Effects of Ambient Ammonia‐Nitrogen Exposure on Uric Acid and Urea Metabolic Pathways and Tissue Distribution in the Swimming Crab Portunus trituberculatus

Abstract

AbstractAmmonia‐nitrogen (ammonia‐N) is an important threat factor to the development of the crustacean breeding industry; however, information on nitrogen metabolism remains limited. In this study, effects of ammonia‐N on the metabolic pathways and tissue distribution of nitrogenous wastes were investigated in swimming crabs Portunus trituberculatus. The results showed that ammonia content in the hemolymph of crabs exposed to 1‐ and 5‐mg/L NH4Cl (ammonia‐N concentrations were 1.36 and 5.31 mg/L, respectively) significantly (P < 0.05) increased with time. The expression of xanthine oxidase was significantly up‐regulated in gills and muscles but was significantly down‐regulated in the hepatopancreas of crabs exposed to 1‐ and 5‐mg/L NH4Cl after 6–12 h. The expression of uricase was significantly up‐regulated in gills and muscles at 3 h, whereas it was significantly down‐regulated in hepatopancreas during 6–12 h but up‐regulated again after 24 h. Moreover, the expression levels of carbamoyl phosphate synthetase III and arginase were significantly up‐regulated in gills and muscles but significantly down‐regulated in the hepatopancreas of crabs exposed to 5‐mg/L NH4Cl after 6–12 h. Furthermore, under 5‐mg/L NH4Cl stress, trace amounts of uric acid were detected, which significantly increased in hepatopancreas and hemolymph at 3 h, in muscles at 6–12 h, and in gills at 6–24 h. In addition, similar to hemolymph ammonia, urea was also significantly increased after NH4Cl exposure. Moreover, uric acid was mainly stored in muscles and urea was primarily synthesized in the hepatopancreas. This study provides a theoretical basis for further study on the nitrogen metabolism mechanism in crustaceans.