Location: Cool and Cold Water Aquaculture Research
2012 Annual Report
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.
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.
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. Cleveland, B.M., Weber, G.M. 2011. Effects of sex steroids on indices of protein turnover in rainbow trout (Oncorhynchus mykiss) white muscle. General and Comparative Endocrinology. 174:132-142. Cleveland, B.M., Kenney, P., Manor, M.L., Weber, G.M. 2012. Effects of feeding level and sexual maturation on carcass and fillet characteristics and indices of protein degradation in rainbow trout (Oncorhynchus mykiss). Aquaculture. 338-341:228-236. Gahr, S.A., Weber, G.M., Rexroad Iii, C.E. 2012. Identification and expression of Smads associated with TGF-beta/activin/nodal signaling pathways in the rainbow trout (Oncorhynuchus mykiss). Fish Physiology and Biochemistry Journal. DOI: 10.1007/s10695-012-9611-7. Hafs, A.W., Mazik, P.M., Kenney, P.B., Silverstein, J. 2012. Impact of carbon dioxide level, water velocity, strain, and feeding regimen on growth and fillet attributes of cultured rainbow trout (Oncorhynchus mykiss). Aquaculture. 350-353:46-53. Weber, G.M., Hostuttler, M.A. 2012. Factors affecting the first cleavage interval and effects of parental generation on tetraploid production in rainbow trout (Oncorhynchus mykiss). Aquaculture. 344-349:231-238.