Role of free D- and L-alanine in the Japanese mitten crab Eriocheir japonicus to intracellular osmoregulation during downstream spawning migration

Changes of D- and L-alanine and other osmolytes were examined in the tissues and hemolymph of the Japanese mitten crab Eriocheir japonicus captured during the maturation in the river and during the course of spawning migration downstream. Only D- and L-alanine and inorganic ions increased significantly in muscle during the maturation in freshwater from July to October and during downstream migration to estuaries in October. Inorganic ions in muscle was the highest in estuaries. In the crabs captured in the sea, glycine and D- and L-alanine were largely elevated in place of the inorganic ions declined. No other free amino acid increased in the muscle of the sea specimens. In hemolymph, total amino acids comprised only 4-10% of total osmolytes and decreased with maturation and during migration. Hemolymph inorganic ions were the highest also in estuaries. These data suggest that, in addition to a role as osmolyte, D- and L-alanine in the tissues of this strong hyperosmoregulator play an important role in the adjustment of salinity tolerance prior to and during downstream migration toward the sea. (C) 1999 Published by Elsevier Science Inc. All rights reserved.