The blood and body fluids of fish are mainly composed of salt and protein. When living in fresh water, the concentration of water is much lower than that of fish body fluids, and the osmotic pressure is higher than that of water. The characteristic of water is that it flows from the place with low osmotic pressure to the place with high osmotic pressure, so the water around the fish will desperately penetrate into the fish.
Therefore, the freshwater fish you see is not drinking water, but needs to continuously excrete excess water in the body in the form of urine through the kidneys with developed renal corpuscles to ensure the osmotic pressure balance in the body.
Extended data:
Freshwater fish:
1, grass carp: it is the most eaten fish, and the most commonly eaten freshwater fish is grass carp, which belongs to herbivorous fish.
2. Herring: It is slightly similar to grass carp, but the color is darker than grass carp, and the appearance is basically the same as grass carp, so it is a carnivorous fish.
3, bighead carp: commonly known as bighead carp, characterized by a big head and a small body, the fish head soup that is often eaten is made of this fish.
4, silver carp: characterized by small scales, shaped like carp but white, also known as silver carp.
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