1, the color of fish is dark and light, which is the protective color of fish. The body is streamlined, big in the middle and small at both ends. The body surface is covered with scales to protect the body; There is a layer of mucus on the surface of scales, which reduces the resistance of water when swimming. There is a lateral line on each side of the body, which is connected with the nerve, and is mainly used to judge the direction and sense the current.
2. Fish's body has pectoral fin, dorsal fin, ventral fin and caudal fin, which are the moving organs of fish in water. Dorsal fin and gluteal fin mainly play the role of stability and balance in action. The caudal fin cooperates with the muscles on the side of the body to push the fish and master the direction. The main functions of pectoral fin and ventral fin are to keep the balance of fish, cooperate with fish turning over and adjust the ups and downs of fish.
But pectoral fin is more versatile than ventral fin, and it can paddle like a paddle to make the fish move slowly. Fish belong to lower vertebrates, because they can't live without water all their lives. They breathe through their gills. Heart-atrium-ventricle, a circulation route, arterial blood and venous blood are mixed, especially the reproduction of fish is naturally hatched by in vitro fertilization, and the body temperature is not constant.
3. There is a squid in the body, whose main function is to adjust the proportion of the body. With the cooperation of fins, the fish can stay in different water layers.
Fish introduction
Fish is the oldest vertebrate. Some hybrid offspring with different chromosome numbers still have fertility. They inhabit almost all aquatic environments on earth, from freshwater lakes and rivers to saltwater oceans. Most fish are warm vertebrates, living in water all the year round, breathing through gills and using fins to help balance and exercise.
The above reference content: Baidu Encyclopedia-Fish