Emergence of Epizootic Ulcerative Syndrome: Large-Scale Mortalities of Cultured and Wild Fish Species in Uttar Pradesh, India

Epizootic ulcerative syndrome (EUS), a disease listed by World Organisation for Animal Health (OIE) has been reported in 26 countries across 4 continents. Till date, 94 fish species have been found to be naturally infected with EUS and its host range is gradually expanding. In the year 2010-11, outbreaks resulting in heavy fish mortality were recorded in wetland districts of Uttar Pradesh, India, and EUS was confirmed as the cause of mortality on the basis of histopathology, isolation of Aphanomyces invadans, bioassay and PCR. A prevalence of ∼69% (371/540) was recorded and 13 fish species were found to be infected. Interestingly, EUS was observed in seven new species (Aristichthys nobilis, Channa punctatus, Wallago attu, Mastacembelus armatus, Mystus cavasius, Anabas testudineus and Puntius conchonius) for the first time in natural outbreaks. Furthermore, the disease was observed even in the month of May when the mean water temperature was 31.6±0.65°C. This suggests that the disease can result in severe losses even after two decades of its emergence.