Salinity Effects on Post-Moribund Plasma Ion Fluctuation in Chinook Salmon

Seawater challenges can assess the osmoregulatory ability of juvenile anadromous salmonids to survive and grow in marine environments.  We tested the effects of tricaine mesylate (MS-222) baths of different salinity on blood plasma magnesium (Mg²⁺) and sodium (Na⁺) ions in seawater challenges, and the time course of post-euthanasia ion fluctuations. Salinity of the euthanasia bath affected both plasma Mg²⁺ and Na⁺ concentrations. Time spent in the bath affected plasma Mg²⁺ but not Na⁺ concentrations. Temporal trends in plasma Mg²⁺ and Na⁺ differed and suggested that Mg²⁺ may be a more sensitive indicator of physiological responses than plasma Na⁺ concentrations. When performing test where electrolytes are measured as end points, care needs to be taken relative to time after death and the salinity of the euthanasia bath.