The prawn Palaemonetes argentinus inhabits freshwater streams, lakes and brackish coastal lagoons in the warm temperate regions of eastern South America. Although this prawn has been characterized as a freshwater species its reproduction and development are feasible in a wide range of salinities (~20 ).Up to this moment, we know that larvae exhibit well developed osmorregulatory capacities already from hatching. Nevertheless, the knowledge about the effects of salinity on embryonic development is scarce. Therefore, the goal of this investigation was to study the effects of salinity on the eggs and embryos of P. argentinus cultured in vitro.