Improved Management of Exotic Aquatic Fauna: R&D for ...Improved Management of Exotic Aquatic Fauna:...

Improved Management of

Exotic Aquatic Fauna:

R&D for Australian Rivers

Occasional Paper 04/95

Angela H. Arthington and David R. Blühdorn

December 1995

Land and Water Resources

Research and Development Corporation

Centre for Catchment and In-Stream Research

Griffith University, Nathan, Qld 4111

Published by:

The Land and Water Resources Research and Development Corporation

© LWRRDC

Land and Water Resources Research and Development CorporationGPO Box 2182Canberra ACT 2601

Phone: (06) 257 3379Fax: (06) 257 3420

Publication data:

Arthington, Angela H. and Blühdorn, David R. (1995) Improved management of exotic aquatic fauna:R&D for Australian rivers. LWRRDC Occasional Paper No. 4/95.

ISSN: 1320-0992ISBN: 0 642 20609 0

Disclaimer

The information contained in this publication has been prepared in good faith by the Land and WaterResources Research and Development Corporation (LWRRDC) on behalf of the research and otheragencies who contributed to the publication content.

Neither LWRRDC nor any of the contributors establish that the contents of this publication arecomplete or accurate, and do not accept any responsibility for any errors or omissions in the contents.

Readers should, where appropriate, conduct their own enquiries or seek their own professional advicebefore relying on this information.

Readers who do rely solely on this information do so at their own risk.

Design: rba Graphic Design, Canberra

iiii

Table of Contents

1.0 Introduction 1

1.1 Background and Aims of 1the Review

1.2 Research Methods 11.3 Definitions 1

2.0 Invertebrates 2

2.12.22.32.4

BackgroundGastropodaCrustaceaResearch and DevelopmentPriorities

3.0 Freshwater Fishes 5

3.13.23.33.4

3.4.13.4.23.4.33.4.43.4.53.4.63.4.73.4.83.4.93.4.103.4.11

IntroductionNumber of Exotic Fish SpeciesMotives for Introducing FishSummary Reviews of ExoticFish SpeciesOncorhynchus mykiss (Walbaum)Salmo salar L.Salmo trutta L.Salvelinus fontinalis (Mitchell)Perca fluviatilis L.Carassius auratus (L.)Cyprinus carpio L.Rutilus rutilus L.Tinca tinca (L.)Gambusia holbrooki (Girard)Other small poeciliids

7

7555

4322

89

1010111214141516

3.4.123.4.133.4.143.4.153.4.163.5

171819192020

3.6 21

3.73.83.93.10

Oreochromis mossambicus (Peters)Tilapia mariae BoulengerCichlasoma nigrofasciatum GüntherMisgurnus anguillicaudatus (Cantor)Acanthogobius flavimanus SchlegelTemporal Sequence of FishIntroductionsEnvironmental Impacts of ExoticSpeciesEconomic Impacts of Exotic SpeciesEcology of InvasionsHuman InfluencesAssessment of Threats andPriority SpeciesManagement Issues and DirectionsResearch and DevelopmentPrioritiesGeneral RecommendationsIndividual Species PrioritiesResearch Coordination

21222222

3.113.12

2323

3.12.13.12.23.13

232526

4.0 Diseases and Parasites 27

4.14.24.3

IntroductionDiseases and ParasitesResearch and DevelopmentPriorities

272728

5.0 Acknowledgments 29

6.0 Bibliography 30

iii

1.0 Introduction

1.1 Background and Aims of theReview

This report presents the findings of a project toreview R & D requirements concerning exoticaquatic biota and their significance in theimproved management and monitoring ofAustralian inland waters. The review forms partof a portfolio of studies commissioned by theLand and Water Resources Research andDevelopment Corporation as part of the “RiverProcesses and Management Program”.

The report is confined to exotic freshwater fishes,and invertebrates (Crustacea, Mollusca andvarious parasitic taxa), where the term exotic istaken to mean species that are not naturallyfound in Australian waters. The problems thatmay arise when indigenous Australian speciesare moved from areas where they occurnaturally to basins where they do not occur now,or have never occurred historically, are alsobriefly outlined.

Although directed to problems in freshwaterenvironments, the review draws attention to theextension of range of some essentially freshwaterspecies into estuarine and more saline systems,and the implications for management andmonitoring of rivers.

The aims of the study are the following:

1. To develop an assessment of issuesconcerning exotic fauna in Australianfreshwater ecosystems.

2. To provide a report suitable for publicationon the topic of exotic biota in Australianfreshwater ecosystems, presenting asummary of problem species, economic andenvironmental costs of their presence inAustralia, and a list of research anddevelopment priorities.

1.2. Research Methods

The report has been prepared using thefollowing methods.

Reviews of published literature, reports,working papers and other materials,primarily on exotic freshwater biota inAustralia but including key papers from theinternational literature;

Meetings and discussions with relevant Stateand Territory Government agencies,consultants, research groups andpractitioners in the fields of freshwaterecology and resource management;

Distribution of a questionnaire to gain anassessment of the problems and researchrequirements on this topic in Australia; and

Distribution of a draft document forcomment and revision before preparation ofthe Final Report.

1.3 Definitions

The following terms are used throughout thereport.

Established: an introduced species whichhas established a self-maintaining population.

Invasive:

Exotic:

Indigenous:

Introduced:

Translocated:

a species which has the abilityto become established innatural or semi-natural waters.

a species not naturally found inAustralian waters.

a species indigenous (native) toAustralia.

an exotic or indigenous speciesreleased into an area in which itdoes not naturally occur.

a species, usually indigenous,moved to an area beyond itsnatural range. This term mayalso be used to describe themovement of an establishedexotic species to a new area.

1R e s e a r c h a n d d e v e l o p m e n t f o r A u s t r a l i a n r i v e r s

2.0 Invertebrates

2.1 Introduction

Invertebrates have so far been neglected in thestudy of introduced freshwater species inAustralia compared to the attention given tothem in marine systems. Pollard and Hutchings(1990) have provided a comprehensive review ofexotic marine invertebrates in the Australianregion and discussed the regulation and controlof such introductions. Although poorlydocumented, freshwater invertebratesintroduced from other countries have beenshown to cause severe medical, veterinary andeconomic problems, and may also have adverseeffects on indigenous biota and freshwaterecosystems.

Williams (1980) presented information on someof the more significant exotic taxa, but a fullreview of exotic freshwater invertebrates inAustralia does not appear to have beenattempted. One of the recommendations of thisstudy is that such a review should becommissioned.

The aim of this chapter is to indicate some of themore important types of introductions andidentify gaps in the current R & D effort inAustralia. As with all of the taxa discussed inthis report, there has been very little research onthe ecological impacts of introduced freshwaterinvertebrates.

The local and interstate translocation offreshwater invertebrates is a related issue and isprobably equally significant in terms ofeconomic and ecological impacts.Crustaceans in particular have been movedinterstate for aquaculture purposes and there areconcerns that some species may cause damage toindigenous freshwater biota aswell as aquaculture facilities, as discussed below.

2.2 Gastropoda

Gastropods can have medical, economic andecological impacts since many species areintermediate hosts of parasites that affectlivestock and humans. The family Lymnaeidae is

important in that many species of these snailsare intermediate hosts of the common liverfluke, Fasciola hepatica. This trematode parasitehas been responsible for large losses and aconsiderable economic impact on the sheep andcattle industry in many countries.

Only two indigenous species of Lymnaeids arerecognised in Australia, Lymnaea tomentosa andL. lessoni and of these, only the former speciescan act as a host of the liver fluke (Ponder 1975).Introduced hosts, however, can be very efficientin transmitting this fluke because they spreadrapidly and are often very abundant in areassubject to human disturbance (S. Schreiber, pers.comm.). Lymnaea columella, a particularly wellknown and successful intermediate host of theliver fluke (Williams 1980), was introduced toAustralia some time prior to 1973, evidently inthe Sydney region (Ponder 1975).

L. columella is native to eastern North Americaand has been introduced into Central America,Cuba, west North America, South Africa,Europe and New Zealand (Williams 1980).Experiences with this snail in New Zealand areinteresting and relevant. It has spread over mostof the North Island and into a few areas of theSouth Island since the initial introduction inabout 1940. The number of liver fluke infectionsincreased following the introduction of thesnail, and the different ecological requirementsof L. columella and the indigenous host of theliver fluke, L. tomentosa, have greatlycomplicated fluke control programs (Ponder1975).

A New Zealand species of Hydrobiid snail,Potamopyrgus antipodarum, was introduced toAustralia in about 1870, probably by way ofdrinking water supplies carried by sea toTasmania (Ponder 1988). It spread rapidly inTasmania and from there to the Australianmainland, where it is common in lakes andstreams in the south-eastern states as far northas Sydney. This species has been reported fromtanks and reservoirs in Sydney, Victoria andAdelaide (S. Schreiber, pers. comm.), and hascaused problems by building up large

I m p r o v e d m a n a g e m e n t o f e x o t i c a q u a t i c f a u n a2

populations in water pipes and distributionsystems (Ponder 1988).

The population biology of P. antipodarum, hasbeen studied in Lake Purrumbete, Victoria, andits distribution, biology and ecological impact onindigenous snails is presently underinvestigation as a Ph D project at MonashUniversity, supported by the CooperativeResearch Centre for Freshwater Ecology (S.Schreiber, pers. comm.).

In Australia, Potamopyrgus is found almostentirely in or close to habitats that have beendisturbed by human activities (urbandevelopment, agriculture and forestryoperations), whereas in New Zealand it occurs inmany natural areas as well as in disturbedhabitats (Ponder 1988). The introducedgastropod host of the common liver fluke inAustralia, Lymnaea columella, has likewise spreadrapidly and is often very abundant inagricultural areas.

This pattern of association with disturbedenvironments is common to many otherintroduced taxa, and is especially evidentamongst freshwater fishes introduced toAustralia (see Chapter 3). It is one of theimportant factors to be considered in theassessment of exotic invertebrates in Australia.

Information on translocated gastropods is verylimited. The estuarine mud welk, Velacumantusaustralis, has been translocated from easternAustralia to the Swan River estuary in WesternAustralia, where it is host to the blood fluke,Austrobilharzia terrigalensis. This fluke has beenfound to cause Schistosome dermatitis in somepeople (S. Schreiber, pers. comm.).

2.3 Crustacea

The predominant crustacean introductions inthis country have not been exotic species, butinvolve three indigenous crayfish of the familyParastacidae. They are the Yabby Cheraxdestructor, the Redclaw C. quadricarinatus, and theMarron C. tenuimanus.

The Yabby Cherax destructor (Clark) has a widenatural distribution in central and southerninland Australia. A commercial fishery operateswithin its natural range and aquacultureactivities are carried out both within the naturalrange and in Western Australia, where thespecies has been imported for this purpose. Arecreational fishery exists throughout its naturalrange (Kailola et al. 1993).

The Tasmanian Inland Fisheries Commission isopposed to the translocation of Cherax destructorinto that State because of the crayfish’s potential

to damage irrigation channel and dam walls byburrowing, to compete with indigenous crayfish,the risk of disease, and the deterioration ofwater quality in farm dams. In Tasmania, Cheraxdestructor is a declared noxious species anderadications of populations have beenundertaken.

Redclaw Cherax quadricarinatus (von Martens)has a natural range in northern Australia, fromthe Daly River in the Northern Territory to theNormanby River on Cape York Peninsula,Queensland. It has been translocated to theCairns—Innisfail area of northern Queenslandand to coastal areas of south-east Queenslandfor aquaculture purposes. There is nocommercial fishery for this species but aregulated recreational fishery exists within itsnatural range (Kailola et al. 1993). Aquacultureproduction is increasing rapidly and wasestimated to approach 150 t in 1991–92 (Kailolaet al. 1993). As the markets for this speciesexpand, and its value increases, there is likely tobe some illegal exploitation of wild stocks.

The Marron Cherax tenuimanus (Smith) has anatural range confined to the south-west cornerof Western Australia. This species has beentranslocated to other rivers and farm dams inWestern Australia, as well as southernQueensland, northern New South Wales, andSouth Australia for aquaculture purposes. Thetranslocations to Queensland were generallyunsuccessful due to high temperature-relatedmortality and the better results achievable withRedclaw. Of the 14 t produced by aquaculture in1989–90, more than 85% was produced inWestern Australia, with most of the remainderbeing produced in South Australia (Kailola et al.1993).

Two fundamental issues arise fromconsideration of the introductions associatedwith freshwater crayfish. The first is that aspecies does not necessarily have to be exotic topose potential environmental problems, and thatany translocations need to be carried out withcare and with as much information as possibleabout their possible impact on local aquaticsystems.

The second is that the crowded conditionsrequired for successful aquaculture greatlyincrease the potential for disease outbreak, andAustralia’s developing crayfish export industryis founded on this country’s disease-free status.Careless translocations and inadequatequarantine precautions could result in theintroduction of the crayfish ‘plague’, the fungusAphanomyces astaci which was responsible for thecollapse of the indigenous European crayfishpopulations, and the industries which dependedon them.


Thompson (1990) cites the introduction of theplague vector animal, the North American signalcrayfish, Pacifasticus leniusculus, as anoutstanding example of deleterioustranslocations, and lists irreparable shifts inspecies diversity, ecosystem stress, and damagedtraditional fisheries as major impacts of thefungus imported via this species. One of the sideeffects of the crayfish plague was thatdecimation of the indigenous Swedish crayfish,Astacus astacus, allowed macrophytes such asChara spp. and Elodea canadensis to proliferate,resulting in the elimination of game fish habitat(Thompson 1990).

2.4 Research and DevelopmentPriorities

The following aspects of exotic and translocatedinvertebrates in Australian freshwater systemsare recommended for further investigation byLWRRDC or as joint venture studies:

•

•

•

•

•

A full review of exotic freshwaterinvertebrates in Australia should becommissioned, possibly with multipleauthors to achieve the necessary taxonomiccoverage. The review should discussecological impacts on indigenous aquaticbiota and ecosystems, and the actual and

potential economic impacts of aquaticinvertebrates (i.e. disease transmission,damage to water supply and aquaculturefacilities, water quality problems, etc);

Research should be commissioned on thedistribution, biology and ecological impactsof exotic invertebrates identified by thereview as locally significant or likely tobecome widespread and problematic inAustralia. The role of disturbance should beaddressed as a factor in the ecology ofinvertebrate invasions;

Quarantine issues and the protocols formanaging new introductions of freshwaterinvertebrates, as well as their movementwithin Australia, may require review andrevision;

Past neglect of this topic suggests that astrategy is required to maintain one or moredatabases on exotic invertebrates in Australia,and to develop a program for routinesurveillance of freshwater systems.Surveillance could be integrated with theState and Territory programs for monitoringriver invertebrates as part of the “MonitoringRiver Health Initiative”; and

Practical management strategies are neededfor some problem species, e.g. the crayfish C.destructor.


3.0 Freshwater Fishes

3.1 Introduction

Exotic freshwater fishes form the mainstay ofrecreational fisheries in south-eastern Australia,as well as providing much of the fish biomass inmany streams, especially the Murray-Darlingand higher altitude rivers. Exotic speciesgenerated in excess of $40 million in commercialproduction in 1991-92 (estuarine cage-farmedtrout; Kailola et al. 1993). They are alsoimplicated in direct and indirect impacts onindigenous aquatic fauna and their habitats, andthe introduction of diseases and parasites whichmay affect indigenous fish species.

Australiaís freshwater fish fauna is distinctive inthat it consists mostly of species which are notshared with other biogeographic regions. Inorder to preserve this heritage and to mitigate, ifpossible, negative interactions, it is important toknow the effects of introduced fish species onthis relatively specialised biota.

The aim of this chapter is to review theinformation available on all established exoticfreshwater fish species, to assess theirenvironmental and economic impact, and torecommend appropriate research anddevelopment priorities.

3.2 Number of Exotic Fish Species

The number of established exotic freshwater fishspecies in Australia is in the range 19–24(Arthington 1991; McKay 1989; Fletcher 1986;Allen 1989) depending primarily on thedefinitions used. This report will assessinformation on twenty species, including foursalmonids, one percid, four cyprinids, sixpoeciliids, three cichlids, one cobitid, and onegobid. This is a marked increase on the ninespecies reported by Weatherley and Lake in 1967,which included two salmonids, one percid, fivecyprinids, and one poeciliid. Table 3.1 lists theexotic species which have become, or are likelyto become, established in Australian freshwaters.

One of the species listed, the Atlantic Salmon(Salmo salar : Salmonidae) has not yet become

established in freshwater but is presentlycultured in large numbers in sea cages inTasmania (Kailola et al. 1993). Escapes from thesecages have resulted from the effects of weatherand seal attack. Whether the escapees will formsea-run populations and return to the estuariesand their associated freshwaters for spawningremains to be seen. Sea-run Brown Trout (S.trutta) have been implicated in the decline of theestuarine fish, Derwent whitebait (Lovettia sealii)(F.B. Michaelis, pers. comm.).

Three other species are occasionally included inlists of exotic species, but do not appear to haveestablished self-sustaining populations. TheChinook Salmon (Oncorhynchus tshawytscha :Salmonidae) populations are maintained bystocking (Allen 1989, MacKinnon 1987, McKay1989, Kailola et al. 1993). The Jack DempseyCichlid (Cichlasoma octofasciatum (Regan) has notbeen recorded since a single individual wasfound in the late 1970s, and is not considered tohave become established (P. Cadwallader, pers.comm.). The Domingo Gambusia (Gambusiadominicensis: Poeciliidae), reported in springs andwaterholes around Alice Springs (Allen 1989),has been identified as G. holbrooki (Lloyd andTomasov 1985).

3.3 Motives for Introducing Fish

Freshwater fish have been moved around byhumans since ancient times (Holcík 1991) andWelcomme (1988) indicates that seven specieswere introduced to various countries before the19th century. World-wide, there have beenreports of 117 introductions in the 19th centuryand 859 in the 20th century (to 1985), with thenumber reaching a peak in the 1960s anddeclining slightly since (Welcomme 1988).

There appear to have been five principal motivesand causes for the spread of exotic fish species.These include: increased food production(aquaculture and wild fisheries); control ofnuisance organisms (malaria mosquitoes,excessive plant and algal growth); recreationalfishing; for ornamental purposes; and accidentalintroductions.


Table 3.1: Fish species introduced to Australia which are reported to haveestablished, or are likely to establish, self-sustaining feral populations.

Salmonidae

Oncorhynchus mykiss (Walbaum)Salmo salar L.Salmo trutta L.Salvelinus fontinalis (Mitchell)

Rainbow TroutAtlantic SalmonBrown TroutBrook Trout

Percidae

Perca fluviatilis L. European Perch or Redfin

Cyprinidae

Carassius auratus L.Cyprinus carpio L.Rutilus rutilus L.Tinca tinca (L.)

GoldfishEuropean CarpRoachTenth

Poeciliidae

Gambusia holbrooki (Girard)Phalloceros caudimaculatus HenselPoecilia latipinna Le SueurPoecilia reticulata PetersXiphophorus helleri (Günther)Xiphophorus maculatus (Heckel)

Eastern Gambusia or MosquitofishOne-spot Live BearerSailfin MollyGuppySwordtailPlaty

Cichlidae

Cichlasoma nigrofasciatum GüntherOreochromis mossambicus (Peters)Tilapia mariae Boulenger

Cobitidae

Misgurnus anguillicaudatus (Cantor)

Gobiidae

Acanthogobius flavimanus Schlegel

Convict CichlidTilapia or Mozambique Mouth-brooderBlack Mangrove or Niger Cichlid

Oriental Weatherloach

Yellowfin Goby

Accidental introductions are those that havearisen largely from unexpected sources orfrom a lack of quarantine. Fish contained inthe ballast water of ships, introducedinadvertently with another species, fishreleased by the flooding or overflow ofoutdoor ponds, and the escape of bait fish areall examples of accidental introductions.

Increased food-fish production has beenachieved by intensive culture (aquaculture) toby enhancing wild fisheries. In manycountries, socio-economic requirements meanthat a high priority is given to increasing fishproduction in reservoirs and otherwaterbodies (Fernando 1991). This oftenleads to the stocking of these sites with exoticspecies because methods of increasing yieldare not available, or are poorly developed, forindigenous species. More than 50% ofintroductions have been made to provide

species for aquaculture or to improvefisheries production (Welcomme 1988).

A number of species with particular dietarypreferences have been introduced widely inan effort to control nuisance organisms.Examples include the larvivorous fishes ofthe genera Gambusia and Poecilia, which havebeen widely dispersed for mosquito controlpurposes (Lloyd and Tomasov 1985), and anumber of herbivorous carps and tilapiasintroduced for the purposes of plant andalgal control (Welcomme 1988).

The demand for recreational fishing hascaused many of the introductions recordedthroughout the world (Radonski et al. 1984).Recreational fishing supports manyaquaculture and stocking operations whichresult in frequent translocations and newintroductions (Welcomme 1988).


Of growing importance is the demand forfish suitable for ornamental purposes. Theability to keep and display colourful orotherwise interesting fishes has promoted aworld-wide traffic in exotic species(Courtenay and Stauffer 1990).

The above five causes have resulted in a numberof introductions of exotic species into Australianfreshwaters, with some of these exoticsbecoming established in the wild.

3.4 Summary Reviews of Exotic FishSpecies

This report provides details of 20 exotic specieswhich are considered to have established self-sustaining populations in fresh water. For mostspecies, an individual summary review ispresented which includes information abouttaxonomic affiliation, common name, indigenousrange, year and purpose of introduction, wherethe stocks originated, and present distribution.Where available, information is presented aboutthe speciesí environmental and economicimpacts, other relevant information, andsuggested research and development priorities.

Information contained in the individualsummary reviews was derived from a number ofsources. Details of a species’ indigenous range,the country from which it was imported, thereason for introduction, and the year ofintroduction were generally obtained fromWelcomme (1988). Information about a species’present distribution was generally obtained fromAllen (1989). Other sources of these data arecited directly.

The environmental impacts listed for eachspecies include proven interactions, which areextremely difficult to demonstrate, and are,therefore, uncommon. Other adverseenvironmental interactions listed are based onpersuasive circumstantial evidence of impact,with special reference to ecologically sensitivespecies.

The ‘threatened status’ classification ofindigenous fish species, for example ‘vulnerable’or ‘endangered’, follows the Australian NatureConservation Agency’s “Action Plan forAustralian Freshwater Fishes” (Wager andJackson 1993).

Specific research and developmentrecommendations are given at the end of eachspecies summary (this section).Recommendations for broader research anddevelopment consideration, such as speciesinteractions, habitat degradation, and ecosystemissues, are given in Section 3.12, together with asummary of the species recommendations.

3.4.1 Oncorhynchus mykiss (Walbaum)

Family: Salmonidae

Common name: Rainbow Trout

Indigenous Range: Western coast of USA,

Canada and NorthernMexico.

Purpose of introduction: Recreational fishery

Year of introduction: 1894

Present Distribution

Established populations exist in high altitudewaters of New South Wales, the AustralianCapital Territory, and Victoria, including theheadwaters of the Murray-Darling River system,and Tasmania. Stocked populations aremaintained in the warmer waters of New SouthWales, Victoria, Tasmania, South Australia(Adelaide region), and Western Australia (southof Perth). Isolated sea-run populations arereported in Victorian and Tasmanian streams.Commercial sea cage aquaculture is carried outin Macquarie Harbour on the west coast ofTasmania (Kailola et al. 1993).

Environmental Impacts

Along with Salmo trutta (Brown Trout), thisspecies is the most widespread of the introducedsalmonids and the one with the most extensiveliterature on known and speculatedenvironmental impacts. These fall into twoclasses: predation on indigenous fishes; andcompetitive exclusion of indigenous species, asevidenced by the fragmented distributions ofsome of those species in areas where trout havebeen introduced. A number of these indigenousspecies are classified as endangered orvulnerable (Wager and Jackson 1993).

Adverse impacts have been reported oninvertebrates and indigenous fish, especiallygalaxiids (P.S. Lake, pers. comm.). O. mykiss hasbeen shown to prey on Barred Galaxias Galaxiasfuscus, an endangered species (Wager andJackson 1993), and the distributions of O. mykissand Galaxias olidus around Canberra appear to bemutually exclusive (Lintermans 1991).

O. mykiss competes for food with the ’vulnerable’indigenous fish Macquarie Perch Macquariaaustralasica and possibly predates juveniles(Wager and Jackson 1993). It is suspected ofpredation on the ‘vulnerable’ indigenous fishesYarra Pygmy Perch Edelia obscura and Ewen’sPygmy Perch Nannoperca variegata (Wager andJackson 1993).

A paucity of indigenous fish species has beenreported in areas where trout (O. mykiss,


S. trutta) occur in south-western WesternAustralia (D. Morgan, pers. comm.).

Although known to interact adversely with someindigenous species, O. mykiss distributionsappear to have stabilised (P. Gehrke, perscomm.) and the threat of further rangeexpansion in eastern Australia, with consequentenvironmental impacts, is generally regarded asslight.

Elsewhere, O. mykiss is reported to beresponsible for declines in indigenous fishes inPeru, Colombia, Chile, Yugoslavia, Himalayanrivers, Lesotho, South Africa, and New Zealand(Welcomme 1988).

Economic Impacts

O. mykiss forms the basis of a multi-milliondollar recreational fishing industry in Australia,and the economic benefits arising from thisindustry ensure that stocking will continue (P.Gehrke, pers comm.). Sea cage aquaculture ofthis species in Tasmania produced about 400tonnes in 1990–91 (Kailola et al. 1993).

A study of the mitochondrial DNA (mtDNA)structure of Tasmanian populations of O. mykisshas shown remarkably little diversity. This isprobably due to repetitive hatchery and wildstock propagation (Ovenden et al. 1993)

R & D Recommendations

Research is required into the effects ofsalmonids in general, and O. mykiss particular, on endangered indigenous fishspecies.

Research is required into the distribution andeffects of salmonids in Western Australia.

It is recommended that lakes which have hadno previous introductions of salmonidsshould not be stocked with O. mykiss in thefuture.

3.4.2 Salmo salar L.

Family: Salmonidae

Common name: Atlantic Salmon

Indigenous Range: North-east coast of USAand Canada and north-

west coast of Europe

Introduced from: USA

Year of introduction: 1864–1870 and 1963–64



This species is found in the headwaters of theMurray River and streams of the south coast ofNew South Wales (P. Gehrke, pers. comm.). It isalso reported in Tasmanian streams (Allen 1989)and in sea cage aquaculture on the south-eastand west coasts of Tasmania (Kailola et al. 1993).


The Atlantic Salmon has yet become establishedin Tasmanian inland waters, but escaped fishfrom the sea cages have the potential to formsea-run populations and return to the estuariesand their associated freshwaters for spawning,with potentially adverse effects on estuarine andfreshwater biota. Elsewhere in Australia, it isuncommon and not well suited to Australianenvironments. It is considered to have littleenvironmental impact at current populationdensities in New South Wales (P. Gehrke, pers.comm.).

Economic Impacts

Tasmanian commercial production of S. salar andOncorhynchus mykiss (Rainbow Trout), using bothfreshwater hatcheries and sea-cage growingstages, exceeded 3400 tonnes in 1991-92, with avalue of over $40 million.

Other Information

Other Information

The low genetic (mtDNA) diversity ofTasmanian stocks is probably the result of smallbrood stock numbers in the 1963–65 introduction(Ovenden et al. 1993)


Monitoring of Tasmanian streams forincursions of sea-run salmonids and, if theseoccur, research into their environmentaleffects.

It is recommended that lakes which have hadno previous introductions of salmonidsshould not be stocked with S. salar in thefuture.

•

•

•

•

•


3.4.3 Salmo trutta L.

Family:

Common name:

Indigenous Range:

Salmonidae

Brown Trout

Western Asia and

Europe

Purpose of introduction:

Year of introduction:

Introduced from:

Recreational fishery

1864

The Wey and River

Itchen, southern

England (Tasmanian

stocks) (Ovenden et al.

1993)


Established populations exist in high altitudewaters of New South Wales, the AustralianCapital Territory, and Victoria, including theheadwaters of the Murray-Darling, andTasmania. Stocked populations are maintained inthe warmer waters of New South Wales, Victoria,Tasmania, South Australia (Adelaide region),and Western Australia (south of Perth). Isolatedsea-run populations are reported in Victorianand Tasmanian streams (Kailola et al. 1993).


Salmo trutta has had a major impact onindigenous fish species and is implicated in thedecline in numbers of four ‘endangered’, four‘vulnerable’, and one ‘poorly known’ species(Wager and Jackson 1993). Its principal impactsare predation on the endangered Swan GalaxiasGalaxias fontanus, the endangered BarredGalaxias Galaxias fuscus, and adverse interactionwith the endangered Clarence Galaxias Galaxiasjohnstoni (Wager and Jackson 1993). Adverseinteractions are also suspected to have producedthe mutually exclusive distributions of BrownTrout and Galaxias olidus in the ACT (Lintermans1991).

The Brown Trout is said to be responsible forreduced abundance in the ‘vulnerable’ SaddledGalaxias Galaxias tanycephalus (Wager andJackson 1993) and to adversely interact with the‘endangered’ Pedder Galaxias Galaxiaspedderensis, causing a dramatic decline innumbers. However, this decline is also linked toinvasion by the translocated Climbing GalaxiasGalaxias brevipinnis (Wager and Jackson 1993).

Apart from galaxiids, S. trutta is suspected ofpredation on juveniles of the ‘vulnerable’Australian Grayling and juveniles of the ‘poorlyknown’ Macquarie Perch Macquaria australasica,the ‘vulnerable’ Yarra Pygmy Perch Edelia

obscura, and the ‘vulnerable’ Ewen’s PygmyPerch Nannoperca variegata (Wager and Jackson1993). In New South Wales, although S. truttainteracts with indigenous species, its distributionappears to have stabilised (P. Gehrke, pers.comm.)

Economic Impacts

The Brown Trout forms the basis of a multi-million dollar recreational fishing industry inAustralia, and the economic benefits derivedfrom recreational fishing ensure that stockingwill continue (P. Gehrke, pers. comm.).

Other Information

Low genetic (mtDNA) diversity of Tasmanianstocks suggests that only the initial introduction(1864) from southern England was successful(Ovenden et al. 1993).


• Research is required into the effects of S.trutta on endangered indigenous fish species.

• Research is required into the distribution andeffects of salmonids in Western Australia.

• It is recommended that lakes which have hadno previous introductions of salmonidsshould not be stocked with S. trutta in thefuture.


3.4.4 Salvelinus fontinalis (Mitchell)

Family: Salmonidae

Common name: Brook Trout

Indigenous Range:



North-eastern NorthAmerica

Recreational fishery

Early 1900s

Present Distribution Purpose of introduction: Recreational fishery

Populations of Brook Trout are recorded inmountain streams of New South Wales andTasmania (Allen 1989). Regular stocking iscarried out in Tasmania, New South Wales, andSouth Australia (Kailola et al. 1993).


The European Perch has become established inthe south-west corner of Western Australia (Laneand MC Comb 1988), in South Australia, NewSouth Wales, the Australian Capital Territory(Lintermans et al. 1990), Victoria and Tasmania(Welcomme 1988).


Salvelinus fontinalis is regarded as uncommonand not well suited to Australian environments.It is considered to have little environmentalimpact at current population densities in NewSouth Wales (P. Gehrke, pers. comm.).

Economic Impacts

This species forms a significant part of therecreational fishing industry in the states inwhich it is stocked.

Other Information

Tasmanian stocks of S. fontinalis appear to havegood genetic (mtDNA) diversity (Ovenden et al.1993).


It is recommended that lakes which have hadno previous introductions of salmonidsshould not be stocked with S. fontinalis in thefuture.

The distribution of S. fontinalis should bemonitored for indications of range expansion.

3.4.5 Perca fluviatilis L.

Family:

Common name:

Indigenous Range:

Percidae

European Perch or Redfin

Europe, excepting Spain,

northern Italy and Greece

Introduced from:


UK

1862 (Tasmania) 1868

(Victoria) (Kailola et al.

1993)


Perca fluviatilis carries the epizootichaematopoietic necrosis virus (EHNV), whichhas been shown to be highly pathogenic forSilver Perch, Mountain Galaxias, MacquariePerch, and Murray Cod (Langdon 1990). Otherindigenous fish are likely to be susceptible(Wager and Jackson 1993). In the ACT, massmortality of juvenile P. fluviatilis has beenattributed to EHNV, and major declines inpopulations of Macquarie Perch in this regionare attributed to this disease (Lintermans 1991).

In New South Wales, P. fluviatilis is regarded as asignificant predator on indigenous fishes, andjuveniles may compete with small indigenousfishes for food, but its impact is perceived to bestable and this species has not been linked withlarge-scale ecological degradation (P. Gehrke,pers. comm.).

A survey of the Murray River in WesternAustralia has shown the distribution of the oncecommon indigenous fish, Edelia vittata (WesternPygmy Perch), to be fragmented, with littleoverlap between it and the introduced P.fluviatilis (Hutchinson 1991). Predation by P.fluviatilis on E. vittata is considered to be themost likely cause. P. fluviatilis is also suspected ofpredation on the ‘vulnerable’ Ewen’s PygmyPerch Nannoperca variegata and the ‘vulnerable’Yarra Pygmy Perch Edelia obscura (Wager andJackson 1993).

Other significant indigenous species on which P.fluviatilis is suspected to prey include the‘vulnerable’ Dwarf Galaxias Galaxias pusilla andjuveniles of the ‘poorly known’ Macquarie Perch


•

•

Macquaria australasica (Wager and Jackson 1993).Adverse interactions, in the form of foodcompetition and possible predation, by P.

11

fluviatilis on the ‘endangered’ Trout CodMaccullochella macquariensis are said to havecontributed to the cod’s decline (Wager andJackson 1993).

Economic Impacts

P. fluviatilis forms the basis of a small commercialfishery in western Victoria and South Australia(Kailola et al. 1993). Large individuals are valuedfor sport fishing and food.


• Basic ecological research is required on thelife history, habitats, diet and distribution ofP fluviatilis.

• Research is required to determine theenvironmental impact of P. fluviatilis in thoselocations (Western Australia and the ACT)where it is identified as undergoing rangeexpansion.

3.4.6 Carassius auratus (L.)

Family: Cyprinidae

Common name: Goldfish

Indigenous Range: Eastern Europe, China,

central Asia (Welcomme

1988)

Purpose of introduction: Ornamental



Goldfish have been recorded from thesouthern half of Australia (Allen 1989), theFitzroy River in Queensland, and the south-west of Western Australia (Kailola et al. 1993).The species is reported to be most abundant inwaters of the Murray-Darling basin (Brumley1991)


Goldfish ulcer disease (Aeromonas salmonica),introduced into Australia by infected importedgoldfish, has been found in feral goldfishpopulations (Langdon 1990). This disease ishighly pathogenic to salmonids, and for thisreason C. auratus is a prohibited import intoTasmania (Kailola et al. 1993). The incidence ofthis disease is also considered a problem forsalmonid fisheries in other states (P. Gehrke,pers. comm.).

C. auratus is suspected to have an adverseimpact on the ‘endangered’ indigenous TroutCod Maccullochella macquariensis (Wager andJackson 1993).

Economic Impacts

A bycatch of the commercial carp fishery, butof little value, C. auratus is probably being soldfor rock lobster bait. C. auratus has no sportingvalue, but is important to the aquarium trade(Kailola et al. 1993).

Other Information

C. auratus is very widespread and is, perhaps,the most widely distributed exotic species inthe country (Brumley 1991). Despite this, itseffects on local biota are generally not known(P.S. Lake, pers. comm.). It is reported toreadily hybridise with European CarpCyprinus carpio (Brumley 1991) and, althoughnot as numerous as carp, may have similareffects (P. Gehrke, pers. comm.). Much of itsspread is attributed to aquarium releases(Kailola et al. 1993) and its use as live bait.

R e s e a r c h a n d d e v e l o p m e n t f o r A u s t r a l i a n r i v e r s

C. aurutus is a prescribed non-indigenous fish inQueensland under the Fisheries Act, whichmeans that it may not be released intoQueensland waters but may be held in aquaria.There is concern that its use as live bait may leadto translocations throughout Queensland (P.Jackson, pers. comm.).


• Basic ecological research is required to Variety (b) Singapore (Yanco)

investigate the environmental requirements strain (koi)

of this species and its effects on indigenous Purpose of introduction Ornamental

biota. Year of introduction 1876

• This species is ubiquitous and generally wellknown. It could be used as the focal point ofeducational activities designed to highlightthe dangers of releasing aquarium fish, andusing exotic or translocated species as livebait.

Variety (c) River (Boolara) strain

Purpose of introduction Aquaculture

Year of introduction 1960–64

3.4.7 Cyprinus carpio L.

Family: Cyprinidae

Common name: European Carp

Variety (a) Prospect strain

Purpose of introduction Ornamental

Year of introduction 1850–60

Native Range:

Introduced from:

Japan, China, central Asia

UK


Carp are found from the Warrego River,Queensland, to the mouth of the Murray River inSouth Australia, including most rivers in theMurray-Darling basin, several coastal streams inNew South Wales (P. Gehrke, pers. comm.),Victoria and South Australia, and Lake Frome inSouth Australia (Kailola et al. 1993). Carp arereported to have been eradicated from Tasmania(Kailola et al. 1993) but were recently found inLake Crescent and Lake Sorell in the headwatersof the Clyde River, a tributary of the Derwentsystem.

Brumley (1991) gives the distributions (and yearsof introductions, above) of the individual strainsas:

(a) Prospect strain: Sydney: restricted

(b) Singapore (Yanco) strain: Murrumbidgeebasin: restricted

(c) River (Boolara) strain: Murray-Darling basin:extremely widespread


The principal impact of C. carpio has been itsmassive range expansion in the Murray-Darlingsystem, where it dominates the indigenous fishfauna in numbers and biomass. P. Gehrke (pers.


comm.) cites overwhelming numbers in regionsof the Murray, Lachlan and Murrumbidgee,comprising more than 80% of the total fishcommunity, and Brumley (1991) reported thatcarp and goldfish were more abundant in someVictorian waters than any indigenous species.

While there is little solid evidence of the habitatimpacts attributed to C. carpio (Fletcher et al.1985; Brumley 1991; Morrison and Hume 1990),it is considered likely that carp contribute tocyanobacterial outbreaks by excreting nutrients,re-suspending sediments and damagingmacrophytes (P. Gehrke, pers. comm.).

It is suspected that habitat modification causedby carp has contributed to the decline of the‘vulnerable’ Dwarf Galaxias Galaxias pusilla, the‘endangered’ Trout Cod Maccullochellamacquariensis, the ‘vulnerable’ Yarra PygmyPerch Edelia obscura, and the ‘vulnerable’ Ewen’sPygmy Perch Nannoperca variegata (Wager andJackson 1993).

The Carp has been implicated as a secondaryfactor in the decline of indigenous gastropods inthe Murray River, Victoria. While riverregulation was considered to cause the greatereffect, habitat changes caused by carp may havechanged the food available to indigenous aquaticsnails (Sheldon and Walker 1993).

C. carpio provides prey for indigenous piscivoresincluding Golden Perch Macquaria ambigua,Murray cod Muccullochella peelii, and RedfinPerch Perca fluviatilis, as well as water rats andbirds (Kailola et al. 1993).

Economic Impacts

Combined commercial catches of around 1000 tyr–1 were recorded from the Murray-Darlingsystem (New South Wales, Victoria, and SouthAustralia) from the mid 1970s to the mid1980s.(Kailola et al. 1993). This fishery hasapparently collapsed in New South Wales andVictoria because of declining catches (Brumley1991; Morrison and Hume 1990). The annualcommercial catch from South Australia, however,has not declined, producing about 450 tonnes(Kailola et al. 1993), although this catch hasrelatively low value, returning only A$340 t–1 in1991–92 (Kailola et al. 1993).

The costs of managing carp and rehabilitatingdamaged aquatic ecosystems have not beenestimated but are considered to be enormous (P.Gehrke, pers. comm.).

Other Information

The CSIRO Division of Water Resources isconducting experiments on the ecologicalimpacts of carp in ponds (J. Roberts, pers.

comm.). In New South Wales, research is inprogress on the recruitment, distribution andabundance, and ecological effects of carp, as wellas its possible influence on cyanobacterialblooms (P. Gehrke, pers. comm.).

Experimental evidence on the effects of high pHon C. carpio indicated that pH values greaterthan 9.0 significantly reduced growth andsurvival, while values greater than 10.0 furthersignificantly reduced growth and survival to asub-lethal level (Korwin-Kossakowski 1992).Such high pH values are often attained insurface waters during blue-green algal blooms(New South Wales Blue-Green Algal Task Force1992, Bl¸hdorn and Arthington 1994).

C. carpio is a declared noxious species in moststates with prohibitions on its use as live bait, thereturn of captured specimens to the water,breeding for sale, and interstate transfers(Kailola et al. 1993).

A Carp Task Force has been established toeradicate carp from Tasmanian waters. In theinterim, the Task Force aims to minimise theeconomic, recreational and ecological impacts ofcarp in Tasmania.


Descriptive and experimental studies arerequired on the impact of carp onpopulations and communities of indigenousfish, invertebrates and plants.

There is an urgent need for research intomethods of controlling carp populations.

Primary research funding is required todemonstrate the cost of carp to ecologicalsustainability, water management,recreational and commercial fisheries,conservation, and water treatment for publichealth.

•

•

•


3.4.8 Rutilus rutilus L.

Family: Cyprinidae

Common name: Roach

Indigenous Range: Europe excluding Spain,Italy, Greece and Ireland

Introduced from: UK

Year of introduction: 1860–30



The Roach is reported from the Murray Riverand coastal drainages of southern New SouthWales and Victoria. It is reported to be veryabundant in the rivers of Port Phillip Bay.


The high abundance of R. rutilus in the rivers ofPort Phillip Bay suggests that there could beconsiderable effects on indigenous biota (P.S.Lake, pers. comm.). It is uncommon in NewSouth Wales, and is considered to have littleimpact at its current low population densities (P.Gehrke, pers. comm.).

Economic Impacts

R. rutilus is unimportant as a recreational orcommercial fishery.


• Research aimed at providing a basicecological understanding of the life history,habitat, diet, and distribution of R.rutilus inareas of high population density is required.

• A monitoring program is needed to evaluatethe distribution and abundance of thisspecies and to give an indication of anysignificant changes in range and biomass.

3.4.9 Tinca tinca (L.)

Family: Cyprinidae

Common name: Tench

Indigenous Range: Western Asia, Europeexcept north Scandinavia

Purpose of introduction: Recreational fishing



The Tench is found in coastal drainages of NewSouth Wales, Victoria, Tasmania, and SouthAustralia. It is locally abundant in the Murray-Darling River system (Brumley 1991).


In Victoria, the Roach is very localised and doesnot appear to have a great effect on local biota(P.S. Lake, pers. comm.). It is uncommon in NewSouth Wales, with apparently little impact atcurrent population densities (P. Gehrke, pers.comm.).

Economic Impacts

T. tinca is unimportant as a recreational orcommercial fishery.


• A monitoring program is needed to evaluatethe distribution and abundance of thisspecies and to give an indication of anysignificant changes in range and biomass.


3.4.10 Gambusia holbrooki (Girard)

Family: Poeclliidae

Common name: Eastern Gambusia or

Mosquitofish

Indigenous Range: Southeastern USA (Lloyd

and Tomasov 1985)

Introduced from: Georgia, USA (via Italy)


Purpose of introduction: Mosquito control

populations (Bence 1988; Lloyd 1990b). Small,indigenous fish species have been shown to bemore suitable for mosquito control than theexotic Gambusia (Lloyd 1990b).


This species is widespread throughout mainlandAustralia (Allen 1989; Arthington 1991).


Gambusia holbrook has demonstrated agonisticbehaviour toward, and predation on, the‘vulnerable’ Dwarf Galaxias Galaxias pusilla, the‘vulnerable’ Yarra Pygmy Perch Edelia obscura,and the ‘vulnerable’ Ewen’s Pygmy PerchNannoperca variegata (Wager and Jackson 1993).

It is suspected of causing a decline in theabundance of the ‘vulnerable’ Honey Blue-eyePseudomugil mellis, the ‘endangered’ Red-finnedBlue-eye Scaturiginichthys vermeilipinnis, the‘vulnerable’ Oxleyan Pygmy Perch Nannopercaoxleyana, and the ‘endangered’ Purple SpottedGudgeon Mogurnda adspersa (Murray-Darlingstock) (Wager and Jackson 1993).

Worldwide, some 35 fish species are reported tohave been reduced in abundance or range due toadverse interactions with Gambusia (Lloyd1990a). These interactions include competitionfor food and space, interference competition, andpredation. In Australia, although much of theevidence is circumstantial, G. holbrooki isimplicated in the decline of indigenousMogurnda, Ambassis, Melanotaenia, Pseudomugil,Craterocephalus and Retropinna species (Lloyd1990a).

Gambusia have been shown to have significantpredatory effects on invertebrate species apartfrom mosquitoes (Lloyd 1990b; Arthington1989b). These effects can lead to changes inzooplankton and phytoplankton abundance,often with unpredictable effects on mosquito

Economic Impacts

G. holbrooki has no economic impact other thanas a pest (P. Gehrke, L. Lloyd, pers. comm.). It isa non-prescribed non-indigenous fish inQueensland under the Fisheries Act, whichmeans that it may not be released intoQueensland waters or held in captivity. TheQueensland Department of Primary Industries,Fisheries Branch has produced educationalmaterial to encourage the use of indigenousspecies for mosquito control.


• Research is required to investigate theimpacts of G. holbrooki on indigenous speciesand aquatic communities, with an emphasison areas supporting endangered andvulnerable indigenous species.

• Educational activities aimed at informing thepublic about the dangers of the release andtranslocation of aquarium fishes could befocussed on this species.


3.4.11 Other small poeciliids

Phalloceros caudimaculatus HenselFamily:

Common name:

Indigenous Range:

Introduced from:



Present distribution:

Poeciliidae

One-spot Live Bearer

Rio de Janeiro to Uruguay

and Paraguay

Unknown

Unknown

Probably mosquito control

Perth, Western Australia

(Allen 1989)

Poecilia latipinna Le Sueur

Family:

Common name:

Indigenous Range:

Introduced from:Year of introduction:


Present distribution:

Poeciliidae

Sailfin Molly

Eastern USA and Mexico

Singapore

1969

Ornamental and mosquito

control

Coastal drainages of

southeastern Queensland

(Allen 1989)

Poecilia reticulata PetersFamily: Poeciliidae

Common name: Guppy

Indigenous Range: Venezuela, Barbados,

Trinidad, northern Brazil,

the Guyanas


Year of introduction: Unknown

Present distribution: Coastal drainages of

northern NSW and eastern

Queensland (Allen 1989;

Arthington 1991)

Xiphophorus helleri (Günther)Family: Poeciliidae

Common name: Swordtail

Indigenous Range: Southeastern Mexico and

Guatemala

Introduced from: Singapore





Queensland (Allen 1989)

Xiphophorus maculatus (Heckel)Family: Poeciliidae

Common name: Platy

Indigenous Range: Eastern Mexico and

Guatemala (Welcomme

1988)


Year of introduction: unknown



Queensland (Allen 1989)


The above five poeciliid species represent a suiteof tropical fishes, introduced for mosquitocontrol and as ornamental fishes, and similar inlife history to Gambusia holbrooki. These specieshave not been spread as widely as G. holbrooki,

with most being confined to disturbed urbanwaterways. The Guppy Poecilia reticulata is theexception to this, with established populations inmany streams along the Queensland east coast(Arthington 1991).

Associations of two poeciliid species,particularly G. holbrooki combined with X. helleri

or P. reticulata, appear to depress populations ofindigenous fishes (Arthington et al. 1983).

Still maintained as aquarium fishes, it is likelythat these poeciliids will continue to betranslocated into urban waterways. While thesespecies have not shown the same capacity forunassisted range expansion as other exotics,some populations have persisted for a number ofyears and the potential for proliferation,especially with human assistance, should not beignored (Arthington and Lloyd 1989).

Economic Impacts

These species have some value as ornamentalfishes. However, outside the aquarium industry,their principal economic impact is that of pestfishes.


• All poeciliid species should be monitored forindications of range expansion, significantincreases in populations and evidence ofecological impact.

• Isolated populations should be eradicatedwhere feasible, and new introductionsprohibited.

Ornamental

Ornamental


3.4.12 Oreochromis mossambicus (Peters)

Family: Cichlidae

Common name: Tilapia or Mozambique

Mouth-brooder


Indigenous Range: Lower Zambesi andassociated east-Africanrivers


Year of introduction: Unknown


This species of Tilapia is found in Brisbane(water supply reservoirs), Townsville (urbandrains, Ross River), Cairns (estuaries), and theGascoyne—Lyons River system, WesternAustralia (Arthington and Bl¸hdorn 1994a). Itsrange is expanding, apparently because oftranslocations. O. mossambicus has recently beenreported from new water supply reservoirs inthe Brisbane area (P. Jackson, pers. comm.) andin other creeks around Townsville and Cairns (R.Wager, J. Harris pers. comm.).


In parts of tropical Asia, O. mossambicuscontributes significant proportions of the animalprotein available to local communities. In 1988this species produced in excess of 100 000 tonnesfrom capture fisheries and aquacultureoperations (Petr 1992). However, in many Asiancountries where this species has been introducedit is now considered a pest fish because of itsinvasive abilities, lack of acceptance as a foodfish, or its propensity to overpopulate smallwaterbodies with masses of stunted individuals(Blühdorn and Arthington 1992).

In Australia, this species has only been studiedin detail in the disturbed habitat of a watersupply reservoir (Blühdorn and Arthington1990a) and no direct evidence of adverseenvironmental impact was found(A. Arthington). Other studies of distributionand abundance have indicated the potential forcompetition with indigenous species for foodand breeding territories, and incidences ofstunting, both in disturbed and relativelypristine habitats (Blühdorn et al. 1990, Blühdornand Arthington 1990b).

O. mossambicus is considered to have thepotential to devastate indigenous fishpopulations if it moves down the Darling Riversystem (P. Gehrke, pers. comm.) and is regardedas a serious threat to the biota of the Murray-Darling River system (B. Lawrence pers comm.).

Economic Impacts

This species presently has no commercial orrecreational value in Australia. There is someinterest in O. mossambicus as a food fish, but itspresent proscribed status, which prohibitstranslocation, means that any development ofthis aspect of the fishery will be localised.

Other Information

O. mossambicus is a prohibited import intoAustralia. As well, it is declared noxious inQueensland, the Northern Territory, New SouthWales and Victoria. It is prohibited in SouthAustralia and commercial utilisation is notpermitted in Western Australia (Blühdorn andArthington 1992).

As the indigenous, highly valued BarramundiLates calcarifer becomes more widespreadthrough the efforts of translocation, there couldbe increasing pressure to use the exotic O.mossambicus as a forage fish. This has seriousimplications both for the illegal spread of O.mossambicus and for the development ofBarramundi fisheries in the Murray-Darlingbasin and the Northern Territory (N. Milward,pers. comm.).

Donnelly (1978) reported accounts of O.mossambicus surviving droughts in sandystreams in southern Africa by burying itself inthe wet sand layer, often as deep as 3 m. Similardrought and habitat conditions occur in theGascoyne—Lyons River system of WesternAustralia, and it is possible that O. mossambicussurvives the long periods without surface flowsin this system in this manner.


• Research aiming to produce practicalmanagement strategies for O. mossambicus isthe highest priority; this may need to involvefurther basic biological studies in key areas.

• A coordinated education program is requiredto make the public aware of the risks to theenvironment from the release of live exoticbiota, as well as a program to educate thepublic on identification of indigenous andexotic species. This should include a messagethat occurrences of exotic species should bereported to the State or Territory authorities.

17

3.4.13 Tilapia mariae Boulenger

Family: Cichlidae

Common name: Black mangrove or Niger

cichlid

Indigenous Range: Coastal rivers of west

Africa




In Victoria, this species is apparently confined tothe heated waters of the Hazelwood PowerStation cooling ponds near Morwell (Allen 1989).Established populations have also been recordedin Queensland, in the Cairns area (Barron River,and estuaries) (Blühdorn et al. 1990).


In Victoria T. mariae is very localised andprobably does not affect local biota because of itsrestriction to thermally disturbed habitats (P.S.Lake, pers. comm., P. Cadwallader, pers. comm.).

In Florida, USA, this species was reported to beextremely aggressive towards other exotic fishesand to be spreading rapidly through thedisturbed canal systems of southern Florida(Courtenay and Hensley 1979). Southern Floridahas similar climatic and habitat conditions toQueensland, so the establishment of Tilapiamariae in the Cairns area could be problematic.Consequently, T. mariae is classified as noxious inQueensland under the Fisheries Act. As yet, nostudies have been conducted in Australia on itsenvironmental effects.

Economic Impacts

This species has no commercial or recreationalvalue in Australia.


T. mariae requires basic ecological research todetermine its distribution, abundance, andeffects in tropical Queensland. It should bestudied in conjunction with research into O.mossambicus in the Cairns area.

•

•

In Victoria, this species, and others found inthe thermally disturbed ponds at Morwell,should be monitored to determine if rangeexpansion into the cooler waters of theadjacent stream system has occurred.


3.4.14 Cichlasoma nigrofasciatum Günther

Family: Cichlidae

Common name: Convict Cichlid

Indigenous Range: Western drainages of

Central America,

eastern drainages of

Costa Rica

Introduced from: Central America

Year of introduction: 1920s



In Victoria, this species in confined to the heatedwaters of the Hazelwood Power Station coolingponds near Morwell (Allen 1989).


In Victoria this species is very localised andprobably does not affect local biota because of itsrestriction to thermally disturbed habitats (P.S.Lake, pers. comm.). Even in these habitats it isnot common, and it is not considered likely tosurvive in the lower temperature regime of theadjacent waterways (P. Cadwallader pers comm.)

Economic Impacts

This species has some commercial value as anornamental fish, but feral populations producemainly negative economic impacts due to thecosts of monitoring and management.


• This species, and others found in thethermally disturbed ponds in the Morwell,Victoria area, should be monitored to see ifany range expansion into the cooler waters ofthe adjacent stream system has occurred.

3.4.15 Misgurnus anguillicaudatus (Cantor)

Family: Cobitidae

Common name: Oriental Weatherloach

Indigenous Range: Northeast Asia to centralChina (Welcomme 1988)




This species is rapidly expanding its range in theAustralian Capital Territory (Lintermans et al.1990). It is abundant in the Yarra, MarybrynongRivers, and present in the Ovens and MurrayRivers, Victoria, where it is actively expandingits range (P.S. Lake, pers. comm.). M.anguillicaudatus is also currently expanding itsdistribution in southern New South Wales (P.Gehrke, pers. comm.). It has not yet becomeestablished in Tasmania (W. Fulton, pers.comm.).


There are presently no Australian data on thisspecies’ interactions with indigenous fishes (P.Gehrke, pers. comm.), although there ispreliminary evidence that the Weatherloach isadversely affecting Galaxias olidus in smalllowland streams in the ACT (M. Lintermans,pers. comm.).

Economic Impacts

In Tasmania, there is concern about the potentialnegative impact on indigenous fauna and thehigh costs of management (W. Fulton, pers.comm.).


• There is a need for basic ecologicalunderstanding of the life history, habitat, dietand distribution of M. anguillicaudatus as wellas descriptive and experimental studies onthe impacts of this exotic species onpopulations and communities of indigenousfish, invertebrates and plants.

•

19

The distributions of known populations ofthe Weatherloach should be monitored andlikely invasion sites examined to fullydetermine the extent and rate of spread ofthis species.


3.4.16 Acanthogobius flavimanus Schlegel

Family: Gobiidae

Common name: Yellowfin Goby

Purpose of introduction: Accidental (ship ballast

or contaminated oyster

shipment)

Year of introduction: Around 1971


This species is mainly established in the marinewaters of Sydney Harbour and Botany Bay, buthas been found in freshwater reaches of theHawkesbury River, New South Wales (P. Gehrke,pers. comm.)


A. flavimanus is uncommon and little is known ofits local biology or interactions with otherspecies (P. Gehrke, pers. comm.).

Economic impacts

This species has no commercial value inAustralia.


• The distributions of known populations ofAcanthogobius flavimanus should bemonitored, especially those found infreshwater.

Introductions3.5 Temporal Sequence of Fish

Aquatic habitats, like all ecosystems, aresubjected to invasions over various time-scales,from geological to historical. Australia’s positionas an island continent has produced a uniquefreshwater fauna but has also physically limitedthe species available for invasions. Humanactivities have, to a certain extent, overcome thephysical limitations on invasive species,providing pathways either by accident or intent.To date, only one accidental introduction of anexotic fish species to Australian freshwaters hasbeen recorded—the Yellowfin GobyAcanthogobius flavimanus. The remaining exoticfish species established in freshwater weredeliberately introduced to Australia, althoughnot always with official sanction.

In Australia, there have been three waves of fishintroductions: the late 19th centuryacclimatisation movement; the poeciliidintroductions for attempted mosquito controlbeginning in the 1920s and apparentlycontinuing today; and the late 20th centurywave of introductions for aquaculture andornamental use.

The acclimatisation societies of the late 19thcentury were responsible for an initial wave of10 exotic species, most of which wereestablished successfully. These introductionswere intended primarily to provide recreationalfisheries based on familiar species, and includedall of the salmonids, percids, and cyprinidswhich are presently established in this country.

Three of these species, Oncorhynchustshawytscha, Salmo salar, and Cyprinus carpio(‘Boolara strain’) were re-introduced in the1960s for aquaculture purposes. Hybrids of thelatter species subsequently achieved a massiverange expansion throughout the Murray-Darling River system, the impacts of which arestill being felt.

From the 1920s onward, Gambusia holbrooki wasintroduced throughout the country for thepurposes of mosquito control. Other poeciliids,including Phalloceros caudimaculatus, Poeciliareticulata, and Poecilia latipinna, were also


introduced for mosquito control, but on a muchsmaller scale.

The remaining group of species, including thepoeciliids, cichlids, and the Weatherloach wereapparently originally introduced as ornamentalfishes in the 1960s and 1970s. Escapees, ordeliberate releases of these fishes, have resultedin the establishment of feral populations, someof which have high potential for rangeexpansion.

Species3.6 Environmental Impacts of Exotic

The potential effects of exotic fish species arecompetition (resource, spatial, interference);predation (by or upon indigenous biota);hybridisation; the introduction of diseases andparasites; and habitat alteration (Wager andJackson 1993; Crowl et al. 1992; Lloyd 1990a;Taylor et al. 1984). All of the above impacts havebeen recorded or are suggested to have occurredin Australian freshwaters (see individual species’summaries, Section 3.4).

In the worst cases, these impacts are indicated bydeclining populations of indigenous fisheswhose distributions no longer overlap with theexotic species, indicating a complete exclusion ofthe indigenous species and, in some cases,endangering their survival. Other symptoms ofenvironmental impact may be found in shifts inrelative abundance of indigenous biota, rapidexpansions in range and abundance of exoticspecies and disturbances of habitat and waterquality (Crowl et al. 1992; Brumley 1991;Arthington 1991).

Causal links between a species’ introduction andthe symptoms of its presence and impact are notalways known or demonstrable. Oneconsequence of this is a general lack ofconclusive scientific evidence of impactsattributable solely to exotic species.

This state of affairs is the result of threeprincipal, interacting elements. Firstly, there isinsufficient information on indigenous biota,which is evidenced by the number ofundescribed species and a general absence ofmonitoring (Wager and Jackson 1993). Secondly,there are the coincident effects of habitatmodifications on indigenous biota (usuallydeleterious) and the exotic species (oftenadvantageous) (Arthington et al. 1990). Thirdly,pre-introduction studies are rarely undertaken(Courtenay 1990), so there is little originalbaseline data on which to base evidence of laterimpacts.

Even the fact that none of the exotic species haveindigenous congeners, thus precludinginterbreeding, has not prevented environmentalimpact as a result of hybridisation. TheEuropean Carp C. carpio had a sedentarydistribution for almost 100 years before a hybrid,believed to be a mixture of the ‘Boolara’ and‘Yanco’ strains (Brumley 1991), dispersed widelywithin the Murray-Darling River system.

The topic of hybridisation raises an issue whichneeds to be considered in association withresearch on exotic fish species. This is thetranslocation of indigenous species to waterways

outside their natural range. Such a practice iseffectively the same as introducing an exoticspecies, with the added danger of hybridisationbetween the translocated fish and locallyoccurring, closely related fishes. It is noteworthythat Australia’s only purported fish extinction,the Lake Eacham rainbowfish Melanotaeniaeachamensis, is attributed to the translocation ofindigenous fishes (Wager and Jackson 1993). Thisnow appears to be a case of extinction of a localpopulation only.

The topic of indigenous translocations is toolarge to be considered in greater detail in thisreport, but it should be considered as part of anystrategies developed for managing exotic fishspecies.

3.7 Economic Impacts of ExoticSpecies

A number of the exotic species found inAustralia generate direct and indirect financialbenefits from commercial (wild caught,aquaculture, and ornamental) and recreationalfisheries (see individual species’ summaries,Section 3.4). Exotic species introduced forrecreational fisheries are stocked directly into thenatural aquatic systems. Generally, for thesespecies, the environmental and managementcosts are perceived to be outweighed by theeconomic benefits they produce.

Wild caught and cultivated exotic species haveescaped, or been deliberately released, into theirreceiving waters. While the financial return fromharvesting these stocks can be considerable (e.g.European Carp), so can the negative economicimpacts, such as the cost of control programs,loss of amenity, and other opportunity costs.

The ornamental fish industry was reported to beworth close to $200 million in 1988 (Kailola1990). As with the aquaculture industry, theornamental exotic fishes which have becomeestablished in the wild are the result of escapesor deliberate releases. These escapees have nocommercial value and will incur high costs fortheir effective control.

For other exotic fishes, expected positiveeconomic effects have not eventuated. Forexample, the Mosquitofish Gambusia holbrookiwas introduced and widely distributed in thiscountry for the purpose of mosquito control.Lloyd (1990b) concluded that G. holbrooki is arelatively poor mosquito predator and thatindigenous fish species are more effective andappropriate for mosquito control in this country.

All of the established exotic fish species have anegative economic impact represented by the


resources required to monitor, investigate,manage and, in a few isolated cases, exterminatethem. However, the principal negative economicimpact of exotic species is the cost ofrehabilitating the aquatic ecosystems damagedby the presence of exotics. Although potentiallymassive, these costs are so intertwined withthose due to habitat degradation and otheranthropogenic impacts as to be impossible todifferentiate them exclusively.

3.8 Ecology of Invasions

Craig (1992) suggests that exotics must be:physiologically adapted to the new environment;able to find and compete for food and habitat ateach life-history stage; able to avoid predation;and have suitable reproductive potential orflexible life-history traits. In Australia, suchspecies are represented by those introducedsuccessfully in the late 19th century It could beargued that, given appropriate data about theexotic species and the habitat into which it is tobe introduced, the process of invasion should bepredictable.

However, most successful invasive species areinfluenced by habitat and anthropogenic factors(fishing pressure, stocking, translocations) whichare independent of the biotic tolerances and life-history traits of the invading species. Theseanthropogenic factors contribute markedly to theinstability of fish communities and make itimpossible to predict the outcomes ofintroductions in terms of the final speciescomposition and the time frame required toregain community stability. Achieng (1990)demonstrated that the effects of fishintroductions into Lake Victoria, central Africa,30 years ago are still apparent, and the fishcommunity and populations of many specieshave not achieved a stable state.

A similar situation could pertain to exotics fishesin the Murray-Darling system, especially theEuropean Carp, which may yet decline or maycontinue to be a major part of the fishcommunity. The outcome is unpredictable.

3.9 Human Influences

The role of some anthropogenic activities isdiscussed in Section 3.8 above. Such activitiesmay be of direct influence, such as theintroduction and maintenance of fish populationsfor food, pets, recreation, or aquaculture. Humaninfluences may also be indirect, such as land useeffects (disturbance of the riparian zone); watermanagement (disruption of the natural flowregime); water storage (destruction of littoral andriparian communities, and riverine habitat); the

creation of lacustrine conditions for which fewindigenous species are adapted; and pollution.

Davies (1989) showed that exotic and indigenousspecies differ in their reactions to both naturallyoccurring and anthropogenic disturbances. Poorrecruitment of S trutta was attributed to lowflows and the lack of suitable ‘nursery’ habitat inheadwater streams in dry years, while thesympatric indigenous species Gadopsismarmoratus showed no adverse effects. Indisturbed areas, changes in the flow regime dueto irrigation water use and river impoundment(i.e. high summer flows, lowered temperatures)reduced recruitment of G. marmorutus.

Meffe (1984) showed a similar pattern of impactof naturally occurring abiotic perturbation inNorth America. In a location prone tounpredictable flash flooding, the indigenouspoeciliid (Poeciliopsis occidentalis, the SonoranTopminnow) was relatively unaffected by flowperturbations, whereas populations of theintroduced poeciliid Gambusia affinis (withsimilar life history traits), were devastated.Periodic, flood-induced reductions in Gambusiapopulations permitted the coexistence of the twopoeciliids. Similar process appear to permit thecoexistence of Gambusia and several indigenousspecies in streams of south-west WesternAustralia (B. Pusey, pers. comm.).

An even broader range of human influences onaquatic invasions arises from variousanthropocentric attitudes towards the aquaticenvironment in general and fish species inparticular. These are the attitudes that definewhether a fish is considered a pest or a resource(a single species can be both); whether, and howa species should be exploited or not; the timeframe for development or for conservation; therequirements for, and strategies applied to, themanagement of aquatic systems; and so on.

A number of protocols, such as EndangeredSpecies Legislation, the policy of EcologicallySustainable Development and the PrecautionaryPrinciple, and State based policies ontranslocations and exotic fish species, have beendeveloped. In the international arena, policiesand procedures concerning such issues arecontained in the “Codes of Practice and Manualof Procedures for Consideration of Introductionsand Transfers of Marine and FreshwaterOrganisms” (Turner 1988).

3.10 Assessment of Threats andPriority Species

While some impacts on indigenous species havebeen demonstrated, and many more suggested, anumber of other factors should be considered in


determining the ecological threat presented byan exotic species.

The group for which most environmentalimpacts have been demonstrated is thesalmonids, in particular Brown Trout (S. trutta)and Rainbow Trout (O. mykiss). These have threecharacteristics which distinguish them from theremainder of the self-maintaining exotic fishspecies in Australia: they have been establishedin this country for a long time; they requireundisturbed or high quality habitat to survive;and they are predacious.

The effects of salmonids have beendemonstrated as a fragmentation of thedistribution of indigenous galaxiids, and therelegation of co-occurring species, for example,the River Blackfish Gadopsis marmoratus, to sub-optimal habitats. These are classic impacts ofpredatory exotic species (Fernando 1991). To acertain extent, the impacts of salmonids havestabilised and they are unlikely to causeunexpected impacts in the future. As well, theireconomic and recreational benefits are generallyperceived to exceed their environmental costs.However, the salmonids are implicated in thedecline of four ‘endangered’ and four‘vulnerable’ indigenous fishes (Wager andJackson 1993). The principal research andmanagement thrust, therefore, should be theconservation of indigenous species threatenedby salmonids.

Another predatory exotic species with a longhistory in Australia is Gambusia holbrooki, whichhas affected a much wider range of indigenousfish species because it is not limited to coolupland streams. It is implicated in the decline oftwo ‘endangered’ and five ‘vulnerable’indigenous fishes (Wager and Jackson 1993).

Of the remaining exotic species, those that arecausing, or are likely to cause, environmentalproblems have the common denominator thatthey are relatively recent introductions and arethus, to a large extent, still in the unstable‘boom-bust’ period caused by their introduction.They have probably not achieved their finaldistribution and their impacts will varydepending on interactions with indigenous biotain new habitats, many of which are likely to bedisturbed or altered from a natural state.

Finally, some of the remaining established exoticfish species are considered to have littlelikelihood of significant range expansion. Theseare generally ornamental species surviving inurban waterways.

Table 3.2 illustrates the grouping of the variousestablished exotic species by their knowninteractions with indigenous species and theirperceived threat.

3.11 Management Issues andDirections

One of the unfortunate effects of currentmanagement of the exotics problem is that theevidence of damage is necessarily after the fact.That is, the damage has been done beforepreventive action can be taken. Obviously,prevention is, in most cases, the best approach tothe management of exotic species. Effectivemonitoring systems could detect subtle changesin fish communities and act as an early warningsystem of potential problems, such as rangefragmentation or the local eradication of anindigenous species. Suitable early warningmethods need to be devised and put in place.

Many of the problems associated with exotic fishspecies are relatively minor, but they persist andmay grow to become major issues. This occurslargely because the responsible managementauthorities are not provided with sufficientresources to allow effective monitoring and‘house-keeping’ activities.

Preventive measures against the spread ofinvasive species are as simple as publiceducation backed by appropriate legislation andeffective enforcement. In general, the legislationis in place, relatively trivial amounts are spent oneducation, and enforcement is ineffective. As aresult, the problems caused by translocation ofboth exotic and indigenous species continueunabated. Aquarium fish are dumped, bait fishescape, and forage fish are deliberately released.All of these activities require humaninvolvement—very little spread of invasivespecies can be attributed to unassisted dispersal.

A four-pronged approach is needed. The fourelements are research, monitoring, education,and political will. All need to be incorporatedinto an integrated approach to the multitude ofstrategies needed for sustainable management offreshwater resources.


3.12.1 General Recommendations

The R & D recommendations for individualspecies were presented with each speciessummary (Section 3.4). These are summarisedbelow. As well, a number of generalrecommendations were put forward by thefisheries scientists who responded to our requestfor information. These have been ordered, tosome extent, into priorities, and include:

• Funding for regional or catchment-basedinventories of aquatic environments and


Table 3.2: Established exotic freshwater fish species ordered by the type ofenvironmental threat or problem.

Species regarded as economically beneficial despite demonstrated or potential environmentalimpacts.

SalmonidaeOncorhynchus mykiss (Walbaum) Rainbow TroutSalmo salar L. Atlantic SalmonSalmo trutta L. Brown TroutSalvelinus fontinalis (Mitchell) Brook Trout

Species regarded as major pests and on which considerable research effort has been or is beingexpended.

CyprinidaeCyprinus carpio L. European Carp

Species regarded as major pests and on which only ad hoc research effort has been or is beingexpended.

PoeciliidaeGambusia holbrooki (Girard) Eastern Gambusia or Mosquitofish

Species which are likely to undergo rapid range expansion if not managed effectively.

CichlidaeOreochromis mossambicus (Peters) Tilapia or Mozambique Mouth-brooderTilapia mariae Boulenger Black Mangrove or Niger Cichlid (in far north Queensland)

CobitidaeMisgurnus anguillicaudatus (Cantor)

PercidaePerca fluviatilis L.

Oriental Weatherloach

European Perch or Redfin (in Western Australia and the ACT)

Species which have been established for sufficient time to allow impacts and distributions to becomestabilised and for which no current research is under way.

PercidaePerca fluviatilis L. European Perch or Redfin (other than in Western Australia and

the ACT)CyprinidaeCarassius auratus L.Rutilus rutilus L.Tinca tinca (L.)

GoldfishRoachTench

Species occurring principally in urban areas, not showing signs of unassisted range expansion, butlikely to be augmented by the release of other aquarium fish.

PoeciliidaePhalloceros caudimaculatus Hensel One-spot Live BearerPoecilia latipinna Le Sueur Sailfin MollyPoecilia reticulata Peters GuppyXiphophorus helleri (Günther) SwordtailXiphophorus maculatus (Heckel) Platy

CichlidaeCichlasoma nigrofasciatum Günther Convict CichlidTilapia mariae Boulenger Black Mangrove or Niger Cichlid

Newly introduced exotic species about which little is known of potential distribution or likelyinteractions with indigenous biota.

GobiidaeAcanthogobius flavimanus Schlegel Yellowfin Goby


biota that are potentially susceptible to exoticspecies. This includes research into thegeneral ecological requirements ofindigenous fish species and the monitoringof indigenous speciesí distributions andabundance. There is a pressing need for long-term records rather than anecdotes.

• Basic ecological research to provide anunderstanding of the life history, habitat,diets and distribution of important exoticspecies, and to provide a betterunderstanding of the effects of exotic fisheson local ecosystems. These should includedescriptive and experimental studies on theimpacts of exotic species at both thepopulation and community level.

Priority should be given to developingstrategies for the practical management ofspecies of major concern, e.g. Tilapias,Gambusia, and Carp. This may involve somebasic biological studies but it must bedirected at practical management outcomes.It should also include examination ofsynergistic effects with other causal factorssuch as habitat degradation and couldinclude a comparison between effects ofexotics in flowing waters andimpoundments.

• Education is a cost effective method ofpreventing ill-informed introductions andtranslocations of aquatic biota and disposalof aquarium fish. Concerted and coordinatededucation programs should make the publicaware of the risks of exotic species to theenvironment, as well as a program toeducate the public on identification ofindigenous and exotic species. This shouldinclude a message that any exotic faunafound should be reported to the State orTerritory authorities.

Priority should be given to a multi-facetededucation campaign aimed at informingdecision makers at the various levels ofindustry and government. Such a campaigncould include information dissemination tothe ornamental fish industry on: the effects,or potential effects, of exotic fishes; theadvantages of utilising indigenous species,along with information about inappropriatetranslocation of these species; ways ofpassing this information on to hobbyists; andestablishing a disposal/recycling system forunwanted aquarium fishes.

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Public health authorities could be betterinformed of the choices available forbiological control of nuisance organisms suchas mosquitoes, and politicians could beapprised of the problems associated withexotic fishes and the wealth of advice

available to them for consultative purposesbefore decisions are made about aquaculturedevelopments, fish stocking programs, and soon.

Methods of risk assessment and problemevaluation are required, with emphasis onAustraliaís tropical environments and faunalassemblages.

Research is required to demonstrate the costof exotic species to ecological sustainability,water management, recreational andcommercial fisheries, conservation, and watertreatment for public health. This informationcould be used to demonstrate the cost of notfunding new research into measures tocontrol exotic species.

Research is needed to determine the effects ofintroduced fish in significant conservationareas, such as the southern acid peat flats andthe southern forests of south-west WesternAustralia, the coastal dune wetlands ofeastern Australia, and the wet tropics area ofnorthern Australia, because of the number ofindigenous species with very restricteddistributions in these systems.

Research should be conducted into thesecondary impacts of introductions, such asincreased angling pressure on indigenousfishes because of the development of arecreational fishery based on exotic speciesthat are more difficult to catch.

Many respondents perceived a need for moreeffective methods of control over movementsof exotic and translocated indigenous fish inAustralia.

A survey of translocated indigenous fish isneeded to monitor their range andabundance. As well, research is required intothe effects of translocated species,particularly those most commonly involved,such as Golden and Silver Perch. There willbe continuing political pressure to translocatefish and hard scientific data are required tocounteract this.

There is a perceived need to investigate ordevelop a policy on utilising establishedexotic fishes in aquaculture. Income fromsuch operations could be used to fundresearch into the control of feral populations.

3.12.2 Individual species priorities

The suggested R & D priorities for individualspecies include:

Continuing financial support for research intothe control of European Carp populations inthe Murray-Darling River system.

Research into the effects of exotic species onthreatened indigenous fishes, and methods


for the conservation of remnant populationsof endangered indigenous species.

Research, with management outcomes, onthose exotic species identified as undergoingrange expansion, including G. holbrooki, O.mossambicus, T. mariae, M. anguillicaudatus andP. fluviatilis.

Regular monitoring of exotic fish populationsto provide baseline information ondistribution and abundance, and also to warnof impending range expansion or othersignificant changes.

3.13 Research Coordination

Research and development programs initiatedby the LWRRDC should be integrated withother national programs to achieve the effectivemanagement of exotic fish species and theconservation of Australia’s indigenous aquaticbiota. Relevant programs include theAustralian Nature Conservation Agency’s FeralPests Program and Endangered SpeciesProgram, and the Natural ResourcesManagement Strategy for the Murray-DarlingBasin.

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4.0 Diseases and Parasites

4.1 Introduction

The topic of exotic parasites and diseasesbrought into Australia with exotic fish is brieflyreviewed as part of this report, but acomprehensive treatment has not beenattempted. This is a very large and specialisedfield which merits a thorough review of theissues relevant to environmental protection andindustries based on fish and shellfish. It goeswell beyond the topic of exotic aquatic biota,extending into the broader realm of localised andinterstate translocations of both indigenous andexotic biota within Australia.

Problems associated with pathogenic organismsas a whole may not fall strictly within the R & Dportfolio of LWRRDC and any essential R & Dinitiatives probably should be undertaken eitherby other organisations/funding schemes, or as ajoint venture (e.g. with the Fisheries Researchand Development Corporation).

The approach taken here is to outline some keyissues concerning diseases and parasites of exoticand translocated fishes, and to comment on highpriority issues for Australia at this time. There islimited information on the types and distributionof pathogens affecting exotic Gastropoda andtranslocated Crustacea, and these taxa are notincluded in the discussion which follows.

4.2 Diseases and Parasites

The dissemination of pathogenic organisms hasaccompanied the introduction and translocationof fish, Crustacea and shellfish throughout theworld. Diseases introduced with exotic specieshave frequently been spread to indigenousspecies within the new country by uncontrolledmovements of fish and other host organisms.

Australia has taken a strong stance on theimportation of exotic fishes partly because exoticdiseases and parasites may be introducedtogether with the fish and the water used duringtheir transport (McKay 1984).

Certain pathogens are considered to affect onlytheir original host species, genus or family, so the

introduction of an infected species within thegroup may threaten other members present inthe new country. Increasingly, however, taxon orspecies-specific diseases are transmitted tounrelated hosts (Langdon 1990).

The bacterial pathogen, Aeromonas salmonica, wasintroduced to Victoria in the 1970s via infectedJapanese goldfish (Trust et al. 1980). This episodebrought goldfish ulcer disease to cultured andwild Australian goldfish and carp populations óan issue of some significance for the aquariumindustry and aquaculturists. Subsequent studiesdemonstrated the pathogenicity of Aeromonas

salmonica to salmonids (Whittington and Cullis1988) and this discovery led to restrictions on themovements of goldfish within Australia.

The spread of imported pathogens from theirexotic hosts to indigenous fish species is of moreimmediate relevance to environmental protectionand may exact a high ecological and economiccost.

Langdon and Humphrey (1987) described a newviral disease of unknown origin, EpizooticHaematopoietic Necrosis Virus (EHNV),affecting Redfin Perch in the wild, which wasfound to have spread to cultured Rainbow Trout.This disease is known to be highly pathogenic toseveral indigenous Australian fishes, includingSilver Perch, Mountain Galaxias and MacquariePerch, and to a lesser extent, Murray Cod; it alsohas a pathogenic effect on Gambusia (Langdon1989).

The translocation of Redfin Perch and salmonidsby angling and government bodies withouthealth certification thus poses a threat tovaluable indigenous fish stocks in the wild.

Langdon (19901 reported several instances whereinfectious agents are more pathogenic, or onlycause clinical disease, in atypical hosts, and sobecome a problem when the typical host speciescome into contact with unusual hosts. Examplesare whirling disease in Rainbow Trout,proliferative kidney disease of salmonids and theNorth American crayfish ëplagueí fungus whichis only mildly pathogenic to the host crayfish buthas devastated indigenous European astacids.


The same phenomenon has been observed withfish parasites. Moyle (1985) noted thatindigenous Californian fishes seemed to be moreheavily parasitised by exotic parasites (e.g. theanchor worm, Lernaea cyprinacea) than exoticfishes. The anchor worm is now common inseveral indigenous Australian fishes and alsofrequently infects G. holbrooki in the RiverMurray (Lloyd et al. 1987).

Rowland and Ingram (1991) have recentlyreviewed the diseases and parasites associatedwith indigenous freshwater fishes in Australia,giving emphasis to the ectoparasitic and fungaldiseases of Murray Cod, Eastern FreshwaterCod, Trout Cod, Golden Perch and Silver Perch.Their report describes the seasonal occurrence,aetiology, diagnosis and treatment of commonpathogens, and also briefly reviews the status ofbacterial and viral diseases in Australia. Theselists have updated earlier compilations of themajor pathogens of Australian and overseas fishand shellfish (Langdon 1988; Langdon 1990).

Mr R. McKay, Curator of Fishes at theQueensland Museum, has compiled a list of theparasites associated with indigenous and exoticfish species maintained in culture facilitiesthroughout Australia.

Langdon (1990) and McKay (pers. comm.)consider that the movement of infectedindigenous fishes from one drainage system toanother, and interstate, is a much more seriousissue that the spread of pathogens via exoticfishes. Fish reared under culture conditions aregenerally much more susceptible to disease thanfish in the wild and there have been majoroutbreaks of disease and mass mortalities ofindigenous fish in several hatcheries.

The recent massive mortalities of cultivatedSilver Barramundi (Lates calcarifer) inQueensland and the Northern Territory due to apicornia-like virus, BPLV (Glazebrook et al. 1990)are a case in point. This disease has beenunequivocally diagnosed from Barramundi inAustralia (Glazebrook et al. 1990; Munday et al.1992), as well as from stocks in Thailand andTahiti. Prior to the introduction of appropriatecontrol measures for this virus, every Australianhatchery using intensive culture of Barramundilarvae suffered massive mortalities attributed tothe virus (Munday 1994).

Control measures have been very successful ineliminating the economic loss due toBarramundi mortalities (Anderson et al. 1993;

Munday 1994), but Munday (1994) has advisedthat the presence of a few infected fish in a batchcould lead to drastic consequences when theyare moved across State boundaries.

Recent proposals to establish growout facilitiesfor Silver Barramundi within the Murray-Darling Basin have led to research on thepossible transmission of BPLV virus toindigenous Australian fishes. In a project fundedby the Natural Resources Management Strategy(Murray-Darling Basin Commission), Dr JohnGlazebrook from James Cook University, hasfound evidence that Macquarie Perch, MurrayCod and Silver Perch are susceptible to BPLV

Asymptomatic carriers of BPLV have beendetected in Barramundi from South Australia.Thus one of the urgent issues is the developmentand ready availability of a sensitive and specifictest for the detection of the virus inasymptomatic fish. Electron microscopetechniques lack the sensitivity to detect latentand low grade infections; the ELISA/PCRtechnique is considered more effective andsensitive (J. Glazebrook, pers. comm).

Research presently in progress to document theincidence of parasites and diseases associatedwith both indigenous and exotic freshwater fishspecies maintained in culture systems, and alsoin the wild, should be continued andaugmented.


The following issues could be considered withinthe context of problems arising from theintroduction of exotic fish and movements ofexotic and indigenous fishes in Australia.

• Problems with fish diseases and parasitesshould be referred to one or more experts fora thorough review of the issues and researchpriorities relevant to the management andmonitoring of Australian freshwater systems.Mr McKay and Dr Glazebrook and theircolleagues could be contacted in the firstinstance to discuss and/or scope the topic.

• There is a perceived need for more effectivemethods of control over movements of exoticand translocated indigenous fish in Australia.

• Avenues for joint funding should be exploredwhere the issues extend beyond LWRRDC’s


immediate R & D portfolio.

5.0 Acknowledgments

This project was funded by the Land and WaterResources Research and DevelopmentCorporation. We thank Dr Nick Schofield and DrPeter Davies for guidance throughout the study,and Mr Glenn Conroy for assistance withpreparation of the final report. Many colleaguescontributed to this review through theirpublished work, as cited below. We particularlythank the following people and institutions fortheir assistance in providing advice, papers andother materials, and for their recommendationson research priorities.

Dr Malcolm Beveridge, University of Stirling,Stirling, Scotland.

Dr Kath Bowmer, CSIRO Division of WaterResources, Griffith, NSW

Dr Andrea Brumley, East Gippsland CommunityCollege of TAFE, Victoria

Dr Stuart Bunn, Griffith University, Brisbane

Dr Phil Cadwallader, formerly Dept. ofConservation and Natural Resources, Victoria

Dr Setish Choy, Queensland Dept PrimaryIndustries, Brisbane

Dr Peter Davies, University of Western Australia,Perth

Dr Wayne Fulton, Inland Fisheries Commission,Tasmania

Dr Peter Gehrke, Fisheries Research Institute,Cronulla, NSW

Dr John Glazebrook, James Cook University,Townsville

Dr Marc Hero, CRC for Tropical RainforestEcology and Management, Cairns

Dr Pierre Horwitz, Edith Cowan University,Western Australia, Perth

Dr Paul Humphries, Murray-Darling FreshwaterResearch Centre, Albury

Dr Peter Jackson, Queensland Dept PrimaryIndustries, Brisbane

Dr John Koehn, Arthur Rylah Institute, Victoria

Prof. Sam Lake, Monash University, Clayton,Victoria

Dr Brian Lawrence, Murray-Darling BasinCommission, Canberra

Dr Mark Lintermans, Parks and ConservationService, Canberra

Dr Lance Lloyd, Rural Water Commission,Victoria

Mr Roley McKay, Queensland Museum,Brisbane

Dr Frances Michaelis, Senate Select Committee,Commonwealth Government, Canberra

Mr Hamar Midgely, Fisheries Consultant, BliBli, Queensland

Prof. Norm Millward, James Cook University,Townsville

Dr D. Morgan, Murdoch University, Perth,Western Australia

Dr John Harris, Fisheries Research Institute,Cronulla, NSW

Dr Richard Pearson, James Cook University,Townsville

Dr David Pollard, Fisheries Research Institute,Cronulla, NSW

Dr Winston Ponder, Curator of Mollusca,Australian Museum, Sydney

Dr Luke Penn, Murdoch University, WesternAustralia

Mr Jamie Pook, Australian Nature ConservationAgency, Canberra

Dr Brad Pusey, Griffith University, Brisbane

Dr Jane Roberts, CSIRO Division of WaterResources, Griffith, NSW

Ms S. Schreiber, Monash University, Clayton,Victoria

Mr Anthony Scott, CSIRO Division of WaterResources, NSW

Dr Stephen Swales, Fisheries Research Institute,Cronulla, NSW

Mr Rob Wager, Scientific Officer, QDPI,Brisbane

Dr Robin Welcomme, FAO, Rome, Italy


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