 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 . 
