Effects of salinity and pH on hatching and larval activity of Lateolabrax maculatus

In order to set up a scientific basis for the suitable salinity and pH and promote early seed extension of Lateolabrax maculatus of northern China, in this study, we used different salinities (0, 15, 20, 25, 30, 35 and 40) and pH(5.5, 6.5, 7.5, 8.5 and 9.5)gradients to investigate the hatching rate and deformity rate of fertilized eggs, as well as the vitality after 10 days’ starvation in spotted sea bass. Meanwhile, the survival rate (SR) and survival activity index (SAI) were measured for newly hatched larvae during starvation experiment. Finally, we studied the effects of low salinity (0), culture salinity (30) and high salinity (45) on the growth performance of juvenile spotted sea bass. The results showed that the optimum hatching salinity was ranging from 20 to 35, with the highest hatching rate appearing at 25. The optimum pH for hatchery was 6.5–7.5, and the highest hatching rate came at pH 6.5. The lowest hatching rate and the highest deformity rate were found at low-salinity of 15, however, the survival rate and activity of fish at salinity of 15 was significantly higher than that in 30 and 35 groups. We speculated that salinity 15 approached the isotonic point of body fluid in L. maculatus. At the isotonic point, energy consumption for osmotic regulation is saved for better survival and growth. The results will provide more detailed guidance for L. maculatus cultivation. During the starvation experiment, the survival rate of newly hatched larvae was the lowest when facing fresh water (salinity of 0) stress on the first day, while the survival rates of low salinity groups of 15 and 20 were significantly higher than those cultured in 30 group. The survival rate in salinity group of 20 declined relatively gently, and the survival rate on the 8^th day is 12.66% (0% in the other groups). On the first day of starvation, the survival rate of each pH group was lower than 90%, and the maximum survival rate was 89.11% appearing at pH 6.5. Compared with the salinity treatment, the larvae were more sensitive to pH change, because the hatching rate and final survival rate were much lower than those of salinity treatment group. For the salinity treatment to juvenile spotted sea bass, salinity groups of 0 and 45 would have greater damage to them, and the salinity of 45 was the most significant, which should be the upper limit of seed salinity extension. While the culture salinity of 30 was relatively appropriate. The results of this study will provide a scientific basis for setting the suitable salinity and pH for the breeding and enhancing the hatching and the survival rate, as well as promoting early seed extension of spotted sea bass in northern China.