Abstract
Objective: This study assessed the pathogenicity of Flavobacterium columnare isolated from the gill-rot of catfish, Clarias batrachus in West Bengal, India. Materials and Methods: The diseased catfish were examined as per standard laboratory practices. F. columnare SGM4 was identified based on the morphological, phenotypic and genotypic characterization. Abrasion-immersion and agar-disc diffusion 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 inflamed kidney. 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 SGM4 induced considerable mortalities (45%) in C. batrachus at 7.2×106 cells/mL at 24-30 °C. In challenged catfish, it caused cutaneous lesions, tail rot, white patches on the gills and degeneration of internal organs. F. columnare strains were highly sensitive to broad-spectrum antibiotics except for sulphafurazole. Conclusion: Adoption of good nursery practices and appropriate health management measures would help to minimize the development and spread of columnaris disease.
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