| Summary: | Neomycin belongs to the family of 2-deoxystreptamine-containing aminoglycoside antibiotics. It is widely used for bacterial infections, targeting most gram-negative and some gram-positive bacteria. Neomycin has also been reported to show antiviral activity. Here, we evaluated the toxicity of neomycin sulfate, and investigated its effect on non-specific immunity and viral infection in crucian carp (Carassius auratus gibelio). The safe concentration of neomycin sulfate for crucian carp was determined to be 102.9 mg/kg in vivo. In oxidative damage assays, neomycin sulfate increased superoxide dismutase and catalase activity and decreased malondialdehyde in the liver of crucian carp. In non-specific blood immune assays, the white blood cell count and complement 3 content significantly increased after neomycin sulfate treatment, while no significant changes were observed in antibacterial or lysozyme activity. In a challenge test, neomycin sulfate protected the crucian carp from cyprinid herpesvirus 2 (CyHV-2) infection and inhibited CyHV-2 replication. In cytotoxicity assays, low concentrations of neomycin sulfate had no cytotoxicity on cells from the fins of crucian carp. The results of the present study indicate that oral administration of neomycin sulfate reduced oxidative damage, enhanced immunity and provided protection against CyHV-2 in crucian carp. Keywords: Neomycin sulfate, Non-specific immunity, Oxidative damage, Crucian carp, Cyprinid herpesvirus 2
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