Hatchery fish get survival training

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Hatchery fish get survival training
 
12:20   04  October  01

James Randerson, New Scientist (UK)
 
Fish raised in hatcheries need to go on training courses to help them cope with life in the wild. This tactic could make a big difference to the survival rates for the fish, which often succumb to predators they do not recognise.

Many countries - in particular the US, Norway and Japan - breed fish and release them into the rivers and oceans to boost stocks for anglers and trawlers, or help re-establish endangered species. But there is a problem: many of the fish don't make it.

Studies suggest that around five billion hatchery-reared salmon are released worldwide each year, but less than five per cent survive to adulthood. Hatchery fish do worse than wild fish because they have not learned the tricks of the trade, such as recognising the predators that will eat them. "Hatchery-reared fish are much more vulnerable than wild fish," says Culum Brown of the University of Edinburgh.

To explore possible solutions, Brown and Kevin Laland of Cambridge University have gathered reports on fish behaviour. They say the key to improving survival is for fish to copy their shoal mates. "Training gives them at least some hope when they get out there," says Brown.


Escape reaction


Fish are great candidates for group training because many species learn from watching the reactions of shoal mates, Brown says. He points out that rainbow trout, for example, can learn the identity of a predator simply by watching another fish's escape reaction.

One tactic for training, he suggests, would be to put clued-up demonstrator fish into a naive shoal and place a predator behind a transparent and porous screen. The inexperienced fish would see the escape responses of their tutors and should learn to associate the sight and smell of the predator with danger. A more drastic way would be to show a "video nasty" of the predator devouring sacrificial fish.

Brown also highlights a more benign alternative suggested by Sampsa Vilhunen of the University of Helsinki, Finland. He fed predator fish on Arctic charr before moving them to a new tank. Simply bathing naive Arctic charr in this water was enough for them to learn to avoid the predator.


Smell of fear


The results suggest that the naive fish associate the smell of faeces derived from eaten Arctic charr with danger, Vilhunen says: "They seem to have an innate ability to avoid these odours."

Markko Pursinen of Saimaa Fisheries Research and Aquaculture, Finland, which sponsors research in this area, says that until now, the main tactic for improving survival has been to feed up hatchery fish. This at least stops the smaller predators trying to eat them, he says.

Pursinen believes that sending the fish on training courses instead could save money because they could leave the hatchery leaner and earlier. "Maybe we don't want to give them the easy living for too long," he says.

Journal reference: Journal of Fish Biology (vol 59, p 471)

 
12:20   04  October  01
 

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