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

Abstract

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) andabrasion-bath treatment followed by histopathology.Results: Flavobacterium sp. KG3 challenge caused extensive damages to the gills and internal organs of C. auratus, resultingin cellular and tissue-level alterations. The i/p challenge resulted in significant mortalities, with an LD50 value of 2.5 × 105CFU/fish. The abrasion-bath challenge resulted in 60% mortality at 6.0 × 106 cells/mL in 5 days. The kidney of the challengedC. auratus exhibited extensive haaemorrhages, polymorphic and constricted nephritic tubules, fibrosis, glomerulopathy,degeneration of nephritic tubular epithelium, disruption of blood vessels, cellular and nuclear hypertrophy, granulomaformation, necrosis of haaematopoietic area, vacuolation in haaematopoietic tissue, widening of lumen, and thickening ofthe luminal lining.Conclusion: Like other recognized bacterial pathogens, Flavobacterium sp. KG3 was moderately virulent to C. auratus andcan produce systemic pathology in the gills, muscle, spleen, and kidney.