The most likely problem to arise from introducing herpesvirus to carp populations in Australian waterways is one of effectiveness, according to an international team of researchers including Griffith University Adjunct Research Fellow Dr Jonathan Marshall.
In a letter published in the latest edition of renowned journal Science, Dr Marshall, of the Australian Rivers Institute, and his co-authors address the federal government’s proposed release of cyprinid herpesvirus 3 (CyHV-3, or koi herpesvirus) among the large numbers of introduced common carp that inhabit and dominate the country’s waterways, in an effort to reduce their numbers and aid the recovery of native species.
While they acknowledge that CyHV-3 can have a devastating effect on farmed carp populations, the broader number of variables at play in the wild, including carp biology, the virus’ pathogenesis and the ecology of local rivers, mean a release of koi herpesvirus would not likely result in the desired outcome.
Due to both the genetic resistance of carp and the environmental dependence of CyHV-3 – the disease develops at 16° to 28° C, while temperatures above 30° C will block infection and aid the development of immunity – the researchers suggest more work should be done before undertaking an expensive and irreversible large-scale release.
Mitigating factors in the virus’ efficacy include the fact that infected carp will seek refuge in warm water, their high fertility likely then leading to a surge in immune or genetically resistant fish as affected waterways are repopulated.
The team also asserts there is little evidence that the virus doesn’t already exist in Australia, given its incidence in carp populations prior to their introduction to the country.
Although there has been a lack of mass carp deaths related to CyHV-3, the researchers suggest this may be reflective of a lack of environmental cofactors. They cite the case of Japan, where CyHV-3 monitoring has been conducted since a mass death in 2004 at Lake Biwa, which has found a continued high rate of infection “without obvious effects”.
Dr Marshall and his co-authors suggest that further assessments should be made on multiple fronts, including demonstrating that the virus is not already active among local carp populations.
They also recommend the use of small-scale field trials to confirm that CyHV-3 can result in sustainable reductions in carp populations without adverse impacts on native species, or the development of alternative approaches altogether, including the release of ‘daughterless’ fish, to better control such populations in the long term.
Along with Dr Marshall, the international research team includes fellow academics Andrew J Davison (MRC-University of Glasgow Centre for Virus Research), R. Keller Kopf (Institute for Land, Water and Society, Charles Sturt University), Maxime Boutier and Alain Vanderplasschen (Department of Parasitic and Infectious Diseases, University of Liege), and Philip Stevenson (School of Chemistry and Molecular Biosciences, University of Queensland).