Arginase specific activity and nitrogenous excretion of Penaeus japonicus exposed to elevated ambient ammonia

Abstract

Mass-specific activity of arginase and nitrogenous excretion of Penaeus japonicus Bate (10.3 +/- 3.7 g) were measured for shrimps exposed to 0.029 (control), 1.007 and 10.054 mg l(-1) ammonia-N at 32 parts per thousand S for 24 h. Arginase specific activity of gill, hepatopancreas and midgut increased directly with ambient ammonia-N, whereas arginase specific activity of muscle was inversely related to ambient ammonia-N. Excretion of total-N (total nitrogen), organic-N and urea-N increased, whereas excretion of ammonia-N, nitrate-N and nitrite-N decreased significantly with an increase of ambient ammonia-N. In the control solution, P. japonicus excreted 68.94% ammonia-N, 25.39% organic-N and 2.87% urea-N. For the shrimps exposed to 10 mg l(-1) ammonia-N, ammonia-N uptake occurred, and the contribution of organic-N and urea-N excretion increased to 90.57 and 8.78%, respectively, of total-N. High levels of arginase specific activity in the gill, midgut and hepatopancreas suggest that there is an alternative route of nitrogenous waste for P. japonicus under ammonia exposure.