Characterization of early gonadal differentiation and induction of sex reversal by 17β-estradiol in largemouth bass (Micropterus salmoides)

In this study, the development of early gonads in largemouth bass ( Micropterus salmoides ) was investigated through histological observations from 10 days post-hatching (dph) to 60 dph. The ovarian cavities in females were detected at 30 dph, while sperm ducts in males appeared at 50 dph. To induce feminization, largemouth bass fry were treated with 17β-estradiol (E2) via oral administration from 22 to 82 dph. Results showed that E2 concentrations of 2, 10, and 50 mg/kg in the diet effectively induced feminization in genotypic male, with 10 mg/kg identified as the optimal concentration for producing neo-females over a 60-day treatment period. Neo-females exhibited significantly slower growth rates compared to the control group but exhibited compensatory growth during the later stages. Higher E2 concentrations (50 mg/kg) led to reduced ovarian volume, diminished cavity structure, and fewer oocytes, while the ovaries of neo-females induced by 10 mg/kg E2 displayed structurally functional but developmentally delayed features. Notably, during later stages (360–600 dph), neo-females induced by 10 mg/kg E2 oral administration exhibited ovarian developmental impairment, evidenced by lower GSI values and delayed ovarian development compared to controls. These findings delineate critical periods for gonadal differentiation in largemouth bass and establish a reliable method for E2-induced feminization. This work provides insights into sex determination mechanisms and supports the development of YY males for all-male population production. • The timing and characteristics of sex differentiation in largemouth bass were determined. • A dietary treatment of 10 mg/kg 17β-estradiol for 60 days was the optimal condition for inducing feminization. • Neo-females displayed structurally functional ovaries but exhibited delayed developmental features.