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 that oysters 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 monitor shellfish 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.