Features of the structure of systems of internal organs of the body of fish and their functional significance.

Fish are the most primitive vertebrates. They are cold blooded. The cardiovascular system of fish consists of only one circle of blood circulation. Their heart is two-chambered. The gills are responsible for obtaining oxygen. Also, fish have a digestive system, which is responsible for the digestion of organic particles and the elimination of unprocessed substances. Also, fish have an excretory system. It consists of the kidneys. The kidneys of fish are elongated. They release ammonia into the water. It does not harm fish, as its concentration in the water is low.