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United States Department of Agriculture

Agricultural Research Service

2008 Annual Report

1a.Objectives (from AD-416)
1. Establish two domesticated strains (even year and odd year populations) of rainbow trout selectively bred for improved growth and disease resistance. Genetic and phenotypic parameters for commercially important traits will be evaluated. The improved lines will be tested under field conditions in collaboration with trout farmers. 2. Provide physiological definition and characterization of growth, stress, and reproductive traits in rainbow trout. 3. Develop techniques for effective polyploidy induction to disrupt sexual development in rainbow trout.

1b.Approach (from AD-416)
A comprehensive multidisciplinary strategy utilizing quantitative genetic, physiological and molecualr biological approaches is being used to produce genetically superior strains of rainbow trout for release to trout producers, and to develop the technologies for rapid and continued innovation and improvement. The initial step in this research will be to evaluate and characterize the broodstock established at NCCCWA. Offspring from crosses of six strains of rainbow trout will be evaluated for important aquaculture production traits e.g., growth, health, and reproductive development. These data will yield estimates of additive genetic variation among and within strains of rainbow trout and provide guidance for designing selection and breeding programs for genetic improvement. We will continue development and testing of rainbow trout lines that are transgenic for disease resistance genes. Physiological research will focus on defining critical pathways, and molecules in those pathways, for economically important traits. Furthermore, animals with extreme phenotypes, identified in the quantitative genetic anaylses, will be used in physiological studies to define the critical physiological differences. Specific breeding aids such as polyploidy and sex-reversal (to produce all female lines) will be applied to select families to provide benefits to rainbow trout aquaculture. Improved lines resulting from this work will be tested under field and farm conditions to demonstrate improvements prior to release of germplasm to the trout farming industry.

3.Progress Report
Fish from the third generation of selection for improved growth and the second generation for resistance to Flavobacterium psychrophilum (Fp), were evaluated. Estimates for genetic parameters from our Fp resistance line indicate high heritabilities for 5-, 7-, 9-, and 12-month body weights, moderate heritability for Fp resistance, and significant genetic gain in disease resistance. In addition, estimates of genetic correlations indicate that body weight traits and Fp resistance can be improved simultaneously. This work is expected to offer growers a fish more resistant to the most important bacterial disease affecting trout culture, bacterial coldwater disease, without sacrificing growth performance. Expression of MAFbx, a gene involved in protein degradation, has been shown to be negatively correlated with feed conversion and body weight. Genetic variation in proteolytic gene expression in response to feed deprivation and growth factor treatment has been observed. These results suggest mechanisms regulating protein turnover and identify family variation in gene expression related to these mechanisms. These findings provide measures and potential criteria for selection for improved feed conversion.

National Program 106, Component 3, Genetic Improvement & 6, Genetic Improvement, Growth and Development and Nutrition.

1. Improved procedures for tetraploid induction. The US Rainbow Trout industry is interested in production of tetraploids to be crossed with diploids to produce 100% sterile triploids for improved growth performance and germplasm protection. Current procedures for tetraploid induction are unreliable and labor intensive because of variability in the time at which pressure must be applied, and thus, must be calculated precisely for each batch of eggs. Factors contributing to this variability were investigated and a strong influence of environment was found. By maintaining broodfish in a common environment, a single time point for the application of pressure can be used to induce tetraploidy in eggs of fish from diverse genetic backgrounds. Egg handling procedures, including time from egg stripping to fertilization, were determined not to affect the time to apply pressure. New methods for sampling up to 20 fish simultaneously for verification of tetraploid induction were established. These results support procedures for induction of tetraploidy that are amply efficient for commercial implementation. NP 106-Aquaculture; Genetic Improvement; Develop techniques for chromosome set manipulation for disrupting sexual development.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of the New MTAs (providing only)3

Review Publications
Hershberger, W.K., Hostuttler, M.A. 2007. Protocols for more effective induction of tetraploid rainbow trout. North American Journal of Aquaculture. 69:367-372.

Last Modified: 12/21/2014
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