Oyster
The largest oyster-producing body of water in the United States is Chesapeake Bay, although these beds have decreased in number due to overfishing and pollution. Willapa Bay in Washington produces more oysters than any other estuary in the US. Other large oyster farming areas in the US include the bays and estuaries along the coast of the Gulf of Mexico from Apalachicola, Florida in the east to Galveston, Texas in the west. Large beds of edible oysters are also found in Japan and Australia. In 2005, China accounted for 80% of the global oyster harvest. Within Europe, France remained the industry leader.
Bivalvia
The Pacific oyster ("Crassostrea gigas") is cultivated by similar methods but in larger volumes and in many more regions of the world. This oyster originated in Japan where it has been cultivated for many centuries. It is an estuarine species and prefers salinities of 20 to 25 parts per thousand. Breeding programmes have produced improved stock that is available from hatcheries. A single female oyster can produce 50–80 million eggs in a batch so the selection of broodstock is of great importance. The larvae are grown on in tanks of static or moving water. They are fed high quality microalgae and diatoms and grow fast. At metamorphosis the juveniles may be allowed to settle on PVC sheets or pipes, or crushed shell. In some cases, they continue their development in "upwelling culture" in large tanks of moving water rather than being allowed to settle on the bottom. They then may be transferred to transitional, nursery beds before being moved to their final rearing quarters. Culture there takes place on the bottom, in plastic trays, in mesh bags, on rafts or on long lines, either in shallow water or in the intertidal zone. The oysters are ready for harvesting in 18 to 30 months depending on the size required.