Oregon Sea Grant

Three experiments were performed to examine the heritability of body weight among adult Pacific oysters (Crassostrea gigas) evaluated in Yaquina Bay, Oregon, USA, and to determine if selection on individual body weight could result in changes in offspring survival and yield. The first two experiments utilized midparent–offspring regressions to estimate the heritability of adult oyster body weight and the coheritability between adult midparent body weight and offspring performance, including juvenile average body weight, survival and yield as well as adult survival and yield. In Experiment 1 both parents and offspring were evaluated in an “upriver” environment in Yaquina Bay. In Experiment 2 parents were evaluated in a “downriver” environment, while offspring were evaluated in an “upriver” environment. Experiment 3 contrasted average body weight, survival, and yield of offspring (evaluated upriver) derived from three large sires and three small sires mated to the same five females that were chosen at random (all parents evaluated downriver). In Spring 2002, 12 full-sib families from Experiment 1, 19 families from Experiment 2, and 26 families from Experiment 3 were stocked into lantern nets and suspended in Yaquina Bay. Measurements of yield (kg tier−1), average body weight (g), and survival (%) were recorded after one and two growing seasons in the field. Heritability estimates for adult body weight at harvest ranged from 0.313 (±0.083) in Experiment 1 to 0.003 (±0.073) in Experiment 2. In Experiment 3, average body weight did not differ between offspring derived from large sires and offspring derived from small sires (P=0.47). Significant negative coheritability estimates were observed between adult midparent body weight and offspring survival in both Experiment 1 and Experiment 2. Significant negative coheritability estimates between adult midparent body weight and offspring yield were observed in Experiment 2 but not in Experiment 1. In Experiment 3, offspring derived from large sires had significantly lower survival and yield than offspring derived from small sires. These results show adult oyster body weight to be heritable but also subject to site-specific adaptation such that selection in the downriver Yaquina Bay environment was ineffective at changing average body weight in the upriver environment. Negative coheritability estimates between performance traits indicate that adult oyster body weight may be a poor indirect measure of oyster yield potential, and that selection solely for increased body weight could lead to a decrease in offspring yield.