Protective efficacy of quercetin against mercury-mediated toxic impact on the hepatic-renal system of economically important food fish rohu (Labeo rohita)

Mercury, a bioaccumulative pollutant, contaminates the food chain and impacts not only aquatic life but also the human health. The present study, therefore, investigates the protective efficacy of quercetin, a plant-derived flavonoid with strong antioxidant properties, on the mercury-induced toxicity in Labeo rohita. The median lethal concentration (LC₅₀) of mercuric chloride (HgCl₂) was determined to be 0.85 mg/L, and a sub-lethal dose (0.17 mg/L; 1/5th of LC₅₀) was used for exposure. Fish were simultaneously administered quercetin-supplemented diets (400 mg/kg) for 45 days. The dosage was selected based on prior research demonstrating its biological effectiveness in fish. The subsequent impact on growth parameters and the histological integrity of hepatic and renal tissues in Labeo rohita was evaluated at 15 and 45 days of the experiment. Mercury exposure significantly impaired growth and caused severe tissue damage, while quercetin supplementation led to a notable improvement in weight gain, feed conversion ratio, and specific growth rate (P < 0.05). Histological analysis revealed reduced hepatic and renal damage in quercetin-treated fish, highlighting its protective role. These findings suggest that dietary quercetin can alleviate mercury-induced toxicity, enhance fish health, and support sustainable aquaculture practices in contaminated environments.