Susceptibility and pathological consequences of catla, Catla catla (Hamilton) experimentally infected with Edwardsiella tarda

The present study tested the susceptibility and pathological changes of catla, Catla catla (Hamilton) infected with Edwardsiella tarda (ET-PG-29). The bacterium was isolated from the kidney of a diseased pangas catfish. To determine the median lethal dose (LD₅₀), C. catla were challenged with this bacterium (10⁸-10³ CFU ml^-1), and the LD₅₀ was calculated as 10^5.5 CFU ml^-1. Another set of healthy C. catla were injected intraperitoneally with the LD₅₀ dose to induce edwardsiellosis. The clinical signs of the infected C. catla were observed and recorded. Tissues such as kidney, liver, intestine, heart, and gill from the infected fish with clinical signs of edwardsiellosis were used for histopathology. The clinical and gross signs were first visible at 1 d post-injection, and the infected fish showed typical signs of hemorrhagic septicemia. The most striking histopathological features were found in the kidney which showed multi-focal necrosis with the formation of granuloma indicating an inflammatory response against the pathogen. The intestine displayed goblet cell hyperplasia, the liver showed hydropic degeneration with hyperemic central veins, and there was inflammation of gill lamellae and cardiac myositis associated with leucocyte infiltration. Collectively, the results confirmed the susceptibility of C. catla to E. tarda infection and that this bacterium is a threat to C. catla in aquaculture practices.