Cycle de reproduction naturelle de l'huître creuse Crassostrea gigas

Since its introduction to French coasts in the 1970s, Crassostrea gigas completes its reproductive cycle?i.e. regular annual recruitment and establishment of natural populations?in only two sectors (Charentes coast and Arcachon Bay). In other areas of Pacific oyster production (Normandy, Brittany, Vendée, Mediterranean), complete gametogenesis may occur, resulting in spawning events and even recruitment in favourable temperatures. Temperature seems to be the main limiting factor for in situ reproduction. Growth and reproduction occur simultaneously. The study of the reproductive cycle of one-year old oysters showed that gametogenesis was asynchronous with high interannual variability and growth appeared to take precedence over reproduction. On the contrary, older individuals showed synchronous sexual maturation giving rise to massive spawning events and metabolic processes were preferentially geared towards reproduction. Reproductive effort increased with age, reaching gamete weights that represented 60% and 80% of dry weight at two and three years old, respectively. The Pacific oyster (C. gigas) is generally considered to be a successive protandric hermaphrodite. Sex inversion has nevertheless been observed in adult animals.