Induction of gonadal intersex in genotypic male rainbow trout (Oncorhynchus mykiss) embryos following immersion in estradiol-17 beta

This investigation was conducted to determine the initial period of gonadal sensitivity to estrogen in genetically male rainbow trout (Oncorhynchus my kiss). Fish were immersed in approximately 250 mu g estradiol-17 beta (E-2) /l for two 2 hr periods during different stages of embryonic development be ginning 30 days postfertilization (DPF) and continuing until 68 DPF. Histol ogical analysis of gonad samples indicated a significant proportion of E-2- treated fish had intersex gonads; these gonads were primarily comprised of testicular tissue with one or more oocytes scattered throughout. The most s ensitive period for altering normal testicular development was found to occ ur between 44 and 51 DPF (63% intersex), while the labile period in general was determined to span 24 days (from 30 to 54 DPF). Additionally, quantita tive RT-PCR was used to measure estrogen receptor (ER) mRNA expression in w hole individual untreated embryos at six weekly time points throughout the period of E-2-exposure. Although the intersex condition was not observed th roughout the entire E-2-exposure period, ER mRNA was detected at each time point assayed. (C) 2000 Wiley-Liss, Inc.