Validation in commercial conditions of the response to selection of the European flat oyster Ostrea edulis for resistance to Bonamia ostreae

Since the outbreaks of the parasitosis with Marteilia refringens and Bonamia ostreae in the last 60's, the French production of the European flat oyster dropped from 20000 mT to less than 1500 mT currently, leaving the French shellfish farming in situation of virtually monoculture of the Pacific cupped oyster Crassostrea gigas. To sustain this traditional culture, Ifremer has developed, at the experimental level, a genetic selection for a better tolerance to Bonamia ostreae which led to an improvement of survivals. The transfer of these results to the business scale requires the control of the reproduction in hatchery and the adaptation of the cycle of production to the constraints of seedlings in deep water as practised in Brittany (France). That's why a project, cofunded by Ofimer (1), and intended to evaluate the technical and economic feasibility of the commercial production of tolerant flat oyster spats, was led between 2002and 2004 in partnership between Ifremer, a private hatchery (Vendee Naissain), the SYSAAF (2) and the SMIDAP (3).Spawning was obtained in 2002 by the Laboratory of Genetics and Pathology of Tremblade of Ifremer (Charente Maritime, France) from breeders descended from the experimental program of genetic selection. Average larval survival rate was 65% and the average settlement rate 40%. In experimental conditions, the contribution of the alga Tetraselmis suecica in larval phase led to an improvement of both survival and growth, which was not checked in commercial conditions. The pre growing step is essential in the cycle of production of Ostrea edulis to obtain asufficient size at seedling. This step, carried out in the Vendee Naissain facilities, does not seem to raise any specific problem, provided some decantation of water is met, if needed: the turbidity indeed is likely an element which blocks the growth in this species...