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United States Department of Agriculture

Agricultural Research Service

2009 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
Genetic improvement of disease resistance to bacterial pathogens is of great importance to the rainbow trout aquaculture industry. To this end we have reared and commenced evaluation of the third generation families of our disease resistant line. This line represents two generations of selection for improved resistance to Flavobacterium psychrophilum, the causative agent of bacterial cold-water disease, the major bacterial pathogen affecting trout aquaculture. We also identified fish with superior growth performance from our growth-select line, which will be selectively mated to produce the fourth-generation.

Understanding the biochemical processes underlying growth performance will facilitate our ability to make progress for this trait through selective breeding and managing nutrient regimens. We used isolated trout muscle cells to identify mechanisms by which certain hormones and nutrients affect protein metabolism in trout. Insulin-like growth factor-I (IGF-I), which we’ve previously shown is associated with faster growth in our population, was shown to slow protein degradation. These findings provide a better understanding of how fish regulate protein metabolism, which is critical for the development of feeding strategies or husbandry practices that optimize growth and feed efficiency. Additionally, these data suggest that the correlation between plasma IGF-I and growth performance in fish is partially a result of the ability of IGF-I to slow protein degradation, thereby promoting protein accretion and growth.

Stress from the aquaculture production environment such as handling and manipulation, overcrowding, sub-optimal water quality parameters, and social interactions have been shown to negatively effect growth, feed intake, feed efficiency, disease resistance, flesh quality, and reproductive performance. To this end we characterized stress response in 460 fish as part of our ongoing effort to identify markers for improved stress resistance in trout. These fish were the third generation in a series of matings designed to identify markers for quantitative trait loci (QTL) for stress response. QTLs are chromosome regions that contain genes affecting traits of interest. This information will be used in breeding fish with different stress responses with the expectation that by altering stress response-growth, disease, and reproductive performance can be improved.

Manipulating the complement of chromosomes of rainbow trout has great potential for the production of sterile fish which grow better than diploids when the fish approach reproductive maturity. We conducted preliminary studies suggesting altering chromosome numbers from two (diploid) to three (triploid) sets reduces stress response and possibly disease resistance. The studies were conducted with only 3 families each and there were very different responses among families, therefore larger scale studies are planned.

1. Breeding Trout with better Growth Performance and Disease Resistance: The U.S. rainbow trout industry is interested in lines of fish with improved growth performance and disease resistance. We have completed evaluations of third-generation families of our line selected for improved growth and third-generation families of our line selected for improved disease resistance. At 9 months of age, fish in our growth-selected line were approximately 73 grams or 24% heavier than fish in our randomly-mated control lines, and at 13 months of age the growth-selected fish were approximately 189 grams or 25% heavier. Preliminary analysis suggests we have made approximately 10% improvement in growth per generation. After two generations of selection, survival following laboratory challenge with F. psychrophilum has increased approximately 45 percentage points in our disease-resistant line. These lines will offer breeders a genetic resource for improving growth and disease resistance in commercial populations.

2. Identified Cellular Pathways Regulating Trout Reproduction: Control of reproduction requires knowledge of pathways regulating reproductive events. Reproductive performance and growth are interdependent and therefore we investigated the effects of the growth factor IGF-I on reproductive function. Unlike in most fish species, we found IGF-I does not participate in inducing a process called follicle maturation in trout. Follicle maturation involves changes in the oocyte and cells surrounding the oocyte required for the fish to spawn fertilizable eggs. Nevertheless, we found activity of signaling molecules normally activated by IGF-I are required for follicle maturation suggesting sex steroids also activate these pathways in trout. Furthermore, we found follicle maturation in the trout requires activity of an enzyme, tyrosine phosphatase, suggesting the regulation of follicle maturation in trout may be different from that thought to be involved in most fish species. These findings provide a better understanding of how reproduction is regulated in trout that may lead to improve husbandry practices that optimize reproductive performance and egg quality.

6.Technology Transfer

Number of the New/Active MTAs (providing only)1

Review Publications
Cleveland, B.M., Blemings, K., Leonard, S.S., Klandorf, H. 2009. Urate oxidase knockdown decreases oxidative stress in a murine hepatic cell line. Oxidative Medicine and Cellular Longevity. 2(2):93-98.

Cleveland, B.M., Kiess, A.S., Blemings, K. 2008. Aminoadipate semialdehyde synthase mRNA knockdown reduces the lysine requirement of a mouse hepatic cell line. Journal of Nutrition. 138:2143-2147.

Picha, M., Silverstein, J., Borski, R. 2006. Discordant regulation of hepatic IGF-I mRNA and circulating IGF-I during compensatory growth in a teleost, the hybrid striped bass (morone chrysops x morone saxatilis). General and Comparative Endocrinology. 147(2):196-205.

Elango, A., Shepherd, B.S., Chen, T.T. 2006. Effects of endocrine disrupters on the expression of growth hormone and prolactin mrna in the rainbow trout pituitary. General and Comparative Endocrinology. 145(2):116-127.

Tipsmark, C., Weber, G.M., Strom, C., Grau, E.G., Hirano, T., Borski, R. 2005. Involvement of phospholipase c and intracellular calcium signaling in the gonadotropin-releasing hormone regulation of prolactin release from lactotrophs of tilapia (oreochromis mossambicus). General and Comparative Endocrinology. 142:227-233.

Weber, G.M., Sullivan, C.V. 2005. Insulin-like growth factor-i induces oocyte maturational competence but not meiotic resumption in white bass (morone chrysops) follicles in vitro: evidence for the rapid evolution of insulin-like growth factor action. Biology of Reproduction. 72:1177-1186.

Shepherd, B.S., Weber, G.M., Vijayan, M., Seale, A., Riley, L., Rodriguez, M.F., Richman III, H., Hirano, T., Grau, G. 2006. Control of growth in tilapia: developments and prospects. Tilapias: Culture, Nutrition, and Feeding (3)73-137.

Vallejo, R.L., Rexroad III, C.E., Silverstein, J., Janss, L.G., Weber, G.M. 2009. Evidence of major genes affecting stress response in rainbow trout using Bayesian methods of complex segregation analysis. Journal of Animal Science. 87:3490-3505.

Elango, A., Shepherd, B.S., Chen, T.T. 2006. Effects of endocrine disrupters on the expression of growth hormone and prolactin mRNA in the rainbow trout pituitary. General and Comparative Endocrinology. 145:116-127.

Silverstein, J., Vallejo, R.L., Palti, Y., Welch, T.J., Wiens, G.D., Rexroad Iii, C.E., Ducrocq, V., Leeds, T.D. 2008. Rainbow trout resistance to bacterial cold-water disease is moderately heritable and is not adversely correlated with growth. Journal of Animal Science. 87:860-867.

Last Modified: 12/21/2014
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