盐度与pH对花鲈孵化、初孵仔鱼成活及早期幼鱼生长性能的影响

为探究我国北方海域花鲈繁育适宜盐度和pH处理的设定,及促进早期花鲈苗种推广,本研究针对不同盐度(0、15、20、25、30、35和40)与pH(5.5、6.5、7.5、8.5和9.5)条件下,北方人工繁殖花鲈受精卵的孵化率、畸形率及饥饿10 d后的存活情况进行了分析,并对花鲈初孵仔鱼进行不投饵耐饥饿实验,记录每日存活率(SR)及最终生存活力指数(SAI)。最后观测低盐0、养殖盐度30与高盐45对花鲈早期幼鱼生长性能的影响。结果显示,北方海域花鲈受精卵适宜孵化盐度为20~35,以盐度25组孵化率最高,适宜pH为6.5~7.5,以pH 6.5组孵化率最高。低盐15组中,具最低的孵化率及最高的畸形率,但在最终饥饿SR的统计中,低盐15组的SR及SAI明显高于盐度30与35组,推测低盐15接近花鲈体液等渗点,降低了渗透调节中的能量消耗,更利于存活。初孵仔鱼饥饿实验中,盐度20组SR下降相对平缓,在第8天仍有12.66%的SR(其他组已为0)。饥饿1 d时,各pH组SR均小于90%,以pH 6.5组SR最高,为89.11%。与盐度处理组相比,花鲈初孵仔鱼对pH变化较为敏感,其孵化率及最终SR显著低于盐度处理组。花鲈早期幼鱼盐度处理组中,低盐0与高盐45将对此规格花鲈幼鱼产生较大损伤,以高盐45抑制最显著,应为苗种盐度推广的上限,而花鲈生长盐度30与各处理盐度相比,较适合花鲈早期幼鱼的生长。研究结果将为北方海域花鲈繁育适宜盐度和pH处理的设定,及提高花鲈孵化率、育苗成活率与早期苗种推广提供基础资料。

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.