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Title: Rainbow trout (Oncorhynchus mykiss) resistance to columnaris disease is heritable and favorably correlated with bacterial cold water disease resistance

item Evenhuis, Jason
item Leeds, Timothy - Tim
item Wiens, Gregory - Greg
item Marancik, David
item Welch, Timothy - Tim
item LAPATRA, SCOTT - Clear Springs Foods, Inc

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2015
Publication Date: 3/1/2015
Citation: Evenhuis, J., Leeds, T.D., Wiens, G.D., Marancik, D.P., Welch, T.J., Lapatra, S. 2015. Rainbow trout (Oncorhynchus mykiss) resistance to columnaris disease is heritable and favorably correlated with bacterial cold water disease resistance. Journal of Animal Science. DOI: 10.2527/jas.2014-8566.

Interpretive Summary: Recently columnaris disease, which is known to infect freshwater finfish species, has emerged in southern Idaho having negative impacts on rainbow trout aquaculture production. Breeding rainbow trout for resistance to bacterial cold water disease has shown to be effective in reducing losses to bacterial cold water disease in production environments, therefore we sought to determine the potential for breeding for resistance to columnaris disease. Three lines of trout (randomly mated, BCWD resistant or susceptible) were shown to contain large amounts of genetic variation in their ability to survive columnaris disease, with a positive correlation between resistance to the two diseases. Correlations with growth traits were negative but weak. These results support the initiation of a selective breeding program to develop fish that are resistant to two bacterial pathogens known to be problematic for US rainbow trout aquaculture.

Technical Abstract: Columnaris disease (CD), caused by Flabobacterium columnare, is an emerging disease affecting rainbow trout aquaculture. Objectives of this study were to 1) estimate heritability of innate CD resistance in a rainbow trout line (ARS-Fp-R) previously selected four generations for improved bacterial cold water disease (BCWD) resistance, 2) estimate genetic correlations among CD resistance, BCWD resistance, and growth performance traits and 3) compare CD resistance among the ARS-Fp-R, ARS-Fp-S (selected for increased BCWD susceptibility), and ARS-Fp-C (unselected control) lines. Heritability of CD resistance was estimated using data from an immersion challenge of 44 full-sib ARS-Fp-R families produced using a paternal half-sib mating design, and genetic correlations were estimated using these data and five generations of BCWD resistance, 9-mo BW, and 12-mo BW data from 405 ARS-Fp-R full-sib families. Survival of ARS-Fp-R families ranged from 0 to 48% following CD challenge and heritability estimates were similar between CD (0.17 ± 0.09) and BCWD (0.18 ± 0.03) resistance, and the genetic correlation between these two traits was favorable (0.35 ± 0.18). Genetic correlations were small and antagonistic (-0.15 ± 0.09 to -0.19 ± 0.17) between the two resistance traits and 9- and 12-mo BW. Two challenges were conducted in consecutive years to compare innate CD resistance among ARS-Fp-R, -C, and -S families. The ARS-Fp-R families (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 CD resistance (56% survival) than ARS-Fp-S (38% survival; P = 0.02) families in the second challenge using a ~2.5-fold greater challenge dose. These data, and the documented improvement of innate BCWD resistance in the ARS-Fp-R line, suggest that similar genetic improvement can be made for CD resistance using selective breeding. The positive genetic correlation between CD and BCWD resistance suggests that both traits will be improved simultaneously when selection is practiced on only one trait, and the greater CD resistance of the ARS-Fp-R line, compared to the ARS-Fp-C and -S lines, supports the estimate of a favorable genetic correlation. However, the antagonistic, albeit small, genetic correlations between resistance and growth traits suggests the need for a multiple-trait selection index to simultaneously improve both trait types.