The ability of an aquatic organism to tolerate wide salinity variations without compromising life processes is termed euryhalinity. This capability requires physiological, biochemical and ecological adaptations. Strategies permitting euryhaline decapods to inhabit aquatic environments with variable salinities have been studied almost exclusively in adults. Although also larval stages have recently received an increasing attention, the salinity tolerance of embryonic stages has remained little known (1). Embryos, larvae and adults of the shrimp Palaemonetes argentinus tolerate a wide range of salinities (1-~25), but osmoregulatory capacities have been demonstrated only in post-embryonic developmental stages (2; 3). As in most other crustaceans, little has been known about osmoregulation during the embryonic phase.