Toxicity Assessment and Plasma Vitellogenin Expression in Nile Tilapia ( <scp> <i>Oreochromis niloticus</i> </scp> ) Exposed to an Endocrine Disruptor, Triclosan

A widely used antibacterial drug, triclosan (TCS), is becoming more commonly acknowledged as an emergent aquatic pollutant with the potential to disrupt hormones. The physiological, biochemical and histological consequences of long-term TCS exposure in Oreochromis niloticus were assessed in this study. For 15, 30 and 45 days, adult fish were exposed to three sublethal doses of TCS (0.146, 0.219 and 0.438 mg L^-1). To ascertain reproductive and hepatic responses, growth indices, hepatosomatic index (HSI), gonadosomatic index (GSI), plasma vitellogenin (VTG) levels and gonadal histopathology were evaluated. The results showed significant increases in HSI and decreases in GSI, indicating hepatic enlargement and gonadal suppression, along with concentration-dependent declines in body weight and total length. Biochemical investigations revealed significant changes in VTG synthesis, with males displaying a brief increase followed by suppression and females showing a dose and time-dependent reduction, indicating a dualistic, sex-specific endocrine response. Reproductive impairment was confirmed by histopathological testing, which revealed severe degenerative alterations in gonadal tissues, including necrosis, vacuolation, interstitial cell infiltration and follicular atresia. Potential effects on breeding fitness, offspring production and population stability are suggested by the incapacity of O. niloticus to tolerate TCS-induced stress during the spawning period. All of these results point to triclosan being a strong endocrine and cytotoxic drug that interferes with the hepatic and gonadal physiology of O. niloticus. The study highlights the critical need for more stringent regulation and monitoring of this molecule in aquatic habitats, as well as the ecological risk connected to persistent TCS contamination.