Location: Cool and Cold Water Aquaculture Research2013 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:
Growth performance evaluation was completed for ~2,500 fish from the 2012 growth-selected and control lines (4th generation). Selection response has averaged ~12% per generation, and currently the growth-selected line is ~60% larger at 13 months post-hatch. Growth superiority was maintained following triploidization. Fish from growth-selected families were characterized for body morphology, composition, fillet yield and quality, and tissue and blood samples were collected for analysis of growth-related indices. These data will be used to derive estimates of genetic (co)variance parameters for use in selective breeding, and to identify traits measurable using live-animal ultrasound that augments live-animal predictions of fillet yield and quality. In addition, ~89% of families in this line have been converted to monosex female using venting status and marker genotyping following steroid treatment. Little is known about the physiological basis of how triploidy affects production traits. We found that following a fasting event, juvenile diploids mobilized and replaced visceral nutrient stores to a greater extent than triploids, while triploids more rapidly regained carcass growth. Differences in kinetics of gene expression between diploids and triploids and between liver and muscle may contribute to improved growth recovery in the triploids. We initiated a second fasting study on 1-kg animals that compares growth-selected and control line fish to identify if these differences are maintained in adults or altered by selection for improved growth. This work is aimed to determine if different feeding strategies or diet formulation designed specifically for diploids or triploid, or superior growth lines, may be required to achieve optimal growth performance. In addition, we continued our investigation of phytoestrogens, compounds found in soybeans which are a potential replacement for the more expensive and unsustainable fishmeal and fish oil. We determined that phytoestrogens reduce rates of muscle cell proliferation and can affect muscle growth through mechanisms independent of their binding to the estrogen receptor, suggesting that soybeans should be processed in a manner that facilitates phytoestrogen removal. We have recently developed and/or applied technologies aimed at improving the efficiency of the genomic analysis of traits and physiological mechanisms related to growth and reproduction. Multiplex assays (~30 genes each) were used in multiple studies related to growth performance, sexual maturation, and egg quality; including actions of phytoestrogens and TGF-beta ligands. Proteomic analysis of ovarian follicles treated with hormones suggested a number of affected proteins, and RNA-seq analysis of those same samples is currently underway. Collectively, the combined analysis will assist in identifying regulatory pathways affected by the hormones. In addition, we found ultrasound can be used to identify eggs at a stage of maturation critical to avoiding poor egg quality due to egg aging, and for optimizing harvesting of eggs for caviar. We are determining the temporal window and variation in the timing of these events.
1. Genetic improvement for bacterial cold water disease (BCWD) resistance in diploid fish also benefits triploid fish production. Fish can be susceptible to many diseases such as BCWD. Fish with 3 sets of chromosomes or triploid fish are often grown because they are sterile and therefore grow to a larger size more efficiently, have better fillet quality, and can’t reproduce in the wild, however, they can be more susceptible to the BCWD disease. ARS researchers at Leetown, West Virginia have previously shown family-based genetic selection can be used to rapidly improve resistance of diploid trout (with 2 sets of chromosomes) to BCWD, increasing survival rate in laboratory challenges from 30% initially, up to 80% in just two generations. However, this selection was based on normal diploid fish which have 2 sets of chromosomes. Now the researchers have demonstrated that selection for improved disease resistance as a diploid can translate into improved disease resistance when the fish are made into triploids. Therefore, the improved line of BCWD-resistant trout they developed is of value to producers of both diploid and triploid rainbow trout used for both food production and fisheries purposes. Furthermore, demonstrating hatcheries can select based on the fertile phenotype (diploid) provides hatcheries the advantage of housing half as many fish as they would otherwise maintain if selection for breeding were based on a trait distinctive to triploids.
Weber, G.M., Wiens, G.D., Welch, T.J., Hostuttler, M.A., Leeds, T.D. 2013. Comparison of disease resistance between diploid, induced-triploid, and intercross-triploid rainbow trout including trout selected for resistance to Flavobacterium psychrophilum. Aquaculture. 410-411, 66-71.