Changes of protein-bound and free amino acids in the muscle of the freshwater prawn Macrobrachium nipponense in different salinities

Growth, hemolymph osmolality, tissue water, ribonucleic acid (RNA)/deoxyribonucleic acid (DNA) ratio, protein-bound amino acids and free amino acids (FAA) of Macrobrachium nipponense were investigated, after they were acclimated to 0 parts per thousand, 7 parts per thousand, 14 parts per thousand and 20 parts per thousand for 14 days. Growth was significantly (P<0.05) influenced by salinity. The highest weight gain of prawns (P<0.05) was achieved at a salinity of 14 parts per thousand. The RNA/DNA ratio, total protein-bound amino acid (TAA) and FAA concentrations in the muscle of prawns increased by hyperosmotic stress. The osmolality of prawns haemolymph increased slightly in salinities from 0 parts per thousand to 14 parts per thousand. A sharp increase in haemolymph osmotic concentration occurs between 14 parts per thousand and 21 parts per thousand, the isosmotic point being reached at 15 parts per thousand (450 mOsm). It is noted that the relationship of total FAA concentration in muscle and salinity in the range of 0-20 parts per thousand revealed a positive linear correlation. The correlation coefficient (R-2) is 0.98. During adaptation, the FAA pool (mainly glycine, alanine and proline) of muscle seems to be directly related to osmoregulation, while the percentage change in alanine in prawns transferred from freshwater to diluted seawater (20 parts per thousand) was most pronounced (116 % approx.). These results are compared with those of M rosenbergii. (C) 2004 Elsevier B.V. All rights reserved.