EXPERIMENTAL-INFECTION OF EDWARDSIELLOSIS IN THE JAPANESE EEL

Experimental infection method for Paracolo disease (Edwardsiella 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 doses used were from 2.6 x 10(4) to 8.4 x 10(7) CFU/eel. Most fish that were challenged with doses from 2.6 x 10(4) to 2.6 x 10(6) CFU/fish formed abscess in either the liver or the kidney and died within 5-23 days 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 x 10(6) CFU/fish mostly underwent acute process without abscess formation and died within first 4 days after the challenge, though abscesses were formed in some survived animals within 6-12 days.