Effects of chronic ammonia nitrogen stress on physiology and biochemistry indexes and hemocyanin gene expression of Litopenaeus vannamei

【Objective】To investigate the effects of chronic ammonia nitrogen stress on the physiology, biochemistry and expression of hemocyanin gene of Litopenaeus vannamei, clarify the toxic effect of ammonia nitrogen stress, and provide reference for farmers in the middle and late stage of healthy culture management of shrimp, and enrich the toxicological research data of L. vannamei at the same time.【Method】540 healthy L. vannamei with an average initial wet body weight of 9.92±0.24 g per shrimp were randomly divided into 6 groups, each group was set with 3 replicates, each of which was exposed to aerated tap water at different ammonia nitrogen concentrations(0, 4, 6, 8, 12 and 16 mg/L). Samples were taken at 16, 17, 18, 19 and 20 d to determine the contents of ammonia nitrogen, urea nitrogen and hemocyanin of L. vannamei, respectively. After the stress, the growth rate of body length, the rate of weight gain and the survival rate were counted. At the same time, the gill tissue and hepatopancreas were taken for paraffin section.【Result】From 16 to 20 d of chronic ammonia nitrogen stress, the survival rate, the growth rate of weight gain and body length of L. vannamei in each stress group decreased in turn with the increase of ammonia nitrogen concentration, and significantly lower than that of the control group(P<0.05, the same below). With the prolongation of ammonia nitrogen stress time, ammonia nitrogen and urea nitrogen in hemolymph of each stress group were higher than those of the control group, and the change trend of the two was basically consistent;the content of hemocyanin in each stress group was significantly lower than that of the control group, and the variation trend of hemocyanin content was negatively correlated with the concentration of ammonia nitrogen in water, the expression of hemocyanin gene was basically consistent with the change trend of hemocyanin content, which generally showed that the longer ammonia-nitrogen stress time was, the lower the relative expression level of hemocyanin gene was. After chronic ammonia nitrogen stress, the gill tissue and hepatopancreas of L. vannamei were seriously damaged, including gill filament swelling, nuclear pyknosis, increased blood lymphocytes, local vacuolation and incomplete structure, and large area of gill respiratory epithelial cells were exfoliated. Pancreatic ducts were enlarged with severe vacuolization, hepatic tubules were arranged disorderly, lumen was enlarged and the boundary was blurred, and broken cells and tissues could be observed in the space between the hepatic tubules and lumen.【Conclusion】Chronic ammonia nitrogen stress has a great inhibition on the growth and survival rate of L. vanname. It will increase the content of ammonia nitrogen and urea nitrogen in hemolymph, decrease the relative expression level of hemocyanin mRNA, block the synthesis of hemocyanin, and cause serious damage to gill and hepatopancreas. Respiratory dysfunction and hepatopancreas metabolic dysfunction caused by chronic ammo nianitrogen stress are the main causes of stress death of L. vannamei.