| Abstract: | Plasma corticosteroid concentrations were determined by competitive protein binding assay in coho salmon, Oncorhynchus kisutch, during smoltification. Between January and April plasma corticosteroid levels decreased from 8.6 to 3.5 ng/ml, but increased to 24.0 ng/ml by the end of May in smolts retained in fresh water. This nearly eightfold increase in corticosteroids occurred as plasma thyroxin levels declined. Thus plasma corticosteroids appear to be increasing during the period when coho salmon normally migrate to sea. |
