Variations de la teneur en acides aminés libres et de l'excrétion ammoniacale chez les post-larves de Penaeus japonicus en fonction de la salinité et des chocs osmotiques

Body free amino acids (FAA) content and ammonia excretion have been measured on the one hand in post-larvae of Penaeus japonicus acclimatized in six water salinities and, on the other hand, in post-larvae after an osmotic stress. Various tested salinities were: 44, 38, 32, 26, 20 and 14‰. When environmental salinity changes, body moisture is not very much affected. However, FAA content and ammonia excretion exhibit large variations. Lowering water salinity from 44 to 14‰. induces an increase of ammonia excretion from 2.3 to 3.5 μatg N/g liver wt/h and a decrease of FAA content from 283 to 204.5 μmol/g live wt. Ammonia excretion is at a maximum at 26‰. (3.7 μatg N/g liver wt/h). FAA content is at a minium at 26‰. (183.7 μmol/g live wt). Modest changes of ammonia excretion and FAA content observed between 26 and 14‰. lead to the hypothesis of a main role played by FAA in osmotic regulation for a salinity range between 44 and 26‰. Intracellular osmotic regulation is effective 8 h after an hyposmotic stress from 44 to 14‰, but does not seem to be realized 24 h after an hyperosmotic stress (14–44‰.). Among analysed amino acids, main variations are registered for glycine, alanine, glutamine and asparagine.