Pacific oyster Crassostrea gigas
Distribution - The Pacific Oyster is endemic to Japan, but has been introduced into a number of other countries including Australia. It was deliberately introduced into Tasmania, Victoria, Western Australia and South Australia and has spread to NSW and southern Queensland. Adult oysters are sessile and will settle on any hard substrate in the intertidal and shallow subtidal zones, to a depth of about 3 metres. They favour brackish waters in sheltered estuaries, however Pacific oysters can tolerate a large range of salinities and water quality.
Size - Pacific Oysters reach a marketable size of 50 grams in 10 months to 2 years.
Characteristics - The Pacific Oyster is a member of the family Ostreidae and possesses a relatively thin shell with no hinge teeth on the inner, upper shell. The adductor muscle (the muscle which holds the two shells together) is purple or brown in colour, whilst the edges of the mantle (the tissue which secretes and lines the shell) are black. The Pacific Oyster has a very high growth rate and rate of reproduction. They are plankton feeders, filtering algae from the water.
Confusing species - The Pacific Oyster is now found throughout most of the range of the Sydney Rock Oyster (Saccostrea commercialis). The Sydney Rock Oyster is distinguished by its smooth, thick shell which has small teeth on the internal rim, generally near the hinge and the mantle edges. Also the adductor muscle scar of the Sydney Rock Oyster are pale in colour.