Effects of chronic salinity and nitrite nitrogen stress on growth, antioxidation and immunity of Litopenaeus vannamei

【Objective】The aim was to analyze the effects of chronic salinity and nitrite nitrogen stress on the growth, antioxidation and immunity of Litopenaeus vannamei, and to investigate the regulatory mechanisms of L. vannamei in response to environmental stress, which could provide a theoretical basis for its healthy culture. 【Method】L. vannamei(average body length 5.20±0.67 cm,average body weight 2.01±0.73 g) were used as the test material, a two-factor experiment was designed with salinity being 0.5‰,1.0‰,3.0‰,and nitrite nitrogen concentrations being 0.07,0.20,0.50,1.50,4.00,10.90 mg/L. A total of 18 treatment groups were carried out for 30 d stress test. The growth performance indexes, enzyme activities of hepatopancreas and gill tissues and relative expression of antioxidant and immune related genes were measured and TUNEL assay was performed. 【Result】Under the same salinity, survival rate,daily growth value of body length,and daily growth value of body weight of L. vannamei all showed an overall decreasing trend with the increase of nitrite nitrogen concentration,under the same nitrite nitrogen concentration, they showed general upward trend with increasing salinity. The total antioxidant capacity(T-AOC),catalase(CAT),and glutathione peroxidase(GPx) in hepatopancreas and gill tissues,as well as the relative expressions of manganese-type superoxide dismutase gene(Mn-sod),CAT gene,GPx gene,cytochrome oxidase gene(CytC), apoptosis factor Caspase-3 gene(CASP3),and antimicrobial peptide gene(Crustin) showed an increasing trend and then a decreasing trend with the increase of nitrite nitrogen concentration under the same salinity, and the showed an increasing trend with increasing salinity under the same nitrite nitrogen concentration. The results of TUNEL assay showed that the rate of L. vannamei hepatocyte apoptosis increased with increasing nitrite nitrogen concentration. The interaction between salinity and nitrite nitrogen did not significantly affect the survival rate,daily growth value of body length and daily growth value of body weight of L. vannamei(P>0.05),but had extremely significant effects on the activities of T-AOC,CAT and GPx in hepatopancreatic and gill tissues,as well as the relative expression of Mn-sod,CAT,GPx,CytC,CASP3 and Crustin(P<0.01). 【Conclusion】Antioxidant enzymes(CAT and GPx)and antioxidant and immune related genes(Mn-sod,CAT,GPx,CytC,CASP3 and Crustin)are involved in the response process of L. vannamei under salinity and nitrite nitrogen stress. Changes in salinity and nitrite nitrogen cause oxidative stress in L. vannamei. When the degree of stress is mild, the body responds to the harsh external environment by increasing the activity of antioxidant enzymes, up-regulating antioxidant and immune related genes. However, as the degree of stress is strengthened, the relative expression of enzymes and genes decreases, which induces apoptosis, causes damage to the hepatopancreas and gills, affects normal physiological functions, and ultimately leads to the death of L.vannamei.