"It affects the European carp by attacking their kidneys, their skin, their gills and stopping them breathing effectively," he said.

"They have the virus for a week before they show any symptoms and it suddenly kills them within 24 hours."

He said the delay in release was due to the significant planning needed to deal with the sudden impact the virus may have on the river.

"Suddenly, there will be literally hundreds of thousands, if not millions of tonnes of carp that will be dead in the River Murray," Mr Pyne said.