Studies on the influence of ambient temperature and food supply on growth rate, carbohydrate content and reproductive output in diploid and triploid Pacific oysters, Crassostrea gigas (Thunberg)

Growth rates measured as changes in whole volume and dry tissue mass in juvenile diploid Pacific oysters (Crassostrea gigas) grown at low density in suspension culture varied in relation with increased ambient temperature and ambient seston levels in Blakely Harbor, WA; increased growth rate occurred at the site having the highest mean total degree days and mean particulate organic seston levels. Similar relationships between organic seston levels and the rate of growth were observed in the same hatchery stock of diploid Pacific oysters maintained at three Puget Sound sites (Mud Bay, Quilcene Bay and Westcott Bay).; Measurements of reproductive output in Pacific oysters from five year classes cultured in Samish Bay, WA demonstrated positive allometry in the allocation of internal volume for the production of germinal tissue in larger and older oysters. Similar results were observed in the hatchery stock of diploid Pacific oysters maintained in Westcott and Quilcene Bays as reproductive output and effort increased annually.; Comparative growth within a hatchery population of diploid and triploid Pacific oysters was investigated over several seasonal growth cycles. Diploid and triploid oysters derived from the same parents were grown in Westcott Bay and Quilcene Bay, and changes in whole volume, tissue mass and carbohydrate content monitored. After 25 months, triploid whole volume and dry mass was significantly greater than that of diploids in the Quilcene Bay cohort. The Westcott Bay triploid group also demonstrated increased rate of somatic growth rates relative to diploids, however the mean difference was not statistically significant. Greatly retarded gametogenic activity in triploid Pacific oysters was observed in oysters from both bays relative to dipioids. The pattern of carbohydrate utilization was also distinctly different in triploid oysters from both bays compared to diploids with rapid carbohydrate depletion occurring in diploid individuals coincident with gametogenesis. In triploid individuals, a pattern of reduced carbohydrate depletion occurred which was coincident with increased rate of somatic growth.; While differences were noted between sites, physiological measurements made in the laboratory and under ambient conditions of temperature and particulate seston levels showed no significant differences between diploids and triploids for uptake rates on particulate seston, absorption efficiency or the rate of oxygen consumption.; Comparative growth of diploid and triploid oysters from five distinctly different commercial oyster-growing areas demonstrated a pattern which suggested that increased growth rate in triploid Pacific oysters is related to the overall productivity of grow out waters; sites demonstrating rapid oyster growth demonstrated significantly higher somatic growth in triploid relative to diploid oysters, while sites demonstrating reduced oyster growth showed no significant differences in size between diploids and triploids after 28 months.