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Aetiopathogenicity of Ulcerative Disease in Koi Carp (Cyprinus carpio Linnaeus)
Thesis Abstract:
The study was conducted to chart the epizootiology and pathogenicity of the chronic persistent ulcerative lesion of the skin in Koi carp (Cyprinus carpio L.) and its aetilogical agents, which included histopathological, bacteriological, viriological, and experimental infection.
A total of 36 diseased Koi carps with skin ulcer were examined. Findings showed that the ulcerative lesion development 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 color, swollen, and friable. In the histopathological study, lesions were found in the skin, gill, kidneys, liver, spleen, and intestine. The changes were characterized by diffuse hemorrhages, 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, hemorrhage in the tunica propria and atrophy of mucosal epithelium were seen. Electron microscopy revealed two types of virus-like particles, which were associated with the histopathological changes in the kidneys. The virus-like particles were presumed to be coronavirus 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 BBL Crystal KitTM. Gram-negative non-lactose fermenting rods were isolated from the skin lesions and kidneys. A total of 11 bacteria species were identified, with Aeromonas hydrophilia as the dominant species. The other species of the ulcer-associated bacteria were (1) Shewanella putrefaciens, (2) Vibrio cholarae, (3) Pseudomonas diminuta, (4) Chryseobacterium meningosepticum, (5) Empedobacter brevis, (6) Pseudomonas aeruginosa, (7) Pantoea agglomerans, (8) Enterobacter sakazakii, (9) Morganella morganii, and (10) Aeromonas veronii.
A. hydrophila, S. putrefaciens, and V. cholarae isolated from Koi carp with skin ulcer were used in experimental infection. The fish were injected 0.1 mL bacteria suspension at 1 x 107 cfu/mL. Bacteria were reisolated from ulcerative lesion and kidneys, and had the same biochemical characteristics as those isolated from naturally infected fish. Ulcers began to appear three post infection as small and flat lesions. No apparent mortality was observed in all groups. Histopathological studies revealed that A. hydrophila individually or in combination with other bacteria could have caused the small superficial ulcerative lesions. Hemorrhages and inflammation were seen in spleen, adipose tissue, and kidneys. While individually or in combination, injection of S. putrefaciens and V. cholarae displayed localized lesion, which was restricted only to the injection site.
In conclusion, ulcerative lesion in Koi carp was primarily caused by multiple infections of several bacteria species, although the possibility of viral involvement must not be ruled out.