Effect of seawater entry date on 24-hour plasma sodium concentration and survival of juvenile spring chinook salmon (Oncorhynchus tshawytscha) reared in marine net-pens
Abstract
On seven dates during the summer and fall of 1987, stream-type chinook salmon juveniles (8-10 g average weight) were placed in marine net-pens with access to a low-salinity lens, to be tested for seawater tolerance. Overwinter survival averaged 72% (range 27-87%). Plasma concentrations of sodium for fish challenged to 30 ppt salinity (full-strength) seawater for 24 hours were above critical (170 mmol/l) on all but the late June challenge date. Plasma concentrations of sodium for fish challenged to 30 ppt salinity with access to a low-salinity lens were below critical for all dates tested. Survival to mid-May 1988 and overwinter mortality rate were not correlated with date of entry into the net-pens or with plasma sodium concentrations 24 hours after entry. The juvenile chinook salmon demonstrated the ability to acclimate, survive, and grow in an environment of predominantly full-strength seawater throughout most of the year when access to a low-salinity environment was provided. Culture of juvenile chinook salmon in marine net-pens with a low-salinity lens might be a useful rearing strategy for salmon hatcheries with access to suitable marine sites.
