盐度胁迫对尼罗罗非鱼免疫相关指标的影响

为探究盐度胁迫对尼罗罗非鱼免疫的影响，对体质量(35.0±5.0) g的尼罗罗非鱼进行了急性和慢性的盐度胁迫实验，对免疫相关指标进行了检测和分析。在急性盐度胁迫中，设置0、5和15盐度组，分别在胁迫后6、12、24、48和96 h进行取样，检测血清SOD、CAT、GSH-Px和AKP的活性。在慢性实验中，设置0、10、20和30盐度组，胁迫8周后检测血清SOD、CAT、GSH-Px和AKP活性，并进行了无乳链球菌易感性实验。结果显示：①血清中SOD活性在急性盐度胁迫6、12和24 h时都有随盐度上升而上升的趋势，但在96 h时盐度15组酶活性显著低于盐度5组；在慢性盐度胁迫下，各组的酶活性呈现出随着盐度升高而显著性下降的趋势。②血清CAT活性在急性盐度胁迫下12和24 h时呈现出随着盐度升高而显著下降的趋势；在慢性胁迫下不存在显著性差异。③血清中GSH-Px活性在急性和慢性胁迫后，均呈现随着盐度升高而降低的趋势。④血清AKP活性在胁迫后6 h随盐度升高呈现出显著下降趋势；在慢性盐度胁迫下，盐度20组显著低于其他实验组。⑤尼罗罗非鱼对无乳链球菌易感性实验中，盐度10组的易感性和盐度0组之间无显著差异，盐度20和30组的易感性高于盐度0组。研究表明，两种盐度胁迫均会引起免疫相关指标的变化，急性盐度胁迫实验表明，盐度5和15可导致尼罗罗非鱼机体氧化损伤，但尼罗罗非鱼可以逐渐适应这一变化；慢性盐度胁迫实验表明，盐度高于20会抑制尼罗罗非鱼多种免疫指标活性，造成其对无乳链球菌的易感性升高。

Effects of salinity stress on immune-related parameters of the Nile tilapia (Oreochromis niloticus)

In order to explore the effects of salinity stress on the immunity of the Nile tilapia (Oreochromis niloticus), we conducted acute and chronic salinity stress experiments on tilapia with body weight of (35±5) g and some immune-related parameters of the serum were tested. In acute salinity stress, the salinities of 0, 5 and 15 were set, and the enzyme activities of SOD, CAT, GSH-Px and AKP in serum were detected by sampling at 6, 12, 24, 48 and 96 h after stress respectively. In the chronic experiment, four salinity levels of 0, 10, 20 and 30 were set, and the enzyme activity of SOD, CAT, GSH-Px and AKP in serum was detected after 8 weeks of stress. The results showed that: SOD activity in serum increased with salinity at 6, 12 and 24 h under acute salinity stress, but at 96 h, enzyme activity in the salinity 15 group was significantly lower than that in 5 group. Under chronic salinity stress, the enzyme activity of each group decreased significantly with the increase of salinity. CAT activity in serum decreased significantly with the increase of salinity at 12 h and 24 h under acute salinity stress, and there was no significant difference after that. GSH-Px activity in serum decreased significantly with the increase of salinity at 6, 12 and 48 h after stress. AKP activity in serum significantly decreased with the increase of salinity at 6h after stress. Under chronic stress, the 20 group was significantly lower than the other groups. In the experiment of susceptibility to Streptococcus agalatiae after chronic stress, the susceptibility of the salinity 10 group to S. agalatiae had no obvious difference compared with 0, the susceptibility of 20 and 30 groups were higher than 0 group. This study showed that both kinds of stress could cause changes in immune-related indicators: acute salinity stress experiment showed that the salinities of 5 and 15 caused oxidative damage to the tilapia, but tilapia could gradually adapt to this change. Chronic salinity stress experiment showed that salinity above 20 could inhibit the activity of many immune indicators of tilapia, resulting in increased susceptibility to S. agalatiae.