Author : Sureerat Butprom

Summary : A chronic persistent ulcerative lesion of the skin in Koi carp (Cyprinus carprio L.) was reported in several commercial aquarium shops in Klang Valley. A study was conducted to chart the epizootiology and pathogenicity of the disease and its aetiological agents which included histopathological, bacteriological, virological and experimental infection. Thirty-six diseased Koi carps with skin ulcer were examined. Findings showed that the ulcerative lesion development of involved deep muscle layers showing tissue necrosis and inflammation in chronic lesions. The fish abdomen was filled with a clear or red-tinged ascitic fluid. The liver and kidneys were pale in colour, swollen and friable. Histopathological examination, lesions revealed in the skin, gill, kidneys, liver, spleen and intestine. Its pales changes were characterized by diffuse haemorrhages, cell degeneration and necrosis in the skin, liver and kidneys. Lamellar epithelial cells showed hyperplasia and hypertrophy at the base of gill lamellae. Depositions of haemosiderin were seen in kidneys, liver, hepatopancreas and spleen. In the intestine, haemorrhage in the tunica propria and atrophy of mucosal epithelium were seen. Electron microscopy revealed two type of virus like particles which were associated with the histopathological changes in the kidneys. The virus-like particles were presumably corona virus and reovirus based on their morphology. Morphological and biochemical characteristics of bacteria isolated from the diseased Koi were determined by routine biochemical tests in combination with the BBL Crystal Kit. In the present study, Gram-negative non-lactose fermenting rods were isolated from the skin lesions and kidneys. In total, 11 bacteria species were identified and Aeromonas hydrophila was the dominant species isolated from the fish in this study. In conclusion, ulcerative lesion in Koi carp was primarily caused by multiple infection of several bacteria species.