Carp in Australia and the Cyprinid herpesvirus-3 'carp virus'

Anyone who regularly goes fishing or boating on our southern inland waters – especially the vast Murray-Darling Basin – knows the problems created by the spread of introduced common or European carp. Over the past half-century or so, the invasive Australian carp, known as the ‘rabbits of the river’, have spread and multiplied, displacing native fish species, muddying the waters with their bottom-sucking habits, spreading disease and undermining banks.

In some parts of the Murray river, carp now represent as much as 90 per cent of the total fish biomass, to the detriment of highly desirable native species such as Murray cod and yellowbelly.

For almost as long as these dreaded carp have been swimming in our rivers and lakes, anglers and environmentalists have dreamt of finding a silver bullet that might rid us of these pests. For a time, the Daughterless Carp Project appeared our best hope. This involves genetically engineering carp to produce only male offspring, resulting in a population crash. But even if it gets the green light, that program is years from fruition.

Carp virus

A more accessible and potentially more effective solution may lie with a naturally occurring viral disease that has decimated carp numbers in other parts of the world. Called Cyprinid herpesvirus-3, this disease that is a carp virus hasn’t reached Australian shores yet. However, scientists have been investigating the potential of deliberately introducing the carp virus here, in much the same manner as myxomatosis and calicivirus have been used to control feral rabbit populations.

Of course, any proposal to deliberately introduce a disease into the wild needs to be very thoroughly researched, and that’s exactly what a CSIRO team led by Dr Ken McColl from the Australian Animal Health Laboratory in Geelong have been doing for the past eight years, with funding from the Invasive Animals Cooperative Research Centre.

Under strictly controlled laboratory conditions, the carp virus has been tested on a huge variety of Australian fauna, including representatives of nearly every group of native fish that occurs in fresh or estuarine waters alongside carp. Introduced rainbow trout were also tested, as were various mammals, birds, reptiles, amphibians and crustaceans. Encouragingly, the only species in which the virus has so far been shown to cause disease is the common carp. While some other species may carry the virus, they don’t suffer from any illness as a result.

This carp virus is deadly on carp. Studies have shown an initial mortality rate in carp populations ranging from 60 to 100 per cent after exposure to the virus. These mass deaths tend to occur within a week or so of carp contracting the virus.

Release of Cyprinid herpesvirus-3 into Australian waters is at least a couple of years away and won’t happen without extensive public consultation and support. When that consultation process begins, it’s important that informed anglers and boaties help educate the public on the potential benefits.

Wiping out anywhere between 60 and 100 per cent of the carp living in our waterways carries significant implications, not least the need for a massive public clean-up campaign to remove tonnes of dead carp from lakes and rivers. But the long-term benefits would also be immense.

How does the Cyprinid herpesvirus-3 ‘carp virus’ work?

As far as I know, no-one is claiming this carp virus will remove every carp from our waterways. Instead, this spectacular reduction in carp numbers would provide native fish with a massive boost, especially if complimentary programs such as environmental repair, re-stocking, removal of barriers to fish migration and so on were implemented alongside it.

With careful planning and smart follow-up work, this could mean our kids have a chance of seeing Australia’s outback rivers the way our grandparents knew them: running clean, with mottled Murray cod and fat golden perch finning around every snag, dense spawning aggregations of silver perch and prolific eel-tailed catfish feeding in the clear shallows. In my opinion, that’s a dream worth pursuing.  

Thanks to NSW DPI senior fisheries manager Matt Barwick for help with my research for this column.