Schools for schools of hatchery fish

Brief by Central Staff

Wildlife – January 2002 – Colorado Central Magazine

Humans often buy or rent videos to learn new skills like yoga or computer assembly, but in the United Kingdom, the training video is becoming a matter of life and death for hatchery trout.

There, studies show that most hatchery fish die within two days after their release. To improve their life-expectancy, scientists are making educational videos.

Hatchery fish are reared in a protected environment with a regular supply of food. But they stand little chance of survival when, at the age of about six months, they are released into rivers to replenish diminished stocks or provide sport for anglers. Most of them die within the first two days, and fewer than 5% make it to adulthood, according to studies of reared salmon. But now scientists are devising training videos for hatchery fish that show fish of their species being devoured by a predator.

Teaching techniques also include group training for fish. One tactic is to put a savvy demonstrator fish in a naive school and place a predator behind a transparent, porous screen. The inexperienced fish learn from the reactions of the demonstrator fish that they should flee, and the sight and smell of the predator reinforces that reaction.

University of Helsinki researcher Sampsa Vilhunen has devised a tactic with even more shock factor. He fed predator fish in a tank of Arctic char, and then removed them. Hatchery-raised Arctic char were then placed in the water, and the mere odor was enough to teach them to avoid the predator fish in the future.

(From the monthly Western Water Round-up assembled by Steve Glazer of Crested Butte. The full report is available on our website,, along with information on how to subscribe to the report.)