Ontogeny of intracellular isosmotic regulation in the European lobster Homarus gammarus (L.)

Intracellular free amino acids were measured in the abdominal muscle of the three larval instars, postlarvae, and juveniles of the lobster Homarus gam marus, acclimated to seawater (35 parts per thousand) and to a dilute mediu m (22 parts per thousand), to study intracellular isosmotic regulation thro ughout the development of this species. Transfer to low salinity was follow ed by a highly significant drop of free amino acids level in all developmen tal stages. The main regulated amino acids were glycine, proline, and alani ne. The level of regulation of total free amino acids changed at metamorpho sis: the decrease in total free amino acids at low salinity was 46% in the three larval instars, but it was only 29% in postlarvae and 20% in juvenile s. These results suggest that free amino acids, mainly glycine, proline, an d alanine, are involved in intracellular isosmotic regulation in the lobste r, with different levels of involvement in pre- and postmetamorphic stages. The ontogenetic changes in intracellular isosmotic regulation are discusse d in relation to the changes in extracellular regulation (osmoregulation) i n the lobster.