Is fish an animal?

According to Baidu Encyclopedia, fish is the oldest vertebrate. It is easy to accumulate heavy metals. 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.

There are more than 0/000 species of freshwater fish/kloc-in China, and the famous "four big fish" (herring, grass carp, silver carp and bighead carp), carp and crucian carp are the main excellent freshwater fish species in China. There are about 2,000 known marine fishes in China, including hairtail, large yellow croaker and giant grouper, as well as migratory fishes such as Chinese sturgeon, salmon and Atlantic salmon.