Hemolymph ammonia, urea and uric acid levels and nitrogenous excretion of Marsupenaeus japonicus at different salinity levels

Arginase specific activity, hemolymph ammonia, urea and uric acid levels and nitrogenous excretion were measured in Kuruma shrimp Marsupenaeus japonicus (7.29±1.16 g) acclimated to different salinities of 18‰, 26‰, 34‰ and 42‰. Arginase activity in the gill, midgut, hepatopancreas and muscle were higher and lower for the shrimp in 42‰ and 18‰, respectively. Arginase specific activity of hemolymph was higher at 34‰. Hemolymph ammonia, urea and uric acid increased directly with salinity, and excretions of total nitrogen (total-N), organic nitrogen (organic-N) and urea-N increased directly with salinity. However, ammonia-N excretion and nitrite-N excretion were inversely related to salinity. Ammonia-N accounted for 90.9%, 75.0%, 67.9% and 38.5% of total-N, whereas urea-N accounted for 3.1%, 4.5%, 7.9% and 10.9%, and organic accounted for 4.2%, 19.8%, 23.1% and 50.4% of total-N excreted by the shrimp in 18‰, 26‰, 34‰ and 42‰, respectively. Significantly higher levels of hemolymph urea and uric acid together with an increase in arginase activity indicated that ureogenesis and uricogenesis are activated for M. japonicus in hyperosmotic conditions.