Gonadal Transcriptomic Atlas Reveals Conserved and Sex-Biased Regulatory Networks in Black-Spotted Croaker (Protonibea diacanthus).

The black-spotted croaker (Protonibea diacanthus) is a commercially important marine fish, in which males possess swimbladders of superior market value. To establish a molecular foundation for all-male breeding, this study presents the first comprehensive gonadal transcriptomic analysis of this species. RNA sequencing of ovary and testis identified 8,251 sex-biased differentially expressed genes. Functional enrichment analyses revealed their significant involvement in key reproductive pathways, including ovarian steroidogenesis and oocyte meiosis. Our analysis validated the sexually dimorphic expression of conserved sex-related genes. Testis-biased expression was confirmed for regulators and enzymes including dmrt1, amh, sox9, sycp3, and genes in the androgen synthesis pathway (star, cyp11a1, cyp11c1, hsd3b1). Conversely, ovary-biased expression was observed for pivotal female development genes such as cyp19a1a, foxl2, hsd17b1, gdf9, and bmp15. Protein-protein interaction network analysis further identified Dmrt1 and Cyp19a1a as central hubs within the sex-regulatory network. These findings provide a foundational transcriptomic atlas and identify candidate genes for future functional studies aimed at all-male production, but substantial downstream validation is still required to enhance the commercial production of P. diacanthus.