Aeromonas hydrophila bacteria was isolated from the suspected EUS-affected shing fish, Heteropneustes fossilis (Bloch). The disease investigations were primarily based on clinical signs and subsequently confirmed by the isolation of bacterial pathogen Aeromonas hydrophila from lesion of liver and kidney. The A. hydrophila isolates were identified by a series of morphological, physiological and biochemical tests. The total bacterial load in liver, intestine and kidney were 1.67 × 10 4 to 6.46 × 10 8 CFU/g, 1.71 × 10 3 to 1.18 × 10 9 CFU/g and 1.47 × 10 4 to 3.70 × 10 8 CFU/g respectively.

Heteropneustes fossilis (shing) of 35g body weight were experimentally infected with Aeromonas hydrophila by two different methods: viz. intraperitonial and intramuscular injection. A standard dose of infection (6.4 × 10 7 CFU/ml) was selected based on predetermined LD 50 . Each method gave rise to the mortality of shing up to 85%. Clinical signs of fish included injury, hemorrhage and large ulcerative lesions on the body at the injected area. In kidney, liver and intestine pathologically, massive atrophy and focal necrosis were found. Hemorrhage, Vacuolation and atrophy of hepatic sinusoids represented by necrosis of the sinusoidal lining cells, degeneration of hepatic tissue and distribution of bacterial cell all over the tissue were found in liver. Atrophy, hemorrhage, villi missing and missing of epithelium were found in intestine of the experimentally infected shing. Bacterial cells were distributed in the whole hematopoietic tissue including the renal tubules. Tissue abscess characterized by focal necrosis, hemorrhage and Vacuolation were also found in the kidney of the infected shing. But the above symptoms were not found in the organs of the apparently healthy shing species.

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