Let minnow if you know a good way to dispose of dead carp Russell Shakespeare/Newspix

Troubled waters? The Australian government’s proposal to control alien carp with a lethal herpes virus will lead to a mass build-up of rotting carcasses that could harm native fish, ecologists are warning.

A carp-specific herpes strain – cyprinid herpesvirus 3 – is set to be introduced into the Murray-Darling river system in 2018 to help wipe out the introduced pest, which have decimated native fish populations since they were introduced in the 19th century and now make up 80 per cent of fish in this river system.

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The virus, which has been shown to kill about three-quarters of carp populations in experimental studies, is expected to cause millions of tonnes of dead carp to pile up.


Cutting off oxygen

The chemical process of decomposition requires oxygen, meaning that large quantities of rotting fish could sap oxygen out of rivers and make it difficult for native fish to breathe, says Richie Walsh at the University of Adelaide in Australia.

To determine the extent of this oxygen removal, Walsh and his colleagues dumped dead carp into 800 litre tubs of water.

Preliminary unpublished results suggest that at room temperature, a single carp can almost completely remove oxygen from the water in less than 2 days.

And dead carp can sink, making them more difficult to remove from rivers, Walsh says. However, the extent to which these things will happen in open river systems remains unclear.

Fish takeaway

The A$15 million (£9 million) carp-control programme will only go ahead if there is a comprehensive plan to deal with the impacts of dead carp on water quality and ecosystems, says a spokesperson for the Federal Department of Agriculture and Water Resources.

“The plan will focus on maximum impact on carp populations, and minimum disruption to industries, communities and the environment,” the spokesperson says. “Learning from experiences of responding to mass fish die-offs overseas will also help development of the plan.”

Most of the $15 million will be directed towards working out how to remove vast quantities of dead fish as quickly as possible, the department says.

The overall goal is to allow native fish populations to bounce back from the stranglehold of carp.

Read more: Australia to destroy alien carp by releasing herpes into rivers