Among the fish in the Southern Ocean, Antarctic fish is the dominant species, accounting for 75% of the offshore fish. There are nearly 20 species of Antarctic Tengyu, Rays, Cod, Cod and Iced Fish with potential economic value.
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In sharp contrast to other oceans, Antarctic fish like to live in deep water, and there are almost no dense surface fish.
Antarctic fish are relatively small, most species are less than 25 cm in length, and few are more than 50 cm in length. Only toothfish of Haddock family can reach 1.8 m in length and weigh 70 kg. Most fish grow slowly, generally increasing their body length by 2 ~ 3 cm every year. Only the big-toothed cod can grow about 7 cm a year, and it can grow to 50 cm after 7 years. The spawning season of Antarctic fish is in late autumn and early winter in the southern hemisphere. Eggs are large, generally 2 ~ 4 mm in diameter and 8 mm in maximum. They are round, full of yolk and rich in nutrition. In spring, fish eggs hatch into small fish. At this time, the phytoplankton in the Southern Ocean is in the season of mass reproduction, which provides a direct or indirect source of nutrition for the growth of young fish. Most fish feed on marine zooplankton, and some also eat some phytoplankton.
The blood of most Antarctic fish is not red, but gray, because there is no hemoglobin.
Antarctic fish are marine warm-blooded animals, which are quite different from warm-blooded animals. The body temperature of warm-blooded animals is constant and generally does not change due to the change of external environment temperature; The body temperature of Antarctic fish will change with the change of environmental temperature, which is consistent with the temperature of seawater, and there is no constant body temperature. The heat in Antarctic fish is rapidly lost through breathing and body surface. When the temperature of seawater drops to freezing point, its body fluid temperature is also close to freezing point. However, because the blood of Antarctic fish contains antifreeze protein, although its body temperature is reduced, its body fluids are not frozen, so it can live normally at a temperature below the freezing point of seawater.
Antarctic fish usually like to eat foods with high fat content and store a lot of fat in their bodies to gain more energy to maintain their normal exercise, growth and reproduction. This is the reason, this is the result of their adaptation to the environment. In addition, the fat in Antarctic fish can also increase buoyancy. Because there is no swim bladder for Antarctic fish, in order to maintain their position and float in seawater, they must overcome the negative buoyancy, that is, sinking force, caused by carbohydrates, protein and bones with a specific gravity greater than that of seawater. However, the specific gravity of fatty compounds is less than that of seawater, which can act as or replace the swim bladder, make up for the shortage of swim bladder, and make Antarctic fish free to move and float.
Although Antarctic fish has the ability to adapt to low temperature, its adaptive temperature range is very small, generally between 7℃ and -2℃, and it belongs to a narrow-temperature species among temperature-changing animals. This is because it has lived in a low temperature environment in Antarctica for a long time, and its metabolic pathway has changed. Some fish have even changed their genetic material. If Antarctic fish is put in warm water, its metabolic capacity is not obviously improved, and the oxygen consumption in Antarctic environment is similar to that in warm water. If the temperature continues to rise, it will be unbearable. When the seawater temperature rises above 7℃, the cell membrane of the central nervous system of Antarctic fish will change, and the lipid compounds in it will become liquid, which will lead to the rupture of the cell membrane, the disorder of intracellular ion concentration, and even the outflow of intracellular substances, which will eventually lead to death. However, temperate fish will not change in such a narrow temperature range.