a relatively narrow distribution in most coastal drainages of eastern Australia from Water Park Creek in central Queensland, south to the Georges River just south of Sydney in central New South Wales [1339, 1349]. This species is also present on Fraser, Bribie, Moreton and North Stradbroke islands off the south-eastern Queensland coast. Hypseleotris galii appears to be patchily distributed toward the northern end of its range. Records of this species from the Fitzroy River [659, 942, 1349] and Calliope River [331, 915] may be mis-identifications of Hypseleotris sp. 1 and it has not been recorded from the Boyne or Kolan rivers. Records of this species north of Water Park Creek such as in the Tully River in the Wet Tropics region [775, 1349] are attributable to Hypseleotris sp. 1. However, translocated populations of H. galii do occur in Tinaroo Dam in the Barron Basin and in an irrigation channel linking this impoundment to the Walsh River (Mitchell Basin) in the Gulf of Carpentaria
Hypseleotris galii and Hypseleotris sp. 1 are very similar in general appearance and both resemble Hypseleotris sp. 2 (Lake’s carp gudgeon). All three species occur in southeastern Queensland, but Hypseleotris sp. 2 is not native to this region, being indigenous to inland drainages only (Cooper Creek and the Murray-Darling Basin). Translocated populations of this species are present in the Burnett and Brisbane rivers and probably originated as contaminants of hatchery reared sport fish stocked into many impoundments in these rivers [1093, 1339]. These species are also superficially similar to H. klunzingeri and H. compressa. All taxa except H. compressa may be particularly
511
Freshwater Fishes of North-Eastern Australia
other rivers and streams of the region (P. Unmack, pers. comm.) [1093]. The following discussion treats both species together as Hypseleotris spp., however for the most part we are referring to H. galii.
[569, 1187]. Hypseleotris galii has reportedly been translocated to Bolgu Island in Torres Strait for mosquito control [775]. Other undocumented translocations of this species in north-eastern Australia are possible via contamination of fish hatchery stock associated with the widespread practice of stocking sport fish in rivers of north-eastern Australia in recent decades.
Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 12 263 individuals from 75.2% of all locations sampled (Table 1). Overall, this was the sixth most abundant taxon collected (7.5% of the total number of fishes collected) and was generally common at sites in which it occurred (12.2% of total abundance). In these sites, Hypseleotris spp. most commonly occurred with the following species (listed in decreasing order of relative abundance): G. holbrooki, P. signifer, M. duboulayi and C. marjoriae. Hypseleotris spp. was the 14th most important species in terms of biomass, forming 0.3% of the total biomass of fish collected. Hypseleotris spp. was widespread and relatively abundant throughout south-eastern Queensland, where it occurred in over 70% of locations sampled and comprised between 6.1% and 12.5% of the total number of fish collected in each basin or region (Table 1). Across all rivers, average and maximum numerical densities recorded in 586 hydraulic habitat samples (i.e. riffles, runs or pools) were 1.01 individuals.10m–2 and 24.66 individuals.10m–2, respectively. Average and maximum biomass densities at 352 of these sites were 0.53 g.10m–2 and 7.79 g.10m–2, respectively (Table 1 [1093]).
Hypseleotris sp. 1 is a widespread species occurring in many coastal drainages of eastern Queensland. Inland, it is present in Cooper Creek and the Bulloo River, and throughout much of the Murray-Darling Basin [585, 775, 1337]. In eastern Australia it has been recorded as far north as the Tully-Murray Swamps in the Wet Tropics region and is also present in the Herbert River. In central Queensland it has been recorded from most drainage basins except the Haughton, Don, Proserpine, O’Connell and Styx basins. In south-eastern Queensland it has been recorded from the Burnett, Burrum and Mary basins, and another isolated population occurs approximately 220 km further south in the Brisbane River. This species is also present on North Stradbroke Island off the south-eastern Queensland coast. Hypseleotris galii and Hypseleotris sp. 1 are both relatively common and widespread within river basins of southeastern Queensland (Table 1). Note that difficulty in identifying small-sized individuals of H. galii and Hypseleotris sp. 1 in rivers where both species co-occurred (i.e. Mary and Brisbane rivers) necessitated that we pool distribution, abundance and biomass data for these rivers. Hypseleotris sp. 1 appears to be most common in the Mary River, with H. galii more widespread and abundant in
Hypseleotris galii has been reported to occur regularly with H. klunzingeri [1339]. Distributional data support this to some extent, with Hypseleotris spp. (mostly H. galii) and
Table 1. Distribution, abundance and biomass data for Hypseleotris galii (H.g.) and Hypseleotris sp. 1 (H. sp.1) in rivers of southeastern Queensland. Data summaries for a total of 12 263 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Note that difficulty in identifying small-sized individuals of Hypseleotris galii and Hypseleotris sp. 1 in rivers where both species co-occurred (i.e. Mary and Brisbane rivers) necessitated that we pool distribution, abundance and biomass data for these rivers. Total
Taxon % locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
H.g./H. sp.1
H.g./H. sp.1
H.g.
H.g.
H.g./H. sp.1
H.g.
H.g.
75.2
84.0
75.9
70.0
73.0
70.6
85.0
7.51 (12.12)
6.15 (9.50)
12.51 (16.07)
9.63 (17.62)
9.04 (14.21)
8.49 (15.97)
6 (4)
6 (4)
3 (2)
2 (2)
2 (2)
5 (3)
4 (4)
0.32 (0.79)
0.27 (0.80)
0.16 (0.16)
0.09 (0.17)
0.63 (1.25)
0.37 (0.74)
0.18 (0.26)
9.87 (10.94)
14 (10)
15 (10)
7 (7)
11 (6)
11 (7)
9 (8)
12 (11)
Mean numerical density (fish.10m–2)
1.01 ± 0.10
0.94 ± 0.14
0.62 ± 0.19
1.27 ± 0.52
0.73 ± 0.12
1.77 ± 0.34
0.27 ± 0.05
Mean biomass density (g.10m–2)
0.53 ± 0.06
0.46 ± 0.07
0.12 ± 0.02
0.42 ± 0.22
0.48 ± 0.13
0.78 ± 0.14
0.12 ± 0.03
512
Hypseleotris galii, Hypseleotris sp. 1
identified this species in runs and pool habitats near the headwaters of the Mary River in south-eastern Queensland [1093].
H. klunzingeri occurring together at 131 of the 233 locations in which either species was sampled in south-eastern Queensland [1093]. Each taxon was collected in similar numbers at those sites in which both occurred (9,800 and 10,097 individuals of Hypseleotris spp. and H. klunzingeri, respectively) and either species could be dominant at individual localities [1093]. Macro/mesohabitat use Hypseleotris galii and Hypseleotris sp. 1 appear to have similarly broad habitat requirements. Both species occur in a variety of lotic and lentic habitats including small coastal streams, throughout large rivers and their floodplain habitats (billabongs and wetlands), coastal wetlands, dune lake and stream systems, and river impoundments (dams and weirs). Hypseleotris sp. 1 is particularly common in floodplain swamps and wetlands (e.g. the Tully-Murray Swamps in northern Queensland), but is not restricted to these lowland areas; we have positively Table 2. Macro/mesohabitat use by Hypseleotris galii/Hypseleotris sp. 1 in rivers of south-eastern Queensland. Data summaries for 12 263 individuals collected from samples of 586 mesohabitat units at 218 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
5.6 3.0 4.0 0 1.2 0
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec–1) 0
Max. 9705.9 246.5 335.0 460 40.0 95.8 2.33 1.20 0.71
Mean
W.M.
622.7 1148.4 43.1 48.0 131.2 147.4 83 84 9.0 7.7 40.4 43.1 0.19 0.46 0.07
Microhabitat use Hypseleotris galii and Hypseleotris sp. 1 probably have very similar microhabitat requirements. Both species may occasionally form loose schools of hundreds of individuals [1093] and masses (thousands) of juveniles and subadults have been observed undertaking upstream dispersal movements (see below). The following discussion of microhabitat use treats both species together.
0.14 0.43 0.06
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
100.0 100.0 70.7 78.2 65.8 53.9 70.0
7.9 24.4 21.6 23.7 15.6 5.2 1.7
12.9 29.0 20.1 18.6 13.5 4.7 1.2
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
86.1 63.6 45.0 65.7 39.1 90.0 37.6 26.8 96.3 100.0
10.7 7.3 1.6 6.0 1.7 15.3 4.7 3.8 16.9 21.5
11.7 6.8 1.5 6.1 2.3 16.2 5.0 3.9 14.0 18.0
The following discussion of macro- and mesohabitat use data derived from our sampling in south-eastern Queensland treats both species together as Hypseleotris spp. Hypseleotris spp. can be widespread within river systems: we have sampled this taxon between 4–335 km upstream from the river mouth and at elevations up to 460 m.a.s.l. (Table 2). It more commonly occurs in the mid- to lower reaches of rivers (within ~150 km of the river mouth) and at elevations around 80 m.a.s.l. It is present in a wide range of stream sizes (1.2–40.0 m width) but is more common in streams less than 10 m wide and with moderate riparian cover (>~40%). Hypseleotris spp. most commonly occurs in pools and runs characterised by low gradient (weighted mean = 0.14%), moderate depth (0.43 m weighted mean depth) and low mean water velocity (weighted mean 0.06 m.sec–1). However, it occasionally has been collected from shallow, riffle habitats of high gradient (maximum 2.33%) and high velocity (maximum 0.71 m.sec–1) (Table 2). It occurs in mesohabitats with a wide range of substrates but was generally most common in habitats with fine to intermediate substrates (sand, fine gravel and coarse gravel). Hypseleotris spp. was most frequently collected where submerged aquatic macrophytes, leaf-litter beds, undercut banks and root masses are common.
In rivers of south-eastern Queensland, Hypseleotris spp. were most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b) reflecting the pattern observed in mesohabitat use. This taxon was collected over a wide range of depths, but most often between 10 and 50 cm (Fig. 1c). A benthic species, it occupies the lower half of the water column, most commonly in direct contact with the substrate (Fig. 1d). Hypseleotris spp. does not appear to prefer particular substrate types as it was found over a wide range of substrates (Fig. 1e). This taxon was often collected close to the stream-bank (66% of 2361 fish collected within 1 m of the bank), and almost always was found in close association with some form of submerged cover (Fig. 1f). It was most frequently collected near leaf-litter beds and
513
Freshwater Fishes of North-Eastern Australia
Hypseleotris sp. 1 in inland desert drainages suggests that the maximum temperature tolerated by this species is likely to be greater than indicated in Table 3.
filamentous algae but also commonly used the substrate, aquatic macrophytes, submerged marginal vegetation, woody debris and root masses (Fig. 1f). 80
(a) 80
60
60
40
40
20
20
0
0
30
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 60
20
40
10
20
0
0
Total depth (cm) 25
Arthington el al. [95] conducted laboratory experiments to establish the chronic lower thermal tolerances of adult H. galii using fish from south-eastern Queensland. Fish acclimated for four days at 15°C, lost orientation at 6.4°C and moved only spasmodically at 5.6°C [95]. In a series of laboratory experiments, Ham [502] observed that adult H. galii from south-eastern Queensland could tolerate minimum temperatures about 1°C lower than juvenile fish. Adults acclimated for seven days at 15°C were observed to lose orientation at temperatures of about 4.0°C, move spasmodically at ~2.5°C and cease movement completely at about 2.2°C [502]. Fish acclimated for seven days at 10°C were reported to have a greater tolerance of low water temperatures, losing orientation at temperatures of about 3.5°C, moving spasmodically at 2.2°C and ceasing movement completely at about 1.9°C [502].
(b)
(e)
20
Dissolved oxygen concentrations in south-eastern Queensland ranged from hypoxic to super-saturated (Table 3), possibly as a result of high rates of photosynthesis and respiration by aquatic macrophytes and algae. Hypseleotris. galii and Hypseleotris sp. 1 often occur in close association with extensive beds of these aquatic plants. Both species, but particularly H. galii, occur in relatively acidic to mildly acidic to basic waters (range 4.4–8.9). The maximum turbidity recorded in south-eastern Queensland is 331.4 NTU but these species usually occur in waters of much lower turbidity. The presence of Hypseleotris sp. 1 in turbid waters of the Murray-Darling Basin is indicative of tolerance to high turbidities. Although no quantitative experimental tolerance data are available, salinity tolerances may be reasonably high as has been observed for H. klunzingeri and other eleotrids. We recorded Hypseleotris spp. in waters with a maximum conductivity of 4123 µS.cm–1. The presence of Hypseleotris sp. 1 in saline lakes of inland Australia (salinities ranging between 0.15–10 ppt) further attests to the salinity tolerance of this species. Mowbray [973] reported that the 96h LC50 of H. galii from central New South Wales to the
Relative depth 20
(f)
15
15 10 10 5
5
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Hypseleotris galii/Hypseleotris sp. 1. Data derived from capture records for 2361 individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
Environmental tolerances Hypseleotris galii is widely regarded as a relatively hardy species, tolerant of poor water quality [553, 748, 749]. We have collected H. galii and Hypseleotris sp. 1 over a relatively wide range of water quality conditions in south-eastern Queensland (Table 3) and both species are often common in heavily degraded habitats in this region [1093]. Water temperatures ranged between 8.4 and 32.0°C but the distribution of H. galii and Hypseleotris sp. 1 in more temperate regions of eastern and inland Australia suggests that minimum thermal tolerances of this species may be lower. Furthermore, the presence of
Table 3. Physicochemical data for Hypseleotris galii/Hypseleotris sp. 1 from 380 samples collected in southeastern Queensland over the period 1994 to 2003 [1093].
514
Parameter
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
8.4 0.3 4.4 51.0 0.1
31.2 19.5 8.9 4123.0 331.4
Mean 19.5 7.2 7.5 556.7 9.1
Hypseleotris galii, Hypseleotris sp. 1
reproductive stage III) for fish from the Tweed River, northern New South Wales, was reported as 23 and 27 mm LCF for males and females, respectively [1133]. In aquaria, H. galii are reported to breed at 40 mm TL for males and 35 mm TL for females [797].
organochlorine insecticide endosulfan was 2.2 µS.L–1, slightly lower than that observed for G. holbrooki (3.1 µS.L–1). Reproduction Quantitative information on the reproductive biology and early development of H. galii is available from several field and aquarium studies [58, 84, 357, 425, 735, 748, 832, 833, 835, 1093, 1133]. Comparatively little has been published concerning the reproductive biology of Hypseleotris sp. 1 [797, 1339, 1354]. Details are summarised in Table 4. Both species spawn and complete their entire life cycle in freshwater. Maturation of H. galii commences at a relatively small size. Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary and Albert rivers, south-eastern Queensland, were 20.8 mm SL and 32.0 mm ± 0.5 SE, respectively for males and 20.0 and 29.4 mm ± 0.8 SE, respectively for females (Fig. 2) [1093]. Gonad maturation in both sexes was commensurate with somatic growth, the mean length at each reproductive stage being different from all other stages. Males of equivalent reproductive stages were larger than females (Fig. 2). The minimum and mean sizes of gravid (stage V) males were 30.7 mm SL and 38.9 mm ± 0.8 SE, respectively; the minimum and mean sizes of gravid females were 22.0 mm SL and 33.1 mm ± 1.7 SE, respectively. Arthington and Marshall [84] reported that the minimum size of ripe females (equivalent to stage V) in the Noosa River was 18.8 mm SL. Length at first maturity (equivalent to
Hypseleotris sp. 1 from the Mary River reproduces at a similar size to H. galii [1093]. The minimum and mean sizes of gravid (stage V) males were 32.4 mm SL and 36.1 mm ± 1.3 SE, respectively; the minimum and mean sizes of gravid females were 30.8 mm SL and 33.3 mm ± 0.8 SE, respectively [1093]. Females are reported to mature at about 25 mm TL [1354]. In aquaria, this species is reported to breed at 35 mm TL for males and 30 mm TL for females [797]. Hypseleotris galii and Hypseleotris sp. 1 are reproductively active for an extended period from late winter through to early autumn in south-eastern Queensland, but spawning Reproductive stage I
II
III
IV
V
Males 100
(51) (6) (5) (16) (38) (12)
(13) (41) (23) (15) (7)
80 60 40
40
Males
20
Females
0
35
Females 100
(28) (7) (8) (11) (12) (7)
(9) (9) (10) (6) (8)
80
30
60
25
40 20
20
0
I
II
III
IV
V
Reproductive stage Figure 2. Mean standard length (mm SL ± SE) for male and female Hypseleotriss galii within each reproductive stage. Fish were collected from the Mary and Albert rivers, south-eastern Queensland, between 1994 and 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 3.
Month Figure 3. Temporal changes in reproductive stages of Hypseleotris galii in the Mary and Albert rivers, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in parentheses.
515
Freshwater Fishes of North-Eastern Australia
for H. galii and Hypseleotris sp. 1, respectively [797]. Spawning cues are probably not associated with rising water levels or flooding [1093, 1354]. The peak spawning period generally coincides with pre-flood periods of low and relatively stable discharge in rivers of south-eastern Queensland. However, in the Mary River, breeding may also continue through the months of elevated discharge at the commencement of the wet season in December– January. The ability of this species to spawn repeatedly over an extended period, may be an adaptation to the relatively unpredictable timing of the onset of wet season flooding. The spawning of adults and presence of larvae tend to occur when the likelihood of flooding is low, but the predictability of high temperatures and low flows are higher. Sampling in rivers of south-eastern Queensland [1093] revealed that juvenile fish (H. galii and Hypseleotris sp. 1 pooled) less than 15 mm SL were present almost yearround, supporting the suggestion that this species has an extended spawning period (fig. 5).
is concentrated between late winter and early summer. Gravid female H. galii (stage V) were present between August and January (Fig. 3) and GSI values were elevated over the same period (Fig. 4). Little seasonal pattern in reproductive activity of males could be discerned from these data, but gravid males were present through to March (Fig. 3). The phenology of reproductive activity for H. galii from the Noosa River [84] and Tweed River [1133] was very similar to that described above, except that a few ripe and spent fish were present later in the year (May and June), suggesting that reproduction may occur well into the cooler months [84]. In the Lane Cove River, central New South Wales, the commencement and period of peak reproductive activity appears to occur later in the year and spawning is concentrated in a slightly shorter period (October–February) than observed in more northerly populations [58, 832, 833].
12
Males 10
Females
Spring (n = 1154)
30
Summer (n = 1742)
8 6
20
AutumnWinter (n = 2703)
4 10
2 0
0
Month Figure 4. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Hypseleotris galii males (open circles) and females (closed circles) in the Mary and Albert rivers, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 3.
The temporal pattern in reproductive activity of Hypseleotris sp. 1 in the Mary River is similar to that described above for H. galii in south-eastern Queensland, with gravid females and elevated GSI values observed in spring and early summer [1093].
Standard length (mm) Figure 5. Seasonal variation in length-frequency distributions of Hypseleotris galii/Hypseleotris sp. 1, from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
Reproductive behaviour of H. galii is generally similar to other species of Hypseleotris. Males display aggressive territorial behaviour throughout the year but this intensifies with onset of the breeding season [58]. Territorial behaviour involves darting movements, flaring of the fins and spreading of the opercula. The non-territorial female is encouraged to deposit demersal, adhesive eggs in the nest site maintained by male. This behaviour is preceded
The spawning stimulus for H. galii and Hypseleotris sp. 1 is unknown but the reproductive period corresponds with increasing water temperatures and photoperiod in late winter and early spring. In aquaria, spawning is reported to occur at minimum water temperatures of 21 and 20°C
516
Hypseleotris galii, Hypseleotris sp. 1
Table 4. Life history information for Hypseleotris galii (H.g.) and Hypseleotris sp. 1 (H. sp.1) in south-eastern Queensland (except where indicated). Age at sexual maturity (months)
H.g.: 4 months [735]; 12 months [797] H. sp.1: 12 months [797, 1354]
Minimum length of gravid (stage V) females (mm)
H.g.: 22.0 mm SL (Mary and Albert rivers) [1093]; 18 mm SL (Noosa River) [84] H. sp.1: 30.8 mm SL (Mary River) [1093]
Minimum length of ripe (stage V) males (mm) H.g.: 30.7 mm SL (Mary and Albert rivers) [1093] H. sp.1: 32.4 mm SL (Mary River) [1093] Longevity (years)
H.g.: Possibly 2–3 years in the wild [1093] H. sp.1: Possibly 2–3 years in the wild [1354]
Sex ratio (female to male)
?
Occurrence of ripe (stage V) fish
H.g.: late winter to early autumn (August–March) [1093] H. sp.1: spring and early summer (September to March) [1093]
Peak spawning activity
H.g.: Elevated GSI between August and January [1093]; H. sp.1: Elevated GSI between September and January [1093]
Critical temperature for spawning
H.g.: ? 20°C [797] H. sp.1: ? 21°C [797]
Inducement to spawning
H.g.: ? Possibly a combination of increasing temperature and increasing day length H. sp.1: ? probably as for H. galii
Mean GSI of ripe (stage V) females (%)
H.g.: 12.0% ± 0.6 (maximum mean GSI in November = 9.7% ± 1.6) [1093] H. sp.1: 9.7% ± 1.4 (maximum GSI in September = 10.2% ± 2.0) [1093]
Mean GSI of ripe (stage V) males (%)
H.g.: 3.7% ± 0.3 (maximum mean GSI in November = 2.4% ± 0.3) [1093] H. sp.1: 4.4% ± 0.6 (maximum GSI in September = 2.5% ± 0.3) [1093]
Fecundity (number of ova)
H.g.: Total fecundity = 266–1370, mean = 544 ± 67 (Mary and Albert rivers) [1093]; Batch fecundity = ~25–170 (Noosa River [84]; In aquaria, females reported deposit between 200–400 eggs in a single spawning session [58, 797] H. sp.1: Total fecundity = 374–785 [1093]; In aquaria, females reported deposit between 250–500 eggs [797, 1339, 1354]
Total Fecundity (TF) and Batch Fecundity (BF)/Length (mm SL) or Weight (g) relationship (mm SL)
H.g.: TF = 57.41 L – 1343.1, r2 = 0.728, p<0.001, n = 42 (Mary and Albert rivers) [1093]; TF = 877.83 W – 57.49, r2 = 0.819, p<0.001, n = 42 (Mary and Albert rivers) [1093]; BF = 8.133 L – 97.26, r2 = 0.89, p<0.01, n = 16 (Noosa River) [84] H. sp.1: ?
Egg size (diameter)
H.g.: Intraovarian eggs from stage V fish = 0.64 mm ± 0.01 [1093]; Water-hardened eggs oblong, 0.91 mm on average [58] H. sp.1: Intraovarian eggs from stage V fish = 0.52 mm ± 0.01 [1093]. Water-hardened eggs 0.8–1.0 mm [1339, 1354]
Frequency of spawning
H.g.: Batch spawner over extended period. In aquaria, females deposit 5–8 batches of eggs approximately weekly over the spawning season [58, 797] H. sp.1: Uncertain whether females spawn more than once in a spawning season [1339]
Oviposition and spawning site
H.g.: eggs attached to the undersurface of firm substrates such as gravel, rocks, woody debris or aquatic plants [58, 797] H. sp.1: eggs attached to hard objects on or near the substrate [1354] and on the roof of caves [1339]
Spawning migration
None known
Parental care
H.g.: Male guards and fans eggs until they hatch [797] H. sp.1: Male guards and fans eggs until they hatch [797, 1339, 1354]
Time to hatching
H.g.: Varies with temperature. 4–5 days at 22–23°C [58], 6–7 days at 21–24°C [797] and 12 days at 23°C [748] H. sp.1: 6–9 days at 20–24°C [797], 7–8 days at 20–24°C [1354] and 8–9 days at 20–24°C [1339]
Length at hatching (mm)
H.g.: Newly hatched prolarvae 2.1–2.9 mm TL (pigmented eyes, functional jaw) [58, 735] H. sp.1: 3–4 mm TL [1339, 1354]
Length at free swimming stage
H.g.: ? H. sp.1: May be free-swimming at hatching [797]
Age at loss of yolk sack
H.g.: 5–6 days [58, 735] H. sp.1: ?
517
Freshwater Fishes of North-Eastern Australia
Table 6 (cont). Life history information for Hypseleotris galii (H.g.) and Hypseleotris sp. 1 (H. sp.1) in south-eastern Queensland (except where indicated). Age at first feeding
H.g.: 2 days [797]; 5–6 days [58, 735] H. sp.1: ?
Length at first feeding
?
Age at metamorphosis (days)
H.g.: 8 mm TL after 60 days [797]; juvenile phase (fins fully rayed) reached after 74 days [735] H. sp.1: ?
Hypseleotris sp. 1 was reported to be about 0.8–1.0 mm [1339, 1354].
by a ‘cleaning’ activity whereby the male makes undulating sweeps in a sinuous path across the nest site while pressing the urinogenital papilla against the surface. The purpose of this behaviour is unknown but may involve preparation of the spawning surface or an inducement of the female to spawn [58, 936]. Before entering the nest site, the female may make a series of rapid vertical movements, followed closely by the male, after which the male repeatedly nudges the female in the region of the urinogenital papilla. The eggs of H. galii are usually attached to the undersurface of firm substrates such as gravel, rocks, woody debris or aquatic plants [58, 797]. Eggs of Hypseleotris sp. 1 have usually been observed attached to hard objects on or near the substrate [1354] and on the roof of caves [1339]. In both species of Hypseleotris, the eggs are guarded and fanned by the male [797, 1339, 1354].
The duration of embryological development in H. galii and Hypseleotris sp. 1 is longer and larvae of both species are more advanced at hatching than larvae of H. klunzingeri or H. compressa. Eggs of H. galii have been reported to hatch in 4–5 days at 22–23°C [58], 6–7 days at 21–24°C [797] and 12 days at 23°C [748]. The duration of embryological development in Hypseleotris sp. 1 is generally similar; eggs are reported to hatch in 6–9 days at 20–24°C [797], 7–8 days at 20–24°C [1354] and 8–9 days at 20–24°C [1339]. Details of embryological development in H. galii are available in Anderson et al. [58] and details of larval morphology are available in Konagai and Rimmer [735]. Newly hatched larvae range from 2.1–2.9 mm TL. Feeding commences after two days [797] but other reports suggest the yolk sac is fully absorbed and feeding commences after five to six days [58, 735]. Larvae of Hypseleotris sp. 1 are about 3–4 mm at hatching [1339, 1354] and may be capable of swimming freely at this point [797].
Hypseleotris galii is a batch spawner [58, 832]. Females in aquaria have been observed to deposit 5–8 batches of eggs approximately weekly during the breeding season [58]. It is uncertain whether female Hypseleotris sp. 1 spawn more than once in a breeding season, but Unmack [1339] observed males to spawn with several females in a season. Total fecundity for H. galii from the Mary and Albert rivers is estimated to range from 266–1370 eggs (mean 544 ± 67 SE, n = 42 fish) [1093]. Batch fecundity for fish from the Noosa ranges from ~25–170 eggs [84]. Relationships between body length, body weight and total fecundity are given in Table 4. Fish of 25 mm SL produced about 250 eggs, whereas fish of 35 mm SL produced about 750 eggs [1093]. In aquaria, H. galii is reported to deposit 200–400 eggs per batch [58, 797]. Total fecundity for six individuals of Hypseleotris sp. 1 from the Mary River (30–36 mm SL) ranged from 374–785 eggs [1093]. In aquaria, this species is reported to deposit between 250 and 500 eggs [797, 1339, 1354].
Growth rates in H. galii appear relatively slow. Leggett and Merrick [797] reported that individuals reached 8 mm TL after about 60 days and Konagai and Rimmer [735] reported that all fins were fully rayed and juvenile phase was reached 74 days after hatching. Six months after hatching individuals are about 25 mm TL [797]. The interval between egg fertilisation and sexual maturity in H. galii may be as little as four months [735] but others have reported that H. galii and Hypseleotris sp. 1 mature at 12 months [797, 1354]. Wager and Unmack [1354] estimated that Hypseleotris sp. 1 may live for up to two to three years; the life-span of H. galii is probably similar [1093]. Movement There is very little quantitative information concerning the movement biology of H. galii and Hypseleotris sp. 1. Small numbers of individuals of both species have occasionally been reported to use fishways on weirs and tidal barrages in south-eastern Queensland rivers. Thirty-one individuals of H. galii were collected in a total of 11 samples at the bottom of a fishlock on a large weir in the
Eggs of both species are demersal, adhesive and relatively small (but larger than eggs of H. klunzingeri or H. compressa). The eggs of H. galii are slightly oblong [58, 1093] and the mean diameter of 139 intraovarian eggs from stage V fish was 0.63 mm ± 0.01 SE [1093]. Waterhardened eggs are 0.91 mm diameter (long axis) on average [58]. The diameter of water-hardened eggs of
518
Hypseleotris galii, Hypseleotris sp. 1
klunzingeri. Hypseleotris galli is a microphagic carnivore consuming aquatic insects (42.0%) (chironomids, emphemeropterans and trichopterans) and microcrustaceans (21.4%) (mostly cladocerans and copepods) and macrocrustaceans (21.4%) (mostly small atyid shrimps). Terrestrial invertebrates, aerial forms of aquatic insects, terrestrial vegetation, algae, molluscs, fish eggs and other macro- and microinvertebrates are also consumed in small quantities. Relatively little spatial variation is evident in the relative proportion of the major food items consumed, except that the diet of fish from a heavily vegetated wallum stream on Moreton Island [82] was composed almost entirely of microcrustaceans (mostly cladocerans that were abundant among large beds of the emergent sedge Eleocharis). Aquatic insects were the dominant food group consumed in all other studies.
Burnett River; none were collected from the top of the fish lock [11]. Three individuals were sampled during December at the base of a tidal Barrage fishway in the Mary River catchment [159]. Little can be concluded from these data. On several occasions during summer electrofishing surveys of the Mary River, we observed large aggregations (hundreds of individuals) of H. galii and Hypseleotris sp. 1 of all size classes undertaking mass upstream movements [1093]. On each occasion, these fish were observed aggregating just downstream of small obstructions to movement (e.g. road culverts) and immediately after an increase in discharge. These observations suggest that upstream dispersal movements may occur when flow conditions allow [1093]. Similar upstream movements have been observed by Hypseleotris sp. 1. in a large tributary of the Fitzroy River [1351] and in Barambah Creek in the Burnett River basin [1093]. However, only a few individuals of this species have been collected in fishways, and only in the Fitzroy River during November [1272, 1274, 1275].
There is very little quantitative diet data available for Hypseleotris sp. 1 except from stomach content analysis of 19 individuals from tributary streams of the Mary River, south-eastern Queensland [1093] (Fig. 7). This species is a microphagic carnivore consuming a large fraction of aquatic insects (77.1%) (larvae of chironomids, trichopterans, and ephemeropterans) and microcrustaceans (15.7%). Small amounts of algae (1.3%) (diatoms and desmids) and other microinvertebrates (hydracarinids and rotifers) were consumed in small quantities.
Hypseleotris galii has been recorded as having fallen to the ground in rain in Brisbane, south-eastern Queensland, possibly as a result of a whirlwind [878, 1018, 1400]. Trophic ecology Dietary information is available from stomach content analysis of 1003 individuals from coastal and dune island wallum streams and lakes in south-eastern Queensland [82, 84, 92, 105], small tributary streams of the Brisbane River [80], and the Tweed River in northern New South Wales [1133] (Fig. 6). The diet of H. galli is relatively diverse in comparison to that of Hypseleotris sp. 1. or H. Fish (0.1%) Other microinvertebrates (4.0%)
Microcrustaceans (21.4%)
Unidentified (0.8%) Fish (0.1%) Algae (1.3%) Detritus (0.4%) Other microinvertebrates (4.7%)
Microcrustaceans (15.7%)
Unidentified (15.0%)
Terrestrial invertebrates (0.6%) Aerial aq. Invertebrates (1.0%) Terrestrial vegetation (0.2%) Algae (1.9%)
Macrocrustaceans (12.2%) Molluscs (0.2%) Other macroinvertebrates (1.2%)
Aquatic insects (77.1%) Aquatic insects (42.0%)
Figure 6. The mean diet of Hypseleotris galii. Data derived from stomach content analysis of 1003 individuals from coastal and dune island wallum streams and lakes in southeastern Queensland [82, 84, 92, 105], small tributary streams of the Brisbane River [80], and the Tweed River in northern New South Wales [1133].
Figure 7. The mean diet of Hypseleotris sp. 1. Data derived from stomach content analysis of 19 individuals from tributary streams of the Mary River in south-eastern Queensland [1093].
519
Freshwater Fishes of North-Eastern Australia
throughout the drainage network.
Conservation status, threats and management Both Hypseleotris galii and Hypseleotris sp. 1 (as Hypseleotris sp. A) were listed as Non-Threatened by Wager and Jackson [1353] in 1993. A decade later, these species remain generally common throughout their geographic range but may suffer local disturbances and depletion. Potential threats in south-eastern Queensland are similar to those identified for many other small-bodied fish species, for example Atherinidae, Melanotaeniidae, Pseudomugilidae, Chandidae and Retropinnidae. Threats include: riparian loss and instream habitat degradation (particularly siltation, reduced inputs of woody debris and loss of aquatic plants), flow regulation (particularly rapid fluctuations in water level that may impact on reproductive processes and recruitment), barriers to movement, and threats associated with alien fish species.
The spawning stimuli for H. galii and Hypseleotris sp. 1 are not known however both species are reproductively active for an extended period in south-eastern Queensland, coinciding with increasing water temperatures and photoperiods in late winter and early spring. The cues to spawning are probably not associated with rising water levels or flooding even though fish have been observed to spawn in artificial ponds soon after a rise in water level [813] and may spawn during the months of high stream flows and flooding. However, the peak spawning period generally coincides with pre-flood periods of low and relatively stable discharge in rivers of south-eastern Queensland [1095]. Low discharge conditions in late winter and early spring are likely to minimise disturbance of the substrates and objects used for spawning (e.g. gravel, rocks, woody debris, aquatic plants [58, 797]). At this time there is also less likelihood that rapidly falling water levels will expose spawning substrates and fish eggs. Larvae hatching during the spring months of stable low flows are likely to encounter high densities of small invertebrate prey, and to experience elevated growth rates, factors that tend to maximise the potential for recruitment into juvenile stocks [82, 84, 1093]. A similar scenario of spawning and recruitment has been suggested for several small-bodied fish species in the Murray-Darling Basin [614, 615]. However, breeding of these species may also continue through the months of elevated discharge at the commencement of the wet season in December–January. Thus conditions suitable for recruitment of larvae through to the juvenile stage and beyond may persist almost year-round in south-eastern Queensland, and recruitment may not necessarily be limited by prevailing temperature and/or discharge regimes. These observations complicate the development of scenarios of impact associated with alterations to stream discharge regimes.
Both species occur in a variety of lotic and lentic habitats including small coastal streams, throughout large rivers and their floodplain habitats (billabongs and wetlands), coastal wetlands, dune lake and stream systems. Hypseleotris sp. 1 is particularly common in floodplain swamps and wetlands. Such habitats are most at risk of reclamation, degradation by clearing and encroachment by agriculture (particularly sugar-cane farming), invasion by noxious weeds such as para grass and Hymenachne, and channelisation to improve drainage. In addition, habitats are frequently close to human population centres (e.g. Brisbane and the south-eastern Queensland coastal strip) and are thus at risk from urban encroachment and associated pressures on aquatic systems. These species of Hypseleotris may be intolerant of riparian habitat degradation as they are most frequently collected near leaf-litter beds and filamentous algae but also commonly use submerged marginal vegetation, woody debris and root masses as cover [1093]. Other members of the genus were suggested to be similarly intolerant of riparian disturbance [440, 484]. Like many other native species, siltation arising from increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of H. galii and Hypseleotris sp. 1 and siltation may also affect aquatic invertebrate food resources.
Alien fish species (particularly Gambusia holbrooki and other poeciliids) threaten many small native species with similar habitat and dietary requirements in south-eastern Queensland streams [96] and dune waterbodies [82, 84]. Species of Hypseleotris may be particularly at risk in degraded stream habitats supporting large populations of G. holbrooki, a microphagic carnivore capable of unusual dietary flexibility [78, 80, 92, 94, 96]. This poeciliid is also aggressive towards other species [983] and is known to consume the eggs and fry of small native fishes [636, 960]. Extensive infestations of introduced para grass, Brachiaria mutica, may also constrain the foraging behaviour of H. galii and Hypseleotris sp. 1 in streams of degraded urban and agricultural environments [96, 118].
The aggregation of hundreds of individuals of H. galii and Hypseleotris sp. 1 of all size classes just downstream of small obstructions to movement (e.g. road culverts) and immediately after an increase in discharge suggest that upstream dispersal movements may occur when flow conditions allow [1093]. The capacity for upstream movements indicates that these eleotrids are likely to be sensitive to in-stream barriers such as dams, weirs, barrages, road crossings and culverts. Barriers to movement may curtail recolonisation events following disturbances and local population declines or affect dispersal of new recruits
Dove [1432] provided a list of parasite taxa recorded from H. galii in south-eastern Queensland. 520
Hypseleotris klunzingeri (Ogilby, 1898) Western carp gudgeon
37 429027
Family: Eleotridae
eye, snout bluntly rounded. No head pores but numerous lines of papillae on head, often several lines surrounding and radiating from eye, other lines over snout, nape and operculum. Gill openings ending below posterior preopercular margin. Ciliated scales on body, becoming cycloid ventrally and anteriorly. Small cycloid scales on cheeks and operculum. First dorsal fin low, rounded and originating just behind level of pelvic fin bases. Second dorsal origin above vent with slightly elongated posterior rays in males. Pelvic fins often reaching, fourth ray long and pointed. Caudal fin truncate or slightly rounded. Urinogenital papilla large and prominent in adults; a flat conical flap with concave tip in males, shorter bulbous lobe with fine projections and fringes at tip in females. Males usually larger than females and may develop slight hump on head. Considerable spatial, sexual and ontogenetic colour variation. Yellowish-grey to greenish-brown on dorsal surface, cream or silvery on ventral surface. Upper lateral and dorsal scales with brownish-black margins which form 8–10 irregular bars across head and nape. Dark scale-bases along middle of side give barred appearance. Elongate brownish-black spot bordered anteriorly by white on upper pectoral fin base. Greyish head with blue-mauve blotch on operculum. Fin colour variable but dusky grey to yellowish basal colour. Dorsal and anal fins with dusky
First dorsal fin: VI–VII; Second dorsal: I, 9–11; Anal: I, 9–11; Pectoral: 13–15; Pelvic: I, 5; Caudal: 15 segmented rays; Vertical scale rows: 27–32; Predorsal scales: 13–20; Gill rakers on first arch: 9–12; Vertebrae: 26–29 [52, 270, 775]. Figure: mature male specimen, 28 mm SL, Mary River, November 1995; drawn 1998. Hypseleotris klunzingeri is a small gudgeon possibly reaching a maximum size of about 60 mm TL, but more common to 40 mm TL [1339]. Of 4643 specimens collected in streams of south-eastern Queensland over the period 1994–2000 [1093], the mean and maximum length of this species were 28 and 52 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 559 individuals (range 19–46 mm SL) from the Mary River, south-eastern Queensland is W = 6 x 10–6 L3.318, r2 = 0.957, p<0.001 [1093]. The following description is derived largely from Larson and Hoese [775], Cadwallader and Backhouse [270] and Ogilby [1013]. Hypseleotris klunzingeri is a slender fish with a moderately compressed and elongate body, tapering towards tail. Terminal mouth small, oblique and extending back to below anterior margin of eye. Tip of tongue truncate. Head relatively large and rounded above 521
Freshwater Fishes of North-Eastern Australia
Murray-Darling Basin, where it is widespread [585, 775, 1337] although it was suggested in 1991 to have declined in abundance in recent decades [778]. This species has been widely translocated with records of successful introductions into the Wimmera and Wannon rivers in western Victoria [775], and into tributaries of the Murray River previously thought to lie beyond its natural range (e.g. Seven Creeks system, Victoria) [267].
basal stripe, remainder of fin orange-red, bordered by white stripe, edge of fin translucent. Basal half of caudal fin reddish-orange, remainder of fin clear. Populations in south-east Queensland may have more yellowish than orange-red fin colouration [270, 775, 1013, 1337, 1339]. Hypseleotris klunzingeri from coastal drainages of eastern Australia can be distinguished from all other sympatric hypseleotrids by the numerous rows of sensory papillae on the head, usually visible to the naked eye or with a hand lens in all but the smallest individuals [1093]. Unmack [1339] suggested that coastal populations differ from those in inland Australia, being stockier, with a deeper more blunted head, and with more prominent scale markings. See also the chapters on H. galii, Hypseleotris sp. 1 and H. compressa for distinguishing characteristics of these species.
The natural northern limit of H. klunzingeri in eastern coastal Australia is uncertain. Unmack [585] lists this species as occurring as far north as Herbert Creek in the Shoalwater Bay drainage basin. However, there are records further north in rivers and streams of the Plane Creek Basin [779] and the Pioneer Basin [1081]. Furthermore, we have collected this species in the Burdekin River upstream of the Burdekin Falls [1093]. It is possible that these northern records are the result of mis-identifications of H. compressa or Hypseleotris sp. 1. Populations in the Burdekin River may have been translocated there as contaminants of fish hatchery stock associated with the common practice of stocking of sport fish in this river in recent decades. South of Shoalwater Bay, H. klunzingeri is present in almost all drainage basins south to the border with New South Wales (the exceptions being the Water Park Creek and Calliope Basins).
Systematics Unmack [1339] detailed the taxonomic history of this species. Hypseleotris klunzingeri was first discovered by Klunzinger in 1872 [722] and again in 1880 [723]; he mistook them for the chameleon gudgeon (H. cyprinoides), a species that does not occur in Australia. Realising this mistake, Ogilby [741] renamed the fish after Klunzinger in 1898 as Carrassiops klunzingeri. No other synonyms for this taxon exist.
Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 10 488 individuals from 51% of all locations sampled (Table 1). Overall, it was the seventh most abundant taxa collected (6.4% of the total number of fishes collected) and was generally common at sites in which it occurred (12.4% of total abundance). In these sites, H. klunzingeri most commonly occurred with the following species (listed in decreasing order of relative abundance): M. duboulayi, G.
Distribution and abundance Hypseleotris klunzingeri is a widespread species occurring in coastal drainages from central Queensland, south to the Hunter River north of Sydney, in central New South Wales [1339, 1349]. This species is also present on Fraser, Bribie, Moreton and North Stradbroke islands off the south-eastern Queensland coast. Inland, it is present in Cooper Creek and the Bulloo River, and throughout much of the
Table 1. Distribution, abundance and biomass data for Hypseleotris klunzingeri in rivers of south-eastern Queensland. Data summaries for a total of 10 488 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
51.0
76.0
24.1
45.0
54.1
42.6
45.0
6.42 (12.35)
7.85 (12.9)
3.21 (15.47)
4.99 (15.71)
7.60 (14.78)
3.30 (8.41)
6.16 (11.87)
7 (2)
5 (3)
7 (3)
6 (2)
3 (2)
9 (5)
6 (4)
0.28 (0.43)
0.33 (0.44)
0.17 (0.48)
0.09 (0.15)
0.30 (0.59)
0.17 (0.40)
0.22 (0.40)
17 (10)
13 (9)
6 (3)
12 (8)
15 (12)
12 (10)
10 (8)
Mean numerical density (fish.10m–2)
1.10 ± 0.12
1.35 ± 0.18
0.44 ± 0.27
0.64 ± 0.14
1.14 ± 0.39
0.76 ± 0.17
0.32 ± 0.09
Mean biomass density (g.10m–2)
0.49 ± 0.05
0.56 ± 0.06
0.60 ± 0.50
0.19 ± 0.18
0.38 ± 0.12
0.39 ± 0.09
0.23 ± 0.17
522
Hypseleotris klunzingeri
and stream systems, and river impoundments (dams and weirs). In the lower Murray River, this species is very common in floodplain billabongs among dense stands of emergent macrophytes (Juncus and Eleocharis) [122].
holbrooki, P. signifer, and R. semoni. Hypseleotris klunzingeri was the 17th most important species in terms of biomass, forming 0.3% of the total biomass of fish collected. It was generally less widespread or abundant in individual river basins than H. galii, except in the Mary River where it occurred in over 76% of locations sampled and comprised 7.9% of the total number of fish collected (Table 1). Across all rivers, average and maximum numerical densities recorded in 420 hydraulic habitat samples (i.e. riffles, runs or pools) were 1.10 individuals.10m–2 and 29.15 individuals.10m–2, respectively. Average and maximum biomass densities at 305 of these sites were 0.49 g.10m–2 and 5.31 g.10m–2, respectively (Table 1 [1093]). Macro/mesohabitat use Like other species of Hypseleotris, H. klunzingeri occurs in a variety of lotic and lentic habitats including small coastal streams, throughout large rivers and their floodplain habitats (billabongs and wetlands), coastal wetlands, dune lake Table 2. Macro/mesohabitat use by Hypseleotris klunzingeri in rivers of south-eastern Queensland. Data summaries for 10 488 individuals collected from samples of 420 mesohabitat units at 151 locations between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min.
Max.
Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
15.6 5.0 0.5 0 2.1 0
10 211.7939.3 1969.9 270.0 55.3 87.3 326.0 149.6 153.4 460 84 58 47.0 11.7 12.4 91.1 38.1 33.2
Gradient (%) 0 Mean depth (m) 0.09 Mean water velocity (m.sec–1) 0
2.86 1.08 0.87
Mean
0.30 0.45 0.13
Microhabitat use Hypseleotris klunzingeri has broadly similar microhabitat requirements to other species of Hypseleotris. Young-ofthe-year fish can form loose schools of hundreds of individuals [1093] and masses (thousands) of juveniles and subadults have been observed undertaking upstream dispersal movements (see below).
W.M.
In rivers of south-eastern Queensland, H. kluzingeri was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b) but occasionally occurred in higher velocity microhabitats than congeners, reflecting the pattern observed in mesohabitat use. It was collected over a wide range of depths, but most often between 10 and 50 cm (Fig. 1c). Hypseleotris klunzingeri is generally a benthic species but occasionally is found in loose schools in the mid-water column (Fig. 1d). This species may also adopt pelagic habits as it has been collected in Cooper Creek in trawl nets deployed in open water near the water surface [1074]. Like other Hypseleotris, H. klunzingeri used a wide range of substrate classes, but used coarser substrates slightly more frequently (e.g. coarse gravel and cobbles) (Fig. 1e). This species showed no particular affinity with the stream margins and was often collected in areas toward the middle of the channel (53% of 2689 fish collected grater than 1 m of the bank), and almost always was found in
0.21 0.38 0.18
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
99.6 100.0 70.7 78.2 65.8 53.9 43.6
7.1 22.5 20.8 26.7 16.5 4.8 1.6
5.9 23.6 20.8 28.3 16.9 3.6 0.9
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
86.1 65.9 26.7 65.7 39.1 92.6 37.6 22.5 96.3 96.3
12.8 8.3 1.2 5.2 1.5 10.8 5.5 3.9 13.5 19.0
11.5 8.5 0.9 4.3 1.2 9.9 6.0 4.5 9.1 14.8
In south-eastern Queensland, H. klunzingeri occurs throughout the major length of rivers, ranging between 0.5 and 326 km from the river mouth and at elevations up to 460 m.a.s.l. (Table 2). In comparison to H. galii, H. kluzingeri more commonly occurs in main channel habitats, at lower elevations (around 60 m.a.s.l.), and in wider streams (weighted mean = 12 m) with less riparian cover (weighted mean = 33%). Hypseleotris klunzingeri is also more common in riffles and runs than H. galii; the average hydraulic characteristics of H. kluzingeri include lowmoderate gradient (weighted mean = 0.21%), moderate depth (0.38 m) and high mean water velocity (0.18 m.sec–1). It occurs in mesohabitats with a wide range of substrates but was generally most common in habitats with substrates of fine to intermediate size and slightly coarser than observed for H. galii (sand, fine gravel and coarse gravel). Hypseleotris klunzingeri showed no obvious association with particular submerged physical structures at the mesohabitat scale, except that aquatic macrophytes, leaf-litter beds and root masses were slightly more common than other forms of cover.
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Freshwater Fishes of North-Eastern Australia
Table 3. Physicochemical data for Hypseleotris klunzingeri from 274 samples in south-eastern Queensland over the period 1994 to 2003 [1093].
close association with some form of submerged cover (Fig. 1f). It was most frequently collected near leaf-litter beds, aquatic macrophytes, filamentous algae, or in close association with the substrate. It less commonly occurred among submerged marginal vegetation, woody debris and root masses (Fig. 1f). (a)
(b)
60
60
40
40
20
20
0
0
30
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
40
10
20
0
0
Total depth (cm) 25
(e)
20
Relative depth 20
(f)
15
15 10 10 5
5 0
0
Substrate composition
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
8.4 0.6 4.8 19.5 0.5
31.7 12.8 9.1 5380.0 65.0
Mean 19.8 7.7 7.7 539.5 5.7
The following observations further attest to the hardiness of H. klunzingeri. The distribution of this species in tropical and temperate regions of eastern and inland Australia suggest that maximum and minimum absolute thermal tolerances may be greater than those presented in Table 3. On the basis of results from experimental thermal tolerance tests, Bowling [214] suggested that H. klunzingeri is capable of surviving at temperatures close to its lethal limits: fish lost locomotory ability at temperatures only a few degrees below the surface temperatures of a lake in the Canberra region in which these experimental fish were collected. The presence of H. klunzingeri in turbid waters of the lower Murray-Darling Basin is indicative of tolerance to high turbidity. For example, Hume [607] collected this species in the Lower Goulburn River at turbidities up to 680 NTU. Lake [751] reported that eggs attached to damp aquatic plants and exposed to the sun and air were intolerant of such exposure, with desiccation occurring within a few hours [751]. Hypseleotris klunzingeri is euryhaline and has occasionally been recorded in brackish waters at the base of tidal barrages (refer to section on Movement). It has also been recorded in saline lakes in inland Victoria at salinities up to 8.8 ppt [301]. Studies of salinity tolerances of adult H. klunzingeri recorded the experimental chronic (four-day) LD50s as 38 ppt [1405, 1406]. Fish showed signs of distress and stopped feeding at salinities over 30 ppt, difficulties in coordination were observed at salinities greater than 40 ppt and death occurred between 26 and 50 ppt [1405, 1406].
60
20
Parameter
Microhabitat structure
Figure 1. Microhabitat use by Hypseleotris klunzingeri. Data derived from capture records for 2689 individuals from the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
Reproduction Quantitative information on the reproductive biology and early development of H. klunzingeri is available from field and aquarium studies and observations in artificial outdoor ponds [203, 232, 585, 614, 750, 751, 752, 809]. Details are summarised in Table 4. This species spawns and complete its entire life cycle in freshwater.
Environmental tolerances Ambient water quality data and experimental tolerance tests suggest that H. klunzingeri is tolerant of a wide range of physicochemical conditions. In south-eastern Queensland rivers and streams we collected this species over a relatively wide range of water temperatures (8.4–31.7°C), dissolved oxygen concentrations (0.6–12.8 mg.L–1), water acidity (4.8–9.1), conductivity (19.5–5380 µS.cm–1) and turbidity (0.5–65 NTU) (Table 3).
Maturation in H. klunzingeri commences at a relatively small size, similar to other Hypseleotris species. Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, south-eastern Queensland,
524
Hypseleotris klunzingeri
reportedly taking place between late spring and early summer when water temperatures rise above 22.5°C [58, 232, 614, 750, 752, 809].
were 23.6 mm SL and 32.5 mm ± 0.6 SE, respectively for males and 22.0 and 28.3 mm ± 0.6 SE, respectively for females (Fig. 2) [1093]. Gonad maturation in both sexes was commensurate with somatic growth, the mean length at each reproductive stage being different from all other stages after stage III. Males of equivalent reproductive stages were slightly larger than females (Fig. 2). The minimum and mean size of gravid (stage V) males was 29.2 mm SL and 34.4 mm ± 0.5 SE, respectively; the minimum and mean size of gravid females was 26.9 mm SL and 35.3 mm ± 1.5 SE, respectively. Lengths at first maturity (equivalent to reproductive stage III) for fish from the Tweed River, northern New South Wales, were reported as 27 and 30 mm LCF for males and females, respectively [1133]. Lake [750] reported that H. klunzingeri spawned in ponds at lengths greater than 30 mm TL.
Reproductive stage I
II
III
IV
V
Males 100
(45) (13) (8) (10) (36) (6)
(13) (64) (43) (14) (14)
80 60 40 20
40
0
Males
Females
Females 100
35
(28) (24) (11 ) (9) (31) (6)
(11) (78) (22) (17) (6)
80
30
60 40
25
20 0
20 I
II
III
IV
V
Month
Reproductive stage Figure 2. Mean standard length (mm SL ± SE) for male and female Hypseleotris klunzingeri within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland between 1994 and 1998 [1093]. Samples sizes can be calculated from the data presented in Figure 3.
Figure 3. Temporal changes in reproductive stages of Hypseleotris klunzingeri in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in parentheses.
As in other Hypseleotris species, H. klunzingeri is reproductively active for an extended period from late winter through to early autumn in south-eastern Queensland, but spawning is concentrated between late winter and early summer. Gravid females (stage V) were present between August and March (Fig. 3) and GSI values were elevated between August and December (Fig. 4). Temporal variation in GSIs of males was similar (Fig. 4). The phenology of reproductive activity for H. klunzingeri from the Tweed River [1133] was very similar to that described above. Spawning in the Murray-Darling Basin appears to occur slightly later than in northern coastal populations,
The spawning stimulus for H. klunzingeri is unknown but in south-eastern Queensland the peak spawning period corresponds with increasing water temperatures and photoperiod in late winter and early spring. Spawning cues are probably not associated with rising water levels or flooding [1093], although spawning and the appearance of larvae in the Murray-Darling River can occur during periods of floodplain inundation [58, 750, 1201]. In southeastern Queensland the peak spawning period generally coincides with pre-flood periods of low and relatively stable discharge. As with other small-bodied species in this region, the ability to spawn repeatedly over an extended
525
Freshwater Fishes of North-Eastern Australia
10
Males 8
Spring (n = 1311)
30
Females
Summer (n = 1158)
6
20
AutumnWinter (n = 2174)
4 10 2
0
0
Month
Standard length (mm)
Figure 4. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Hypseleotris klunzingeri males (open circles) and females (closed circles) in the Mary River, southeastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 3.
Figure 5. Seasonal variation in length-frequency distributions of Hypseleotris klunzingeri, from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
period may be an adaptation to the relatively unpredictable timing of the onset of wet season flooding. The spawning of adults and presence of larvae probably occurs when the likelihood of flooding is low, coinciding with high temperatures and low flows. Sampling in rivers of south-eastern Queensland [1093] revealed that juvenile fish less than 15 mm SL were most common in the summer months (Fig. 5).
no reports of this can be found in the literature. Fecundity of H. klunzingeri is lower than that of H. compressa, but is greater than that observed in other species of Hypseleotris. Total fecundity for H. klunzingeri from the Mary River is estimated to range from 328–5418 eggs (mean 1352 ± 297 SE, n = 49 fish) [1093]. Body length and weight were poor predictors of fecundity in these fish. However, Lake [750, 752] implied that fecundity was greater in larger fish and reported that females contained between 1000–2000 eggs.
Reproductive behaviour of H. klunzingeri is generally similar to other species of Hypseleotris. Males establish and defend territories [270] and will aggressively guard and fan eggs until hatching [203, 270, 750]. The location of spawning in south-eastern Queensland streams is unknown but we have observed large aggregations of breeding adults in main channel riffles and runs between September and January; spawning in these areas may occur among aquatic and submerged marginal vegetation [1093]. In inland drainages, spawning may occur in quiet flooded backwaters [750, 752]. In artificial ponds, eggs have been observed attached to submerged vegetation and woody debris at the water’s edge [750, 752]. It appears characteristic of H. klunzingeri to deposit the eggs close to the water’s surface as this has been reported several on several occasions for fish in outdoor ponds and aquaria [58, 203, 615, 749, 750, 751].
Eggs are ovoid, demersal, adhesive and relatively small. The mean diameter (long axis) of 139 intraovarian eggs from stage V fish from the Mary River was 0.45 mm ± 0.01 SE [1093]. Intraovarian eggs form the fish in the MurrayDarling Basin ranged from 0.26–0.36 mm diameter. Water-hardened eggs vary between 0.48–0.53 mm diameter (long axis) [58, 751, 752]. The duration of embryological development is relatively rapid and larvae are poorly developed at hatching. Eggs of H. klunzingeri have been reported to hatch in 42 hours at ~17–low 20°C [615], 47–53 hours at 18–23°C [58, 751], ~3 days (temperature not stated [203]. Details of embryology and larval development are available in Lake [749, 751] and Anderson et al. [58]. Newly hatched larvae are very small, ranging from 1.76–2.10 mm TL [751] and are transparent, colourless and poorly developed [749, 751]. At this stage, larvae are barely capable of swimming, instead undertaking periodic vertical ‘drifting’ movements [751]. The yolk sac is absorbed after about 3.5 days, at
Spawning may be spread out over several days or even weeks [750], however it is uncertain whether female H. klunzingeri spawn more than once in a breeding season as
526
Hypseleotris klunzingeri
Table 4. Life history information for Hypseleotris klunzingeri. Age at sexual maturity (months)
12 months [1354]
Minimum length of gravid (stage V) females (mm)
26.9 mm SL [1093]
Minimum length of ripe (stage V) males (mm) 29.2 mm SL [1093] Longevity (years)
Possibly 2–3 years in the wild [1354]
Sex ratio (female to male)
?
Occurrence of ripe (stage V) fish
Late winter to early autumn (August–March) [1093]
Peak spawning activity
Elevated GSI between August and December [1093]
Critical temperature for spawning
? 22.5°C [750, 752]
Inducement to spawning
? Possibly a combination of increasing temperature and increasing day length; spawning can occur during periods of floodplain inundation in the Murray-Darling Basin [614, 750, 832]
Mean GSI of ripe (stage V) females (%)
11.5% ± 0.6 (maximum mean GSI in August = 8.0% ± 1.1) [1093]
Mean GSI of ripe (stage V) males (%)
4.5% ± 0.1 (maximum mean GSI in November = 3.7% ± 0.3) [1093]
Fecundity (number of ova)
Total fecundity = 328–5418, mean = 1352 ± 297 [1093]; Females reported to contain between 1000–2000 eggs [750, 752]
Total Fecundity (TF) and Batch Fecundity (BF) / No significant relationships detected [1093] Length (mm SL) or Weight (g) relationship (mm SL) Egg size (diameter)
Intraovarian eggs from stage V fish = 0.45 mm ± 0.01 [1093]
Frequency of spawning
? Spawning may be spread out over several days or even weeks [750]. However spawning may only occur once per breeding season as no reports of repeat or batch spawning exist [1093]
Oviposition and spawning site
In south-eastern Queensland spawning may occur among aquatic and submerged marginal vegetation [1093]. In inland drainages, spawning may occur in quiet flooded backwaters [750, 752]. In artificial ponds, eggs have been observed attached to submerged vegetation and woody debris at the water’s edge [750, 752]. Eggs are deposited close to water surface [58, 203, 614, 749, 750, 751]
Spawning migration
None known
Parental care
Male guards and fans eggs until they hatch [203, 270, 750]
Time to hatching
Varies with temperature. 42 hours at ~17–low 20°C’s [614], 47–53 hours at 18–23°C [58, 751], ~3 days (temperature not stated) [203]
Length at hatching (mm)
Newly hatched prolarvae 1.76–2.10 mm TL (transparent, colourless and poorly developed) [58, 735]
Length at free swimming stage
Larvae are barely capable of swimming at hatching, instead undertaking periodic vertical ‘drifting’ movements [751]. Larvae are capable of swimming freely after 5–6 days at 3.2–3.5 mm TL [58, 751]
Age at loss of yolk sack
3.5 days at 2.7–3.0 mm TL [751]
Age at first feeding
5–6 days [751]
Length at first feeding
3.2–3.5 mm TL [751]
Age at metamorphosis (days)
?
galii. Available data suggests that the eggs of H. klunzingeri are more numerous, smaller and have a shorter time to hatching, than for sympatric Hypseleotris sp. 1 and H. galii. Larvae are also less well developed at hatching but develop relatively rapidly as for the larvae of H. compressa. It has been speculated that these characteristics result from adaptations to the local environmental conditions where spawning occurred (i.e. temporarily inundated floodplain and backwater habitats subject to rapid fluctuations in water level) [58, 750].
which time larvae were 2.7–3.0 mm TL [751]. Feeding commences after 5–6 days when larvae are 3.2–3.5 mm TL, and are capable of swimming freely [58, 751]. No further information is available concerning the growth rates of H. klunzingeri, however Wager and Unmack [1354] suggested that this species reaches spawning size after one year and speculated that it may live for two to three years. The fecundity, embryology and early development characteristics of H. klunzingeri resemble those of H. compressa more so than those of sympatric Hypseleotris sp. 1 and H.
527
Freshwater Fishes of North-Eastern Australia
Wales [1133], streams, rivers and floodplain habitats of the lower Murray-Darling Basin [214, 267, 607], and floodplain habitats in Cooper Creek [246] (Fig. 6). Hypseleotris klunzingeri is a microphagic carnivore consuming aquatic insects (51.2%) (chironomids, emphemeropterans and trichopterans) and microcrustaceans (40.1%) (mostly cladocerans and copepods). Macrocrustaceans, terrestrial invertebrates, and algae are also consumed in small amounts. Spatial variation in the relative proportion of the major food items consumed is evident. Fish from lowland rivers and floodplain habitats in southern and central Australia [214, 246, 607] in northern Australia [193, 1099] and wallum habitats of south-eastern Queensland [82, 84] consumed greater amounts of planktonic microcrustaceans (39–76%) than fish from lotic stream environments (0–8%) [267, 1133]. Fish in these latter habitats tended to consume greater amounts of aquatic insects (74–75%), than those from more lentic habitats (18–58%).
Movement There is very little quantitative information concerning the movement biology of H. klunzingeri. Small numbers of individuals have occasionally been reported to use fishways on weirs and tidal barrages in south-eastern Queensland rivers. Russell [1173] sampled two individuals descending a fishway on a tidal barrage on the lower Fitzroy River (time of year not stated). In a subsequent study of this fishway, 21 individuals were collected at the base of the fishway during November [1272, 1274, 1275]. Stuart and Berghuis [1276, 1277] collected a total of 35 individuals in samples of tidal barrage fishway on the Burnett River. These fish were suggested to be moving upstream in low numbers over an extended period between August and March [1276]. Johnson [658] also collected small numbers of juveniles and adults downstream of this barrage during December and April. Small numbers of H . klunzingeri have also been collected within and downstream of tidal barrages in the Mary River catchment between November and April [158, 159, 658]. Access to estuarine areas is not an obligatory component of the life cycle of H. klunzingeri, hence the purpose of the longitudinal movements and the occasional presence downstream of tidal barrages is unclear. However it is possible that these fish were attempting to return to freshwaters after being displaced downstream into estuarine areas below the barrage by elevated flows, as has been suggested for other species in central and south-eastern Queensland [162]. Although H. klunzingeri appears tolerant of elevated salinities (see above), the presence of tidal barriers may impact on this species by preventing or hindering recolonisation of freshwaters if fish are displaced by floods to brackish estuarine areas downstream of tidal barrages. Like other species of Hypseleotris, we have occasionally observed large aggregations (hundreds of individuals) of H. klunzingeri undertaking mass upstream movements [1093]. These fish were observed aggregating just downstream of small obstructions to movement (e.g. road culverts) and immediately after an increase in discharge. These observations suggest that upstream dispersal movements may occur when flow conditions allow [1093]. Similar upstream movements have been observed in a large tributary of the Fitzroy River [1351] and in Barambah Creek in the Burnett River basin [1093].
Other microinvertebrates (0.1%)
Unidentified (5.4%) Terrestrial invertebrates (0.9%) Algae (0.4%) Detritus (0.3%)
Microcrustaceans (40.1%)
Macrocrustaceans (1.6%) Aquatic insects (51.2%)
Figure 6. The mean diet of Hypseleotris klunzingeri. Data derived from stomach content analysis of 253 individuals from the Tweed River in northern New South Wales [1133], streams, rivers and floodplain habitats of the lower MurrayDarling Basin [214, 267, 607], and floodplain habitats in Cooper Creek [246].
Conservation status, threats and management The conservation status of Hypseleotris klunzingeri was listed as Non-Threatened by Wager and Jackson [1353]. It remains generally common throughout most of its range, although some concern was expressed about its possible decline distribution and abundance in the Murray-Darling Basin over recent decades [778]. Potential threats to H. klunzingeri in south-eastern Queensland are similar to those identified for H. galii and many other small-bodied members of the families Atherinidae, Melanotaeniidae, Pseudomugilidae, Chandidae and Retropinnidae. Threats include: riparian loss and instream habitat degradation (particularly siltation, reduced inputs of woody debris and loss of aquatic plants), flow regulation (particularly rapid
Hypseleotris klunzingeri has been recorded as having fallen to the ground in rain in western New South Wales, possibly as a result of a whirlwind [878, 1018, 1400]. Trophic ecology Data derived from stomach content analysis of 253 individuals from the Tweed River in northern New South
528
Hypseleotris klunzingeri
vulnerable to erratic fluctuations in water level. Lake [751] reported that eggs attached to damp aquatic plants and exposed to the sun and air were intolerant of such exposure, with desiccation occurring within a few hours [751]. Larvae hatching during months of stable low flows are likely to encounter high densities of small invertebrate prey, and to experience elevated growth rates. The security of spawning and larval habitats and an abundance of food would tend to maximise the potential for recruitment into juvenile stocks [82, 84, 1093]. A similar scenario of spawning and recruitment has been suggested for several smallbodied fish species in the Murray-Darling Basin [614, 615]. However, breeding of H. klunzingeri may also extend from the spring spawning peak through to early autumn in south-eastern Queensland, suggesting that recruitment is not necessarily limited by prevailing temperature and/or discharge regime. The development of scenarios of impact associated with alterations to stream discharge regime can be complicated by such issues, and more work is required on the reproductive ecology of members of this genus to ensure sound advice on environmental flows.
fluctuations in water level that may impact on reproductive processes and recruitment), barriers to movement, and threats associated with alien fish and plant species. Hypseleotris klunzingeri occurs in the same range of lotic and lentic habitats as other members of this genus. Habitats include small coastal streams, large rivers and their floodplain habitats (billabongs and wetlands), coastal wetlands, dune lakes and streams draining coastal dune systems. In the lower Murray River, this species is very common in floodplain billabongs among dense stands of emergent macrophytes (Juncus and Eleocharis) [122]. Lowland and floodplain habitats are particularly at risk from reclamation, degradation by clearing and encroachment by agriculture (e.g. sugar-cane farming in the northern parts of the range), invasion by alien weeds such as para grass (Brachiaria mutica) and Hymenachne, and channelisation to improve drainage. Such habitats are frequently close to human population centres (e.g. Brisbane and the south-eastern Queensland coastal strip) and are thus at risk from urban encroachment and associated pressures on aquatic systems.
Like other species of Hypseleotris, large aggregations of H. klunzingeri have been observed downstream of small obstructions to movement (e.g. road culverts) and immediately after an increase in discharge. These observations suggest that upstream dispersal movements may occur when flow conditions allow [1093]. The capacity, and possible requirement, for upstream movements suggests that this species may be sensitive to in-stream barriers such as dams, weirs, barrages, road crossings and culverts. Barriers to movement may curtail recolonisation events following disturbances and local population declines or affect dispersal of new recruits throughout the drainage network. Although H. klunzingeri appears tolerant of elevated salinities (see above), the presence of tidal barriers may prevent or hinder recolonisation of freshwaters when fish are displaced downstream of tidal barrages during flooding.
Hypseleotris klunzingeri is generally a benthic species but occasionally is found in loose schools in the mid-water column and may also adopt a pelagic habit. Wide ranging usage of depth zones in aquatic environments may enable this species to avoid particular disturbances, for example siltation of coarse bottom substrates, and overgrowth of stream margins and open water by alien pasture grasses or water hyacinth (Eichhornia crassipes). Nevertheless, H. klunzingeri remains susceptible to disturbances that affect cover elements such as leaf-litter beds, aquatic macrophytes, filamentous algae, submerged marginal vegetation, woody debris and root masses. Other members of the genus are similarly intolerant of disturbances affecting instream cover [440, 484]. Like many other small native species, H. klunzingeri spawning cues are probably not associated with rising water levels or flooding [1093], although spawning and the appearance of larvae in the Murray-Darling river system can occur during periods of floodplain inundation [58, 614, 750]. In south-eastern Queensland the peak spawning period generally coincides with pre-flood periods of low and relatively stable discharge [1093]. H. klunzingeri may be particularly vulnerable to erratic fluctuations in water level caused by aseasonal releases of water from impoundments for irrigation purposes during the dry season. This species deposits its eggs close to the water surface [58, 203, 614, 749, 750, 751] typically among aquatic and submerged marginal vegetation and woody debris at the water’s edge, often in quiet flooded backwaters [750, 752, 1093]. These spawning sites are especially
Alien fish species (particularly Gambusia holbrooki and other poeciliids) threaten many small native species in south-eastern Queensland streams [96, 1093] and dune waterbodies [82, 84]. We suggest that species of Hypseleotris including H. klunzingeri may be particularly at risk in degraded stream habitats supporting large populations of G. holbrooki, a pelagic microphagic carnivore capable of unusual dietary flexibility [78, 80, 92, 94, 96]. This poeciliid is also aggressive towards other species [983] and is known to consume the eggs and fry of small native fishes [636, 960]. Extensive infestations of introduced para grass, Brachiaria mutica, may also constrain the foraging behaviour of H. klunzingeri in degraded urban streams [94, 96].
529
Gobiomorphus australis (Krefft, 1864) Striped gudgeon
37 429020
Family: Eleotridae
relatively broad and cheeks are bulbous. Relatively small eyes are positioned high on sides of head near the dorsal profile and separated by a narrow flat interorbital space. It has a small oblique upturned mouth with a prominent lower jaw; maxillary barely extends to anterior margin of the eye. Rows of small pointed (villiform) teeth are present on both jaws. The body is covered with moderate to large ctenoid scales. Lateral line absent. Predorsal scales reach forward to level of the eyes, with several smaller scales between eyes, no scales on snout. Sides of head completely scaled, but those on cheeks are smaller and not easily seen. Three to five large pores present on preopercular margin. Lines of minute papillae extend across cheek and operculum, around preopercular margin and from each side of snout to above eye. Urinogenital papilla lanceolate and nearly twice as long as broad in male; oblong, truncated and barely longer than broad in female. Two separate dorsal fins; the first is rounded with deep notches between spines; the second is larger, slightly elongate, with posterior rays longest. Anal fin similar to second dorsal fin and positioned opposite. Posterior rays of second dorsal and anal fin elongated in males. Pectoral fins rounded, broad and large. Pelvic fins thoracic, elongate, pointed and of moderate size, forth ray longer in males; fin bases entirely
Description First dorsal fin: VI–VIII (usually VII); Second dorsal: I, 8; Anal: I, 8–9; Pectoral: 14–16; Pelvic: I, 5; Caudal: 15 segmented rays; Vertical scale rows: 30–34 (29–33, Merrick and Schmida [936]); Horizontal scale rows: 8; Gill rakers on first arch: 10–12 (8–9, first ones reduced to spiny knobs, Ogilby [1012]); Vertebrae: 28 (29, Whitely [1397]) [34, 52, 270, 741, 775, 936]. Gobiomorphus australis is a small to moderate-sized gudgeon known to reach 225 mm but more common to 120 mm [936]. Of 1153 specimens collected in streams of south-east Queensland [699, 704, 709, 1093], the mean and maximum length of this species were 58 and 150 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 40 individuals (range 20–136 mm SL) sampled from the Mary and Albert rivers, south-eastern Queensland is W = 0.8 x 10–5 SL3.228, r = 0.998, p<0.001. The following description is taken largely from Cadwallader and Backhouse [270]. Gobiomorphus australis is a relatively stout and robust species with an elongate body, tapering and becoming compressed posteriorly. The head is rounded and slightly dorsally flattened, the snout is
530
Gobiomorphus australis
separate but close together. Caudal fin rounded and large. Caudal peduncle shorter and deeper in adult males than in females of similar size [270, 741, 775, 1012].
genera) are distinguished from other eleotrids in having an interneural gap (an interneural space without a pterygiophore) between the two dorsal fins [577].
Head and body dark yellowish-brown to greyish-green dorsally, grading to cream or light grey ventrally. Five to seven characteristic thin, dark, longitudinal stripes run from just behind opercular opening to caudal peduncle, stripes varying in intensity. A short, broad stripe extends from eye to snout; a second narrower stripe extends from eye to preopercular margin, then divides, one branch running to top of operculum, the second to the base of pectoral fin. Small, iridescent green-gold blotch sometimes present on operculum. Narrow bright yellow band and/or dark spot at base of pectoral fin. Caudal and dorsal fins with transverse dark bands or rows of brown spots, two horizontal rows on first dorsal, four to six 6 horizontal rows on second dorsal, and 6–10 vertical rows on caudal fin forming wavy bands; fins otherwise grey to yellow, translucent. Anal fin occasionally with faint purple bands. Colouration intensifies during breeding season with brown, purple, green and gold patches on body and brown spots on fins becoming more prominent. Anal fin of males becomes orange with lilac border, that of females golden yellow. Preserved colouration brown or greyish with darker stripes and spotted fins as described above [34, 52, 270, 741, 775, 936].
The systematics of Gobiomorphus, particularly the New Zealand species, has a confused history. In 1941, Stokell [1269] revised the genus and partly resolved some of the problems associated with the New Zealand species. McDowall [886] further revised the genus in 1975, recognising and providing full descriptions of six New Zealand species of the genus Gobiomorphus (these included two species formerly placed within the genus Philypnodon). An additional New Zealand species, G. alpinus, has since been recognised [892, 1270]. It was suggested that the Gobiomorphus from New Zealand (the only eleotrid genus present there) are derived from, or have a common ancestry with, the Australian species of Gobiomorphus and reached New Zealand by passage through prevailing ocean currents [886]. The two Australian species of Gobiomorphus have been variously placed within the following genera: Eleotris, Krefftius and Mulgoa. The striped gudgeon, G. australis, was originally described by Krefft in 1864 [741] as Eleotris australis. It was subsequently placed into a new genus Krefftius by Ogilby [1012] in 1897, but later relegated to a subgenus of Mogurnda by McCulloch and Ogilby [880] in 1919. Its close affinities with G. coxii were recognised and it was placed in the genus Gobiomorphus, but it is unclear by whom. The earliest record in the literature of G. australis appears to be in 1978 by Lake [755] and in 1980 Hoese et al. [580] alluded to research revealing the close affinities with G. coxii.
Gobiomorphus australis is similar in general appearance to G. coxii, especially juveniles and subadults. Distinguishing characteristics of G. australis include 14–16 pectoral fin rays, 30–34 midlateral scales and 5–7 thin, dark, longitudinal stripes running along sides of body.
Distribution and abundance Gobiomorphus australis occurs in Australian coastal catchments from central Queensland, south through New South Wales to Wilsons Promontory in eastern Victoria [775]. In Queensland, G. australis has been recorded as far north as the Pioneer River near Mackay [658], however it appears to be patchily distributed and relatively uncommon north of the Mary River, south-eastern Queensland. Laxton et al. [779] recorded it from Plane Creek, a short coastal stream near Sarina, 50 km south of Mackay. Trnski et al. [1328] recorded it approximately 150 km further south in small streams draining into Shoalwater Bay, Water Park Creek (south of Shoalwater Bay) and in Moore Creek (a small tributary of the Fitzroy River). It has also been collected in the Calliope River [915], Burnett River [237, 658, 700], Lagoon Creek (a small coastal stream near Woodgate) [1110], Gregory River [157] and Beelbi Creek [1110]. From the Mary River [158, 159, 643, 658, 660, 1093, 1234] south, it is present in most streams and rivers to the Queensland–New South Wales border [61, 82, 84,
Systematics Gobiomorphus Gill (1863) [449] contains two Australian species, G. australis and G. coxii, and seven New Zealand species. However, the relationships of the New Zealand and Australian species of Gobiomorphus have not received detailed examination and hence their congeneric status remains uncertain [891]. Gill originally established the genus Gobiomorphus (although he did not formally define it) to firstly contain the New Zealand eleotrid Eleotris gobiodes Valenciennes (in Cuvier and Valenciennes, 1837 [355]) (now known as Gobiomorphus huttoni Ogilby [1011]) and secondarily to reduce the size and diversity of the very large genus Eleotris [886]. The morphological similarity between Gobiomorphus and the European gudgeon, Gobio gobio, is reflected in the genus name; morphus is from the Latin word for form or shape [891]. The proposed genus was recognised by Bleeker, who published a definition of it in 1874 [201]. Gobiomorphus (together with a few related
531
Freshwater Fishes of North-Eastern Australia
Wales they occur together more often (16 of the 27 locations in which either species was present) [553].
699, 704, 709, 1093]. This species is also present on Fraser, Moreton and Stradbroke islands, off the south-eastern Queensland coast.
Gobiomorphus australis appears to be relatively common and widespread in coastal rivers of New South Wales [437, 441, 443, 484, 814, 1066, 1067, 1201]. In Victoria, this species appears generally uncommon (although occasionally locally abundant [1112]) and patchily distributed in coastal streams, probably as far west as the Franklin River near Wilsons Promontory in South Gippsland [135, 206, 270, 497, 775, 872, 1111, 1112, 1113].
Gobiomorphus australis is moderately common and widely distributed in south-eastern Queensland. Surveys undertaken by us between 1993 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 2122 individuals of G. australis and it was present at 29% of all locations sampled (Table 1). Overall, it was the 15th most abundant species collected (1.3% of the total number of fishes collected) but was relatively common at sites in which it occurred (9.1% of total abundance, fourth most common species). In these sites, G. australis most commonly occurred with the following species (listed in decreasing order of relative abundance): G. holbrooki, M. duboulayi, H. compressa, and H. galii. Gobiomorphus australis was the 8th most important species in terms of biomass, forming 0.8% of the total biomass of fish collected. This species is very common and widespread in short coastal streams of the Sunshine Coast region, the Logan-Albert Basin and the South Coast Basin. It is also locally abundant in small, often degraded urban streams of the Brisbane region [94, 95, 704, 709]. Across all rivers, average and maximum numerical densities recorded in 179 hydraulic habitat unit samples (i.e. riffles, runs or pools) were 0.66 individuals.10m-2 and 14.29 individuals.10m–2, respectively. Average and maximum biomass densities at 111 of these sites were 5.88 g.10m–2 and 86.44 g.10m–2, respectively. Highest numerical densities and biomass densities were recorded from the LoganAlbert Basin. In freshwaters of south-eastern Queensland, Gobiomorphus australis does not often occur in the same location as its congener, G. coxii. Both species occurred together at only eight of the 97 locations in which either species was sampled [1093]. In freshwaters of New South
Macro/mesohabitat use Gobiomorphus australis occurs in a variety of lotic and lentic habitats ranging from small coastal streams and lowland sections of large rivers to coastal and floodplain wetlands, estuaries and dune lake systems. Usually found in freshwater habitats but juveniles [270, 446, 580], adults [151] and individuals of unspecified length [806, 1067] have been reported from estuarine areas and the freshwater-tidal interface. In rivers and streams of south-eastern Queensland it occurs at low to moderate elevations (0–160 m.a.s.l.) but most commonly at less than 20 m.a.s.l. (Table 2). This species most frequently occurs in the middle to lower sections of rivers and short coastal streams (within 40 km of the river mouth), but has been recorded up to 250 km upstream from the mouth of the Mary River [643]. It is present in a wide range of stream sizes (range = 1.3–30.0 m width) but is more common in streams between 5 and 10 m wide and with moderate riparian cover. In streams of south-eastern Queensland, G. australis most commonly occurs in pools and runs characterised by low gradient (<0.3% weighted mean gradient), moderate depth (0.4 m weighted mean depth) and low mean water velocity (weighted mean <0.1 m.sec–1) but can occur in shallow, high velocity (maximum 0.87 m.sec–1) riffle
Table 1. Distribution, abundance and biomass data for Gobiomorphus australis in rivers in south-eastern Queensland. Data summaries for a total of 2122 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
28.9
6.0
75.9
35.0
11.7
42.6
60.0
1.30 (9.13)
0.01 (1.07)
13.77 (16.79)
0.23 (1.82)
0.23 (2.03)
3.53 (10.30)
4.75 (7.95)
15 (4)
21 (12)
2 (2)
17 (9)
20 (11)
7 (3)
7 (4)
0.75 (5.76)
0.02 (3.51)
0.99 (1.99)
1.34 (1.80)
0.44 (2.88)
2.27 (6.08)
6.50 (14.11)
8 (4)
22 (5)
2 (2)
7 (6)
13 (5)
4 (4)
3 (3)
Mean numerical density (fish.10m–2)
0.66 ± 0.10
0.11 ± 0.02
0.51 ± 0.08
0.10 ± 0.02
0.24 ± 0.05
0.95 ± 0.18
0.38 ± 0.16
Mean biomass density (g.10m–2)
5.88 ± 1.00
2.70 ± 0.77
0.80 ± 0.27
1.80 ± 1.52
2.24 ± 0.82
7.17 ± 1.35
5.85 ± 3.63
532
Gobiomorphus australis
collected near leaf-litter beds, small and large woody debris, and submerged root masses (Fig. 1f).
habitats (Table 2). This species is most abundant in mesohabitats with fine substrates (sand and gravel) and where submerged leaf-litter beds, undercut banks and root masses are common.
(a)
Table 2. Macro/mesohabitat use by Gobiomorphus australis in rivers of south-eastern Queensland. Data summaries for 2122 individuals collected from samples of 179 mesohabitat units at 84 locations undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter Catchment area (km2 ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
6.0 10 087.7 3.0 268.0 0.5 164.0 0 160 1.3 30.0 0 91.0
Gradient (%) 0 Mean depth (m) 0.10 Mean water velocity (m.sec–1) 0 Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0.1 0 0 0 0
1.14 1.10 0.87
Mean 764.9 42.6 51.6 33 7.8 42.0 0.22 0.44 0.10
80
60
60
40
40
20
20
0
0
W.M. 30
454.8 34.9 39.4 17 6.3 48.6
9.8 31.0 18.9 20.3 13.3 2.9 3.9
10.1 33.4 16.7 22.3 12.7 1.5 3.3
86.1 19.0 13.4 58.2 33.5 49.5 30.3 26.8 85.0 80.0
6.5 2.3 2.3 4.4 1.7 12.4 7.3 4.5 19.1 25.9
7.1 1.8 3.9 5.9 1.3 18.5 5.5 4.3 18.9 23.5
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
80 60
20
40 10
20
0
0.29 0.40 0.08
70.9 100.0 82.7 68.8 62.9 42.9 76.0
(b)
80
0
Total depth (cm) 40
(e)
Relative depth 20
30
15
20
10
10
5
0
0
Substrate composition
(f)
Microhabitat structure
Figure 1. Microhabitat use by Gobiomorphus australis. Data derived from capture records for 544 individuals from 47 samples collected in the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
Microhabitat use In streams of south-eastern Queensland, G. australis was most frequently collected from areas of low water velocity reflecting the pattern observed in mesohabitat use (Fig. 1a and b). This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 1c). A benthic species, it occupies the lower half of the water column, most commonly in direct contact with the substrate (Fig. 1d). It is most often found over fine substrates (mud, sand and gravel) (Fig. 1e). This species was usually collected within 1 m of the stream-bank (74% of 544 fish collected) and in close association with some form of submerged cover (Fig. 1f). Most frequently
Environmental tolerances Information on tolerance to water quality extremes is lacking and the data listed below (Table 3) reflect the water quality of aquatic habitats in which G. australis has been collected (see above). Like many eleotrids, G. australis appears to be a relatively hardy species, able to tolerate low dissolved oxygen levels (minimum 1.7 mg.L–1), highly acidic waters (minimum 4.4), high conductivity (maximum 2247 µS.cm–1) and high turbidity (maximum 200 NTU). The likely estuarine larval phase of G. australis (see sections on Movement and Reproduction) and the recorded presence of adult fish in estuaries [151] suggest
533
Freshwater Fishes of North-Eastern Australia
[1397] reported that they spawn in April or May. In the Tweed River, maturing and mature females (gonad maturity stages IV and V, respectively) were present in February and June, respectively; maturing males were present in February [1133]. In rivers of south-eastern Queensland, spawning probably occurs in autumn and winter as juveniles less than 20 mm SL first appeared in freshwater samples in the winter months but were most commonly collected in spring (Fig. 2). In the Pioneer River, central Queensland, Johnson [658] found that juveniles were common during sampling in October but were present through to December (data on sizes of fish collected not given).
that this species is able to tolerate elevated salinities throughout its life cycle. The local abundance of this species in degraded urban streams of the Brisbane region attests to its hardiness [94, 95, 704, 709]. Table 3. Physicochemical data for Gobiomorphus australis. Data summaries for 2032 individuals collected from 127 samples in south-east Queensland streams undertaken between 1994 and 2003 [1093]. Parameter
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
8.4 1.7 4.4 97.5 0.3
29.3 11.9 8.5 2247.0 200.0
Mean 18.7 6.9 7.3 471.5 12.5
Fecundity estimates are unavailable but a similarly sized species of amphidromous Gobiomorphus from New Zealand (the giant bully, G. gobiodies), produces many thousands of comparatively small (1 mm long) oval eggs [890, 891]. Gobiomorphus australis is reported to lay demersal eggs in a single, uniform, compact layer on solid surfaces such as rocks or logs that are then guarded by the male [270]. The eggs hatch in about four days, after which the free-swimming larvae are thought to be carried downstream to estuaries where they spend the winter [270]. It is unknown whether access to saline environments is necessary for successful larval development. Attempts to breed this species in captivity have reportedly been unsuccessful
Reproduction There is relatively little published information on the reproductive biology of G. australis (Table 4). Size at reproductive maturity is suspected to be 60 mm TL in males and 75 mm TL in females from the Tweed River, northern New South Wales [1133]. This species spawns in freshwater and is possibly amphidromous (see section on Movement below). In southern states spawning is thought to occur during late summer and autumn, at temperatures around 21°C [270, 580]. Llewellyn [814] indicated the spawning season is during March and April. Whitely
40
Upstream (n=468)
30 Spring (n=243)
30
25
Summer (n=224)
20
20
Autumn-Winter (n=643)
10 0
15
10 10
20 30
5
Downstream (n=564) 40
0
Standard length (mm) Standard length (mm) Figure 2. Seasonal variation in length-frequency distributions of the striped gudgeon, Gobiomorphus australis, from sites in the Mary, Logan and Albert rivers, south-eastern Queensland [1093]. The number of fish from each season is given in parentheses.
Figure 3. Length–frequency distributions of the striped gudgeon, Gobiomorphus australis, from sites located upstream (open bars) and downstream (closed bars) of Luscombe Weir in the Albert River, situated approximately 1 km upstream of the tidal limit [1093]. Sites sampled downstream were in fresh water but all were subject to tidal influence. The number of fish from each location is given in parentheses.
534
Gobiomorphus australis
Table 4. Life history information for Gobiomorphus australis. Age at sexual maturity (months)
?
Minimum length of ripe females (mm)
75 mm [1133] (Length at first maturity)
Minimum length of ripe males (mm)
60 mm [1133] (Length at first maturity)
Longevity (years)
?
Sex ratio (female to male)
?
Occurrence of ripe fish
? maturing and mature females present in February and June, respectively; maturing males present in February [1133]
Peak spawning activity
late summer and autumn [270, 580], February? [1133], possibly autumn and winter in south-eastern Queensland
Critical temperature for spawning
21°C [270, 580]
Inducement to spawning
?
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
possibly relatively high compared with other non-amphidromous eleotrids of similar size [1093]
Fecundity /length relationship
?
Egg size
possibly relatively small compared with other non-amphidromous eleotrids of similar size [1093]
Frequency of spawning
?
Oviposition and spawning site
eggs are laid in a single, uniform, compact layer on solid surfaces such as rocks or logs [270]
Spawning migration
none known
Parental care
male guards the nest [270]
Time to hatching
4 days [270]
Length at hatching (mm)
newly hatched larvae may be free-swimming [270]
Length at free swimming stage
?
Length at metamorphosis (days)
?
Duration of larval development
?
Age at loss of yolk sack
?
Age at first feeding
?
species as amphidromous in the strictest sense. Juveniles are thought to begin migrating upstream into freshwaters during spring, after winter floodwaters subside [270]. Hydrological or physicochemical cues for movement of adults, larvae and juveniles are unknown. Johnson [658] found that juveniles and adults were common downstream and upstream of Marian Weir in the Pioneer River, but were not actually collected in the fishway, which he regarded as inefficient. Large numbers of adults and juveniles have been recorded using fishways in the Mary and Brisbane rivers [658] but the timing or environmental conditions during which these movements occurred are unclear. Gobiomorphus australis is reputed to have good climbing abilities and is able to negotiate wet rock surfaces around rapids and waterfalls [270]. This species has also been recorded as having fallen to the ground in rain at Mullumbimby, northern New South Wales, possibly as a result of a whirlwind [1397].
[580] but Lake [755] suggests it will breed in aquaria and Waite [1355] and Robertson [1150] observed G. australis spawning in aquaria (but did not report further egg development). Length–frequency data from the Albert River, south-eastern Queensland (Fig. 3), strongly support the suggestion that larvae and juveniles spend at least part of their life in estuarine or freshwater-tidal habitats: individuals less than 30 mm (SL) were collected from these areas only. In addition, the absence of G. australis from areas upstream of large dams strongly suggests that they recruit from downstream areas [441, 442, 704, 859]. Movement There is little information on the movement patterns of Gobiomorphus australis. It is possibly amphidromous: adults spawn in freshwaters and the larvae are carried downstream to estuaries, migrating upstream later in life [580]. It is unknown whether any part of the life history is actually spent at sea: a condition required to classify this
535
Freshwater Fishes of North-Eastern Australia
barrages, road crossings and culverts. These barriers may affect successful recruitment of this species by inhibiting the ability of adults to access preferred freshwater spawning habitats, the ability of new-hatched larvae to access downstream or estuarine habitats that are possibly critical for larval development, and finally, the ability of juveniles to undertake upstream dispersal movements back into freshwaters. River regulation, independent of the imposition of barriers, may also impact on striped gudgeon populations in rivers. Changes to the natural discharge regime and hypolimnetic releases of unnaturally cool waters from large dams may interrupt possible cues for movement or de-couple optimal temperature/discharge relationships during critical phases of spawning, larval movement and development, and juvenile recolonisation. In coastal rivers of New South Wales, Gehrke et al. [435, 438, 441] collected fewer individuals of G. australis in areas subject to flow regulation than in unregulated reaches. They speculated that these differences were due, in part, to flow regime changes associated with dams. Water resource development which inhibits the transfer of water and biota between the main river channel and off-stream wetland habitats is likely to lead to reductions in long-term sustainability of this species. Although widely distributed, G. australis is most common in lowland streams and rivers or in lowland wetland habitats. Such habitats are also most at risk of reclamation, degradation by clearing and encroachment by agriculture (particularly sugar-cane farming), invasion by noxious weeds such as para grass, and channelisation to improve drainage. In addition, and perhaps just as importantly, such habitats are frequently close to human population centres (e.g. Brisbane and the southeastern Queensland coastal strip) and are thus at risk from urban encroachment. The prevalence of marina and canal developments in coastal and estuarine areas of south-eastern Queensland and New South Wales has potential to impact on the possible larval and juvenile habitat of this species.
Trophic ecology Quantitative dietary information for Gobiomorphus australis is available from a single study of 37 individuals in the Tweed River, northern New South Wales [1133]. Gobiomorphus australis is a carnivore, thought to consume prey primarily from the benthos [917, 1133]. Aquatic insects comprised the largest proportion of the total mean diet (57%) (Fig. 4). Macrocrustaceans and molluscs comprised a further 10.4% and 8.5% of the diet, respectively. Small amounts of microcrustaceans (ostracods) and detritus were also consumed. This species has also been reported to ingest fish (including eastern gambusia, Gambusia holbrooki) and filamentous algae [270, 917]. It is reputedly an important source of food for larger carnivorous fish species such as Australian bass (Macquaria novemaculeata) [936]. Microcrustaceans (1.9%) Macrocrustaceans (10.4%)
Unidentified (21.8%)
Molluscs (8.5%)
Detritus (0.3%)
Aquatic insects (57.1%)
Figure 4. The mean diet of the striped gudgeon Gobiomorphus australis. Data derived from stomach content analysis of 37 individuals from the Tweed River, northern New South Wales [1133].
Conservation status, threats and management The conservation status of Gobiomorphus australis is listed as Non-Threatened by Wager and Jackson [1353]. It is generally common throughout the central core of its range from south-east Queensland through New South Wales. In Victoria, where it is generally uncommon, patchily distributed and, possibly, often confused with G. coxii, the conservation status of this species was initially listed as Restricted distribution or Rare in 1984 [273]. After a subsequent review in 1990, this listing was changed to Indeterminate [731, 1112] but upgraded to Rare three years later, in 1995 [1113]. It has since been further upgraded to Vulnerable [1004].
Siltation arising from increased erosion rates and sediment transport in catchments has been identified as a possible threat to the spawning habitats (probably rocky substrates) of G. australis populations in East Gippsland, Victoria [572]. Predation of juveniles and adults by alien fish species (e.g. trout and eastern Gambusia) and reductions of invertebrate food resources are other factors identified as potential threats to G. australis in this region [572]. Two protozoan parasites, Childonella cyprini and Ichthyophthirius multifiliis, have been found in specimens of G. australis from southern Australia [114, 185]. The former parasite is widely distributed and has been known to cause high fish mortalities in aquaculture facilities, including
Gobiomorphus australis is likely to be sensitive to barriers to movement caused by structures such as dams, weirs,
536
Gobiomorphus australis
Tetracerasta blepta (Lepocreadiidae) [338, 339].
some in Australia [114]. Gobiomorphus australis is also known to be infected naturally by the adult digenic trematode parasite Opecoelus variabilis (Opecoelidae) where it acts as a definitive host; and it is also second intermediate host to Stemmatostoma pearsoni (Cryptogonimidae) and
The absence of detailed life history information on this species is of concern. Greater research effort to elucidate the biology of this species is needed.
537
Gobiomorphus coxii (Krefft, 1864) Cox’s gudgeon
37 429002
Family: Eleotridae
Description First dorsal fin: VI; Second dorsal: I, 9; Anal: I, 9; Pectoral: 18–19; Pelvic: I, 5; Caudal: 15 segmented rays; Vertical scale rows: 36–40; Gill rakers on first arch: 9–12; Vertebrae: 26-27 [34, 52, 270, 741, 775, 936].
pointed (villiform) teeth are present on both jaws. The body is covered with moderate-sized ctenoid scales, becoming cycloid anteriorly and on the abdomen. Lateral line absent. Predorsal scales reach forward to opercula and between eyes, no scales on cheeks. Three to five large pores present on preopercular margin. Lines of minute papillae extend across cheek and operculum, around preopercular margin and from each side of snout to above eye. Urinogenital papilla long and slender and pointed in males, broad and truncate in females with numerous small flaps surrounding the opening. Two separate dorsal fins: the first is rounded with notches between spines; the second is higher and slightly longer. Anal fin smaller and more rounded than second dorsal fin and positioned opposite. Pectoral fins are rounded and large. Pelvic fins thoracic, small, elongate and pointed. Caudal fin moderately large and truncated [270, 741, 775, 880, 936].
Gobiomorphus coxii is a small to moderate-sized gudgeon known to reach 190 mm but more common around 120–150 mm. Females grow larger than males [52, 270, 775]. Of 61 fishes collected in streams of south-east Queensland [709, 1093], the mean and maximum length of this species were 69 and 140 mm SL, respectively. No length-weight equation is available for this species but it is very similar in size and shape to G. australis. The following description is taken largely from Cadwallader and Backhouse [270]. Gobiomorphus coxii is a relatively slender species with an elongate, almost cylindrical body, tapering and becoming compressed posteriorly. The head is rounded and slightly dorsally flattened, the snout bluntly rounded and the cheeks bulbous. Moderately small eyes are positioned high on sides of head near the dorsal profile and separated by a narrow interorbital space. This species has a small oblique upturned mouth with lower jaw prominent; maxillary barely extends to anterior margin of the eye. Rows of small
Colour of head and body varies from dark yellowish-brown, to greyish-green dorsally, grading to light brown or cream ventrally. Blue, gold and yellow flecks may be present on lower lateral scales. Adults have single, broad, dark brown to black midlateral stripe running from just behind opercular opening to caudal peduncle. Juveniles have a series of midlateral elongate blotches along body. Head is dark brown, 538
Gobiomorphus coxii
distribution of this species closely parallels that of G. australis with the exception that in Queensland, G. coxii has been recorded only as far north as the Brisbane River, where it is now thought to be rare and possibly locally extinct [662, 907], probably due to the presence of large barriers (dams and weirs) in this catchment. Gobiomorphus coxii was not recorded during recent extensive surveys in the Brisbane River catchment, nor was it recorded from coastal streams draining into Moreton Bay, to the immediate north and the south of the Brisbane River (Table 1). This species probably now occurs only as far north as the Logan-Albert Basin, and has been recorded from most coastal streams south of here to the border with New South Wales. It has not been recorded on Fraser, Moreton and Stradbroke islands, off the coast of south-eastern Queensland [62, 1258].
lower jaw and throat often black. Two faint, dark stripes radiate from behind eye across operculum. A distinct black spot is present at upper pectoral fin base, with a single black spot on lower pectoral fin base also present in large individuals. Fins colourless, yellowish or dusky-grey; first dorsal fin with two dark stripes separated by areas of yellow or orange; second dorsal fin with three dark stripes separated by areas of yellow or orange; fin margins clear to yellow. Caudal fin yellowish-brown with numerous dark spots forming five to six irregular vertical bands. Males are more brightly coloured than females when in breeding condition. Preserved colouration brown or greyish with dark brown midlateral stripe and fins with dark grey or blackish bands as described above [34, 270, 741, 775, 936]. Gobiomorphus coxii is similar in general appearance to G. australis, especially juveniles and subadults. Distinguishing characteristics of G. coxii include 18–19 pectoral fin rays, 36–40 midlateral scales and a single, broad, dark brown to black midlateral stripe running along sides of body in adults; juveniles have a series of midlateral elongate blotches along body.
Gobiomorphus coxii is generally uncommon and patchily distributed in south-eastern Queensland. Surveys undertaken by us between 1993 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected only 76 individuals of G. coxii and it was present at only 6% of all locations sampled (Table 1). This species was most widespread in coastal rivers and streams of the South Coast Basin, where it was present at 35% of locations sampled. Overall, it was the 25th most abundant species collected (0.05% of the total number of fishes collected), but was the 11th most abundant species collected in the South Coast Basin (0.82%). Overall, it was relatively uncommon at sites in which it occurred (2.1% of total abundance, eighth most common species). In these sites, G. coxii most commonly occurred with the following species (listed in decreasing order of relative abundance): R. semoni, C. marjoriae, A. reinhardtii, H. galii, and M. duboulayi. Across all rivers, it was the 24th most important species in terms of biomass, forming 0.06% of the total biomass of fish collected, but was the fourth most important species in the South Coast Basin (1.56%).
Systematics Cox’s gudgeon, Gobiomorphus coxii, was originally described by Krefft in 1864 [741] as Eleotris coxii. It was also described as Eleotris richardsonii by Steindachner in 1866 [1261] and as Eleotris marstersii by Macleay in 1881 [844]. It was subsequently placed into a new genus Mulgoa by Ogilby [1012] in 1897 and then into Krefftius by Waite [1355] in 1904. Finally, in 1919, McCulloch and Ogilby [880] placed it within the genus Gobiomorphus. Distribution and abundance Gobiomorphus coxii is restricted to Australian coastal rivers from southern Queensland, south through New South Wales to Wilsons Promontory in eastern Victoria [775]. The
Table 1. Distribution, abundance and biomass data for Gobiomorphus coxii in rivers in south-eastern Queensland. Data summaries for a total of 76 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
6.4
—
—
—
—
17.6
35.0
0.05 (2.08)
—
—
—
—
0.11 (1.51)
0.82 (5.50)
25 (8)
—
—
—
—
19 (8)
11 (5)
0.06 (1.83)
—
—
—
—
0.17 (1.67)
1.56 (3.35)
24 (5)
—
—
—
—
13 (5)
4 (4)
Mean numerical density (fish.10m–2)
0.14 ± 0.03
—
—
—
—
0.10 ± 0.02
0.21 ± 0.09
Mean biomass density (g.10m–2)
1.85 ± 0.31
—
—
—
—
1.82 ± 0.38
1.92 ± 0.58
Rank biomass
539
Freshwater Fishes of North-Eastern Australia
australis, which is usually found in lowland areas. Larvae and juveniles of G. coxii are generally found in downstream reaches, in or close to the freshwater-tidal interface or estuarine areas [270, 580]. In rivers and streams of south-eastern Queensland, this species occurs at moderate to high elevations (20–300 m.a.s.l.) but most commonly at elevations greater than 110 m.a.s.l. (Table 2). Elsewhere, it has been recorded at elevations up to 700 m [580]. In south-eastern Queensland, it most frequently occurs in the middle to upper sections of streams, close to the stream source (Table 2) and has been recorded in similar habitats elsewhere [580, 1133]. It is present in small to moderatesized streams (range = 3.0–17.5 m width) but is more common in streams less than 6 m wide and with moderate riparian cover. In rivers and streams of south-eastern Queensland, G. coxii most commonly occurs in rapids, riffles and runs characterised by high gradient (weighted mean gradient >1%), moderate depth (<0.4 m weighted mean depth) and moderate mean water velocity (weighted mean velocity = 0.13 m.sec–1) (Table 2). This species is most abundant in mesohabitats with coarse substrates (cobbles, rocks and bedrock) but shows little apparent affinity for habitats with particular submerged cover attributes. A similar pattern in mesohabitat use by this species has been documented in the Tweed River, northern New South Wales [1133].
Average and maximum numerical densities recorded in 28 hydraulic habitat unit samples (i.e. riffles, runs or pools) were 0.14 individuals.10m–2 and 0.77 individuals.10m–2, respectively. Average and maximum biomass densities at 21 of these sites were 1.85 g.10m–2 and 4.87 g.10m–2, respectively. Gobiomorphus coxii appears to be relatively uncommon in rivers of the north coast of New South Wales but is relatively widespread and abundant in coastal rivers from the Hawkesbury River south to the border with Victoria [188, 282, 435, 437, 441, 814, 1066, 1201]. In Victoria, this species appears relatively uncommon and patchily distributed in coastal streams, probably as far west as the Franklin River near Wilsons Promontory in South Gippsland [135, 270, 775, 1111, 1112, 1113]. Macro/mesohabitat use Gobiomorphus coxii usually occurs in upland sections of small to moderate-sized coastal streams, in contrast to G. Table 2. Macro/mesohabitat use by Gobiomorphus coxii in rivers of south-eastern Queensland. Data summaries for 76 individuals collected from samples of 28 mesohabitat units at 19 locations undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
Mean
W.M.
5.0 5.0 5.0 20 3.0 8.9
584.0 80.5 165.0 300 17.5 93.4
97.6 25.8 76.6 126 7.7 33.1
55.6 18.0 56.2 112 5.8 51.7
Gradient (%) 0 Mean depth (m) 0.13 Mean water velocity (m.sec–1) 0
2.16 0.74 0.55
0.98 0.34 0.18
Microhabitat use In the Albert River, south-eastern Queensland, G. coxii was most frequently collected from areas of low to moderate water velocity, often in interstices of the substrate in areas of otherwise high velocity (i.e. rapids, riffles and runs) (Fig. 1a and b). This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 1c). A benthic species, it occupies the lower part of the water column, most often in direct contact with the substrate (Fig. 1d). It is usually found among coarse substrates (coarse gravel, cobbles and rocks) (Fig. 1e). This species was not usually present close to the stream bank (only 32% of 25 fish collected within 1 m of the bank) but was always found in close association with some form of submerged cover, most frequently the interstices of coarse substrates (cobbles and rocks) and occasionally, attached filamentous algae (Fig. 1f).
1.20 0.37 0.13
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
39.3 61.1 23.6 27.9 51.9 59.4 70.0
4.8 5.9 5.3 14.6 33.2 26.7 9.4
4.1 2.0 4.4 15.6 31.3 23.0 19.6
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0.2 0 0.3 0 0 0 0
53.9 19.6 2.1 11.5 12.2 25.2 20.0 10.1 45.0 45.0
6.1 5.0 0.4 3.6 0.7 7.6 2.1 1.3 4.3 7.6
3.5 3.7 0.3 2.7 0.5 11.6 0.8 0.8 2.5 5.2
Environmental tolerances Information on tolerance to water quality extremes is lacking and the data listed below (Table 3) reflect the physicochemical conditions of the well-forested upland flowing streams in which G. coxii typically occurs in south-eastern Queensland (see section on Macro/mesohabitat use above). These streams have comparatively low water temperatures, neutral pH, low conductivities and high
540
Gobiomorphus coxii
30
(a) 40
movement below) suggests that this species may be able to tolerate elevated salinities for at least part of its life history. Richardson [1134] speculated that G. coxii may be tolerant of heavy sedimentation and elevated turbidity associated with forestry road and causeway construction in the Murrah River Catchment, southern New South Wales.
(b)
30
20
20 10 10 0
50
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 80
40
60
30 20
40
10
20
0
0
Total depth (cm) 40
Reproduction There is relatively little published information on the reproductive biology of G. coxii (Table 4) but it probably resembles that of G. australis. Size at reproductive maturity is unknown but maturity probably occurs at relatively small size. It is unknown whether the entire life cycle occurs in freshwater but this species is possibly amphidromous (see section on movement below). Spawning probably occurs in freshwater, possibly during late summer and autumn in southern states. In south-eastern Queensland, spawning probably occurs in autumn and winter as the smallest individuals (less than 30 mm SL) first appeared in freshwater samples in spring (at a site 80 km upstream from the point of tidal penetration) (Fig. 2).
(e)
30
Relative depth 60
(f)
40
40
20 20
10 0
Spring (n = 6) Summer (n = 22)
0
30
Autumn-Winter (n = 33) 20 Substrate composition
Microhabitat structure
10
Figure 1. Microhabitat use by Gobiomorphus coxii. Data derived from capture records for 25 individuals from eight samples collected in the Albert River, south-eastern Queensland, over the period 1994–1997 [1093].
water clarity (low turbidity). Waters are also comparatively well-oxygenated, reflecting the fast-flowing riffle/run habitats frequented by this species. The possible estuarine larval phase of G. coxii (see sections on reproduction and Table 3. Physicochemical data for Gobiomorphus coxii. Data summaries for 75 individuals collected from 25 samples in south-eastern Queensland streams collected between 1994 and 2003 [1093]. Parameter
Min.
Max.
Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
13.4 5.5 6.5 54.0 1.0
28.0 16.2 8.8 590.0 36.0
0
Standard length (mm) Figure 2. Seasonal variation in length-frequency distributions of Cox’s gudgeon, Gobiomorphus coxii, from sites in the Albert River, south-eastern Queensland [1093]. The number of fish from each season is given in parentheses.
Estimates of fecundity are unavailable but a similarly sized species of amphidromous Gobiomorphus from New Zealand (the giant bully, G. gobiodies) produces many thousands of comparatively small (1 mm long) oval eggs [890, 891]. Female G. coxii lay demersal eggs on rocks and after fertilisation the male guards and fans the nest [580]. The duration of egg development is thought to vary with
Mean 19.0 8.4 7.5 158.0 4.2
541
Freshwater Fishes of North-Eastern Australia
Table 4. Life history information for Gobiomorphus coxii. Age at sexual maturity (months)
?
Minimum length of ripe females (mm)
?
Minimum length of ripe males (mm)
?
Longevity (years)
?
Sex ratio (female to male)
?
Occurrence of ripe fish
?
Peak spawning activity
? possibly late summer and autumn in southern states and autumn and winter in southeastern Queensland [1093]
Critical temperature for spawning
?
Inducement to spawning
?
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
? probably relatively high compared with other non-amphidromous eleotrids of similar size [1093]
Fecundity /length relationship
?
Egg size
? probably relatively small compared with other non-amphidromous eleotrids of similar size [1093]
Frequency of spawning
?
Oviposition and spawning site
females lay eggs on solid surfaces such as rocks [270, 580]
Spawning migration
none known
Parental care
after fertilisation the male guards and fans the nest [270, 580]
Time to hatching
3–5 days, depending on water temperature [270]
Length at hatching (mm)
?
Length at free swimming stage
?
Length at metamorphosis (days)
?
Duration of larval development
?
Age at loss of yolk sack
?
Age at first feeding
?
(where adults of this species usually occur) and larvae move large distances downstream. Juveniles are thought to migrate upstream, probably during spring and summer. Tens of thousands of fish between 30–80 mm were observed below Tallowa Dam, located relatively close to the mouth of the Shoalhaven River, New South Wales, during November and December [188]. In a separate study, large numbers of juveniles (around 40 mm TL) were observed congregating at the base of Tallowa Dam, during January and February, presumably having had their migration interrupted by the barrier [859]. Gobiomorphus coxii has been widely documented to climb up the wet surfaces of waterfalls, weirs and dams [188, 270, 580, 748, 755, 859]. While climbing the vertical wall of Tallowa Dam on the Shoalhaven River, fish were observed to prefer surfaces with a covering of algae, rather than bare wet surfaces [188]. Many individuals have been observed negotiating an overfall pool fishway on the Penrith Weir in the Nepean River, New South Wales, by climbing the wet sides of each pool [543], and by climbing vertical baffles in a vertical-slot fishway at Cobbity Weir, also in the Nepean
water temperature but hatching occurs after three to five days [270]. It is thought that the larvae are carried downstream to lowland rivers or estuaries, migrating upstream later in life [270, 580]. Movement There is little information on the movement patterns of G. coxii, but it appears to be similar to G. australis. Adults probably spawn in freshwaters and it is thought that the larvae are carried downstream to lowland rivers or estuaries, migrating upstream later in life [270, 580]. It is unclear whether larvae of this species actually enter estuaries, as do G. australis and some New Zealand species of Gobiomorphous [891], however Cadwallader and Backhouse [270] suggest they may. It is unknown whether any part of the life history is actually spent at sea: a condition required to classify this species as amphidromous in the strictest sense. It is also uncertain whether reproductively active adults migrate downstream to lower freshwater reaches to spawn (and if so, how close to the point of tidal penetration), or if spawning occurs far upstream
542
Gobiomorphus coxii
has since been further upgraded to Endangered [1004]. It is also listed under the Victorian Flora and Fauna Guarantee Act 1998 and the Endangered Species Protection Act 1992.
River [859]. The ability of this species to negotiate vertical surfaces is aided by their broad pectoral fins as well as their pelvic fins, which when spread out, form a cup-shaped disc similar to the pelvic fin of gobies [270]. This species has also been observed to leap out of the water to pass minor obstacles to movement [544].
Gobiomorphus coxii is likely to be sensitive to barriers to movement caused by structures such as dams, weirs, barrages, road crossings and culverts, given the possible dependence of this species on access to estuarine areas to complete its life cycle. These barriers may affect successful recruitment by inhibiting the ability of adults to access preferred freshwater spawning habitats, the ability of newhatched larvae to access downstream or estuarine habitats that are possibly critical for larval development, and finally, the ability of juveniles to undertake upstream dispersal movements back into freshwaters. Although able to climb large barriers such as dams and weirs, abundances of G. coxii have greatly declined upstream of the Tallowa Dam in the Shoalhaven River [859] and it now appears to be absent upstream of Wivenhoe Dam in the Brisbane River [662, 704, 907]. River regulation, independent of the imposition of barriers, may also impact on Cox’s gudgeon populations in rivers. Changes to the natural discharge regime and hypolimnetic releases of unnaturally cool waters from large dams may interrupt possible cues for movement, or de-couple optimal temperature/discharge relationships during critical phases of spawning, larval movement and development, and juvenile recolonisation. In coastal rivers of New South Wales, Gehrke et al. [435, 438, 441] collected fewer individuals of G. coxii in areas subject to flow regulation than in unregulated reaches, and speculated that these differences were due, in part, to flow regime changes associated with dams in the study area. G. coxii has relatively narrow adult macrohabitat requirements, being most common in upland and mid-catchment streams. This species also has a distinct preference for fastflowing rapids, riffles and runs, these habitat types being most sensitive to reductions in discharge magnitude. Flow regime changes due to dams and water abstraction in these areas are likely to impact the availability of shallow fast flowing habitat suitable for this species.
Trophic ecology Quantitative diet data for G. coxii is available for 55 individuals from a study in the Tweed River, northern New South Wales [1133], and from a tributary of the Murrah River, southern New South Wales [1134], (Fig. 3). Gobiomorphus coxii is a carnivore, consuming prey primarily from the benthos. Aquatic insects comprised the largest proportion of the total mean diet (83.9%). Molluscs, macrocrustaceans and microcrustaceans (ostracods) comprised a further 6.3%, 5.0% and 3.0% of the diet, respectively. This species, like G. australis, is thought to be an important source of food for birds (it has been found in the stomachs of bittern [1397]) and larger carnivorous fish species [936]. Microcrustaceans (3.0%) Macrocrustaceans (5.0%)
Unidentified (1.8%)
Molluscs (6.3%)
Aquatic insects (83.9%)
Figure 3. The mean diet of Cox’s gudgeon Gobiomorphus coxii. Data derived from stomach content analysis of 55 individuals from the Tweed River [1133] and the Murrah River Catchment [1134], southern New South Wales.
Siltation arising from increased erosion rates and sediment transport in catchments has been identified as a possible threat to the spawning habitats (probably rocky substrates) of G. coxii populations in East Gippsland, Victoria [572]. Predation of juveniles by alien fish species (e.g. trout and eastern Gambusia), competition with alien fish species for habitat, and reductions of invertebrate food resources are other factors identified as potential threats to G. coxii in this region [572].
Conservation status, threats and management The conservation status of Gobiomorphus coxii is listed as Non-Threatened by Wager and Jackson [1353]. It is generally common throughout the central core of its range but may be under threat at its northern (i.e. Brisbane River) and southern (Victoria) extremities. In Victoria, where it is generally uncommon, patchily distributed and, possibly often confused with G. australis, the conservation status of G. coxii was initially listed as Indeterminate [731, 1112] but upgraded to Vulnerable three years later, in 1995 [1113]. It
The absence of detailed life history information on this species is of concern. Greater research effort to elucidate the biology of this species is needed.
543
Mogurnda adspersa (Castelnau, 1878) Purple-spotted gudgeon
37 429033
Mogurnda mogurnda (Richardson, 1844) Northern trout gudgeon
37 429034
Family: Eleotridae
mm) and weight (W in g) for 136 individuals (range 18–79 mm SL) from the Mary River, south-eastern Queensland is W = 1.0 x 10–5 L3.197, r2 = 0.990, p<0.001 [1093]. The equivalent relationship for 178 individuals (15–88 mm SL) from the Wet Tropics regions is W = 5.093 x 10–6 L3.394; r2 = 0.948, p<0.001.
Description Mogurnda adspersa First dorsal fin: VI–IX (usually VII–VIII); Second dorsal: I, 11–13; Anal: I, 10–12 [52] (11–14 [775]); Pectoral: 14–16; Pelvic: I, 5; Caudal: 15 segmented rays; Vertical scale rows: 30–36; Horizontal scale rows: 10–12; Predorsal scales: 16–21; Gill rakers on first arch: 10–12; Vertebrae: 31 [34, 52, 270, 775]. Note that meristics vary considerably between localities but are usually consistent within a locality [775]. Figure: mature male, 83 mm SL, Mena Creek, South Johnstone River, August 1996; drawn 1997.
Mogurnda adspersa has an elongate and robust body, slightly compressed posteriorly. The mouth is moderatelysized and oblique, reaching below the anterior margin of the eye; bands of small teeth are present in each jaw; the lower jaw protrudes beyond the upper jaw. The head is rounded; bearing papillae around the eyes, another row extending back in a line from the eye to the top of the operculum, two broken rows of papillae across cheeks, a further row along preopercular margin. Ciliated scales are of moderate size, and present on head, opercula, cheeks and body. The first dorsal fin is rounded, originating behind the level of pelvic and pectoral fin bases. The second dorsal fin is elongate, with the posterior rays longest, originating approximately in line with the anal fin origin. The caudal fin is rounded. This species is sexually dimorphic. Mature males may be characterised by a bulge on the head above eyes; genital papilla elongated, curved downward and backward, tapering to point. Mature
Mogurnda adspersa is a moderate-sized gudgeon thought to reach 140 mm TL but more commonly 70–80 mm TL [52, 755, 775, 936]. Allen and Jenkins [50] list the maximum size as 90–100 mm SL. An individual 152 mm TL identified as M. adspersa was recorded from the Barron River [222]. Of 3710 specimens collected from streams of the Wet Tropics region over the period 1994–1997 [1093], the mean and maximum lengths of this species were 41 and 88 mm SL, respectively. Of 1512 specimens collected in streams of south-eastern Queensland over the period 1994–2000 [1093], the mean and maximum length of this species were 42 and 100 mm SL, respectively. The equation best describing the relationship between length (SL in
544
Mogurnda adspersa, Mogurnda mogurnda
adspersa has been described or referred to as Eleotris concolor De Vis 1884; E. mimus De Vis 1884; and Krefftius adspersus Ogilby 1898. Some authors have also referred to M. adspersa as E. striatus (or striata) Steindachner 1866.
females are without bulge on head and have broader genital papilla (with rugose edge). Males have three diagonal brown stripes on cheeks, running from the eye to the lower operculum; females have two paler stripes. The dorsal surface is brown, fading on sides and ventral surface to grey or yellow-brown. The sides have 9–12 black, grey or bluish patches that may extend dorsally to form bars; patches/bars are overlaid and surrounded by white, purple and red spots, which become more intense in colour during the breeding season. Fins are yellowish; dorsal, caudal and anal fins becoming darker towards margins; red spots present on dorsal, caudal and pelvic fins, more numerous at fin bases. Preserved colouration dark brown dorsally, becoming tan ventrally; dark blotches on sides; fins becoming tan-dark brown [34, 270, 755, 775, 936].
Mogurnda adspersa is widespread (see below) occurring in coastal drainages of the east coast and in the MurrayDarling system. Wager and Jackson [1353] cite unpublished genetic research indicating that remnant populations of M. adspersa from the Murray-Darling Basin are electrophoretically similar but considerably divergent from east coast populations and therefore warrant classification as a separate taxon. East coast populations were also reported to show considerable genetic variation between drainages [1353]. Allen and Jenkins [50], in their review of the Australian species of Mogurnda, examined specimens of this species from east (n = 37) and west (n = 41) of the Great Dividing Range but did not comment on any morphological differences between these populations. Nor did these authors comment on the existence or extent of morphological variation in eastern populations of M. adspersa, although the series examined contained specimens from localities as distant as southeastern Queensland and from near Townsville.
Mogurnda mogurnda First dorsal fin: VII–IX; Second dorsal: I, 9–14; Anal: I, 10–13; Pectoral: 14–17; Pelvic: I, 5; Caudal: 13–15 (usually 15) segmented rays; Vertical scale rows: 34–47; Horizontal scale rows: 13–15 (usually 13–14); Predorsal scales: 16–23; Vertebrae: 32–33. Mogurnda mogurnda attains a slightly large size than M. adspersa, reportedly reaching 175 mm TL but more commonly 100 mm TL [580, 755]. Bishop et al. [193] report the relationship between length (TL in cm) and weight (g) as taking the form W = 8.84 x 10–3 L3.19, n = 263, r2 = 0.98. This species is very similar in morphology and general appearance to M. adspersa but M. mogurnda can be distinguished by a higher vertical scale count, a higher horizontal scale count, and a higher abdominal vertebrae count (15–16 in M. mogurnda versus usually 14 in M. adspersa) [50, 52].
Hurwood and Hughes [617] undertook sequence analysis of the extent of genetic variation in M. adspersa in the Wet Tropics region of northern Queensland and identified the presence of three distinct haplotypes in the headwaters of the Tully River. One haplotype was ~3.4% divergent from the remaining two and formed part of a clade comprised of populations from the Herbert River, Johnstone River and the Barron River, and secondarily, populations from the lower Tully River and Liverpool Creek. Hurwood (pers. comm.) believed that the extent of variation present in M. adspersa in the Wet Tropics region warranted the erection of at least one new species and potentially the recognition of subspecies level differentiation between populations of M. adspersa in south-eastern Queensland and the Wet Tropics region. Given the extensive distribution of M. adspersa and the fact that it extends north into Cape York Peninsula, the potential for further genetic and accompanying morphological variation between stocks is substantial. Research addressing this issue is being undertaken (D. Hurwood, pers. comm.).
Systematics Mogurnda Gill is composed of at least six Australian and 16 New Guinean species of small to moderate-sized freshwater gudgeons [50]. The genus is comprised of three distinct species complexes deserving of subgeneric recognition, two of which are confined to New Guinea. The third contains both Australian and New Guinean species and is typified by M. mogurnda [50]. The Australian species within this genus include M. adspersa, M. mogurnda, M. larapintae (Zietz 1896) (long considered a junior synonym of M. mogurnda), M. ologolepis Allen and Jenkins 1999, M. thermophila Allen and Jenkins 1999 and M. clivicola Allen and Jenkins 1999. The latter four species have restricted distributions [50]. Both M. adspersa and M. mogurnda were originally placed in the genus Eleotris (as E. adspersa and E. mogurnda) and Ogilby [1012] erroneously placed M. adspersa in the invalid genus Krefftius. No other synonyms exist for M. mogurnda, but M.
Morphological variation across the broad range of M. mogurnda was commented upon by Allen and Jenkins [50]. Specimens from western drainages of Cape York Peninsula tend to be characterised by an elevated dorsal and anal fin ray count (12–13) and vertical scale count (42–47) than those from the western portions of its distribution (11 rays, and 35–39 scales). More specimens are needed to quantify the extent of variation in this species
545
Freshwater Fishes of North-Eastern Australia
streams and dune lakes in the Jeanie Basin (Muck Creek, Jeanie River, McIvor River, Cape Flattery dune lakes) [562, 571], and the Endeavour Basin (Endeavour River and Annan River) [571, 1349]. In this area, fish identified as M. mogurnda have been recorded more often and generally in greater numbers than have M. adspersa (see above).
and more than one species may be involved [50]. Indeed, Allen and Jenkins cautioned that there was a critical need for more collections to fully resolve the systematics of this genus in Australia. Distribution and abundance Mogurnda adspersa is a relatively widespread species occurring in most major coastal drainages of eastern Australia from central Cape York Peninsula possibly as far south as the Clarence River in northern New South Wales. It is also present on Fraser, Moreton, Bribie and Stradbroke islands, off the coast of south-eastern Queensland. It occurs in the Murray-Darling Basin and once was present in coastal drainages of the South Australian Gulf [34, 506, 775].
In a survey of rivers of the Wet Tropics region, north Queensland, M. adspersa was the fifth most abundant species collected, occurring in over 31% of the 92 sites surveyed and present in seven of the 10 major drainage basins examined [1087]. It has subsequently been found to occur in every major drainage basin within the region [643, 1093, 1110, 1179, 1183, 1185, 1186, 1349]. This species is often very abundant in headwater streams of this area [1085, 1087].
Mogurnda mogurnda is a relatively widespread species also, with the Australian distribution ranging from northwestern Australia to Cape York Peninsula [50], and possibly further south in north-eastern Queensland. Mogurnda mogurnda is thought to occur throughout the Gulf of Carpentaria and western Cape York Peninsula. It has been recorded from the Nicholson and Flinders basins in the southern Gulf [661, 997]. It has also been recorded from the Mitchell, Coleman, Holroyd, Archer, Embley, Mission, Wenlock and Jardine rivers, and from small streams near the tip of Cape York [41, 571]. Mogurnda mogurnda is apparently relatively widespread and common throughout many of the drainage basins of eastern Cape York Peninsula and also the dune lake systems near the eastern tip of Cape York, Shelburne Bay and Cape Flattery [571, 1101]. The distributional limits of M. mogurnda, and of M. adspersa, in northern Queensland are unclear. Both species have been recorded in drainages from the Normanby River south to the Bloomfield River [533, 571, 791, 1094, 1099, 1110, 1349]. Occasional records of this species in other rivers and lakes of the Wet Tropics region may be found [132, 584, 585, 1170, 1186, 1349] and it may also occur as far south as the Burdekin [533, 586] and Fitzroy [1173] rivers. The two species appear to have overlapping distributions in the northern part of the Wet Tropics region and the south-eastern Cape York Peninsula but it is highly likely that the taxonomic uncertainties and morphological similarities associated with these taxa have led to frequent mis-identifications. Records south of the Herbert River are likely to be in error.
Table 1. Distribution, abundance and biomass data for Mogurnda adspersa in the Wet Tropics region. Data summaries for a total of 4009 individuals collected from rivers in the Wet Tropics region over the period 1994–1997 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total % locations % abundance Rank abundance % biomass Rank biomass
Mulgrave River
Johnstone River
54.6
45.5
66.2
11.4 (16.3)
2.6 (9.9)
14.0 (18.0)
4 (2)
8 (4)
3 (1)
1.3 (8.7)
0.23 (7.8)
1.9 (9.0)
19 (9)
8 (4)
7 (4)
Mean numerical density 1.52 ± 0.3 (fish.10m–2)
0.50 ± 0.10 1.79 ± 0.37
Mean biomass density (g.10m–2)
1.24 ± 0.28 3.62 ± 0.75
3.11 ± 0.60
Mogurnda adspersa is both widespread and common in rivers of the Wet Tropics regions (Table 1) and may comprise between about 10–20% of the total number of fishes present at locations in which it occurs. This species is more widespread in the Johnstone River than in the Mulgrave River and may be up to three times more abundant in terms of numerical density and biomass in the former river (Table 1). It may frequently be the dominant species in small upland streams [1093, 1186]. It may frequently co-occur with (in decreasing order of abundance) C. rhombosomoides, H. compressa, P. signifer, M. s. splendida; all of which are locally widespread and abundant species.
Mogurnda adspersa occurs as far north as the Normanby River in Cape York Peninsula [697]. A record of this species from the Jardine River [571] is most probably a mis-identification of M. mogurnda. South of the Normanby River, M. adpsersa appears to be patchily distributed and uncommon in eastern Cape York Peninsula, having been collected from relatively few rivers,
Mogurnda adspersa is moderately common and widespread in most major rivers and streams of the central Queensland coast. It comprised 6.5% of the total
546
Mogurnda adspersa, Mogurnda mogurnda
total of 3256 individuals and it was present at 30.9% of all locations sampled (Table 2). Overall, it was the seventh most abundant species collected (2% of the total number of fishes collected) and was present in moderate abundances at sites in which it occurred (5.8%). In these sites, M. adspersa most commonly occurred with the following species (listed in decreasing order of relative abundance): P. signifer, C. marjoriae, M. duboulayi, G. holbrooki, and H. galii.
electrofishing catch, but was almost always absent from seine-netting catches in a study undertaken in the Burdekin River between 1989 and 1992, and was much more common upstream of the Burdekin River Falls [1098]. Its distribution in this river extends from wetlands of the Burdekin River delta, throughout the Bowen River and into its headwaters in the Broken River, the highly turbid Belyando/Suttor and Cape/Campaspe rivers, both western and eastern tributary rivers and streams of the upper Burdekin River itself [256, 258, 940, 1046, 1082, 1284, 1408]. This species is similarly widespread and abundant in the Pioneer River [1081]. It is worth noting that collection methodology has great potential to bias estimates of abundance in this species. Its propensity to hide in complex cover makes it difficult to collect by means other than electrofishing in numbers reflecting its true abundance.
Mogurnda adspersa was most widespread in the Mary River where it occurred at 66% of locations surveyed. It achieved the highest relative abundances in the Pine River (Moreton coastal region) and in the Brisbane River (9% and 5.3% of the total abundance sampled in each river, respectively). We rarely collected this species in other streams of south-eastern Queensland and it appears to be absent from many of the small coastal streams of the Noosa, Maroochy and Pine Drainage Basins.
Mogurnda adspersa is common in short coastal streams near Sarina [779], Shoalwater Bay and Water Park Creek [1328]; it is widespread but not overly abundant in the Fitzroy River [160, 405, 942, 1173, 1351], Calliope River [915] and Baffle Creek [826]. It is patchily distributed in other streams of the central Queensland region.
Mogurnda adspersa was the 13th most important species in terms of biomass, forming only 0.3% of the total biomass of fish collected by us. Across all rivers, average and maximum numerical densities recorded in 273 hydraulic habitat samples (i.e. riffles, runs or pools) were 0.58 individuals.10m–2 and 8.14 individuals.10m–2, respectively. Average and maximum biomass densities at 180 of these sites were 1.09 g.10m–2 and 18.06 g.10m–2, respectively. Highest numerical densities were recorded from the Pine and Brisbane rivers and highest biomass densities were recorded from the Brisbane River.
This species is relatively common but patchily distributed in south-eastern Queensland and has been collected as far south as Tallebudgera Creek in the South Coast Basin. In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that it had been collected at only 30 of 63 locations surveyed (seventh most widespread species in the catchment) and formed 3% of the total number of fishes collected (seventh most abundant). It has not been recorded from the Elliott River and is present but relatively uncommon in rivers of the Burrum Basin [7, 157, 736, 987]. Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a
Mogurnda adspersa is reported to occur in coastal drainages of north-eastern New South Wales, possibly as far south as the Clarence River [814, 965, 1340], although we can find no actual survey data to support this. This species was previously widespread but patchily distributed throughout the Murray-Darling Basin and in the Torrens
Table 2. Distribution, abundance and biomass data for Mogurnda adspersa. Data summaries for a total of 3256 individuals collected from rivers in south-eastern Queensland over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
30.9
66.0
10.3
25.0
44.1
1.5
5.0
1.99 (5.82)
1.75 (3.32)
0.12 (2.01)
8.98 (55.84)
5.31 (12.85)
0.01 (0.26)
0.14 (12.82)
13 (7)
12 (11)
19 (8)
3 (1)
5 (2)
29 (6)
17 (3)
0.32 (1.61)
0.37 (1.47)
—
—
1.30 (2.16)
—
—
13 (6)
11 (6)
—
—
5 (4)
—
—
Mean numerical density (fish.10m–2)
0.58 ± 0.06
0.41 ± 0.06
0.10 ± 0.09
1.21 ± 0.34
0.82 ± 0.13
0.04 ± 0.00
0.21 ± 0.00
Mean biomass density (g.10m–2)
1.09 ± 0.17
0.77 ± 0.09
—
—
2.90 ± 0.92
—
—
% biomass Rank biomass
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Freshwater Fishes of North-Eastern Australia
common in reaches with abundant cover, particularly those with abundant submerged marginal vegetation and especially those reaches with abundant root masses and undercut banks.
and Onkaparinga rivers in South Australia [775, 965, 1353]. It has undergone substantial declines in distribution and abundance, especially throughout the southern portion of the Murray-Darling Basin and may be extinct in Victoria and South Australia [965]. In Queensland, it was occasionally collected in small numbers in recent surveys of the Condamine River (upper Darling Basin) [807]. Refer to Morrison et al. [965] for further information on the current distributional status of M. adspersa in the MurrayDarling Basin. See also the section on Conservation status, threats and management requirements.
Table 3. Macro/mesohabitat use by Mogurnda adspersa in the Wet Tropics region. Data summaries for 1135 individuals collected from 54 locations in the Johnstone and Mulgrave rivers between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
Macro/mesohabitat use Mogurnda adspersa is found in a variety of lotic and lentic habitats including small coastal streams, rainforest streams, large rivers and in dune lake and stream systems. Although usually found in freshwater habitats, it has been reported to occur in estuaries [513]. It has been classified as a pool-dwelling species [553] and has been reported to occur in slow-flowing weedy areas [814] and slow moving or still waters in rivers, creeks and billabongs [270].
Parameter 2
Catchment area (km ) Distance from source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
Mean
W.M.
0.13 0.5 10.3 0 2.0 0
334.8 67 104.5 790 53.7 100
29.9 9.1 43.0 158.9 8.9 43.8
11.6 5.4 46.6 171.6 8.8 30.5
Gradient (%) 0.02 Mean depth (m) 0.09 Mean water velocity (m.sec–1) 0
In the Mulgrave and Johnstone river systems, M. adspersa is very widespread (Table 1) and may occur in a wide diversity of different stream types ranging from the main river channel at low elevation and close to the river mouth through to headwater streams at high elevation, and including most stream types between these two extremes (Table 3). The average macrohabitat description is one of moderately small streams (third order) with an average gradient of about 1%, an intact riparian cover located in the coastal uplands moderately distant from the river mouth. The disparity between mean characteristics and those weighted by abundance suggests that this species is more abundant in small streams of lower gradient (0.5%) with a more open riparian canopy. Mogurnda adspersa occurs across a range of mesohabitat conditions from small shallow riffles with moderately fast current velocities to long, moderately deep pools with no appreciable flow, and accordingly, may be found in habitats with a substrate ranging from being almost completely dominated by mud and sand to those dominated by rocks or bedrock (Table 3). On average, this species occurs in streams less than 10 m wide, about 40 cm deep and with a moderate current velocity, however it appears to prefer habitats with comparatively reduced current velocity. Such run habitats tend to have a diverse average substrate composition, although the disparity between average and weighted values suggest that this species is more common in habitats with fine substrates, probably reflecting its preference for reduced current velocity. Although this species may be found in habitats with no appreciable cover other than that provided by the substrate itself, it is most
7.33 0.72 0.45
0.95 0.36 0.17
0.55 0.43 0.08
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
48.0 88.0 73.0 73.0 38.0 76.0 97.0
5.9 17.3 19.1 14.0 11.3 21.0 16.4
18.8 23.9 11.3 11.2 9.2 16.4 9.5
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
23.7 6.9 18.0 91.0 10.0 81.2 12.3 13.8 30.0 75.0
0.8 0.4 2.2 10.8 0.6 8.0 1.8 1.6 3.8 14.5
0.1 0.1 6.3 10.3 2.8 8.9 1.0 2.1 12.4 33.4
Mogurnda adspersa occurs throughout the major length of the larger rivers of south-eastern Queensland, ranging between 18 and 303 km from the river mouth and at elevations up to 400 m.a.s.l. (Table 4). It most commonly occurs around 200 km from the river mouth and elevations around 120 m.a.s.l. It is present in a wide range of stream sizes (range = 0.8–39.9 m width) but is more common in streams of intermediate width (5–10 m) and with low to moderate riparian cover (<50%). In rivers and streams of south-eastern Queensland, this species has been recorded in a range of mesohabitat types but it most commonly occurs in pools characterised by low gradient (weighted mean = 0.14%), shallow to moderate depth (weighted
548
Mogurnda adspersa, Mogurnda mogurnda
Table 4. Macro/mesohabitat use by Mogurnda adspersa in rivers of south-eastern Queensland. Data summaries for 3256 individuals collected from samples of 191 mesohabitat units at 91 locations in south-eastern Queensland streams undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter 2
Catchment area (km ) Distance from source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
Min.
Max.
Mean
W.M.
15.6 5.0 18.0 0 0.8 0
3872.3 98.0 303.0 400 39.9 91.1
264.8 30.9 191.7 109 7.7 50.4
192.8 26.5 200.2 119 6.0 47.5
Gradient (%) 0 Mean depth (m) 0.05 Mean water velocity (m.sec–1) 0
2.48 1.08 0.71
0.26 0.40 0.07
100
0 0 0 0 0 0 0
99.5 100.0 70.7 76.0 58.3 40.0 41.4
6.9 18.6 23.2 30.3 17.0 3.0 1.0
7.8 18.8 24.2 30.6 16.1 1.7 0.8
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
60.7 68.7 45.0 65.7 39.1 65.5 37.6 22.5 87.5 87.5
14.9 10.8 1.6 7.7 2.2 15.4 4.3 4.0 13.5 16.6
19.9 11.7 2.0 9.9 3.1 16.5 3.4 3.4 9.0 11.9
mean = 0.35 m) and low mean water velocity (weighted mean = 0.05 m.sec–1) (Table 4). This species is most abundant in mesohabitats with fine to intermediate-sized substrates (sand, fine gravel, coarse gravel and cobbles) and where aquatic macrophytes, filamentous algae, leaf-litter beds, root masses and undercut banks are common. These data mirror the habitat conditions recorded for populations in the Wet Tropics region except that southern populations appear more abundant in streams of much lower gradient and lower mean water velocity. Mogurnda adspersa occurs in streams with greater abundances of aquatic macrophytes and filamentous algae in south-eastern Queensland than in the Wet Tropics region, whereas root masses and undercut banks are less abundant.
100
80
80
60
60
40
40
20
20
0
0
Mean water velocity (m/sec) 30
0.14 0.35 0.05
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
(a)
(c)
(b)
Focal point velocity (m/sec) 60
20
40
10
20
0
0
(d)
Total depth (cm) 30
(e)
Relative depth 30
20
20
10
10
0
0
Substrate composition
(f)
Microhabitat structure
Figure 1. Microhabitat use by Mogurnda adspersa in the Wet Tropics region (solid bars) and in south-eastern Queensland (open bars). Summaries derived from capture records for 387 individuals from the Johnstone and Mulgrave rivers in the Wet Tropics region and for 517 individuals from the Mary River, south-eastern Queensland, over the period 1994–1997 [1093].
occurring in mesohabitats with higher mean velocities (Fig. 1a and b, Table 3). It is most common in depths of between 30 and 60 cm and rarely occurs in depths less than 10 cm or greater than 80 cm (Fig. 1c). It may be found over a range of relative depths but most commonly occurs in the lower one-third of the water column. This species was most frequently collected over areas of mud and sand reflecting the distribution of these elements in those sites in which it was most abundant. It was never recorded distant from cover, rather it is highly dependent on bankside structures such as root masses and submerged, emergent or overhanging vegetation. A pronounced dependency on cover enables this species to inhabit reaches of high gradient and elevated average velocities.
Microhabitat use In streams of the Wet Tropics region, M. adspersa occurs most frequently in areas of low water velocity despite
549
Freshwater Fishes of North-Eastern Australia
tolerant of a wide range of temperatures: populations from south-eastern Queensland have been collected at temperatures ranging from 11.9 to 31.7°C, whereas those in rainforest streams of the Wet Tropics have been collected over a smaller range (13.3–29.7°C). Other reports include temperatures ranging from 10.5°C [228] up to 34°C [513, 936]. Laboratory experiments revealed that M. adspersa from south-eastern Queensland lost orientation at 6.5°C and moved only spasmodically at 6.1°C [95]. Ham [502] also conducted temperature tolerance experiments on juvenile M. adspersa from south-eastern Queensland (actual lengths of fish not stated). Fish acclimated for seven days at 15°C were observed to lose orientation at temperatures of about 4°C and ceased movement completely at about 3°C [502].
In rivers of south-eastern Queensland, M. adspersa was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b) reflecting the pattern observed in mesohabitat use. This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 1c). A benthic species, it occupies the lower half of the water column, most commonly in direct contact with the substrate (Fig. 1d). Although not a schooling species, loose aggregations of 5–10 individuals are sometimes collected from the same microhabitat location [1093]. It is found over a wide range of substrate types but most often over fine and coarse gravel (Fig. 1e). This species was most frequently collected within 1 m of the stream-bank (65% of 517 fish collected), and was always found in close association with some form of submerged cover (Fig. 1f). It was most frequently collected near leaflitter beds, aquatic macrophytes, filamentous algae, submerged marginal vegetation and small woody debris (Fig. 1f).
Mogurnda mogurnda in the Alligator Rivers region has been collected from waters in which temperatures ranged from 24–35°C (bottom), 2.9–5.5 mg O2.L–1, pH of 3.9–6.7, conductivities of 4–60 µS.cm–1 and Secchi depths of 1–190 cm [193]. The 96-hour LC50 for uranium of M. mogurnda is 1.11 and 1.46 mg/L for larvae and juveniles, respectively [263]. Acute toxicities to uranium have also been reported as 1.57 and 3.29 mg.L–1 for larvae and juveniles, respectively [592].
In the Wet Tropics region, larvae show a marked preference for low flow environments (mean water velocities <0.1 m.sec–1) and depths between 10 and 40 cm. Larvae aggregate close to the stream margins, within the upperthird of the water column and also show a strong preference for areas of dense cover (especially submerged root masses) [1109].
Table 5. Physicochemical data for Mogurnda adspersa in the Wet Tropics region and south-eastern Queensland over the period 1994 to 2003 [1093] (the number of sites from each study is given in parentheses).
Environmental tolerances Little quantitative data concerning the environmental tolerances of M. adspersda is available (Table 5). It has been collected over a relatively wide range of physicochemical conditions and appears to tolerate low dissolvedoxygen concentrations (minimum recorded dissolved oxygen level in south-eastern Queensland is 0.6 mg.L–1) and moderately acidic to basic (range 5.6–8.8) water conditions in both the Wet Tropics region and south-eastern Queensland (Table 5). The maximum turbidity at which this species has been recorded in south-eastern Queensland is 200 NTU, but it appears to prefer less turbid waters (mean 5.8 NTU). Similarly, streams of the Wet Tropics region in which this species occurs tend to have low levels of suspended sediment (Table 5). We have collected this species in freshwaters up to 2495 µS.cm–1 conductivity, however the reported occurrence of this species in estuarine conditions [513] suggests it can tolerate high salinities. Nevertheless, increasing salinities have been implicated in the decline of populations inhabiting lakes near Mildura, Victoria [965]. Experimental acute and chronic LD50s for salinity have been observed as 14.8 ppt and 17.1 ppt, respectively [311, 641]. Populations of this species in the Wet Tropics region occur in very freshwater and are unlikely to tolerate elevated salinities. It appears
Parameter
Min.
Max.
Wet Tropics region (n = 140) Water temperature (°C) 13.3 Dissolved oxygen (mg.L–1) 4.9 pH 5.9 Conductivity (µS.cm–1) 13.3 Turbidity (NTU) 0.1
29.9 10.0 8.48 63.8 14.4
South-eastern Queensland (n = 179) Water temperature (°C) 11.9 31.7 Dissolved oxygen (mg.L–1) 0.6 12.8 PH 5.6 8.8 Conductivity (µS.cm–1) 72.0 2495.0 Turbidity (NTU) 0.2 200.0
Mean 22.5 7.16 7.14 36.4 3.4 19.8 7.3 7.5 654.5 5.8
Reproduction The reproductive biology and early development of M. adspersa is comparatively well studied [203, 228, 421, 424, 505, 513, 563, 755, 797, 1150, 1297] (Table 6). Details of reproduction in M. mogurnda are available in Bishop et al. [193] and are not repeated here. Both species spawn and complete their entire life cycle in freshwater and will breed in ponds and aquaria.
550
Mogurnda adspersa, Mogurnda mogurnda
and declines quickly thereafter. Such a spawning strategy is observed in many other small-bodied fishes in the region, with spawning coinciding with increasing water temperature (i.e. 20–22°C is exceeded from August to April or May), but most importantly coincides with a period of stable low flows with a reduced frequency of flooding.
In rainforest streams of the Wet Tropics region, male and female M. adspersa commence maturity (stage II) at approximately 55 mm SL although many fish of this length show no evidence of sexual maturation (Fig. 2). Sexual maturity and gonad recrudenscence are not associated with increasing size in rainforest streams M. adspersa, as they are in south-eastern Queensland (Fig. 5)
Reproductive stage 80
I
120
60 100
40
II
III
IV
V
Males (3) (8) (3) (5)
(2) (8) (18) (9) (1) (4) (4)
80
60
20 40
20
0 I
II
III
IV
V
Reproductive stage
0 120
Jan Feb Mar Apr May Jun
Females
Figure 2. Mean standard length (mm SL ± SE) for male and female Mogurnda adspersa within each reproductive stage. Fish were collected from the Johnstone and Mulgrave rivers over the period 1994 to 1998 [1093]. Sample sizes can be calculated from the data presented in Figure 3.
100
(8) (10) (16) (16)
Jul Aug Sept Oct Nov Dec
(1) (16) (25) (8) (13) (7) (8)
80
60
Temporal changes in gonad development were not wellexpressed in rainforest populations of M. adspersa; most identifiable males were at stage II only, irrespective of the time of the year and few females at stage IV or greater were collected (Fig. 3). Nonetheless, temporal changes in mean GSI levels were evident, with peak values occurring from July to October in females and from October to November in males (Fig. 4). Note that very few fully mature specimens of either sex were collected and the mean GSI values presented represent an underestimate of what might be maximum GSI values. The abundance of larval M. adspersa varies greatly throughout the year in rainforest streams of the Wet Tropics region [1109]. In upland locations (Dirran Creek), larvae are present but uncommon in September, abundant in October and November, and uncommon in December. In lowland streams (Mena Creek), small numbers of post-flexion larvae may persist until February but the majority of larvae are produced in October and November [1109]. These data and that shown in Figures 3 and 4 suggest that while stage II individuals may be present year-round, gonad recrudescence commences in July and peaks in October and November
40
20
0
Month Figure 3. Temporal changes in reproductive stages of Mogurnda adspersa in the Johnstone River, Wet Tropics region, during 1998 [1093]. Sample sizes for each month are given in parentheses.
Maturation commences at a moderate size in fish from the Mary River, south-eastern Queensland. Minimum and mean lengths of early developing (reproductive stage II) fish were 29.3 mm SL and 47.5 mm ± 1.8 SE, respectively for males and 26.1 mm SL and 42.4 mm ± 2.1 SE, respectively for females (Fig. 5). Females of equivalent reproductive stage were generally similar in size to males for populations from the Mary River, south-eastern Queensland (Fig. 5). Gonad maturation in both sexes was
551
Freshwater Fishes of North-Eastern Australia
Mogurnda adspersa has an extended breeding season from spring through to late summer in south-eastern Queensland, but spawning appears to be concentrated between November and February. In the Mary River, late developing fish (stage IV) were present almost year-round (Fig. 6). Gravid (stage V) males were present only in December and February, but gravid females were present from September to February and were most common from November to February. This phenology is in stark contrast to that observed in the Wet Tropics region.
5
4
3
2
1
Reproductive stage
0
I
II
III
IV
V
Month Males
Figure 4. Temporal changes in mean Gonadosomatic Index (GSI% ± SE) of Mogurnda adspersa males (open squares) and females (closed circles) in the Johnstone River, during 1998 [1093]. Sample sizes for each month are given in Figure 3.
100
(5) (5)
(11) (16) (9)
(5) (8) (10) (4)
(12) (10) (5)
(3) (7)
(4)
80 60
commensurate with somatic growth until stage IV and there was little difference between sexes in size at each reproductive stage (Fig. 5). The minimum recorded size for a gravid (stage V) male was substantially larger (56.2 mm SL) than that of a female (40.9 mm SL) ([1093], Fig. 5). Elsewhere, this species has been reported to mature at 45 mm and 49 mm for males and females, respectively [936].
40 20 0 Females 100
(11) (4)
(4)
(4) (4)
80
70
Males 60
Females
60
40 20
50
0
40
Month 30
20 I
II
III
IV
V
Figure 6. Temporal changes in reproductive stages of Mogurnda adspersa in the Mary River, south-eastern Queensland, during 1998 [1093]. Sample sizes for each month are given in parentheses.
Reproductive stage
Temporal patterns in reproductive stages mirrored those observed for variation in GSI values. Peak monthly mean GSI values (0.6% ± 0.1 SE for males, 5.6% ± 0.4 SE for females) occurred in December for males and January for females (Fig. 7). Females GSI vales were almost always
Figure 5. Mean standard length (mm SL ± SE) for male and female Mogurnda adspersa within each reproductive stage. Fish were collected from the Mary River, south-eastern Queensland, between 1994 and 1998 [1093]. Sample sizes can be calculated from the data presented in Figure 6.
552
Mogurnda adspersa, Mogurnda mogurnda
Overall sex ratios for M. adspersa (n = 133) from the Barron River have been reported as 0.96 females for every male [222]. The spawning stimulus for M. adspersa is unknown but is has been speculated that increasing water temperatures, increasing day length, the abundance of food and the availability of spawning sites may all be factors influencing the timing of spawning [513, 809]. Length-frequency data indicate that the smallest juvenile fish (less than 20 mm SL) were present in streams of south-eastern Queensland during summer and autumn–winter, suggesting that the development of a larval cohort can occur during elevated flow conditions experienced during this time (Fig. 8) [1093].
higher than those of males and remained elevated during the breeding season for longer (Fig. 7). The mean GSI of ripe (stage V) fish was 0.6 % ± 0.1 SE for males and 4.8 % ± 0.4 SE for females [1093]. 6
5
Males
Females
4
3
2
Spawning is reported to occur at temperatures ranging from 18°C to 34°C [203, 580, 755, 809, 1297]. Several accounts of the pre-spawning and spawning behaviour of fish in aquaria are available [203, 424, 505, 513, 1150]. The male can be very aggressive and is territorial when in breeding condition, usually remaining near a suitable site for spawning [513].
1 0
Month Figure 7. Temporal changes in mean Gonosomatic Index (GSI% ± SE) stages of Mogurnda adspsersa males (open circles) and females (closed circles) in the Mary River, south-eastern Queensland, during 1998 [1093]. Samples sizes for each month are given in Figure 6.
40
Spring (n = 416)
30
Summer (n = 464) Winter (n = 632)
20
10
Mogurnda adspersa is a repeat spawner with females capable of producing between 7–10 successive broods over a spawning season [424, 505]. Females can deposit anywhere between 100 and 1300 eggs in a spawning session which may last for several hours [203, 755, 797, 809, 936, 1297]. Total fecundity for M. adspersa collected from the Mary River has been estimated as ranging from 267–727 eggs (mean 465 ± 32, n = 23 fish) and 66–1778 eggs (mean 658 ± 64 , n = 32) for fish from the Wet Tropics region [1093]. Fecundity is significantly related to fish size; the regression equations for relationships between weight and fecundity are given in Table 6. Fish of 45 mm SL from the Mary River produced about 280 eggs in total, whereas fish of 75 mm SL produced about 640 eggs [1093]. Fecundity estimates for equivalent-sized fish from the Wet Tropics region are 386 and 893 eggs, respectively [1093]. Fish of 2 g from the Mary River produced about 300 eggs in total, whereas fish of 12 g produced about 650 eggs [1093]. Fecundity estimates for fish of equivalent size from the Wet Tropics region are 428 and 1019 eggs, respectively [1093]. The demersal eggs are transparent, distinctively elongated and pointed at both ends, with a sticky basal disc at one end allowing attachment to solid spawning substrates [424, 755, 809]. Eggs are relatively small relative to body size. The mean diameter of 137 intraovarian eggs from stage V fish from the Mary River was 1.03 mm ± 0.02 and that of 150 intraovarian eggs from stage IV and V fish from the Wet Tropics was 1.08 mm ± 0.05 [1093]. Water-hardened eggs vary in size from 2.0 to 3.8 mm long and 1.1 to 1.3 mm wide [580, 755, 809].
0
Standard length (mm) Figure 8. Seasonal variation in length–frequency distributions of Mogurnda adspersa, from sites in the Mary and Brisbane rivers, south-eastern Queensland, sampled between 1994 and 2000 [1093]. The number of fish from each season is given in parentheses.
553
Freshwater Fishes of North-Eastern Australia
until hatching and parental care of larvae may continue for a further 24 hours after hatching [424, 505, 1297]. A single male has been observed tending the various batches of eggs for up to three months [424, 505]. The incubation
Eggs are laid in rows forming a single circular or elongate cluster, and are deposited on rocks, woody debris, broadleafed aquatic plants and other hard substrates [424, 505, 936, 1297]. The male is reported to guard and fan the eggs
Table 6. Life history information for Mogurnda adspersa. Where available, reference is given to data from populations collected from south-eastern Queensland (SEQ) and northern Queensland (NQ) [1093]. Age at sexual maturity (months)
6 months [513, 936, 1093]
Minimum length of gravid (stage V) females (mm)
SEQ: 56.2 mm SL [1093]; NQ:54 mm SL [1093]
Minimum length of ripe (stage V) males (mm)
SEQ: 40.9 mm SL [1093]; NQ: no stage V males collected
Longevity (years)
Possibly at least 3 years in the wild [222]
Sex ratio (female to male)
0.96:1 [222]
Occurrence of ripe (stage V) fish
SEQ: spring and late summer (September–February) [1093]; NQ: few ripe fish found [1093]
Peak spawning activity
SEQ: Elevated GSI November and February [1093]; NQ: Elevated GSI between September and November [1093]
Critical temperature for spawning
? 18–34°C [203, 580, 755, 809, 1297]
Inducement to spawning
? Possibly a combination of some of the following factors: increasing temperature, increasing day length, abundance of food and availability of spawning sites [513, 809]
Mean GSI of ripe (stage V) females (%)
SEQ: 4.8% ± 0.4 (maximum mean GSI in January = 5.6% ± 0.4) [1093]; NQ: 6.7 % ± 4.9 (maximum GSI in October = 3.6% ± 0.8) [1093]
Mean GSI of ripe (stage V) males (%)
SEQ: 0.6% ± 0.1 (maximum mean GSI in December = 0.6% ± 0.1) [1093]; NQ: no stage V males collected [1093]
Fecundity (number of ova)
SEQ: Total fecundity = 267–727, mean = 465 ± 32[1093]; NQ: Total fecundity = 66–1778, mean = 658 ± 64 [1093]; Batch fecundity = 33–889, mean 228 ± 22 [1093] In aquaria, females reported deposit between 100–1300 eggs in a single spawning session [203, 755, 797, 809, 936, 1297]
Total Fecundity (TF) and Batch Fecundity (BF)/ SEQ: TF = 11.43 L – 234.96, r2 = 0.586, p<0.001, n = 24; TF = 33.947 W + Length (mm SL) or Weight (g) relationship (mm SL) 238.01, r2 = 0.574, p<0.001, n = 73 [1093]; NQ: TF = 16.35 L – 346.7, r2 = 0.258, p<0.01, n= 31; TF = 59.1 W + 310.3, r2 = 0.221, p<0.01, n = 30 [1093] Egg size (diameter)
SEQ: Intraovarian eggs from stage V fish = 1.03 mm ± 0.02 [1093]; NQ: Intraovarian eggs from stage IV and V fish = 1.08 mm ± 0.05 [1093]. Water-hardened eggs elongate, varying from 2.0–3.8 mm long and 1.1–1.3 mm wide [580, 755, 809]
Frequency of spawning
Repeat spawner over an extended breeding period. Can spawn 7–10 times over a spawning season [424, 505]
Oviposition and spawning site
Eggs deposited on rocks, woody debris, aquatic vegetation and other hard substrates [424, 505, 936, 1297]
Spawning migration
None known
Parental care
Male guards and fans eggs until they hatch, parental care of fry may be given for a further 24 hours after hatching [424, 505, 1297]
Time to hatching
Varies with temperature; 3 to 9 days (at 20–29°C) [228, 421, 513, 580, 809]; may take up to 14 days at low temperatures [203]
Length at hatching (mm)
Newly hatched prolarvae 5.5 mm SL [1214]
Length at free swimming stage
Postlarvae 3.2–5.0 mm TL [1214]
Age at loss of yolk sack
Usually 6.5 days but ranges between 1–1.5 days [228] and 17 days [809]
Age at first feeding
As above
Length at first feeding
?
Age at metamorphosis (days)
? 10 mm TL (at 32 days) [513], 25 mm TL (at 60 days) [1297]
Duration of larval development
?
554
Mogurnda adspersa, Mogurnda mogurnda
period varies with water temperature and is reported to range from three to nine days at temperatures between 20 and 29°C [228, 421, 513, 580, 809], and may take up to 14 days at low temperatures [203].
be examined. Substantial temporal changes in abundance have been reported in this species and have been interpreted as being due to movements to and from refuge habitats [203, 222]. This species has been recorded on land following a severe thunderstorm in Brisbane, south-eastern Queensland, possibly as a result of a whirlwind [1018]. However, the large size of the fish reported (98 mm TL) suggests that this movement may have been via surface waters that subsequently contracted and stranded the fish. A short-term (16 days) mark-recapture study examining local movements of M. adspersa in a small tributary of the Barron River revealed that this species undertakes frequent small-scale movements [222]. The study area consisted of 30 pools interspersed with partial barriers (riffles and a small 2.6 m cascading waterfall) within a 1 km stream reach. Thirty-nine of 92 individuals marked and released were recaptured at least once in the study area. No difference in the frequency of upstream or downstream movements was observed and no significant effect of fish size on the spatial scale of movements was observed. Male fish showed a slight tendency to move larger distances than females; the median number of pools moved per day was 0.7 for males and one male moved 17 pools within a single day; females tended to move very little during the study. Sex-specific differences in movement patterns observed during the April study period were attributed to prespawning behaviour with males suggested to be searching for suitable spawning substrates in anticipation of the impending spawning season [222].
Larvae are 3.2–5.0 mm long at hatching and usually have pigmented eyes. Substantial variation in growth rates has been reported for larvae and juveniles maintained in aquaria [222, 228]. The yolk is usually fully absorbed after 6.5 days (but may take as short as 1–1.5 days [228] or as long as 17 days [809]), at which time feeding commences [228, 580, 755, 809, 936]. Larvae at this stage possess about five rows of melanophores forming longitudinal bands and the continuous fin-fold has divided into individual fins [809]. Juveniles 12–20 mm long have visible opercular stripes [580]. They have been reported to grow to 10 mm after six weeks, [513], 25 mm after two months [1297] and 50 mm at 6–7 months, at which time males and females can be distinguished [513]. The life-span of M. adspersa is unknown but three year-classes have been discerned from length–frequency data of wild populations [222]. Lifespan in aquaria is probably longer. Movement There is little information on the movement biology of M. adspersa. Like many other freshwater eleotrids, juveniles and subadults of this species may have a facultative mass dispersal phase, although there are few reports of this in the literature. It is rarely reported as having been collected in fishway studies. An unknown number of juvenile and adult M. adspersa (misidentified as M. mogurnda) were observed moving upstream through the Claire Weir fishway on the Burdekin River in January during high summer discharges [586]. A single fish was collected ascending a fishway on the Burnett River barrage (timing not stated) [1173]. Cotterell [332] suggested that both Mogurnda species move between December and April but the source of this information was not stated. Mogurnda mogurnda has been observed migrating in Magela Creek in the Alligator Rivers region of the Northern Territory, but in low numbers only [190]. Bishop et al. [193] report observing M. mogurnda climbing vertical wet surfaces around waterfalls and suggested that this ability may allow this species to colonise headwaters above apparently insurmountable waterfalls. In rivers of the Wet Tropics region M. adspersa commonly occurs upstream of potential barriers to movement such as cascades and waterfalls, leading Pusey and Kennard [1085, 1087] to speculate that this species was a good coloniser, capable of negotiating such potential barriers. However, in light of the substantial genetic differentiation between populations in streams systems of close proximity due to drainage re-arrangement [617], the generality of this speculation may need to
Trophic ecology Diet data for M. adspersa is available for individuals sampled from rivers and streams in the Wet Tropics region of northern Queensland [599, 1097], central Queensland [1080], and south-eastern Queensland [80, 205, 863]. Diet data for M. mogurnda is available for individuals sampled from floodplain habitats in the Alligator Rivers region in the Northern Territory [193] and from eastern Cape York Peninsula [1099]. Mogurnda adspersa is a microphagic carnivore, consuming a broad range of prey items from the benthos, water column and the water surface (Fig. 9). Aquatic insects comprised the largest proportion of the total mean diet in all studies (58.2%). Terrestrial invertebrates (12.3%) were also relatively important prey items, particularly in small streams of the Brisbane Region [80]. Molluscs (7.3%), microcrustaceans (4.1%) and macrocrustaceans (3.5%) formed relatively minor components of the diet in most studies. This species occasionally consumes fish (including Gambusia holbrooki [580] and fish eggs [599]), aerial forms of aquatic insects and algae (diatoms and desmids) (Fig. 9). Other studies of this species in northern Queensland [1378] and south-eastern Queensland [917] report a generally similar diet to that
555
Freshwater Fishes of North-Eastern Australia
of feeding on infusorians, rotifers, brine shrimp and zooplankton [797].
described above; this species is also reported to prey upon tadpoles [270]. The alien fish Perca fluviatilis is reported to prey upon M. adspersa [936]. Fish (0.9%) Microcrustaceans (4.0%) Macrocrustaceans (3.5%)
Unidentified (7.5%)
Molluscs (7.3%)
Terrestrial invertebrates (12.3%)
Other macroinvertebrates (3.3%) Aerial aq. Invertebrates (1.5%) Terrestrial vertebrates (0.1%) Terrestrial vegetation (0.2%) Detritus (0.3%) Algae (1.0%)
Aquatic insects (58.0%)
Figure 9. The mean diet of Mogurnda adspersa. Data derived from stomach content analysis of 642 individuals from eastern Cape York Peninsula [599], the Wet Tropics region of northern Queensland [1097], central Queensland [1080], and southeastern Queensland [80, 205, 863].
Mogurnda mogurnda has a similarly broad diet to that described above for M. adspersa. This species is a microphagic carnivore, with aquatic insects (67.5%) dominating the total mean diet (Fig. 10). Microcrustaceans (9.8%) were also relatively important, perhaps not surprising as most fish were collected from slow-flowing floodplain habitats in which zooplankton production is likely to be high. Macrocrustaceans (2.9%), terrestrial invertebrates (2.4%), molluscs (1.9%) and fish (1.4%) were also consumed. Other studies of this species in the Northern Territory [644, 1064] and Papua New Guinea [625] have reported generally similar diets. No information on the trophic ecology of larval Mogurnda spp. is available, however larval fish in aquaria are capable Fish (1.4%) Microcrustaceans (9.8%)
Unidentified (11.4%) Terrestrial invertebrates (2.4%) Aerial aq. Invertebrates (0.7%) Terrestrial vegetation (0.4%) Detritus (0.6%) Algae (0.4%)
Macrocrustaceans (2.9%) Other macroinvertebrates (1.0%) Molluscs (1.5%)
Aquatic insects (67.3%)
Figure 10. The mean diet of Mogurnda mogurnda. Data derived from stomach content analysis of 275 individuals from the Alligator Rivers region, Northern Territory [193], and eastern Cape York Peninsula [1099].
556
Conservation status, threats and management Mogurnda adspersa has undergone substantial declines in distribution and abundance, especially throughout the southern portion of the Murray-Darling Basin. However, it is still widespread and relatively abundant in coastal drainages of eastern Australia. In 1993, Wager and Jackson [1353] listed M. adspersa as Rare, probably on the basis of declines in inland populations. This species was declared extinct in South Australia where it is listed as Protected by regulations under the Fisheries Act 1982. However, it was reportedly successfully reintroduced to the Murray Bridge area from a remnant population in Queensland (N. Austin (1999), cited in [965]). In Victoria it is listed as Critically Endangered [1004] and was presumed to be extinct in this State [1353] until an isolated population was discovered recently at Cardross Lakes near Mildura [1116, 1117]. However, these populations have not been found in recent surveys [1114, 1115, 1118, 1119, 1120, 1121] and it is again thought to be extinct in Victoria (T. Raadik, pers. comm.). Prior to 2000, M. adspersa was not listed as being of conservation significance in New South Wales or Queensland, but Morris et al. [965] recently recommended that it be upgraded to Endangered in New South Wales and Rare in southern inland waters of Queensland. This species is widespread and relatively common in coastal catchments of Queensland and so does not warrant an elevated conservation status in these areas. In New South Wales, western populations of this species have recently been declared as Endangered under the New South Wales Fisheries Management Act 1994 [1006]. Under this Act, M. adspersa is also listed as a member of an Endangered Ecological Community in the lower Murray River [1005] and in the lowland catchment of the Darling River [329]. Morris et al. [965] recommended that the conservation status of M. adspersa be listed as Endangered in the IUCN Red List of Threatened Species, Vulnerable under the National Environment and Protection and Biodiversity Act 1999, and Vulnerable under the Australia Society for Fish Biology listing of the conservation status of Australian Fishes [117]. However, at the time of writing this text (December 2003) this species is not listed in the IUCN Red List and is listed as Lower Risk–Least Concern in the most recent (2003) listing by the ASFB [117]. Mogurnda mogurnda was listed as Non-Threatened by Wager and Jackson in 1993 [1353] and it still appears to be relatively common throughout its range in northern Australia. The genetic distinctiveness of some populations in north-eastern Queensland, may however require management as evolutionarily distinctive units.
Mogurnda adspersa, Mogurnda mogurnda
Although little is known of movement patterns, M. adspersa appears to make upstream dispersal movements, suggesting that it may be sensitive to barriers caused by weirs and impoundments.
Potential threats to M. adspersa in the Murray-Darling Basin are suggested to include those associated with alien fish species (particularly Gambusia and redfin), habitat degradation (particularly loss of aquatic plants), flow regulation (particularly rapid fluctuations in water levels that may impact on reproduction and recruitment by exposing fish eggs), and degraded water quality [412, 965]. Similar threats to this species probably exist throughout much of its range in Queensland coastal rivers.
Mogurnda adspersa appears to be tolerant of elevated salinities (acute and chronic LD50s of 14.8 ppt and 17.1 ppt salinity [311, 641]), but increasing salinities have been implicated in the decline of populations inhabiting lakes near Mildura, Victoria [965].
The translocation of sleepy cod (Oxyeleotris lineolatus) into river basins from which it is otherwise not naturally present or into reaches in which it does not occur due to the presence of natural barriers, may pose some threat to Mogurnda species. This large predator has had a negative impact on M. adspersa in the Burdekin River (see chapter on O. lineolatus).
Catchment and riparian disturbances that disrupt cover elements of aquatic habitat (e.g. aquatic macrophytes, filamentous algae, leaf-litter beds, root masses and undercut bank) may impact on this species. Mogurnda adspersa is susceptible to the fungus Saprolegnia at low water temperatures (<16oC) [203]. Fungal infections are common during winter in M. adspersa populations occurring in streams of the Atherton Tablelands [1093]. This species is known to be infected naturally by the adult digenic trematode parasite Opecoelus variabilis (Opecoelidae) where it acts as a definitive host [338, 339]; it is also second intermediate host to Stemmatostoma pearsoni (Cryptogonimidae) [339]. It has been found to be naturally infected by the larval stage of the strigeate trematode Diplostomum spathaceum [185, 669] and by several nematodes [185, 668].
Rapid fluctuations in water levels resulting from river regulation in Barker-Barambah Creek, a tributary of the Burnett River, south-eastern Queensland may be deleterious to successful reproduction and recruitment [76]. In this study, poor recruitment was observed at regulated sites which were subject to frequent rises and falls in water level due to short-term water releases and subsequent abstraction for irrigation during the months of peak spawning activity. In contrast, successful recruitment was observed at unregulated sites nearby. Fish in sites subject to regulation also had substantially lower mean condition factors than those from unregulated sites [76].
Dove [1432] provided a list of parasite taxa recorded from M. adspersa in south-eastern Queensland.
557
Philypnodon grandiceps (Krefft, 1864) Flathead gudgeon
37 429002
Family: Eleotridae
compressed posteriorly. The head is relatively large, broad and dorsally flattened; the snout is sharply rounded; the cheeks are broad, becoming bulbous in large males. Moderately large eyes are positioned close together high on sides of the head near the dorsal profile and separated by an interorbital space greater than one eye diameter. The mouth is large, slightly oblique and upturned with the gape reaching back to at least the middle of the eye, often further. Rows of small pointed (villiform) teeth are present on both jaws. Tip of tongue slightly notched. No spines on head or body. Gill openings broad, lower margin extending forward on ventral surface of head to below eyes. The body is covered with moderate-sized ciliated scales. Predorsal scales variable in extent, nearly to eyes except in northern populations in which they reach only to the area above preopercle, no scales on cheeks or opercula. Cycloid scales on belly. Lateral line absent. Numerous rows of papillae across head, lower jaw and operculum. Two separate dorsal fins; the first is rounded with notches between spines, origin well behind level of pelvic fin bases; the second is larger, elongate, with posterior rays longest. Anal fin similar to second dorsal fin and positioned opposite or just posterior to second dorsal fin origin. Anus positioned just before anal fin origin. Pectoral fins rounded, broad and large. Pelvic fins thoracic, originating just
Description First dorsal fin: VI–VIII (usually VII); Second dorsal: I, 8–10 (usually 9); Anal: I, 7–10; Pectoral: 16–20 (usually 18–19); Pelvic: I, 5; Caudal: 15 segmented rays; Vertical scale rows: 33–44 (33–34 [34, 52], 38–44 [936]); Horizontal scale rows: 12; Gill rakers on first arch: 14–20 (usually 16–18) (11–12 on lower limb [1012], 13 for individuals from south-eastern Queensland [1093]); Vertebrae: 29 (29–30, rarely 31 [460]) [34, 52, 270, 460, 580, 741, 936, 1093]. Figure: mature male specimen of P. grandiceps, 73 mm SL, Mary River at Amamoor Creek, September 1995; drawn 2002. Philypnodon grandiceps is a small-sized gudgeon known to reach 120 mm TL but more commonly 80 mm TL [936]. Of 769 specimens collected in streams of south-east Queensland over the period 1994–2000 [1093], the mean and maximum length of this species were 41 and 82 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 167 individuals (range 32–74 mm SL) from the Mary and Albert rivers, south-eastern Queensland is W = 0.8 x 10–5 SL3.227, r = 0.964, P<0.001 [1093]. Philypnodon grandiceps has an elongate body, depressed anteriorly, cylindrical at the mid-point, becoming 558
Philypnodon grandiceps
before pectoral fin insertions, elongate, pointed and small; fin bases entirely separate but close together. Caudal fin rounded, broad and moderately large. The caudal peduncle is deep and slender [34, 270, 460, 580, 775, 936].
genera – Mogurnda and Gobiomorphus [186]) are distinguished from other eleotrids in having an interneural gap (an interneural space without a pterygiophore) between the two dorsal fins [577].
Colour varies considerably depending on size and habitat. Head and body vary from black, grey, brown, reddishbrown to greenish-brown dorsally, fading to yellowish ventrally. Irregular, faint, darker blotches on dorsal and lateral surfaces; blotches on sides sometimes forming irregular broken midlateral stripe. May also have four to five thin dark lines on sides of belly. A faint transverse bar sometimes present on dorsal surface just before first dorsal fin origin. Up to four dark bars radiate from eye. Dorsal and caudal fins with transverse dark bands or rows of dark brownish-orange spots, two horizontal rows on first dorsal, three horizontal rows on second dorsal, and five to seven vertical rows on caudal fin forming thin bands; fins otherwise clear to yellowish, translucent. Two stripes present on anal fin, the innermost thinner. Pectoral and pelvic fins yellowish to grey; a faint bar at pectoral fin base. A characteristic dark blotch is usually present at caudal fin base. All bands and spots on fins and body may be very faint. Preserved colouration generally similar to that described above but less colourful [34, 460, 580, 775, 936].
The systematics of Philypnodon has a confused history, probably due in large part to the marked sexual dimorphism and considerable ontogenetic and spatial variation in morphology evident in the two notional species of this genus. Bleeker [201] established the genus Philypnodon to contain Eleotris nudiceps Castelnau 1872 [285]. Waite, 1904 [1355] considered two other genera, Gymnobutis Bleeker, 1874 [201] and Ophiorrhinus Ogilby, 1897 [1012] to be synonymous with Philypnodon and listed the following species as synonymous with P. grandiceps: Eleotris grandiceps Krefft, 1864 [741]; Eleotris gymnocephalus Steindachner, 1866 [1261]; Gymnobutis gymnocephalus Bleeker, 1874 [201]; Ophiorrhinus grandiceps Ogilby, 1897 [1012] and Ophiorrhinus angustifrons Ogilby, 1898 [1013]. McCulloch and Ogilby [880] agreed with these designations but continued to recognise a second species, P. nudiceps, with which the following were considered synonymous: Eleotris (Philypnus) nudiceps Castelnau, 1872 [285]; Philypnodon nudiceps Bleeker, 1874 [201] and Ophiorrhinus nudiceps Ogilby, 1897 [1012]. Subsequently, Hoese et al., 1980 [580] considered P. nudiceps to be synonymous with P. grandiceps. Gomon et al., 1994 [460] also lists Eleotris melbournensis Sauvage, 1880 [1196] as synonymous with P. grandiceps.
Philypnodon grandiceps is distinctly sexually dimorphic: mature males have a larger mouth reaching to at least below rear of pupil, in females it extends only as far back as the anterior margin of the eye. Males also have a more bulbous head, broader interorbital space and larger pelvic fins than females. Urinogenital papilla similar in the two sexes but breeding females develop several flaps around opening of elongate papilla, while males have only small bumps around opening. During breeding season, males may become very dark and display more vibrant fin markings [270, 580, 775]. Philypnodon grandiceps is similar in general appearance to Philypnodon sp., especially juveniles and subadults. Distinguishing characteristics of P. grandiceps include 16–20 (usually 18–19) pectoral fin rays, 14–20 gill rakers (11–13 on lower limb), lower margin of gill opening extending forward on ventral surface of head to below eyes, and black blotch sometimes present on caudal fin base. Systematics Philypnodon Bleeker (1874) [201] contains two notional Australian species, P. grandiceps and another, as yet undescribed, species known as the dwarf flathead gudgeon. The genus Philypnodon is endemic to Australia. Two New Zealand species of Gobiomorphus (G. breviceps and G. hubbsi) were formerly placed within the genus Philypnodon [886]. Philypnodon (together with the related 559
Distribution and abundance Philypnodon grandiceps is a relatively widespread species occurring in coastal and inland drainages of eastern and southern Australia. This species occurs in coastal catchments from central Queensland, south through New South Wales and Victoria and west to at least the Gawler River, near Adelaide in eastern South Australia. Inland, it occurs throughout much of the Murray Basin and is patchily distributed in the Darling Basin. It is also present on Kangaroo Island (South Australia) and along the north coast of Tasmania [52, 56, 245, 423, 506, 553, 574, 607, 775, 778, 817, 1201]. In central Queensland, P. grandiceps has been recorded as far north as the Burdekin River near Townsville [755, 940, 1082] where it is very uncommon, only a few individuals having been collected from two widely separated locations [940, 1082]. The next most northerly record for this species is approximately 150 km further south in the Pioneer River near Mackay [658] where it was abundant. It has also been recorded a further 300 km south in small streams draining into Shoalwater Bay where it was recorded as common [1328]. It appears to be widespread
Freshwater Fishes of North-Eastern Australia
P. signifer, M. duboulayi, C. marjoriae, H. klunzingeri and H. galii. It was the 21st most important species in terms of biomass, forming only 0.1% of the total biomass of fish collected. This species is never common or widespread in individual rivers of south-eastern Queensland: the highest relative abundance observed was in the Brisbane River (1.5% of the total abundance) and it was most widespread in the Mary River (present at 42% of locations sampled). Across all rivers, average and maximum numerical densities recorded in 168 hydraulic habitat unit samples (i.e. riffles, runs or pools) were 0.25 individuals.10m–2 and 9.27 individuals.10m–2, respectively. Average and maximum biomass densities at 121 of these sites were 0.45 g.10m–2 and 4.68 g.10m–2, respectively. Highest numerical densities and biomass densities were recorded from the Brisbane River and streams of the South Coast Basin, respectively.
and relatively common throughout much of the Fitzroy Catchment [160, 404, 405, 658, 659, 942, 1351], and has also been collected in Baffle Creek [1110] and the Kolan River [658]. Philypnodon grandiceps is moderately common and widely distributed in south-eastern Queensland. It has been recorded from the Burnett River [11, 205, 237, 565, 658, 1173, 1276], Elliot River [825], Gregory River [157], Isis River [7], Burrum River [736] and the Mary River [158, 159, 162, 643, 658, 660, 1093, 1234]. It is patchily distributed in streams of the Sunshine Coast region, but has been recorded from the Noosa River [643], Maroochy River [1093, 1349], Mellum Creek [1349], Beerburrum Creek [768] and the Caboolture River [1093]. From the Pine River south, it is present in most major streams and rivers to the Queensland–New South Wales border [61, 643, 699, 704, 709, 1093, 1255, 1349]. This species has also been recorded from North Stradbroke Island off the south-eastern Queensland coast [988].
Philypnodon grandiceps appears to be relatively common and widespread in coastal catchments of New South Wales [82, 282, 437, 441, 443, 484, 814, 1066, 1067, 1201] and Victoria [148, 245, 270, 272, 497, 498, 499, 642, 733, 910, 911, 1111, 1112]. It is patchily distributed but common in coastal South Australia, occurring at least as far west as the Gawler River [238, 506, 574]. It also occurs in northern Tasmania where it is thought to be rare [423, 775]. Inland, it is present throughout much of the Murray Basin [56, 607, 817] where it was historically common [778], particularly in the upper Lachlan River [749]. More recently, it is reported as being very common in the lower Murray River at Lindsay Island [930] and in the Campaspe River [613, 1217]. It is patchily distributed in the Darling Basin (but probably not present within the Queensland section of the upper Darling Catchment) [553, 817, 1201]. A recent assessment of the status of freshwater fish in New South Wales reported that P. grandiceps has undergone reductions in distribution and abundance in the
In a review of existing fish sampling studies in the Burnett River, Kennard [1103] noted that Philypnodon spp. had been collected at 18 of 63 locations surveyed (12th most widespread species in the catchment) and formed 4.75% of the total number of fishes collected (sixth most abundant). Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New South Wales border [1093] collected a total of 1,137 individuals of P. grandiceps and it was present at 21% of all locations sampled (Table 1). Overall, it was the 16th most abundant species collected (0.7% of the total number of fishes collected) and was relatively uncommon at sites in which it occurred (2.9% of total abundance, 11th most common species). In these sites, P. grandiceps most commonly occurred with the following species (listed in decreasing order of relative abundance):
Table 1. Distribution, abundance and biomass data for Philypnodon grandiceps in rivers of south-eastern Queensland. Data summaries for a total of 1137 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance Rank abundance % biomass Rank biomass
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
21.1
42.0
6.9
15.0
14.4
22.1
30.0
0.70 (2.86)
0.62 (1.80)
0.23 (3.70)
0.74 (5.47)
1.50 (12.61)
0.40 (2.53)
0.37 (2.94)
16 (11)
16 (11)
15 (8)
13 (4)
15 (3)
13 (11)
15 (7)
0.12 (0.67)
0.12 (0.59)
—
—
0.23 (2.86)
0.11 (0.63)
0.26 (4.35)
21 (8)
17 (11)
—
—
16 (4)
14 (8)
9 (2)
Mean numerical density (fish.10m–2)
0.25 ± 0.06
0.18 ± 0.02
0.05 ± 0.01
0.25 ± 0.09
0.76 ± 0.47
0.18 ± 0.04
0.07 ± 0.03
Mean biomass density (g.10m–2)
0.45 ± 0.06
0.38 ± 0.05
—
—
0.70 ± 0.50
0.52 ± 0.13
1.00 ± 0.00
560
Philypnodon grandiceps
ern Queensland it occurs at low to moderate elevations (0–160 m.a.s.l.) but most commonly at less than 60 m.a.s.l. (Table 2). This species occurs throughout the major length of streams and rivers, ranging between 8 and 292 km from the river mouth. It is present in a wide range of stream sizes (range = 1.8–38.0 m width) but is more common in streams of intermediate width (10–15 m) and with low to moderate riparian cover (<40%). In rivers of south-eastern Queensland, P. grandiceps most commonly occurs in pools and runs characterised by low gradient (weighted mean = 0.09%), moderate depth (0.40 m weighted mean depth) and low mean water velocity (weighted mean 0.12 m.sec–1) but can occur in shallow, high velocity (maximum 0.87 m.sec–1) riffle habitats (Table 2). This species is most abundant in mesohabitats with substrates of intermediate to coarse particle size (fine gravel, coarse gravel, cobbles and bedrock). This species was most frequently collected where submerged aquatic macrophytes, filamentous algae, leaf-litter beds, undercut banks and root masses are common. Elsewhere, this species has been classified as a riffle-dwelling species [553, 1200]. It has also been reported to prefer slow-flowing stretches of river [642] and quiet waters, particularly lakes and dams [580]. Larvae were extremely abundant in runs and pools in regulated sections of the Campaspe River (a tributary of the Murray River, north-western Victoria) [615].
Murray-Darling Basin [710] and is now considered by some researchers to be quite rare in the basin [1200, 1201]. In inland Victoria, it is also present in the Wimmera Catchment [57, 65, 642]. Macro/mesohabitat use Philypnodon grandiceps occurs in a variety of lotic and lentic habitats including small coastal streams, throughout large rivers and their floodplain habitats (billabongs and wetlands), inland saline lakes and coastal wetlands. Although usually found in freshwater habitats, it is also common in brackish and estuarine waters [158, 301, 434, 446, 460, 658, 806, 817, 1059, 1060, 1062, 1066, 1067, 1276, 1397]. Philypnodon grandiceps usually occurs at low elevations, but has been recorded at elevations up to 700 m.a.s.l. in rivers of coastal New South Wales [553], 440 m.a.s.l. in coastal Victoria [642] and 520 m.a.s.l. in the MurrayDarling Basin [553]. In rivers and streams of south-eastTable 2. Macro/mesohabitat use by Philypnodon grandiceps in rivers of south-eastern Queensland. Data summaries for 1137 individuals collected from samples of 168 mesohabitat units at 63 locations undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions. Parameter
Min.
Max.
Catchment area (km2) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
22.5 7.0 8.0 0 1.8 0
9734.3 260.5 292.0 160 38.0 86.1
Gradient (%) 0 Mean depth (m) 0.10 Mean water velocity (m.sec–1) 0
2.33 1.08 0.87
Mean
Microhabitat use In rivers of south-eastern Queensland, P. grandiceps was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b) reflecting the pattern observed in mesohabitat use. This species was collected over a wide range of depths, but most often between 10 and 60 cm (Fig. 1c). A benthic species, it occupies the lower half of the water column, most commonly in direct contact with the substrate (Fig. 1d). Although not a schooling species, loose aggregations of up to 10 individuals are sometimes collected from the same microhabitat location [1093]. It is found over a wide range of substrate types but most often over sand, fine gravel and coarse gravel (Fig. 1e). This species was most frequently collected within 1 m of the stream bank (59% of 233 fish collected), and was always found in close association with some form of submerged cover (Fig. 1f). It was most frequently collected near leaf-litter beds, but was also found close to large and small woody debris, undercut banks, submerged root masses, aquatic vegetation and the substrate (Fig. 1f).
W.M.
806.1 5515.5 57.7 168.0 134.9 108.7 61 29 10.6 14.7 39.1 16.6 0.22 0.47 0.10
0.09 0.40 0.12
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
76.4 100.0 58.5 66.2 65.8 44.0 76.0
6.1 26.9 22.1 25.0 14.6 3.3 2.0
7.8 14.6 15.8 22.8 17.1 2.8 19.2
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
62.5 62.0 26.7 65.7 11.1 90.0 30.3 17.1 87.5 100.0
10.6 7.7 1.3 6.5 0.8 14.9 6.6 4.5 18.2 23.1
16.7 10.7 1.1 4.5 1.7 10.9 4.8 3.4 11.7 14.3
Elsewhere, this species has been reported to often lie motionless on the substrate, prefers areas with abundant cover and is often found in close association with mud, rocks, logs and aquatic vegetation [270, 642, 814]. It is reportedly also capable of rapid bursts of movement over short distances if disturbed or when pursuing prey [270]. 561
Freshwater Fishes of North-Eastern Australia
80
(a) 80
60
60
40
40
20
20
0
0
20
sendentary habits in older individuals [434]. Marked diel variation in larval size distributions was also evident, with small larvae dominating the plankton net samples during the day and larger larvae dominating the catch at night. These data suggest that small larvae congregate in surface waters during the day and disperse from the surface at night, larger larvae doing the opposite. Gehrke [434] interpreted this as evidence of reciprocal vertical migration patterns associated with foraging and variations in prey availability (see section on trophic ecology).
(b)
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
Environmental tolerances Information on tolerance to water quality extremes is lacking and the data listed below (Table 3) reflect the water quality of aquatic habitats in which P. grandiceps has been collected (see above).
60 15 40
10 5
20
0
0
Total depth (cm) 30
(e)
20 10
Table 3. Physicochemical data for Philypnodon grandiceps. Data summaries for 1050 individuals collected from 121 samples in south-eastern Queensland streams collected between 1994 and 2003 [1093].
Relative depth 20
(f)
15
Parameter
10
Water temperature (oC) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
5
0
0
Substrate composition
Min.
Max.
11.0 2.6 6.0 122.1 0.7
31.0 12.0 8.6 2495.0 36.0
Mean 20.4 7.8 7.7 586.3 5.4
Philypnodon grandiceps appears to be tolerant of a wide range of physicochemical conditions including low dissolved-oxygen levels (minimum 2.6 mg.L–1), mildly acidic waters (minimum 6.0), and high conductivity (maximum 2495 µS.cm–1). The recorded presence of juvenile and adult fish in saline lakes [301, 1059, 1060, 1062] and brackish and estuarine waters [158, 446, 658, 806, 912, 1066, 1067, 1276, 1397] suggests that this species is able to tolerate elevated salinities throughout much of its life cycle. It has been observed in salinities at least as high as 24.6 ppt [538] and experimental acute and chronic LD50s have been observed as 23.7 ppt and 40.0 ppt, respectively [311, 641]. The maximum turbidity at which this species has been recorded in south-eastern Queensland is 36 NTU, although it is likely to be able to tolerate much higher levels. Unlike other eleotrids (e.g. Gobiomorphus australis and Hypseleotris spp.), this species is not common in degraded urban streams of the Brisbane region [94, 95, 704, 709], suggesting that it may be sensitive to habitat degradation. However, this species was found to be present only where in-stream and riparian habitat conditions were considered to be degraded in the Lower Plenty River, Victoria [910]. Harris and Gehrke [553] and Gehrke and
Microhabitat structure
Figure 1. Microhabitat use by Philypnodon grandiceps. Data derived from capture records for 233 individuals in the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
Information on the microhabitat use of early life history stages is available. In a study of fish larvae in a billabong of the Murray River floodplain in Millewa Forest, Gehrke [434] found that eleotrid larvae (primarily those of P. grandiceps) were around nine times more common in midnight samples than in those taken at midday. Although larvae were much more common in plankton net samples than in pump samples, no significant differences in larval densities were observed between samples taken in open water, woody debris or beds of emergent vegetation (Typha spp.), irrespective of sampling method used. Larvae collected from emergent vegetation were significantly larger than those collected from other habitats, possibly reflecting a transition from pelagic to
562
Philypnodon grandiceps
Harris [438] classified P. grandiceps as tolerant of water quality and habitat degradation.
50
Reproduction The reproductive biology of P. grandiceps is comparatively well-studied (Table 4). This species spawns and can complete its entire life cycle in freshwater and has been bred in captivity [775, 809]. Despite frequently occurring in estuaries, it is not known to spawn in such habitats. Spawning is thought to occur in spring and summer in inland drainages and apparently through to autumn or winter in northern coastal rivers [580, 814, 936]. Humphries et al. [614] classified the life history style of this species in the Murray-Darling Basin as Mode 3a, characterised by an extended spawning period, but concluded that there was insufficient information to determine whether this species is a protracted, serial or repeat spawner. Serafini and Humphries [1217] reported that fish in a regulated section of the Campaspe River (a tributary of the Murray River, north-west Victoria) had a protracted spawning period with a peak in mid-spring to early summer (October to December) and larvae were present from spring through to autumn [615]. Pollard [1059] reported that fish in a central Victorian saline lake spawned in early spring. Llewellyn [814] reported that fish in New South Wales breed between October and March when water temperatures are above 18°C. The inducement for spawning is unknown but possibly involves a rise in water temperature. It has also been reported that a breeding response can be triggered by the provision of environmental flows but no details on the timing, magnitude or duration of these flows was given [385]. Spawning in ponds and aquaria has been reported to occur at temperatures between 21°C and 27°C and if the adults are well fed [755].
40
30
Spring (n = 126) Summer (n = 338) Autumn-Winter (n = 305)
20
10
0
Standard length (mm) Figure 2. Seasonal variation in length–frequency distributions of Philypnodon grandiceps, from sites in the Mary, Brisbane, Logan, Albert and Nerang rivers, south-eastern Queensland [1093]. The number of fish from each season is given in parentheses.
of larvae can occur when the likelihood of flooding is low, and the predictability of high temperatures and low flows are higher. These conditions are likely to increase the potential of larvae to encounter high densities of small prey, avoid physical flushing downstream due to high flows and thereby maximise the potential for recruitment into juvenile stocks [614, 615]. The length at first breeding for fish in the Campaspe River was reported to be 42–45 mm for females and 48–50 mm for males, and the maximum length of fish in reproductive condition was 92 mm for females and 78 mm for males [1217]. Fecundity for these fish ranged from 1400 to 2300 eggs, the number of eggs apparently increasing with fish size [1217]. Elaborate courtship displays prior to spawning have been observed in aquaria [1150]. Depending on the size of the female, fish in captivity have been reported to lay between 500 and 900 or 1000 demersal, adhesive eggs [270, 755, 809]. Eggs are attached in a single circular to oval cluster to a solid substratum such as a rock or piece of wood by means of a sticky basal mass. During spawning in aquaria, the male has been observed to hover in a stationary position adjacent to the eggs mass being deposited by the female, occasionally fertilising the eggs during her spawning activities. The male commences parental care of the eggs immediately following spawning, reportedly chasing away intruders and fanning the eggs with his pectoral fins, and this continues until the eggs
In Queensland rivers, P. grandiceps appears to have an extended breeding season from spring through to autumn, but concentrated in spring and summer. In the Pioneer River, central Queensland, Johnson [658] found that juveniles (actual fish sizes not reported) were abundant during sampling in October and December, and only adults were collected during June. In the Kolan River, juveniles were most common from October to December, but were also present in March and July. In the Burnett River, juveniles were present in samples during July but were common during December and April [658]. In rivers of south-eastern Queensland, juveniles less than 20 mm SL first appeared in freshwater samples in the summer months and individuals between 20–30 mm SL were most common in summer (Fig. 2). The extended breeding season (but with a concentration in spring and summer) of P. grandiceps throughout its range indicates that the spawning of adults and presence
563
Freshwater Fishes of North-Eastern Australia
mouth gape (0.24–0.51 mm) and limited mobility [614]. At 10 days, the larvae only have a single broken line of pigment ventral to the vertebral column and the fin-fold is still divided. It is reportedly difficult to rear larvae in captivity for longer than 10 days. The adult morphological characteristics become obvious at about six months [809, 814].
hatch [52, 755, 809, 936, 1150]. Each egg is clear, elongate or elliptical, pointed at the basal sticky end and blunt at the other [755, 809, 814]. Egg size varies from 1.5 mm to 2.2 mm long and 0.7 mm to 0.9 mm wide. Infertile eggs have been observed to turn white, become detached from the egg mass after several days and were eaten by the male. Hatching occurs four to six days after fertilisation. Newly hatched larvae are from 3.7 mm to 3.9 mm in length and usually have pigmented eyes. The oil globules in the yolk sac coalesce at hatching and the single oil globule is situated anteriorly in the yolk mass. The swim bladder is situated posterodorsally to the yolk sac and is well pigmented when larvae are three days old. The yolk sac is absorbed in about three days, at which time feeding commences [614, 809, 814, 1150]. The larvae are relatively small (3.7–5.3 mm SL) and undeveloped at this stage and have a small
Movement There is little information on the movement biology of P. grandiceps. Like many other freshwater eleotrids, juveniles and subadults of this species may have a facultative mass dispersal phase and instances of mass migrations between estuaries and freshwater have been recorded. There are several instances where juveniles and adults of this species have been recorded using riverine and tidal barrage
Table 4. Life history information for Philypnodon grandiceps. Age at sexual maturity (months)
?
Minimum length of ripe females (mm)
42–45 [1217]
Minimum length of ripe males (mm)
48–50 [1217]
Longevity (years)
?
Sex ratio (female to male)
?
Occurrence of ripe fish
?
Peak spawning activity
Concentrated in spring and summer but extends through to autumn or winter in northern coastal rivers [580, 814, 936]
Critical temperature for spawning
18°C [814]; in ponds and aquaria 21°C–27°C [755]
Inducement to spawning
? temperature [1093]
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
1400–2300, the number of eggs increasing with fish size [1217]. Depending on the size of the female, between 500 and 900 or 1000 demersal, adhesive eggs are laid [270, 755, 809]
Fecundity /length relationship
?
Egg size
Elongate, pointed at the basal sticky end and blunt at the other; 1.5 mm to 2.2 mm long, 0.7 mm to 0.9 mm wide [755]
Frequency of spawning
? extended spawning period but unknown whether protracted, serial or repeat spawner [614]
Oviposition and spawning site
Eggs are attached in a single cluster to a solid substrate such as a rock or piece of wood by means of a sticky basal mass [52, 755, 936]
Spawning migration
None known
Parental care
The male commences parental care of the eggs immediately following spawning, reportedly chasing away intruders and fanning the eggs with his pectoral fins, and this continues until the eggs hatch [52, 755, 936, 1150]
Time to hatching
After fertilisation, hatching takes four to six days [755]
Length at hatching (mm)
Newly hatched larvae are from 3.7 mm to 3.9 mm in length [755]
Length at free swimming stage
?
Length at metamorphosis (days)
?
Duration of larval development
?
Age at loss of yolk sack
3 days [809]
Age at first feeding
3 days [809]
Length at first feeding
3.7–5.3 mm SL [614]
564
Philypnodon grandiceps
fishways. Johnson [658] trapped P. grandiceps in pooloverfall type fishways on Bingara Weir (Burnett River) during December 1979 and Mt Crosby Weir (Brisbane River) (details on the timing of these movements are unclear). Johnson [658] also sampled juvenile and adult P. grandiceps at the spillway outwash on the Ben Anderson tidal barrage in the Burnett River. The river at this point is slightly brackish (up to 5 ppt, depending on river flow) as it is subject to tidal influence. Russell [1173] sampled large numbers (up to 16.5 fish per hour) of individuals (20–56 mm TL) descending a pool-weir type fishway on the same tidal barrage on two occasions during September 1986 but at no other time during weekly sampling over 21⁄2 years. In March 1999, Stuart and Berghuis [1276] sampled large numbers of fish moving downstream through a fishway on the same tidal barrage but did not sample them at any other time despite frequent sampling over the 11 ⁄2-year study period. These authors speculated that this apparently spasmodic mass migration downstream to the estuary might have been a short-term movement to access saline waters to kill an external freshwater ectoparasite (the copepod Lernaea sp.) that was observed to have infested all of the individuals examined. In the Mary River catchment, this species has also been collected downstream of a tidal barrage [158] and in a tidal barrage fishway [159] during summer. In a separate study in the same catchment, large numbers of juveniles and adults were collected at unspecified times at both locations, and juveniles were sampled in April descending a tidal barrage fishway [658]. Although juveniles and adults of this species have often been found downstream of tidal barrages and dams in lowland rivers (e.g. [442, 1319] and references cited above), access to estuarine areas is not an obligatory component of the life cycle of this species, and no significant difference in the size distribution of this species upstream and downstream of large barriers has been observed (e.g. [859]). Hence the movement pattern of P. grandiceps may be classified as facultative potamodromy and/or facultative semi-amphidromy. There is no quantitative data on the stimulus for movement of this species. Cotterell and Jackson [333] suggested that P. grandiceps in the Fitzroy River, central Queensland, would move ‘anytime there is a flow between August and April’, although the source of this information was not given. In the Burnett and Mary rivers, southeastern Queensland, tens to hundreds of fish have been observed aggregating in pools immediately downstream of obstructions to movement (e.g. culverts and weirs) soon after rises in discharge during late spring, suggesting that P. grandiceps undergoes upstream dispersal/recolonisation movements cued by elevated flows [1093]. A similar phenomenon was observed for this species in the Fitzroy
River [1351]. Humphries et al. [615] collected numerous larvae of P. grandiceps during drift-net sampling in the Campaspe River and postulated that this species utilised larval drift as a facultative dispersal mechanism. This species has also been recorded as having fallen to the ground in rain at Warwick, south-eastern Queensland, possibly as a result of a whirlwind [1037]. Trophic ecology Quantitative dietary information for P. grandiceps is available for 145 individuals from studies in the Burnett River, south-eastern Queensland [205], Tweed River, northern New South Wales [1133], and Lake Modewarre, southwestern Victoria [1062]. Philypnodon grandiceps is a microphagic carnivore, probably consuming prey primarily from the benthos. Aquatic insects comprised the largest proportion of the total mean diet (58.3%) (Fig. 3). Molluscs comprised a further 12.4% of the diet. Small amounts of other macroinvertebrates (amphipods), fish (including fish eggs), macrocrustaceans (atyid shrimps) and microcrustaceans were also consumed. This species has also been reported to be cannibalistic [580] and to eat tadpoles [270]. Fish (4.0%) Microcrustaceans (3.8%)
Unidentified (13.3%)
Macrocrustaceans (3.0%) Molluscs (12.4%)
Other macroinvertebrates (5.3%)
Aquatic insects (58.3%)
Figure 3. The mean diet of Philypnodon grandiceps. Data derived from stomach content analysis of 145 individuals from the Burnett River, south-eastern Queensland [205], Tweed River, northern New South Wales [1133], and Lake Modewarre, south-western Victoria [1062].
Marked ontogenetic variation in the diet of larval P. grandiceps has been observed in a billabong of the Murray River floodplain. Larvae less than 5 mm in length preyed exclusively on rotifers, whereas the diet of larger larvae was dominated by larger prey including calanoid copepods and cladocerans [434]. Diel variation in feeding activity among small and large larvae was also evident and was possibly associated with variation in vertical migration
565
Freshwater Fishes of North-Eastern Australia
patterns among these size classes (see section on microhabitat use). In contrast to large larvae, smaller larvae did not feed at night, possibly due to visual constraints on the ability to capture microscopic prey during darkness [434].
disturbed Broken River, despite being predicted to occur there. No explanation for this apparent discrepancy was given [613, 615]. In some coastal rivers of New South Wales, Gehrke et al. [435, 438, 441] collected more individuals in areas subject to flow regulation than in unregulated reaches, although this pattern was inconsistent among the rivers and types of flow regulation examined. They suggested P. grandiceps was a tolerant species (after Harris and Gehrke [553]) and hence able to persist in rivers degraded by flow regulation. Philypnodon grandiceps was also observed to be more common in regulated reaches of the Brisbane River where flow releases from Wivenhoe Dam have resulted in elevated baseflows during naturally low-flow periods in spring [704].
In streams of the Mount Lofty Ranges, South Australia, P. grandiceps can form an important component of the diet of alien fish species including redfin perch and trout [506]. Other larger fishes and birds have also been reported to prey on P. grandiceps [580]. Conservation status, threats and management The conservation status of Philypnodon grandiceps is listed as Non-Threatened by Wager and Jackson [1353]. It is generally common throughout most of its coastal distribution, except at the most northerly extent of its range in the Burdekin River. A recent assessment of the status of freshwater fish in New South Wales listed P. grandiceps as a species of concern, as it has undergone reductions in distribution and abundance in the Murray-Darling Basin [710]. This species has also been listed as a member of an Endangered Ecological Community in the lower Murray River [1005] and in the lowland catchment of the Darling River [329]. However, P. grandiceps is apparently thriving in a section of the Campaspe River (a tributary of the Murray River degraded by river regulation), unlike other native species [613, 615, 1217] (see also below).
Philypnodon grandiceps also appears to be tolerant of changes in lotic riverine habitat to lentic conditions associated with impoundments. Gehrke et al. [443] collected higher numbers of P. grandiceps in Lake Yarrunga, an impoundment on the Shoalhaven River, southern New South Wales, than in lotic reaches of the river. They speculated that the littoral zone of the lake had increased the overall amount of spawning habitat for this species, whereas episodic high flows in the upstream riverine habitats may have displaced fish in these areas. Gehrke et al. [440] suggested that P. grandiceps appears tolerant of riparian habitat degradation as it was found to be significantly more abundant in river reaches with disturbed riparian zones and grassy banks than in reaches with well-vegetated banks. They suggested that this species was able to utilise macrophytes beds that were abundant in these river reaches with cleared riparian canopies.
The capacity for facultative migrations by P. grandiceps indicates that it is likely to be sensitive to barriers to movement caused by structures such as dams, weirs, barrages, road crossings and culverts. The impact of barriers to movement on key life cycle processes is unclear, however they have the potential to affect dispersal and recolonisation movements or the ability to move between estuaries and freshwaters for most life history stages.
Like many other native species, siltation arising from increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of P. grandiceps and affect aquatic invertebrate food resources.
River regulation, independent of the imposition of barriers, may also impact on P. grandiceps populations in rivers. Changes to the natural discharge regime and hypolimnetic releases of unnaturally cool waters from large dams may disrupt possible cues for movement or de-couple optimal temperature/discharge relationships during critical phases of spawning, larval movement and development. Nevertheless, P. grandiceps has been documented to thrive in areas subject to flow regulation. Humphries et al. [613, 615, 1217] recorded very high larval abundances in regulated sections of the Campaspe River that are subjected to elevated summer flows and reduced duration of high winter flows. It was suggested that the ability of P. grandiceps to spawn over an extended period, in contrast to some other native species, enabled a subset of larvae to experience optimal conditions for successful recruitment [615]. However, it was not present in the nearby and less
This species is common in lowland streams, rivers and wetlands. Such habitats are also most at risk of reclamation, degradation by clearing and encroachment by agriculture (particularly sugar-cane farming), invasion by noxious weeds such as para grass and Hymenachne, and channelisation to improve drainage. In addition, and perhaps just as importantly, such habitats are frequently close to human population centres (e.g. Brisbane and the south-eastern Queensland coastal strip) and are thus at risk from urban encroachment. Although the importance of access to brackish and estuarine habitats for the life history of this species is not clearly understood, the prevalence of marina and canal developments in coastal and estuarine areas of south-eastern Queensland and New South Wales has potential to impact on certain populations and life history stages of this species.
566
Philypnodon grandiceps
(Opecoelidae) where it acts as a definitive host [338]; it is also second intermediate host to Stemmatostoma pearsoni (Cryptogonimidae) [339]. It has been found to be naturally infected by the larval stage of the strigeate trematode Diplostomum spathaceum [185, 669]. It is also known to be infected by several nematodes [185, 1063].
Predation of juveniles and adults by alien fish species has been identified as another potential threat to P. grandiceps in the southern part of its range [506]. An external freshwater copepod ectoparasite (Lernaea sp.) has been found to infest individuals of P. grandiceps in the Burnett River [1276]. It is known to be infected naturally by the adult digenetic trematode parasite Opecoelus variabilis
567
Philypnodon sp. Dwarf flathead gudgeon
37 429047
Family: Eleotridae
flattened; the snout is broad and of moderate length; the cheeks are broad, becoming bulbous in large males. Interorbital space greater than eye diameter. Mouth slightly oblique, reaching to below front half of eyes in females and young males, reaching to beyond rear of eyes in adult males. Tip of tongue rounded to truncate. Gill openings broad, lower margin extending forward to below gill covers or preoperculum. The body is covered with moderate-sized ciliated scales. Predorsal scales variable in extent: nearly to eyes in southern areas; only to around posterior end of preoperculum in populations from northern New South Wales and south-eastern Queensland; no scales on top of head in populations from the Macquarie River near Bathurst. No scales on cheeks or opercula. Cycloid scales on belly. Lateral line absent. Rows of papillae across head, lower jaw and operculum, resembling that of P. grandiceps. Two separate dorsal fins; the first is rounded with notches between spines, origin well behind level of pelvic fin bases; the second originating just behind end of first dorsal fin is larger, elongate, with posterior rays longest. Anal fin similar in size and shape to second dorsal fin and positioned opposite or just posterior to second dorsal fin origin. Anus positioned just before anal fin origin. Pectoral fins rounded, broad and large.
Description First dorsal fin: VI–VII; Second dorsal: I, 8–9; Anal: I, 7–9; Pectoral: 15–16; Pelvic: I, 5; Caudal: 15 segmented rays; Vertical scale rows: 32–36 (32–44 [460]); Gill rakers on first arch: 11–12 (8–9 on lower limb for individuals from south-eastern Queensland [1093]); Vertebrae: 30–31 (30–32 [460]) [580]. Figure: mature male specimen of Philypnodon sp., 45 mm SL, Mary River at Kandanga Creek, June 1997; drawn 2003. Philypnodon sp. is similar in general appearance to P. grandiceps but smaller, known to reach 50 mm but rarely exceeding 40 mm [775]. Of 523 specimens collected in streams of south-eastern Queensland [699, 704, 709, 1093], the mean and maximum length of this species were 29 and 49 mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g) for 45 individuals (range 24–45 mm SL) sampled from the Mary and Albert rivers, south-eastern Queensland is W = 0.9 x 10–5 SL3.189, r = 0.944, P<0.001 [1093]. Philypnodon sp. has an elongate body, depressed anteriorly, cylindrical at the mid-point, becoming compressed posteriorly. The head is relatively large, broad and dorsally
568
Philypnodon sp.
whether Philypnodon sp. should retain the species epithet angustifrons as the diagnostics given in the original description of this species by Ogilby 1898 [1013] closely match those currently used to distinguish P. grandiceps. Ogilby [1013] distinguished P. angustifrons (as Ophiorrhinus angustifrons) primarily on the basis of the narrow interorbital region, however this is likely to vary considerably with sex and age and is insufficient to warrant consideration as a separate species (see also Waite 1904 [1355]). It is quite likely that individuals of the dwarf flathead gudgeon have been included among those specimens used by previous workers to describe P. grandiceps.
Pelvic fins thoracic, originating approximately level with pectoral fin insertions (or sometimes just before in individuals from south-eastern Queensland), elongate, pointed and small; fin bases entirely separate but close together. Caudal fin rounded, broad and moderately large. The caudal peduncle is deep and slender [460, 580, 775]. Philypnodon sp. is strongly sexually dimorphic: mature males have a larger mouth, more bulbous head, broader interorbital space and larger pelvic fins than females [460, 580, 775]. Colour varies considerably depending on size and habitat. Head and body vary from black to brown dorsally, fading to reddish-brown, yellowish or whitish-grey ventrally. Chin varies from grey, reddish-brown to brownish-yellow. Lips sometimes blackish, dark brownish, orange or red. Irregular, dark blotches on dorsal and lateral surfaces, often resembling broad saddles on sides. Black vertical bar sometimes present at base of pectoral fins and caudal fin. Two or three dark bars radiate posteriorly from eye across gill covers. First dorsal fin with two distinctive dark bands, areas between bands and tip of fin whitish, yellowish or orange. Second dorsal with three to five oblique dark lines sloping towards body posteriorly, areas between lines whitish, yellowish or orange. Five to six faint wavy lines or rows of spots sometimes present on caudal fin; basal twothirds of fin yellowish, orange or grey, and margins grey or blue. Anal fin dusky to clear. Pectoral and pelvic fins clear to whitish. During breeding season, males may become very dark, with vivid reddish-yellow on ventral surface and display more vibrant fin markings than females. Preserved colouration generally similar to that described above but less colourful [34, 460, 580, 775, 936]. Philypnodon sp. is similar in general appearance to P. grandiceps, especially juveniles and subadults. Distinguishing characteristics of Philypnodon sp. include 15–16 pectoral fin rays, 11–12 gill rakers (8–9 on lower limb for individuals from south-eastern Queensland), lower margin of gill opening extending only as far forward as below gill covers or preoperculum, and black vertical bar sometimes present on caudal fin base. Systematics This species has not been formally described. In 1978, Lake [755] referred to the existence of this taxon and cited Dr Doug Hoese (Australian Museum) as having informed him of its status as a separate species. Prior to this (in 1954 and 1961), Whitley [1394, 1397] recognised a subspecies of P. grandiceps, P. g. angustifrons (Ogilby 1898) and provided good quality illustrations of the latter, and it closely resembles Philypnodon sp. (the dwarf flathead gudgeon). Upon formal description, it is questionable
569
Distribution and abundance Philypnodon sp. is a relatively widespread species occurring in coastal and inland drainages of eastern Australia. This species occurs in coastal catchments from southern Queensland, south through New South Wales and Victoria and as far west to at least the streams draining off the Mount Lofty Ranges into Lake Alexandrina in eastern South Australia. Inland, it is relatively uncommon and patchily distributed in the Murray River in South Australia and Victoria, and in New South Wales it has only been recorded in the upper Murrumbidgee River and the Macquarie River near Bathurst [574, 775, 778, 808, 817, 1282]. A single individual has also recently been recorded in the Condamine River (upper Darling Catchment) near Surat in western Queensland [864]. It has been suggested that this species has undergone dramatic declines in distribution and abundance in the Murray-Darling Basin [1200, 1201]. Philypnodon sp. appears to be relatively common and widespread in coastal rivers of New South Wales [282, 437, 441, 443, 814, 1066, 1067, 1201]. In Victoria, this species has been recorded from the East Gippsland area [1111, 1112] where it is thought to be common [572]. It is probably more widespread throughout coastal Victoria but has been confused with Philypnodon grandiceps [1111, 1112]. Philypnodon sp. is patchily distributed and rare in coastal South Australia, and is present in a few streams flowing off the Mount Lofty Ranges into Lake Alexandrina and the lower Murray River [507, 817]. It is possible that this species has a wider distribution in Australia but has been confused with P. grandiceps. Philypnodon sp. has been recorded as far north as Baffle Creek [1110] in southern central Queensland. It is relatively uncommon and patchily distributed in coastal south-eastern Queensland, having been recorded from the Burnett [107, 237], Mary [643, 1093, 1095] and Noosa rivers [643]. It has not been recorded elsewhere in the Sunshine Coast area, but is present further south in the Caboolture [413] and Pine rivers [1255, 1349] and it is present in most other major streams and rivers south to
Freshwater Fishes of North-Eastern Australia
Table 1. Distribution, abundance and biomass data for Philypnodon sp. in rivers in south-eastern Queensland. Data summaries for a total of 925 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred. Total
% locations % abundance
Mary River Sunshine Coast Moreton Bay rivers and rivers and streams streams
Brisbane River
Logan-Albert River
South Coast rivers and streams
26.2
36.0
—
15.0
32.4
23.5
25.0
0.57 (1.96)
0.55 (1.35)
—
0.53 (4.46)
1.15 (4.38)
0.27 (2.04)
0.70 (7.44) 12 (4)
17 (11)
18 (12)
—
15 (4)
16 (8)
15 (11)
0.03 (0.13)
0.03 (0.15)
—
—
0.06 (0.24)
0.01 (0.07)
—
26 (21)
21 (17)
—
—
21 (13)
23 (17)
—
Mean numerical density (fish.10m–2)
0.22 ± 0.03
0.16 ± 0.02
—
0.18 ± 0.08
0.36 ± 0.10
0.17 ± 0.07
0.11 ± 0.07
Mean biomass density (g.10m–2)
0.10 ± 0.01
0.09 ± 0.01
—
—
0.18 ± 0.06
0.08 ± 0.02
—
Rank abundance % biomass Rank biomass
the Queensland–New South Wales border. This species has also been recorded from Bribie Island off the south-eastern Queensland coast [1110].
Table 2. Macro/mesohabitat use by Philypnodon sp. in rivers of south-eastern Queensland. Data summaries for 925 individuals collected from samples of 200 mesohabitat units at 74 locations undertaken between 1994 and 2003 [1093]. W.M. refers to the mean weighted by abundance to reflect preference for particular conditions.
Surveys undertaken by us between 1994 and 2003 [1093] collected a total of 925 individuals and it was present at 26% of all locations sampled (Table 1). Overall, it was the 17th most abundant species collected (0.6% of the total number of fishes collected) and was relatively uncommon at sites in which it occurred (2.0% of total abundance, 11th most common species). In these sites, Philypnodon sp. most commonly occurred with the following species (listed in decreasing order of relative abundance): P. signifer, M. duboulayi, C. marjoriae, H. galii and G. holbrooki. It was the 26th most important species in terms of biomass, forming only 0.03% of the total biomass of fish collected. This species is never common or widespread in individual rivers of south-eastern Queensland: the highest relative abundance observed was in the Brisbane River (1.2% of the total abundance) and it was most widespread in the Mary River (present at 36% of locations sampled). Across all rivers, average and maximum numerical densities recorded in 200 hydraulic habitat unit samples (i.e. riffles, runs or pools) were 0.22 individuals.10m–2 and 4.35 individuals.10m–2, respectively. Average and maximum biomass densities at 130 of these sites were 0.10 g.10m–2 and 0.96 g.10m–2, respectively. Highest numerical densities and biomass densities were recorded from the Brisbane River. Philypnodon sp. has been reported to occur regularly with P. grandiceps [580]. Distributional data supports this to some extent, with both species occurring together at 35 of the 106 locations in which either species was sampled in south-eastern Queensland [1093] and 15 of the 31 locations in which either species was present in New South Wales [553].
Parameter
Min. 2
Catchment area (km ) Distance to source (km) Distance to mouth (km) Elevation (m.a.s.l.) Stream width (m) Riparian cover (%)
15.6 10 087.7 5.0 268.0 5.0 300.0 0 240 1.5 44.0 0 80.9
Gradient (%) 0 Mean depth (m) 0.07 Mean water velocity (m.sec–1) 0
570
Max.
2.48 1.08 0.71
Mean
W.M.
881.9 55.3 159.6 79 8.6 42.5
652.4 50.7 176.3 81 6.3 42.5
0.29 0.43 0.08
0.28 0.31 0.09
Mud (%) Sand (%) Fine gravel (%) Coarse gravel (%) Cobble (%) Rocks (%) Bedrock (%)
0 0 0 0 0 0 0
69.3 100.0 58.5 68.0 58.0 44.0 54.0
5.5 19.7 21.4 27.4 19.3 4.8 1.8
4.3 15.6 24.0 33.4 19.7 2.3 0.7
Aquatic macrophytes (%) Filamentous algae (%) Overhanging vegetation (%) Submerged vegetation (%) Emergent vegetation (%) Leaf litter (%) Large woody debris (%) Small woody debris (%) Undercut banks (% bank) Root masses (% bank)
0 0 0 0 0 0 0 0 0 0
59.6 62.0 20.0 40.9 9.9 90.0 29.9 15.3 87.5 87.5
11.2 8.7 1.5 4.5 0.6 16.9 5.0 4.4 17.7 21.4
11.6 7.7 2.6 9.2 0.7 14.7 5.5 4.3 11.1 14.2
Philypnodon sp.
Macro/mesohabitat use Philypnodon sp. occurs in a variety of lotic and lentic habitats including small coastal streams, large rivers, and coastal and floodplain wetlands. Although usually found in freshwater habitats, it is also common in brackish and estuarine waters [446, 460, 806, 1067].
(a) 80 60 40
Philypnodon sp. usually occurs at low elevations, but has been recorded at elevations up to 700 m.a.s.l. in rivers of coastal New South Wales [553]. In rivers of south-eastern Queensland it occurs at low to relatively high elevations (0–240 m.a.s.l.) but most commonly at around 80 m.a.s.l. (Table 2). This species occurs throughout the major length of streams and rivers, ranging between 5 and 300 km from the river mouth. It is present in a wide range of stream sizes (range = 1.5–44.0 m width) but is more common in streams less than 10 m wide and with moderate riparian cover (around 40%). Philypnodon sp. most commonly occurs in pools and runs characterised by low gradient (weighted mean <0.3%), moderate depth (0.31 m weighted mean depth) and low mean water velocity (weighted mean 0.09 m.sec–1) but can occur in shallow, high velocity (maximum 0.71 m.sec–1) riffle habitats (Table 2). This species is most abundant in mesohabitats with substrates of intermediate size (fine gravel, coarse gravel and cobbles) and where submerged aquatic macrophytes, leaf-litter beds, undercut banks and root masses are common. Elsewhere, Philypnodon sp. has been classified as a riffle-dwelling species [553, 1200], and as a ‘ubiquitous’ species, occurring in both pools and runs [1124]. Microhabitat use In rivers of south-eastern Queensland, Philypnodon sp. was most frequently collected from areas of low water velocity (usually less than 0.1 m.sec–1) (Fig. 1a and b) reflecting the pattern observed in mesohabitat use. This species was collected over a wide range of depths, but most often from less than 10 cm up to 70 cm (Fig. 1c). A benthic species, it occupies the lower half of the water column, most commonly in direct contact with the substrate (Fig. 1d). Although not a schooling species, loose aggregations of up to 10 individuals are sometimes collected from the same microhabitat location. Philypnodon sp. was found over slightly more coarse substrates than its congener, P. grandiceps, usually over fine gravel, coarse gravel and cobbles (Fig. 1e). Philypnodon sp. was slightly more frequently collected within 1 m of the stream-bank (57% of 161 fish collected), and was usually found in close association with some form of submerged cover (Fig. 1f). It was usually collected near leaf-litter beds, but occasionally used small and large woody debris, aquatic vegetation and the substrate (Fig. 1f). Elsewhere, this species has been reported to prefer relatively calm waters and lives over mud, rocks, or in weedy areas [580].
(b)
60
40
20
20
0
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d) 60
20
40 10 20 0
0
Total depth (cm) 30
Relative depth
(e)
(f) 30
20
20
10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Philypnodon sp. Data derived from capture records for 161 individuals from 58 samples collected in the Mary and Albert rivers, south-eastern Queensland, over the period 1994–1997 [1093].
Environmental tolerances Information on tolerance to water quality extremes is lacking and the data listed below (Table 3) reflect the water quality over the broad range of aquatic habitats in which Philypnodon sp. has been collected (see above). Philypnodon sp. appears to be tolerant of a wide range of physicochemical conditions including low dissolved oxygen levels (minimum 0.3 mg.L–1), mildly acidic waters (minimum 6.3), and very high conductivity (maximum 4002 µS.cm–1). The recorded presence of juvenile and adult fish in brackish and estuarine waters [446, 806, 1067] suggest that this species is able to tolerate elevated salinities for much of its life cycle. The maximum turbidity at which this species has been recorded is 36 NTU although it is likely to be able to tolerate much higher levels.
571
Freshwater Fishes of North-Eastern Australia
cycle in freshwater and has been bred in captivity [413]. The cue for spawning is unknown but may involve a rise in water temperature as spawning of captive fish was speculated to have been triggered by variations in temperatures and water quality during transport between aquaria [413]. Spawning in aquaria has been reported to occur at temperatures between 19°C and 22°C [413]. In rivers of southeastern Queensland, Philypnodon sp. appears to have a breeding season extending from spring through to autumn, but concentrated in spring and summer. Juveniles less than 15 mm SL first appeared in freshwater samples in the spring months and individuals between 15–25 mm SL were most common in spring and summer (Fig. 2) [1093].
Table 3. Physicochemical data for Philypnodon sp. Data summaries for 838 individuals collected from 143 samples in south-eastern Queensland streams collected between 1994 and 2003 [1093]. Parameter Water temperature (°C) Dissolved oxygen (mg.L–1) pH Conductivity (µS.cm–1) Turbidity (NTU)
Min.
Max.
8.4 0.3 6.3 107.0 0.2
31.7 12.7 8.9 4002.0 36.0
Mean 20.3 7.5 7.6 608.5 4.7
Harris and Gehrke [553] and Gehrke and Harris [438] classified Philypnodon sp. as tolerant of water quality and habitat degradation. Like P. grandiceps but in contrast to some other eleotrids such as. Gobiomorphus australis and Hypseleotris spp., Philypnodon sp. is not common in degraded urban streams of the Brisbane region [94, 95, 704, 709], suggesting that it may be sensitive to habitat degradation.
In captive spawnings, approximately 50–60 transparent teardrop-shaped eggs were laid in a 3 cm by 4 cm mass attached to a vertical surface [413, 414]. A few of these eggs were observed to be infertile within 24 hours of spawning [413]. Reliable estimates of fecundity are unknown but the ovaries of three mature females (24.3–28 mm SL) were observed to contain between 160 and 180 similarly sized but irregular ovoid-shaped eggs, 0.7 mm long at the longest axis [1093]. In aquaria, the male cares for the eggs, reportedly fanning the egg patch every 10–15 seconds [413]. Males are also reported to confront intruders with a colourful aggressive display, including head-to-head encounters with mouths fully open to display bright red lips and biting/butting of rival fish. These confrontations usually ending after a short chase [413]. Four days after fertilisation, eyespots are visible in the eggs and the body developed to a characteristic teardrop-shape on a short stalk. Within 12 hours of the eyespots being observed, 2–3 larvae were free-swimming, suggesting that hatching occurs four to five days after fertilisation. By day eight, all larvae were free swimming, were 6–8 mm long and were translucent grey in colour. No larvae survived in the aquaria beyond day nine, possibly due to an inappropriate food supply [413].
Reproduction There is relatively little published information on the reproductive biology of Philypnodon sp. (Table 4). This species matures at a relatively small size. One female specimen from south-eastern Queensland was observed to be sexually mature (reproductive stage V) at 24.3 mm SL [1093]. This species spawns and can complete its entire life 40 Spring (n=138) 30
Summer (n=205) AutumnWinter (n=180)
20
Movement There is no information on the movement biology of Philypnodon sp. however, it is possible that studies documenting the movement patterns of P. grandiceps may also have included individuals of Philypnodon sp. Like many other freshwater eleotrids, juveniles and subadults of this species may have a facultative mass dispersal phase. Although juveniles and adults of this species often occur in estuaries, access to estuarine areas is not an obligatory component of the life cycle. Hence the movement pattern of this species may be classified as facultative potamodromy and/or amphidromy.
10
0
Standard length (mm) Figure 2. Seasonal variation in length–frequency distributions of Philypnodon sp., from sites in the Mary, Brisbane, Logan and Albert rivers, south-eastern Queensland. The number of fish from each season is given in parentheses [1093].
572
Philypnodon sp.
Table 4. Life history information for Philypnodon sp. Age at sexual maturity (months)
?
Minimum length of ripe females (mm)
24.3 mm [1093]
Minimum length of ripe males (mm)
?
Longevity (years)
?
Sex ratio (female to male)
?
Occurrence of ripe fish
?
Peak spawning activity
? probably spring through to autumn south-eastern Queensland, but concentrated in spring and summer [1093]
Critical temperature for spawning
19–22°C [413]
Inducement to spawning
? temperature
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
? 160–180 eggs in ovaries [1093], 50–60 eggs laid in aquaria [413, 414]
Fecundity /length relationship
?
Egg size
irregular ovoid-shaped eggs, 0.7 mm long at longest axis [1093], transparent and teardrop-shaped [413, 414]
Frequency of spawning
?
Oviposition and spawning site
?
Spawning migration
None known
Parental care
In aquaria, the male cares for the eggs, reportedly fanning the egg patch every 10–15 seconds [413]
Time to hatching
4–5 days [413]
Length at hatching (mm)
?
Length at free swimming stage
Some newly hatched larvae were free-swimming; 3–4 days after hatching, all larvae were free swimming and were 6–8 mm long [413]
Length at metamorphosis (days)
?
Duration of larval development
?
Age at loss of yolk sack
?
Age at first feeding
?
Trophic ecology The only quantitative dietary information available for Philypnodon sp. is for 15 individuals from two lotic habitats in the Mary River and one in the Albert River, south-eastern Queensland [1093]. Philypnodon sp. is a microphagic carnivore, probably consuming prey primarily from the benthos. Aquatic insects dominated the total mean diet (90.4%) and comprised mostly chironomid larvae, and emphemeroptera and trichoptera nymphs (Fig. 3). Organic detritus (3.0%) and aerial forms of aquatic insects (chironomid pupal cases and adults) (0.7%) were the only other identifiable dietary items consumed.
Unidentified (5.9%) Aerial aq. invertebrates (0.7%) Detritus (3.0%)
Conservation status, threats and management The conservation status of Philypnodon sp. is listed as Non-Threatened by Wager and Jackson [1353]. It is generally common throughout most of its coastal distribution but it has been suggested that this species has undergone dramatic declines in distribution and abundance in the
Aquatic insects (90.4%)
Figure 3. The mean diet of Philypnodon sp. Data derived from stomach content analysis of 15 individuals from the Mary Albert rivers, south-eastern Queensland [1093].
573
Freshwater Fishes of North-Eastern Australia
of reclamation, degradation by clearing and encroachment by agriculture (particularly sugar-cane farming), invasion by noxious weeds such as para grass, and channelisation to improve drainage. In addition, and perhaps just as importantly, such habitats are frequently close to major population centres (e.g. Brisbane and the south-eastern Queensland coastal strip) and are thus at risk from urban encroachment. Although the importance of access to brackish and estuarine habitats for the life history of this species is not clearly understood, the prevalence of marina and canal developments in coastal and estuarine areas of south-eastern Queensland and New South Wales may potentially impact on certain populations and life history stages of this species.
Murray-Darling Basin [1200, 1201]. This species has been listed as a member of an Endangered Ecological Community in the lower Murray River [1005] and in the lowland catchment of the Darling River [329]. The capacity for facultative migrations by Philypnodon sp. indicates that it is likely to be sensitive to barriers to movement caused by structures such as dams, weirs, barrages, road crossings and culverts. The impact of barriers to movement on key life history processes is unclear, however they have the potential to affect dispersal and recolonisation movements or the ability to move between estuaries and freshwaters for potentially all life history stages. River regulation, independent of the imposition of barriers, may also impact on Philypnodon sp. populations in rivers. Changes to the natural discharge regime and hypolimnetic releases of unnaturally cool waters from large dams may disrupt cues for movement or de-couple optimal temperature/discharge relationships during critical phases of spawning, larval movement and development.
Predation of juveniles and adults by alien fish species has been identified as another potential threat to Philypnodon sp. in the southern part of its range [506]. In a recent survey of New South Wales rivers, a relatively high number of Philypnodon sp. sampled (13% of 145 individuals examined) had some form of visible external abnormality [553]. The types of abnormalities observed in this species were not stated but may have included infestation with the copeopod parasite Lernaea, wounds, ulcers and cysts.
Like many other native species, siltation arising from increased rates of erosion and sediment transport in catchments may be a threat to the spawning habitats of Philypnodon sp. and affect aquatic invertebrate food resources.
The taxonomic status of this species requires urgent attention. The absence of detailed life history information on this species is of concern. Greater research effort is needed to elucidate the biology of this species.
Philypnodon sp. is common in lowland streams and rivers and in lowland wetland habitats. Such habitats are at risk
574
Conclusion: prospects, threats and information gaps
taken place in the last one and a half decades [15, 680, 965, 1070, 1353]. The major threats identified in these studies are listed in Table 1 (retaining the terminology used) and although the number of major categories varies between studies, perusal of the accompanying supporting documentation clearly reveals that when only a few major threats were listed (e.g. Pollard et al. [1070]), many factors were grouped within each major threat. For example, the category ‘Deforestation and agriculture’ used by Pollard et al. [1070] contained a range of threats contributing to instream habitat alteration, riparian degradation and changes in water quality. Salient features of Table 1 are: 1) the major threats facing the fauna of different regions are much the same as those at a national level; and 2) the same threats exist now as they did in 1990. In fact, many of these same threats were identified by Lake [749, 754, 755] over 30 years ago. Notably, the same major threats have been identified in both global and regional assessments elsewhere in the world of the conservation future of freshwater fishes [26, 89, 558, 680, 948]. Worldwide, freshwater fishes are more imperiled than are marine fishes or terrestrial vertebrates [870].
Approximately 30% of the species listed in the International Union for the Conservation of Nature (IUCN) Red List are fishes and most of these are freshwater species [17]. It has been estimated that in some areas such as North America, the projected mean future extinction rate is comparable to the range of estimates for tropical rainforest communities [1132]. This is a very grim forecast indeed. The forecast for the freshwater fishes of north-eastern Australia is perhaps not so dire, notwithstanding the fact that the long-term survival of some species is of concern. The Australian Society for Fish Biology [117] lists Maccullochella peelii mariensis as Critically Endangered, Nannoperca oxleyana and Pseudomugil mellis as Endangered, and Cairnsichthys rhombosomoides and Guyu wujalwujalensis as Vulnerable [117]. Furthermore, Neoceratodus forsteri is listed as Vulnerable under the Environment Protection and Biodiversity Conservation Act 1999. Although this group represents less than 5% of the total number of species of the region, it does serve to indicate that some species may face extinction in the near future. Moreover, the increasing rate of development in the region, including land clearing and the construction of water resource infrastructure, is potentially threatening to many more species.
The various threatening process identified in Table 1 can be broadly classified within six major types of threat. In addition, we have added a seventh recently identified threat: global climate change. Rarely are species imperiled by single threats acting in isolation. More frequently, threats are many and varied, their effects are additive and often synergistic and associated impacts may be felt at the level of individual species, communities or entire ecosystems (Figure 1). Threatening processes may act upon autecological aspects of individual species such as reproduction, recruitment processes, feeding ecology, movement and the way in which individual species are arranged within riverine landscapes. Alternatively, they may alter the strength and types of interactions that occur between other species (i.e. predation, competition, disease transmission and hybridisation), as well as the way in which individual species, groups of interacting species or entire assemblages respond to changes in the processes occurring in the aquatic ecosystem of which they are an important part (Table 2). Table 2 is intended to illustrate the large number of impacts associated with different threat types and the effects that may arise. The reader is advised to consult the following sources for detailed accounts of the way in which these threats impact on freshwater fishes [15, 89, 109, 110, 247, 680, 965, 1353].
A recurring theme throughout this book is the role that history (over evolutionary time scales) has played in shaping the composition, distribution and ecology of the freshwater fishes of north-eastern Australia. Some of the region’s ichthyofauna, such as Neoceratodus forsteri, are indeed very ancient and persistent; others such as some of the melanotaeniid rainbowfishes are much more recent, expansions in distribution of this group occurring perhaps within the last 200 000 years [618]. Ancient landscape processes such as mountain formation, scarp retreat, drainage capture and river-mouth realignment have all played a part in influencing this rich and diverse fauna, and giving rise to new species and lineages. Global climate change and associated sea level changes during the Miocene and Pleistocene have altered the nature and availability of aquatic habitats. Sea level changes during the Pleistocene have repeatedly formed a single landmass (Sahul) combined from New Guinea and Australia. The freshwater fishes of north-eastern Australia have adapted and persisted, but what does the future hold for this fauna? Threats Several assessments of the threats faced by freshwater fishes (or fisheries) of Australia or selected regions have 575
Freshwater Fishes of North-Eastern Australia
Table 1. Major threats facing the freshwater fishes of Australia. Authors
Pollard et al. [1070]
Wager and Koehn [729] Jackson [1353]
Kearney et al. [680]
Morris et al. [965]
Anon. [15]
Year
1990
1993
1995
1999
2001
2002
Geographic coverage
national
national
national
national
NSW
MurrayDarling
North-eastern Australia
Water conservation (including barriers to movement)
Flow modification (including barriers to movement)
Water Reduced extraction/flow environmental regulation flows
Altered flow regimes
Flow regulation
Flow regulation
Barriers
Barriers to fish passage
Barriers
Barriers to movement
Barriers to movement
In-stream habitat removal/ destruction, sedimentation Geomorphic alteration Deforestation and agriculture Degraded water quality
In-stream habitat degradation
Loss of instream cover Habitat degradation
Habitat degradation
Riparian vegetation removal
Loss of riparian vegetation
Reduced water quality Pollution
Thermal pollution
This book
Introduced weeds Riparian degradation
Lowered water quality
Water quality degradation
Aliens Translocation and stocking
Alien species and translocated native species
Exploitation
Exploitation
Diseases
Diseases and parasites
Chemical pollution Introduced alien and translocated species
Introduced alien and native species
Interactions Introduced with introduced species and translocated species
Overfishing
Overfishing
Overfishing/ collection
Alien, translocated and stocked fish species
Fishing
Lack of knowledge
Lack of knowledge
THREATENING PROCESSES
Species level processes
Ecosystem level processes
• •Movement ••Reproduction ••Recruitment ••Population genetics ••Habitat associations ••Disease resistance •Trophic • dynamics
•Energy transfer •Connectivity with adjacent ecosystems
Community level processes •Competition • ••Predation •Hybridisation • •Energy use and availability • •Assemblage regulation •
Figure 1. The inter-relationship between processes threatening freshwater fishes.
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Conclusion: Prospects, threats and information gaps
Table 2. Ecosystem, community and species level responses to threats impacting on freshwater ecosystems of north-eastern Australia. Type of threat 1. Hydrological alteration
Impacts
Ecosystem and species responses
• • •
• • • • • • • •
• • •
Reduction in total discharge Altered seasonality of flow regime Altered frequency, timing, duration and magnitude of flood flows Changes in rates of rise and fall Change in low flow regimes (e.g. elevated baseflows) Transition from ephemeral to perennial hydrology
• • • • • • 2. Loss of longitudinal and lateral connectivity
•
•
• • •
Physical barriers to within-channel movement (i.e. dams, barrages, weirs, culverts, reaches of degraded habitat quality) Chemical barriers to within-channel movement (i.e. persistent and widespread reductions in water quality parameters such as temperature or dissolved oxygen Barriers to lateral movement (i.e. bund walls, drop boards and levee banks) Barriers to out-of-river movement (i.e. overexploitation of migrating stock) Barrages located at freshwater/estuarine interface cause a reduction in the penetration of tidal prism and a decrease in overall amount of brackish and freshwater tidal habitat
• • • • • •
• • • • •
• •
3. Changes in habitat structure, quality and chemical composition
• • • • • •
Degraded riparian zones Loss of in-channel diversity (i.e. woody debris) Loss of bank diversity and stability (i.e. undercuts and root masses) Invasion by alien water weeds and ponded pasture grasses Sedimentation and smothering of substrates Colmation of sediment interstices and reduction of hyporheic exchange
• • • • • •
577
Species loss Decreased carrying capacity and reduction in species diversity Loss of cues for migration and spawning Disruption to food web processes Impaired recruitment processes Desynchronisation of local and global factors Increased competition for available resources Reduction in connectivity between in-channel and out-ofchannel habitats Stranding of eggs and larvae Physical removal of larvae due to elevated velocities Changes in channel forming processes and altered habitat structure Increased incidence and dominance of introduced species Loss of species with specialist life histories Declining fisheries production Species loss Changes in distribution and supply of carbon and energy within river system Altered food web structure and supply of energy and carbon within river systems Fragmentation of metapopulations with attendant risks of population genetic change due to drift Fragmentation of metapopulations with attendant risks of extinction due to small population size Reduced potential for recolonisation of areas experiencing localised extirpation of species due to other threats and impacts Loss of species requiring access to floodplains for reproduction and/or recruitment Loss of species requiring access to estuarine or marine systems for reproduction Loss of species requiring access to upstream areas for reproduction or juvenile rearing Loss of spawning and rearing habitat for larvae and juveniles requiring brackish and freshwater tidal habitat Inability of freshwater species to recolonise freshwaters if displaced by floods to brackish estuarine areas downstream of tidal barrages Reduction in gene flow between rivers in catadromous species Changes in assemblage structure due to the absence of diadromous predators Species loss Change in species composition to favour subset of tolerant and/or generalist species Altered food web structure and dynamics Reduction in allochthonous food supply may impact on specialist frugivores and terrestrial insectivores Changes in assemblage structure due to habitat modifications associated with proliferation of weeds Changes in fitness and population size due to changed light environment
Freshwater Fishes of North-Eastern Australia
Table 2 (cont). Ecosystem, community and species level responses to threats impacting on freshwater ecosystems of northeastern Australia. Type of threat
Impacts
Ecosystem and species responses
• •
•
• • • • • •
Persistent hypoxia or acute anoxia Altered thermal regimes downstream of dams and in areas with degraded riparian zones Eutrophication Acidification Salinisation Heavy metal and biocide contamination Reduced water transparency Modified disease and parasite resistance
• • • • • • • • •
4. Impacts of introduced species (alien and translocated native species)
• • • • • •
5. Overexploitation • •
Increased predation pressure Dilution of genetic distinctiveness Breakdown of phylogeographic structure Altered foraging behaviour Increased competition for food and space Transmission of disease and parasites
• • • •
Reduced predation pressure Interference to migration
• •
•
• • 6. Global climate change
• • •
• 7. Inadequate knowledge and understanding
• •
Altered flow regimes Changes in habitat structure Elevated sea level (loss of wetlands, supra-littoral swamps, isolation of drainage basins) Altered thermal regimes
• • • •
Inability to effectively manage existing threats Inability to plan for future threats
•
•
• • •
Disrupted reproduction due to desynchronisation of altered thermal regime and flow regime Reductions in species diversity due to reduced habitat diversity Impaired reproduction due to loss of spawning habitat (aquatic macrophyte beds, woody debris) or substrates Increased impacts of predation due to reduction in available refuge Reduced secondary production and carrying capacity due to smothering of sediment and reduced hyporheic exchange Reduced fitness due to exposure to biocides and heavy metals Changes in growth, morphology and fitness due to changes in temperature and oxygen regimes Changes in within-river distribution due to changes in thermal regime, salinity profile Reduced fitness, growth and population size due to increased susceptibility to pathogens Increased potential for invasion by alien species in degraded habitats Species loss Reduced fitness and reductions in population size Altered food web structure and dynamics Altered community dynamics due to the presence of novel top level predators Altered within-river distribution Species loss Altered community dynamics due to absence of top level predators Altered community dynamics due to absence of migratory bycatch species Declining fisheries production Loss of species Altered recruitment processes Reduced fitness Desynchronisation of global and regional cues for reproduction Fragmentation of lowland populations Unsustainable management of, and (possibly) irreversible changes to, aquatic ecosystems Increase in costly mistakes Escalating costs of rehabilitation and restoration Rising social unrest and political conflict
for the vast majority of species there is insufficient quantitative information to enable their effective management. A few species of economic or recreational significance such as barramundi, sooty grunter and eels are comparatively well studied. However, even in these species, several critical aspects of their biology are poorly understood. For
The large number of existing threats and the multifarious ways in which they impact on and influence freshwater fishes do not suggest a very promising future for the region’s freshwater fishes. Although the information presented in this text may suggest that some aspects of the ecology of the region’s freshwater fishes are well known,
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Conclusion: Prospects, threats and information gaps
with detailed morphological analysis and the examination of the relationship between meristic and morphological variation under varying ambient conditions during development is required. Similarly, an increased understanding of the phylogeography and biogeography of much of the fauna is needed to identify the role of history and landscape evolution in shaping the fauna.
example, quantitative data on meso- and microhabitat use by barramundi are lacking (although recreational fishers have a good understanding of this aspect of its biology). The phylogeographic structure of sooty grunter remains unknown, contributing to problems associated with the translocation of this species between rivers. Very little is known about the ecology of eels in freshwater habitats: how much space do they require? Do they compete for food and space? Are eels ‘keystone species’ and does their importance as structuring agents change with stream size? What quantity of glass eels and elvers can be harvested before detriment to the species and the ecosystem occurs? Consider also, that we have presented information on only 79 species from a total pool of about 130 species. The biology and ecology of many fishes of the region are very poorly known. Knowledge gaps The structure of the various species chapters in this book was designed to focus attention on the key areas of knowledge needed for effective management. We detail below areas of research or research questions needing examination in order to provide a better understanding and more effective management of the region’s freshwater fish fauna, and to thus improve their future prospects in regard to long-term survival. The reader is referred to the various species chapters for an expanded discussion of the examples we have used below. Systematics and taxonomy There still remain significant gaps in our knowledge of the systematic relationships of the fauna of northern Australia and of their taxonomy. For example, subspecific designation for several species (e.g. Glossamia aprion, Arrhamphus sclerolepis, Melanotaenia splendida and Maccullochella peelii) requires validation. Also requiring validation is the specific identity of some species. Ophisternon bengalense is a good example and one that is currently being examined. Some species have been known to science for many years but are currently without formal classification; rather they are referred to by number (e.g. Glossogobius sp. 1–4). Persuading the general public or natural resource managers primarily concerned with economic or rural development that such taxa are worth protecting but not apparently so worthy as to deserve formal description is problematic. This is not intended to denigrate our nation’s hard-working and highly skilled fish taxonomists. There are just too few of them for the work required. Current day educational policies and institutions do not, in general, teach taxonomy or encourage higher research degrees in this field. Increased application of modern techniques for genetic research, particularly mtDNA sequence analysis, coupled
These are not just esoteric research questions of interest to a few specialists. Better understanding of evolutionary process is critical in understanding: 1) how species have adapted to past conditions and how they might respond to current or future pressures; and 2) how they have arrived where they are now and in framing the context in which research questions about other aspects of biology and ecology are examined. For example, are the marine characteristics of many aspects of the life history of Hyspeleotris compressa related to its phylogenetic position or are they derived adaptive characters? Do the apparent differences in reproductive phenology and behavior of Hephaestus fuliginosus across its range represent genetic adaptations to different flow regimes and habitat structure or are they simply manifestations of a highly plastic life history? What are the consequences of translocation or stock supplementation of this species if such differences are genetically based? Should this taxon be recognised as a species complex, composed of geographically isolated species that, it should be stressed, were once formerly recognised as distinct but are no longer considered so? Similarly, are many widespread taxa such as Mogurnda adspersa composed of significantly distinct populations or Evolutionary Significant Units (ESU) [869], the conservation status of which warrant closer examination? In the Wet Tropics region, significant differentiation in species within other genera such as Craterocephalus and Melanotaenia has been identified. Do these populations warrant classification as different species, sub-species or ESU? How should we manage such taxonomic units? One of the most interesting outcomes of the application of modern genetic techniques is the recognition of ‘cryptic’ species, that is, populations exhibiting high levels of genetic divergence without accompanying morphological divergence. Such research clearly identifies the problem of managing such divergent stocks and even the assignation of conservation status. Moreover, it raises the question of why such extensive divergence can take place in the genome whilst form remains relatively constant? Is the Australian ichthyofauna unique in this regard, i.e. can this phenomena inform us about the way in which fish assemblages are structured in Australian rivers? Modern systematic research also has the potential to inform scientists and managers about the extent and
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Freshwater Fishes of North-Eastern Australia
pattern of gene flow between populations. Such information is critical in designing strategies concerned with regulating the translocation of different stocks, of how processes occurring in one catchment may impact on other catchments, and whether populations within an individual river constitute a single metapopulation or a number of isolated populations experiencing little or no gene flow between them. Such information is useful in determining the extent to which natural dispersal may repopulate areas having suffered previous localised extinctions or whether active remediation (a much more expensive option) coupled with habitat restoration is required to rehabilitate degraded areas.
characteristic of south-eastern Australia also. At present we have a poor understanding of the habitat requirements of many species and how they vary between rivers or regions. It is essential to know whether the knowledge gained by examination of habitat use in one river can be meaningfully applied to other rivers in different regions or even within the same region. Similarly, we lack information on the habitat needs of many species at different periods of their life history, especially during the larval period. Often, the habitat requirements of many species are so poorly known that the available information is restricted to such phrases as ‘…inhabits pools’. From a management perspective, this is of little value. For example, does a pool need to be of a certain depth and current velocity?; does it need to contain particular types of instream cover?; do pools require an intact riparian zone?; do reservoirs and weir pools fulfill the same function as natural pools?; do pools form just one of several critical habitats types required by a species throughout its life history? We need to know whether species are reliant on certain habitat types and what habitat factors determine the distribution of species within individual rivers. Furthermore, we need to know whether factors identified as being important in determining distribution and habitat use in rivers of the east coast of north-eastern Australia are also important in the lower gradient large rivers draining into the Gulf of Carpentaria. In this regard, one factor that we have not specifically addressed in this book is the hydraulic component of habitat structure. Fish may assort along habitat gradients according to the hydraulic nature of the interaction between flow and physical stream structure rather than according to mesoscale habitat variation, i.e. riffles, runs or pools.
Distribution and abundance The distribution of many species in easterly flowing rivers of north-eastern Australia is reasonably well known as these rivers have been the focus of much research (see Appendices 1 and 2). This is not the case for many rivers draining into the Gulf of Carpentaria however. In fact, the ecology of these rivers remains largely unstudied and there is an urgent need for well-designed surveys in this region. Indeed, much of the information presented in this book has arisen from survey work. Providing they are well designed, such studies have great potential to inform managers and scientists not only about biodiversity in particular rivers and regions, but also to inform about critical issues such as distribution patterns within rivers, interspecific and ontogenetic variation in patterns of habitat use and the identification of critical habitat types (e.g. certain wetlands or dry season refugia). Greater emphasis needs to be placed on developing robust quantitative methods for sampling fish communities enabling comparison across years, seasons, different habitat types and different studies. Application of rapid assessment methods of river health using fish as indicators is useful only if the data collected is of sufficient quality to enable: 1) validation of the method itself; and 2) comparison over a range of physical and temporal conditions. Moreover, detecting the impacts of human activity, the relative importance of different threats, or the effects of rehabilitation efforts, remedial actions or management strategies can only be achieved when the data is of sufficient quality to allow a meaningful and rigorous assessment.
A better understanding of the relationship between flow regime and habitat use is fundamental to the management of riverine fishes. In addition, the functional importance to fish of key facets of the flow regime (e.g. magnitude, timing, frequency, variability, and rates of rise and fall of particularly discharges) and their interactions with fluvial geomorphology and hydraulics are very poorly understood. For example, fish may be more generalist in their habitat requirements in rivers with strong seasonal or interannual variation in discharge compared to more temporally stable and predictable rivers [1100]. This raises interesting questions about the carrying capacity and biodiversity of rivers with variable flow regimes and the effect of flow manipulation. For example, what is the response of fish communities to changes in the extent of variability of a flow regime? How long before impacts on fish are realized? Are species lost? Are impacts the same in variable rivers made more stable by flow supplementation as those in stable rivers in which dry season flows are
Habitat use at landscape to local scales Habitat is the focus of much of current management practices, particularly with regard to rehabilitation and environmental flow management in Australia, both being largely predicated on the relationship between fish and habitat; yet there is still a great degree of uncertainty about the habitat requirements of many of Australia’s freshwater fishes. This is particularly so for northern Australia but is
580
Conclusion: Prospects, threats and information gaps
abstracted or captured thus magnifying the seasonal flow signal? Some habitat types may only become available under certain flow conditions. Floodplain wetlands may need a large flow in order to establish connectivity. Often, the estimation of such flows required for inundation is relatively simple to quantify, but estimation of other factors such as the frequency of inundation in individual years or over longer time scales (i.e. a decade) in order to sustain fish populations, or the length of time that connectivity persists, are less so tractable problems, yet are critical to effective management in lowland rivers. Some habitat types are highly threatened or have been reduced enormously in extent in the last century (e.g. wetlands), yet the long-term impact of such changes is poorly known.
unstudied in this respect. Life history studies appear limited to those south-eastern species of economic importance or to those species that can be found close to major population centers. Few studies have addressed the interaction between hydrology and life history and few studies have compared how life histories vary within species or assemblages in regions of differing flow variability. The investigation of larval fish biology of freshwater fishes is still in its infancy in Australia. It would seem that the appropriate management of flows and habitat for spawning and for larval fishes is a necessary prerequisite for the management of fish stocks and productivity, yet this aspect remains little studied in north-eastern Australia. There seems little point in elegant and complicated computer simulations examining the impact of exploitation on adult stocks or the effect of flow manipulations on adults and juveniles if the needs of larval fishes are not first met. Further examination of the environmental cues that stimulate spawning is also warranted. Research is needed to distinguish the degree to which floods stimulate spawning and the degree to which floods or periods of low flow enhance recruitment through the provision of suitable habitat and food resources, thereby increasing survivorship.
Environmental tolerances The extent of information regarding the tolerance of fishes of north-eastern Australia to water quality extremes or toxicants is extremely limited, being restricted to a few parameters (i.e. temperature and dissolved oxygen) for a few species such as Melanotaenia splendida or Leiopotherapon unicolor only. The impact of elevated turbidity on stream fishes has received scant attention, yet the existing extent of cleared land and the increasing rate at which land is being cleared in the region, coupled with the current trend for grazing land to be turned to more profitable crop-based activities, suggest that sediment inputs to freshwater systems are higher now than natural. What are the direct impacts of elevated turbidity on riverine fishes? Are impacts felt equally by different species or by different age classes within species? (i.e. do elevated levels of suspended solids interfere with feeding in larval fishes?). Are impacts mediated by changes in food supply or direct physiological or pathological effects on the individual? To our minds, investigations of the tolerance of freshwater fish to water quality extremes are not recognised as valuable contributions to freshwater fish ecology and management. Many see this sort of science as less than interesting, laborious and repetitive. It need not be if such investigations are placed within the appropriate management context or if interspecific comparisons are placed within the appropriate landscape and phylogenetic context. This information is urgently needed particularly considering the increased emphasis being placed on setting water quality standards to protect biodiversity in catchments feeding into the Great Barrier Reef Lagoon and the reef itself.
It is of great concern that research focused on aspects of the life history of individual species (or groups of species) is no longer encouraged in post-graduate studies. The limited time scales in which post-graduate degrees must now be completed, make life history investigations very risky. Moreover, many students may feel that such studies are not worthy or strategic enough to warrant investigation, not amenable to the application of advanced technology, or unlikely to lead to future employment at a an appropriate level. National funding bodies are perhaps not so interested in organismal biology as they should be. There no longer seems to be much emphasis placed on curiosity driven research. Movement Fish movement, for whatever purpose, is an important process in rivers of northern Australia but, with the exception of a few studies such as Bishop et al. [190], studies related to this area have been primarily limited to assessments of the efficiency of fishways [162, 232, 586, 739, 740, 828, 1173, 1238, 1274, 1275, 1276, 1277]. These studies have, however, revealed important insights into the degree of movement exhibited by freshwater fishes of northern Queensland. Several of these studies are particularly noteworthy, revealing that different species migrate under different flow conditions and therefore, fishway designs must be able to accommodate low flow conditions. The value of fishways as sampling devices needs to be more
Reproduction The definition of critical habitat and flow requirements of fish is virtually impossible without detailed life history information. The freshwater fish fauna of many parts of Australia, particularly northern Australia, is essentially
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Freshwater Fishes of North-Eastern Australia
fully realised. Rarely are fishway studies used to examine why fishes are moving; fish are identified, counted, sometimes measured but rarely retained for examination in the laboratory as part of systematic investigation of life history biology. Empirical studies (e.g. [769, 853, 855]) of the swimming abilities of adult and juvenile fishes are needed for many species. Without such data, assertions that the passage requirements of one species of particular economic value is sufficient to accommodate most other species or all life history stages remain unvalidated. Greater attention to the movement biology of the freshwater fishes of north-eastern Australia is needed, particularly given the continuing development of dams, weirs and other infrastructure that form barriers to fish movement.
biomass to accumulate in otherwise small streams? Do they buffer stream fish communities during periods of low instream secondary production or do they make such communities less stable (i.e. more prone to variation in structure when particular food sources are in short supply)? Many species occurring in northern rivers are catadromous, whereas others are more properly considered marine. To what extent is carbon and energy derived from freshwater ecosystems incorporated into marine food webs? Conversely, how important to freshwater ecosystems and freshwater fishes is marine-based carbon? For example, how important is the huge biomass of marine derived carbon incorporated in eel leptocephali and glass eels given that a relatively small percentage appear to recruit into the adult population? Does the relative transfer of energy between marine and freshwater ecosystems change over the relatively large latitudinal gradient encompassed by the Queensland coast? What are the ecological implications of blocking these transfers of energy between marine and freshwater systems and vice versa?
Trophic ecology Dietary information is available for many of the fishes of northern Australia, one of the few aspects of ecology that is comparatively well investigated. However, there still remains the need for quantification of ontogenetic variation in diet, particularly that of larval fishes, and of spatial variation in diet at a variety of scales (i.e. habitat type, between rivers and between regions). There has been, and probably will continue to be, considerable debate about the role of biotic factors in the regulation of freshwater fish communities and few northern Australian studies have examined fish trophic ecology from a community level perspective. The extent of species interactions is of considerable importance in assessing the potential impacts of river regulation, habitat modification and the impacts of translocated and alien species. For example, flow releases from dams often result in an increase in the constancy and predictability of downstream flows. If the trophic structure of a fish assemblage occurring in a river has evolved under conditions of flow variability and is presumably characterised by trophic generalism, what are the expected outcomes of an increase in flow predictability with respect to species richness and assemblage structure? This question has not been addressed in depth in any of the world literature. Experimental evaluation of this problem will prove useful in predicting the impacts of flow regulation on fish assemblages, trophic structure and aquatic ecosystem function.
Identification and quantification of the links between the trophic structure of fish assemblages and sources of production, particularly with respect to the importance of off-stream sources such as floodplains and their associated waterbodies, will prove a useful aid in defining strategies for environmental flow and habitat maintenance, especially with respect to the need for, and characteristics of, large flushing flows and floodplain inundation. For example, if it can be shown that the major role of floodplain inundation with respect to riverine food webs is the transport of terrestrial carbon to the riverine environment and that this occurs rapidly, then the appropriate strategy may be one of a single short flood-flow. If, however, such transfer occurs slowly or is mediated by the passage of organisms from the river to the floodplain and back again, then the appropriate strategy may be one of either multiple or more prolonged single flood events. The incorporation of flows large enough to result in floodplain inundation is likely to be the most expensive and contentious issue in many environmental flow studies. It is therefore critical that the need for such flows be unequivocally demonstrated and quantified.
Also of interest is the role that freshwater fishes play in the transfer of energy between adjacent ecosystems. Many fish species consume terrestrial insects and some such as Toxotes rupestris, Kuhlia rupestris and Cairnsichthys rhombosomoides specialise on this food source to greater or lesser extents. Similarly, some terapontids consume large amounts of fruits. How important are such subsidies to freshwater ecosystems? Do they allow an increased
Conservation, mitigation and restoration The increasing rate of development in north-eastern Australia, particularly land clearing and the construction of water resource infrastructure, is potentially threatening to many freshwater fish species, as chapters throughout this book demonstrate. Six species (5% of the fauna) are already listed as Critically Endangered, Endangered or Vulnerable under the Environment Protection and
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Conclusion: Prospects, threats and information gaps
Biodiversity Conservation Act 1999 (EPBC Act). To address ongoing degradation of freshwater habitats and the pressures threatening riverine fishes will require intervention and management at many levels. Here we emphasise the need for river protection and conservation, briefly review strategies for mitigation of existing threatening processes, and outline potential rehabilitation or restoration measures recognised globally as integral to river management for biodiversity conservation.
757]. Several mitigation measures are available to offset the effects of catchment land use and river corridor engineering, including: buffer strips to protect rivers from direct agricultural runoff; land and waste management to minimise erosion and pollution; in-stream habitat protection and restoration. Environmentally sensitive design and operation of dams, weirs and flood control embankments can make a great deal of difference to the integrity of riverine ecosystems. Other measures include installation of fishways, creation of spawning substrate for focal fish species, eradication of alien species and instituting fish stocking programs founded on ecological protocols. The design of comprehensive flow prescriptions (in-stream or environmental flows) to protect river ecosystems and their fish faunas is essential and should involve maintenance or restoration of flow volumes and key hydrological patterns [93, 247]. Large rivers can be protected from further deterioration by prohibiting mainstream dams, limiting development on the floodplain and restricting activities designed to constrain the main channel, such as dredging, straightening and hardening of banks. Boulton et al. [212] have stressed the importance of maintaining the intimate linkages between groundwater and many surface aquatic systems. The impacts of exploitation can be addressed by regulating fishing activities through restrictions on fish size, total effort, gear types, and seasonal or spatial closures. Fish introductions should be strongly resisted or restricted by rigorously applying the Queensland Department of Primary Industries policy on alien species and translocations of native species.
Perhaps the most immediate challenge for managers and scientists is to review the level of protection of aquatic biodiversity, including freshwater fishes, in north-eastern Australia and identify those systems most in need of inclusion in conservation reserves. Arthington and Pusey [93], Barmuta [134], Cullen [353] and Dunn [392] have promoted the concept of a national system of Heritage Rivers set aside to protect the biodiversity and ecological functions of relatively undisturbed rivers and their floodplain wetlands. Boulton et al. [212] recently called for legislative protection of rare and threatened subterranean communities and species. Phillips et al. [1056] have developed a set of principles and tools for protecting Australian rivers and Dunn [392] has reviewed legislation and policy instruments designed to protect nature conservation values and to provide for sustainable water management (e.g. COAG Water Resources Policy, National Action Plan for Salinity and Water Quality, National Wetlands Policy). At a regional level, important attributes of individual rivers in north-eastern Australia have been identified as part of Water Resource Plans (WRPs) for major coastal and inland basins, however there is no generally accepted policy or set of practices in place to evaluate the relative conservation value of each river in the broader regional, national and international context. Apart from their heritage values, rivers and wetlands in conservation reserves will provide the major sources of propagules and colonists for degraded rivers and wetlands that have already lost much of their biological diversity [93]. Species-focused conservation measures are also needed to protect threatened fish species that cannot be conserved by declared protected areas alone; for example, large migratory species spending much of their life cycle outside protected areas, and species that may be heavily exploited. Species-focused strategies will typically involve multiple measures such as protection or restoration of key habitats, provision of passage facilities and environmental flows, restriction or eradication of alien species, and limits to recreational and commercial fisheries exploitation.
Rehabilitation and restoration are assuming a high profile in many countries as an extension of soil conservation programs and initiatives to improve water quality. Interventions focused on restoring the morphology and connectivity of river systems are increasing, for instance by restoring portions of the floodplain by local piercing of bund walls, setting back levees from the main channel and removing infrastructure from river banks. Many of these strategies are based on recognition of the importance of inter-connected backwaters, billabongs and side-arm channels and their role in sustaining riverine fish biodiversity [613, 614]. Adequate protection of riparian zones and the ecological processes linking terrestrial and aquatic systems is another very effective strategy for addressing many existing problems of river ecosystem degradation and impacts on freshwater fishes [1092]. Effective implementation of conservation, mitigation and restoration strategies to protect freshwater fish diversity relies upon a thorough understanding of the many aspects of fish ecology discussed in this book, from systematics and taxonomy, autecology and community ecology, to the complexities of ecosystem level processes such as energy
Attempts to mitigate rather than remove existing threats are a common approach to conservation of river resources and most aim to retain something of the original diversity and ecological functions of the aquatic ecosystem [93,
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Freshwater Fishes of North-Eastern Australia
of fish ecology as a fascinating, rewarding and worthy area of scientific and personal endeavor, essential to the future security of Australia’s unique array of freshwater fishes and aquatic biodiversity.
flow and food web interactions. Future research on the freshwater fishes of north-eastern Australia needs to be focused at all of these levels and should range from the local scale to processes operating far across terrestrial, freshwater and marine landscapes. We commend the study
584
Glossary of terms used in the text (sourced largely from Coad and McAllister [312], McDowall [884], Merrick and Schmida [936] and Allen [37]).
A abdomen — refers to the lower part of the body of fish, the belly. abdominal cavity — the part of the body containing the viscera or guts, liver, ovaries, testes, kidneys, etc. acid lake — any lake with a pH less than 6.0. acidity — a measure of the hydrogen ion concentration, a pH less than 7.0. acute — ending in a sharp point. adductor — a muscle that brings one body part towards another. adhesive disk — a sucker-like organ for clinging to various surfaces (e.g. the modified pelvic fins in the Gobiinae). adhesive egg — a fish egg that is deposited on sand, gravel, plants, etc. to which it sticks by means of the egg’s sticky surface or filaments adipose eyelid — transparent membrane(s) over the anterior and posterior regions of the eye (e.g. in Mugil cephalus). adipose fin — a small fleshy fin lacking rays or spines (e.g. in Ariidae). adnate — closely attached to, joined along whole length without a free tip. adult — a sexually mature animal. adventitious — a) accidental, occurring at an unusual locality; b) when used to describe streams refers to small stream entering directly into the main stem of the river. aestivation — dormancy during the dry season (e.g. in Lepidogalaxias salamandroides and Galaxias cleaveri). No fish species in north-eastern Australia are known to aestivate. Also spelled estivation. age at first maturity — mean or median age at first maturity when 50% of a cohort spawn for the first time. age class — individuals of a given (same) age within a population; a cohort. age distribution — the number or percentage of individuals in each age class of a population; age structure. algae — simple rootless aquatic plants. algivore — feeding on algae. alien — in this text refers to any species not native (indigenous) to Australia (see also exotic). allochthonous — food items, organic matter, nutrients, etc. that enter an aquatic ecosystem from outside (i.e. from the terrestrial environment). allopatric — refers to populations or taxa whose ranges do not overlap.
ambient — the conditions in the environment (e.g. temperature). amphidromous — fishes which migrate between the sea and fresh water (or vice versa) at some definite stage in their life cycle but not for the purpose of reproduction (e.g. Mugil cephalus (i.e. hard gut runs), some Gobiinae and Eleotridinae). anabranch — a diverging branch of a river which re-enters the main stream. anadromous — fishes which spend much of their life in the sea and which migrate to freshwater as adults to reproduce (e.g. Mordacia mordax). The opposite is catadromous. anaerobic — without oxygen, either as a presence or needed as part of a process. anal — pertaining to the anus. anal fin — the median ventral fin behind the anus. anal fin ray count — enumeration of the softrays in the anal fin. anal papilla — a fleshy protuberance through which the end of the digestive tract passes. anal spine (s) — a spine or spines at the origin of the anal fin before the soft rays. anastomosing — joining in a network, forming a network (i.e. braided). anguilliform — eel-like in shape or motion. animal pole — the location on the fish egg where polar bodies emerge; also the point of fertilisation just below where the sperm penetrates the chorion through the micropyle. anoxia — the lack of oxygen in an environment. anterior — in front; or towards the front. anthropogenic — arising from the actions or activities of humans. anus — the posterior opening of the digestive tract through which faeces are voided. apical — at the apex or end. apode fishes — fishes without pelvic fins (e.g. Anguilla). apomorph — a derived character differing from the ancestral condition. apomorphy — a state derived by evolution from a primitive state (plesiomorphy). aquatic — living in or near water or pertaining to water. articulated — jointed (e.g. soft fin rays). assemblage — co-existing organisms at a particular locality and at a specific time.
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Freshwater Fishes of North-Eastern Australia
bifid — divided in two (e.g. a forked preopercular spine). billabong — an isolated pool, a stream filled with water only in the rainy season, or a backwater, equivalent to an oxbow lake. binomen — the combination of a generic (first word with its initial letter capitalised) and a specific name (second word, always lower case) which together constitute the scientific name of a species; Also called binomial name. binomial nomenclature — the system of nomenclature in which a species, but no taxon or any other rank, is denoted by a combination of two names. biomass — the weight, volume or energy of living material in a given area, sample, fraction such as spawners, stock or for one or more given species (species biomass) or of all the species in a biotic community (community biomass). In fisheries the weight of a fish stock or some defined part thereof; abbreviated as B (Ricker, 1975). blotch — an irregular pigment mark, often with poorly defined margins. BOD — biological oxygen demand. Body depth —- maximum straight line depth excluding fins or fleshy and scaly structures at fin bases. body length — the length of the trunk which is taken as the distance between the posterior end of the head to the base of the caudal fin. bone — the hard connective tissue consisting of cells (osteoblasts, osteocytes) in a mixture of collagen fibres and hardened by calcium and phosphate salts (calcium hydroxyapatite), serving to support the body. brackish — fresh water with some salt content, as in estuaries, in the range 0.5–17.0 parts per thousand. braided stream — a complex tangle of converging and diverging stream channels (anabranches) separated by sand bars or islands. branched ray — a soft or segmented ray which divides distally into two or more parts. branchia (plural branchiae) — gill. branchial — relating to the gills. branchial arch — the gill arch. brood — a group of fish spawned at the same time. buccal — relating to the mouth cavity. buccal incubation — the retention of eggs in the buccal cavity until hatching (e.g. in Glossamia aprion (Apogonidae)).
aufwuchs — organisms and detritus coating rocks and plants in an aquatic environment. autecology — the ecology of individual organisms or species. author (authority) — the person to whom a zoological name is attributed or who first publishes a name satisfying nomenclatural criteria (e.g. Whitley is the authority for Nannoperca oxleyana). The author’s name is placed in parentheses if the species is now placed in a genus other than that in which it was originally described (e.g. Mogurnda adspersa (Castelnau, 1878)). autochthonous — referring to nutrients generated within an aquatic system. axillary process or scale — a small triangular appendage or a modified scale at the upper or anterior base of a paired fin. Also called accessory scale or fleshy appendage (e.g. Mugil cephalus or Megalops cyprinoides). B backpack shocker — an electroshocker on a frame used for sampling fish in streams and shallow waters. backwater — a stillwater section of a stream or river beside the main flow. bank — a) an area where the depth of water is relatively shallow, but normally sufficient for safe surface navigation; b) the side of a river, the right bank being on the right when facing downstream. barbel — a slender fleshy process located close to the mouth, usually possessing tactile and/or gustatory sense (e.g. in eel-tailed catfishes (Plotosidae) and fork-tailed catfish (Ariidae)). barrage — dams or weirs, often located at or near the tidal/freshwater interface. basal — at or towards the base; pertaining to the base. base flow — flow of a river composed entirely of groundwater from springs. basin — that part of a watershed that slopes towards a common low-lying area where all surface and subsurface water drains (i.e. an area drained by a river and its tributaries). batch fecundity — number of eggs released by a batch spawner in one spawning. batch spawner — a fish which sheds eggs more than once through a spawning season (e.g. Melanotaenia spp.) rather than within a short period (a fractional spawner). before present — conventionally before 1950 A.D. Abbreviated as B.P. benthic — bottom-dwelling, pertaining to the sea, lake or river bed. benthos — organisms which live on the bottom of a water body, in it or near it. bicuspid — with two points or cusps, usually applied to teeth.
C caecum (plural caeca) — a blindly ending sac arising from the gut (e.g. pyloric caeca). Cambrian — the earliest period of the Palaeozoic Era ca. 570–504 million years ago. canopy — overhanging vegetation, branches and leaves, providing shade and cover for fishes.
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Glossary of terms used in the text
Carboniferous — a period within the Paleozoic Era ca. 365–290 million years ago. carnivorous — animal or flesh eating; zoophagous. cartilage — the flexible, semi-rigid connective tissue consisting of rounded cells (chondrocytes) in a matrix with collagen fibres and low in calcium and phosphate salts. Serves to support the body. cascade — a short, steep drop (usually <1 m) in a stream bed often marked by boulders and white water. catadromous — those fishes which spend most of their lives in freshwater and which migrate to the sea to reproduce (e.g. Anguilla spp., Kuhlia rupestris, Lates calcarifer). catch per unit effort — catch in numbers or weight taken for a given amount of fishing effort over time using specific gear. catchment area — the area drained by a river or body of water or the area draining into a body of water. caudal — referring to the tail. caudal fin — the tail fin. In some families, such as the Anguillidae and Plotosidae, the dorsal, caudal and anal fins are united and are externally indistinguishable. caudal fin ray count — usually only the principal or mainrays are counted, the tiny rudimentary, often procurrent rays are not included. caudal fork length (CFL or LCF) — the distance from the most anterior point of the body to the deepest point of the fork in the caudal fin. caudal peduncle — the posterior part of the body between the end of the anal fin and the base of the caudal fin. caudal vertebra — one of the posterior vertebrae lacking ribs, found behind the abdominal vertebrae and extending to the tail, each with a ventral haemal arch, canal and spine. Cenozoic — a geological era, the age of mammals, ca. 65 million years ago to present day, comprising the Quaternary and Tertiary. cephalic — pertaining to the head. cephalic lateral line (or cephalic sensory canals) — the head canals opening to the surface in pores and containing neuromasts (sometimes the canals are lost and the neuromasts are exposed). channelisation — the process of changing, deepening and straightening the natural path of a waterway. character — a structure or feature of a species or taxon that enables it to be distinguished from another species or taxon. cheek — the area between the eye and the preopercle. cheek scale count — the number of scales crossing a straight line from the eye to the corner of the preopercle. chevron — V-shape. chorion — an embryonic membrane, elaborated by the follicle cells, which encloses the egg.
chromatophore — a dermal pigment cell. ciliated — fringed with projections. ciliated scale — a ctenoid scale having soft flexible ctenii (spines) on its posterior margin (e.g. Hypseleotris compressa). circadian — pertaining to a daily and rhythmic biological cycle. circulus (plural circuli) — the concentric ring or polygon found on scales. circumneutral — said of water with a pH of 5.5 to 7.4. circumpeduncular scale count — number of scales around the narrowest portion of the caudal peduncle. cirrus (plural cirri) — fringe-like fleshy appendages, usually slender and elongate. clade — a group defined by at least one shared derived character or synapomorphy inherited from a common ancestor; a monophyletic higher taxon, a branch on a cladogram. cladistics — a method used by systematists to determine evolutionary relationships. cladogram — a dendrogram or tree-like diagram expressing the evolutionary relationships among a group of organisms in terms of recency of common ancestry or descent. class — the taxonomic group above order and below phylum (e.g. Class Actinopterygii). classification — like organisms grouped within a hierarchical system. cline — a geographical gradient in a character (e.g. increase southwards in number of scale rows). clutch — the number of eggs laid at any one time. cohort — a group of individuals of the same age recruited into a population at the same time. common name — the vernacular name of a species, varying from place to place, by language and over time. competitive exclusion — two species cannot co-exist when they have identical needs of a limited resource, one is exluded. complex — a group of closely related species that have yet to be adequately described and distinguished. compressed — flattened from side to side (e.g. Melanotaeniidae). condition — the nutritional status of a fish or the amount of flesh on a carcass, varying with reproductive status and feeding. confluence — the meeting or junction of two or more streams or the place where these streams meet; the stream or body of water formed by the junction of two or more streams; a combined flow. congeneric — belonging to the same genus. conspecific — belonging to the same species. convergence — similarities which have arisen independently in two or more organisms that are not closely related.
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Freshwater Fishes of North-Eastern Australia
dentate — having teeth or tooth-like points; serrate. denticulate — tooth bearing. dentition — tooth pattern, including arrangement and shape. depauperate — impoverished; said of ichthyofaunas or areas with little diversity in numbers or species. depressed — flattened from top to bottom. Opposite to compressed. depth — a) distance from water surface to stream bed; b) morphometric term for vertical distance (e.g. body depth). derived — a character or character state not present in the ancestral stock; apomorphic. description — a more or less complete statement of the observed characters of a taxon. detritivore — feeder on detritus. detritophagy — feeding on detritus, q.v. detritus — debris, disintegrated or particulate organic material that enters into an aquatic system. Devonian — a geological period within the Palaeozoic Era ca. 413–365 million years ago; called the Age of Fishes. diadromous — those fishes which regularly migrate between fresh and salt water during a definite period of the life-cycle (e.g. Macquaria novemaculeata). diagnosis — a succinct and formal statement of the characters that distinguish a taxon. diagnostic character — any character or character state that clearly differentiates one taxon from another. dichotomous key — an identification key using a series of alternative choices, each pair forming a couplet, that eventually lead to a species identity; the usual form of keys for fish identification. diel — daily, a 24-hour period. dimorphic — having two forms. diphycercal — an internally and externally symmetrical tail fin (e.g. in Dipnoi (Ceratodontidae), Australian lungfish). May be secondarily acquired from the homocercal condition by loss of the real caudal fin and the gaining of a new one from dorsal and anal elements. diplostomiasis — infestation of the fish eye by metacercaria of the fluke Diplostomum sp., eventually resulting in blindness. Snails are the intermediate host and piscivorous birds the final host. discharge — flow of water in a river, measured in cubic metres per second (m3/s) or megalitres per day. discontinuity — an interruption; an obstacle to a stream continuum. disjunct — distinctly separate; said of ranges that are discontinuous so that discrete, but potentially interbreeding, populations cannot interbreed. disruptive colouration — an irregular colour pattern, often patches of light and dark, functioning as camouflage.
couplet — a pair of contrasting descriptive statements; used in identification keys to give a choice leading to a species identification or to the next couplet. cover — any materials in a water body to create fish habitat, spawning and nursery areas. CPUE — catch per unit effort. creek — a small fast-flowing stream. crenulate — minutely crenate or scalloped. crepuscular — relating to dawn or dusk, often used in the sense of when a species is active. crescentic — shaped like the moon in the first or last quarter. crest — a ridge; a median bony or fleshy ridge on the upper surface of the head. Cretaceous — a geological period of the Mesozoic Era ca. 140–65 million years ago. critically endangered — in the IUCN Criteria for threatened species, a taxon is Critically Endangered when it is facing an extremely high risk of extinction in the wild in the immediate future. cryptic — hidden, concealed, difficult to see. ctenii — small marginal spines or denticles on scales. ctenoid scale — a scale having small spines (ctenii) on the posterior exposed portion. cue — a stimulus (e.g. temperature is often a spawning cue). cumecs (m3/s) — rate of discharge, typically used in measuring streamflow. cusp — projection or point as on a tooth or spine. cutaneous — pertaining to the skin. cycloid scale — a smooth-edged round or oval scale lacking small spines on the posterior exposed edge. D daily increment — zones on an otolith formed in a day. dam — a barrier controlling the flow of water and backing up water, transforming lotic habit into lentic habitat. data deficient — in the IUCN Criteria for threatened species, a taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction based on its distribution and/or population status. delta — a fan-shaped alluvial deposit at a river mouth formed by the deposition of successive layers of sediment. demersal — sinking; bottom (e.g. eggs which sink to the bottom or are deposited on the bottom). Opposite of pelagic. dendritic — tree-like, branching. dendritic organ — a small arborescent organ with an osmoregulatory function found between the anus and the anal fin in certain Plotosidae (e.g. Plotosus, Cnidoglanis).
588
Glossary of terms used in the text
electrical stimulation. Used to determine the chemical content of fishes and other organisms and thereby to distinguish and relate them. electro-shocker — a device generating an electrical current used to paralyse fish and facilitate their capture. See electro-fishing. element — a unit of some larger structure (e.g. a ray or spine of a fin). elver — young, fully pigmented, cylindrical transformed Anguilla greater than about 8 cm long, at the stage in their migration where they have reached the coasts and begin ascending rivers (cf. glass eel). emarginate — having an edge slightly concave; shallowly forked (particularly of caudal fin). embedded — enveloped in skin, lacking free edges (e.g. scales of Anguillidae). embryo — developmental stages to the moment of hatching or of birth. embryonic period — the time from union of gametes until exogenous nutrition. endangered — said of a species facing imminent extirpation (nationally) or extinction (worldwide), in the IUCN Criteria for threatened species. endemic — restricted to a certain region; peculiar to; native to. endoparasite — an internal parasite. endorheic — said of an area where rivers do not discharge into the sea but terminate in a closed basin (e.g. rivers draining into Lake Eyre). endoskeleton — the inner bony support for the body. Eocene — a geological epoch within the Tertiary Period ca. 54–38 million years ago. epaxial — any structure morphologically dorsal to the horizontal plane of the notochord or vertebral column; body muscles above the horizontal septum. ephemeral — a) short-lived, transitory; b) streams which flow only in direct response to precipitation. epilimnion — the warm uppermost layer of water in a stratified lake, above the thermocline. epiphyte — organisms growing on or associated with the substrate, especially plants. epithet — the second word of a binomial name of a species (or the second and third of a subspecies); specific name; trivial name. erect — establish, or standing more or less upright. establish — to publish a zoological name so that it is available in the meaning of the International Code of Zoological Nomenclature, or make available (a name that was previously unavailable) for whatever reason. estuarine — condition in that portion of a river, the estuary, where it meets the sea and fresh and salt waters mingle or alternate. estuary — see estuarine.
dissolved organic matter — minute organic matter. dissolved oxygen — the amount of oxygen freely available in water. Abbreviated as DO. distal — at or near the outer edge or margin. Opposite of proximal. distensible — capable of being extended or dilated. diurnal — pertaining to daylight, active during the day; daily. diverse — taxa or biota with many members, a wide range of morphology or of life histories. diversity — a parameter describing, in combination, the species richness and evenness of a collection of species. dorsal — of or pertaining to the back. Opposite of ventral. dorsal fin ray count — enumeration of the soft dorsal fin rays. dorsal fin(s) — the unpaired fin(s) on the midline of the back. dorsolateral — between the back and the middle of the side, the upper area of the side. drainage — a group of interconnected streams that eventually enter the sea or the main channel of basin. drainage basin — the total surface land area drained by a stream or river; often used in the sense of the water bodies in the basin. dystrophic — a type of lake with low productivity, low nutrient availability and limited photosynthesis. E early life history — the stages from egg to juvenile in development. ecology — the science of the interaction between organisms and their physical and biological environment. ecosystem — the complex of living organisms and environmental conditions that function as a unit, although few ecosystems are entirely separate from other adjacent ecosystems. ectoparasite — an external parasite, on fishes often lice or leeches. Also includes parasites found in the gill cavity. ectotherm — an organism with a body temperature determined by the environment; poikilotherm; coldblooded. eddy — a circular movement of water where currents flow counter to each other or pass obstructions. edentate — toothless. egg size — the greatest diameter of a spherical egg, both the length and width of elongate or elliptical eggs. electrofishing — a method of capturing fish in which an electrical current is used to cause fish to orient themselves to the anode and swimming towards it involuntarily thus facilitating capture. electrophoresis — the movement and separation of chemicals in a fluid or semi-solid (i.e. gel) medium under
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Freshwater Fishes of North-Eastern Australia
foregut — anterior part of the larval gut from which the stomach and oesophagus develop. formalin — formaldehyde gas dissolved in water used as a fixative and preservative in fish collections. Formalin is a 37–40% solution of formaldehyde in water, making 100% formalin. fractional spawning — release of eggs at intervals, usually over several days or weeks. Also called batch spawner. frenum — the tissue joining the lip to the symphysis of the lower or upper jaw. fresh water — water having a salinity of less than 2 part per thousand (although precise definitions differ). frugivorous — fruit eating (e.g. adult Hephaestus fuliginosus). fry — a young fish at the post-larval stage but may include all fish stages from hatching to fingerling. fyke net — a bag-shaped, cylindrical or cone-shaped fish trap, mounted on rings, with funnels which direct the fish to successive compartments. The net is fixed in place by stakes or anchors.
etymology — used in taxonomy for the derivation and meaning of a scientific name. eustasy — worldwide simultaneous change in sea level. eutrophic — type of lake which is highly productive, with high nutrient levels and usually subject to periods of oxygen depletion. eutrophication — the process by which a water body moves to a state characterised by high nutrients and excessive production. evolutionarily significant unit — a population or group of populations inhabiting a defined geographical area that comprises a unique segment of the species. Abbreviated as ESU. exotic — not native; introduced from a foreign place or country. extant — currently still in existence. extinct — no longer living in existence. extirpated — no longer living in an area under consideration (e.g. nationally). F facultative — not limited to; not dependent on. Opposite of obligatory (e.g. the Queensland lungfish, Neoceratodus forsteri is a facultative air breather). family — a category next above genera (or subfamily) and next below order. fanning — movement of the fins over an egg mass or fry to aerate them and remove sediment. fecundity — number of eggs, fertility, the potential reproductive capacity of an organism or a population. filamentous — with thread-like projections. filter feeder — a fish that obtains small particles of food (plankton) by filtering them out of the water fin — flap-like external organ concerned with locomotion in fishes. fin element — a fin ray, spine or pterygiophore. fish kill — a die off of fishes within a relatively short period due to the onset of man-caused or natural factors.. fish ladder — a series of steps with flowing water and pools enabling a fish to circumvent an obstruction such as a dam (more generally known as a fishway or fishpass). fish passage facilities — features of a dam or road crossing that enable fish to move around, through, or over without harm. flexion — one of three substages in the larval stage of fishes (the others being preflexion and postflexion) characterised by upward displacement of the notochord and development of caudal fin rays. floodplain — low lying areas next to a river that are inundated from the river. May be used by fish for spawning, or as foraging habitat. focal point velocity — water velocity as measured in front of a fish.
G gape — the opening of the mouth. gas bladder — a thin membranous sac in the dorsal portion of the abdominal cavity. May function as one or more of: hydrostatic organ, sound producing organ, sound receptor, respiratory organ. Found in Actinopterygii. Often lacking in bottom fishes. Sometimes called swim bladder or air bladder, although less appropriate terms. genera — plural of genus, q.v. genetic drift — the occurrence of random change in gene frequencies within a small, isolated population over a short period without mutation or selection. genital papilla — a small fleshy projection behind the anus, through which the genital and sometimes urogenital system communicates with the exterior. genotype — the genetic constitution of an individual, or all the individuals sharing the same genetic constitution. genus (plural genera) — a category above species and next below the family-group, may be divided into subgenera. gill — a paired respiratory organ in fishes consisting of gill filaments on the gill arch in the posterior portion of the head and usually providing the primary exchange of gases between the blood and the surrounding water. gill arch — the endochondral skeletal support of the gill. gill cover — the side of the head covering the gills, comprising the bones (mostly the operculum) and associated tissues of the opercular series. gill filament — the thread-like, soft, red respiratory and excretory structure projecting outward from the gill arch.
590
Glossary of terms used in the text
head canals — the extension of the lateral line system on the head, opening to the surface through pores and containing neuromasts. head pore — an external opening of the cephalic sensory system. head spines — spines on the head (e.g. of Scorpaenidae or Chandidae members). headwaters — upper reaches of tributaries in a drainage basin. herbivore — feeder on plant material. hermaphrodism — the condition where both ovarine and testicular tissue are present in one individual, though both gametes are not necessarily produced at the same time. heterodont(y) — having more than one type of teeth within the same fish. heterothermic — cold-blooded; an organism whose body temperature follows closely that of their environment as in most fishes. Opposite of homeotherm. hindgut — posterior part of the gut that includes the intestine and rectal area. Holocene — a geological epoch within the Quaternary Period ca. 10 000 years B.P. to the present day. Also called Recent. holotype — the single specimen designated or indicated as ‘the type-specimen’ of a nominal species-group taxon (species or subspecies) by the author at the time of the original publication. homeotherm — organisms maintaining a constant internal temperature. home range — the area over which an animal normally travels in its day to day activities. homogenous — uniform; used to describe egg yolk in larval fishes as opposed to segmented. homology — similarity of characters due to close ancestry, a common evolutionary origin. homonym — one of two or more identical names denoting different species-group taxa (species or subspecies) within the same nominal genus. hybrid — the offspring of the crossing of two different taxa (most commonly two different species). hydrology — the study of water, its distribution, circulation, properties and effects, on the surface, subsurface and in the atmosphere. hypaxial — any structure morphologically ventral to the chordal axis; a muscle on the lower side of the body below the horizontal septum. hypolimnion — the cold lower layer of a stratified lake, under the epilimnion and beginning just below the thermocline. hyporheic — the saturated zone under a river or stream, comprising substrate with the interstices filled with water.
gill net — a net suspended in the water at varying depths by means of floats on the upper margin and weights on the lower margin. The mesh size determines the size of fishes caught, the fish being entangled around the gill region or gilled. gill raker — one of a series of variously shaped bony or cartilaginous projections on the inner side of the branchial arch. gill ray — branchial ray (the cartilaginous rod projecting out from the gill arch into the interbranchial septum which it supports and from the hyoid arch into the first hemibranch. Homologous with branchiostegal. Found in Elasmobranchii and Acanthodii). girdle — the skeletal support of the paired fins. glass eel — young transparent, cylindrical transformed Anguilla about 5–8 cm long, which have lost the leaf-like leptocephalus form, and are at the stage in their migration where they have reached the coasts, entered estuaries and often have begun ascending rivers. glide — a shallow stream habitat with smooth and slow flow and no turbulence. gonad — the organ, ovary and testis, producing the primary sexual products (eggs and sperm). gonopodium (plural gonopodia) — the specialised rays at the front of the anal fin in males, modified as a trough or united as a tube, used to transfer sperm to the female (e.g. in Poeciliidae). Gonosomatic (gonadasomatic) index — gonad weight expressed as a percentage of whole body weight. Abbreviated GSI. gorge — a small, narrow canyon with steep sides with a stream running through it. gradient — rate of vertical fall of a stream or river, expressed as metres per kilometre or as a percentage (i.e. a stream with a gradient of 1% falls 10 m every kilometre). granulated — rough with small bumps. gravid — full of eggs or embryos. guild — a group of species, possibly unrelated taxonomically, that exploit overlapping resources or share common resources by similar modes (e.g. a reproductive guild). gut — the alimentary or digestive tract and associated organs. H habitat — the place a species lives, defined by necessary biological and physical parameters (e.g. dune lake, stream, riffle). hardness — the concentration of calcium and magnesium ions in water expressed as p.p.m. or mg/L of calcium carbonate equivalents. hatch — the process of an embryo leaving the egg envelopes.
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Freshwater Fishes of North-Eastern Australia
seasonal batches, as is the case in most fishes, cf. semelparous. IUCN — International Union for Conservation of Nature and Natural Resources.
hypoxic — very low oxygen levels. I ichthyofauna — fish life of a region, fish fauna. ichthyology — the study of fishes; usually restricted to the scientific study of and the resulting knowledge about fishes. imbricate — overlapping like shingles on a roof (with reference to scales). immature — not ripe, not fully developed sexually. impoundment — an enclosed body of water, of artificial construction and with variable environmental conditions. indigenous — native to a particular area. inferior — ventral, below. ingestion — taking in food, usually by swallowing. inshore — in shallow waters near the shore. instream cover — living and dead aquatic and terrestrial vegetation within the stream channel plus associated structures such as undercut banks that may afford refuge for fish. insular — isolated geographically. inter-annual — between years, in terms of comparing populations or events. interbasin transfer — the diversion of water from one drainage basin to one or more other drainage basins. intermittent — said of a stream with interrupted flow or discontinuous flow. Opposite of perennial. intermittent spawning — spawning at intervals; see batch or fractional spawner. internal fertilisation — the deposition of sperm within the female by the male. International Code of Zoological Nomenclature – the rules and recommendations adopted worldwide for zoological nomenclature. interoparity — repeated reproduction, usually on an annual basis, in contrast to reproducing once and dying (semelparity). interspecific — between two or more species. intestine — often used for most of the gut of fishes as many lack a stomach, although strictly this stretches from the stomach, when present, to the anus. intraspecific — within a species. introduced — any species accidentally or deliberately moved and released outside its natural range. invalid — any name (available or unavailable) for a given taxon other than the valid name; a nomenclatural act not valid under the International Code of Zoological Nomenclature. invertivore — feeding on invertebrates. isthmus — strip of flesh lying between the gills on the underside of the head. iteroparous — producing offspring in successive years or
J junior synonym — see synonym, junior (the junior synonym is that with the later publication date of two or more different names applied to one and the same taxon. Jurassic — a geological period of the Mesozoic Era ca. 210–140 million years ago. juvenile — a young fish essentially similar to the adult but not sexually mature. K keel — a ridge or carina. key — a tabulation of characters used to identify a species. Two rubrics form a couplet, the usual arrangement of keys. Each couplet gives an alternative set of characters leading to the species identity or to the next couplet. L labial — pertaining to the lip; viewed from the lip or outside of the mouth (opposite of lingual). lacustrine — pertaining to or inhabiting lakes or ponds. lagoon — in northern Australia lagoon is used to denote a standing body of water associated with a river. It may be a floodplain water body that is occasionally connected to the river by flood flows or a long deep reach of the river proper that becomes isolated at times of low flow. Elsewhere this term strictly mean a shallow pond or elongate channel separated from the open ocean by a sand bar or reef, or by a narrow outlet, with little or no freshwater input. lake — a large, standing, inland body of water, usually fresh but may be saline. lamella (plural lamellae) — a layer, a thin plate. lanceolate — spear-shaped; broad at the base and tapering to a point. larva (plural larvae) — a developmental stage occurring hatching and metamorphosis into the juvenile condition. lateral — relating to the side. lateral canal — the horizontal part of the cephalic lateral line system behind the eye. lateral line — a tube-like sensory organ (usually bearing pores) extending along the side of the body from the rear of the head to the tail. lateral line pore — one of the series of the apertures of the lateral line canal. lateral line scale — one of the scales along the side of the body bearing lateral line pores (or pit organs). lateral stripe — a longitudinal band of pigment along the side.
592
Glossary of terms used in the text
median — in or at the middle. median fin — one of those fins located on the sagittal plane of the body, the dorsal, caudal and anal fins. melanin — indole compounds which give skin its black, grey or brown colour. Distributed in melanophores. melanophore — a black chromatophore (capable of producing yellows and brown when pigment is thinly dispersed). mental — relating to the chin. mental barbel — a barbel on the chin. meristic — pertaining to serially repeated structures (e.g. scales, vertebrae, fin rays, fin spines, other spine sand other structures that can be counted). mesh size — the stretched length from corner to corner of the mesh of a net (i.e. the size of the holes, used to denote size). meso- (prefix) — middle, intermediate. Mesozoic — a geological era ca. 245–65 million years ago, comprising the Cretaceous, Jurassic and Triassic periods. meta- (prefix) — after, between, among, change, transformation, distal to, beyond, behind. Metacercaria — an encysted preadult stage in the life cycle of digenetic trematodes. metamorphosis — a major structural change taking place during development from larvae to adult. microhabitat — a portion of a larger habitat. microphagous — an animal eating small particles or organisms. micropyle — the minute aperture in the egg membrane for the entry of the sperm. migration — a directed (not aimless) journey and return occurring regularly in a species. Miocene — a geological epoch within the Tertiary ca. 26–5 million years ago. molar — a large flat or ridged-topped tooth adapted for crushing or grinding. molariform — shaped like a molar. Molariform teeth are used for crushing molluscs and crustaceans. monophyletic — having a single unbranching line of evolution. A monophyletic taxon includes all descendents from the common ancestor of its members. A ‘monophyletic group’ usually refers to a clade. monotypic — a taxonomic unit including only one lower unit (e.g. a monotypic genus includes only one species). morph — a form, variant. morphology — the appearance, form and structure of an organism, especially based on external characters. morphometric character — a character based on measurement. mouth brooder — oral brooder MS-222 — tricaine methanesulphonate, a fish anaesthetic applied by immersion in dosed water.
lectotype — one of several syntypes designated after the publication of a species-group name, as the type-specimen of the taxon bearing that name. Designated only where there was no original holotype. left bank — the left side of a river when facing downstream. length-frequency distribution — the number of individuals encountered in each length interval. length-weight relationship — mathematical formula for the weight of a fish in terms of its length. lentic — referring to standing (or slow moving) waters in swamp, pond, or lake, as opposed to lotic or running waters. leptocephalus — the transparent ribbon- or leaf-like larvae (e.g. In Anguilla spp. and Megalops cyprinoides). levee — a natural embankment formed by sediment deposit during flooding. lifespan — the maximum expected age, on average. limnetic — living in or pertaining to marshes wetlands or lakes. limnion — fresh water including all water bodies. lithophilic — associated with a stony substrate. littoral — the intertidal zone between high and low tides marks. In lakes littoral is applied to the zone from the waters edge to the lakeward limit of rooted aquatic vegetation. locality — the geographical position of an individual, population or collection. lordosis — an abnormal dorso-ventral curvature of the fish vertebral column. lotic — referring to running water as in rivers or streams, as opposed to lentic or still waters. lower limb — the horizontal portion of gill arch or interopercle. lower risk — in the IUCN Criteria for threatened species, a taxon is Lower Risk when it has been evaluated, does not satisfy the criteria for any of the categories Critically Endangered, Endangered or Vulnerable. M m.a.s.l. — metres above sea level (elevation). macro- (prefix) — large, long, great. macrophagous — an animal eating large pieces or organisms (e.g. Macquaria ambigua or Lates calcarifer). macrophyte — a large plant, used especially for aquatic plants. mandible — the lower jaw. marine — pertaining to the sea. maturation — becoming adult and sexually mature. maturity — fish of a given age/size capable of reproduction. medial — towards the vertical plane running through the middle of the body (the sagittal plane).
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Freshwater Fishes of North-Eastern Australia
mtDNA — mitochondrial DNA. multiradial — radiating out in several directions. multiserial — arranged in several rows or series. m.y.b.p. — abbreviation of million years before present. myomere — a lateral muscle segment of the body, separated from its neighbours by connective tissue. myr — abbreviation of million years.
oil globule — a sphere of fat or oil in the yolk of some fish eggs. Variable in number, size, position and colour and so a useful character for identification. olfactory — pertaining to the nasal organs or the sense of smell. Oligocene — a geological epoch within the Tertiary Period ca. 38–26 million years ago. oligotrophic — a type of lake with low productivity. omnivore — feeder on both plants and animals. ontogeny (adjective ontogenetic) — the development from embryo to adult. opercular opening — gill opening. operculum — the flap externally closing the gill chamber. opportunistic feeding — feeding in which the fish is able to adapt to whatever food becomes available. oral — pertaining to the mouth. oral brooder — a fish which broods or protects the eggs (ovophile) or young (larvophile) by taking them into the mouth. orbit — the cavity in the skull enclosing the eye, the eye socket. orbital bones — the bones around the eye. order — a taxonomic category above the family-group and below the class-group. origin (fin) — the anterior end of the base of a fin. osteology — study of the structure and development of bones. otic — relating to hearing. otolith — a free calcium carbonate body in the inner ear used for perception of acceleration including gravity. ova (singular ovum) — eggs. ovary — the female reproductive organ, producing eggs. ovate — egg-shaped. oviposit — to deposit an egg during spawning. ovo-testes — gonad containing both male and female primary reproductive tissue (e.g. occasionally seen in Lates calcarifer during sex inversion). ovoviviparity — production of eggs that are fertilised and hatch inside the mother but the embryos lack a placental connection to the oviduct or uterus and so do not feed off the mother. The young are born as miniature adults, free-swimming and feeding (e.g. Gambusia holbrooki). oxbow — a U-shaped bend in a river. oxbow lake — a U-shaped section of river isolated from the main channel when a meandering river cuts across the neck of a meander; billabong in Australia.
N N — number of fish studied; n is often used. naked — lacking scales. nape — the region behind the back of the top of the head immediately posterior to the occiput. natal — of or connected with birth, birthplace (e.g. stream of a fish). native — organisms historically indigenous to an area. nekton — organisms of relatively large size which have fairly strong locomotory powers (as compared to plankton) and swim in the water column independent of currents. nest — a structure created for housing eggs and sometimes young (e.g. in Plotosidae and Eleotridinae). neural spine — the dorsal spine on top of the neural arch, directed backwards. neurocranium — the portion of the skull surrounding the brain, including the elements that surround the olfactory, optic, orbital or sphenotic, and otic or auditory capsules and the anterior end of the notochord. neuromast — a sensory cell with a hair-like process capable of detecting motion or vibrations in the water. The hair is sheathed in a gelatinous cupula terminalis. neuston — organisms that float or swim in surface waters. nocturnal — active at night; pertaining to the night. nomenclature — the system of scientific names applied to taxa, or the application of these names. nominal taxon — the taxon defined by its type, type-genus in the case of family, type-species in the case of genus, and type-specimen in the case of species. notochord — the skeletal rod consisting of a sheath firmly packed with cells which lie above the gut and below the nerve cord. nuptial — associated with breeding (e.g. nuptial colouration, nuptial tubercles). nursery — an area favoured for birth or egg deposition where young can grow. O obligatory — limited to; dependent on. Opposite of facultative. obtuse — blunt, having an angle of more than 90 degrees. occlusal — relating to the biting or grinding of tooth surfaces or the bringing of the opposing surfaces of the teeth of the two jaws into contact. ocellus (plural ocelli) — an eye-like spot, usually rounded with a lighter border.
P paired fin — the pectoral and the pelvic fins (as opposed to the vertical fins). Palaeocene — a geological epoch within the Tertiary Period ca. 65–54 million years ago.
594
Glossary of terms used in the text
palaeochannel — a former river channel. Palaeozoic (Paleozoic) — a geological era ca. 570–245 million years ago comprising the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. pan- (prefix) — a) all, all pervading; b) a shallow pond or lake, often dry and salt-encrusted. papilla (plural papillae) — a small, nipple-like, fleshy protuberance. papillose — covered with papillae. paraphyly (adjective paraphyletic) — a taxon that does not include all descendants from the common ancestor of its members. paratype — every specimen, other than the holotype, in the type-series; all the specimens on which the author bases the series. partial spawner — fish that spawn over a long time span, having eggs at various stages of development in the ovaries. particulate feeding — catching each prey item individually, whether a zooplankter or a whole fish. parts per thousand — a chemical concentration used to express salinity. Symbol ‰. passage — the movement of migratory fish through, around, or over dams, reservoirs and other obstructions in a stream or river. pectinate — comb-like. pectoral — pertaining to the pectoral fin, its skeleton, or the adjacent region. pectoral fin — the paired fin born by the pectoral girdle, usually just behind the gill opening or slightly dorsal or ventral to this position. pectoral girdle — the bony support of the pectoral fin behind the gills and usually attached to the posterior part of the skull. peduncle — caudal peduncle (the wrist-like portion of the posterior part of the body between the end of the anal fin and the base of the caudal fin. pelagic — occurring above the bottom; non-benthic. pelagic egg — an egg which floats above the bottom. pelvic — relating to the pelvic fins or girdle. pelvic fin — the paired fin which is located posterior, ventral or anterior to the pectoral fins (abdominal, thoracic or jugular in position). pelvic girdle — the skeletal support of the pelvic fins. periphyton — plants and animals adhering to parts of rooted aquatic plants, rocks or woody debris. peritoneal cavity — the coelomic cavity containing the viscera. peritoneum (plural peritonea) — a membrane covering the body cavity (coelomic cavity) including the viscera. perivitelline space — the fluid-filled space between the embryo and chorion of an egg.
Permian — a geological period of the Palaeozoic ca. 290–245 million year ago. pH — a measure of how acidic or alkaline a solution is (i.e. the concentration of hydrogen ions in a solution (log to base10 of the reciprocal of the hydrogen ion concentration)). pH 7.0 is neutral, lower values are acidic and higher values are alkaline. pharyngeal — pertaining to the region of the pharynx. phenology — the study of the timing of recurring biological phases, the causes of their timing with regard to biotic and abiotic forces, and the interrelation among phases of the same or different species. phenotype — the observable structural and functional properties of an organism, produced by the interaction between the genotype and the environment. photoperiod — the length of sunlit portion of the day, which changes seasonally and latitudinally. phytophagy — plant eating; herbivorous. phytoplankton — plant plankton; minute, floating aquatic plants. piebald — with two colours irregularly arranged, usually black and white. pinnate — feather-like, having parts arranged on each side. pisci- (prefix) — pertaining to fish, from the Latin piscis, fish. planktivore — consumer of plankton. plankton — small aquatic organisms with weak locomotory powers living above the bottom. planktonivorous — plankton feeding. Pleistocene — a geological epoch of the Quaternary Period ca. 1.6–0.01 million years ago. plesiomorphy — the primitive state from which an apomorphy is derived. plicate — having plicae or a series of folds, grooves or wrinkles in the skin. Pliocene — a geological epoch within the Tertiary Period ca. 5–1.6 million years ago. plunge pool — a basin scoured out by a waterfall. poikilotherm — an organism whose body temperature follows closely that of their environment as in most fishes; ‘cold-blooded’. polyphyletic — having more than one origin or lines of descent, not closely related. Species may be grouped polyphyletically as a convenience until a monophyletic classification can be made. pool — a stream habitat having smooth surface, slow current and some moderate to deep water. population — a local group of individuals which form a potentially interbreeding community with other such populations. pore — a tiny opening in the skin, often associated with sensory perception in fishes. posterior — behind, opposite of anterior.
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Freshwater Fishes of North-Eastern Australia
postflexion — one of three substages in the larval stage of fishes (the others being preflexion and flexion). Postflexion ends with beginning of transformation to the juvenile stage. postlarva — a larva following the time of absorption of yolk; applied only when the structure and form continues to be strikingly unlike that of the juvenile (i.e. prior to metamorphosis). posttemporal — the superficial, Y-shaped dermal bone connecting the pectoral girdle with the skull. potamodromous — those fishes which make true migrations wholly in freshwater (e.g. Macquaria ambigua). ppb or p.p.b. — parts per billion. ppm or p.p.m. — parts per million. ppt or p.p.t. — parts per thousand. precaudal vertebrae — the anterior vertebrae lacking haemal spines and mostly bearing ribs. predatory — preying or feeding on other animals. predorsal — before the dorsal fin. preflexion — one of three substages in the larval stage of fishes (the others being flexion and postflexion, q.v.). The notochord is straight and caudal fin structures are beginning to form on the ventral side of the notochord. primitive character — a character or character state possessed by an ancestral species; a plesiomorphy. principal ray — a large ray, branched or unbranched, larger than the minor or rudimentary rays. pristine — an unaltered and undisturbed fish habitat. process — any projection from a body such as a bone. procurrent ray — one of a series of small, unsegmented rays on the dorsal and ventral edges of the caudal fin. profile — the outline of the head from the snout to the occiput or to the front of the dorsal fin, as viewed from the side. prolarva — larva still bearing yolk. protrusible — capable of being protruded, extended or thrust out (e.g. the upper jaw or both jaws project forward to form a tube or scoop-like cutting surface). proximal — situated towards the base or toward the body; inner, nearest, basal. Opposite of distal. psammophil — sand-loving. pungent — sharp. pyloric caecum (plural pyloric caeca) — a finger-like outpocketing of the intestine where it meets the end of the stomach (pylorus).
rains of fishes — fishes falling from the sky like rain or in rain, the result of waterspouts and whirlwinds. range — the geographical area inhabited by a species or other group. The range may be continuous or discontinuous (with gaps). rank — the position of a taxon in a hierarchy of classification. rapids — a stretch of water in a stream or river with small waterfalls and turbulent, rapid water over coarse substrate. rare (or vulnerable) — any indigenous species of fauna or flora that is particularly at risk because of low or declining numbers, occurrence at the fringe of its range or in restricted areas, or for some other reason, but is not a threatened species. Such vulnerable species require careful watching. ray — a ray (excluding spines) is a flexible, rod-like segmented and often branched, bilaterally paired fin support of dermal origin. reach — a section of a stream or river between two defined points, a continuous extent of water. rear — to feed and care for in a natural or artificial environment. Recent — a geological epoch within the Quaternary Period ca. 10, 000 years B.P. to the present day. Also called Holocene. recrudescence — beginning renewed growth. recruit — an individual fish that has moved into a certain class, such as the spawning class or fishing-size class. recruitment — the new members by immigration and/or numbers of fishes born in a given year, or entering a certain class, such as the spawning class or a fishing-size class. Red Data Book — list of threatened and extinct species for a given country. reduced — a less-developed condition of character. relative abundance — an index of fish population abundance used to compare fish populations from year to year. Usually expressed as a percent. relict — a) survivors of a formerly widespread fauna existing in certain isolated areas or habitats, b) a phylogenetic relict, a form in an otherwise extinct taxon (e.g. Neoceratodus forsteri). restricted (geographically) — confined to a small area (e.g. Glossogobius sp. 4 is restricted to the Mulgrave/Russell River). restricted (morphologically) — reduced (e.g. gill openings restricted; reduced in size refer to range. rheo- (prefix) — current, flowing. rheophilous — having an affinity for, or thriving in, flowing water. rheotaxis — orientation to water currents. Positive rheotaxis means facing upstream, negative rheotaxis oriented downstream.
Q Quaternary — a geological period of the Cenozoic Era ca. 1.6 million years ago to the present day, comprising the Pleistocene and Holocene (or Recent). R radial formula — counts of fin rays (see ray and individual fins for counting methods).
596
Glossary of terms used in the text
direction. scientific name — the Latin or latinised name of a taxon as opposed to its popular or vernacular name. Consists of two words, the genus name and the species or trivial name (e.g. Leiopotherapon unicolor is the scientific name for spangled perch). Secchi disc — a 20 cm diameter disc marked in 2 black and 2 white opposing quadrants, lowered into the water. The average of the depth at which it disappears from sight and the depth at which it reappears when lowered and raised in the water column is the Secchi disc reading, a measure of transparency. segmented — divided, particulate; used to describe egg yolk in larval fishes as opposed to homogenous. segmented ray — a fin ray divided into segments along its length. seine — a net shaped like a curtain used to encircle fishes, usually weighted at the bottom and with floats at the top, and often with a bag in the centre. semelparous — organisms having only one brood per lifetime, the adult dying after spawning. sensory canal — see lateral line. sensu — in the sense of. Used in nomenclature in front of the name of the author misapplying a name.. septum — a thin partition. series — the sample available for study. serrate — notched like a saw. seston — particulate organic matter such as plankton, organic detritus and inorganic particles such as silt. setiform — bristle-like; brush-like. sex inversion — change of sex naturally or after steroid hormone application. Also called sex reversal. Silurian — a geological period within the Palaeozoic ca. 441–113 million years ago. Most of the major groups of fishes are thought to have originated in the Early Silurian. simple — not divided or branched. simple ray — an unsegmented, unbranched soft ray. size distribution — the number of fish of various lengths or weights in a sample or catch. size limit — a legal limit on the size of fish that can be caught, either minimum or maximum. size-at-age — length or weight at a particular age. size-at-first-maturity — length or weight at maturity. Maturity is defined as minimal size attained at maturity or the size at which 50% of the fish at that size are mature. SL — abbreviation for standard length. snout — the tip of the head in front of the eyes. soft ray — an articulated or segmented fin ray, simple or branched. soft water — water with a low concentration of dissolved calcium and magnesium salts.
rhomboidal — shaped like a rhomboid (a non-rectangular parallelogram); wedge-shaped. riffle — a shallow stream habitat with broken or choppy surface water and moderate to fast current. Gradient is about 1–4%. riparian — pertaining to river or stream banks. ripe fish — one which is ready for spawning. river basin — total land area drained by a river and its tributaries. riverine — pertaining to a river, river-inhabiting. robust — strongly or stoutly built, husky; said of fish body shape and form. rostral — relating to the snout. rotenone — a fish poison derived from the roots of the South American jewel vine plant, Derris, hence ‘derris dust’ in Australia. rudimentary — very small and poorly formed; undeveloped; imperfectly developed. rudimentary ray — a simple fin ray usually an unbranched, unsegmented soft ray, often too small or obscure to include in counts. rugose — wrinkled, corrugated, rough. run — a) transitional segments of streams, between a riffle and a pool, with moderate to fast current and depth; b) seasonal migration undertaken by fish, usually as part of their life history. running ripe — ready to spawn as evidenced by a slight pressure on the abdomen causing eggs or milt to be shed. runoff — precipitation that flows across the ground and enters streams, rivers and lakes; may carry pollutants. Also used for the total discharge of a stream, both surface and subsurface, over a given time period. Defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it. S saddle — pigment extending over the back like a saddle. salinity — a measure of salts dissolved in a solution; the sea is 35‰ (35 parts of salts by weight per thousand parts of water). salt wedge — a layer of higher salinity water moving along the bottom towards the head of an estuary. sample — in ichthyology a collection of fishes made from a locality; a subset of a population; a representative part of a larger unit used to study the properties of the whole. sampling — the collecting of a sample; a general term used for field work. scale — a small, stiff, typically plate-like body in the skin of fishes. school — a group of fishes, usually constituted of the same species, which tends to orient and move in the same
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Freshwater Fishes of North-Eastern Australia
sp. — abbreviation for species (in the singular). spate — a heavy rainstorm, excessive runoff, a sudden flood. spatulate — spoon-shaped, depressed and concave. spawn (verb) — to lay (and fertilise) eggs in the process of reproduction. spawning substrate — the bottom type required by a fish for spawning. speciation — the evolution of species. species (singular and plural) — biologically, a group of populations of actually or potentially interbreeding organisms which are reproductively isolated (by behaviour, ecology, morphology or physiology) from other such groups. Abbreviated as sp. (singular) spp. (plural). species complex — a group of species that are morphologically similar and therefore difficult to identify. specific name — the second component of the binomial name of a species. When a species is placed in a given genus, the combination of the generic name and the specific name forms a binomen. A specific name has no meaning in nomenclature when cited in isolation. speciose — having many species. spent fish — a fish which has recently completed spawning. Fat content and general condition is usually low. spermatozoa — the flagellated male gamete or sperm. spicule — minute, hard, needle-like or sharp-pointed processes or projections. spine (body) — sharp hard bony structures on the skeleton or skin (e.g. preopercular spines). spine (fins) — a usually stiff, sharp, dermal rod which supports and or arms the fin; spinous ray. spp. — abbreviation for species (in the plural). squamation — the arrangement of scales; scalation. standard length (SL) – from the anterior-most part of the snout (even when the lower jaw projects) to the end of the hypural plate. stocking — moving fish to a water body so that ongrowing can occur. stomach — the part of the digestive tract after the oesophagus, not differentiated as a distinct section of the intestine in all fishes. stratification — the separation of a lake or body of water into layers of different temperature, due to heating of the surface and failure of heat to reach the bottom. stream — a small body of running water. stream bed — the channel occupied or formerly occupied by a stream. stream capture — the process by which the range of a species is extended through the switch of the flow of a stream or a part of a stream from one drainage basin to another. stream order — a classification of stream complexity based on the number of tributaries. The smallest
unbranched tributary in a watershed is called order 1; a stream formed by the confluence of two order 1 streams is called order 2; a stream formed by the confluence of two order 2 streams is called order 3; and so on. stream reach — section of a stream between two points. streamflow — the discharge that occurs in a natural channel. striated — with fine lines or grooves, often parallel. striated gut — a gut with many sinusoidal folds resembling lines or bands in lateral view. stripe — a horizontal band of pigment, often along the flank of a fish (a bar is a vertical band of pigment). subadult — an individual similar to the adult in appearance but not yet capable of breeding. subfamily — a category of the family-group subordinate to family. The recommended ending is -inae. subgenus (plural subgenera) — a category of the genusgroup subordinate to genus. subspecies (singular and plural) —a category of the species-group subordinate to species; the lowest category recognised by the International Code of Zoological Nomenclature. substrate — bottom or bottom materials. supralittoral swamp — brackish habitat on the landward side of mangrove swamps, inundated at times of very high tide or flood flow. surface feeder — a fish that takes it food from the air/water interface, or feeds just below the water surface. swim bladder — gas bladder: a thin membranous sac in the dorsal portion of the abdominal cavity that may function as a: hydrostatic organ (for regulating buoyancy), sound producing organ, sound receptor, respiratory organ. symmetrical — divisible by a plane through the centre into similar parts, each side a mirror image of the other (e.g. bilateral symmetry). sympatric — sharing, at least in part, the same geographical range. symphysis — the joining point between two bones effected by cartilage allowing a slight movement (e.g. joint between the tips of the lower jaw bones). synapomorphy — a character shared by two or more organisms or groups and inherited from an immediately preceding or recent common ancestor (shared derived character). Diagnoses a clade or monophyletic group. synecology — the ecology of communities rather than individual species. synonym — each of two or more names with different spelling applied to one and the same taxon. The junior synonym is that with the later, the senior synonym is that with the earlier, publication date. synonymy — the relationship between different names designating the same taxon.
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Glossary of terms used in the text
total spawners — synchronous development of eggs and sperm in a spawning population with all sex products released over a short period of time. trait — any character or property of an organism. translocation — movement of native or introduced species to waters or habitats outside their natural or previous distribution. Triassic — a geological period of the Mesozoic Era ca. 245–210 million years ago. tricuspid — with three points or cusps (e.g. tricuspid tooth). trophic — pertaining to nutrition. tubercle — a small, usually hard protuberance or excrescence of the skin. turbid — water opaque with suspended matter. type — the standard of reference for determining the precise application of a zoological name. type locality — the geographical place of origin of the type-specimens of a species-group taxon. type-series — the type-series of a species consists of all the specimens on which its author bases the species description. type-species — the nominal species that is the type of a taxon in the genus-group. Although many species may be included in a genus, a generic taxon is based on a single type species. type-specimen — the single specimen (holotype, lectotype, or neotype) that is the type of a taxon in the species-group.
syntopic — two or more species commonly occurring together. syntype — every specimen in a type-series numbering two or more in which no holotype nor a lectotype has been designated. The syntypes collectively constitute the name-bearing type. systematics — the study and classification of organisms into hierarchies and their phylogenetic interrelationships. T tail — the part of the body posterior to the abdominal cavity, thus including the caudal peduncle and the tail fin; also used for the tail fin alone. tailwater — the area immediately below a dam where the river water is cooler than normal and rich in nutrients. tautonym — one and the same name applied to both a genus and to an included species (e.g. Mogurnda mogurnda). taxis — a directed response or orientation of a motile organism towards (positive taxis) or away (negative taxis) from a stimulus. taxon (plural taxa) — any taxonomic unit (named or not) or category such as a family, genus, or species. It includes all taxa of lower rank and all individual organisms. taxonomic group — any taxon, including all subordinate taxa and their individuals. temporal — a) pertaining to the region just behind the eyes; b) pertaining to time. tendril — a slender, curling barbel or other structure. territorial — relating to the defence of an area in fish behaviour. testis (plural testes) — the male reproductive organ, producing sperm. thalweg — a) the river centre, the part with the greatest flow and depth; b) the lowest thread along the axial part of a valley or stream channel. threatened — a general term used to cover all taxa whose survival is uncertain. tide (adjective tidal) — the periodic rise and fall of ocean water produced by gravitational effects of the moon and sun on the earth. tooth plate — a flattened structure bearing teeth or a type of tooth which is the form of a flattened plate (e.g. in lungfishes). total dissolved solids — the total residue remaining after evaporation of a water sample filtered to remove suspended matter larger than 1.0 mm. total length (TL) — the greatest length of the whole body between the most anterior point of the body and the most posterior point, in a straight line, not over the curve of the body.
U ubiquitous — having a worldwide distribution, common to abundant in a given area. uniserial — arranged in a single row or series. unsegmented ray — a soft ray, usually small, without segments and found at the beginning of a fin. upper limb — the vertical portion of the gill arch. urogenital papilla — genital papilla. urogenital region — the area of the abdomen near the urinary and genital openings. V vagile — freely motile; wandering; mobile. vegetal pole — opposite to the animal pole on the egg. velocity — the speed of water flowing in a watercourse. vent — the posterior opening of the intestine, gonads and kidney ducts in front of the anal fin. ventral — pertaining to the lower surface or abdomen, opposite to the back or dorsal side. ventral fins — the paired fins other than the pectoral fins (placed right behind the gill slit); may be located behind, below or in front of the pectoral fins. Also called pelvic fins. verrucose — covered with small dermal warts.
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water column — the water mass between the surface and the bottom. water hardness — the concentration of calcium and magnesium ions in water expressed as p.p.m. or mg/l of calcium carbonate equivalents. Soft water is 0–60, moderately hard 60–120, hard 120–180 and very hard 180+ p.p.m. weir — a dam in a river to impound water. wet weight — the weight of a whole fresh fish. wetlands — lands where water saturation is the dominant factor determining the nature of soil development and the types of plant and animal communities living in the surrounding environment.
vertebra (plural vertebrae) — bony or cartilaginous elements surrounding the notochord or replacing it and often protecting the spinal cord and caudal vein. vestigial — rudimentary, degenerate; said of structures that have degenerated during evolution or ontogeny. vicariance — the presence of closely-related taxa or biota in different geographical areas; these have been separated by a natural barrier, a vicariant event (e.g. the rise of a mountain range isolating drainages). villiform teeth — fine, long, crowded teeth in a patch or band having the appearance of velvet. villus (plural villi) — a slender hair-like process, as those which extend into the intestine. They normally function as sensory organelles or to increase surface area for absorption. vitelline membrane — a membrane, product of the ooplasmic surface which adheres closely to the outer boundary of the ooplasm, but as fertilization separates from the surface as a distinct membrane. viviparity — the condition of giving birth to active, freeswimming young. voucher specimen — a specimen archived in a permanent collection (usually in a museum, an institution with a mandate to preserve materials indefinitely). Type specimens are voucher material. vulnerable — in the IUCN Criteria for threatened species, a taxon is Vulnerable when it is not Critically Endangered or Endangered but is facing a high risk of extinction in the wild in the medium-term future.
Y year class — all the individuals of a population of fishes born or hatched in the same year. yolk — granules of semi-crystalline phospholipoprotein used as a nutrient store during embryonic development. yolk sac — a sac containing yolk used for nourishment in larval fish. young-of-the-year (YOY) — members of age group zero. Z zoobenthos — animals living on or in the bottom of the sea or fresh water. zoophagy — feeding on plankton and benthos, relatively small animals. zooplankton — animal plankton. zygote — the fertilised egg.
W wallum — coastal heath vegetation dominated by the genus Banksia (also Melaleuca).
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Appendix 1. Fish species composition in rivers of north-eastern Australia
This list includes the known distribution of native, translocated and alien species. A key to the symbols used to denote the origin and distributional status of each species is given below. The basic unit of distribution follows the drainage basin designations used by the Queensland Department of Natural Resources, Mines and Energy (formerly Queensland Water Resources Commission) and used by Wager [1349]. Drainage basins are grouped according to their generalised location in Queensland. Note that some basins have been split into more biologically meaningful sub-basins (these have been denoted by the original basin number with an additional alphabetic post-script). A numeric key to the drainage basin names and the major rivers and streams within each basin is also given below. Within each drainage basin, major rivers within the same catchment are separated by / (e.g. Fitzroy/Dawson/Comet rivers) and unique catchments (e.g. small coastal streams) are separated by ,. Australian native fish families are arranged in approximate phylogenetic order (after Paxton and Eschmeyer [1041]) and genera and species within each family are listed in alphabetical order. Taxon designations follow Allen et al. [52]. Taxa with strong marine or estuarine affinities, but that are often also found in fresh water, are denoted with * (note that we have not included all such species here, only some members of those families that can be abundant in freshwaters and/or where similarities in morphology may cause confusion in identification
(e.g. Chandidae and Gobiidae). Taxa are listed with our preferred common name. Several studies identified some taxa to genus level only (due to uncertainty in specific identity). In cases where this genus has not been recorded in a given basin by any other study, it is listed by the genus name followed by spp.? (e.g. Ambassis spp.?) to denote that one or more members of the genus may actually be present. Due to uncertainty in the identity of synbranchid eels in Queensland, all records of Ophisternon gutturale are listed as such, but other records of taxa within this family are listed as Synbranchidae spp.?. Australian native species translocated to Queensland freshwaters beyond their natural distribution and alien fish species introduced into Queensland freshwaters are also listed (these lists are not exhaustive). Changes in species taxonomy and incorrect identifications have led to records of taxa in certain basins to be incorrect or confusing. We have largely (but not entirely) followed the corrections to fish records in the literature, museums and other taxonomic decisions made by Unmack [1338]. Refer also to the individual species chapters in this book for more information on errors in species distributions in the literature. The distributional information must be treated with caution as during the period where the majority of sampling has been undertaken (i.e. the last 30 years), there has been considerable habitat modification, fish translocations and introductions in many parts of Queensland which may have altered
Key to symbols: Symbol
Explanation
l Native (definite)
Taxa that have been sampled from a given basin and their identity is certain.
¡ Native (possible)
Taxa that have been reported from a given basin but their identity is uncertain.
l/n Native/Translocated (established) ¡/n Native/Translocated (established)
Australian native taxa that have been sampled from a catchment, their identity is certain (l) or uncertain (¡), and it is uncertain whether they are indigenous to a given basin or they have been translocated there and are thought to have become established.
n Translocated (established)
Australian native taxa that are not indigenous to a given basin but have been translocated there and are known to have become established, or in the case of diadromous species stocked into impoundments, that translocations are continuing.
o Translocated (uncertain/failed)
Australian native taxa that are not indigenous to a given basin but may have been translocated there at some point in the past, and the success of the translocation is uncertain or is known to have failed.
Alien (established)
Alien taxa (species from other countries) that have been introduced to a given basin and are known to have become established.
Alien (uncertain/failed)
Alien taxa that have been introduced to a given basin, but the success of the introduction is uncertain or is known to have failed.
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Freshwater Fishes of North-Eastern Australia
native and alien species distributions and abundances considerably. The information in this appendix does however, accurately reflect the current state of knowledge of the distribution of each species within Queensland. It is likely that future more intensive sampling will reveal that many species are more widely distributed in Queensland
river basins than that presented in this appendix, particlarly for some relatively poorly studied basins such as those in the Gulf of Carpentaria. We have not speculated on the distribution of species beyond those basins in which they have actually been recorded, but such information can be found in Wager [1349] and Allen et al. [52].
Key to drainage basins
Drainage basins and major rivers and streams within each basin are arranged heading west to north in the Gulf of Carpentaria and heading south along the eastern Queensland coast. Basin No.
Basin name
Basin area (km2)
Sub-basin Major rivers and streams No.
Gulf of Carpentaria and Western Cape York Peninsula 910
Settlement
11 760
910
Settlement Creek
912
Nicholson
36 105
912
Nicholson/Gregory/O’Shannassy/Lawn Hill rivers
913
Leichhardt
33 020
913
Leichhardt River
914
Morning
4040
914
Morning Inlet, Spring Creek
915
Flinders
108 780
915
Flinders/Saxby River, Bynoe River
916
Norman
48 950
916
Norman River, Brannigan Creek,
917
Gilbert
46 880
917
Smithburn River, Gilbert/Einesleigh rivers, Spring Creek
918
Staaten
25 460
918
Staaten River
919
Mitchell
71 795
919
Nassau River, Mitchell/Palmer/Walsh/Tate/Lynd rivers
920
Coleman
13 080
920
Coleman River, Chapman River, Edward River
921
Holroyd
10 425
921
Holroyd River
922
Archer
13 595
922
Archer/Coen rivers
923
Watson
4715
923
Watson River
924
Embley
4715
924
Embley River, Weipa creeks and lagoons, Mission River
925
Wenlock
7575
925
Wenlock River
926
Ducie
6655
926
Ducie/Dalhunty River, Jackson River, MacDonald River, Cotterell River
927
Jardine River
3265
927
Jardine River, Cowal Creek, Skull Creek, Bursta Creek, Polo Creek
Eastern Cape York Peninsula 101
Jacky Jacky
2770
102
Olive-Pascoe
4350
103
Lockhart
2825
104
Stewart
2795
105
Normanby
24 605
106
Jeannie
3755
101a
Jacky Jacky Creek, Escape River, Somerset and Ussher Point dune lakes and streams
101b
Harmer Creek, Shelburne Bay dune lakes and streams
102a
Olive River, Temple Bay Creek
102b
Pascoe River
103a
Claudie River
103b
Lockhart River
103c
Scrubby Creek, Three Quarter Mile Lake
104a
Rocky River, Massey Creek
104b
Stewart River
105
Morehead/Hann/Kennedy/Bizants/Normanby rivers
106a
Cape Melville, Muck Creek, Alex Creek, Howick River, Jeannie River, Starcke River
106b
Cape Flattery dune lakes and streams
106c
McIvor River
656
Appendix 1
Basin No.
Basin name
Basin area (km2)
107
Endeavour
2200
Sub-basin Major rivers and streams No. 107a 107b
Cape Bedford dune lakes, Endeavour River Annan River Wet Tropics
108
Daintree
2125
109
Mossman
490
110
Barron
2175
111
Mulgrave-Russell
2020
112
Johnstone
2330
113
Tully
1685
108a
Bloomfield River
108b
Cape Tribulation streams
108c
Daintree River
108d
Saltwater Creek
109a
Mossman River
109b
Mowbray River, Hartleys Creek
110a
Barron River
110b
Atherton Tableland Crater Lakes (Lake Barinne, Lake Eacham, Lake Euramo)
111a
Trinity Inlet, Cairns Creeks
111b
Mulgrave River, Russell River, Bramston Beach and Ella Bay coastal streams
112a
North and South Johnstone River
112b
Moresby River, Liverpool Creek, Maria River
113a
Hull River
113b
Tully River
114a
Tully-Murray floodplain lagoons, Murray River
114b
Rockingham Bay coastal streams and Hinchinbrook Channel coastal streams
114
Murray
1140
115
Hinchinbrook Island
415
115
Hinchinbrook Island
116
Herbert River
10 130
116
Herbert River, Herbert River floodplain, north Halifax Bay coastal streams
117
Black
1075
117
South Halifax Bay coastal streams, Black-Alice River
118
Ross
1815
118
Bhole River, Ross River, Cleveland Bay streams
119
Haughton
3650
119
Haughton River, Bowling Green Bay streams and wetlands
120
Burdekin
129 860
120
Burdekin River
121
Don
3885
121
Don River
122
Proserpine
2485
122
Eden Lassie Creek, Proserpine River
124
O’Connell
2435
124
O’Connell River, St. Helens Creek
125
Pioneer
1490
125
Pioneer River
126
Plane
2670
126
Plane Creek and other coastal streams
127
Styx
3055
127
Styx River
128
Shoalwater
3705
128
Herbert Creek, Shoalwater Bay coastal streams
129
Water Park
1840
129
Water Park Creek
130
Fitzroy
142 645
130
Fitzroy/Dawson/Comet rivers
132
Calliope
2255
132
Calliope River
133
Boyne
2540
133
Boyne River
134
Baffle
3860
134
Baffle Creek and other coastal streams
135
Kolan
2980
135
Kolan River
Central Queensland
657
Freshwater Fishes of North-Eastern Australia
Basin No.
Basin name
Basin area (km2)
Sub-basin Major rivers and streams No. South-eastern Queensland
136
Burnett
33 150
136
Burnett River
137
Burrum
3340
137
Elliott River, Gregory/Isis/Cherwell/Burrum rivers, Hervey Bay coastal streams
138
Mary
9595
138
Mary River
140
Noosa
1915
140a
Tin Can Bay coastal streams, Cooloolah coastal lakes and streams
140b
Noosa River, Sunshine Beach and Perigian Beach streams and wetlands
141a
Maroochy River
141
Maroochy
1410
141b
Mooloolah River
141c
Pummicestone Channel coastal streams
142a
Deception Bay coastal streams
142b
Pine River
142c
Sandgate coastal streams
143
Brisbane/Bremer rivers
145a
Redland Bay coastal streams
145b
Logan River
145c
Albert River
146a
Pimpana River, Coomera River, Nerang River
146b
Mudgerebah Creek, Tallebudgera Creek, Currumbin Creek
139
Fraser Island
142
Pine
1555
143
Brisbane
13 560
145
Logan-Albert
4195
146
South Coast
1295
139
Fraser Island
1685
141d
Bribie Island
141d
Bribie Island
144b
Moreton Island
144b
Moreton Island
144c
Stradbroke Islands
144c
North Stradbroke Island
505
658
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
920
921
922
923
924
925
926
927
918
917
916
915
914
919
Mordaciidae Mordacia mordax Ceratodontidae Neoceratodus forsteri Osteoglossidae Scleropages jardinii Scleropages leichardti Megalopidae Megalops cyprinoides* Anguillidae Anguilla australis Anguilla megastoma Anguilla obscura Anguilla reinhardtii Clupeidae Nematalosa erebi Engraulidae Thryssa scratchleyi Ariidae Arius berneyi Arius graeffei Arius leptaspis Arius paucus/midgleyi Arius paucus Plotosidae Anodontoglanis dahli Neosilurus ater Neosilurus brevidorsalis Neosilurus hyrtlii Neosilurus mollepsiculum Porochilus argenteus Porochilus obbesi Porochilus rendahli Tandanus tandanus Retropinnidae Retropinna semoni Galaxiidae Galaxias maculatus Hemiramphidae Arramphus sclerolepis Zenarchopterus buffonis* Zenarchopterus novaeguineae* Belonidae Strongylura krefftii Atherinidae Craterocephalus marjoriae Craterocephalus munroi Craterocephalus stercusmuscarum Craterocephalus stramineus Melanotaeniidae Cairnsichthys rhombosomoides Iriatherina werneri Melanotaenia duboulayi Melanotaenia eachamensis Melanotaenia maccullochi Melanotaenia nigrans Melanotaenia splendida Melanotaenia trifasciata Melanotaenia utcheensis Rhadinocentrus ornatus Pseudomugilidae Pseudomugil cyanodorsalis* Pseudomugil gertrudae Pseudomugil inconspicuous Pseudomugil mellis Pseudomugil signifer Pseudomugil tenellus Synbranchidae Ophisternon gutturale Synbranchidae spp.? Scorpaenidae Notesthes robusta Chandidae Ambassis agassizii Ambassis agrammus Ambassis elongatus Ambassis gymnocephalus Ambassis interruptus* Ambassis macleayi Ambassis marianus*
913
Native species
Alien (failed/uncertain)
Gulf of Carpentaria and Western Cape York Peninsula 912
Common name 910
Taxon
l
l/n
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
Short-headed lamprey Queensland lungfish Northern saratoga Saratoga Tarpon Short-finned eel Pacific long-finned eel Pacific short-finned eel Long-finned eel
l l
Bony bream
l
l
l
Freshwater anchovy
l
l
l
Berney’s catfish Lesser salmon catfish Triangular shield catfish Fork-tailed catfish Fork-tailed catfish
l
l
l l
l l
l l l l l
Toothless catfish Narrow-fronted catfish Short-finned catfish Hyrtl’s tandan Soft-spined catfish Silver tandan Obbes’ catfish Rendahl’s catfish Eel-tailed catfish
¡ l l
l
l
l
l
l
l
l
l
l
l
l
l
l l l l l
l l l l l
l l l l
l l
l l
l l
l l l
l
l
l
l
l
l
l
l
l
l
l l
l l l l
l
l
l
l
l
l
l
l
l
l
l l l
l l l l
l l
l l
l
l
l
l
l
l
l
l
l
l
¡
l
l l
l l
l l
l l
l l
l
l l
Australian smelt Common jollytail Snub-nosed garfish Buffon’s river-garfish Fly River garfish Freshwater longtom
l
l
Marjorie’s hardyhead Hardyhead Fly-specked hardyhead Strawman, Blackmast
l l l
l
Cairns rainbowfish Threadfin rainbowfish Duboulay’s rainbowfish Lake Eacham rainbowfish McCulloch’s rainbowfish Black-banded rainbowfish Eastern rainbowfish Banded rainbowfish Utchee Creek rainbowfish Ornate rainbowfish
l
l
l
l
l l
l l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l ¡
l l l
l l
l l l
l l l
l l
l l l l
l
l
l
l
l
Blueback blue-eye Spotted blue-eye Inconspicuous blue-eye Honey blue-eye Pacific blue-eye Delicate blue-eye
l
Swamp eel Unidentified swamp eel
l
l ¡
l ¡
l ¡
¡ l
l
l l
l l
l
l
l
l
l
l
l l
l l
l l
l
l l
l l
l l
l l
l
l
l
l l
l
Bullrout Agassiz’s glassfish Sailfin glassfish Elongate glassfish Bald glass perchlet Long-spined glassfish Macleay’s glassfish Estuary perchlet
l l
l l
l
l l
l
l
l
l
659
l
l
Freshwater Fishes of North-Eastern Australia
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
927
926
925
924
923
920
919
918
917
916
l
915
l
l
914
l
922
Flag-tailed glassfish Northwest glassfish Unidentified Ambassis Vachelli’s glassfish Pennyfish Giant glassfish
921
Ambassis miops Ambassis sp. (cf. muelleri) muelleri Ambassis spp.? Ambassis vachellii* Denariusa bandata Parambassis gulliveri Centropomidae Lates calcarifer Percichthyidae Guyu wujalwujalensis Maccullochella peelii Macquaria ambigua Macquaria novemaculeata Nannoperca oxleyana Terapontidae Amniataba percoides Bidyanus bidyanus Hephaestus carbo Hephaestus fuliginosus Hephaestus tulliensis Leiopotherapon unicolor Pingalla gilberti Pingalla lorentzi Scortum hillii Scortum ogilbyi Scortum parviceps Variichthys lacustris Kuhliidae Kuhlia marginata Kuhlia rupestris Apogonidae Glossamia aprion Toxotidae Toxotes chatereus Toxotes jaculatrix* Kurtidae Kurtus gulliveri Mugilidae Mugil cephalus* cephalus Myxus petardi* Gobiidae Awaous acritosus Chlamydogobius ranunculus Glossogobius aureus Glossogobius bicirrhosis* Glossogobius circumspectus* Glossogobius concavifrons Glossogobius giuris Glossogobius sp. 1 Glossogobius sp. 2 Glossogobius sp. 3 Glossogobius sp. 4 Mugilogobius notospilus Psammogobius biocellatus* Redigobius bikolanus* Redigobius chrysosoma* Schismatogobius sp. Sicyopterus lagocephalus Stenogobius psilosinionus Stiphodon alleni Eleotridae Bostrichthys zonatus Bunaka gyrinoides Butis Butis* Eleotris acanthopoma* Eleotris fusca* Eleotris melanosoma* Giurus margaritacea Gobiomorphus australis Gobiomorphus coxii Hypseleotris compressa Hypseleotris galii Hypseleotris klunzingeri Hypsleotris sp. 1 Hypseleotris sp. 2 Mogurnda adspersa Mogurnda mogurnda Ophiocara porocephala* Oxyeleotris aruensis Oxyeleotris fimbriata Oxyeleotris lineolatus
913
Native species
Alien (failed/uncertain)
Gulf of Carpentaria and Western Cape York Peninsula 912
Common name 910
Taxon
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l l
l l
l
l
l
l
l
l
l
l l
Barramundi
l
l l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l l
l l
l
l l
l
l
l
l l
l l
l l
l l
l
l
l
l
l l
l
Bloomfield River cod Mary River/Murray Cod Yellowbelly Australian bass Oxleyan pygmy perch Barred grunter Silver perch Coal grunter Sooty grunter Khaki grunter Spangled perch Gilbert’s grunter Lorentz’s grunter Leathery grunter Gulf grunter Small-headed grunter Lake grunter
l l
l
l
l
l
l
l
l
l
l
Spotted flagtail Jungle perch
l
Mouth almighty Seven-spot archerfish Banded archerfish
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
Nurseryfish
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l l
l
l
l
l
l
l
l l
Sea mullet Freshwater mullet Roman nose goby Tadpole goby Golden goby Bearded goby Circumspect goby Concave goby Flathead goby False Celebes goby Munro’s goby Dwarf goby Mulgrave goby Pacific mangrove goby Mangrove goby Speckled goby Spotfin goby Scaleless goby Rabbithead cling-goby Goby Allen’s cling-goby Barred gudgeon Greenback gauvina Crimson-tipped gudgeon Spinecheek gudgeon Brown gudgeon Ebony gudgeon Snakehead gudgeon Striped gudgeon Cox’s gudgeon Empire gudgeon Firetail gudgeon Western carp gudgeon Midgley’s carp gudgeon Lake’s carp gudgeon Purple-spotted gudgeon Northern trout gudgeon Spangled gudgeon Aru gudgeon Fimbriate gudgeon Sleepy cod
¡ l l
l
l l
l
¡ l
l
l
l l
l
l
l l
l l
l l
l
l
l
l
l
l
l
l
l
l
l l l
l
l l l
¡
l l
¡
l
l o
l
l
l
l
l
660
l
l
l
l
l
l
l l
l
l
l
l
l
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
Saltpan sole Selheim’s sole
924
925
926
927
l
923
l l
922
l
921
l
920
l
919
l
918
l
917
914
916
Poreless gudgeon Giant gudgeon Flathead gudgeon Dwarf flathead gudgeon
915
Oxyeleotris nullipora Oxyeleotris selheimi Philypnodon grandiceps Philypnodon sp. Soleidae Brachirus salinarum Brachirus selheimi Alien species Cyprinidae Carassius auratus Cyprinus carpio Puntius conchonius Cyprinidae sp. A Cobitidae Misgurnus anguilicaudatus Poeciliidae Gambusia holbrooki Poecilia latipinna Poecilia reticulata Xiphophorus helleri Xiphophorus maculatus Cichlidae Aequidens pulcher Aequidens rivulatus Amphilophus citrinellus Archocentrus nigrofasciatus Astronotus ocellatus Cichlasoma trimaculatum Haplochromis burtoni Hemichromis bimaculatus Heros severus Oreochromis mossambicus Thorichthys meeki Tilapia mariae Belontiidae Trichogaster trichopterus
913
Native species
l l
l l
l l
l l
l
l
l l
l
l
l l
Goldfish Common carp Rosy barb Unidentified cyprinid Oriental weatherloach Eastern Gambusia Sailfin molly Guppy Swordtail Platy
Alien (failed/uncertain)
Gulf of Carpentaria and Western Cape York Peninsula 912
Common name 910
Taxon
Blue acara Green terror Midas cichlid Convict cichlid Oscar Three spot cichlid Burton’s haplochromis Jewel cichlid Banded cichlid Tilapia Firemouth cichlid Black mangrove cichlid Three-spot gourami
661
l
l l
l
l l
Freshwater Fishes of North-Eastern Australia
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
103c
104a
104b
105
106a
106b
106c
107a
107b
103b
102b
l
l
l
Tarpon
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l l
l l
l l
l l
l
l l
l
l l
l l
l l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
103a
102a
Northern saratoga Saratoga
Native species Mordaciidae Mordacia mordax Ceratodontidae Neoceratodus forsteri Osteoglossidae Scleropages jardinii Scleropages leichardti Megalopidae Megalops cyprinoides* Anguillidae Anguilla australis Anguilla megastoma Anguilla obscura Anguilla reinhardtii Clupeidae Nematalosa erebi Engraulidae Thryssa scratchleyi Ariidae Arius berneyi Arius graeffei Arius leptaspis Arius paucus/midgleyi Arius paucus Plotosidae Anodontoglanis dahli Neosilurus ater Neosilurus brevidorsalis Neosilurus hyrtlii Neosilurus mollepsiculum Porochilus argenteus Porochilus obbesi Porochilus rendahli Tandanus tandanus Retropinnidae Retropinna semoni Galaxiidae Galaxias maculatus Hemiramphidae Arramphus sclerolepis Zenarchopterus buffonis* Zenarchopterus novaeguineae* Belonidae Strongylura krefftii Atherinidae Craterocephalus marjoriae Craterocephalus munroi Craterocephalus stercusmuscarum Craterocephalus stramineus Melanotaeniidae Cairnsichthys rhombosomoides Iriatherina werneri Melanotaenia duboulayi Melanotaenia eachamensis Melanotaenia maccullochi Melanotaenia nigrans Melanotaenia splendida Melanotaenia trifasciata Melanotaenia utcheensis Rhadinocentrus ornatus Pseudomugilidae Pseudomugil cyanodorsalis cyanodorsalis* Pseudomugil gertrudae Pseudomugil inconspicuous Pseudomugil mellis Pseudomugil signifer Pseudomugil tenellus Synbranchidae Ophisternon gutturale Synbranchidae spp.? Scorpaenidae Notesthes robusta Chandidae Ambassis agassizii Ambassis agrammus Ambassis elongatus Ambassis gymnocephalus Ambassis interruptus* Ambassis macleayi Ambassis marianus*
Alien (failed/uncertain)
Eastern Cape York Peninsula 101b
Common name 101a
Taxon
Short-headed lamprey Queensland lungfish
Short-finned eel Pacific long-finned eel Pacific short-finned eel Long-finned eel
l l
Bony bream
l
l
Freshwater anchovy Berney’s catfish Lesser salmon catfish Triangular shield catfish Fork-tailed catfish Fork-tailed catfish Toothless catfish Narrow-fronted catfish Short-finned catfish Hyrtl’s tandan Soft-spined catfish Silver tandan Obbes’ catfish Rendahl’s catfish Eel-tailed catfish
l
l
l
l
l
l l l
l l
l
l l l
l l l
l
l
l
l
l
l
l
l
l l
l
l l
l
l
l l
l
Australian smelt Common jollytail Snub-nosed garfish Buffon’s river-garfish Fly River garfish
l
l
Freshwater longtom Marjorie’s hardyhead Hardyhead Fly-specked hardyhead Strawman, Blackmast Cairns rainbowfish Threadfin rainbowfish Duboulay’s rainbowfish Lake Eacham rainbowfish McCulloch’s rainbowfish Black-banded rainbowfish Eastern rainbowfish Banded rainbowfish Utchee Creek rainbowfish Ornate rainbowfish
l
l
l
l
l
l
l l l l
l
l
l l
l l
l l
l
l
Blueback blue-eye Spotted blue-eye Inconspicuous blue-eye Honey blue-eye Pacific blue-eye Delicate blue-eye
¡
Swamp eel Unidentified swamp eel
l l
l
l
l
l
l l l
l l
l l
l l
l l
l
l l
l
l
l
l
l
l l
l
l l
l l
l
l
l
l
l
l
l
l
l
l
l
l
Bullrout Agassiz’s glassfish Sailfin glassfish Elongate glassfish Bald glass perchlet Long-spined glassfish Macleay’s glassfish Estuary perchlet
l l
l
l
l
l
l
l
l
l
l
l
¡ l
l
l
l
¡ l
l
l l l
662
l
l
¡ l
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
Barramundi
l
l
l
l
l
l
l
l
l
l
l
l l
¡ ¡
¡ ¡
l
l
l
l
l
l
l
l
l
l
107b
106b
106a
105
104b
104a
103c
103b
103a
102b
l
107a
Flag-tailed glassfish Northwest glassfish Unidentified Ambassis Vachelli’s glassfish Pennyfish Giant glassfish
106c
Ambassis miops Ambassis sp. (cf. muelleri) muelleri Ambassis spp.? Ambassis vachellii* Denariusa bandata Parambassis gulliveri Centropomidae Lates calcarifer Percichthyidae Guyu wujalwujalensis Maccullochella peelii Macquaria ambigua Macquaria novemaculeata Nannoperca oxleyana Terapontidae Amniataba percoides Bidyanus bidyanus Hephaestus carbo Hephaestus fuliginosus Hephaestus tulliensis Leiopotherapon unicolor Pingalla gilberti Pingalla lorentzi Scortum hillii Scortum ogilbyi Scortum parviceps Variichthys lacustris Kuhliidae Kuhlia marginata Kuhlia rupestris Apogonidae Glossamia aprion Toxotidae Toxotes chatereus Toxotes jaculatrix* Kurtidae Kurtus gulliveri Mugilidae Mugil cephalus* Myxus petardi* Gobiidae Awaous acritosus Chlamydogobius ranunculus Glossogobius aureus Glossogobius bicirrhosis* Glossogobius circumspectus* Glossogobius concavifrons Glossogobius giuris Glossogobius sp. 1 Glossogobius sp. 2 Glossogobius sp. 3 Glossogobius sp. 4 Mugilogobius notospilus Psammogobius biocellatus* Redigobius bikolanus* Redigobius chrysosoma* Schismatogobius sp. Sicyopterus lagocephalus Stenogobius psilosinionus Stiphodon alleni Eleotridae Bostrichthys zonatus Bunaka gyrinoides Butis Butis* Eleotris acanthopoma* Eleotris fusca* Eleotris melanosoma* Giurus margaritacea Gobiomorphus australis Gobiomorphus coxii Hypseleotris compressa Hypseleotris galii Hypseleotris klunzingeri Hypsleotris sp. 1 Hypseleotris sp. 2 Mogurnda adspersa Mogurnda mogurnda Ophiocara porocephala* Oxyeleotris aruensis Oxyeleotris fimbriata Oxyeleotris lineolatus
102a
Native species
Alien (failed/uncertain)
Eastern Cape York Peninsula 101b
Common name 101a
Taxon
l
l
l
l l
l
l
l
l
l
Bloomfield River cod Mary River/Murray Cod Yellowbelly Australian bass Oxleyan pygmy perch Barred grunter Silver perch Coal grunter Sooty grunter Khaki grunter Spangled perch Gilbert’s grunter Lorentz’s grunter Leathery grunter Gulf grunter Small-headed grunter Lake grunter
l
Spotted flagtail Jungle perch
l
l
l
l
l
Mouth almighty
l
l
l
l
l
Seven-spot archerfish Banded archerfish
l
l
l l
l
l
l
¡
n
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l l
l
l
l
l
l
l
l
l
l
l
l
l l
l
Nurseryfish Sea mullet Freshwater mullet Roman nose goby Tadpole goby Golden goby Bearded goby Circumspect goby Concave goby Flathead goby False Celebes goby Munro’s goby Dwarf goby Mulgrave goby Pacific mangrove goby Mangrove goby Speckled goby Spotfin goby Scaleless goby Rabbithead cling-goby Goby Allen’s cling-goby Barred gudgeon Greenback gauvina Crimson-tipped gudgeon Spinecheek gudgeon Brown gudgeon Ebony gudgeon Snakehead gudgeon Striped gudgeon Cox’s gudgeon Empire gudgeon Firetail gudgeon Western carp gudgeon Midgley’s carp gudgeon Lake’s carp gudgeon Purple-spotted gudgeon Northern trout gudgeon Spangled gudgeon Aru gudgeon Fimbriate gudgeon Sleepy cod
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l l
l
l
l
l l
l l
l
l
l
l l
l l
l l
l
l
l l
l l
l
l
l l
l
l
l
¡
l l
l
l l
l
l l l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l l
l
l
l
l
l
l
l
l
¡ ¡
¡ ¡
¡ ¡
l
l ¡ l
l
l
l
l
663
l
l l
l
l
l
l
l
l l
l
l
l
¡ ¡
¡ ¡
¡ ¡ l
¡ l
l
l
l
Freshwater Fishes of North-Eastern Australia
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
Saltpan sole Selheim’s sole
Goldfish Common carp Rosy barb Unidentified cyprinid Oriental weatherloach Eastern Gambusia Sailfin molly Guppy Swordtail Platy Blue acara Green terror Midas cichlid Convict cichlid Oscar Three spot cichlid Burton’s haplochromis Jewel cichlid Banded cichlid Tilapia Firemouth cichlid Black mangrove cichlid Three-spot gourami
664
l
l l
l l
l
107b
l
107a
l
106c
l
106b
l
106a
l
105
103c
l
104b
103b
l
104a
103a
Poreless gudgeon Giant gudgeon Flathead gudgeon Dwarf flathead gudgeon
102b
Oxyeleotris nullipora Oxyeleotris selheimi Philypnodon grandiceps Philypnodon sp. Soleidae Brachirus salinarum Brachirus selheimi Alien species Cyprinidae Carassius auratus Cyprinus carpio Puntius conchonius Cyprinidae sp. A Cobitidae Misgurnus anguilicaudatus Poeciliidae Gambusia holbrooki Poecilia latipinna Poecilia reticulata Xiphophorus helleri Xiphophorus maculatus Cichlidae Aequidens pulcher Aequidens rivulatus Amphilophus citrinellus Archocentrus nigrofasciatus Astronotus ocellatus Cichlasoma trimaculatum Haplochromis burtoni Hemichromis bimaculatus Heros severus Oreochromis mossambicus Thorichthys meeki Tilapia mariae Belontiidae Trichogaster trichopterus
102a
Native species
Alien (failed/uncertain)
Eastern Cape York Peninsula 101b
Common name 101a
Taxon
l l
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
l
l
l l
l l
l l
l
l
l
l
l
l
l
l
l
l l
l l
l
116
114b
l
115
114a
113a
112b
112a
111b
111a
110b
110a
109b
109a
108d
113b
Mordaciidae Mordacia mordax Ceratodontidae Neoceratodus forsteri Osteoglossidae Scleropages jardinii Scleropages leichardti Megalopidae Megalops cyprinoides* Anguillidae Anguilla australis Anguilla megastoma Anguilla obscura Anguilla reinhardtii Clupeidae Nematalosa erebi Engraulidae Thryssa scratchleyi Ariidae Arius berneyi Arius graeffei Arius leptaspis Arius paucus/midgleyi Arius paucus Plotosidae Anodontoglanis dahli Neosilurus ater Neosilurus brevidorsalis Neosilurus hyrtlii Neosilurus mollepsiculum Porochilus argenteus Porochilus obbesi Porochilus rendahli Tandanus tandanus Retropinnidae Retropinna semoni semon Galaxiidae Galaxias maculatus Hemiramphidae Arramphus sclerolepis Zenarchopterus buffonis* Zenarchopterus novaeguineae* Belonidae Strongylura krefftii Atherinidae Craterocephalus marjoriae Craterocephalus munroi Craterocephalus stercusmuscarum Craterocephalus stramineus Melanotaeniidae Cairnsichthys rhombosomoides Iriatherina werneri Melanotaenia duboulayi Melanotaenia eachamensis Melanotaenia maccullochi Melanotaenia nigrans Melanotaenia splendida Melanotaenia trifasciata Melanotaenia utcheensis Rhadinocentrus ornatus Pseudomugilidae Pseudomugil cyanodorsalis* cyanodorsalis Pseudomugil gertrudae Pseudomugil inconspicuous Pseudomugil mellis Pseudomugil signifer Pseudomugil tenellus Synbranchidae Ophisternon gutturale Synbranchidae spp.? Scorpaenidae Notesthes robusta Chandidae Ambassis agassizii Ambassis agrammus Ambassis elongatus Ambassis gymnocephalus Ambassis interruptus* Ambassis macleayi Ambassis marianus*
108c
Native species
Alien (failed/uncertain)
Wet Tropics 108b
Common name 108a
Taxon
Short-headed lamprey Queensland lungfish Northern saratoga Saratoga
o o
Tarpon
l
Short-finned eel Pacific long-finned eel Pacific short-finned eel Long-finned eel
l l
l l
Bony bream
l
l
l
l l l
l l
l l
o
l
l
l
l l n
l
l
l
l l
l l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l/n l&o
l l
l l
l
l
l
l l
l
l l
l l
Freshwater anchovy Berney’s catfish Lesser salmon catfish Triangular shield catfish Fork-tailed catfish Fork-tailed catfish Toothless catfish Narrow-fronted catfish Short-finned catfish Hyrtl’s tandan Soft-spined catfish Silver tandan Obbes’ catfish Rendahl’s catfish Eel-tailed catfish
l
l l
l
l
l
l
l
l
Australian smelt Common jollytail Snub-nosed garfish Buffon’s river-garfish Fly River garfish
l l
l
l l
l
Freshwater longtom
l
Marjorie’s hardyhead Hardyhead Fly-specked hardyhead Strawman, Blackmast Cairns rainbowfish Threadfin rainbowfish Duboulay’s rainbowfish Lake Eacham rainbowfish McCulloch’s rainbowfish Black-banded rainbowfish Eastern rainbowfish Banded rainbowfish Utchee Creek rainbowfish Ornate rainbowfish Blueback blue-eye Spotted blue-eye Inconspicuous blue-eye Honey blue-eye Pacific blue-eye Delicate blue-eye
l
¡ l l
l
l
l
l
l
l
l l
l
l
n
l
l
l
l
l
l
l
l
l
l
l l
l
l o
l o l
l
l
l
l
l
l
l
l
l
l
l
l
Swamp eel Unidentified swamp eel
l l
l l
l l
l
l
l l
l l
l l
Bullrout
l
l
l
l
l
l
l
l l
l l
l l
l l
l l
l l
l l l
Agassiz’s glassfish Sailfin glassfish Elongate glassfish Bald glass perchlet Long-spined glassfish Macleay’s glassfish Estuary perchlet
l
l
l l
l
l
l
l l
l
l
665
l l n
l
l
l
l
¡ l
l
l
l
l
l
l
l
l
l
l
l
l
l
¡
l
l
l
l
l l l
l
l l
l
l
l
l l
l l
l l
l l l l l
Freshwater Fishes of North-Eastern Australia
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
l
l
l l
l
l
l l
l l
l
l
l
l
l
l
l
l
l
116
l l
115
l
l
114b
l
113a
114a
l
113b
l
l
111a
l
110b
l
l
110a
l
109b
l
l
l
o o
Barred grunter Silver perch Coal grunter Sooty grunter Khaki grunter Spangled perch Gilbert’s grunter Lorentz’s grunter Leathery grunter Gulf grunter Small-headed grunter Lake grunter Spotted flagtail Jungle perch
l
112b
l
l
112a
l
Bloomfield River cod Mary River/Murray Cod Yellowbelly Australian bass Oxleyan pygmy perch
l
111b
Barramundi
109a
l
108d
Flag-tailed glassfish Northwest glassfish Unidentified Ambassis Vachelli’s glassfish Pennyfish Giant glassfish
108c
Native species Ambassis miops Ambassis sp. (cf. muelleri) muelleri Ambassis spp.? Ambassis vachellii* Denariusa bandata Parambassis gulliveri Centropomidae Lates calcarifer Percichthyidae Guyu wujalwujalensis Maccullochella peelii Macquaria ambigua Macquaria novemaculeata Nannoperca oxleyana Terapontidae Amniataba percoides Bidyanus bidyanus Hephaestus carbo Hephaestus fuliginosus Hephaestus tulliensis Leiopotherapon unicolor Pingalla gilberti Pingalla lorentzi Scortum hillii Scortum ogilbyi Scortum parviceps Variichthys lacustris Kuhliidae Kuhlia marginata Kuhlia rupestris Apogonidae Glossamia aprion Toxotidae Toxotes chatereus Toxotes jaculatrix* Kurtidae Kurtus gulliveri Mugilidae Mugil cephalus* Myxus petardi* Gobiidae Awaous acritosus Chlamydogobius ranunculus Glossogobius aureus Glossogobius bicirrhosis* Glossogobius circumspectus* Glossogobius concavifrons Glossogobius giuris Glossogobius sp. 1 Glossogobius sp. 2 Glossogobius sp. 3 Glossogobius sp. 4 Mugilogobius notospilus Psammogobius biocellatus* Redigobius bikolanus* Redigobius chrysosoma* Schismatogobius sp. Sicyopterus lagocephalus Stenogobius psilosinionus Stiphodon alleni Eleotridae Bostrichthys zonatus Bunaka gyrinoides Butis Butis* Eleotris acanthopoma* Eleotris fusca* Eleotris melanosoma* Giurus margaritacea Gobiomorphus australis Gobiomorphus coxii Hypseleotris compressa Hypseleotris galii Hypseleotris klunzingeri Hypsleotris sp. 1 Hypseleotris sp. 2 Mogurnda adspersa Mogurnda mogurnda Ophiocara porocephala* Oxyeleotris aruensis Oxyeleotris fimbriata Oxyeleotris lineolatus
Wet Tropics 108b
Common name 108a
Taxon
Alien (failed/uncertain)
l
l o
l
l l
l l
l l
Mouth almighty
l
l
l
Seven-spot archerfish Banded archerfish
l l
l
l l
l
l l
l
l
n
l
l
l l l
l l l
l l l
l/n l l
l l l
l l l
l l l
l
l l
l l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
¡ ¡
l
l
n
l l
n
l
l
l
Nurseryfish Sea mullet Freshwater mullet Roman nose goby Tadpole goby Golden goby Bearded goby Circumspect goby Concave goby Flathead goby False Celebes goby Munro’s goby Dwarf goby Mulgrave goby Pacific mangrove goby Mangrove goby Speckled goby Spotfin goby Scaleless goby Rabbithead cling-goby Goby Allen’s cling-goby Barred gudgeon Greenback gauvina Crimson-tipped gudgeon Spinecheek gudgeon Brown gudgeon Ebony gudgeon Snakehead gudgeon Striped gudgeon Cox’s gudgeon Empire gudgeon Firetail gudgeon Western carp gudgeon Midgley’s carp gudgeon Lake’s carp gudgeon Purple-spotted gudgeon Northern trout gudgeon Spangled gudgeon Aru gudgeon Fimbriate gudgeon Sleepy cod
l
l
l
l
l l
l l
l l
l
l
l
l l
l l l l l l
l
l
l
l
l l l
l
l l
l ¡ l
l l
l l
l
l l
l
l
l l
l
l
l l l
l l l l l l
l l
l l l l
l
l l l l l
l
l
l
l
l
l l l
l
l
l
l
l
l l
l
l
l
l l l
l l
l
¡ ¡ l
l l
l
l l l
l l l
l l l
l
l
l
l
l
l
l
l
¡ ¡
l
l
l l
l l
l
l l l
l l l
l l l
l l l
l l
l l l
l l
l
l l
l l
l
l n
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
¡ ¡
l
l
¡ ¡ l
l l
l l
l l
l
l
l/n
l
l
l
l
666
l l
l
¡ ¡ l
l
l
l l
l l l l
¡ ¡
l
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
Saltpan sole Selheim’s sole
116
l
115
l
114b
114a
113a
112b
112a
111b
111a
110b
110a
113b
Poreless gudgeon Giant gudgeon Flathead gudgeon Dwarf flathead gudgeon
109b
109a
108d
108c
Native species Oxyeleotris nullipora Oxyeleotris selheimi Philypnodon grandiceps Philypnodon sp. Soleidae Brachirus salinarum Brachirus selheimi Alien species Cyprinidae Carassius auratus Cyprinus carpio Puntius conchonius Cyprinidae sp. A Cobitidae Misgurnus anguilicaudatus Poeciliidae Gambusia holbrooki Poecilia latipinna Poecilia reticulata Xiphophorus helleri Xiphophorus maculatus Cichlidae Aequidens pulcher Aequidens rivulatus Amphilophus citrinellus Archocentrus nigrofasciatus Astronotus ocellatus Cichlasoma trimaculatum Haplochromis burtoni Hemichromis bimaculatus Heros severus Oreochromis mossambicus Thorichthys meeki Tilapia mariae Belontiidae Trichogaster trichopterus
Wet Tropics 108b
Common name 108a
Taxon
Alien (failed/uncertain)
¡
l/n
¡
¡
¡
¡
Goldfish Common carp Rosy barb Unidentified cyprinid Oriental weatherloach Eastern Gambusia Sailfin molly Guppy Swordtail Platy Blue acara Green terror Midas cichlid Convict cichlid Oscar Three spot cichlid Burton’s haplochromis Jewel cichlid Banded cichlid Tilapia Firemouth cichlid Black mangrove cichlid
Three-spot gourami
667
Freshwater Fishes of North-Eastern Australia
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
Mordaciidae Mordacia mordax Ceratodontidae Neoceratodus forsteri Osteoglossidae Scleropages jardinii Scleropages leichardti Megalopidae Megalops cyprinoides* Anguillidae Anguilla australis Anguilla megastoma Anguilla obscura Anguilla reinhardtii Clupeidae Nematalosa erebi Engraulidae Thryssa scratchleyi Ariidae Arius berneyi Arius graeffei Arius leptaspis Arius paucus/midgleyi Arius paucus Plotosidae Anodontoglanis dahli Neosilurus ater Neosilurus brevidorsalis Neosilurus hyrtlii Neosilurus mollepsiculum Porochilus argenteus Porochilus obbesi Porochilus rendahli Tandanus tandanus Retropinnidae Retropinna semoni Galaxiidae Galaxias maculatus Hemiramphidae Arramphus sclerolepis Zenarchopterus buffonis* Zenarchopterus novaeguineae* Belonidae Strongylura krefftii Atherinidae Craterocephalus marjoriae Craterocephalus munroi Craterocephalus stercusmuscarum Craterocephalus stramineus Melanotaeniidae Cairnsichthys rhombosomoides Iriatherina werneri Melanotaenia duboulayi Melanotaenia eachamensis Melanotaenia maccullochi Melanotaenia nigrans Melanotaenia splendida Melanotaenia trifasciata Melanotaenia utcheensis Rhadinocentrus ornatus Pseudomugilidae Pseudomugil cyanodorsalis* Pseudomugil gertrudae Pseudomugil inconspicuous Pseudomugil mellis Pseudomugil signifer Pseudomugil tenellus Synbranchidae Ophisternon gutturale Synbranchidae spp.? Scorpaenidae Notesthes robusta Chandidae Ambassis agassizii Ambassis agrammus Ambassis elongatus Ambassis gymnocephalus Ambassis interruptus* Ambassis macleayi Ambassis marianus*
Short-headed lamprey
135
134
133
132
130
129
128
127
126
125
124
122
121
120
119
Native species
Alien (failed/uncertain)
Central Queensland 118
Common name 117
Taxon
l
Queensland lungfish Northern saratoga Saratoga
o o
Tarpon
l
l
l
l
Short-finned eel Pacific long-finned eel Pacific short-finned eel Long-finned eel
l
l
l
l l
Bony bream
l
l
l
n
l l
l
l
n l
l
l l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l n
l l
l l
l
l
l
l
l
l
l l
n
Freshwater anchovy Berney’s catfish Lesser salmon catfish Triangular shield catfish Fork-tailed catfish Fork-tailed catfish Toothless catfish Narrow-fronted catfish Short-finned catfish Hyrtl’s tandan Soft-spined catfish Silver tandan Obbes’ catfish Rendahl’s catfish Eel-tailed catfish
l
¡
l
l
l
l
l
l l
l
l l
l
Australian smelt
l
¡
Common jollytail Snub-nosed garfish Buffon’s river-garfish Fly River garfish
l
l
l
Freshwater longtom
l
l
l
Marjorie’s hardyhead Hardyhead Fly-specked hardyhead Strawman, Blackmast Cairns rainbowfish Threadfin rainbowfish Duboulay’s rainbowfish Lake Eacham rainbowfish McCulloch’s rainbowfish Black-banded rainbowfish Eastern rainbowfish Banded rainbowfish Utchee Creek rainbowfish Ornate rainbowfish Blueback blue-eye Spotted blue-eye Inconspicuous blue-eye Honey blue-eye Pacific blue-eye Delicate blue-eye Swamp eel Unidentified swamp eel
o l
l
l
l
l
l
l
l
l ¡
l
l
l
l
l
l
l
l
l
l
l
l
l
¡ l
l
l
l
l
l
l
l
l
¡
¡
¡
l
l
l
l
l
l
l
¡
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
l
l
l
l l
Bullrout Agassiz’s glassfish Sailfin glassfish Elongate glassfish Bald glass perchlet Long-spined glassfish Macleay’s glassfish Estuary perchlet
l
l
l ¡
l l
l
l l
l
l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
¡ l
668
l
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
133
134
135
128
127
126
125
124
122
121
120
l
l
l
l
l
l
l
l
l
l
l
l
Bloomfield River cod Mary River/Murray Cod Yellowbelly Australian bass Oxleyan pygmy perch Barred grunter Silver perch Coal grunter Sooty grunter Khaki grunter Spangled perch Gilbert’s grunter Lorentz’s grunter Leathery grunter Gulf grunter Small-headed grunter Lake grunter
132
Barramundi
130
Flag-tailed glassfish Northwest glassfish Unidentified Ambassis Vachelli’s glassfish Pennyfish Giant glassfish
129
Ambassis miops Ambassis sp. (cf. muelleri) muelleri Ambassis spp.? Ambassis vachellii* Denariusa bandata Parambassis gulliveri Centropomidae Lates calcarifer Percichthyidae Guyu wujalwujalensis Maccullochella peelii Macquaria ambigua Macquaria novemaculeata Nannoperca oxleyana Terapontidae Amniataba percoides Bidyanus bidyanus Hephaestus carbo Hephaestus fuliginosus Hephaestus tulliensis Leiopotherapon unicolor Pingalla gilberti Pingalla lorentzi Scortum hillii Scortum ogilbyi Scortum parviceps Variichthys lacustris Kuhliidae Kuhlia marginata Kuhlia rupestris Apogonidae Glossamia aprion Toxotidae Toxotes chatereus Toxotes jaculatrix* Kurtidae Kurtus gulliveri Mugilidae Mugil cephalus* Myxus petardi* Gobiidae Awaous acritosus Chlamydogobius ranunculus Glossogobius aureus Glossogobius bicirrhosis* Glossogobius circumspectus* Glossogobius concavifrons Glossogobius giuris Glossogobius sp. 1 Glossogobius sp. 2 Glossogobius sp. 3 Glossogobius sp. 4 Mugilogobius notospilus Psammogobius biocellatus* Redigobius bikolanus* Redigobius chrysosoma* Schismatogobius sp. Sicyopterus lagocephalus Stenogobius psilosinionus Stiphodon alleni Eleotridae Bostrichthys zonatus Bunaka gyrinoides Butis Butis* Eleotris acanthopoma* Eleotris fusca* Eleotris melanosoma* Giurus margaritacea Gobiomorphus australis Gobiomorphus coxii Hypseleotris compressa Hypseleotris galii Hypseleotris klunzingeri Hypsleotris sp. 1 Hypseleotris sp. 2 Mogurnda adspersa Mogurnda mogurnda Ophiocara porocephala* Oxyeleotris aruensis Oxyeleotris fimbriata Oxyeleotris lineolatus
Central Queensland 119
Native species
118
Common name 117
Taxon
Alien (failed/uncertain)
l
l
l
l
l
o l
n
l
l
l o
l
l
n
l/n
l
l
l
l
l
l
l o
l
n
n
n
n
l
l
l
l
l
l
l
¡
n
o n
l o
l
l o
l
l o
o
o
o
l
l
l
l
l
o
l
l
Spotted flagtail Jungle perch
l
Mouth almighty
l
Seven-spot archerfish Banded archerfish
l
l
l
l
l
l
l l
l
l
l
l
l
¡
l
l
l
l
l
l
l l
l
l
l
l
l
l ¡
l
l
l
l ¡
l
l
l
l
l
l
l
l
l
Nurseryfish Sea mullet Freshwater mullet Roman nose goby Tadpole goby Golden goby Bearded goby Circumspect goby Concave goby Flathead goby False Celebes goby Munro’s goby Dwarf goby Mulgrave goby Pacific mangrove goby Mangrove goby Speckled goby Spotfin goby Scaleless goby Rabbithead cling-goby Goby Allen’s cling-goby Barred gudgeon Greenback gauvina Crimson-tipped gudgeon Spinecheek gudgeon Brown gudgeon Ebony gudgeon Snakehead gudgeon Striped gudgeon Cox’s gudgeon Empire gudgeon Firetail gudgeon Western carp gudgeon Midgley’s carp gudgeon Lake’s carp gudgeon Purple-spotted gudgeon Northern trout gudgeon Spangled gudgeon Aru gudgeon Fimbriate gudgeon Sleepy cod
l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l/n
l
l
l
l
l
¡ l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l/n l l
l l
669
l l
l
l
¡/n ¡/n l l
l
l/n
l l
l
l
l
l
l/n
l
l
l
l
l
l
l
l l
l ¡
l l
l
l ¡ l l
l
l
l
l l
l
l l
l l l l
l
l
l
l
l/n
l/n
l l l
l
l
l
n
n
n
Freshwater Fishes of North-Eastern Australia
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
l
l
l
133
132
130
129
128
127
126
125
124
122
121
120 l/n
135
Poreless gudgeon Giant gudgeon Flathead gudgeon Dwarf flathead gudgeon
134
Oxyeleotris nullipora Oxyeleotris selheimi Philypnodon grandiceps Philypnodon sp. Soleidae Brachirus salinarum Brachirus selheimi Alien species Cyprinidae Carassius auratus Cyprinus carpio Puntius conchonius Cyprinidae sp. A Cobitidae Misgurnus anguilicaudatus Poeciliidae Gambusia holbrooki Poecilia latipinna Poecilia reticulata Xiphophorus helleri Xiphophorus maculatus Cichlidae Aequidens pulcher Aequidens rivulatus Amphilophus citrinellus Archocentrus nigrofasciatus Astronotus ocellatus Cichlasoma trimaculatum Haplochromis burtoni Hemichromis bimaculatus Heros severus Oreochromis mossambicus Thorichthys meeki Tilapia mariae Belontiidae Trichogaster trichopterus
119
Native species
Alien (failed/uncertain)
Central Queensland 118
Common name 117
Taxon
l l
l
Saltpan sole Selheim’s sole
Goldfish Common carp Rosy barb Unidentified cyprinid
Oriental weatherloach Eastern Gambusia Sailfin molly Guppy Swordtail Platy Blue acara Green terror Midas cichlid Convict cichlid Oscar Three spot cichlid Burton’s haplochromis Jewel cichlid Banded cichlid Tilapia Firemouth cichlid Black mangrove cichlid Three-spot gourami
670
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
Mordaciidae Mordacia mordax Ceratodontidae Neoceratodus forsteri Osteoglossidae Scleropages jardinii Scleropages leichardti Megalopidae Megalops cyprinoides* Anguillidae Anguilla australis Anguilla megastoma Anguilla obscura Anguilla reinhardtii Clupeidae Nematalosa erebi Engraulidae Thryssa scratchleyi Ariidae Arius berneyi Arius graeffei Arius leptaspis Arius paucus/midgleyi Arius paucus Plotosidae Anodontoglanis dahli Neosilurus ater Neosilurus brevidorsalis Neosilurus hyrtlii Neosilurus mollepsiculum Porochilus argenteus Porochilus obbesi Porochilus rendahli Tandanus tandanus Retropinnidae Retropinna semoni Galaxiidae Galaxias maculatus Hemiramphidae Arramphus sclerolepis Zenarchopterus buffonis* Zenarchopterus novaeguineae* Belonidae Strongylura krefftii Atherinidae Craterocephalus marjoriae Craterocephalus munroi Craterocephalus stercusmuscarum Craterocephalus stramineus Melanotaeniidae Cairnsichthys rhombosomoides Iriatherina werneri Melanotaenia duboulayi Melanotaenia eachamensis Melanotaenia maccullochi Melanotaenia nigrans Melanotaenia splendida Melanotaenia trifasciata Melanotaenia utcheensis Rhadinocentrus ornatus Pseudomugilidae Pseudomugil cyanodorsalis* Pseudomugil gertrudae Pseudomugil inconspicuous Pseudomugil mellis Pseudomugil signifer Pseudomugil tenellus Synbranchidae Ophisternon gutturale Synbranchidae spp.? Scorpaenidae Notesthes robusta Chandidae Ambassis agassizii Ambassis agrammus Ambassis elongatus Ambassis gymnocephalus Ambassis interruptus* Ambassis macleayi Ambassis marianus*
Short-headed lamprey
l
l
l
Northern saratoga Saratoga
n
n
n
Tarpon
l
l
l
l
l
l
Short-finned eel Pacific long-finned eel Pacific short-finned eel Long-finned eel
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
Bony bream
l
l
l
l
l
l
l
l
l
l l
l l
l l
l
l l
l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
144c
142d
141d
l
Queensland lungfish
o
o
l
139
146b
146a
145c
145b
145a
143
142c
142b
142a
141c
141b
141a
140b
140a
136
South-eastern Queensland 138
Common name
Native species
137
Taxon
Alien (failed/uncertain)
o
n
o
n
n
o
l
o
o
o
n
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
l
Freshwater anchovy Berney’s catfish Lesser salmon catfish Triangular shield catfish Fork-tailed catfish Fork-tailed catfish Toothless catfish Narrow-fronted catfish Short-finned catfish Hyrtl’s tandan Soft-spined catfish Silver tandan Obbes’ catfish Rendahl’s catfish Eel-tailed catfish Australian smelt
l
l
l
l
Freshwater longtom
l
l
l
Marjorie’s hardyhead Hardyhead Fly-specked hardyhead Strawman, Blackmast
l
Cairns rainbowfish Threadfin rainbowfish Duboulay’s rainbowfish Lake Eacham rainbowfish McCulloch’s rainbowfish Black-banded rainbowfish Eastern rainbowfish Banded rainbowfish Utchee Creek rainbowfish Ornate rainbowfish Blueback blue-eye Spotted blue-eye Inconspicuous blue-eye Honey blue-eye Pacific blue-eye Delicate blue-eye
l
l l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
Swamp eel Unidentified swamp eel
l l
Bullrout
l
l
l
Agassiz’s glassfish Sailfin glassfish Elongate glassfish Bald glass perchlet Long-spined glassfish Macleay’s glassfish Estuary perchlet
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
l
Common jollytail Snub-nosed garfish Buffon’s river-garfish Fly River garfish
l
l l l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l
¡
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l l
l
l
l
l
l l
l
l
l
l l
l
l
l
l
l
l
l
l
l
l
¡
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
671
l
l
l l
l
l
l
Freshwater Fishes of North-Eastern Australia
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
142d
144c
141d
139
146b
146a
145c
145b
145a
143
l/o
142c
n n n
l
142b
l
142a
l
141c
138
l
Bloomfield River cod Mary River/Murray Cod Yellowbelly Australian bass Oxleyan pygmy perch
141b
137
Barramundi
141a
136
Ambassis miops Ambassis sp. (cf. muelleri) muelleri Ambassis spp.? Ambassis vachellii* Denariusa bandata Parambassis gulliveri Centropomidae Lates calcarifer Percichthyidae Guyu wujalwujalensis Maccullochella peelii Macquaria ambigua Macquaria novemaculeata Nannoperca oxleyana Terapontidae Amniataba percoides Bidyanus bidyanus Hephaestus carbo Hephaestus fuliginosus Hephaestus tulliensis Leiopotherapon unicolor Pingalla gilberti Pingalla lorentzi Scortum hillii Scortum ogilbyi Scortum parviceps Variichthys lacustris Kuhliidae Kuhlia marginata Kuhlia rupestris Apogonidae Glossamia aprion Toxotidae Toxotes chatereus Toxotes jaculatrix* Kurtidae Kurtus gulliveri Mugilidae Mugil cephalus* Myxus petardi* Gobiidae Awaous acritosus Chlamydogobius ranunculus Glossogobius aureus Glossogobius bicirrhosis* Glossogobius circumspectus* Glossogobius concavifrons Glossogobius giuris Glossogobius sp. 1 Glossogobius sp. 2 Glossogobius sp. 3 Glossogobius sp. 4 Mugilogobius notospilus Psammogobius biocellatus* Redigobius bikolanus* Redigobius chrysosoma* Schismatogobius sp. Sicyopterus lagocephalus Stenogobius psilosinionus Stiphodon alleni Eleotridae Bostrichthys zonatus Bunaka gyrinoides Butis Butis* Eleotris acanthopoma* Eleotris fusca* Eleotris melanosoma* Giurus margaritacea Gobiomorphus australis Gobiomorphus coxii Hypseleotris compressa Hypseleotris galii Hypseleotris klunzingeri Hypsleotris sp. 1 Hypseleotris sp. 2 Mogurnda adspersa Mogurnda mogurnda Ophiocara porocephala* Oxyeleotris aruensis Oxyeleotris fimbriata Oxyeleotris lineolatus
South-eastern Queensland 140b
Common name
Native species
140a
Taxon
Alien (failed/uncertain)
l
l
Flag-tailed glassfish Northwest glassfish Unidentified Ambassis Vachelli’s glassfish Pennyfish Giant glassfish
Barred grunter Silver perch Coal grunter Sooty grunter Khaki grunter Spangled perch Gilbert’s grunter Lorentz’s grunter Leathery grunter Gulf grunter Small-headed grunter Lake grunter
l n
l n n l/n l/n l l n
l l
l l
l l
o
l
l l
l l
n
n n l
l
l n l
l n l
n o
n
l l
l n l
l l n
n
n
o l
l
l
l/n l/n l/n l/n l/n l/n l/n l/n l/n l/n l/n l/n
Spotted flagtail Jungle perch
l
l
l
l
Mouth almighty
l
l
l
l
l l
l l
l l
l
l
l
l
l
l
l
l l
l
l l
l
l
l
l
l/n
Seven-spot archerfish Banded archerfish Nurseryfish Sea mullet Freshwater mullet Roman nose goby Tadpole goby Golden goby Bearded goby Circumspect goby Concave goby Flathead goby False Celebes goby Munro’s goby Dwarf goby Mulgrave goby Pacific mangrove goby Mangrove goby Speckled goby Spotfin goby Scaleless goby Rabbithead cling-goby Goby Allen’s cling-goby Barred gudgeon Greenback gauvina Crimson-tipped gudgeon Spinecheek gudgeon Brown gudgeon Ebony gudgeon Snakehead gudgeon Striped gudgeon Cox’s gudgeon Empire gudgeon Firetail gudgeon Western carp gudgeon Midgley’s carp gudgeon Lake’s carp gudgeon Purple-spotted gudgeon Northern trout gudgeon Spangled gudgeon Aru gudgeon Fimbriate gudgeon Sleepy cod
l
l
l
l l
l l
l l
l l
l l
l l
l
l l
l l
l l
l l
l l
l
l
l
l
l
l
l
l
l
l
l
l
l
¡ l
l
l
l
l
l
l
l
l
l
l
l l l l n l
l l l l
l l l l
l l
l l l
l l l
l l l
l l l
l l l
l l l
l l l
l
l
l
l
l
l
l
l
l
l
n
o
l l l l l l n l
l l l l
l l l l l
l l l l l
l l l l l
l l l l l
l
l
l
l
l l l
l l l
l l l
l l l l
l
l
l
l
l
l
l
l
l
o
672
Appendix 1
l Native (definite); ¡ Native (possible); l/n Native/Translocated; n Translocated (established); o Translocated (failed/uncertain); Alien (established);
l l
l l
l l
144c
l l
142d
146b
l l
141d
146a
l l
139
145c
145b
l l
145a
l l
143
l
142c
l
142b
l l
142a
l
141c
l l
141b
l
141a
l l
140b
Poreless gudgeon Giant gudgeon Flathead gudgeon Dwarf flathead gudgeon
140a
Oxyeleotris nullipora Oxyeleotris selheimi Philypnodon grandiceps Philypnodon sp. Soleidae Brachirus salinarum Brachirus selheimi Alien species Cyprinidae Carassius auratus Cyprinus carpio Puntius conchonius Cyprinidae sp. A Cobitidae Misgurnus anguilicaudatus Poeciliidae Gambusia holbrooki Poecilia latipinna Poecilia reticulata Xiphophorus helleri Xiphophorus maculatus Cichlidae Aequidens pulcher Aequidens rivulatus Amphilophus citrinellus Archocentrus nigrofasciatus Astronotus ocellatus Cichlasoma trimaculatum Haplochromis burtoni Hemichromis bimaculatus Heros severus Oreochromis mossambicus Thorichthys meeki Tilapia mariae Belontiidae Trichogaster trichopterus
138
Native species
Alien (failed/uncertain)
South-eastern Queensland 137
Common name 136
Taxon
l
Saltpan sole Selheim’s sole
Goldfish Common carp Rosy barb Unidentified cyprinid
Oriental weatherloach Eastern Gambusia Sailfin molly Guppy Swordtail Platy Blue acara Green terror Midas cichlid Convict cichlid Oscar Three spot cichlid Burton’s haplochromis Jewel cichlid Banded cichlid Tilapia Firemouth cichlid Black mangrove cichlid
Three-spot gourami
673
Appendix 2. Studies undertaken in rivers of north-eastern Australia
The numbers in the tables correspond to the reference numbers in the Bibliography. These references form the source of fish species distributional information used in Appendix 1. Included are those studies with original survey data and review studies (we included the latter as they occasionally also reported previously unpublished distributional data and they are often more accessible than the original information). Studies were included only if they made reference to actual species occurrences in specific rivers.
Studies listed for each river basin included those in which actual surveys were conducted, together with other specific rivers not surveyed but in which reference to actual species distributions was made (e.g. Allen et al. [52]). Surveys of estuarine sections of rivers were included if reference was made to fish species potentially entering freshwater and listed in Appendix 1. Only references referring to specific river basin were used (references to ‘Cape York’ for example, were excluded). See Appendix 1 for the key to river basins.
Gulf of Carpentaria and Western Cape York Peninsula 910
912
913
1
41
28
2
1349
914
915
916
917
918
919
920
921
922
923
924
925
926
927
3
28
45
41
364
28
38
569
31
216
68
38
41
23
31
41
31
47
47
675
41
73
571
38
1349
69
41
52
41
3
38
47
47
163
49
677
47
510
1146
41
70
52
72
47
4
47
163
163
198
364
1220
230
514
1349
47
73
69
216
73
5
49
298
298
287
365
1349
298
531
68
74
70
365
74
6
345
393
345
318
367
307
534
69
197
71
511
216
7
350
570
364
345
393
318
569
74
198
72
520
218
8
352
593
393
364
533
365
571
216
216
74
905
220
9
393
1090
529
365
569
393
675
220
220
216
1349
511
10
399
1349
570
367
570
533
677
307
356
220
520
11
526
675
371
675
569
1146
365
365
307
523
12
643
676
393
677
570
1299
384
519
511
568
13
881
677
524
1349
571
1349
511
520
520
569
14
997
881
593
618
518
523
527
571
15
1349
1349
795
643
520
569
528
631
16
881
675
527
571
568
785
17
1146
676
568
802
569
786
18
1174
677
569
829
571
788
19
1220
787
570
916
787
789
20
1349
791
571
1146
791
799
21
1392
802
848
676
1190
1151
22
881
787
1193
1242
905
23
1186
791
1202
1349
1146
24
1187
905
1203
1194
25
1220
991
1294
1290
26
1349
1151
1349
1299
27
1426
1202
1349
28
1433
1242
1427
29
1349
30
1427
674
Appendix 2
Eastern Cape York Peninsula 101a
101b
102a
102b
103a
103b
103c
104a
104b
105
106a
106b
106c
107a
107b
1
149
38
530
38
74
568
569
569
569
28
47
149
38
28
129
2
511
183
531
68
216
569
571
571
571
216
533
562
41
47
372
3
569
568
568
70
220
571
787
795
795
298
571
569
216
149
533
4
571
569
569
74
512
1148
791
1094
393
793
571
533
533
569
5
785
571
571
216
568
1149
1303
1099
511
898
909
569
569
571
6
789
781
1299
220
569
1299
1349
520
902
985
571
571
593
7
1148
1101
1349
518
571
1349
533
1349
986
916
593
599
8
1149
1102
568
787
569
1414
1088
1148
881
787
9
1349
569
791
571
1101
1149
1349
791
1426
10
571
991
697
1102
1202
11
787
1202
787
1349
1299
1202
12
791
1203
791
1426
1223
13
905
1242
1094
14
991
1099
15
1094
1101
16
1099
1102
17
1151
1175
18
1242
1220
19
1349
1349
675
882
Freshwater Fishes of North-Eastern Australia
Wet Tropics 108a 108b 108c 108d 109a 109b 110a 110b 111a 111b 112a 112b 113a 113b 114a 114b
115
116
1
533
47
28
28
183
47
19
35
194
23
35
218
257
49
38
1085
521
393
2
654
183
38
800
533
524
38
38
257
25
38
569
1085
98
41
1087
782
520
3
1085
372
47
1185
569
1185
47
132
319
38
49
598
1087
257
49
1204
851
569
4
1087 1085
49
898
87
240
898
49
69
617
1179
569
257
1349 1349
584
5
1091 1087
183
900
222
241
902
183
183
721
593
569
1369
593
6
1105 1349
257
902
230
292
1180
257
218
898
617
585
617
7
1375
643
1085
240
349
1349
343
240
899
618
898
618
8
898
1087
241
569
1369
349
241
902
898
902
643
9
902
1146
268
608
1414
352
257
1179
900
1085
898
10
905
1185
349
628
471
306
1179
902
1087
899
11
1085
1349
352
634
520
349
1183
1085 1105
900
12
1087
1369
393
904
522
520
1291
1087 1146
902
13
1105
1414
493
906
569
593
1369
1105 1175
1105
14
1146
533
908
593
617
1170 1349
1187
15
1185
569
1170
631
618
1187
1349
16
1203
593
1187
721
634
1339
1369
17
1303
617
1203
898
643
1349
1414
18
1349
618
1303
899
734
1414
1426
19
1369
634
1425
900
898
20
1414
881
1426
902
899
21
898
903
900
22
899
1085
903
23
900
1087
904
24
902
1096
905
25
904
1097 1096
26
905
1100 1097
27
908
1146 1100
28
1085
1184 1105
29
1087
1187 1106
30
1170
1190 1108
31
1186
1202 1109
32
1187
1291 1177
33
1202
1301 1187
34
1226
1303 1202
35
1227
1349 1294
36
1228
1369 1300
37
1300
1414 1301
38
1303
1426 1303
39
1349
1349
40
1369
1369
41
1414
1414
42
1426
1426
43
1427
1436
44
1436
1440
45
1447
676
Appendix 2
Central Queensland 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
117
118
119
120
121
122
124
125
126
127
128
129
130
132
133
134
135
28 172 173 174 176 352 598 609 1053 1349 1369
38 87 268 352 408 466 467 593 600 1030 1052 1148 1149 1170 1187 1222 1349 1368 1369 1414 1442 1446
393 593 1053 1349 1369
28 38 48 49 268 298 318 338 339 350 352 393 409 493 508 533 586 593 634 847 848 881 897 905 1079 1098 1202 1284 1300 1303 1349 1369 1426 1427
393 898 1349 1414
593 898 900 901 902 1081 1349 1414
183 621 1349
268 352 419 493 593 621 658 898 901 902 908 1044 1081 1349 1414
621 779 1303 1349
1328 1349
393 631 1101 1102 1328 1339 1349
25 38 517 533 621 631 862 1328 1339 1349
13 45 87 156 160 165 171 259 261 268 284 298 328 333 343 352 393 400 404 405 415 486 524 569 593 597 621 658 659 676 739 740 821 823 843 881 898 901 908 942 1194 1202 1272 1274 1275 1302 1339 1349 1351 1426 1433 1439 1440
69 331 898 900 901 902 915 1202 1349 1414
38 268 393 593 676 908 1202 1349
493 525 556 826 1202 1287 1339 1349
11 227 232 268 328 351 593 658 1202 1349 1414
677
Freshwater Fishes of North-Eastern Australia
South-eastern Queensland 136
137
138 140a 140b 141a 141b 141c 142a 142b 142c 143 145a 145b 145c 146a 146b 139 141d 144b 144c
1
2
7
23
23
24
75
82
25
25
20
78
4
82
171
61
5
82
23
8
6
2
11
157
25
24
38
397
84
38
94
25
80
21
84
350
397
268
84
25
23
25
84
3
12
231
44
82
44
517
104
82
104
94
94
78
94
397
621
328
104
38
38
77
104
4
76
491
45
84
82
569
397
84
196
397
95
80
104
593
624
397
397
62
77
82
517
5
85
593
47
104
84
621
593
104
397
398
397
87
397
616
643
593
517
77
82
84
768
6
99
621
75
328
84
650
709
397
413
485
709
91
661
623
664
624
621
82
84
104
960
7
107
701
82
351
104
653
768
516
768
593
837
94
709
643
702
664
709
84
104
517 1034
8
171
736
84
410
251
698 1169 517
960
624 1265
95
960
699
709
709
960
104
153
536
9
205
825
104
482
297
709
621 1034 637 1293 223
969
702
912
898
970
106
517
631
10
235
898
158
517
351
908
631 1169 664 1363 239 1034 709 1100 901 1034 149
606
726
11
236
901
159
532
397 1349
709 1374 695 1432 338 1363 801 1136 908 1136 219
631
743
12
237
987
162
606
410
726
696
339 1432 838 1169 960 1349 343
726
783
13
253 1309 166
631
470
768
905
350
867 1237 968
471
881
920
14
318 1349 242
726
517
783
908
351
881 1278 971
494
924
926
15
327
343
922
606
861
1232
397
908 1279 972
508
925
988
16
343
350
926
621
927
1237
413
1022 1314 1136
509 1034 1034
17
350
351 1034 631
960
1349
493
1136 1349 1169
513 1101 1101
18
351
393 1202 643
1101
1414
502
1237 1421 1237
517 1102 1102
19
352
410 1216 650
1102
1419
540
1278 1439 1293
600 1258 1166
20
393
517 1289 653
1296
1432
593
1279
1349
606 1292 1292
21
493
561 1294 709
1339
621
1293
1421
621 1293 1293
22
503
593 1414 726
624
1349
631 1348 1349
23
504
606
861
637
1421
637 1349
24
565
621
881
658
654
25
593
624
960
662
726
26
621
643
1034
664
796
27
622
654
1039
676
1034
28
624
658
1071
685
1101
29
658
660
1101
704
1102
30
664
664
1102
709
1146
31
700
701
1146
764
1190
32
761
703
1154
796
1288
33
764
709
1190
843
1296
34
793
726
1203
849
1298
35
827
761
1349
867
1300
36
828
847
881
1348
37
840
848
904
1349
38
881
881
905
1402
39
896
898
907
1414
40
898
901
908
41
902
902
920
42
908
904
921
43
967
908
928
44
1020
923
950
45
1154
926
951
46
1172
941
966
47
1173
982
982
48
1190
1029
1020
49
1202
1034
1034
50
1231
1039
1043
51
1276
1095
1150
678
82
Appendix 2
South-eastern Queensland (cont.) 136
137
138 140a 140b 141a 141b 141c 142a 142b 142c 143 145a 145b 145c 146a 146b 139 141d 144b 144c
52
1277
1100
1161
53
1339
1146
1169
54
1349
1161
1190
55
1359
1190
1195
56
1391
1211
1219
57
1414
1234
1264
58
1424
1235
1293
59
1432
1236
1317
60
1237
1339
61
1239
1349
62
1300
1359
63
1349
1363
64
1359
1403
65
1414
1427
66
1419
1432
679
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Index
blue-eye, delicate 269–71 honey 247–53 Pacific 254–68 spotted 269–71 bony bream 92–101 bony herring 92–101 bream, black 378–89 bony 92–101 khaki 390–94 broadhead sleeper 468–72 brown gudgeon 468–72 bullrout 278–83 Bunaka gyrinoides 473–76 butter Jew 121–28
A acritosus, Awaous 456–60 adspersa, Mogurnda 544–57 Agassiz’s glassfish 292–301 agassizii, Ambassis 292–301, 310 agrammus, Ambassis 284–91, 302 Ambassis agassizii 292–301, 310 agrammus 284–91, 302 macleayi 302–05, 306 miops 306–08 ambigua, Macquaria 326–36, 338, 346 Amniataba percoides 361–68 Anguilla australis 71–91 obscura 71–91 reinhardtii 71–91 Anguillidae 71, 73 Apogonidae 409, 410 aprion, Glossamia 409–418 archerfish, seven-spot 419–25 Ariidae 102, 104, 113 Arius graeffei 102–11 leptaspis 102–11 midgleyi 102–11 Arrhamphus sclerolepis 161–65 Aru gudgeon 487–90 aruensis, Oxyeleotris 479, 487–90 ater, Neosilurus 113, 121–28, 130 Atherinidae 171, 172, 180, 198 aureus, Glossogobius 435, 440–44 Australian bass 337–44 Australian river gizzard shad 92–101 Australian smelt 152–60 australis, Anguilla 71–91 australis, Gobiomorphus 530–37, 539 Awaous acritosus 456–60
C Cairns rainbowfish 205–310 Cairnsichthys rhombosomoides 198, 205–10 calcarifer, Lates 61, 313–25 catfish, black 121–28 eel-tailed 137–51 fork-tailed 102–11 Rendahl’s 133–36 soft-spined 129–32 Centropomidae 313, 314 cephalus, Mugil 426–33 Ceratodontidae 49 Chandidae 284, 285, 292, 293, 302, 306, 309 chatareus, Toxotes 419–25 Clupeidae 92, 93 cod, Bloomfield River 345–47 Mary River 348–52 sleepy 477–86 striped sleepy 477–86 compressa, Hypseleotris 498–509, 511, 522 Cox’s gudgeon 538–43 coxii, Gobiomorphus 531, 538–43 Craterocephalus marjoriae 171–79, 181 stercusmuscarum 172, 180–96 crimson-spotted rainbowfish 221–30 cyprinoides, Megalops 64–70
B bandata, Denariusa 309–12 banded grunter 361–68 barramundi 313–25 barred grunter 361–68 bass, Australian 337–44 Belonidae 166–67 bikolanus, Redigobius 449–55 black bream 378–89 black catfish 121–28 Bloomfield River cod 345–47
D delicate blue-eye 269–71 Denariusa bandata 309–12 duboulayi, Melanotaenia 197, 212, 221–30, 232, 238 Duboulay’s rainbowfish 221–30 dusky sleeper 468–72 dwarf flathead gudgeon 568–74
681
Freshwater Fishes of North-Eastern Australia
mountain 434–39 Mulgrave River 445–48 Pacific mangrove 461–64 Roman-nosed 456–60 scaleless 465–67 speckled 449–55 golden goby 440–44 golden perch 326–36 graeffei, Arius 102–11 grandiceps, Philypnodon 558–67, 568–69 greenback gauvina 473–76 grunter, banded 361–68 barred 361–68 small-headed 395–400 sooty 378–89 Tully 390–94 gudgeon, Aru 487–90 brown 468–72 Cox’s 538–43 dwarf flathead 568–74 ebony 468–72 Empire 498–509 firetailed 510–20 flathead 558–67 giant 477–86 Midgley’s carp 510–20 northern trout 544–57 purple-spotted 544–57 snakehead 491–97 striped 530–37 western carp 521–29 gutturale, Ophisternon 272–77 Guyu wujalwujalensis 345–47 gyrinoides, Bunaka 473–76
E eachamensis, Melanotaenia 211, 212, 231–36, 237, 238 eastern rainbowfish 211–20 ebony gudgeon 468–72 eels, longfinned 71–91 Pacific shortfinned 71–91 shortfinned 71–91 swamp 272–77 eel-tailed catfish 137–51 Eleotridae 435, 468, 469, 473, 477, 487, 491, 498, 510, 521, 530, 538, 544, 558, 568 Eleotris fusca 468–72 melanosoma 468–72 Empire gudgeon 498–509 erebi, Nematalosa 92–101 F false Celebes goby 434–39 firetailed gudgeon 510–20 flagtail, rock 401–08 flag-tailed glassfish 306–8 flathead goby 440–44 flathead gudgeon 558–67 fly-specked hardyhead 180–96 fork-tailed catfishes 102–11 forsteri, Neoceratodus 49–59 freshwater longtom 166–70 fuliginosus, Hephaestus 378–89, 390–91 fusca, Eleotris 468–72
G galii, Hypseleotris 499, 510–20, 522 garfish, snub-nosed 161–65 gauvina, greenback 473–76 gertrudae, Pseudomugil 269–71 giant gudgeon 477–86 Giurus margaritacea 478, 491–97 giuris, Glossogobius 440–44 gizzard shad, Australian river 92–101 glassfish, Agassiz’s 292–301 flag-tailed 306–08 Macleay’s 302–05 sailfin 284–91 Glossamia aprion 409–418 Glossogobius aureus 435, 440–44 giuris 440–44 sp. 1 434–39 sp. 4 445–48 Gobiidae 434, 435, 440, 445, 449, 456, 461, 465 Gobiomorphus australis 530–37, 539 coxii 531, 538–43 goby, false Celebes 434–39 flathead 440–44 golden 440–44
H hardyhead, fly-specked 180–96 Marjorie’s 171–79 Hemiramphidae 161–162 Hephaestus fuliginosus 378–89, 390, 391 tulliensis 379, 390–94 herring, bony 92–101 oxeye 64–70 honey blue-eye 247–53 Hypseleotris compressa 498–509, 511, 522 galii 499, 510–20, 522 klunzingeri 499, 511, 521–29 sp. 1 499, 510–20, 522 Hyrtl’s tandan 112–20 hyrtlii, Neosilurus 112–20, 124–27, 130–32
J Jew, butter 121–28 jungle perch 401–08
682
Index
K
N
khaki bream 390–94 klunzingeri, Hypseleotris 499, 511, 521–29 krefftii, Strongylura 166–70 Kuhlia rupestris 401–08 Kuhliidae 353, 401, 402
Nannoperca oxleyana 51, 353–60 narrow-fronted tandan 121–28 Nematalosa erebi 92–101 Neoceratodus forsteri 49–59 Neosilurus ater 113, 121–28, 130 hyrtlii 112–20, 124–27, 130–32 mollespiculum 113, 129–32 northern trout gudgeon 544–57 Notesthes robusta 278–83 notospilus, Mugilogobius 461–64 novemaculeata, Macquaria 337–44, 346
L Lake Eacham rainbowfish 231–36 Lates calcarifer 61, 313–25 leichardti, Scleropages 60–63 Leiopotherapon unicolor 369–77 leptaspis, Arius 102–11 lineolatus, Oxyeleotris 473, 477–86 longtom, freshwater 166–70 longfinned eel 71–91 lungfish, Queensland 49–59
O obscura, Anguilla 71–91 olive perchlet 292–301 one-gilled swamp eels 272–77 Ophisternon gutturale 272–77 spp.? 272–77 ornate rainbowfish 197–204 ornatus, Rhadinocentrus 197–204, 205 Osteoglossidae 60–61 oxeye herring 64–70 Oxleyan pygmy perch 353–60 oxleyana, Nannoperca 51, 353–60 Oxyeleotris aruensis 479, 487–90 lineolatus 473, 477–86 selheimi 477–86
M Maccullochella peelii mariensis 348–52 MacCulloch’s rainbowfish 242–46 maccullochi, Melanotaenia 242–46 Macleay’s glassfish 302–05 macleayi, Ambassis 302–05, 306 Macquaria ambigua 326–36, 338, 346 novemaculeata 337–44, 346 sp. B 326–36, 338 margaritacea, Giurus 478, 491–97 marjoriae, Craterocephalus 171–79, 181 Marjorie’s hardyhead 171–79 Mary River cod 348–52 Megalopidae 64, 65 Megalops cyprinoides 64–70 melanosoma, Eleotris 468–72 Melanotaenia duboulayi 197, 212, 221–30, 232, 238 eachamensis 211, 212, 231–36, 237, 238 maccullochi 242–46 splendida 207, 211–20, 222, 231, 232, 237, 238, 243 utcheensis 211, 212, 237–41 Melanotaeniidae 197, 198, 205, 211, 221, 231, 237, 242 mellis, Pseudomugil 247–53 Midgley’s carp gudgeon 510–20 midgleyi, Arius 102–11 miops, Ambassis 306–08 Mogurnda adspersa 544–57 mogurnda 544–57 mogurnda, Mogurnda 544–57 mollespiculum, Neosilurus 113, 129–32 mountain goby 434–39 mouth almighty 409–18 Mugil cephalus 426–33 Mugilidae 426, 427 Mugilogobius notospilus 461–64 Mulgrave River goby 445–48 mullet, sea 426–33
P Pacific blue-eye 254–68 Pacific mangrove goby 461–64 Pacific shortfinned eel 71–91 parviceps, Scortum 395–400 peelii mariensis, Maccullochella 348–52 pennyfish 309–12 perch, golden 326–36 jungle 401–08 spangled 369–77 perchlet, olive 292–301 sailfin 284–91 Percichthyidae 326, 327, 337, 338, 345, 346, 348, 353 percoides, Amniataba 361–68 Philypnodon grandiceps 558–67, 568–69 sp. 559, 568–74 Plotosidae 112, 113, 121, 129, 133, 137 Porochilus rendahli 113, 133–36 Pseudomugil gertrudae 269–71 mellis 247–53 signifer 247, 248, 254–68 Pseudomugilidae 198, 206, 247, 248, 254, 269 purple-spotted gudgeon 544–57 pygmy perch, Oxleyan 353–60
683
Freshwater Fishes of North-Eastern Australia
snub-nosed garfish 161–65 soft-spined catfish 129–32 soft-spined rainbowfish 197–204 sooty grunter 378–89 sp. 1, Glossogobius 434–39 sp. 1, Hypseleotris 499, 510–20, 522 sp. 4, Glossogobius 445–48 sp. B, Macquaria 326–36, 338 sp., Philypnodon 559, 568–74 sp., Schismatogobius 465–67 spangled perch 369–77 speckled goby 449–55 splendida, Melanotaenia 207, 211–20, 222, 231, 232, 237, 238, 243 spotted blue-eye 269–71 spp?, Ophisternon. 272–77 stercusmuscarum, Craterocephalus 172, 180–96 striped gudgeon 530–37 striped sleepy cod 477–86 Strongylura krefftii 166–70 swamp eels 272–77 Synbranchidae 272
Q Queensland lungfish 49–59
R rainbowfish, Cairns 205–310 crimson-spotted 221–30 Duboulay’s 221–30 eastern 211–20 Lake Eacham 231–36 MacCulloch’s 242–46 ornate 197–204 soft-spined 197–204 Utchee Creek 237–41 Redigobius bikolanus 449–55 reinhardtii, Anguilla 71–91 Rendahl’s catfish 133–36 rendahli, Porochilus 113, 133–36 Retropinna semoni 152–60 Retropinnidae 152, 153 Rhadinocentrus ornatus 197–204, 205 rhombosomoides, Cairnsichthys 198, 205–10 robusta, Notesthes 278–83 rock flagtail 401–08 Roman-nosed goby 456–60 rupestris, Kuhlia 401–08
T tandan, Hyrtl’s 112–20 narrow-fronted 121–28 Tandanus tandanus 137–51 tandanus, Tandanus 137–51 tarpon 64–70 Terapontidae 361, 362, 369, 378, 390, 395 Toxotes chatareus 419–25 Toxotidae 419 tulliensis, Hephaestus 379, 390–94 Tully grunter 390–94
S sailfin glassfish 284–91 sailfin perchlet 284–91 saratoga 60–63 scaleless goby 465–67 Schismatogobius sp. 465–67 sclerolepis, Arrhamphus 161–65 Scleropages leichardti 60–63 Scorpaenidae 278 Scortum parviceps 395–400 sea mullet 426–33 selheimi, Oxyeleotris 477–86 semoni, Retropinna 152–60 seven-spot archerfish 419–25 shortfinned eel 71–91 signifer, Pseudomugil 247, 248, 254–68 sleeper, broadhead 468–72 dusky 468–72 sleepy cod 477–86 small-headed grunter 395–400 smelt, Australian 152–60 snakehead gudgeon 491–97
U unicolor, Leiopotherapon 369–77 Utchee Creek rainbowfish 237–41 utcheensis, Melanotaenia 211, 212, 237–41
W western carp gudgeon 521–29 wujalwujalensis, Guyu 345–47
Y yellowbelly 326–36
684
