Effects of Ammonia-N Stress on Digestive Enzyme Activities of Swimming Crab Portunus trituberculatus

To study the effects of ammonia-N stress on the activities of digestive enzymes in the midgut gland,stomach and intestine of Portunus trituberculatus,groups in different ammonia-N concentrations(0,1,5 and 20 mg·L-1) were setup in laboratory condition for comparison among the groups.Results showed that ammonia-N stress had significant effects on the activities of trypsin-like enzyme,pepsin,lipase and amylase(P0.05).The activities of trypsin-like enzyme and pepsin in the three digestive organs showed peak changes within 48 h,and trypsin-like enzyme recovered to the control level at 48 h;while pepsin related to the ammonia concentration positively in the midgut gland became stable from 24 h;pepsin in the stomach and intestine restored to the control level at 48 h and 24 h.The activity of lipase in the midgut gland and stomach also showed peak changes within 24 h,and lipase related to the ammonia concentration positively in the midgut gland became stable;while lipase in the stomach decreased gradually and returned to the control level at 48 h.The activity of amylase in the midgut gland and intestine decreased gradually within 12 h,reached the minimum which was related to the ammonia concentration negatively at 12 h and then kept stable;while amylase in the stomach increased firstly and then decreased.Moreover,ammonia-N stress induced the activities of pepsin and lipase in the midgut gland significantly and had a significant inhibition effect on the activity of amylase in the three digestive organs at 48 h.The present study suggested that the activities of pepsin and lipase in the midgut gland and amylase in the three digestive organs could be used as evaluation indexes for the abilities of digestion and absorption of the crabs during ammonia-N stress.