Effects of seawater acclimation on the levels of free D- and L-alanine and other osmolytes in the Japanese mitten crab Eriocheir japonicus

During artificial seawater acclimation in the laboratory of freshwater Japanese mitten crab Eriocheir japonicus, glycine and L-proline other than D- and L-alanine increased significantly in the muscle of the immature group, while no significant increase in glycine and L-proline was found in the mature group. Total inorganic ions in the muscle of the mature crabs increased significantly along with the salinity increments and reached the levels of estuarine specimens captured during downstream migration. In the immature group, inorganic ions also increased during salinity stress but the increase was far lower than those in the mature group. These data suggest that immature crabs cannot tolerate high ionic concentrations in muscle and have to increase glycine and L-proline during seawater acclimation. After adjustment of salinity tolerance, mature crabs incorporate inorganic ions in muscle and their cell volumes are likely regulated mainly by D- and L-alanine and inorganic ions. Hemolymph ion concentrations and osmolalities increased largely during seawater acclimation for both immature and mature crabs and reached the same levels as those for estuarine and sea specimens in the natural environment. These data suggest that no special adjustment of hemolymph osmoregulatory capability occurs along with the maturation.