Aquaculture America 2024

February 18 - 21, 2024

San Antonio, Texas

SELECTIVE BREEDING TO IMPROVE RESISTANCE TO COLUMNARIS DISEASE IN RAINBOW TROUT

Timothy D. Leeds*, Jason P. Evenhuis, and Gregory D. Wiens

 

  USDA, ARS, National Center for Cool and Cold Water Aquaculture

 Kearneysville, WV  25430

 tim.leeds@usda.gov



A line of rainbow trout with improved resistance to Flavobacterium psychrophilum, the causative agent of bacterial cold water disease (BCWD) ,  was developed  over five generations of selective breeding. As a result of selection ,  mean survival following laboratory F. psychrophilum challenge in the resistant (ARS-Fp-R) and contemporary control (ARS-Fp-C) and susceptible (ARS-Fp-S) lines was 84.9, 50.5, and 22.0%, respectively, and the g enetic trend  for survival in the ARS-Fp-R line was +10.1 percentage points per generation.  Importantly, improved survival in the ARS-Fp -R line based on laboratory challenges translated to improved resistance to BCWD in production-scale field challenges where fish were naturally exposed to the pathogen.

 Preliminary  laboratory  challenges of families from the three genetic lines with  F. columnare , the causative agent of columnaris disease, suggested that: 1) survival following  F. columnare challenge is heritable; and 2) resistance to F. psychrophilum and  F. columnare has a positive (favorable) genetic correlation in this population.   As a result,  selection to improve survival following  F. columnare challenge became the sole breeding objective.  Fifth-generation families (n = 100) from the ARS-Fp -R line served as the base population, and selection is currently being practiced to develop double-resistant (ARS-Fp/Fc-R), randomly-mated control (ARS-Fp-R), and susceptible (ARS-Fc-S) lines over five subsequent generations of selection. 

 Contrary to expectations,  no upward selection response and only modest downward selection response  was observed  through  the first  two generations; mean survival following  F. columnare challenge of second-generation families was 19.2, 19.7, and 6.2% for the ARS-Fp/Fc-R, ARS-Fp-R, and ARS-Fc-S lines, respectively. Whereas typical family variation in survival was observed each generation (i.e., ranges of 27 – 98%, 9 – 89%, and 1 – 62% survival in the base, first, and second generations, respectively) , mid-parent breeding values were not predictive of progeny survival in the subsequent generation (within-line correlations ≤ 0.06).

Compared to the BCWD challenge (injection-based, flow-through challenge model), increased variation (~1.4-fold) in survival across replicates (challenge tanks) within a family was observed for the columnaris challenge (immersion-based, flow-through challenge model ), suggesting reduced accuracy of the survival phenotype due to unknown non-genetic effects.  Efforts are currently underway to develop and evaluate the utility of a mixed-family (common garden) recirculation-based columnaris challenge model to improve accuracy of the survival phenotype and resulting breeding value estimates.