The objective of the present investigation was to evaluate the effects of the combination of medicinal herbs extracts (CMO: Coriander (Coriandrum sativum), common mallow (Malva sylvestris), and oak acorn (Quercus brantii)) on growth, digestive enzymes activity, immune parameters, and disease resistance in common carp, Cyprinus carpio. A total number of three hundred fish (20.80 ± 0.25 g) were randomly attributed to five treatments fed with diets containing 0 (control), 0.5%, 1%, 3%, and 5% of CMO for a period of 60 days then were challenged with A. hydrophila infection. Based on the results, there were significant differences in all growth parameters, including final weight (FW), weight gain (WG), specific growth rate (SGR), and food conversion ratio (FCR) between CMO supplemented fish and control with the maximum values in the 5% CMO treatment (P < 0.05). Despite the control fish, no mortality was observed in CMO treatments (P < 0.05). CMO diets increased red blood cells (RBC), white blood cells (WBC), hematocrit (Hct), hemoglobin (HB), and mean corpuscular volume (MCV), while decreased mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC). Feeding the fish with CMO diets markedly increased total protein, albumin, and globulin values, while triglyceride, cholesterol, glucose, and cortisol decreased (P < 0.05). Antioxidant biomarkers in CMO-fed fish were significantly higher than those of the control group. Immune parameters in serum and mucus including lysozyme, total immunoglobulin (Total Ig), nitroblue tetrazolium (NBT), alternative complement activity (ACH50), protease, alkaline phosphatase (ALP), and antioxidant enzymes were significantly higher in CMO-fed fish compared to the control group (P < 0.05). The highest and the lowest survival rates following a challenge with A. hydrophila were observed in 3% CMO and the control treatments, respectively. Polynomial regression analysis showed that the the best recommended inclusion level of CMO was 1% to maximize growth performance and improved feed conversion values. In conclusion, our findings revealed that the 3% CMO could elevate the growth, immune systems, antioxidant activity, and resistance to A. hydrophila in common carp.
