Assessing the Apparent Prevalence, Pathology and Molecular Detection of <i>Aphanomyces invadans</i> in Native Fish Species of the Sylhet Region, Bangladesh

ABSTRACT The primary objective of this study was to investigate the presence of Aphanomyces invadans and its association with Aeromonas hydrophila in naturally infected fish from two wetlands ( beels ) in the Sylhet, Bangladesh. Over a 6‐month period (October 2020 to March 2021), a total of 396 fish were examined from Singari beel , of which 90 were found positive for A. invadans infection, resulting in an apparent prevalence of 22.7% (95% confidence intervals: 18.8%–27.1%) and in Aral beel , 33 out of 300 fish exhibited ulcerative lesions and tested positive with apparent prevalence of 11.0% (95% CI: 7.7%–15.1%). Under normal temperature conditions of 25 ± 0.4°C, A. invadans formed opaque, irregular, white translucent colonies on Czapek Dox agar. Microscopic examination revealed elongated, non‐septate hyphae. Histopathological analysis showed chronic granulomatous inflammation surrounding deeply penetrating fungal hyphae. The presence of A. invadans was confirmed through PCR, producing a specific 234 bp product from infected tissue. In addition, the study detected the prevalence of A. hydrophila , associated with Motile Aeromonad Septicemia (MAS), through PCR amplification of a 1450 bp product. Sequence analysis confirmed its similarity to A. hydrophila sequences in the NCBI database (Accession no.: ON833076.1). Among the various fish species studied, it was evident that Clarias batrachus and Anabas testudineus were particularly susceptible to the pathogen. Additionally, the infection of A. invadans appeared to spread notably during the month of January. In summary, the outcomes of this investigation underscore the continued prevalence of Epizootic Ulcerative Syndrome (EUS) within the water bodies of the Sylhet region. This study sheds light on the intricate interactions between these pathogens and the susceptible fish species, contributing valuable insights into the dynamics of these infections in aquatic environments.