Broodstock conditioning of the oyster Crassostrea gigas: origin and temperature effect

Abstract

Broodstock conditioning of the pacific oyster Crassostrea gigas (Thunberg) was examined in the laboratory under controlled conditions. Three experiments were undertaken to determine (i) the effect of the origin on gametogenesis, (ii) the time necessary to obtain the first mature oocytes in standard conditioning procedures, and (iii) the impact of different conditioning temperatures (16, 19, 22 and 25 °C) on gametogenesis. Oocyte size was used to identify mature oocytes. Significant differences among populations were observed in the number of mature oocytes produced. Only the oysters from northern locations (Normandy and Brittany) reached the mature stage by the end of the standard conditioning. Concerning the effect of different temperatures during conditioning, the first mature oocytes were detected (absolute days) by the 27th day at 16 °C, 23rd day at 19 °C, 19th day at 22 °C and 22nd day at 25 °C. This information was applied to fit a logistic model to predict oocyte growth using temperature and time as main affecting parameters; D= D max/(1+ ae − kt ) with D—oocyte diameter at time t (μm), D max—the asymptotic oocyte diameter (μm), a—adjustment parameter, k—slope of the curve during growing stage and t—time (days). The model fit consistently with values achieved at 16, 19 and 22 °C. The results obtained during this study could be used to improve conditioning procedures for C. gigas.