Determination of optimal temperature, salinity, and stocking density combinations for larval growth and survival of diploid, triploid, and tetraploid Fujian oyster (Crassostrea angulata)

For nurseries, thriving larvae mean higher incomes. Three factors - temperature, salinity and stocking density - are critical to the success of larval rearing. However, the effects of these three factors on the performance of diploid, triploid and tetraploid Crassostrea angulata larvae have not yet been comprehensively investigated. In this study, the combined effects of temperature (T, 12.0–35.0 °C), salinity (S, 10.0–38.0 psu) and stocking density (D, 0.5–10.0 ind. ml−1) on the accumulated growth rate (AGR) and survival rate (SR) of diploids (DD), triploids (DT) and tetraploids (TT) C. angulata larvae were comprehensively assessed using a central composite design and response surface methodology. The results revealed that suitable temperature-salinity-stocking density combinations significantly increased the AGR and SR of larvae from all three groups, while unsuitable environments (e.g., ultra-high temperature - extra-high salinity -high stocking density combinations or ultra-high temperature - extra-low salinity - high stocking density combinations) significantly reduced the AGR and SR of the larvae, albeit to different magnitudes. The optimal temperature-salinity-stocking density combinations were obtained by model optimization. The maximum AGR and SR of DT reached at 23.6 °C, 26.5 psu and 0.5 ind. ml−1 combinations with values of 17.13 μm day−1 and 64.81%, respectively. The combinations of 24.0 °C - 25.89 psu - 1.99 ind. ml−1 and 25.9 °C - 25.96 psu - 0.5 ind. ml−1 were the optimal breeding conditions for DD and TT (DD: AGR = 13.10 μm day−1, SR = 63.55%; TT: AGR = 10.11 μm day−1, SR = 25.89%). In addition, validation experiments were carried out under the obtained optimum conditions. The AGR and SR of DD, DT and TT obtained from the validation experiments were basically in conformity with the maximum AGR and SR obtained under the theoretically predicted conditions. Moreover, the growth and survival of tetraploids remained lower than those of diploid and triploid counterparts, even under optimal breeding conditions. This means that more attention should be paid to the tetraploids so as to safeguard the succession of this fragile population. The application of the findings of this study will help to improve the breeding efficiency of C. angulata with different ploidies in larval culture.