Ascophyllum nodosum enhances hepatic antioxidant capacity, serum immunity, immune gene expression, and disease resistance in Oreochromis niloticus

Abstract Brown seaweed has gained special attention in aquaculture nutrition studies due to its functional bioactive compounds, such as polysaccharides. This study evaluated the functional potential of the brown seaweed, Ascophyllum nodosum , as a natural immunostimulant and growth promoter in Nile tilapia. A 74-day feeding experiment was conducted using 540 fingerlings (initial body weight 18.4 ± 0.2 g), randomly allocated to six dietary treatments (0, 0.5, 1.0, 1.5, 2.0, and 2.5 g AS/kg diet) in six triplicate groups. Fish were reared under optimal water conditions. Growth performance improved significantly with AS supplementation, achieving optimal responses at approximately 1.9 g/kg, as reflected in superior specific growth rate and feed conversion ratio. Hepatic antioxidant defenses, superoxide dismutase, catalase, glutathione peroxidase, and total antioxidant capacity were markedly enhanced, whereas malondialdehyde levels declined, signifying reduced oxidative stress. Serum lysozyme activity, bactericidal activity, and total protein levels increased notably, supported by the upregulation of immune-related genes ( IL-1β , TLR2 , lysozyme , hepcidin ). Upon Aeromonas hydrophila challenge, fish receiving diets with 1.0–2.0 g AS/kg exhibited significantly higher survival, confirming strengthened immune protection. Cooperatively, A. nodosum supplementation reinforced growth, antioxidant responses, and disease resilience in Nile tilapia, highlighting its promise as an eco-friendly nutraceutical for sustainable aquaculture development.