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The aim of the present study was to investigate effects of dietary Lactobacillus delbrueckii (L. delbrueckii) on immune response, disease resistance against Aeromonas hydrophila (A. hydrophila), antioxidant capability and growth performance of Cyprinus carpio Huanghe var. 450 fish (mean weight of 1.05 ± 0.03 g) were randomly distributed into five groups that fed diets containing different levels of L. delbrueckii (0, 1 × 105, 1 × 106, 1 × 107 and 1 × 108 CFU g−1) for 8 weeks. The results showed that intestinal immune parameters such as lysozyme, acid phosphatase, and myeloperoxidase activities, immunoglobulin M content, and the survival rate were improved in fish fed with 1 × 106 and 1 × 107 CFU g−1L. delbrueckii. In addition, 1 × 107 CFU g−1L. delbrueckii supplementation down-regulated mRNA levels of TNF-α, IL-8, IL-1β and NF-κBp65, and up-regulated IL-10 and TGF-β mRNA levels in the intestine. The survival rate was significantly (P < 0.05) higher (68.33%) in fish fed 1 × 106 CFU g−1L. delbrueckii than the control diet-fed group (40%) after challenge by A. hydrophila. Fish fed with diet containing 1 × 106 CFU g−1L. delbrueckii showed higher antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and total antioxidant capacity (T-AOC) and lower MDA concentrations than those of the control group (P < 0.05). The relative gene expression (SOD, CAT, GPX) showed the same trend with their activities. In addition, the growth performance was significantly improved in fish fed with the diet containing 1 × 106 and 1 × 107 CFU g−1L. delbrueckii (P < 0.05). These results demonstrated that dietary optimal levels of L. delbrueckii enhanced immunity, disease resistance against A. hydrophila antioxidant capability and growth performance in Cyprinus carpio Huanghe var.L. delbrueckii improved immunity of Cyprinus carpio Huanghe var.L. delbrueckii enhanced disease resistance to Aeromonas hydrophila in Cyprinus carpio Huanghe var.L. delbrueckil-fed fish showed improved antioxidant capability.L. delbrueckil-fed fish showed enhanced growth performance.The optimal level of L. delbrueckii was from 1 × 106 CFU g−1 to 1 × 107 CFU g−1.