Potassium, sodium, magnesium and calcium contents of Chinook salmon tissues during various stages of the life cycle

1. 1. The potassium, sodium, magnesium and calcium contents of plasma, red cells, brain, heart, muscle, liver, kidney and gills have been measured in Chinook salmon ( Oncorhynchus tshawytscha) during four stages of the life cycle: (1) while juveniles in fresh water, (2) after 2 weeks in seawater, (3) as mature adults in the ocean, and (4) after 3–4 months of fasting at the spawning grounds. 2. 2. Although plasma cation concentrations changed with each alteration in ionic environment, a remarkable constancy of cellular cation composition is maintained except for the juveniles in seawater. 3. 3. The normal potassium/nitrogen ratio in the muscle of spawning salmon is inconsistent with the hypothesis that pathological hyperadrenocorticism occurs at this stage.