Osmotic and ionic regulation in embryos, alevins, and fry of the five species of Pacific salmon

Abstract

The physiological basis of the differences in the early life histories of pink (Oncorhynchus gorbuscha), chum (O. keta), coho (O. kisutch), chinook (O. tshawytschd), and sockeye (O. nerka) were examined.The LD₅₀ values indicated that the embryos and alevins of the five species are stenohaline; that coho, chinook, and sockeye fry are stenohaline; and that pink and chum fry are euryhaline. However, pink and chum embryos and alevins showed significantly greater salinity resistance and osmoregulatory ability than embryos and alevins of the other species. This ability of pink and chum alevins was correlated with better serum regulation of sodium and chloride. Similarly, pink and chum fry manifested better blood sodium and chloride regulation than coho, chinook, and sockeye fry.Osmotic and ionic blood concentrations indicated that the greater salinity resistance of chinook alevins and fry over coho and sockeye alevins and fry was due to high tissue tolerance.The five species of embryos and fry, taken as a group, have greater salinity resistance and osmoregulatory ability than the five species of alevins.