Carp and Goldfish, are they a cause, or effect, of environmental degradation? What happens after KHV is released?

I attended a fantastic presentation by Dr Stephen Beatty last night.

Dr Stephen Beatty is a Senior Research Fellow at Murdoch University, and his work aims to make real impact on the conservation of aquatic ecosystems. Past and current research includes the impacts of water abstraction, climate change, introduced species, and water quality decline on aquatic ecosystems with a particular focus on fish communities.

Dr Beatty spoke of the importance of riverine and estuarine fishes and crustacea, as being the connectors between the aquatic and terrestrial food webs. He briefed us on the threats to aquatic environments being:

Pollution and habitat alteration (eutrophication, salinisation, land clearing, draining)
In-stream barriers (dams inhibit spawning migration, increase predation, thermal pollution, and favour introduced species)
Water abstraction (surface and ground water)
Climate change
Introduced species (mosquito fish, redfin, yabbies, goldfish and carp)

On the topic of introduced/alien species, he says the impacts are difficult to quantify, because we don’t have baseline data on how the aquatic environment was, prior to human influence. And the more altered the environment is, the more likely it is for an introduced species to flourish (much like rabbits). Controlling their abundance is the most viable option. And of the 14 alien species, the most harmful to river ecology is the little mosquito fish (Gambusia). Goldfish, on the other hand, tend to colonise areas that are affected by salinity higher than 3g/L (thus, the lack of freshwater mussels and other native species is not due to displacement by goldfish). He also warns that there would be significant resource investment, and can be a waste of time and money.

He spoke on the practical solutions they’ve had success with, for rehabilitating aquatic ecosystems:

Maintaining complex habitat (protecting and rehabilitating vegetation in the riparian zone, artificial habitats)
Oxygenation programs
Addressing nutrients and salinity
Fair allocation of water
Education (prevent alien species introduction)
Addressing high priority in-stream barriers (incorporate fishways)
Invest in monitoring for pollution and water quality at multiple trophic levels
Novel management approaches underpinned by research.

At the conclusion, I posed this question to the panel, “Are Carp and Goldfish, a cause, or the effect of, environmental degradation? What happens after KHV is released?”

Dr Beatty answered, “I’m very hesitant to point the finger at goldfish as a major ecological impact in its own right in south-western Australia. I don’t think it helps in terms of water quality, in the greater systems they’re in… the virus they’re releasing is specific for carp [including koi]… the one point I’d made to the researchers over east is that if all (80-90%) of koi/carp die, there is going to be a massive clean-up operation. If there is a free niche there, and goldfish occupy a similar niche, will goldfish do better than they currently do now. Anecdotally, over east, goldfish do very well where there is no carp. So research needs to be done on what the ecological impact goldfish will have in the Murray Darling Basin.”

If the release of KHV is a political stunt for freshwater angler votes, I wonder if, when it’s all over and done with, will anglers be happier to catch goldfish instead?

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Yours sincerely,

Dr Richmond Loh DipProjMgt, BSc, BVMS, MPhil (Pathology), MANZCVS (Aquatics & Pathobiology), CertAqV, CMAVA, NATA Signatory.
Aquatic Veterinarian & Veterinary Pathologist

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