Effects of high-salt stress on daily weight gain, osmoregulation and immune related enzyme activities in Litopenaeus vannamei postlarvae

In order to investigate salt tolerance and immune response under high-salt stress in postlarvae of Litopenaeus vannamei, a 30-day feeding trial was conducted with different high-salt stress (40, 50, 60, 65 and 30 as CK). Body weight were detected at the start and end of the trial to get average daily gain, and the activities of T-ATPase, Na⁺-K⁺-ATPase, ACP, AKP, SOD, CAT, LZM and MDA were detected at the end of the trial. The results showed that high-salt stress significantly inhibited average daily gain of postlarvae. The average daily gain showed decreasing trend with the increase of salinity, those of salinity 40, 50, 60, 65 were 84.53%, 60.99%, 46.19% and 27.71% compared with 30, respectively; Survival rate decreased significantly as salinity increased. The T-ATPase activity of postlarvae showed a tendency to decrease first and then stabilize at about 1.4 U/mg prot with salinity increasing. However, the change trend of Na⁺-K⁺-ATPase activity was opposite to T-ATPase activity. When salinity was 60 and 65, the activity of Na⁺-K⁺-ATPase was stable. In addition, high-salt stress also significantly affected the activities of non-specific immunity enzymes of L.vannamei postlarvae. With the increase of salinity, the enzymes activities of T-SOD and CAT had the same trend, rising first and decreasing then. Their highest values, 16.118 U/mg prot and 1.378 U/mg prot respectively, were detected at the salinity of 50. The changes of ACP and AKP activities were positively correlated with salinity. Under different salt stress treatments, the content of MDA changed significantly, and LZM content did not significantly change at all salinity levels. The result indicated that the higher salinity, the slower the growth rate and the increase of the energy for osmotic regulation of L.vannamei postlarvae. In a certain salinity range, high-salt stress can stimulate some non-specific immunity enzymes to cope with the salt stress environment and reduce the damage to the body.