Winter is approaching, migratory birds flew to the warm south for the winter, hedgehogs burrowed into warm caves, and humans put on thick winter clothes to keep out the cold. Where did the fish in the rivers and lakes go? How do they spend their winter?
Fish do not hibernate
Fish are temperature-changing animals, and their body temperature will increase or decrease as the outside temperature changes. Unlike mammals, amphibians and reptiles, which are completely paralyzed in winter, fish do not hibernate in the true sense. They just reduce or even stop eating, and their breathing becomes weak; they hide in the cracks of water plants or rocks. , And some will snuggle together in groups and spend the harsh winter loving each other.
Feel comfortable in the right water temperature
Someone will definitely ask, if the water freezes in winter, will the fish freeze to death?
In many people’s minds, as long as the water is clear enough and the water quality is good enough, fish can survive. In fact, the water temperature has a great influence on the fish.
Currently, there are approximately 24,000 species of fish in the world. Under the dual effects of natural selection and survival of the fittest, fishes distributed in various waters around the world have formed various types that can survive under different water temperature environmental conditions. Therefore, water temperature is the most closely related to fish’s circulatory system and respiratory system, and then an important factor affecting fish survival.
Generally speaking, within a certain range, a higher temperature will make the fish grow faster, and a lower temperature will grow slower. This is because fish have less secretion of neurohormones and low digestive enzyme activity at low temperatures. However, it is more difficult for fish to tolerate high temperature than low temperature, because the biologically active substances in the fish, such as proteins and enzymes, will be denatured and inactivated under high temperature. Most fishes are very vulnerable to water temperature. The sharp rise and fall of water temperature can cause fish to die because they cannot adapt immediately.
The suitable water temperature for ordinary fish is generally 12℃～30℃, beyond this temperature range, their survival will be affected. However, you don’t need to worry that fish living in nature will freeze to death due to low water temperature in winter, because different fish have completely different temperature tolerance ranges. Since the fish have lived in their respective waters for hundreds of millions of years, naturally HOLD can withstand the changes in water temperature.
People divide fish into three types according to their adaptation to water temperature:
Cold water fish
Refers to fish that can withstand the low temperature of -20°C but cannot withstand the high temperature of 20°C
Warm water fish
Refers to fish that live in water temperatures of 20°C to 40°C. Tilapia, sardines, small yellow croaker, etc. are very common warm-water fishes. The colorful tropical fish we saw in the flower and bird fish market are also warm water fish.
Warm water fish
Compared with cold-water fish and warm-water fish, warm-water fish live easily at 10℃～30℃.
In addition, different fish have different tolerance to temperature.
Wide temperature fish are very adaptable to changes in temperature, such as carp, can withstand high temperatures of 30 ℃, swimming in ice water will not kill it, most warm water fish are wide temperature fish Both cold-water fish and warm-water fish belong to the narrow temperature fish. They all live in waters with relatively small water temperature changes. Once the temperature changes suddenly, their lives will be endangered.
However, as long as the temperature does not exceed their tolerance, fish can continue to enjoy their winter freely without any discomfort.
Why doesn’t the fish freeze under low temperature?
A friend asked, will the fish freeze below 0°C? Especially the fish that live in the polar regions, will they not be frozen?
In fact, fish living in low-temperature waters naturally have a unique skill to fight the severe cold. There is a substance in their blood called “antifreeze glycoprotein”. The more the fish in the high-cold area, the higher the content of “antifreeze glycoprotein” in their body. high.
Unlike automobile antifreezes that lower the freezing point of water, “antifreeze glycoproteins” work through physical means. “Antifreeze glycoprotein” flows in the body and connects with ice crystals, thereby preventing ice crystals from connecting to each other and forming larger crystals. In this way, the cells in the fish body will not form ice crystals and cause the cell membrane and cell tissue to rupture, and naturally they will not freeze.
At the same time, scientists also found in their research that the genomes of polar fishes continue to evolve during the long-term adaptation to the environment, and they will lose the function of some genes, such as the hemoglobin gene that transports oxygen to the mitochondria, which leads to the hemoglobin content in these fishes. Much lower than warm water and warm water fish.
You can find that the bodies of many polar fishes are translucent, and there is hardly any “red blood” after anatomy. The reason is that this evolutionary method can reduce the energy consumption of cold-water fish blood flow and better maintain body temperature.
But you don’t have to worry about these fishes being unable to breathe, because they have lost some genes while amplifying other genes to ensure the efficiency of oxygen transportation and utilization at low temperatures.
Scientists very much hope that in the future, the cold-tolerance mechanism and functional genes of polar fish can be applied to the fields of food freezing and medical cold storage of cells and organs for the benefit of mankind.
In winter, the fishes are not to sit back and relax
Seeing this, you may envy the carefree life of fish in winter. In fact, fish also take great risks in winter.
After the ponds and lakes in the northern alpine region are frozen, most of the dissolved oxygen in the water depends on the photosynthesis of phytoplankton in the water, and photosynthesis requires sunlight.
When the gate is closed by heavy snow and thick snow covers the ice surface, the transparency of the ice layer will be reduced, photosynthesis will be correspondingly weakened, and fish excrement, fish and insect carcasses in the water body will be abundant. With oxygen consumption, fish are likely to die due to lack of oxygen.
At the same time, the feeding activity of fish in winter will be greatly reduced, and in many cases they can only rely on the consumption of accumulated physical energy to maintain their lives. Waiting for the end of the freezing period, fish with weak physical fitness is likely to die due to physical exhaustion.