Fish on the earth appeared in the early Ordovician 430 million years ago, and now there are 2 1723 species of fish, accounting for 52.6% of vertebrates. There are mainly two outlines of fish: cartilaginous and bony, and there are also ancient groups of roundworms. According to the latest research data, among modern fishes, there are 50 species of rotifer, and 4 species live in China. There are 5 15 species of cartilage, and there are about 140 species living in China. There are19135-20908 kinds of hard bones, and there are 2700 kinds of left and right hands living in our country. Among the 2 1723 species of fish, there are 84 1 1 species of freshwater fish, accounting for 40. 1 1%, and the other 133 12 species are marine fish and very few migratory fish. A large number of fish live on the earth, providing a rich food source for human beings.

_ _ I tried my best.