abundances tend to have a larger proportion of male adults. Spawning Spawning in the Pacific oyster occurs at 20 °C. This species is very fecund, with females releasing about 50–200 million eggs in regular intervals (with a rate at 5–10 times a minute) in a single spawning. Once released from the gonads, the eggs move through the suprabranchial chambers (gills), are then pushed through the gill ostia into the mantle chamber, and finally are released in the water, forming a small cloud. In males, the sperm is released at the opposite end of the oyster, along with the normal exhalent stream of water. A rise in water temperature is thought to be the main cue in the initiation of spawning, as the onset of higher water temperatures in the summer results in earlier spawning in the Pacific oyster. Life cycle The larvae of the Pacific oyster are planktotrophic, and are about 70 µm at the prodissoconch 1 stage. The larvae move through the water column via the use of a larval foot to find suitable settlement locations. They can spend several weeks at this phase, which is dependent on water temperature, salinity, and food supply. Over these weeks, larvae can disperse great distances by water currents before they metamorphose and settle as small spat. Similar to other oyster species, once a Pacific oyster larva finds a suitable habitat, it attaches to it permanently using cement secreted from a gland in its foot. After settlement, the larva metamorphoses into a juvenile spat. The growth rate is very rapid in optimum environmental conditions, and market size can be achieved in 18 to 30 months. Unharvested Pacific oysters can live up to 30 years. Genetics The genome of M. gigas has been sequenced, revealing an extensive set of genes that enables it to cope with environmental stresses. The expression of genes such as arginine kinase and cavortin is particularly important in regulating the metabolic response of this species to stress events including the reduction of seawater pH, as observed under ocean acidification. Aquaculture Historical background M. gigas was originally described by the Swedish naturalist Carl Peter Thunberg in 1795. It is native to the Northwest Pacific, and occurs primarily in temperate waters between 30° N and 48° N. It is now the most widely farmed and commercially important oyster in the world, as it is very easy to grow, environmentally tolerant, and easily