Chronological Changes in Gonadotropin-Releasing Hormone 1, Gonadotropins, and Sex Steroid Hormones along the Brain–Pituitary–Gonadal Axis during Gonadal Sex Differentiation and Development in the Longtooth Grouper, Epinephelus bruneus

(1) Fshβ and Lhβ showed stronger signals and higher transcript levels from 590 to 1050 dph than at earlier stages, implying their active involvement during primary oocyte development. (2) Fshβ and Lhβ at lower levels were detected during the phases of ovarian differentiation and oogonial proliferation. (3) E(2) concentrations increased significantly at 174, 333, and 1435 dph, while T concentrations exhibited significant increases at 174 and 333 dph. These findings suggest potential correlations between serum E(2) concentrations and the phases of oogonial proliferation and pre-vitellogenesis.