Heteropneustes fossilis, commonly called singhi is an obligatory air-breathing fish occurring shallow inland waters of India. For the past two decades this species is declining due to habitat loss, high fishing pressure and easy prone to Epizootic Ulcerative Syndrome (EUS). The infected individuals showing external symptoms like unresponsiveness, wounds, superficial lesions, swelling, discoloration, and deep ulcerative hemorrhages were subjected to bacteriological examination and the pathogens

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... ssociated with EUS were isolated. The highest microbial load 6.3 ± 0.4 × 10 7 cfu g-1 was observed in muscle followed by 5.7 ± 0.6 10 6 cfu g-1 in gills and 7.2 ± 0.9 × 10 5 cfu g-1 in liver whereas the lowest load 4.3 ± 0.7 × 10 4 cfu g-1 was found in intestine. Similarly, a higher percentage of A. invadans (15%) and A. hydrophila (12.5%) was determined from the muscle of the diseased H. fossilis whereas the same was found to be low in the intestine (6% and 5.5% respectively). One fungal species, Aphanomyces invadans and nineteen bacterial species were isolated and identified. Among the 20 isolates, A. invadans was the only fungus and A. hydrophila was dominant among the bacterial isolates from muscle, gill, liver and intestine.