Histological observations and transcriptome analyses reveal the gonadal changes in blotched snakehead (Channa maculata) during sex reversal induced by 17β-estradiol

Blotched snakehead ( Channa maculata ) exhibits pronounced sexual dimorphism, with males demonstrating superior growth rates and larger body sizes than females, rendering all-male aquaculture populations economically and ecologically advantageous. However, the histological characteristics during E 2 -induced sex reversal and the transcriptional regulation following hormonal treatment remain insufficiently explored. This study combined histological and transcriptomic analyses to investigate gonadal development and gene expression dynamics during 17β-estradiol (E 2 )-induced feminization of XY-genotype C. maculata . By 20 days post-fertilization (dpf), both E 2- treated groups displayed paired primordial gonads with undifferentiated germ and somatic cells. Initial signs of ovarian differentiation (e.g., oogonia and ovarian cavity) emerged in the 60 mg/kg E 2 -treated group at 30 dpf, whereas the 30 mg/kg group remained undifferentiated, demonstrating dose-dependent acceleration of gonadal development. Subsequent histological analysis confirmed that dietary administration of 30 mg/kg or 60 mg/kg E 2 from 15 to 45 dpf successfully induced sex reversal in XY-genotype individuals. The 30 mg/kg E 2 -treated group achieved a 70 % sex reversal rate, with gonads developing into functional ovaries. In contrast, although the 60 mg/kg E 2 -treated group exhibited accelerated feminization, this dosage concurrently induced gonadal degeneration in a subset of individuals, resulting in a significantly lower final reversal rate of 50 %. Transcriptome profiling identified E 2 -mediated up-regulation of oocyte development-associated genes ( bmp15 , dnd1 , pat12 , nanos3 , gdf9 , ybx2 , zar1 , figla , and zp3 ) and significant down-regulation of male-related genes ( amh , amhr2 , dmrt1 , cyp17a1/2 , cyp11a1 , cyp11b , hsd11b2 , hsd17b3 , gsdf , inha , inhbba , tgfb3a , smad1/6b/9 , bmpr1bb , and bmpr2 ) in ovaries from XY neofemales. qPCR validation of eight randomly selected differentially expressed genes (DEGs) corroborated transcriptomic findings, confirming data reliability. Functional enrichment analysis further implicated E 2 in modulating gonadal development and sex differentiation through key pathways, including the TGF-β signaling pathway, Wnt signaling pathway, and steroid hormone biosynthesis. By integrating histological and transcriptomic data, this study elucidates the molecular and developmental basis of E2-induced feminization in C. maculata , offering critical insights for advancing sex control strategies in this commercially significant species. • E2 successfully induced sex reversal in blotched snakehead. • 30 mg/kg E2 induced complete ovarian development in 70 % of genotypic XY individuals. • Oocyte-associated genes were up-regulated, testis-associated genes were down-regulated after E2 induction. • TGF-β, Wnt, and steroid biosynthesis pathways play crucial roles in E2-induced gonadal transformation