Fish feel the cold

Trout do not hibernate

Trout do not hibernate

The days are getting cooler and the first snow has even fallen. The water temperature in the Thur is currently around eight degrees Celsius, and the trend is falling. How do the brown trout stand it? Do you bed yourself softly in the river bed and do you hibernate?

The days are getting cooler and the first snow has even fallen. The water temperature in the Thur is currently around eight degrees Celsius, and the trend is falling. How do the brown trout stand it? Do you bed yourself softly in the river bed and hibernate?

“No,” laughs the cantonal fisheries supervisor Christoph Birrer. “Unlike mammals or us humans, the brown trout adapts its body temperature to the water”. The colder it gets, the less food she eats and the more economically she uses her energy.

The fish usually stands still in the water, its head turned against the current, and hardly moves visibly.

I stay where I am

Whenever possible, the brown trout retreat to a deep water hole. But because they are not schooling fish, the best spots are soon occupied by the stronger animals and the smaller ones have to look elsewhere, says Christoph Birrer.

Places behind stones are popular with the younger fish. The place that the fish occupies in late autumn, it hardly leaves without disturbance until spring. Trout are not bothered by the fact that the river carries less water in winter. «Colder water contains more oxygen. That's why the fish don't feel uncomfortable even when the water level is low, ”explains Christoph Birrer. And because the water in a river never freezes completely, the brown trout have no problems.

Do not disturb!

The situation is different with stagnant waters. “The lake trout can also overwinter well in Lake Constance,” explains the cantonal fisheries supervisor Fredi Fehr. Even when the surface of the lake is covered by a layer of ice. It gets trickier with small ponds, because a gas exchange is necessary so that oxygen for the fish can get under the ice layer and digestion gases can escape.

“This is the case, for example, where reeds or deadwood protrude from the ice,” explains Christoph Birrer.

Similar to wild animals that need to rest in winter, fish are also very sensitive to disturbances. One such option is ice skating on a frozen pond. "The fish begin to move too much, which can be fatal," says Fredi Fehr. The energy requirement increases, but the fish finds less food in winter than in summer. (sas)