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

Abstract

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 18parts per thousand, 26parts per thousand, 34parts per thousand and 42parts per thousand. Arginase activity in the gill, midgut, hepatopancreas and muscle were higher and lower for the shrimp in 42 parts per thousand and 18 parts per thousand, respectively. Arginase specific activity of hemolymph was higher at 34 parts per thousand. 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 18parts per thousand, 26parts per thousand, 34parts per thousand and 42parts per thousand, respectively. Significantly higher levels of hernolymph urea and uric acid together with an increase in arginase activity indicated that ureogenesis and ureogenesis are activated for M. japonicus in hyperosmotic conditions. (C) 2002 Elsevier Science B.V. All rights reserved