COMPARING TWO POPULATIONS OF RAINBOW TROUT AGAINST Flavobacterium columnare

Flavobacterium columnare (Fc) is the causative agent for columnaris disease (CD) and this pathogen infects both warm water and cool water aquaculture species.  Recently, columnaris has become an emerging problem in rainbow trout farmed within southern Idaho.  Herein, we compare 2 production lines of rainbow trout to determine if selective breeding has the potential to be part of an integrated approach for controlling CD.  The objectives of this study were to 1) determine family variation in innate resistance to an Fc immersion challenge in 2 populations of rainbow trout, 2) compare and contrast the heritability of disease resistance, 3) examine whether there is a genetic correlation between bacterial cold water disease resistance and CD resistance, and 4) identify quantitative trait locus (QTL) in both populations that influence Fc resistance.  The results indicate that resistance against BCWD and CD are heritable (BCWD - h²=0.29±0.03 and 0.34±0.08; CD - h²=0.17±0.07 and 0.35±0.09, respectively for NCCCWA and TLUM populations) on both populations and favorably genetically correlated. The genetic correlation between the resistance of BCWD and CD were favorably positive in both studied populations (0.17±0.25 and 0.40±0.17, respectively for NCCCWD and TLUM). These findings are encouraging because they suggest that both traits can be improved simultaneously if genetic selection is applied for only one of those traits. Based on weight single step genome wide association (WssGWAS) of both trout populations, resistance to CD is a polygenic trait being ruled by a few genomic regions explaining variations >1%. However, the SNP windows found to be associated with CD do not explain a proportion of variance high enough for choosing marker assisted selection (MAS) instead of genome-wide selection (GS). In addition, because of few overlapping windows, this information should not be used for selection decisions across populations.