To understand the influences of environmental conditions on the performance of pearl oyster spat, we conducted four experiments to evaluate separately the effects of salinity (21, 24, 27, and 30), diet (Isochrysis zhanjiangensis, Platymonas subcordiformis, Chlorella; 50% I. zhanjiangensis/50% P. subcordiformis, 50% I. zhanjiangensis/50% Chlorella, and 50% P. subcordiformis/50% Chlorella), diet availability (high, medium and low), and rearing site (hatchery and sea) on the growth and survival of pearl oyster Pinctada maxima spat. Results showed that environmental conditions exerted significant effects on the growth of P. maxima spat. Salinity and rearing site also had significant effects on survival, but no significant differences were observed in terms of survival between the diet and diet availability treatments. Growth declined with decrease in salinity. Spat reared at high salinities (30 and 27) showed larger shell length growth and greater survival than those at low salinities (24 and 21). Spat fed on a single diet (Chlorella) had poorer shell length growth than those fed on diets composed of more than one species. Spat reared on a medium ration (4.0 × 104 cells/mL/day) had greater shell length growth than those reared at high (8.0 × 104 cells/mL/day) and low (2.0 × 104 cells/mL/day) rations. Spat held in the sea had greater shell length growth than those held in the hatchery. However, survival rate of spat was greater in the hatchery than in the sea. These results suggest that seed production of P. maxima spat could be optimized by extending the nurture period in the hatchery. Moreover, various diets should be provided to ensure balanced food intake.
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Vol. 32 • No. 3