不同浓度亚硝酸盐亚急性胁迫对凡纳滨对虾生长与免疫功能的影响

为阐明盐度为5条件下不同浓度亚硝酸盐亚急性胁迫对凡纳滨对虾(Litopenaeus vannamei)生长与免疫功能的影响，本研究设置5个亚硝酸盐浓度组(0.50、0.90、1.70、3.20和6.00 mg/L)和对照组(0.05 mg/L)，检测分析了亚硝酸盐胁迫40 d后凡纳滨对虾免疫相关酶活性、丙二醛(MDA)含量以及免疫和生长相关基因表达的变化。结果显示，凡纳滨对虾死亡率随亚硝酸盐浓度的增加而升高，6.00 mg/L浓度组体质量增长率(WGR)和体长增长率(LGR)均显著低于对照组(P<0.05)。部分浓度组亚硝酸盐对凡纳滨对虾肝胰腺和血清中的免疫相关酶活性具有一定的诱导作用。其中，当亚硝酸盐浓度高于0.50 mg/L时，肝胰腺超氧化物歧化酶(SOD)活性显著高于对照组(P<0.05)；0.50、0.90和1.70 mg/L浓度组的过氧化氢酶(CAT)活性显著高于对照组(P<0.05)；血清中CAT和SOD活性随亚硝酸盐浓度的增加均呈先降低后升高再降低的趋势；0.90 mg/L浓度组的肝胰腺和血清中酸性磷酸酶(ACP)和碱性磷酸酶(AKP)活性均显著高于对照组(P<0.05)。MDA含量变化无明显规律。此外，血清中谷丙转氨酶(GPT)活性显著升高(P<0.05)。实时荧光定量PCR结果显示，除0.50 mg/L浓度组外，其他浓度组的mn-sod和hsp70基因表达量显著升高(P<0.05)；各浓度组的cat、trx、tgase、trypsin和chitinase基因表达量显著低于对照组(P<0.05)。经亚硝酸盐胁迫40 d后，各浓度组凡纳滨对虾的生长和免疫功能均受到明显的阻遏作用。在盐度为5条件下，为确保凡纳滨对虾的健康养殖，亚硝酸盐浓度应控制在0.50 mg/L以内。

Changes in immune system and growth performance of Litopenaeus vannamei after 40-day challenge with different concentrations of nitrite

After 40 days of exposure to different concentrations of nitrate at a salinity of 5, the effect of nitrite on the immune system and growth performance of Litopenaeus vannamei was explored to provide a theoretical basis for constraining the effect of nitrite subacute stress on the species. Five nitrite concentration groups (0.50, 0.90, 1.70, 3.20, and 6.00 mg/L) and a control group (0.05 mg/L) were used in this experiment. Furthermore, we detected the activity of immune-related enzymes, malondialdehyde (MDA) content, and relative expression of immune- and growth-related genes. Results showed that the mortality rate of L. vannamei increased with an increasing nitrite concentration, and the weight gain rate (WGR) and length gain rate (LGR) in the 6.00 mg/L group were significantly lower than those in the control group (P<0.05). The activity of superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP), and alkaline phosphatase (AKP) in the serum and hepatopancreas increased under the influence of nitrite in 0.90 and 3.20 mg/L groups. The activity of SOD in the hepatopancreas was significantly higher than those in the control group when the concentration was higher than 0.50 mg/L (P<0.05). CAT activities in the 0.50, 0.90, and 1.70 mg/L groups were significantly higher than those in the control group. The activity of SOD and CAT in the serum first decreased, then increased, and then decreased again with an increasing concentration of nitrite. The activities of AKP and ACP in the serum and hepatopancreas in the 0.90 mg/L group were significantly higher than those in the control group (P<0.05). There was no obvious change in MDA content across groups. In addition, serum glutamic-pyruvic transaminase (GPT) activity was significantly higher in the serum than in the control group (P<0.05). The results of quantitative real-time PCR showed that the relative expression of mn-sod and hsp70 genes in the hepatopancreas was significantly higher than that in the control group, except in the 0.50 mg/L concentration group (P<0.05). The relative expression of cat, trx, tgase, trypsin, and chitinase genes in the hepatopancreas was significantly lower than that in the control group (P<0.05). After 40 days of challenge with different concentrations of nitrite, the growth and immune function of L. vannamei clearly diminished. The concentration of nitrite should be controlled below 0.50 mg/L in the production process at a salinity of 5 to ensure the healthy farming of L. vannamei.