DAO 100:83-88 (2012)  -  DOI: https://doi.org/10.3354/dao02478

ABSTRACT: The bacterium Flavobacterium columnare was recovered and identified as the aetiological agent causing freshwater columnaris infection in farmed striped catfish Pangasianodon hypophthalmus (Sauvage) fingerlings that had suffered high mortality rates within commercial hatchery ponds in Vietnam. The gross clinical signs were typical of columnaris-infected fish. Histological examination found numerous Gram-negative, filamentous bacteria present on the skin, muscle and gill tissues of affected fish. The yellow-pigmented bacteria were isolated and identified as F. columnare using primary, biochemical and PCR methods. An experimental immersion-challenge study with 2 strains was also performed. It fulfilled Koch’s postulates and showed a median lethal concentration (LC₅₀) of 4.27 × 10⁵ and 1.66 × 10⁶ cfu ml⁻¹ for the F. columnare strains FC-HN and FC-CT, respectively. To the best of our knowledge this is the first report of freshwater columnaris infection in P. hypophthalmus.

KEY WORDS: Flavobacterium columnare · White patch disease · Pangasianodon hypophthalmus