Rainbow Trout (Oncorhynchus mykiss) Resistance to Columnaris Disease Is Heritable and Favorably Correlated with Bacterial Cold Water Disease Resistance

Columnaris disease (CD) is an emerging disease affecting rainbow trout aquaculture. Objectives were to estimate heritability of CD resistance in a line (ARS-Fp-R) selected 4 generations for improved bacterial cold water disease (BCWD) resistance; estimate genetic correlations among CD resistance, BCWD resistance, and growth traits; and compare CD resistance among ARS-Fp-R, ARS-Fp-S (selected 1 generation for increased BCWD susceptibility), and ARS-Fp-C (selection control) lines.  Heritability of CD resistance was estimated using data from waterborne challenge of 44 full-sib ARS-Fp-R families, and genetic correlations were estimated using these data and 5 generations of BCWD resistance and 9- and 12-month body weight data from 405 ARS-Fp-R families.  Heritability estimates were similar for CD (0.17±0.09) and BCWD (0.18±0.03) resistance, and genetic correlation was favorable (0.35±0.18).  Genetic correlations were small and antagonistic (-0.15±0.09 to -0.19±0.17) between resistance traits and 9- and 12-month body weights. Two challenges were conducted to compare CD resistance among genetic lines.  ARS-Fp-R (83% survival) had greater CD resistance than ARS-Fp-C (73.5%; P=0.02) and ARS-Fp-S (68%; P<0.001) families, which did not differ (P=0.16), in the first challenge, and greater resistance (56% survival) than ARS-Fp-S (38% survival; P=0.02) families in the second challenge using ~2.5-fold greater challenge dose. Favorable correlation between CD and BCWD resistance is supported by greater CD resistance of the ARS-Fp-R line, and suggests both traits will be improved when selection is practiced on only one trait.  These data support further selective breeding of the ARS-Fp-R line for increased CD resistance to produce a double pathogen resistant line.