Submitted to: Trout Talk
Publication Type: Trade Journal
Publication Acceptance Date: 6/1/2010
Publication Date: 7/1/2010
Citation: Leeds, T.D., Rexroad Iii, C.E., Wiens, G.D. 2010. Validating selective breeding approaches for disease resistance. Trout Talk. 2010:6.
Technical Abstract: Selective breeding of rainbow trout at the USDA/ARS National Center for Cool and Cold Water Aquaculture (NCCCWA) in Leetown, West Virginia is designed to accomplish four goals: 1) define commercially important traits such as disease resistance, growth rate, stress response, and feed efficiency; 2) determine the amount of genetic variation for those traits in commercially relevant populations; 3) produce improved germplasm that can be provided to the industry; and 4) help us understand the biology underlying complex traits and their interactions with environmental variables. We are using selective breeding to study resistance to Flavobacterium psychrophilum, the causative agent of bacterial cold water disease (BCWD). This pathogen poses a major fish health concern for trout and salmon aquaculture around the world, and has been documented to be an important cause of fish loss. Losses can be severe in young fish, and currently, no approved, commercial vaccine is available in the US. Our first goal was to determine how much genetic variation was in our population for BCWD resistance, and whether disease resistance was correlated with growth. We used an experimental BCWD challenge model to evaluate 71 full-sib families in 2005 and found that there was a large amount of variation in survival among families. From these data we predicted that disease resistance was moderately heritable - in other words, superior BCWD resistance could be passed from parents to offspring. Furthermore, there was no correlation between disease resistance and growth traits in this population suggesting that selection for improved BCWD resistance would not adversely affect growth performance. We then tested these predictions by using selective breeding for improved BCWD resistance for two generations. After two generations, the mean survival of resistant-line families increased approximately 45 percentage points, while growth performance was unaffected. Samples of fish from our populations have been distributed to Stakeholder farms to evaluate their disease resistance and growth in production settings. From these field trials we hope to learn if our selective breeding approach has made a practical difference. If so, the improved germplasm will be made available to the industry. In parallel with our traditional selective breeding approach, we have developed specialized sub-populations to conduct genomics and immunology research. Our genomics research is aimed at identifying genetic markers associated with disease resistance. These markers will allow producers to expedite genetic improvement, and without the need for laborious challenge tests and complex data analysis. Our immunology research aims to unravel complex host/pathogen interactions to understand virulence factors in the pathogen and mechanisms the host uses to fight off infection. This will facilitate development of effective vaccines that can be used synergistically with traditional and marker-based genetic improvement programs. Collectively, our selective breeding, genomics, and immunology research will improve the industry’s ability to produce, and maintain, healthy fish.