We could reduce pest carp in Australian rivers using a disease that came from Israel

Everyone wants to give Australian carp the herpes virus. That’s right, introduced carp are a serious pest species and research suggests that a viral control agent may be the most effective solution.

I love stories like this one, where groups that would normally disagree come together in an “unlikely coalition”. That is to say, fishers, conservationists, irrigators, scientists and farmers agree on the desirability of an environmental release of the carp-specific virus.

After all, it worked for rabbits. The release of the myxomatosis virus in the 1950s and the more recent release of calicivirus have permanently decreased rabbit numbers on our continent. Using viral pathogens to control vertebrate pests can be extremely effective because it does not require ongoing human intervention.

Like rabbits, carp were introduced to Australia deliberately. The first introductions in the 1800s did not cause problems, but a strain bred for European aquaculture escaped from farm dams near Mildura in the 1960s and spread throughout the Murray Darling Basin. The impact of carp on our rivers has been well documented, including increasing turbidity (making the water muddy), destroying aquatic vegetation, and contributing to the decline of native fish.

In other parts of the world, carp are an important food species, often raised in fish farms. When I worked on a kibbutz in Israel in 1980 we caught and sorted carp from geothermal pools near the Sea of Galilee. The fish were a desirable food item and water from the fish ponds was used to fertilise banana crops via drip irrigation. I admired the sustainable farming practice that was then ahead of its time.

Twenty years later while participating in a fish survey at Horseshoe Lagoon near Albury, I remember pulling dozens of giant carp out of our nets, lamenting the lack of native fish. Because we were not allowed to return the carp to the water due to its pest status, we had to kill each one, resulting in a large pile of stinky dead fish that nobody wanted to eat.

The only similarity between these two memories was the method of death: although it looks brutal and cruel, hitting carp on the back of the head with a heavy wooden stick dispatches them instantly and humanely. On those two occasions this peaceful vegetarian turned into a lethal killing machine.

Ironically, at about the time I was whacking pest carp in Australia, the carp industry in Israel was affected by a new disease. The koi herpesvirus, or Cyprinid herpesvirus 3 (CyHV-3) appeared in Israel in 1998 and was so contagious that it soon spread throughout Europe and Asia. The carp industry was devastated.

While this virus is bad news for carp farming, it could be good news for managing feral carp in Australia. With an expected mortality rate of 70-80%, CyHV-3 may be just what we need to curb the plague of carp in our rivers.

Of course, given our sometimes disastrous experience with biological control species, caution is warranted. That’s why scientists have spent the last eight years doing research to ensure that the herpes will not affect other species. Ken McColl is a leader of the team that has examined the host specificity of the virus in an Australian context.

The good news is that CyHV-3 has no impact on other native fish, yabbies and trout. It cannot infect mammals, amphibians or reptiles. In other words, it looks safe.

The bad news is that it will affect ornamental carp (koi) which are highly valued, so people who keep koi will need to monitor their water and food sources. I see this as something like vaccinating your pet rabbits against calicivirus, an inconvenient but reasonable impost given the benefit for the nation and our environment.

What happens now? There are a number of government organisations that are responsible for biosecurity. Getting approval to introduce a virus into our waterways will probably take a few years, so the research will continue as the Invasive Animals Cooperative Research Centre goes through the application process.

There is also research underway to identify locations suitable for early releases, and this is where members of the public can get involved. Hotspots for invasive fish species will be identified by gathering data from concerned citizens at a new website called Feral Fish Scan. Anyone interested in learning how to identify invasive fish and record observations of their local waterways can do so at this link.

Other conventional approaches to reducing carp are still underway, from the development of traps that target carp to better ways for Charlie Carp to turn those feral fish into fertiliser. But harvesting tons of carp and turning them into pellets will never reduce the impact of this noxious pest as effectively as a carp-specific disease.

This is why virtually everyone is excited about the possibility of giving herpes to Australian carp. And even though I think it sounds like a good idea, I am also grateful that we have robust regulations about biocontrol, because there was a time when cane toads seemed like a good idea, too.

We can wait a couple of years to ensure that we do not regret our decision, but then we may enjoy a great irony: a disease that caused huge financial losses overseas could save freshwater environments in Australia.