Variabilité et bioénergétique de la reproduction chez l'huître creuse Crassostrea gigas

The variability in reproductive cycle of Pacific oyster, Crassostrea gigas, was evaluated in situ (Bay of Veys, BOV and Marennes-Oléron bay, MOB) and in hatchery culture conditions. Two trophic levels were tested over one year: high food level (HFL) and low food level (LFL). We observed that the phytoplanktonic concentration (chlorophyll a) was the principal factor that influenced gametogenesis intensity and duration. The oysters reared within a high trophic ration (BOV and HFL) shown a hyper-gonad development. However, the spawning efficiency was reduced and partial. Therefore, the resorption period was prolonged until winter. Meanwhile, the oysters reared in a low trophic ration (MOB and LFL) produced a normal gonad with a total spawning in summer and their resorption period through the autumn. The ecophysiological measures in the conditioning oysters, showed that the gametogenesis period influenced the clearance rate, absorption efficiency and respiration responses. Furthermore, the scope for growth was influenced negatively during active gametogenesis and resorption period, meanly in the oyster fed in high trophic conditions. On the other hand, we observed that the genetic factor, was another variability found in the reproductive cycle. Two selected genetic families by their summer survival character (the R or resistant oysters and the S or susceptible oysters at summer mortality), were reared in a common environment (Fort Espagnol, sud Brittany ) and were evaluated. The susceptible oyster presented a reproductive cycle similar to that observed in oysters fed in high trophic levels (BOV and HFL). While resistant oyster showed a reproductive cycle similar to the oysters reared in low trophic conditions. In conclusion, Crassostrea gigas showed a reproductive plastic strategy, influenced by the trophic level and genetic factors. The oysters that developed a hyper-gonad, could be more susceptible to summer mortality.