Fish is a kind of aquatic vertebrate with variable temperature, its body surface is covered with bone scales, it breathes through gills, uses fins as moving organs and feeds on upper and lower jaws. It belongs to the vertebrate subfamily of Chordata. Vertebrates are generally divided into fish (53%), birds (18%), reptiles (12%), mammals (9%) and amphibians. According to the statistics of the late Canadian scholar Nelson1994, there are 246 18 species of fish * * in the world, accounting for more than half of the named vertebrates, and new fish species are constantly being discovered, with an average of about 150 species per year, which should increase by more than 1500 species in more than ten years.