Abstract
Experimental infection method for Paracolo disease (Edwacdsiella tarda infections) was studied to imitate histopathologically natural infections in the Japanese eel Anguilla japonica. Prior to the bacterial challenge, the intestine of eel was damaged by 0.1 or 0.05 ml of 30% hydrogen peroxide introduced through a silicon tube (1 mm in diameter) which was inserted 3 to 5 cm into the intestine from the anus. E. tarda was mixed with a sterilized eel diet and administered into the stomach by a cannula 18 hours after the hydrogen peroxide treatment. Bacterial dosesused were from 2.6×104 to 8.4×107 CFU/eel. Most fish that were challenged with doses from2.6×104to 2.6×106 CFU/fish formed abscess in either the liver or the kidney and died withi5-23days after the challenge. Histopathological changes of their kidneys or livers were principally identical to those observed in the natural infection. On the other hand, fish challenged with doses over 7.9×106 CFU/fish mostly underwent acute process without abscess formation and died within first 4 days after the challenge, though abscesses were fbrmein someme survived animals within 6-12 days
