There are many types of fish, which are the oldest vertebrates. There are about 32,100 named fish species, which are distributed in various waters on the earth. Among them, there are about 2,500 species in my country, and the vast majority live in seawater. There are more than 1,500 species of seawater fish. There are about 800 species of freshwater fish. In the past, fish were usually divided into two categories: cartilaginous fish and bony fish based on the similarities and differences in the