Stenohaline
Stenohaline is the name given to those aquatic organisms (usually fish) that are only capable of living in a narrow range of salt concentrations. It cannot tolerate a wide fluctuation in the salinity of the water. Stenohaline is derived from the words: "steno", meaning narrow, and "halino", which means salt. Many freshwater fish, such as goldfish (Carassius auratus), tend to be stenohaline and die in high-salinity environments such as the ocean. Many marine fish, such as haddock (Melanogrammus aeglefinus), are also stenohaline and die in waters with lower salinity.
Alternatively, fish living in coastal estuaries and tidal pools are often euryhaline (tolerant of changes in salinity, as opposed to stenohaline), as are many species that have a life cycle that requires tolerance freshwater and seawater, such as salmon (Salmo) and herring (Clupea).