Betaine attenuates chronic azoxystrobin toxicity in Oreochromis niloticus: Hemato-biochemical, antioxidant, immunological, genotoxic, and histological insights.

Environmental contamination with azoxystrobin (AZX), a widely used strobilurin fungicide, presents an increasing toxicological risk to freshwater ecosystems due to agricultural runoff. This study investigated the sublethal, chronic effects of environmentally relevant concentrations of AZX (28.63 µg/L) in Oreochromis niloticus, a key freshwater model species, and evaluated the potential protective role of dietary betaine (BT, 0.2 %) as a natural detoxifying agent. Acute toxicity testing revealed that the 96-h LC₅₀ of AZX was 2.863 mg/L. The fish were subsequently divided into four groups, namely, the control, BT (0.2 %), AZX, and AZX+BT groups, and exposed for six weeks. Chronic AZX exposure resulted in significant mortality (22.22 %) and induced pronounced oxidative stress, as evidenced by elevated malondialdehyde (MDA) levels, decreased activities of antioxidant enzymes (SOD, CAT, GPx) and reduced glutathione (GSH) levels. Additionally, AZX exposure induced hepatic and renal dysfunction, elevated genotoxicity, and severe histopathological lesions in multiple organs, including the gills, liver, kidney, intestine, and brain. Genotoxicity was confirmed by a comet assay, which revealed pronounced DNA strand breaks reflected by increased tail length, tail DNA%, and the olive tail moment. Dietary BT supplementation significantly mitigated AZX-induced toxicity, reducing mortality to 8.89 %, restoring antioxidant defenses, improving hematological and biochemical parameters, and alleviating DNA damage and tissue pathology. Furthermore, BT modulated immune responses, as evidenced by restored nitric oxide and globulin levels, partially counteracting AZX-induced immunosuppression. These findings highlight the chronic toxicity potential of AZX at environmentally realistic concentrations and demonstrate the efficacy of dietary BT in protecting freshwater fish against oxidative, genotoxic, and immunotoxic effects. This study emphasizes the potential of nutritional strategies for mitigating the impacts of aquatic pollutants.