Doubts raised over Australia’s plan to release herpes to wipe out carp

Warm water may render the virus ineffective against the invasive fish, say researchers.

An Australian plan to kill invasive carp by releasing a virus into waterways has come under fire from researchers who argue that the tactic will not eradicate enough fish... The proposal is to infect carp with a strain of herpes called CyHV-3, which has caused mass fish deaths in the United States and Japan.

Many researchers have previously warned of possible far-reaching consequences of the plan, including rivers clogged with decaying fish corpses and further disruption to native ecosystems. Now, six researchers argue in a letter published in Science1 on 22 February that the virus is unlikely to be effective.

Carp carnage

The common carp was first introduced to Australia from Europe in the nineteenth century, but the biggest disruptions to ecosystems happened after a particularly hardy strain escaped from a fish farm in the early 1960s. With a single fish capable of producing more than one million eggs in a breeding cycle, carp now make up an estimated 80–90% of the fish biomass in parts of the Murray–Darling Basin, the breadbasket region of southeast Australia...

In 2016, the Australian government... tested the effects of the virus on animals including 13 native fish species, as well as chickens, mice, frogs and turtles, and concluded that it is safe for them. The virus is only known to affect the common carp and ornamental koi, in which the expected mortality rate is over 70%.

However, the Science letter says... that the disease develops only when water temperatures are between 16 ºC and 28 ºC. Populations of carp that survive the initial viral epidemic in hot or cold spots would be able to replenish the population quickly, say the authors.