L'huître portugaise en Bretagne

1. - The arrival and deposit of Portuguese oysters in the Breton rivers of Etel and Pénerf have had, since 1948, positive consequences on the economy and prosperity of these two areas, without jeopardizing flat oyster culture. No grypheae invasion has been observed in the rivers where the trials occurred, nor in the collectors and farms of the Morbihan basin, which is the production centre of flat oysters. The natural spreading of G. angulata limited itself to the Vilaine and its estuary.2. - In every Morbihan river, the Portuguese oyster has formed, from 1954 to 1956, genital products which attained their maturity at the end of June or in July when water temperature reached 18-19° C. However, the egg-laying only occurred in the Vilaine River, and, to a lesser extent in the Pénerf and Etel Rivers. In the Morbihan basin, it was very low and limited. The gamete release occurred earlier and was more complete in the Vilaine River than in other rivers; starting in July or August, it was intense in September. In the absence of egg-laying, the genital products degenerated.a) A salinity equal or inferior to 34 0/00 seemed to contribute to the development of gonads, the egg-laying and the larval evolution. These conditions, usually matched in the Vilaine River, could be observed at the same period of time in the Seudre River and the Arcachon Bay, but not in the other Morbihan Rivers where the salinity was superior to 35 0/00 in summer. b) A water temperature equal or superior to 20-22° enabled numerous settlements (1955); a lower temperature did not prevent settlements but limited them (1954-1956).[...]