Sharks belong to cartilaginous fish, a subclass of vertebrates, and live in the ocean. A few species enter fresh water, which is a group of medium and large marine fish with fast swimming speed. The endoskeleton of sharks is completely composed of cartilage, which is often calcified, but there is no real bone tissue. The exoskeleton is not developed or degenerated. The body is often covered with skin teeth (thin-walled scales), with various teeth and hard muscles, but the membranous bone never exists and the skull is seamless. The upper forehead is composed of palatal cartilage and the lower forehead is composed of Mayer cartilage. The latest research shows that sharks contain many bioactive components, such as anticancer factors, squalene, mucopolysaccharide and so on. The medicinal use of sharks was first seen in Notes on Materia Medica. In China, shark cartilage extract and shark liver oil have long been used to treat cancer and other diseases. The body is spindle-shaped with cheeks on both sides of the head, but it is similar to ordinary fish. With a few exceptions, the typical shark skin is hard and dark gray, and the dentate scales make the skin look rough. The tail is strong, asymmetrical and upturned; Fins are pointed; The nose and mouth are pointed and protruding, the mouth is crescent, and there are triangular fangs under the nose and mouth. Sharks don't have swim bladders, so they need to swim constantly to avoid sinking into the water.