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Abstract
The pathogenic bacteria, Aeromonas hydrophila from naturally infected silver carp, Hypophthalmichthys molitrix were
isolated and identified from a fish farm in Mymensingh. Fish showed motile Aeromonas septicemia (MAS) like reddish
head and anal region, pale body colour and external haemorrhages. Intestine, liver, kidney and environmental
samples such as sediment, feed and water were inoculated onto the Aeromonas isolation medium (AIM) and TSA
plates. The AIM colonies were undergone specific characterization for Aeromonas hydrophila. Quantitative studies of
bacterial flora of fish on TSA plates showed that the total bacterial load in intestine, liver and kidney of the sampled
fish, sediment, feed and water of the environment were 1.00 × 105
to 1.50 × 105 CFU/g, 2.7 × 102 to 4.46 × 104
CFU/g, 1.00 × 103 to 2.17 × 103
CFU/g, 1.90 × 104 CFU/g, 4.10 × 103 CFU/g and 2.50 × 103 CFU/ml, respectively.
After isolation, A. hydrophila was finally identified by their specific morphological, physiological and biochemical
characteristics. They were gram negative, rod shaped, motile bacteria that showed positive reaction for oxidase and
catalase, fermented glucose and were resistant to vibriostatic agent 0/129. They showed positive result in esculin
hydrolysis test.