Some aspects of osmotic and ionic regulation in Adriatic sturgeon Acipenser naccarii.: I:: Ontogenesis of salinity tolerance

The salinity tolerance of various early life stages (prelarvae, larvae and fry) of the Adriatic sturgeon (Acipenser naccarii) was investigated using acute exposures in a 96h-LC50 test. The results were compared with a series of parallel observations on the morphological development of the osmoregulatory organs. The highest salinities tolerated by prelarave and larvae were approximately iso-osmotic with sturgeon plasma. Once, however. the organs involved in homeostatic osmoregulatory mechanisms in the adult had developed (renal-branchial-gut system), the sturgeon was able to switch from hyperosmoregulation to hypo-osmoregulation. Nevertheless, at the most advanced age tested (150 days old), water at a salinity of approximately 20 parts per thousand appeared to be the upper threshold for tolerance of acute exposure by this species.