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

Abstract

Radioimmunoassay (RIA) procedures suitable for measuring L-thyroxine (T 4 ) and 3,5,3′-triiodo-L-thyronine (T 3 ) levels in 0.1 ml of rainbow trout plasma are described. Mean detection limits were 12.5 ng/100 ml (T 4 RIA) and 9.5 ng/100 ml (T 3 RIA); mean indices of precision were 0.056 (T 4 RIA) and 0.042 (T 3 RIA). Both 'within' and 'between' assay reproducibilities were satisfactory. Mean T 4 levels in two plasma pools from 2-year-old trout were 157 and 171 ng/100 ml; mean T 3 levels in two other plasma pools were 130 and 204 ng/100 ml.