Changes in Body Chloride, Density, and Water Content of Chum (Oncorhynchus keta) and Coho (O. kisutch) Salmon Fry when Transferred from Fresh Water to Sea Water

Abstract

Changes in body chloride, density and water content of chum and coho salmon fry were measured when these fish were transferred from fresh water to sea water, and the reverse. Both species tolerated 50% sea water (8–9‰ Cl). Chum fry survived direct transfer from fresh water to sea water (15–17‰ Cl), but showed a marked increase in body chloride during the first 12 hours, followed by a return to the normal range between 12 and 24 hours. Coho, however, died within the first 36 hours, after a 60% increase in chloride. Coho fry lost more water than chum fry after introduction to sea water. The density of both species approximated that of the water within an hour of transfer to the new medium. When returned to fresh water after 12 hours in sea water the body chloride, density, and water content of both species regained normal levels within 10 hours. Chum salmon go to sea as fry, whereas cohos remain in fresh water a year or more. Although coho fry seem capable of some adjustment to sea water after a preliminary period in 50% sea water, permanent acclimatization could not be demonstrated under the experimental conditions.