Swim for it

Hatchery fish need training to avoid predators

source: James Randerson
New Scientist October 6 2001 p11

Hatchery fish need training to avoid predators. They are often bred to restock rivers and seas, especially in Japan, Norway and the US. Under 5% of salmon released from hatcheries are believed to survive to be adults. University of Edinburgh’s Culum Brown and Cambridge University’s Kevin Laland have studied fish behaviour, and they see training in shoals as a way for fish to survive. Fish tend to learn from each other in shoals, for example, by observing escape reactions. Demonstrator fish could teach naïve shoals by reacting to predators behind screens. University of Helsinki’s Sampsa Vilhunen has taught Arctic charr to avoid predators. The predators were fed on charr, and then put in another tank. Naïve charr put into the water where charr had been eaten learnt that the predator should be avoided.

Hatchery fish tend to be fed until they are quite large in a bid to protect them from predators, since the smaller predators are unable to eat larger fish. Training the fish would save on food and allow for an earlier release of fish from hatcheries. This research was reported in more detail in Journal of Fish Biology vol 59 p471.