Pacific cupped oyster Magallana gigas

The Pacific cupped oyster, long catalogued as Crassostrea gigas and now placed in Magallana, is a north-west Pacific bivalve carried around the world for culture - into Washington State from Japan in the 1920s - and is the dominant farmed oyster, with 714,116 tonnes reported for 2024. Hatchery larvae swim for two to three weeks, then settle onto shell cultch and cement themselves there for life; the spat are grown on the bottom, on racks in the intertidal zone, or suspended from rafts, reaching a 70 to 100 g market animal in eighteen to thirty months. Nothing is fed after the hatchery: the oyster filters its own food, up to fifty gallons of seawater a day. That physiology is the clinical point. A filter feeder concentrates whatever the catchment sends it, which makes the oyster both a sentinel of water quality and a vehicle for human norovirus and for Vibrio parahaemolyticus, neither of which depuration reliably clears. Oysters begin life as males and some later become female. There is no vaccine; against WOAH-listed ostreid herpesvirus 1 microvariants, which kill spat within a week in warm water, control is hatchery biosecurity and selective breeding.