Can native Australian percichthyid fishes control invasive common carp (Cyprinus carpio)

Research output: ThesisDoctoral Thesis

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The common carp, Cyprinus carpio, is an invasive fish that has been introduced to every continent except Antarctica. In some areas of its introduced range, carp have become extremely abundant and can dominate the fish biomass, and this is true of south-eastern Australia. Because carp are benthic feeders, they reputedly degrade water quality and impact aquatic macrophytes and macroinvertebrates detrimentally. Managing their populations is a major priority.
As a result of Australia’s arid climate and isolation, its ichthyofauna is unique. In particular, the south-east Australian ichthyofauna is dominated by the percichthyid fishes, a Gondwanan family almost entirely restricted to Australia. Anthropogenic disturbances have resulted in dramatic declines in most percichthyid populations. Community groups, fisheries managers and some scientists advocate that if populations of native predatory fish are enhanced through the release of hatchery-reared native percichthyids, these fish will consume carp and thus may provide a carp control method. This suggestion perhaps stems from the belief that carp are ‘ecological generalists’ and therefore occur in all riverine habitats, and offer a highly abundant prey resource that may be readily exploited by native percichthyids with generalised diets.
This thesis assessed four percichthyid species for the potential biological control of carp populations in Australia; Australian bass (Macquaria novemaculeata), which occur only in the eastern drainages of Australia, and three species that are located in the Murray-Darling Basin (MDB), namely golden perch (Macquaria ambigua), Murray cod (Maccullochella peelii) and trout cod (Maccullochella macquariensis).
A literature review (Chapter 2) examined the environmental relationships of the life stages of carp, golden perch and Murray cod in the MDB. Adaptations of young carp, including adhesive eggs, rapid development of free embryos and larvae and benthic feeding in juveniles, mean that the early life stages are likely to be located in shallow (<1m), slow flowing floodplain-type habitats. Native percichthyids are, by contrast, main channel specialists and generally do not enter the shallow floodplain-type habitats inhabited by the early life stages of carp. Thus predation on carp may well be restricted to the deeper sections of the main channels of the MDB, where the vulnerable juvenile stages are mostly absent. The subsequent chapters of the thesis set out to test these hypotheses as a basis for assessing the biological control potential of native percichthyids against carp.
Chapter 3 assessed the potential for Australian bass to control carp in the east Australian drainages. Predation on carp in the presence of native prey species was relatively frequent, but Australian bass were limited in what size carp they ate, in part because of gape size limitations. The maximum dorso-ventral gape measurement of bass was 47mm. When plotted against carp body depth and length, bass are theoretically restricted to eating carp that are <150mm in fork length (FL), because these fish have a body depth of 50mm or less. In aquaria trials, however, bass mostly consumed carp that were much smaller than this limit
(<60mm FL, 15mm body depth). Furthermore, the literature shows that bass avoid the shallow floodplain-type habitats where most of the small size class individuals of carp are located. These features indicate strongly that bass are limited in their potential to control carp.
The potential for golden perch, Murray cod and trout cod to interact in predator-prey interactions with carp in the MDB was examined in Chapter 4. Based on gape limitations, golden perch are restricted to carp <190 mm FL (<60 mm body depth), while trout cod have the potential to consume carp up to to ~220 mm (<65 mm body depth). In contrast, Murray cod have a large dorso-ventral gape (up to 150 mm) and can consume a wide range of carp sizes (<510 mm FL and <150 mm body depth). Field sampling during a flood event supported the hypothesis that most individuals of the early life stages of carp (<250 mm FL) are located in shallow, floodplain-type habitats, whereas golden perch (n=105), Murray cod (n=139) and trout cod (n=94) were all caught in the deeper sections of the main channel habitats. Like bass, golden perch, trout cod and small Murray cod are limited by gape restrictions and their habitat requirements and so are predicted to have only minor predatory impacts on carp populations at best. Although Murray cod have a large dorso-ventral gape, they are only found in main channel and anabranch habitats and thus predation on carp is restricted to the largest Murray cod in main channel and anabranch habitats.
Native percichthyids are commonly described as having a broad diet, and thus may be expected to consume carp when available. Chapter 5 examined the diet of golden perch, trout cod and Murray cod when in the presence of carp. In clear aquaria, like the bass, golden perch consumed more carp that were far smaller (<60mm FL and 15 mm body depth) than their maximum gape (56mm). Murray cod consumed all size ranges of carp at about the same frequency, and so were different in this respect from Australian bass and golden perch. Golden perch and Murray cod exposed to carp and native prey species at equal and altered relative prey abundances in aquaria trials consumed carp relatively infrequently compared to native prey species. In particular, when the abundance of carp was increased relative to native prey abundance, carp were rarely consumed by either predator species because of their ‘grouping’ behaviour. Stomach flushing of Murray cod and trout cod collected from rivers of the southern MDB similarly revealed that carp consumption by wild Murray cod was low, with <7% of Murray cod stomachs sampled (n=86) containing carp and no trout cod (n=71) contained carp. Overall, the rate of carp consumption by native percichthyids is probably too low to warrant their release to control carp
The general conclusion drawn from the research conducted is that despite carp presenting a highly abundant prey resource, their behaviour, morphology and environmental requirements, together with the dietary and habitat specialisations of native percichthyid species, are likely to substantially restrict any substantial predatory impacts on carp populations by these native predators.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Queensland
Award date20 Jan 2013
Place of PublicationAustralia
Publication statusPublished - 2012
Externally publishedYes


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