Moribund fish in tanks dosed with F. columnare displayed clinical
signs consistent with columnaris infection. Gross pathologies were typical
and included necrotic skin lesions that spread as the infection
progressed; eye, mouth and gill lesions; and severely frayed fins.
In Experiment 1, fishwere exposed to a high bacterial challenge dose
of F. columnare in aquaria with either SNARC or WARU water. Mortality
occurred on days 3 and 4, and was very high in SNARC water while no
fish died in WARU water (Table 2), the experiment was ended 4-d
post-challenge. Bacterial adhesion to gill surfaces also differed dramatically
in the two waters and was approximately 1900-times higher for
fish challenged in SNARC water (more than 800,000 bacterial CFUs/ng
extracted DNA) than for fish challenged in WARU water (fewer than
450 CFUs/ng).
In Experiment 2, no fish died in challenges conducted in un-altered
WARU water, WARU water filtered through activated carbon, or
SNARC water filtered through ion-exchange resin. The only mortalities
were in the challenges conducted in un-altered SNARC water
(Table 3); the experiment was ended 4-d post-challenge. Bacterial
adhesion to gill tissues was highest for fish challenged in un-altered
SNARC water, followed by fish challenged in ion-exchange-filtered
SNARCwater. Bacterial adhesion did not differ significantly for fish challenged
in un-altered WARU water and carbon-filtered WARU water,
whichwere both lower than for fish challenged in either SNARCwaters.
In an additional experiment,we tested the relative ability of bacteria
to survive in the two waters using an in vitro test where a standardized
inoculum of 2.0 × 108 F. columnare cellswas added to test tubes containing
10mL of sterilized water (n=3). Tubes were incubated at 19 °C for