Effects of elevated temperature on growth, gametogenesis, physiology and biochemical composition in diploid and triploid Pacific oysters, Crassostrea gigas Thunberg

Growth, gametogenesis, physiology, and biochemical composition of 1-yr-old diploid and triploid Pacific oysters, Crassostrea gigas Thunberg, were simultaneously examined at ambient (8–15°C) and at elevated (30°C) temperatures. Triploid oysters grew significantly faster (P ≤ 0.01) and exhibited a significantly higher (P < 0.0001) condition index than diploid oysters at the elevated temperature. No significant differences were found between diploid and triploid oysters in rates of oxygen consumption and ammonia excretion at either temperature. Biochemical composition (total protein, carbohydrate, lipid and ash) was similar for both groups at ambient temperature. At elevated temperature, however, triploid oysters had significantly higher levels of carbohydrate (P ≤ 0.016) and protein (P≤0.003) than diploid oysters. Both diploid and triploid oysters developed gametes at ambient temperature, but gonadal development in triploid individuals was 60–80% lower than in diploid individuals. At elevated temperature, 92% of the diploids were found to be ripe, compared to 0% of the triploids. The greater dry tissue weight, condition index, and protein and carbohydrate levels of triploid oyster at 30°C may be attributable to their decreased reproductive effort compared to diploids, thereby giving triploid oysters an energetic advantage at stressful temperatures.