17α,20β-Dinydroxy-4-Pregnene-3-One Suppresses Plasma IgM Levels in Rainbow Trout (Oncorhynchus mykiss)

The relationships between 17α,20β-dihydroxy-4-pregnene-3-one (17α,20β-DP) and plasma IgM and total protein levels were investigated in rainbow trout,Oncorhynchus mykiss.IgM and total protein levels decreased in both sexes of mature rainbow trout when 17α,20β-DP levels increased during the spawning season,while the elevated 17α,20β-DP suppressed IgM levels and reversibly enhanced total protein concentrations in immature trout.This represents the first report of the effect of 17α,20β-DP on fish immunity.These data suggest that the increase of 17α,20β-DP in spawning season may be related to infectious skin diseases.