Isolation, Identification and Pathogenicity of Flavobacterium columnare SGM4 in Catfish Clarias batrachus (Linnaeus 1758)

Abstract

Objective: This study assessed the pathogenicity of Flavobacterium columnare isolated from the gill-rot of catfish, Clariasbatrachus in West Bengal, India.Materials and Methods: The diseased catfish were examined as per standard laboratory practices. F. columnare SGM4 wasidentified based on the morphological, phenotypic and genotypic characterization. Abrasion-immersion and agar-discdiffusion methods were followed to assess the pathogenicity and antibiotic sensitivity of F. columnare, respectively.Results: The diseased catfish had white gills, tail rot, body discolouration, saddle-back, peeled skin, emaciation, and inflamedkidney. The yellow-pigmented rhizoid colonies from the gills of catfish were identified as F. columnare. Phylogenetically,F. columnare SGM4 branched with F. columnare strains. In abrasion-immersion challenge experiments, F. columnare SGM4induced considerable mortalities (45%) in C. batrachus at 7.2×106 cells/mL at 24-30 °C. In challenged catfish, it causedcutaneous lesions, tail rot, white patches on the gills and degeneration of internal organs. F. columnare strains were highlysensitive to broad-spectrum antibiotics except for sulphafurazole.Conclusion: Adoption of good nursery practices and appropriate health management measures would help to minimize thedevelopment and spread of columnaris disease.