Fisheries project officer Iain Ellis, from the New South Wales Department of Primary Industries (DPI), said the spawning event was great news as native fish populations had not been strong.

"There has been a massive spawning event by the cod that remain in that part of the river," he said.

"Our monitoring team out there has detected larger numbers of cod larvae than pretty much ever detected in the Basin before, so that's been a great response.

"Right now, what we are hoping to see is further increases in flows.

“Even just marginal increases, that will start to fill a bit more of the river channel and  inundate a few more snags, sand banks and benches which all produces nutrients and therefore food for these guys."

Murray cod populations have declined severely over the decades due to a number of causes, including severe overfishing, river regulation, and habitat degradation and are now a listed threatened species.

However, they once inhabited almost the entire Murray-Darling basin, Australia's largest river system, in very great numbers.

A long-lived fish, adult Murray cod are carnivorous and mainly eat other fish.

The species exhibits a high degree of parental care for their eggs.

The eggs are spawned in the spring and are generally laid in hollow logs or on other hard surfaces.

Murray cod are a popular angling target and aquaculture species.

Often available through the aquarium trade, they are also a popular aquarium species in Australia.

Mr Ellis said the huge spawning event could be attributed to the cod's instinct to rapidly reproduce in times of flood, having evolved to suit the Murray-Darling Basin's cycles of boom and bust.

He said the fish larvae would find it challenging to survive if no additional releases were sent down the river from the Menindee Lakes as they would rapidly run out of food.

"It's pretty clear, as a fish ecologist, that with the flows coming through past Menindee Lakes from the northern Darling catchment.

“Those flows are carrying important flood cues, so there's lots of nutrients in the water," he said.

"As a result, the adult fish in the lower Darling, below Menindee, have responded and invested heavily in eggs and in spawning this year.

"Those fish are assuming, as they are evolved to do, that there's more water on the way and the river will continue to rise.

"When you do get higher flows or some floodwaters, you do get stronger recruitment or survival or the larvae in to adulthood."

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