The sea fish is different from the freshwater fish, which is known to all. Sea fish live in the generation after generation in a vast expanse of water, while freshwater fish is a lifetime living in freshwater lakes in the river. Therefore, in the thousands of years of biological evolution, development and reproduction, from generation to generation, the two major fishes have been differentiated: sea fish and freshwater fish.
Generally speaking, the salinity of the earth's Sea water is 16 - 47 (generally 35), while the salt concentration of fresh water is only 0.01-0.5. So different environments make two species of fish differ one hundred and eight thousand miles. Sea fish can not leave saltwater water in fresh water, fresh water fish can not leave fresh water and live in the sea.
This difference is ultimately due to the different salt content of seawater and fresh water, while that of fish is very adaptive to the salinity of water environment. The adjustment of fish's adaptability to various water environment is limited to a certain salinity range.
The salt content of the sea fish is lower than that of the sea water, and the density and density of the sea water is higher than that of the fish because of the large amount of salt in the sea water. In this way, the water in the fish body of the sea fish is constantly exuding out from the gills and body surface to keep the water balance, and the sea fish have to suck up a large amount of seawater. But in this way, the salt in the sea fish is greatly increased, forming a cycle. Besides removing some salt from the kidneys, marine fish mainly rely on "chloride cells" in the gill tissue to complete the task of salt removal. Some cartilaginous fishes, such as sharks, store the metabolized nitrides in urea form in the blood.
Fresh water fish is different. Freshwater fish contain more salt than fresh water, that is to say, the concentration of fresh water is low and the density is small. According to the osmotic pressure principle, fresh water will continuously enter large quantities of fish.
In accordance with the adaptability of fish to salt tolerance, fish can be divided into two types, which are wide salt and narrow salt style. The widely salting fish can tolerate the change of salinity, which can be transported both in water and in sea water. The narrow salt fish can not change the salinity of the fish slightly, and the mutation of the salinity is often the important cause of the death of the narrow salt fish.
It will help us play fishing game if we know about it about sea fish and fresh fish