Magallana gigas (Thunberg 1793)

Shell solid, inequivalve, extremely rough, extensively fluted, and laminated; left (lower) valve deeply cupped, its sides sometimes almost vertical, the right (upper) valve flat or slightly convex sitting withing left; inequilateral, beaks and umbones often overgrown; tending to be oblong in outline but often disorted and very irregular. The shape of the shell varies with the environment. Colour usually whitish with many purple streaks and spots radiating away from the umbo. The interior of the shell is white, with a single muscle scar that is sometimes dark, but never purple or black. Can be confused with: It differs from Crassostrea virginica in never having a purple or black muscle scar, and from Ostrea lurida in its extremely large size and heavy shell. In addition, the inside of an O. lurida shell is iridescent green.

Cosmopolitan. Recorded from Japan, Korea, Siberia, Australia, United States and Canada. Introduced in North America is found Southeast Alaska to Baja California. In Europe from the British Isles south to Portugal and in the Mediterranean.

Maximum length is 30 cm (exceptional specimens can attain 40 cm), but normally the length is from 8-15 cm.

Is an exotic species introduced into west coast estuaries americaines from Japan. Prefer firm bottoms, and usually attach to rocks, debris or other oyster shellsat depths of between 5 and 40 m.However, they can also be found on mud or mud-sand bottoms. Pacific oysters are protandrous hermaphrodites. They change sex, but their timing is erratic and seasonal. Spawning depens on a rise in water temperatures above eighteen degrees Celsius. When spawning does occur, it occurs primarily in July and August; eggs (50-100 millions in single spawning) and larvae are planktonic distributed throughout the water column in estuarine waters. Later stage larvae settle out of the water column and crawl on the bottom searching for suitable habitat before settling. Juveniles and adults are sedentary and are found in lower intertidal areas of estuaries.

The commercial fishery for this species has grown rapidly since its introduction from Japan to the west coast of the United States in 1903. The United States now consumes almost 60 percent of the world's total oyster production. The Pacific oyster is a dominant shellfish in a growing United States aquiculture industry along the Pacific Coast. The 60-70 percent of the Pacific oyster production is marketed in the Pacific Coast States.The total catch reported for this species to FAO for 1999 was 12 271 t. The countries with the largest catches were Korea, Republic of (11 609 t) and USA (539 t).