The feminization of the protandric teleost Centropomus undecimalis was evaluated under contrasting salinity conditions using 17β-estradiol (E2) administered orally to juveniles and via implants to adults. Two factorial experiments were designed to assess the hormonal effect on histological, hormonal, molecular, and zootechnical indicators. A 100% feminization rate was achieved in both life stages, confirmed by histological analysis and the expression of female sex- and reproduction-related genes (foxl2a, cyp19a1a, zar1l, ddx5, and H2A), particularly in marine environments. Hormonal assays showed increased plasma vitellogenin and decreased 11-ketotestosterone in treated groups, indicating suppression of male endocrine pathways. Zootechnical performance was not significantly affected in adults, but juveniles reared in freshwater exhibited better feed conversion and protein efficiency, likely due to lower osmoregulatory demands. These findings demonstrate that E2-induced feminization is highly effective in C. undecimalis across different salinities, with improved physiological outcomes in freshwater conditions. This study provides valuable insight into the reproductive manipulation of a commercially important species and supporting its sustainable aquaculture.