Virulence and histopathology of Aeromonas hydrophila (SAH93) in experimentally infected Tilapia, Oreochromis mosambicus

Abstract

Tilapia, Oreochromis mossambicus, held in sea water, was experimentally infected with Aeromonas hydrophilla (SAH 93) via intramuscular injection. The pathogen has an LD of 10 CFU/fish produced characteristic ulceration leading to open wounds. More than 80 per cent of the experimentally infected fish, injected with the doses higher than LD50, died within eight days. Dermal necrosis and liquifying muscular degeneration with infiltration of cellular serum factors to the site of injection were noticed. Focal necrosis of the hepatocytes, tubular degeneration and sloughing, glomerular necrosis, necrosis and depletion of the cells in the renal tubular interstitia, loss of sub-mucosa and sloughing of the intestinal microvilli were the major histopathological manifestations of the experimental infection. Aggregation of macrophages and melano macrophage centres (MMC) in the head kidney and spleen were also noticed. Gill lamellar basement epithelium showed mid hyperplasia and hypertrophy. Lifting and seperation of the epithelium of the secondary lamellae and arterial congestion in the primary lamellae were observed as delayed responses. The study indicated that Tilapia could be a potential carrier of A. hydrophila, and thus, has to be used with caution as a forage fish.