Determination of lethal dose of Aeromonas hydrophila Ah17 strain in snake head fish Channa striata.

Aeromonas hydrophila is a major bacterial fish pathogen which causes economic losses in the aquaculture. The study determined the Letha Dose (LD50-96h) of A. hydrophila Ah17 strain (isolated from EUS infected Channa striata) in C. striata. C. striata were challenged with three different concentration of A. hydrophila Ah17 strain 1.0 × 107, 1.0 × 108, 1.0 × 109 CFU/mL. The LD50-96h values were found to be 4.1 × 108 CFU/mL. Percentage of mortality was observed as 10%, 40% and 70% in 1.0 × 107, 1.0 × 108 and 1.0 × 109 CFU/mL respectively in challenged fish. Microbial load was calculated on muscle, kidney, liver and spleen with highest load was observed in muscle and lowest in kidney. Level of liver enzymes such as Aspartate aminotransferase (AST), Alanine Aminotransferase (ALT), and Alkaline Phosphatase (ALP) were increased compared to control fish. Level of mRNA expression of antioxidant genes such as Catalase (cat), Manganese Superoxide Dismutase (MnSOD), Glutathione Peroxidase (GPx) were high in liver tissue of all treated groups than control. Clinical signs were observed after intraperitoneal treatment of Ah17 in C. striata. Clinical signs such as lesions on the site of injection, imbalanced state, changes in the movement of pectoral fins, depigmentation on the tail of caudal fin and irregular lesions on the muscle region were observed. Thus the study concluded that, the LD50-96h value of A. hydrophila Ah17 strain was 4.1 × 108 CFU/mL and exhibited potential pathogenic effect upon experimental infection in snakehead murrel C. striata.