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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 don鈥檛 recognise.

Many countries鈥攊n particular the US, Norway and Japan鈥攂reed fish
and release them into the rivers and oceans to boost stocks for anglers and
trawlers, or help re-establish endangered species. But there鈥檚 a problem: many
of the fish don鈥檛 make it.

Studies suggest that around 5 billion hatchery-reared salmon are released
worldwide each year, but less than 5 per cent survive to adulthood. Hatchery
fish do worse than wild fish because they haven鈥檛 learned the tricks of the
trade, such as recognising the predators that will eat them. 鈥淗atchery-reared
fish are much more vulnerable than wild fish,鈥� 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. 鈥淭raining gives them at least some hope
when they get out there,鈥� says Brown.

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鈥檚 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 鈥渧ideo nasty鈥� 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.

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

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. 鈥淢aybe we
don鈥檛 want to give them the easy living for too long,鈥� he says.