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Teaching Young Cod New Tricks

AUSTRALIA - Fisheries scientists have doubled the survival rate of Murray cod by training them to recognise predators before they are released into open river systems and lakes and have to fend for themselves.

Agri-Science Queensland scientist Michael Hutchison said that hatchery-reared fish typically had behaviours that could reduce their ability to survive in the wild but research and training had overcome this.

"The main problem for pond-reared fingerlings has been their inability to recognise and respond appropriately to predators, making them more likely to be eaten," Dr Hutchison said.

"Our world-first research has released trained fingerlings into the wild en masse for the first time and found that by training hatchery reared fish before release, their survival rate can double.

"Fingerlings were trained in special tanks which exposed them to a predatory fish behind a screen. The fingerlings could pass through the screen but the predator could not.

"Three times a day skin extracts were added to the tank on the predator side. Skin extract contains chemical signals (pheromones) that warn fingerlings of danger. The fingerlings associate the warning signals with the odour of the predators, thereby recognising them as a threat."

Both silver perch and Murray cod positively changed their behaviour within three days, while eel-tailed catfish adjusted their behaviour in just two days.

"Specially-marked fish, both trained and untrained were released into the wild up to 2 kilometres apart at three sites. They were then recaptured after 24 hours and then every few months, with twice as many trained Murray cod captured as untrained cod."

Silver perch, a known schooling fish, were recaptured in equal numbers of trained and untrained stock and were found together in mixed schools.

"We expect that due to the social behaviour of silver perch the trained fish taught the untrained fish," Dr Hutchison said.

"In laboratory testing the trained fish avoided predators, while the untrained would swim right up to predators."

Research also found that releasing fingerlings at several locations increases survival as the risk associated with high predator numbers at the time of release is spread.

This joint programme with the Murray-Darling Basin Authoritys Native Fish Strategy will improve post-stocking survival rates for certain endangered fish species and also benefit recreational fishing stocking programmes.

"While the results are positive for conserving endangered freshwater species they also have exciting possibilities for recreational fishing stocking programmes as more fish can survive for recreational catching," said Dr Hutchison.

Agri-Science Queensland is now working with fish hatcheries and stocking groups to encourage uptake of the training and boost the results of stocking across Queensland.

the Fish Site Editor

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