Pathology of Flavobacterium sp. KG3 in Experimentally Challenged Ornamental Goldfish Carassius auratus (L.)

DOI: 10.26650/EurJBiol.2018.0012 Objective: This study investigated the pathogenicity and pathology of the gill rot-associated bacterium Flavobacterium sp. KG3 in experimentally challenged Carassius auratus. Material and Methods: The pathogenicity of Flavobacterium sp. KG3 was assessed by intraperitoneal injection (i/p) and abrasion-bath treatment followed by histopathology. Results: Flavobacterium sp. KG3 challenge caused extensive damages to the gills and internal organs of C. auratus, resulting in cellular and tissue-level alterations. The i/p challenge resulted in significant mortalities, with an LD50 value of 2.5 × 105 CFU/fish. The abrasion-bath challenge resulted in 60% mortality at 6.0 × 106 cells/mL in 5 days. The kidney of the challenged C. auratus exhibited extensive haaemorrhages, polymorphic and constricted nephritic tubules, fibrosis, glomerulopathy, degeneration of nephritic tubular epithelium, disruption of blood vessels, cellular and nuclear hypertrophy, granuloma formation, necrosis of haaematopoietic area, vacuolation in haaematopoietic tissue, widening of lumen, and thickening of the luminal lining. Conclusion: Like other recognized bacterial pathogens, Flavobacterium sp. KG3 was moderately virulent to C. auratus and can produce systemic pathology in the gills, muscle, spleen, and kidney.