Abstract
The multiplication and distribution of Pseudomonas anguilliseptica in artificially infected Japanese eels were studied by viable cell count.
When the eels were injected intramuscularly with the lethal doses (107, 109/100 g fish weight) of a K antigen-possessing virulent strain at 12°C or 20°C, the viable cell numbers in blood and tissues decreased from 1 h to 12 h post-inoculation. This phase was followed by a static phase, in which the organism persisted at lower concentration or grew slowly, and the duration of this phase depended on the inoculated dosage and ambient water temperature. At the final phase, the organism appeared in rapidly increasing number and rose to high levels (108-10 viable cells/g or ml), which persisted until the death of fish.
On the contrary, when inoculated with sublethal dose (105 CFU) of the virulent strain, with lethal dose of virulent strain at a higher water temperature(28°C), or with a dose of a K antigen-lacking avirulent strain, the organism disappeared completely from the tissues except the muscle of the inoculated site within 1-3 days.
The final level of viable cell count in the moribund eels was higher than those of Aeromonas hydrophila or Vibrio anguillarum, and this difference was thought to reflect toxin production.
