The aim of this study was designed to analyze the effect of Persian shallot (Allium hirtifolium) extract (PSE) on growth performance, biochemical parameters, antioxidant and immunity status of rainbow trout (Oncorhynchus mykiss) fingerlings. The rainbow trout (25.33 ± 0.15 g) were treated with four effective dosages of 0.5, 1, 2, and, 3% PSE in four separated with one control group for 60 days. At the end of experiment, the rainbow trout treated with PSE showed minimum feed conversion ratio (FCR), maximum weight gain (WG) and specific growth rate (SGR). Increased values of total protein, albumin and globulin were observed in PSE-fed fish; meanwhile, aspartate and alanine aminotransferases (AST, ALT) and alkaline phosphatase (ALP) activities as well as triglyceride, cholesterol, glucose, and cortisol levels significantly decreased in animals fed with 1–2% PSE diet. Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), total immunoglobulin (total Ig), lysozyme activity, alternative complement hemolytic activity (ACH50), and respiratory burst (NBT) significantly (P < 0.05) increased in the PSE, with highest values in the treatments of 1–2% diet. The dietary PSE supplementation significantly (P < 0.05) decreased levels of malondialdehyde (MDA). A maximum significant amount (P < 0.05) in skin mucus was found in 1–3% PSE, while significant enhancement in total Ig and ACH50 were found in 0.5–3% PSE. All parameters analyzed in this study point at the usefulness of employing PSE in aquaculture as growth, antioxidant and immune system promoter. The optimum inclusion level was estimated to range between 1 and 2%. © 2022 Elsevier B.V.