Radioimmunoassays, combined with thin-layer chromatography, have been used to test for the presence of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one, 17 alpha,20 beta,21-trihy-droxy-4-pregnen-3-one, and 20 beta-hydroxy-4-pregnen-3-one, and for the presence of their 5-pregnene and 5 alpha-pregnane analogs, in the blood and ovarian incubation media of maturing/ovulating female rainbow trout (Salmo gairdneri). All of these steroids have previously been shown to be more or less equipotent in in vitro oocyte final maturation assays. Only two steroids were found: 17 alpha,20 beta-dihydroxy-4-pregnen-3-one, the presence of which has already been firmly established, and 17 alpha,20 beta, 21-trihydroxy-4-pregnen-3-one, which has not been previously identified in rainbow trout. The amounts of 17 alpha,20 beta, 21-trihydroxy-4-pregnen-3-one found in vivo and in vitro were, however, only 1-1.5% of those of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one, and therefore seem unlikely to play a significant role in the induction of oocyte final maturation.

http://www.ncbi.nlm.nih.gov/pubmed/2737457?dopt=Abstract