Location: Cool and Cold Water Aquaculture Research2012 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:
Fourth-generation growth-selected rainbow trout families (n = 101) were hatched and are being evaluated for growth performance. Eighteen families were made into triploids (3N; three chromosome sets, sterile) to determine if performance as diploids (2N; normal two chromosome sets) reflects performance as 3Ns. Live-animal ultrasound measures made on 3rd-generation families were highly correlated (=0.84) with the same measures made on the carcass, and exhibited statistically-significant correlations with fillet quality traits including yield, fat content, moisture content, color, and texture. Preliminary estimates of heritabilities and genetic correlations for feed efficiency, body composition, and fillet quality traits from 3rd-generation families were generally moderate to large suggesting most of the traits will respond favorably to genetic selection. These studies suggest live-animal ultrasound can be used to enhance selection for carcass quality traits in our fish. We concluded studies demonstrating that estradiol exerts negative effects on protein retention in skeletal muscle of rainbow trout and initiated studies to determine if phytoestrogens mimic the effects of estradiol. Phytoestrogens are found in soybeans and other legumes that show promise as replacements for the unsustainable and expensive fishmeal and fish oil currently used in aquafeeds. In vitro studies indicate that the phytoestrogens and their metabolites promote protein turnover in muscle, predominantly through reductions in protein synthesis. Additionally, genistein, the phytoestrogen found in highest abundance in soybeans, further promotes protein loss by increasing protein degradation. These studies indicate that phytoestrogens may contribute to slower growth rates and reduced nutrient retention commonly observed in rainbow trout consuming plant-based diets. We repeated in vitro studies on the effects of members of the TGF-beta superfamily of genes and their inhibitors on follicle maturation and associated transcript levels in trout follicle-enclosed oocytes. Preliminary analysis identified 95 detectable proteins in the tissues. Two gene multiplexes (>30 transcripts each) were developed to characterize the effects of the treatments. Ovulated eggs were shown to not convert precursor steroids into the progestin that regulates maturation processes despite transcript levels for the responsible enzyme being high in eggs. We initiated microinjection of a vasa-GFP transgene after use of electroporation to transfect sperm failed to produce transgenic fish. Growth performance was compared among families of 2N, pressure-induced 3N (industry standard method), and tetraploid-derived 3N (progeny of tetraploids with four chromosome sets [4N] crossed with 2Ns) rainbow trout. The 4N-derived 3Ns were about 25% heavier than the other groups at the end of a 2-year trial supporting a strong growth advantage to 3Ns produced by this alternative approach. Studies comparing the quality of 3N progeny derived from 1st- and 2nd-generation and two- and three-year-old female 4Ns were conducted but await data analysis.
1. Sex steroids linked to muscle degradation in rainbow trout. Management of sex steroids, particularly anabolic steroids, is central in the efficient production of meat in most terrestrial livestock but little is known about their actions in fish. Understanding how sex steroids affect muscle growth and quality will enable development of strategies for more efficient fillet production. ARS researchers at the National Center of Cool and Cold Water Aquaculture at Leetown, West Virginia investigated actions of different sex steroids on protein turnover in muscle of rainbow trout. The researchers discovered increased rates of muscle protein degradation occur in sexually maturing rainbow trout with high sex steroid levels, even when protein intake is high. Subsequent studies indicated that estrogens, but not androgens, act directly in muscle to reduce protein retention by both increasing rates of protein degradation and decreasing rates of protein synthesis. These data demonstrate that approaches that minimize sex steroid exposure should result in the most efficient production of high quality fillets in the rainbow trout.
Aussanasuwannakul, A., Weber, G.M., Salem, M., Yao, J., Slider, S.D., Manor, M.L., Kenney, P. 2012. Effect of sexual maturation on thermal stability, viscoelastic properties, and texture of rainbow trout, Oncorhynchus mykiss, fillets. Journal of Food Science. 77(1):S77-S83.