Seafood has a long history of consumption and is an important source of food for people. There are many varieties of seafood, divided into fish, shrimp and crab, shellfish and other seafood four categories.　　Fish is rich in vitamin B, especially folic acid and vitamin B6, these vitamins are required for protein metabolism, and may also play a significant role in the prevention of skin and nervous system diseases. Fish also contains minerals such as phosphorus, potassium, iron, iodine and selenium, which is an anti-cancer agent. Eating fish basically prevents dental caries because seafood contains high levels of fluoride.　　Cod liver oil is rich in vitamins A and D, both of which are extremely important for human eyes, skin, teeth and bones.　　Shellfish is one of nature's most zinc-rich foods, and zinc is important for the proper functioning of the immune system. Shrimp, clams and salmon contain high levels of calcium, which helps bones.