Dietary co-supplementation of silymarin and stevioside enhances growth, immunity, and disease resistance in Nile tilapia

This study evaluated the effects of dietary silymarin, stevioside, and their combined supplementation on the growth performance, physiological responses, immune competence, antioxidant status, and disease resistance of Nile tilapia (Oreochromis niloticus, initial body weight: 2.49 ± 0.10 g) over a 90-day feeding period. Fish were fed either a basal diet (control) or diets supplemented with silymarin (850 mg/kg), stevioside (450 mg/kg), or a combination of both (850 mg/kg silymarin and 450 mg/kg stevioside). Dietary supplementation significantly improved growth performance and feed efficiency, with the combined treatment yielding the greatest response (P < 0.05). Enhanced digestive enzyme activity and improved intestinal and hepatic structure were observed in supplemented groups. Blood biochemical analyses revealed enhanced protein status and reduced glucose, cortisol, and cholesterol levels without adverse effects on hepatic or renal function. Immune and antioxidant responses were enhanced, accompanied by reduced lipid peroxidation. Following Aeromonas hydrophila challenge, supplemented fish reduced cumulative mortality, particularly in the combined treatment. At the molecular level, dietary additives upregulated genes associated with growth, metabolism, immunity, and antioxidant defense. In conclusion, co-supplementation with silymarin (850 mg/kg) and stevioside (450 mg/kg) produced beneficial effects, supporting their potential as functional feed additives to enhance growth performance, health status, and disease resistance in Nile tilapia.