Osmoregulation and fish transportation

Cellular osmoregulation constitutes a phylogenetically conserved set of highly complex responses to changes in external osmolality/tonicity to maintain cell volume, intracellular concentrations of macro- and micromolecules, protein structure and function, and genomic integrity. The successful establishment of the fish species in different habitats and environments depends on its ability to cope with salinity differences between internal (plasma) and external (water) environments through osmoregulation. Although osmoregulation in fishes is mediated by a suite of structures, including the gastrointestinal epithelium and kidney, the gill is the major site of ion movements that balance diffusional gains or losses. Sodium chloride has been used as a mean of stress reduction and increases survival during transportation of freshwater fish in order to balance with water gain and electrolytes losses. Net ionic losses in the urine and diffusional outflux across the gill are balanced by active uptake mechanisms in the gill epithelium plus any ionic gain from food.