Oyster is a saltwater shellfish belonging to the family of bivalve mollusks. Although indigenous to many parts of the world, oysters are now farmed to avoid depletion and to minimize their contamination from polluted water. East Coast and West Coast varieties are available in the United States. In oyster cultivation, small seed oysters are first attached to a stationary support. As they grow in size they are transferred to beds, where their growth can be supervised. Traditionally it was recommended thatoysters and clams be harvested only in months containing an “r” (September through April) to avoid contamination by blooms of “red tide” microorganisms. These organisms produce a toxin that accumulates in oysters and mussels and can cause food poisoning. State health departments monitorshellfish and may restrict harvest in other months. A marine bacterium, Vibrio vulnificus, can infect warm, brackish waters and infest shellfish such as oysters. The bacterium can cause blood poisoning in individuals with a weakened immune system.

Fresh oysters are traditionally eaten raw with lemon juice or sauce. However, the consumption of raw or partially and cooked shellfish substantially increases the risk of food poisoning and of diseases transmitted by sewage, such as hepatitis A and Norwalk virus. Cooked oysters are far safer. They can be poached, browned, cooked on skewers, or used in soups and sauces. Oysters canned in oil contain more calories than fresh oysters. Oysters are an excellent source of ZINC, though different varieties contain differing amounts. One oyster, cooked (100 g), provides 90 calories; protein, 5 g; carbohydrate, 5 g; fat, 5 g; cholesterol, 35 mg; calcium, 49 mg; iron, 3 mg; zinc, 9 mg; thiamin, 0.15 mg; riboflavin, 0.29 mg; niacin, 2.1 mg.