The effects of inbreeding on performance traits of adult Pacific oysters (Crassostrea gigas)

Understanding the effects of inbreeding is critical to the long-term viability of shellfish breeding programs, especially as breeders attempt to develop selected lines in hatcheries with small effective population sizes. Inbreeding depression in shellfish is well documented among the offspring of selfed individuals and full-sib crosses. This study was conducted to determine if crossing more distantly related parents would result in measurable inbreeding depression of performance traits in adult Crassostrea gigas raised in a commercial intertidal growing environment. Families were created with expected inbreeding coefficients (F) of 0, 0.0625, and 0.203. Average family yield, individual growth rate, and survival were recorded after the first and second growing seasons. Significant inbreeding depression in yield, individual growth rate and survival was observed after the first growing season in families with F=0.203 (P<0.0001), but not in families with F=0.0625 (P>0.058). After two growing seasons, significant inbreeding depression of yield and individual growth rate was observed in families with F=0.0625 (P<0.01) and F=0.203 (P<0.001). Significant depression of survival at harvest was observed only in families with F=0.203 (P=0.009). These results emphasize the importance of maintaining pedigree records in shellfish breeding programs to help avoid the deleterious effects of inbreeding depression, even among crosses of distantly related parents.