Salt Regulation in Fish and Prawns: Implications for Research and Management

The aquatic environment comprises a complex mixture of ions that can impose physiological challenges to fishes and crustaceans. In natural settings, changes in ionic environments occur in estuaries or are brought about by diadromous movements. In research and resource management an understanding of the capacity for osmo- and ionoregulation is critical for species management. In culture, manipulating saline environments is often attempted to increase growth and survival, reduce disease, and increase consumer palatability and acceptance of product. To understand the role of specific ions in osmo- and ionoregulation, several experiments were conducted using a euryhaline fish, the green sturgeon Acipenser medirostris, and a euryhaline crustacean, the giant freshwater prawn Macrobrachium rosenbergii. Both species were subjected to experiments with gradually increasing concentrations of different salt constituents, such as NaCl, KCl, CaCl₂, MgSO₄, artificial seawater mixes and a fresh water control.  Survival, circulating ionic concentrations and related enzyme activities were measured. Results indicate that certain salts are essential for ionic regulation and in the case of cultured crustaceans, may have an added benefit of improving flavor.