Variations in Viable Cell Counts of Released Edwardsiella tarda from Experimentally Infected Eel at Different Temperatures

Abstract

To obtain neccessary information about the infection mechanisms of edwardsiellosis in eel, variation in the number of pathogenic bacterial cells released from the diseased eel was investigated. Eel were injected with Edwardsiella tarda intramuscularly and kept individually in aquaria incubated at 20°C, 25°C and 30°C respectively. Two sets of aquaria were prepared at specified temperature. Dead eel were taken off from one set while they were left in the other set.
The number of released cells reached almost the same level ranging from 10⁵ to 10⁶ cells/ml at the three temperatures in common, but the increase in the number of cells was faster at higher temperature than at lower temperature. The number of cells increased very much in aquaria in which dead eel were left, and reached about 1, 000 times as many as that in aquaria from which dead eel were taken off. The level of the number was maintained throughout the experimental period of 21 days.
From these results, it is confirmed that diseased eel release a great number of pathogenic becteria, consequently the infection would spread throughout the pond if diseased eel are not taken off.