Sharks are chondrichthyans, belonging to the vertebrate phylum Chondrichthyes Platyhelminthes subclass, is a group of fast-swimming medium to large marine fish. The main features of sharks are: gill slits on both sides of the head, long fusiform body, hard skin, dark gray in color, sharp teeth, sharp muzzle, protruding forward, generally use gills to breathe, and use fins to swim in the water. Sharks need to swim constantly to avoid sinking to the bottom because they have no swim bladder.

The species of sharks include six-gill sharks, porbeagle sharks, tiger sharks, mako sharks, horn sharks, saw sharks, flat sharks, whisker sharks, and so on.

1, six-gill shark order: widely distributed in the Pacific Ocean and Atlantic tropical and subtropical waters, the structure of the original, gill holes have 6-7, the eye without transient membrane or transient folds, there are water spray holes.

2, Porbeagle Sharks: there are five families, including cone tooth sharks, sword-nosed sharks, mackerel sharks, basking sharks and thresher sharks.

3, tiger sharks: distributed in the Pacific Ocean, Indian Ocean tropical and temperate sea areas. Is a small and medium-sized shark, up to 1.5 meters long, body thick and short, head high nearly square.

4, Mako Sharks: 4 suborders, 7 families, 49 genera, more than 200 species, including catsharks, wrinkled-lipped sharks, sharks and hammerhead sharks suborder.

5, squark order: our country only 1 species of Japanese saw shark, distributed in the Yellow Sea and the East China Sea, occasionally seen in the South China Sea and the coast of Korea and Japan. Six-gill saw shark genus, gill holes 6, only 1 species, distributed in southern Africa southeast coast.

6, flat shark order: only 1 family 1 genus, about 13 species. The pectoral fins are wide and extended to the side of the head to free such as the sleeve of the robe, the old name of the sleeve shark, commonly known as angelfish or monkfish in the West.