This study was carried out to assess the effects of Pediococcus acidilactici on zebrafish -Danio rerio-. Different levels of P. acidilactici including 0, 1 × 106, 2 × 106, 4 × 106 and 8 × 106 colony‐forming unit per g of the diet -cfug−1- were examined in fish with 120 ± 10 mg weight for 60 days in a completely randomized design. The results showed that the best growth indices were recorded in group 4 × 106 cfug−1 -p < 0.05-. The highest number of total viable count and lactic acid bacteria of intestine were found in group 4 × 106 cfug−1 -p < 0.05-. The maximum activity of digestive enzymes including amylase, lipase, protease and alkaline phosphatase was observed in group 4 × 106 cfug−1. The highest activity for superoxide dismutase was recorded in group 4 × 106 cfug−1 while catalase, glutathione peroxidase and glutathione reductase showed the highest activity in group 8 × 106 fug−1. The most growth inhibition zone of Aeromonas hydrophylla, Flavobacterium columnare, Vibrio anguillarum and Edwardsiella tarda was found in group 4 × 106 cfug‐1 -p < 0.05-. Therefore, P. acidilactici as a probiotic improved growth and immunity of the zebrafish and could be used by zebrafish farmers.

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