For some years now, scientists have been questioning the wisdom of the Australian authorities’ plans to release the carp herpes virus (KHV) into rivers colonized by common carp (Cyprinus carpio) in order to control or eliminate this invasive alien species. As far back as 2018, for example, Belgian, English and Australian scientists called on the Australian authorities to reconsider their decision, emphasizing that not only would the measure be ineffective in controlling the carp, but that it would also represent a risk to native ecosystems.
At the time, one of the researchers, professor Alain Vanderplasschen, from the University of Liege, stated: “The discovery in our laboratory of the beneficial role of the behavioral fever expressed by carp, as well as other recent results, indicate that the Australian government’s biocontrol plan will not meet its objectives. This may even cause serious damage to the ecosystems.” (See Further Reading).
Even earlier than this, in May 2016, I published my first report on the subject, following the initial announcement of the plan. I introduced the item with these words: “Let’s suppose that the ornamental aquatic industry were to suggest the release of a deadly virus into native waters to control the spread of an invasive fish species. What do you think the reaction of the authorities and conservation or recreational agencies would be? We can’t be certain, of course, because this is a hypothetical example, but it would not seem too unreasonable to imagine the industry being accused of irresponsibility towards the welfare of indigenous fish fauna, the environment and, probably, much else besides.”
As I pointed out at the time, it wasn’t the industry but the Australian government and several supporting agencies that published the proposal. Quite reasonably, they didn’t plan to release the deadly virus in the immediate future, but they seemed to be convinced that this was the solution to the carp problem.
Since then, numerous objections have been raised to this proposed radical approach. These have ranged from the immense challenge posed by the millions and millions of rotting carp corpses to doubts about the efficacy of the virus itself, as not all the carp would die, with the survivors becoming carriers of the disease. It has also been highlighted that infected carp seek warm water and that temperatures above 30 degrees Celsius will block infection. In addition—and hugely worrying for our industry—the Australian koi sector could end up being wiped out in due course, as koi and carp are one and the same species.
In October 2020, a team of scientists from the University of Exeter and the University of East Anglia (both U.K. institutions) posted the latest opposition to the plan. They believe that not only is the strategy unlikely to work, but that it should be dropped altogether.
Their research demonstrates that common carp “would evolve resistance to the virus and carp numbers would soon recover.”
They agreed that control is necessary but asserted that releasing KHV is not the answer. In addition to recovery of the carp population, the scientists maintained that: “Releasing KHV carries significant risks to human and ecosystem health, which will likely outweigh the benefits, and we have previously urged further detailed research to avoid an unnecessary environmental catastrophe.”
In their words, they believe that “the plan to control Australia’s carp with KHV is dead in the water.”
One key element affecting recovery is the fact that global carp populations carry a “genetic component of resistance to KHV.” The team carried out a simulation model to estimate how long carp populations would take to recover, even if 95 percent was eradicated by the virus. They found that populations would recover to 80 percent of their pre-KHV densities within some 10 years. If the mortality level was between 50 and 60 percent, full recovery would take just five years.
In conclusion, the team said: “Our findings support that habitat restoration for native fauna and reduction of carp spawning grounds (e.g. by increasing managed river flow) would provide the first steps to reducing carp numbers in the Murray–Darling Basin. Although this cannot eradicate carp, it poses zero risk to human and ecosystem health, and is a sustainable solution to reduce carp numbers. Furthermore, reducing the fecundity or population growth rate potential, for example, through genetically modification, could increase the efficacy of KHV biocontrol, but requires further research and feasibility studies.”
The full paper makes fascinating reading, and I urge everyone to go through it in detail (see Further Reading).
Marshall, J., Davison, A. J., Kopf, R. K., Boutier, M., Stevenson, P., and Vanderplasschen, A. (2018). Biocontrol of invasive carp: Risks abound. Science, 359(6378), 877
Kate S. Mintram, Cock Oosterhout, Jackie Lighten. Genetic variation in resistance and high fecundity impede viral biocontrol of invasive fish. Journal of Applied Ecology, 2020; http://dx.doi.org/10.1111/1365-2664.13762
John Dawes is an international ornamental aquatic industry consultant. He has written and/or edited more than 50 books and has contributed more than 4,000 articles to hobby, trade and academic publications. He is the editor of the OFI Journal and a consultant to AquaRealm, the trade show that took place June 2017 in Singapore.