Estrogenic and androgenic effects in mosquitofish (Gambusia affinis) from streams contaminated by municipal effluent in Guangzhou, China

► We use mosquitofish to investigate the estrogenic and androgenic effects of municipal wastewaters contaminated stream system. ► We dissected and analyzed the anal fin, hemal spines characteristics and VTGa, ERa, ARa mRNA expression of mosquitofish. ► Increased VTGa mRNA expression in males, decreased VTGa mRNA expression in females were observed in samples from study sites. ► A significant correlation between hemal spine morphology index and gene expression relative to the reference site was proved. ► Mosquitofish were altered by discharged wastewater, as reflected in their morphological changes and relative gene expression. The study reported in this paper used mosquitofish to investigate the estrogenic and androgenic effects of municipal wastewater contamination on the stream system in Guangzhou, China. Western mosquitofish collected from a reference site and five study sites in streams forming part of the Pearl River network were dissected and analyzed for their morphological characteristics (anal fin and hemal spine characteristics) and target mRNA expression of genes (VTGα and ERα mRNA expression). Increased VTGα mRNA expression in males and decreased VTGα mRNA expression in females were observed in samples taken from four of the five study sites, with no such observations being made at the reference site. Correlation analysis indicated a significant correlation between the hemal spine morphology index and the gene transcription relative to the reference site. The multiple index also indicated that both male and female mosquitofish in contaminated streams were altered by discharged wastewater, as reflected in their morphological changes and relative induction of mRNA expression of genes in comparison to fish collected from the reference site.