NON-TECHNICAL SUMMARY: Growing demand for finite supplies of fish meal worldwide has led to an intensive search for alternative sources of dietary protein to feed fish. Plant protein sources are abundant but often contain high levels of carbohydrates too. Unfortunately, high levels of carbohydrates in cultured rainbow trout diets result in prolonged, elevated blood sugar which adversely affects their growth performance and health over time. This project directly addresses how dietary carbohydrates are regulated in rainbow trout and what amount can used or stored effectively without causing metabolic problems. Current research suggests a possible acclimation period to a high carbohydrate diet exists in rainbow trout between 28 - 56 days after which blood sugar, liver enzyme activity and gene expression change dramatically. Our objective is to examine blood sugar profiles along with enzyme activities and gene expression and determine whether acclimation to a carbohydrate-rich diet is a consequence of the size or age of the fish or the result of another metabolic process. The results will aid trout and salmon aquaculture throughout the US and the world by addressing; 1) the usefulness of commercial diets for rainbow trout trending toward increased carbohydrate content and; 2) use of alternative plant proteins in fish diets.
OBJECTIVES: The goal of the current study is to further refine our understanding of the metabolic use and adaptation to exogenous dietary carbohydrate in cultured rainbow trout. This study builds upon significant current knowledge and preliminary evidence with three objectives: 1) Assess post-prandial plasma glucose profiles over a 10 week feed trial along with growth performance, gene expression and enzyme activities to determine whether acclimation to a carbohydrate-rich diet is a consequence of size/age, or a result of transcriptional modulation or glucose sensing. 2) Assess transcriptional responses to dietary adaptation to a high carbohydrate diet in hepatic genes associated with intermediary metabolism, lipid synthesis, and oxidation-reduction reactions. 3)Evaluate the utility of glycosylated hemoglobin (HbA1C) as a novel method to assess long-term plasma glucose concentrations in rainbow trout. This study is meant to provide further preliminary information as to dietary adaptation in the liver so that larger, integrated studies involving additional metabolic pathways and tissues such as gut transport, kidney excretion/reabsorption etc. may be proposed. Alternative feeds utilizing plant-based diets and selection for trout to utilize these diets are emphasized research at the Hagerman Fish Culture Experiment Station in collaboration with the USDA-ARS Trout-Grains Project located on the station. Expected Outcomes. The proposed project will produce information on exogenous carbohydrate utilization in rainbow trout. Data will include growth performance, proximate composition, feed intake and retention, plasma profiles of glucose, lactate, alanine, triglycerides, glycerol and free fatty acids, liver and muscle glycogen and expression profiles for 13 metabolic genes. Additionally, the project may also provide information on the utility of using glycosylated hemoglobin (HbA1C) as a measure of long-term plasma glucose levels. Uses of Expected Results. Endpoint determinations of post-prandial plasma glucose after one meal or at the end of a 4 or 8 week study in rainbow trout are not novel nor are the expression profiles of any of the genes proposed in this study per se. However, the combination of such analyses and the level of sampling will provide novel information to be used to further understand exogenous glucose utilization in rainbow trout. Ultimately, rainbow trout diets in the future must be supplied with alternative sources of protein rather than solely by fish meal. Plant proteins and the effects these alternative proteins and carbohydrates may have on the performance and health of the fish will be the source of much future investigation.