Abstract: In order to explore the ammonia conversion and metabolic mechanism of Boleophthalmus pectinirostris exposed to environmental ammonia nitrogen stress,an acute ammonia nitrogen stress test（8 mmol/L NH₄Cl）in 72 h was conducted in this study. The protein concentration assay was used for detecting enzymes involved in ammonia metabolism,such as glutamine synthetase（GS）activity and blood ammonia levels. Enzyme-linked immunosorbent assay（ELISA）was employed to analyze the expression levels of ammonia metabolic cotransporter,carbonic anhydrase（CA）and sodium hydrogen exchange factor 3（Na⁺/H⁺ exchanger,NHE3）. Meanwhile,quantitative polymerase chain reaction（qPCR）was applied to check the relative expression levels of ammonia metabolism-related genes,such as GS,CA15,NHE,and ammonia transporter Rh type C-1（Rhcg1）. The results showed that under acute ammonia-nitrogen stress,the blood ammonia concentration of B. pectinirostris significantly increased at 12 h and then decreased to the steady level. The hepatic expression of GS gene significantly increased at 12 h and 48 h while its enzyme activity significantly increased at 24 h. The changing tendency of NHE3 protein expression in gill was the same as that of GS activity,while the levels of CA protein significantly increased at 12 h and 48 h,respectively,after stress. The expression levels of ammonia excretion related genes CA15,NHE and Rhcg1 were up-regulated under ammonia-nitrogen stress. The NHE gene was up-regulated earliest（24 h）while CA15and Rhcg1 significantly increased until 48 h,indicating that they participated in ionic ammonia excretion. In brief,under the ammonia-nitrogen stress,B. pectinirostris adopt two main ammonia excretion pathways：1）conversion of toxic ammonia into non-toxic glutamine by hepatic GS enzyme to avoid the excessive accumulation of ammonia in the body;2）facilitating the ammonia excretion through the Rhcg1 and NEH3 synergistically promoted by H⁺ provided by CA enzyme via the protonation of CO₂ in gills.

Key words: Boleophthalmus pectinirostris, acute ammonia-nitrogen stress, serum ammonia concentrations, ammonia metabolic genes