Biodiversity & Conservation

Pacific oyster - Crassostrea gigas

Crassostrea gigas

Image Guy Baker - Crassostrea gigas at Batten Bay, Plymouth Sound. Image width ca 20 cm.
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Distribution map

Crassostrea gigas recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Crassostrea gigas is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Mollusca Snails, slugs, mussels, cockles, clams & squid
Class Bivalvia Clams, cockles, mussels, oysters, and scallops
Authority (Thunberg, 1793)
Recent synonyms Crassostrea angulata
Map icon Recorded Distribution in Britain and Ireland Introduced initially in Cornwall, Essex and Wales for mariculture. It has been farmed on around 300 sites throughout England, Scotland, Wales and Northern Ireland. 'Escapees' have established populations in various regions.
Habitat information icon Habitat information Found on the lower shore and shallow sublittoral to a depth of around 80 m.
Text page icon Description The shell can grow up 18 cm long. An off-white to yellow or bluish grey in colour, the shell often has deep purple patches. The left valve is deeply cupped with 6 or 7 bold ribs making the shell margin rough. The right valve is flat or slightly convex and has ribs corresponding to channels of left valve.
Identifying features
  • An elongate oval shell with a crenulate shell margin.
  • The left valve is deeply cupped with a coarse concentric sculpture and has 6 or 7 prominent ribs.
  • The flat or slightly convex right valve sits inside the left valve.
  • The troughs of the right valve correspond to the ridges on the left valve.
  • The shell often overgrows the beaks and umbones.
  • The external colour may be off-white to brown with patches or streaks of purple.
  • Internally the shell is white with the adductor scar typically purple (mauve).
Additional information icon Additional information Similar to Crassostrea virginica although this species lacks the crenulate shell margin and bold ribs of Crassostrea gigas. Crassostrea gigas was introduced from Portugal to Essex in 1926 as a commercial crop and has since established itself in the wild. It occurs naturally in Japan and south-east Asia. Crassostrea gigas is also known as the Portuguese or Japanese oyster.

This review can be cited as follows:

Joelene Hughes 2008. Crassostrea gigas. Pacific oyster. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26/11/2015]. Available from: <>