Abstract: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.
