Therefore, DOM does
not contribute to the differences in mortality seen in Experiment 1.
However, removal of most of the calcium and magnesium from
SNARC water by ion-exchange filtration resulted in decreased bacterial
adhesion to gill and decreased mortality compared to un-altered SNARC
water. Accordingly, we believe that the concentration of divalent cations
(hardness) affects pathogenesis of columnaris disease and accounts
for differences in mortality seen in Experiment 1. Specifically, bacterial
adhesion and resulting fish mortality were less when challenges were
conducted in water with low hardness.