Overwintering of fish - an adaptation that ensures fish survival in unfavorable winter conditions (freezing of water bodies, lack of food, low water temperature, lack of oxygen). It is characterized by a decrease in the level of vital activity and metabolism (torpor) or even the absence of visible manifestations of vital processes (anabiosis).

Winter is the time when the increase of aquatic vegetation and plankton stops. Fish, whose food base becomes scarce, reduce their vital activity, gather in flocks, and look for suitable places for wintering. Individuals of the same age and size gather in wintering pits. In this way it is easier for them to endure the frost, tightly clustered in flocks. To resist the cold, to minimize energy expenditure fish help mucus, abundantly secreted on the surface of the scales.