Dietary dose-dependent effects of Ginkgo biloba leaf extract on growth, immunity, antioxidant status, and hepatic integrity in Nile tilapia

Abstract The increasing demand for sustainable alternatives to in-feed antibiotics has stimulated interest in phytogenic feed additives. This study investigated the dose-dependent effects of dietary Ginkgo biloba leaf extract (GBLE: 0, 6, 12, 18, and 24 g/kg diet) in Nile tilapia during a 98-day feeding trial. A completely randomized design was used with three replicates per treatment (40 fish per hapa; initial body weight: 8.39 ± 0.14 g). Dietary GBLE supplementation improved final body weight, body weight gain, specific growth rate (SGR), and feed conversion ratio (FCR) in a dose-dependent manner, with the 18 g/kg group exhibiting superior performance ( P < 0.05). Second-order polynomial regression suggested estimated dietary levels of approximately 20.75 g/kg for maximum SGR and 16.44 g/kg for minimum FCR within the tested inclusion range. Polynomial regression identified optimal dietary levels of 20.75 g/kg for maximum SGR and 16.44 g/kg for minimum FCR. All GBLE-supplemented groups exhibited increased hemoglobin concentration, lymphocyte percentage, and total serum protein, together with lower serum cholesterol, triglycerides, and ALT activity. In addition, AST activity was reduced in fish fed the highest dietary GBLE level (24 g/kg). lysozyme activity, immunoglobulin M, and complement C3 were elevated in all GBLE groups relative to the control. Hepatic and serum antioxidant enzymes (SOD, GSH-Px) and total antioxidant capacity were increased, while malondialdehyde was markedly reduced across all supplemented groups. Intestinal amylase, lipase, and protease activities were enhanced. Representative liver sections from GBLE-supplemented fish showed well-preserved hepatocellular morphology, clearly defined sinusoidal spaces, and prominent pancreatic acini with no evidence of necrosis, inflammatory infiltration, or degenerative changes. These findings suggest that dietary GBLE at approximately 16–21 g/kg, as estimated by polynomial regression analysis under the present experimental conditions and supported by the superior responses observed in the 18 g/kg treatment group, may represent an exploratory inclusion range for Nile tilapia. However, these estimates should be validated in future practical studies before recommendation for commercial application. Within this range, the tested commercial GBLE preparation shows potential as a promising phytogenic feed additive that could contribute to reduced reliance on antibiotic growth promoters in intensive tilapia aquaculture.