ABSTRACT

Three species of oysters have been or are cultivated in Europe: Crassostrea angulata, C. gigas, and Ostrea edulis. Before diseases, which comprised the range of the flat species particularly on the Atlantic coast, O. edulis, the native oyster, was abundant in several European countries. The oyster can persist for several weeks in wintertime when rivers are in spate, even in freshwater, by closing its valves. On a tidal cycle, it has an active metabolism during high tide and stops its activity at low tide with the freshwater input. O. edulis has a restricted fecundity and is larviparous. It is hermaphroditic, with a consecutive rhythmic sexuality. The duration of sexual maturation is a function of the quantity of heat that the reproductive oyster receives. Substantial differences in the amount of growth are recorded not only from different sites in different countries, but also in the same site at different levels in exploitation of a bay.