Final Report Summary - GLUCOSE USE IN FISH (Carbohydrate utilization by the working muscle of rainbow trout) Commercial fish diets commonly contain a high percentage of carbohydrates, despite fishes´ apparent low natural capacity to utilize them. This is an important area for research, because a high proportion of carbohydrates in the diet can provide readily available glucose to supply most of the energy needed for maintenance, so that a greater proportion of protein can be reserved to build up muscle tissue. We have previously shown that exercise can increase carbohydrate utilization in salmonids (rainbow trout and brown trout), a carnivorous group of fish cultured world-wide. In this part of the project we studied further the use of carbohydrate rich-diets in pejerrey (Odonthestis bonariensis) an omnivorous species with great potential for aquaculture in Argentina. The goal of this part of the project is strengthen the understanding of the effects of the use of high carbohydrate feeds on the physiology of pejerrey by studying its metabolic response to that condition. We arecurrently studying how glucose homeostasis is regulated in this species, analyzing metabolic changes that may occur in these fish under different dietary conditions, including the regulation of glucose transporters at transcriptional level in target tissues.The results of this research may have a positive impact on the optimal use of food resources available in the region for feeding farmed fish species. If carbohydrates could be effectively utilized to spare the use of dietary protein, the benefits to the aquaculture industry in Argentina would be significant. The development of optimized diets will make possible a decrease in feed costs and a reduction in the output of harmful nitrogenous wastes, while still meeting the world’s ever increasing demand for commercially farmed fish.