Sex—specific vitellogenin production in immature rainbow trout

Vitellogenin (Vg) was measured in sexually immature rainbow trout ( Oncorhynchus mykiss ) exposed to 17β‐estradiol (E 2 ) in the diet. Mixed—sex populations of trout aged 3, 6, 12, or 18 months were maintained separately and fed E 2 at 0.05 or 2.5 mg/kg for 7 d. Females fed E 2 at 0.05 mg/kg consistently produced three‐ to fourfold greater amounts of Vg than similarly aged males. Age‐ and sex—matched fish fed E 2 at 2.5 mg/kg produced equivalent amounts of Vg. Sex differences in Vg production were apparent only at a dose of E 2 (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.