1. Introduction
Growth of aquaculture into a significant contributor to global agriculture
has emphasized the importance of improving farm efficiency
and profitability by reducing crop losses. Columnaris disease, caused
by the bacteriumFlavobacteriumcolumnare, is one of the most prevalent
pathogens of cultured and wild fish, and continues to cause large losses
in a wide range of important fish species raised in aquaculture. Despite
considerable worldwide research effort (reviewed by Declercq et al.,
2013), some basic questions remain unanswered, particularly regarding
the role of environmental factors in columnaris disease initiation and
pathogenesis.