盐度变化对金钱鱼感染嗜水气单胞菌后血清及肾脏免疫状态的影响

季节性降雨和洋流运动常常使沿岸海水盐度呈现波动状态。环境盐度的改变往往导致鱼类更易受到病原的侵害而患病死亡。因此, 探究盐度对金钱鱼(Sscatophagus argus)免疫功能的影响在渔业养殖业具有相当重要的参考价值。本文通过比较各盐度组金钱鱼经嗜水气单胞菌(Aeromonas hydrophila)感染后96h(96hpi)内血清和肾脏抗氧化酶(superoxide dismutase, SOD)浓度以及免疫相关参数Complement 4(C4)、Interleukin-6(IL-6)和Immunoglobulin M(IgM)的变化, 来分析盐度的改变对其血清和肾脏免疫功能的影响。结果显示, 除96hpi外, 血液和肾脏组织中淡水组和低盐组中金钱鱼体内SOD浓度总体均比25‰盐度组高, 且最大差异可达150ng·mL^-1左右, 其中血清结果差异极显著(P<0.01); 淡水组与低盐组中金钱鱼经嗜水气单胞菌感染后96h内血清和肾脏组织C4浓度总体均比25‰盐度组高100~600μg·mL^-1 (P<0.01)左右; 虽然三个盐度感染嗜水气单胞菌后组肾脏组织IL-6浓度(14.2±0.1、17.9±0.0和17.9±0.0pg·mL^-1) 显著低于对照组(P<0.01), 25‰盐度组肾脏组织IL-6水平仍显著高于淡水组和低盐组(P<0.01), 而淡水组的血清IL-6浓度在96hpi内显著增加至56.9±1.0pg·mL^-1 (P<0.01); 25‰盐度组金钱鱼血清和肾脏组织IgM浓度(71.8±2.9和6.3±0.4μg·mL^-1)比淡水组和低盐组高约1~20μg·mL^-1, 且差异显著(P<0.05)。同时, 25‰盐度组血清和肾脏组织大量产生抗体IgM时间(12hpi)早于淡水组和低盐组(24hpi)。综上所述, 25‰盐度组在细菌感染后受到的损伤较小, 肾脏及血清免疫状态优于淡水组与低盐组, 且免疫应答反应更迅速。因此推测, 盐度的降低将会导致金钱鱼血清和肾脏免疫状态下降。本研究可为调节金钱鱼的养殖盐度提供参考。

Effects of salinity changes on serum and kidney immune status associated with injection of Aeromonas hydrophila in Scatophagus argus

The salinity in coastal waters fluctuates frequently due to seasonal rainfall and ocean currents. Salinity change makes fish more susceptible to pathogens, leading to disease and death. As the main lymphoid tissue of teleosts, kidney is closely related to fish’s immune function. This study aims to explore effects of environmental salinity on the kidney immune function of Scatophagus argus. In order to analyze the relationship between the change of environmental salinity and immune situation in fish’s kidney after Aeromonas hydrophila injection, we compared the changes of superoxide dismutase (SOD) concentration in serum and kidney, and immune-related parameters Complement 4 (C4), Interleukin-6 (IL-6), and Immunoglobulin M (IgM) concentrations in kidney before and after infection within 96 h of each salinity group. Our results show that except for 96 hpi, SOD concentrations in the serum and kidney tissues of the freshwater group and low-salinity (?‰) group were higher than those of the 25‰ salinity group (P<0.01), and that the maximum difference between low-salinity group and 25‰ salinity group was about 150 ng·mL^-1. The concentration of C4 in the serum and kidney of the freshwater group and low-salinity group was about 100-600 μg·mL^-1 higher than that of the 25‰ salinity group within 96 hpi (P<0.01). The concentration of IL-6 in the kidney tissues of S. argus in the 25‰ salinity group was higher than that in the freshwater group and low-salinity group (P<0.01), although IL-6 concentrations in kidney of the three groups were significantly lower than that of the control group (14.2±0.1 pg·mL^-1, in freshwater; 17.9±0.0 pg·mL^-1, in low-salinity; 17.9±0.0 pg·mL^-1, in 25‰ salinity) at 96 hpi (P<0.01), while the serum IL-6 concentration in the freshwater group was significantly increased to 56.9±1.0 pg·mL^-1 (P<0.01). The serum and kidney IgM levels of fish in the 25‰ salinity grop (71.8±2.9 μg·mL^-1 and 6.3±0.4 μg·mL^-1) were about 1-20 g·mL^-1 higher than those of the freshwater group and low-salinity group (P<0.05). The time of IgM production in serum and kidney tissues of the 25‰ salinity group (12 hpi) was earlier than that of the freshwater group and low-salinity group (24 hpi). In summary, the 25‰ salinity group suffered less damage after bacterial infection, and the immune status of kidney and serum was better than that of the freshwater group and low-salinity group; and the immune response was faster in the 25‰ salinity group. Therefore, we speculate that a decrease of salinity would lead to a decrease of kidney immune state of S. argus. This research provides a reference value for S. argus mariculture.