Optimisation des conditions hydrobiologiques pour la conservation de l'huître creuse Crassostrea gigas en système re-circulé

The maintenance of bivalve commercialisation du ring periods when sales are prohibited represents a major economic issue for shellfish-farming. To ensure their survival and to preserve the oyster Crassostrea gigas quality, their storage in land-based systems has been studied i) out of water in a cold room at 3°C with controlled humidity, enabling the bivalve sensory quality to be retained for 15 days, and ii) in recirculating systems in immersed conditions for 30 days. For the latter, the oysters were stored at 167 kg.m3 density in a tank equipped with an air-lift system, with water treated with UV and thermoregulated. A minimum of food was supplied to avoid mass tissue loss. A temperature of 16°C was defined as optimal to limit mortality and to avoid spawning risks. The thermal stress linked to the transfer of oysters into this environment induced disruptions of the ecophysiological responses for around 30 hours. The speed of the water current within the system, which is essential to transport food and oxygen, presented a significant negative effect on bivalve clearance rate. The oyster nitrogen excretion was quantified according to the temperature and food supply. The ammonia excreted by bivalves is nitrified by a bacterial population which is mainly located on the oyster shells. This process keeps NH4+ and NO3- concentrations below the toxic level for the bivalve. The modelling of nitrogen and organic matter fluxes in the recirculating system enabled the optimal conditions of storage to maintain oyster dry weight and survival to be simulated.