How do fish spend the winter?

Posted on Jan 12, 2021      98

With the onset of winter, big changes occur in water bodies, which affect the behavior of underwater inhabitants. The water temperature decreases. The light period of the day gradually decreases. Then bodies of water are covered with ice, and snow covers them from above - the light intensity drops even more. For 4 long months underwater dwellers exist in conditions of cold, oxygen deficiency and half-darkness. During hibernation, the fish have slashed activity, almost complete cessation of food consumption, growth retardation, reduced heart rate, slower response to stimuli, the rate of metabolism in the body slows down and is maintained at the expense of accumulated summer fat reserves.

Wintering pits.

Different fish species survive this difficult period in different ways. Many thermophilic fish species such as bream, carp and tench already gather in vast flocks in October and November and head for the wintering pits. Here they spend about 3 months almost without movement, like herrings in a barrel! Those fish that are at the very bottom even get bedsores on their belly.

Here, fish of the same species and age winter together and in large clusters. If the pit is small, then absolutely identical individuals settle in it! Ichthyologists explain this mystery of nature because the massive accumulation of fish of the same species and age ensures optimal conditions for hibernation, because the metabolic processes in the fish's body are less intense than they would be if the fish wintered alone. In addition, this is a more rational use of mucus, which fish excrete as an insulating agent.

Catfishes are placed higher near the wintering pits - at the exits from the depths, on the borders of the pits and elevations of the bottom. This is because in the pit itself, even a month after the formation of the ice cover of oxygen regime is transforming in a worse direction, which the catfish do not tolerate.

How predatory fish spend the winter

Predatory fish in wintering pits do not hide. But the inhabitants of these pits do not touch, even though they could thus ensure a well-fed existence for the whole winter. Mostly, pike, perch and pike-perch go after those fish that do not mind the ice over their heads and do not leave their usual habitats for the winter - perch, roach, bleak, roach and ruff.

When the ice cover appears, the behavior of predatory fish changes. Predatory fish are divided according to their relation to light, thus, perch is a crepuscular-day predator, pike is a crepuscular predator and pikeperch is a deep-dark predator.

At the beginning of winter, there is a semi-darkness under the ice, which “plays into the hands” of crepuscular predators. And then in the first days of the establishment of the ice cover, they organize their victims’ bloody carnage. This bout of predator is called “the first ice”.

But for the burbot, winter is a favorable time of year. Warm summer water depresses it. At temperatures above 15-16 ° C burbot stops feeding and hibernates, hiding in coastal burrows, under large rocks or snags, and at 27 ° C dies. Only in the fall, when the water in the rivers noticeably cools, it awakens and begins to intensively fatten up. Burbot prefer to hunt at night. Young burbots feed on zooplankton, while yearlings switch to a “fish diet”. When cracking frosts come and rivers are covered with a thick layer of ice (in November and December in the north, or December and February in the temperate zone), burbot become even more active and begin reproduction, hatching their eggs on the rocky seabed.

Fish migration

Some fish from temperate and arctic latitudes do not want to change their habitual way of life in winter. They prefer to move to warmer waters. Khamsa, which lives in the Sea of Azov, feeds intensively in summer, accumulating fat. As the water gets colder, they migrate through the Kerch Strait into the Black Sea, where they spend the winter sinking to a depth of 100-150 meter. It is during the wintering migration of the Azov khamsa that fishing for this fish begins. Caspian herring migrate to the south in winter, where the water is warmer.

“Frozen fish”.

What if the reservoir is shallow, non-flowing and freezing through in winter? There are such lakes in the Arctic. Their inhabitants, the common crucian carp and the black dallia fish, burrow into the silt with the onset of winter. When such ponds freeze to the bottom, the fish often find themselves frozen in the ice. But their endurance to low temperatures is amazing. Even when trapped in ice, fish do not die - unless their gills and body fluids freeze over. In spring, when bodies of water thaw, the dahlia revive, and in the short polar summer, they have time to fatten up and leave their offspring.

It happens, too.

In equatorial bodies of water, where there is never winter, fish can be active all year round. But some of them also have problems during the winter months. Only they are not, of course, associated with cold weather, but, on the contrary, with unbearable heat and drought. Some tropical fish burrow into the mud and fall asleep. This helps them endure the heat, and the associated lack of oxygen.

If crucian carp and billfish are the most frost-resistant freshwater fish, then the little carp fish Cyprinodon macularius (Cyprinodon macularius), which lives in the south of North America, is the record holder for withstanding the highest water temperature. It lives and manages not to boil in hot springs in California, where the water temperature is 52°C! For reference, it is impossible to hold a hand for any length of time in water of that temperature.