This is the first histological evidence of intersex in a fish species inhabiting a South African water source. One hundred catfish (Clarias gariepinus) were collected randomly from the Marais Dam (MD) and the Rietvlei Dam (RVD) in the Rietvlei Nature Reserve (RNR), South Africa. These dams drain water from a stream that receives effluent from industrial sites, agricultural activities, informal settlements, and municipal treatment plants. Each fish was evaluated macroscopically and had blood drawn, and its gonads were macroscopically and histologically examined to verify intersex potentially related to endocrine disruption. Gonadal histology of several fish showed primary oocytes scattered in testicular tissue, indicative of intersex. The results showed intersexuality in 20% of fish from both the dams. The GSI value for intersex fish was closer to male GSI values, suggesting that the sampled intersex fish were more likely to have occurred from the feminization of male catfish. Target chemical analyses showed that the water, sediment, and serum samples tested positive for p-nonylphenol (p-NP). The p-NP level in water and sediment at MD was 6360 and 4.0 microg/kg, respectively, whereas in sediment at RVD it was 113 microg/kg. Commonly found in the effluent from sewage treatment plants, p-NP in water and sediment indicates estrogenic water pollution, which might affect wildlife and humans dependent on these sources.
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