People have been enjoying clams, oysters, and mussels for thousands and thousands of years. In fact, the ancient Romans actually farmed oysters. Today, almost all of the molluscan shellfish (clams, oysters, and mussels) sold come from farms or aquaculture where the shellfish are raised under semi-controlled conditions.
Molluscan shellfish farms can operate in a variety of ways, using several different production methods. In general, shellfish are grown either on-bottom, where juvenile shellfish are planted directly on the sediment, or off-bottom, where shellfish are placed in racks, bags, or cages that are suspended or off-the-bottom lifted. In some situations, those structures are located in the intertidal zone, which means the shellfish are covered during high tide and are exposed during low tide. This makes it easier to perform routine maintenance. While shellfish larvae and juveniles can begin their lives in tanks, final grow-out to market size typically occurs in natural water bodies in coastal areas.