The impact of triclosan exposure during the growth and development period on ovarian differentiation in female zebrafish and its mechanisms.

Triclosan (TCS), a common antimicrobial agent, has been identified as an environmental estrogenic compound. Our previous studies have demonstrated that post-embryonic exposure to TCS disrupts the reproductive endocrine system in male zebrafish. Given that estrogenic compounds may differentially affect gonadal development in male and female fish, this study aims to investigate reproductive toxicity of post-embryonic TCS exposure in female zebrafish from endocrine perspective. Zebrafish were exposed to TCS from fertilization until adulthood (120 day post-fertilization). We measured growth parameters, examined the expression of genes related to gonadal differentiation and determination, assessed vitellogenin (VTG) and sex hormone levels, and analyzed ovarian histology via hematoxylin-eosin (HE) staining, along with ovarian and brain transcriptome sequencing in female zebrafish. The results showed that TCS reduced body weight and ovarian index in female zebrafish while altering plasma VTG and sex hormone levels. High-concentration TCS upregulated the expression of wt1 and ff1d genes but downregulated cyp19a1b, fshβ, erα, and vtg2. Low-concentration TCS downregulated gata4 and upregulated gnrh2 genes. Gene Set Enrichment Analysis (GSEA) of transcriptome sequencing revealed that TCS affected biological processes related to germ cell development, steroid biosynthesis, and steroid hormone biosynthesis pathways in female zebrafish. HE staining analysis indicated that low-dose TCS decreased the percentages of primary oocytes, postovulatory follicles, and atretic follicles, whereas high-dose TCS increased these percentages. These findings suggest that low concentrations of TCS accelerate ovarian development in zebrafish, while high concentrations delay it. The abnormal ovarian development is associated with the estrogenic effects of TCS.