| Popis: |
Columnaris disease (CD), caused by Flavobacterium columnare, is an emerging disease affecting rainbow trout aquaculture. Objectives of this study were to 1) estimate heritability of CD resistance in a rainbow trout line (ARS-Fp-R) previously selected 4 generations for improved bacterial cold water disease (BCWD) resistance; 2) estimate genetic correlations among CD resistance, BCWD resistance, and growth to market BW; and 3) compare CD resistance among the 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 a waterborne 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 5 generations of BCWD resistance, 9-mo BW (approximately 0.5 kg), and 12-mo BW (approximately 1.0 kg) data from 405 ARS-Fp-R full-sib families. The CD and BCWD challenges were initiated at approximately 52 and 84 d posthatch, or approximately 650 and 1,050 degree days (°C × d), respectively. 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 2 traits was favorable (0.35 ± 0.25). Genetic correlations were small and antagonistic (-0.15 ± 0.08 to -0.19 ± 0.24) between the 2 resistance traits and 9- and 12-mo BW. Two challenges were conducted in consecutive years to compare CD resistance among ARS-Fp-R, ARS-Fp-C, and ARS-Fp-S families. In the first challenge, ARS-Fp-R families (83% survival) had greater CD resistance than ARS-Fp-C (73.5%; P = 0.02) and ARS-Fp-S (68%; P0.001) families, which did not differ (P = 0.16). In the second challenge, using an approximately 2.5-fold greater challenge dose, ARS-Fp-R families exhibited greater CD resistance (56% survival) than ARS-Fp-S (38% survival; P = 0.02) families. The favorable genetic correlation between CD and BCWD resistance is supported by greater CD resistance of the ARS-Fp-R line compared to the ARS-Fp-C and ARS-Fp-S lines and suggests that both traits will be improved simultaneously when selection is practiced on only 1 trait. In summary, these data indicate the feasibility of further selective breeding of the BCWD-resistant ARS-Fp-R line for increased CD resistance to produce a double pathogen-resistant line of rainbow trout. |
