Relevant Synonyms Crassostrea angulata (Lamarck, 1819) [Menzel, 1974] Ostrea gigas Thunberg, 1793 Misidentification -  photo: S. Gofas

SHORT DESCRIPTION Shell inequivalve, inequilateral, extremely variable in shape depending on substrate: roundish shape with extensive fluting on hard substrata, ovate smooth shell on soft substrata, solid with irregular margins on mini-reefs. Upper valve (rv) flattened with a low round umbo. Lower valve (lv) larger, more convex having a well developed umbo that is much higher than on rv. Anterior margin longer than the posterior. color : shell white with purple patches. common size : 80-300 mm in length: exceptional specimens can attain 400 mm. DISTINGUISHING CHARACTERISTICS Indistinguishable prodissoconch and adult shells, plus ease of hybridisation, support the contention that the Portuguese oyster C. angulata and the Japanese C. gigas are the same species. Differs from O. edulis Linnaeus, 1758 in the heavily colored adductor muscle scar, in the much more pink or purple color pattern and in the absence of crenulations on the margin. BIOLOGY / ECOLOGY Filter feeder. Epifaunal, immobile organisms cemented to rocks/hard substrata. Oviparous animals spawn at water temperatures of 18.5-24°C and salinities 23-28‰. Temperature appears to be the main limiting factor for reproduction in the wild. Salinity reduced to 18‰ results in 98% mortality. habitat : prefers shallow water. On muddy as well as on rocky bottoms in sheltered areas, rarely on exposed shores. Extremely large shells are usually dredged at depths between 20 and 40 m.

1st Mediterranean record France, 1964 [no collecting date]. DISTRIBUTION Worldwide: North West Pacific; introduced in the Atlantic coast of France, Spain, Portugal and Morocco. Mediterranean: imported in Etang de Thau, France, (Raimbault, 1964) and in Adriatic lagoons (Venice, Grado, Varano, Foggia) (Matta, 1969). Successively recorded from Malta (Agius et al., 1978); Spain (Poutiers, 1987); Tunisia, Ichkeul (Madhioub and Zaouali, 1988); Ionian Sea-Tyrrhenian Sea (Minelli et al., 1995); now widely established in the northern Adriatic (De Min and Vio, 1997). Suspected records in Greece: Patraikos, Korinthiakos (Dimitrakis, 1989) and Yurkey (Çevik et al., 2001). ESTABLISHMENT SUCCESS Widely common in natural sites outside the influence of marine farming. speculated reasons for success : broad environmental tolerance. MODE OF INTRODUCTION Introduced for oyster farming. The type locality of Ostrea angulata in the Tagus estuary, Portugal, is probably the site of an old introduction, from which it has been introduced to the French Atlantic coast, then to the French Mediterranean and Moroccan Atlantic coasts. Direct imports from Japan started in France in the late 1960s after a disease had decimated the stock of Portuguese origin (see Zibrowius, 1992, for details). IMPORTANCE TO HUMANS Edible. Importation of Japanese oysters into France has permitted the oyster industry to remain in existence; the overall economic impact has been positive.

KEY REFERENCES Goulletquer P., 1997. Cycle de reproduction naturelle de l'huître creuse Crassostrea gigas. Pp. 7-19. In: La reproduction naturelle et controlée des Bivalves cultivés en France, Nantes (France), 14-15 Nov. 1995. IFREMER Rapport Interne DRV/RA/RST/97-11 RA /Brest. ICES, 1998. Report of the working group on introductions and tranfers of marine organisms. C.M. 1998/ACME:4, Ref.: E+F, 73p. Menzel R.W., 1974. Portuguese and Japanese oysters are the same species. Journal of the Fisheries Research Board of Canada, 31: 453-456.   Raimbault R., 1964. Croissance des huîtres atlantiques élevées dans les eaux méditerranéennes françaises. Science Pêche, 126: 1-10. FEEDBACK / COMMENTS TO AUTHORS

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