Effects of estradiol-17β on survival, growth performance, sex reversal and gonadal structure of bluegill sunfish Lepomis macrochirus

We systematically investigated the feminization of bluegill Lepomis macrochirus by oral administration of various doses of estradiol-17β (E 2 ) and evaluated their effects on the growth performance, production and gonadal structure of sex-reversed female bluegill at both sex ratio and histological levels. With positive control treatment, 30-day-old fry were fed with E 2 at 50, 100, 150 and 200 mg kg − 1 diet for 60 days. The survival of fish in the E 2 treated and control groups was not significantly different ( P > 0.05). The growth of the treated fish was significantly retarded during the period of treatment, while there was no side effect detected post-treatment and the retarded fish caught up during 120 days of culture after E 2 treatment. All the treated groups produced 100% monosex female populations based on the macroscopic shape of gonads, and there were no significant differences detected between any E 2 treatment and control group in the mean GSI of females during the spawning season from June to October ( P > 0.05). Histologically, 13.3% and 5.0% of the intersex fish were determined to come from the 50 and 100 mg kg − 1 E 2 treatment groups, respectively, with 6.9% and 4.1% of the gonadal area containing spermatocytes. Most of genotypical male fish treated with exogenous E 2 developed gonadal structures histologically indistinguishable from the gonads of females. This study suggests that 150 mg kg − 1 E 2 is the optimal dosage for feminization in bluegill, with 50 and 100 mg kg − 1 E 2 being sub-optimal and 200 mg kg − 1 E 2 being over-optimal.