Unlikely alliance says specialised disease will transform rivers and protect native fish species after exponential growth in numbers of the European invader.
Conservationists and recreational fishers have joined forces to support the release of a specialised herpes virus targeting carp in the Murray river.
Scientists at the Commonwealth Scientific and Industrial Research Organisation have been testing the koi herpes virus in Australian native fish species, birds, amphibians and other animals found along the river for seven years to see if it is safe to release into the ecosystem.
“The virus doesn’t cause disease in any species that we have looked at,” said Dr Ken McColl, the project’s lead researcher. “It doesn’t even seem to multiply in other species. We are very confident that it’s only going to affect carp.”
The virus affects the fish’s skin and kidneys, which control its water balance. It spreads from direct carp-to-carp contact and takes about seven days to have a noticeable effect. Once the carp is visibly sick it usually dies within 24 hours.
“The virus comes along and makes a mess of those tissues and the carp basically drowns,” McColl said.
He said it was genetically unrelated to other herpes viruses, including those that affect humans, but was similar in affect and structure. “Virtually every species have their own specific herpes virus and very few of those viruses cross into other species,” he said.
In Europe, where the virus was discovered in the late 1990s, the result was piles of dead fish at carp fisheries. By 2004 the disease had spread to wild rivers in Britain, threatening the angling industry, which relies heavily on carp.
But McColl said the virus typically spread slowly down river systems, which would allow for the Murray to be cleaned of dead fish as it moved along. “We’ve even had some inquiries from commercial operations looking to collect the dead carp for use in fertilisers,” he said.
European carp were introduced to Australia in the 1800s but did not become a problem until the 1950s, when a species used in carp farms in Europe found its way into the river system. The carp population increased exponentially and the bottom-feeding fish, which is neither fished recreationally nor eaten in Australia, has been compared to rabbits in its effect on the environment.
“It’s said that they make up up to 90% of the fish biomass in parts of the Murray-Darling basin and, with that sort of population intensity, there’s not much chance for our native fish species,” McColl said.
“The main problem is the way they feed. They sort of rip plants out of the river bed and they make the water very muddy so that the plants can’t grow back and the native fish can’t breed.”
The acting campaign director for the Australian Conservation Foundation, Jonathan La Nauze, said half of the native fish in the Murray-Darling basin were listed as vulnerable or threatened, in large part because of carp numbers.
The ACF has formed an unlikely alliance with the Australian Recreational Fishing Foundation, the Invasive Species Council, the National Farmers’ Federation and the National Irrigators Council to push for the release of the virus.
“We are united in calling for clearer, healthier waterways and fish communities,” La Nauze said. “Australia now has a once-in-a-generation opportunity to achieve this through broad-scale biological control using a naturally occurring virus that is specific to common carp.”
Allan Hansard, the managing director of the Australian Recreational Fishing Foundation, said it was a “tremendous opportunity to transform our rivers”.
A proposal is being prepared for government approval by the Invasive Animals Cooperative Research Centre in Canberra.