Location: Cool and Cold Water Aquaculture Research2010 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
This report documents progress for 1930-31000-010-00D which started 1/11/2010 and continues research from 1930-31000-007-00D. Third-generation families (n=98) were hatched from the growth-selected line and are being evaluated for survival, growth, feed efficiency, and fillet yield and quality. Progress was made towards converting this mixed-gender line to an industry preferred all-female line by using a phenotypic marker, failure to release sperm, to identify neomales (i.e., genetic females that produce sperm following hormone treatment) as sires. Fecundity and egg quality attributes were characterized for the females in our growth-selected and control lines to determine if selection for improved growth affects reproductive performance. Multiple physiological responses to stress in fish experimentally exposed to 5 different stressors common to the culture environment were measured. This information together with elucidation of genomic responses to these treatments being conducted in project 1930-31000-009 will identify common and disparate components of responses to diverse stressors and thereby lead to identification of markers that can be used to select for fish that can better resist stress. In vitro incubations of ovarian follicles were used to identify the interactions among 7 members of the TGF-beta superfamily system with sex steroids and gonadotropin in regulating ovarian development. The growth factors had little effect on steroid production or the resumption of meiosis, although a progestin and gonadotropin preparation altered expression of TGF-beta superfamily system genes. These finding support interactions among the hormone systems in fish, as in mammals. Molecular characterization of two genes involved with protein degradation was conducted, with expression of FBXO32 in muscle and intestine being particularly responsive to changes in nutritional status. There is a quadratic relationship between feed intake and feed efficiency, with optimum feed efficiency occurring at 76% of satiation, as well as a quadratic relationship between plasma IGF-I and feed intake, and FBXO32 expression and feed intake, suggesting optimal feed efficiency is associated with slower rates of protein degradation. These findings provide a better understanding of the impact that different feeding strategies have on the metabolic mechanisms that affect growth and feed efficiency in trout. The value of tetraploid induction is the ability to cross tetraploid fish with normal diploid fish (2 sets) to produce 100% triploid fish (3 sets [tetraploid derived triploids]) which are sterile. Triploids cannot breed with wild fish and also grow faster after the age of gonadal development. To evaluate performance traits of these tetraploid derived triploids sibling tetraploid and diploid rainbow trout families were developed in 2008. This year these animals were crossed to make diploids, tetraploid derived triploids, and pressure induced triploids (industry standard method), for comparing growth, disease resistance, and stress performance among these different types of animals.
1. Development of protocols to induce tetraploidy in salmonids. Procedures similar to those developed by ARS Scientists at Leetown, WV to induce tetraploidy in rainbow trout and Atlantic salmon were shown to also induce tetraploidy in brook trout and brown trout. Tetraploid induction is the treatment of fish in a way that causes them to have 4 sets of chromosomes as opposed to the usual 2 sets of chromosomes. The value of tetraploid induction is the ability to cross tetraploid fish with normal diploid fish to produce 100% triploid fish (3 sets) which are sterile. Currently used methods of triploid induction are less efficient. Tetraploid induction of brown and brook trout is important to many small rural aquaculture businesses that supply fish to stocking and fee fishing operations where only triploid fish can be used due to environmental considerations. A commercial Atlantic salmon farming operation and a state hatchery have successfully applied the procedures to develop tetraploid salmon and brook trout, respectively.
2. Identification of pathways regulating protein turnover. Improvements in growth and feed efficiency in rainbow trout can occur by increasing the efficiency of dietary protein retention. Protein retention is affected by rates of protein synthesis and protein degradation, therefore it is critical to understand how these processes are regulated. A series of studies by ARS Scientists at Leetown, WV determined how protein metabolism is affected by genetic variation, hormones, and nutrients. It was determined that genetic variation affects how fish respond to insulin-like growth factor-1, a hormone that increased rates of protein synthesis and reduced rates of protein degradation. Insulin and leucine also increased protein retention in cell cultures. These findings provide a better understanding of how protein degradation is regulated, which is essential for the development of feed formulations, feeding strategies, and husbandry practices that improve feed efficiency and growth.
Cleveland, B.M., Weber, G.M., Blemings, K.P., Silverstein, J. 2009. Insulin-like growth factor-I treatment and genetic variation affect changes in indices of protein degradation in response to food deprivation in rainbow trout (Oncorhynchus mykiss). American Journal of Physiology - Regulatory Integrative & Comparative Physiology. 297:R1332-R1342.