Modulation of growth, immunity, and immune-antioxidant gene expression in Nile tilapia, Oreochromis niloticus, culture under biofloc system by dragon fruit, Hylocereus undatus, peel powder

This study examines the use of dragon fruit peel (DFP) powder as a dietary supplement on growth performance, immune responses, and gene expression of Nile tilapia, Oreochromis niloticus, cultured within biofloc systems. A total of 300 Nile tilapia fingerlings (14.64 ± 0.09 g) were subjected to five dietary treatments, with DFP added to a basal diet at doses of 0, 20, 40, 80, and 160 g kg⁻¹ DFP. Growth and immunological responses were assessed after 4 and 8 weeks of feeding, and the transcriptional level of immune and antioxidant-related genes was measured after 8 weeks. Fish fed diets containing DFP exhibited significantly greater weight gain, faster growth, and enhanced levels of key indicators of immunity than control fish (p < 0.05). A diet containing 40 g DFP kg⁻¹ produced the best result in terms of growth, enhanced immune response indicators in skin mucus and blood serum, and the upregulation of IL-1, IL-8, LBP, GPx, GST-α, and GSR expression (p < 0.05). Based on the quadratic regression analysis, the optimum concentration of DFP was 80 g kg⁻¹. These findings collectively suggest that powdered DFP may serve as a promising feed supplement for Nile tilapia raised in biofloc systems.