Natural transmission of invasive fungus is associated with Epizootic Ulcerative Syndrome (EUS) in Indian fresh and brackish water fishes. The fungus invades and proliferates in tissues away from the site of dermal ulcers. Totally five fresh water fishes and one brackish water fish species were selected for this study, and 100 individual of the each species were investigated for EUS infection , more then 10 fishes were infected with EUS positive from each species were identified by lesion on the fish tissue and it conformed by histopathology studies. The infection was occurred only during monsoon and post monsoon season not in summer and pre monsoon. Hyphae were associated with cellular debris and severe mycotic granulomas in muscle lesion. Finally concluded it the temperature variation is main reason for (EUS) infection and also it may due do caused by mixing of polluted water from domestic waste, fecal matter and Sewage through rain runoff. 1374568807.php