Sex-specific vitellogenin production in immature rainbow trout

Vitellogenin (Vg) was measured in sexually immature rainbow trout (Oncorhynchus mykiss) exposed to 17β-estradiol (E₂ ) in the diet. Mixed-sex populations of trout aged 3, 6, 12, or 18 months were maintained separately and fed E₂ at 0.05 or 2.5 mg/kg for 7 d. Females fed E₂ at 0.05 mg/kg consistently produced three- to fourfold greater amounts of Vg than similarly aged males. Age- and sex-matched fish fed E₂ at 2.5 mg/kg produced equivalent amounts of Vg. Sex differences in Vg production were apparent only at a dose of E₂ (0.05 mg/kg) that results in submaximal Vg induction. Our results document the importance of considering the sex of juvenile fish when using Vg production as a marker of xenoestrogen exposure.