Optimal ammonia concentration for fertilization success in Pinctada martensii (Dunker) under the simultaneous influence of temperature and salinity

Pinctada martensii is one of several important pearl oysters. Ammonia is typically added to the seawater and used during artificial reproduction to improve the fertilization rate. However, the optimal ammonia concentration has not been determined. To determine the optimal ammonia concentration for fertilization success, the effect of the ammonia concentration on the fertilization rate in P. martensii was investigated under the simultaneous influence of temperature and salinity. A Box-Behnken design and response surface method were used in this study. The results showed that the ammonia concentration had a significant effect, which varied quadratically with the ammonia concentration in the ranges of the factor regimes (P < .01). The interactions between the ammonia concentration and the temperature/salinity had a significant effect (P < .05), indicating that the effect of the ammonia concentration depended on the combination of temperature and salinity; therefore, their combined effects should be taken into account when determining the optimal ammonia concentration. The effect of the ammonia concentration was less than that of the temperature but more than that of the salinity. A reliable model of the fertilization rate using the three factors was constructed. The results of the model optimization demonstrated that a fertilization rate of 96.16% was achieved at an ammonia concentration of 1.85 mmol L−1 and a temperature-salinity combination of 27 °C/32 practical salinity unit (psu). The ideal fertilization rate was verified experimentally using the optimal ammonia concentration while maintaining the temperature and salinity at natural levels during the spawning season. The results of this study can be used to refine the seed production efficiency of the pearl oyster.