There are about 20,000 species of fish*** in the world. Among them, there are about 73 species of round-mouthed fishes, about 800 species of cartilaginous fishes, and about 20,000 or so species of scleractinian fishes. China's fish species of about 3,000 species. Among them, there are about 2,100 species of marine fishes and about 1,010 species of freshwater fishes.

Categorized according to animal appearance

1, fusiform, carp, carp, shark, also known as the basic type, is the general body shape of fish, suitable for swimming in the water, the whole body is fusiform and slightly flat. In the three body axis, the head and tail axis is the longest, dorsal and abdominal axis, followed by the shortest axis, so that the whole body is streamlined or slightly flattened, in order to facilitate the movement in the water when moving forward to reduce the resistance, so this kind of fish is good at swimming.

2, lateral flat type, pomfret, butterfly fish, bream, coelacanth, swallowfish, this kind of fish in the three body axis, the left and right axis is the shortest, the proportion of the head and tail axis and dorsal and abdominal axis is not too much difference, the formation of symmetrical left and right sides of the flattened shape, so that the whole body type is obvious and flattened wide, so the ability to swim worse than spindle-type, live in the water in the middle and lower layers.

3, stick type, eel, eel, sea eel, this kind of fish head and tail axis is particularly long, while the left and right axis and the abdominal axis is almost equal, are very short, so that the whole body shape is stick-shaped. Its swimming ability is stronger than the lateral and flat type. It is suitable for burrowing in underwater mud and living in underwater gravel.

4, flat type, this kind of fish in the three body axis, the left and right axis is particularly long, the dorsal and abdominal axis is very short, so that the body shape is up and down flat, slow action, not as flexible as the first two types, more benthic life. For example, stingrays, rays, anglerfish and catfish.

5, special body type, such as sea dragon, cartwheel fish, river jack, flounder, boxfish, etc..

Baidu Encyclopedia - Fish