放养规格对银化期大西洋鲑生长的影响及生理响应机理

Effect of different sizes on growth during smoltification in atlantic salmon(Salmo salar L.) and its mechanism of physiological response

内分泌系统在调节大西洋鲑（Salmo salar L.）的银化过程中,除了要尽快建立更高效的渗透调节机制外,鱼体自身的生理反应变化还要更好地适应降海后的生活。试验研究了平均体质量（30.25±2.12）g（SW1）、（24.27±1.59）g（SW2）和（18.05±2.46）g（SW3）大西洋鲑,1～42 d光照周期为12L：12D;43～84 d为全光照下（24L：0D）的生长及生理响应机理。试验结果表明,SW2组大西洋鲑的肥满度、日增质量、饲料转化率、净增质量最高,与其他组差异显著（P〈0.05）。SW2组体质量、体长特定生长率均显著高于其他处理组（P〈0.05）,各组间体质量、体长变异系数差异显著（P〈0.05）。试验前6周不同处理组大西洋鲑体长变异系数差异不显著（P〉0.05）。后6周全光照时,SW1、SW2组体长变异系数显著增加,且SW1组显著高于其他组（P〈0.05）。SW3组的大西洋鲑体质量变异系数变化较大。前6周光照期为12L：12D时,SW1、SW2两组体质量变异系数差异不显著（P〉0.05）,后6周改为全光照时,3个处理组间体质量变异系数差异减小。但在84 d时,SW3组体质量变异系数显著高于其他组（P〈0.05）。随着养殖规格的增大,血红蛋白浓度升高,红细胞数目增加,说明鱼体需氧量增加。SW3组白细胞数目、淋巴细胞数目和中性粒细胞数目最高,表明鱼体抗病能力强。红细胞数目在SW1和SW2组间无显著差异（P〉0.05）,但均显著高于SW3组（P〈0.05）。血栓细胞数目随着放养规格的增加而下降,且在3个规格组之间差异显著（P〈0.05）。中性粒细胞数目在3个规格组之间并没有显著性差异（P〉0.05）。SW2组总蛋白、白蛋白含量最高,且各组间差异显著（P〈0.05）。总胆固醇、甘油三酯浓度随鱼体规格增大而增加（P〈0.05）,表明大西洋鲑血液和体内对能量的利用增强。SW2组代谢产物尿酸、尿素浓度最高,且SW1、SW2组的浓度值均显著高于SW3组（P〈0.05）。SW3组大西洋鲑血清中总胆红素显著高于其他两组（P〈0.05）。各组间大西洋鲑血清中葡萄糖浓度没有显著性差异（P〉0.05）。SW3组肌酸激酶浓度最高,但各组间没有显著性差异（P〉0.05）。该研究结果建议选择体质量（24.27±1.59）g的大西洋鲑开始银化,利于优化养殖条件、以较低成本增加单位水体养殖产量和苗种规模化生产。

Atlantic salmon Salmo salar L. juveniles with various initial body weight of （30.25±2.12） g （SW1 group）, （24.27g±1.59）g （SW2 group）, （18.05±2.46）g （SW3 group） were reared in a recirculating system under a photoperiod of 12：12 light： dark in 1-42 days and 24 light： 00 dark in 43-84 days to evaluate the effects of size on growth performance and mechanism of physiological response during smoltification. The results showed that the maximal condition factor, daily weight gain, food conversion efficiency, and net yield were found in SW2, with significant difference in different experimental groups （P〈0.05）. There were significantly higher special growth rate in body length and body weight in SW2 than in other groups （P〈0.05）; and there were significant differences in coefficient of body length and body weight variation among the three groups （P〈0.05）. The CV of body length ofS. salar in the different groups did not significantly change in the first 6 weeks of the study. But when the condition was changed to full light the coefficient of variation of body length significantly increased in the SW1 and SW2 groups, and the change was more significant in group SW1 compared to the other groups （P〈0.05）. The CV of body weight of S. salar in group SW3 varied greatly over the course of the experiment. Within the first 6-week light cycle （12L：12D）, the coefficient of variation of body weight in SW1, SW2 showed insignificant difference （P〉0.05）. After the condition was changed to full light in the last 6 weeks, the coefficient of variation of body weight in 3 groups was narrowly varied. At 84 d, the value in the SW3 group was significantly higher than that in any other group （P〈0.05）. The hemoglobin concentration and the number of red blood cell （RBC） were found to be increased with the increase in size, indicating that the increase demand of oxygen for fish. The maximal white blood cell （WBC）, lymphocyte, neutrophils was found in SW3 group, which showed that enhanced their disease-resistant capability. The number of red blood cells did not differ significantly between groups SW1 and SW2 （P〉0.05）, but the value was significantly higher than that in group SW3 （P〈0.05）. The number of thrombocytes fell with the increase of culture size, and the three groups differed significantly （P〈0.05）.The number of neutrophil was close among these groups, and no significant difference was identified （/：＇〉0.05）. The highest values of total protein （TP） and albumin （ALB） appeared in SW2 group, and the difference of three groups were marked （P〈0.05）. The concentration of total cholesterol （TC） and triglycerides （TG） increased with the increase in size （P〈0.05）, which suggested that the enhancement of energy utilization in the blood and body. The concentration of uric acid and carbamide in metabolites was highest in group SW2. Their concentrations in groups SW1 and SW2 did not differ significantly （P〉0.05）, and they were significantly higher than those in group SW3 （P〈0.05）. The concentration of T-Bil in group SW3 was significantly higher than those in the other two groups （P〈0.05）.The concentration of glucose were no significant difference （P〉0.05）, which suggests that utilization rate of glucose by Salmo salar L. is lower. The concentration of CK was highest in group SW3, but no significant difference was identified among the three groups （P〉0.05）. So Salmo salar L. in 24.27±1.59g should be selected for the smoltification, thereby optimizing the culture condition and increasing the culture yield per water body at lower cost, which can theoretically referenced for the scale aquaculture ofSalmo salar L. seeds.