Measurement of L-thyroxine and 3,5,3′-triiodo-L-thyronine levels in fish plasma by radioimmunoassay

Abstract

Radioimmunoassay (RIA) procedures suitable for measuring L-thyroxine (T4) and 3,5,3′-triiodo-L-thyronine (T3) levels in 0.1 ml of rainbow trout plasma are described. Mean detection limits were 12.5 ng/100 ml (T4 RIA) and 9.5 ng/100 ml (T3 RIA); mean indices of precision were 0.056 (T4 RIA) and 0.042 (T3 RIA). Both 'within' and 'between' assay reproducibilities were satisfactory. Mean T4 levels in two plasma pools from 2-year-old trout were 157 and 171 ng/100 ml; mean T3 levels in two other plasma pools were 130 and 204 ng/100 ml.