盐度胁迫对遮目鱼幼鱼存活、生长及性状相关性的影响

Effects of salinity stress on the survival, growth and correlation of characters of juveniles of Chanos chanos

设置盐度梯度为0、10、20、27(自然海水)、35,共5个实验组,每组3个平行。遮目鱼(Chanos chanos)幼鱼不经过过渡直接放入各梯度盐度中,养殖30 d后统计存活率,测量每尾鱼的体质量及各表型形态性状,以体质量为因变量(y),各形态性状为自变量(x)进行通径分析和决定系数分析。结果表明,盐度0组的幼鱼存活率最低(73.33%),增重率(573.94±231.58)%和特定生长率(6.23±1.16)%最高,与其他组差异极显著(P<0.01)。除盐度0组外,其他各组幼鱼的存活率均在90%以上,且幼鱼特定生长率和增重率在各组之间差异不显著(P>0.05)。相关分析表明,幼鱼的各形态性状与其体重之间呈极显著的相关关系(P<0.01)。通径分析表明,遮目鱼幼鱼的体长、全长和体高对体重的影响最大,且在不同盐度胁迫下对幼鱼体重的决定作用不同,其他性状对体重的影响较小。建立了盐度胁迫下形态性状对体重影响的最优回归方程。

The growth and development of teleost were more or less directly affected by the environmental factors. Salinity is one of the important ecological factors. The influence of salinity on the survival and growth of marine fish has been demon-strated in many studies. However, distinct results were displayed due to the different abilities of tolerance to salinity among fish species. The milkfish （Chanos chanos）, which has a nice marine habitat and an efficient osmoregulation, is widely dis-tributed throughout tropical and subtropical Indo-Pacific. This species occurs naturally and is commercially cultured in fresh, brackish, and oceanic waters as well as in hypersaline lagoons. In the present study, the influences of salinity stress on the survival and growth of milkfish juveniles were assessed and the effects of morphometric attributes on body weight were also evaluated. Juveniles of milkfish [mean weight and total length： （0.215±0.083） g; （2.850±0.356） cm, respectively] were reared at salinities of 0 （fresh water）, 10, 20, 27 （sea water） and 35 without acclimation, in triplicate, for 30 d cultivation. The survival rate was recorded and the body weight and morphometric attributes of each individual were measured. Results showed, the lowest survival rate was founded at salinity 0 group （73.33%） when compared with other groups （〉90%）. The juvenile stage is a special stage during the life history of fish, the juvenile developed not as well as the adults, and cannot adapt to the short-term drastic changes of external osmolality, which may be one of the reasons of the high mortality rate at salinity 0 group. On the other hand, however, the highest rates of weight gain rate （573.94±231.58）% and specific-growth rate （6.23±1.16）% were obtained at salinity 0 group （P〈0.01）. Meanwhile, there was no significantly difference among other groups （P〉0.05）. The higher weight gain rate and specific-growth rate were also found in the intermediary groups with salin-ity 20 and 27. It has been suggested that the marine fish often has a better growth rate in water with lower salinity for the rea-son of fish spending less energy on osmoregulation in such conditions. Although it has not been reported that milkfish require a fresh water environment for any part of its life cycle, it did showed well growth performance at fresh water in many studies. Furthermore, recent studies indicated that the true proportion of energetic cost of osmoregulation remains under debate as thought before. The total length （x1）, body length （x2）, tail length （x3）, trunk length （x4）, head length （x5）, postorbital length of head （x6）, eye diameter （x7）, snout length （x8）, caudal peduncle height （x9）, and body height （x10） were measured by QCapture Pro 6.0 software after the cultivation. The correlation analysis, path analysis and determination coefficients were calculated by SPSS 13.0 software. Significant differences （P〈0.01） were found in all correlation coefficients between each morphometric attributes and the weight. The results of path analysis showed that the traits which had the strongest effect on body weight were total length, body length and body height, and the direct effects of morphometric attributes on body weight were differ-ent at salinity stress. The analysis of determinant coefficients revealed that the determinant coefficient of body length was the largest （d=0.949 30） in the salinity 0 group. For salinity 10 group, the determinant coefficients of total length and body height were larger compared with other traits, among which total length had a predominant determinative effect （d=0.338 41）. For salinity 20 group, the determinant coefficients of total length, body length, and body height were larger, among which body length had a predominant determinative effect （d=12.158 45）. For salinity 27 group, the determinant coefficient of total length was the largest （d=0.898 38）. For salinity 35 group, the determinant coefficients of body length, eye diameter, snout length, and body height were larger, among which body length had a predominant determinative effect （d=0.320 91）. In addition, the best multiple linear regression equations were established at salinity stress, which will be helpful to the cultivation of milkfish.