Communications: Validation of a Solid-Phase Enzyme Immunoassay Technique for the Measure of Plasma Cortisol in Rainbow Trout

Abstract

A kit for a solid-phase enzyme immunoassay (SOPHEIA®) of cortisol in human sera was evaluated and validated for measuring cortisol in plasma of rainbow trout Oncorhynchus mykiss. The accuracy of the SOPHEIA was demonstrated by the recovery of exogenous cortisol concentrations of 25, 50, 100, and 250 ng/mL in charcoal-stripped fish plasma. The amounts (mean ± SE) recovered from triplicate samples were 29.9 ± 2.75, 47.5 ± 3.41, 101.7 ± 12.08, and 232.0 ± 11.06 ng/mL, respectively. The intra- and interassay coefficient of variation (CV = 100 × SD/mean) for cortisol levels in undisturbed fish (26.6 ± 1.18 ng/mL) were 14 and 10%, respectively. The intra- and interassay CV for elevated cortisol levels in stressed fish (330.8 ± 19.90 ng/mL) were 8 and 13%, respectively. Cross-reactivity determined for nine steroids in teleostean fish was negligible. Cortisol concentrations in serial dilutions of pooled fish plasma were parallel to the standard curve. Sensitivity (minimum detection limit) was 3.04 ng/mL. The SOPHEIA compared favorably to radioimmunoassay measurements of cortisol (r = 0.98; P < 0.001).