Why are fish in the sea? Why do fish live in the water

Because the fish know that the sea can't live without it.

Fish have the characteristics of being suitable for living in water: the color of the body of the fish is the protective color of the fish. The body is streamlined, large in the middle and small at the end.

The surface of the body is covered with scales, which protect the body; There is a layer of mucus on the surface of the scales, which reduces the resistance of the water when swimming. There is a lateral line on both sides of the body, which is connected to the nerve, which is mainly used to determine the direction and sense the flow of water. The body of a fish has pectoral fins, dorsal fins, pelvic fins, and caudal fins, which are the locomotor organs of the fish in the water.

Fish breathe with gills. There is a swim bladder in the body, the main role is to regulate the specific gravity of the body, the swim bladder in the coordination of the fins, can make the fish stay in different water layers. Fish belong to the lower animals of vertebrates because they cannot live without water all their lives, breathe with gills, heart-atrium-ventricles, a circulatory route, and arterial and venous blood are mixed; In particular, the reproduction of fish is naturally hatched by in vitro fertilization, and the body temperature is not constant.

The role of the fin: The dorsal and anal fins mainly play a stabilizing and balancing role when moving. The tail fin works with the muscles on the side of the body to propel the fish and control the direction.

The main function of pectoral and pelvic fins is to maintain the balance of the fish, cooperate with the body of the fish, and adjust the lifting of the fish. However, pectoral fins are more versatile than pelvic fins, and they can be used like oars to move the fish forward slowly. Because the gills of a fish are only adapted to absorb oxygen from the water and cannot absorb oxygen from the air, it can only live in the water.

Summary. Hello, I'm glad to answer for you, this is mainly determined by the fish's own respiratory organs and breathing patterns.

Why do fish live in the water

Hello, I'm glad to answer for you, this is mainly determined by the fish's own respiratory organs and breathing patterns.

Since the respiratory organs of fish are gills, and water is denser than air, it is only in water that the gill plates, gill filaments, and gill patches of the fish can be fully opened. By increasing the contact area between the gills and the water, the chance of taking up dissolved oxygen in the water increases the chance of obtaining more oxygen. Once out of the water, the water on the surface of the gill plates is quickly evaporated, and the fish lose the ability to take in oxygen and cannot survive.

So, the fish have to live in the water.

As the saying goes: fish can't live without water. It is a natural law that fish live in the water, and it is common sense that people know, so why do fish live in the water and cannot do without it?

This is mainly determined by the respirator tubes and breathing patterns of the fish itself. One of the basic conditions for the survival of living organisms is the need for oxygen, and fish live in water and need to breathe. However, the respiratory organ of the fish is not the nose, its nostrils do not communicate with the mouth, it is a simple olfactory organ, and the gills are the main respiratory organs of the fish, which determines the difference between the breath of the fish and other land animals.

The water where the fish live is oxygen-dissolved, but the dissolved oxygen is very low, and the structure of the gills is adapted to this living condition. First, let's take a look at the structure of the gills. Now take the bony fish as an example, there are four gills on each side of the throat inside the gill cap, each gill is divided into two rows of gill pieces, each row of gill pieces is arranged by countless gill filaments, and each row of gill filaments has many gill patches on both sides, and there are many capillaries inside.

Second, let's look at the gills in the water. In the water, the gill plates, gill filaments and gill patches are fully opened, which greatly expands the contact area with the water, increases the oxygen uptake capacity of the capillaries from the water, and the fish swallows and drains water from time to time by the movement of the mouth and gill cover, and completes the gas exchange when the water flows through the gills. Therefore, the breathing movement of the fish is divided into two processes, water absorption and drainage.

When absorbing water, the operculum expands outward, the mouth and oral flap open, the operculum flap is tightly closed, and water flows from the mouth into the throat, then the operculum flap opens, the mouth and oral flap are tightly closed, the operculum moves inward, the pressure in the oral cavity increases, and the inhaled water flows through the gill fissure and is discharged from the gill hole. At this time, the carbon dioxide carried by the blood in the small blood vessels of the gills enters the water through the thin wall, and the oxygen in the water enters the small blood vessels of the gill and combines with the red blood cells in the blood, and reaches the tissue cells throughout the body with blood circulation. Again, the density of water is much greater than that of air, it can support the gill sheets, gill filaments and gill patches of the fish completely, complete the gas exchange, once the fish leaves the water, in the air, the gill filaments and gill filaments and gill flakes will be pressed together, only the appearance of the gills and the air contact, the area is greatly reduced, and sufficient oxygen can not be obtained.

In addition, the oxygen absorbed by the fish is oxygen dissolved in the water, and when the surface of the gill plates evaporates, the fish completely lose their oxygen uptake function and cannot survive. Therefore, the fish cannot live without the water, but must live in the water, which is determined by its own structure. Of course, different fish live for different times after leaving the water, mainly because the difference in the size of the gill aperture has an effect on the rate of water evaporation on the gill piece.

The slower the evaporation, the longer it will survive; On the contrary, the survival time is shorter. At the same time, it is also related to the fact that fish have other auxiliary respiratory organs, and those with auxiliary organs can survive longer after leaving the water.

Marine fish live in the vast ocean all their lives, while freshwater fish live in the freshwater of rivers, rivers, lakes and streams throughout their lives. During the tens of millions of years of evolution, fish have lived and multiplied, passed down from generation to generation, creating two major systems that live in different waters. Generally speaking, the salt concentration of seawater on Earth is much greater than that of freshwater.

Fish have great adaptability to the salinity of the water environment, and all kinds of fish can live normally in waters with different salinity, which is related to its perfect physiological regulation mechanism, but the regulatory effect is limited to a certain salinity range, otherwise its survival will be affected.

The salt concentration of marine fish body tissue is much lower than that of external seawater, and the specific gravity is high and dense due to the large amount of salt in seawater. According to the principle of osmotic pressure, the water force in the body tissues of marine fish continuously seeps out from the gills and body surface. In order to maintain water balance in the body, marine fish have to swallow large amounts of seawater to compensate for the water loss in their bodies.

However, due to the large gulp of seawater, the amount of salt entering the fish has also increased greatly, so that in addition to removing some salt from the kidneys, marine fish mainly rely on chlorine cells in the gill tissue to complete the task of salt excretion.

1. There are all kinds of fish in the sea, some are dolphins, some are carp, and some are sharks.

2. There are all kinds of fish in the sea, some are large yellow croaker, some are sturgeon, and some are crucian carp.

3. There are all kinds of fish in the sea, some are clownfish, some are shooting fish, and some are green pufferfish.

4. There are all kinds of fish in the sea, some are strawberry fish, some are red apple beauties, and some are clownfish.

5. There are all kinds of fish in the sea, some are white hidden parrots, some are black panther clownfish, and some are horned butterflies.