Radioimmunoassay of cortisone in the adult Atlantic salmon, Salmo salar L.

A radioimmunoassay (RIA) was developed to measure cortisone in Atlantic salmon plasma. Diatomaceous earth microcolumn chromatography was used to separate the cortisone from other steroids. The RIA method following chromatography was validated by analyzing each of six samples of blood by double isotope derivative assay (DIDA) and RIA. The RIA gave significantly lower plasma cortisone concentrations (P less than 0.05) than the DIDA: the correlation coefficient was 0.84. Accuracy of the RIA was also demonstrated by addition of radioinert cortisone and measurement of increasing volumes of plasma. Specificity of the antisera was very good. Sensitivity of the RIA was 11 pg/RIA tube or 0.025 micrograms cortisone/dl plasma corrected for recovery and fraction assayed. Plasma cortisone concentrations in adult Atlantic salmon ranged from 2 to 26 micrograms/dl. The mean plasma cortisone concentration of salmon in fresh water was not significantly different from that in sea water. The mean cortisone/cortisol ratio in both adult and juvenile Atlantic salmon was between 1.40 and 1.92 indicating that cortisone and not cortisol may be the principal corticosteroid in Atlantic salmon.