Changes in free amino acids in the hemolymph of giant freshwater prawn Macrobrachium rosenbergii exposed to varying salinities: relationship to osmoregulatory ability

Changes in free amino acids (FAA) in the hemolymph of the giant freshwater prawn, Macrobrachium rosenbergii, were examined in individuals exposed to v arying salinities for up to 1 week. In freshwater and under conditions of l ow salinity, total FAA concentrations were maintained between approximately 0.85 and 1 mM and did not exhibit changes in response to salinity exposure . Under high salinities, total FAA concentrations increased dramatically, r eaching up to 2.1 mM depending on treatment. Examination of individual amin o acid concentrations revealed that these increases were based on specific changes in glycine, arginine, alanine, proline and lysine. Among these, ala nine showed the greatest increases, resulting in levels six-fold higher und er high salinity than in freshwater and under low salinity. The other amino acid species showed increases of 2.5-fold compared to original values. The se five FAAs in freshwater and under low salinity together occupied approxi mately 45% of total FAA contents and under high salinity comprised more tha n 70% of total FAA contents. These results suggest that specific hemolymph FAAs are involved in mediating response to salinity exposure in freshwater prawns. (C) 2001 Elsevier Science Inc. All rights reserved.