Muddying the waters with their bottom-feeding ways, carp have had a huge impact on the native fish of the Murray-Darling river system.

Story by Kirsty McKenzie and Photos by Ken Brass

Are carp the curse of the Murray-Darling river system or innocent victims of a nasty smear campaign? Jim Barrett, of the Murray-Darling Basin Commission (MDBC), is not prepared to paint carp, an exotic pond species believed to have been deliberately released from a northern Victorian farmer’s dam some 50 years ago, as the only ‘bad guys’ of the river. “Carp have been accused of everything from muddying the water because they are bottom feeders to eating native fish,” he says. “While they are occasionally found with larvae or eggs in their stomachs, there’s little evidence that they are crunching predators such as trout or redfin. But in some parts of the system carp account for 90 percent of the biomass of fish, which means in terms of competition for food, space and shelter in the river they must be having an impact on the native fish. While it would take a budget similar to the Department of Defence to get rid of them, it would be good if we could control their numbers to some degree.”
Many of the carp in the Murray weigh between five and 10 kilograms. As female carp can produce 200,000 eggs per kilo of body weight, and they can reproduce twice a year, it’s hardly surprising that they have become a serous concern for the custodians of the river. Scientists from the MDBC and Invasive Animals Cooperative Research Centre are contributing one piece to the carp control jigsaw by working on a daughterless carp intervention that will bias sex ratios in carp towards males. After a number of generations, this could significantly reduce carp populations.

This story excerpt is from Issue #45

Outback Magazine: Feb/Mar 2006