This study evaluated dietary quinoa seed extract (QSE) in Nile tilapia fingerlings (initial weight 6.32 ± 0.09 g). Fish were fed a basal diet (CTR) or a diet supplemented with QSE at 0.25, 0.5, or 1.0 g kg⁻¹ for 56 days. Results showed that 1.0 g kg⁻¹ QSE significantly improved final body weight (33.46 vs. 27.76 g in CTR), weight gain, feed conversion ratio, and protein efficiency ratio (P < 0.05). Furthermore, serum total protein and globulin increased, while liver enzymes (ALT, AST) decreased in QSE-fed fish. Also, digestive enzyme activities (amylase, lipase) and antioxidant capacity (catalase, GSH) were enhanced. Notably, all QSE-supplemented groups showed 100% survival following A. veronii challenge versus 50% in controls. Meanwhile, whole-body lipid content increased with QSE supplementation, correlating with upregulated pparγ and lpl and downregulated pparα expression. In conclusion, dietary QSE at 0.5–1.0 g kg⁻¹ effectively enhances growth, immunity, and disease resistance in Nile tilapia