Effects of chronic ammonia nitrogen stress on indexes related to ammonia metabolism and apoptosis in hepatopancreas of Litopenaeus vannamei

【Objective】 To study effects of chronic ammonia nitrogen stress on ammonia metabolism and apoptosis of Litopenaeus vannamei under three salinities, in order to provide reference for the study of immune mechanism and production of L. vannamei.【Method】 480 healthy L. vannamei with initial body mass of 6.49±0.14 g were randomly divided into 4 groups, 6 of which were exposed to 0 (control group), 0.9, 5.2 and 12.0 mg/L ammonia nitrogen. After 20 and 40 d of ammonia nitrogen stress, the body weight growth rate and survival rate of L. vannamei were calculated, and ammonia metabolism-related substances and enzyme activity, antioxidant-related enzyme activity and expression of apoptosisrelated genes in hemolymph and hepatopancreas of L. vannamei were determined. Meanwhile, the hepatopancreas were taken to make paraffin section and stained with Tunnel.【Result】 With the increase of ammonia nitrogen concentration, the growth rate and survival rate of body mass decreased, ammonia nitrogen and urea nitrogen in hemolymph and the indexes in 20 d were similar with those in 40 d;glutamate dehydrogenase(GDH) activity, glutamine synthetase(GS) activity and catalase(CAT) activity in hepatopancreas increased at 20 d, and decreased in 5.2 and 12.0 mg/L group at 40 d;total superoxide dismutase(T-SOD) activity of hepatopancreas was significantly lower in the 12 mg/L group than that in the control group(P<0.05, the same below);expression of Cyt C and Caspase-3 of hepatopancreas was significantly higher in the stress group than that in the control group. The results of TUNEL showed that the number of apoptotic cells increased with the increase of ammonia nitrogen concentration, and the number of apoptotic cells was higher at 40 d than that at 20 d.【Conclusion】 After chronic ammonia nitrogen stress, as ammonia nitrogen in environment spreads to hemolymph, with more and more ammonia nitrogen accumulated in hemolymph of L. vannamei, urea-nitrogen content increased, then the pathway of L-glutamine synthesis is inhibited, so ammonia metabolism is hindered. Here reactive oxygen species(ROS) stemmed from stress overwhelms regulation ability of antioxidant system, which poses damages to hepatopancreas, leading to apoptosis, causing negative impact to growth and survival of L. vannamei.