Shark bone is cartilage, and shark is another name for the suborder Sideforamina of Cladocera, a class of cartilaginous fishes. Its ancestors first appeared in the Paleozoic Devonian (about 45-345 million years ago), and the most famous fossil species is Cladocodactyl shark. Living species appeared from Mesozoic (about 23 million to 65 million years ago) to Cenozoic (about 65 million years ago to the present). Sharapoda is divided into tiger sharks, bearded sharks, true sharks, mouse sharks, six-gill sharks, hornsharks, flat sharks and sawsharks. Among the modern sharks, the frilled shark of the order Hexbranchiatus, which leaves many primitive features, is very similar to the dentate shark. Secondly, the primitive tiger sharks are similar to the sharks that appeared from the end of Paleozoic (about 6-23 million years ago) to Mesozoic. Evolved white sharks called "cannibalism", large whale sharks, elephant sharks and yaji sharks with specialized heads. Japanese saw sharks and horseshoe crabs close to horseshoe crabs. It is said that sharks can smell blood from far away and gather. Sharks can transmit sound waves, know the location of prey by hearing, get close to a certain degree, then rely on smell, and get closer, then rely on vision.

Scholars who study shark ecology agree that the white shark is the most terrible shark, so it is also called a man-eating shark or a man-eating shark. There is no swim bladder, and it is said that the regulation of ups and downs mainly depends on its large liver. The shark's mouth grows in the lower part of the head, and there are vertical rows of parallel teeth. When the outer teeth fall, the inner teeth will protrude. Two nostrils are like two narrow eyes. Seen from below, the mouth and nose form a sad face. There are spray holes behind the eyes. There are several gill holes on each side of the back of the head. Sharks have pectoral fins, dorsal fins, ventral fins, anal fins and caudal fins, and there is a crack at the back of the caudal fin. Shark scales are like shields, so they are called shield scales. Sharks have a keen sense of smell, especially when they can smell blood quickly. If whales are killed, they can smell it from far away. Usually sharks live quite far from the coast and feed on tuna, bonito, mackerel, salmon and other fish. But once hungry, it will also approach the coast and sometimes attack swimmers.

There are many kinds of sharks, and their body length ranges from less than 1 meter to 18 meters. Its body color also varies from white to black, some are red or pink, and some are striped. Most kinds of sharks are viviparous, and the eggs are in the female's abdomen and don't come out until they hatch. Some spiny sharks have larvae that live in their mothers for as long as a year. The newborn spiny shark also comes with yolk sac.

The "shark skin" feels a little rough, which is caused by its shield scales (unique scales of sharks). Under the microscope, if you enlarge it several times, you can see the shield-shaped scales with sharp tips like chopping boards side by side. Scales, like the structure of teeth, protrude from the skin, also known as "skin teeth".

The sharks that are harmful to fisheries are Pacific mouse sharks, mako sharks, white sharks, etc.

Shark pulp can be used as the material of "fish cake". Fin (commonly known as shark's fin) can be used in cooking in China.