Location: Cool and Cold Water Aquaculture Research2011 Annual Report
1a. Objectives (from AD-416)
1: Define phenotypic measures and estimate genetic and phenotypic parameters and correlations for production, product quality, and reproductive quality traits. • 1.a. Estimate genetic and phenotypic parameters and correlations for production and product quality traits. • 1.b. Estimate genetic parameters and correlations for reproduction traits. • 1.c. Evaluate accuracy of live-animal ultrasound measures to predict body composition and fillet quality. 2: Identify physiological basis for variation in, and strategies to improve growth and nutrient utilization in rainbow trout. • 2.a. Identify regulatory mechanisms for nutrient utilization in muscle and liver. • 2.b. Identify genetic variation in expression of regulatory proteins within nutrient signaling pathways. 3: Identify physiological basis for variation in, and strategies to improve reproductive performance in rainbow trout. • 3.a. Identify growth factors that affect final maturation and their signaling pathways. • 3.b. Identify effects of the maturation-inducing hormone MIH, candidate growth factors and signaling pathways on translation of maternal proteins during follicle maturation and in response to fertilization. • 3.c. Identify changes in germ cell transcription of TGF-beta superfamily growth factors during oogenesis and oocyte recruitment with the aid of transgenic trout carrying a green fluorescent protein gene driven by the vasa gene promoter (GFP-vasa). 4: Improve procedures for natural triploid (2Nx4N) production and evaluate their performance. • 4.a. Evaluate performance of natural triploid (2Nx4N). • 4.b. Improve procedures for natural triploid (2Nx4N) production.
1b. Approach (from AD-416)
A comprehensive multidisciplinary strategy utilizing quantitative genetic, physiological and molecular 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. As part of this research we will continue to evaluate and characterize the broodstock established at the NCCCWA selected for improved growth performance. Offspring from this line of rainbow trout will be evaluated for important aquaculture production traits e.g., growth, feed efficiency, and reproductive development. These data will yield estimates of additive genetic variation among and within families of rainbow trout and provide guidance for designing selection and breeding programs for genetic improvement. Physiological research will focus on defining critical pathways, and molecular components in those pathways, for economically important traits. Furthermore, animals with extreme phenotypes, identified by quantitative genetic analyses, will be used in physiological studies to define the critical physiological differences. Procedures for tetraploid induction will be improved for the development of natural triploids and this technology will be applied to standard and improved lines to evaluate its potential to provide additional benefits to rainbow trout aquaculture.
3. Progress Report
The selective breeding program for growth aims to understand, improve, and effectively use fish genetic resources (NP106 Components 1) to achieve improved products for producers and consumers. Progress towards Objective 1 included evaluation of third-generation families (n=98) from our growth-selected line for performance and development of a breeding matrix based on breeding value estimates for 2,617 fish. Data were also collected from these families to estimate variation in, and heritability of, additional traits including feed intake, feed efficiency, yield, composition, and fillet quality. Ultrasound was evaluated as a non-lethal means of measuring body composition and fillet quality. Efforts to identify factors having the potential to improve growth and nutrient utilization (NP106 Component 2) include understanding mechanisms of protein turnover under Objective 2. Muscle degradation is known to occur in sexually maturing trout and sterile triploid fish that lack normal sex steroid production are gaining prominence, but little is known of sex steroid actions in nutrient partitioning and muscle growth. We found protein degradation rates increase in muscle during maturation, even when total protein levels are maintained by high feed levels. Similarly, preliminary results suggest in vitro and in vivo treatment with estrogen but not androgens directly promote protein degradation in white muscle. Overall, these studies suggest estrogens but not androgens, promote protein turnover during maturation regardless of feeding rate and muscle protein balance. Progress towards enhancing reproductive performance in rainbow trout (NP106 Component 2) focuses on improving egg quality. Under Objective 3 we characterized the time course of the effects of the progestin maturation inducing hormone on expression of mRNA transcripts for gonadotropin receptors and the transforming growth factor beta superfamily inhibitor bambi. We showed that post-ovulatory decreases in MAPK do not underlie reductions in egg quality in fish as it does in mammals. We demonstrated that milt release (venting) can be used to distinguish genetic females from genetic males when trout are masculinized with the androgen methyltestosterone, thereby facilitating the development of all-female lines preferred by the industry. Efforts to develop breeding strategies which produce sterile fish that commit energy to growth and permit control of reproduction fall under Objective 4 (and NP106 Component 2). Tetraploid fish are crossed with normal diploid fish to produce 100% triploid fish which are sterile. Tetraploid and diploid rainbow trout families that were developed in 2008 were crossed this year to make genetically-related diploids, tetraploid-derived triploids, and pressure-induced triploids (industry standard method). Studies to compare growth, disease resistance, and stress performance among these different types of animals are ongoing.
1. Creation of sterile, fast growing salmonids made easier and more reliable. Currently used methods of creating sterile rainbow trout by manipulating entire sets of chromosomes are less than 100% effective, therefore benefits associated with more efficient growth and reproductive isolation are not fully realized. ARS researchers in Leetown, WV identified that egg age is a major factor in protocols that aim to double chromosome sets in fish. This information allows sampling of very few fish to determine parameters for efficiently manipulating chromosomes for entire populations. As a result, farmers can more predictably create sterile trout with much less effort.
Lankford, S.E., Weber, G.M. 2010. The maturation-inducing hormone 17a-20b-dihydroxy-4pregnen-3-one regulates gene expression of inhibin A and bambi (bone morphogenetic protein and activin membrane bound inhibitor) in the rainbow trout ovary. General and Comparative Endocrinology. 168:369-376.