This experiment aimed to determine the possible bene cial effects of dietary ascorbic acid (AA) on hematological indices, immune responses, and antioxidative capacity of Oncorhynchus mykiss treated with antibiotic oxytetracycline (OTC). 150 sh were divided evenly among ve experimental groups (30 sh of each, in 3 replicates) receiving diets containing OTC (0 and 100 mg per kg sh weight) and AA (100, 200, 400 and 800 mg per kg sh diet) for 28 days. Treatments include group A or control (100 mg AA without OTC), group B (100 mg AA with OTC), group C (200 mg AA with OTC), group D (400 mg AA with OTC), and group E (800 mg AA with OTC). The results obtained showed that the hematological indices (red blood cells, white blood cells, hematocrit, hemoglobin and neutrophils), immunological parameters (plasma lysozyme, plasma complement and skin mucus alkaline phosphatase activities), and antioxidant enzymes activities (superoxide dismutase and catalase) were signi cantly decreased by OTC in O. mykiss fed control diet (P < 0.05). The results also revealed that OTC signi cantly increased the activity of biochemical enzymes (aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase) in the plasma of O. mykiss fed control diet (P < 0.05). However, in comparison to the control diet, feeding sh with higher amounts of AA (400 and 800 mg/kg diet) signi cantly restored the hematological, immunological, and antioxidative responses in OTC treated groups (p < 0.05). These ndings show that the dietary supplementation of AA at 400 or 800 mg/kg diet is bene cial in relieving O. mykiss from OTC-induced oxidative stress and immunosuppression.

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