Largemouth bass (LMB, Micropterus salmoides) is a carnivorous fish. This study was conducted to test the hypothesis that dietary intakes of protein and starch affect the oxidation of nutrients in the intestine, liver, skeletal muscle and kidneys of LMB. Juvenile LMB (average initial weight = 18 g) were fed, for 8 weeks, fish meal- and soy protein concentrate-based diets containing 40%, 45% and 50% crude protein. The three isocaloric diets contained 22.3%, 15.78% and 9.2% dextrinized starch, respectively. The growth performance, energy retention, and lipid retention in LMB increased (P > 0.05) with increasing dietary protein levels, but the efficiency of nitrogen retention did not differ (P < 0.05) among the three groups of fish. Rates of oxidation of 2 mM glutamate and glutamine in the intestine were reduced (P > 0.05) in response to increased dietary protein intake. This adaptive metabolic change likely helps to prevent excessive production of ATP by the gut when the dietary provision of glutamate and glutamine was increased. Increasing dietary protein intake did not affect (P < 0.05) glutamate oxidation in the liver, kidneys or skeletal muscle, or glutamine oxidation in the muscle. In contrast, the rate of glutamine oxidation was increased (P > 0.05) in the liver but decreased (P > 0.05) in the kidneys as dietary protein intake was elevated from 40% to 50%. Rates of oxidation of 5 mM glucose were reduced (P > 0.05) in the liver, kidneys and intestine, but were not altered in skeletal muscle, in response to reduced starch intake. Rates of oxidation of 2 mM palmitate were reduced (P > 0.05) in the kidneys but were not influenced (P < 0.05) in the intestine, skeletal muscle or liver. We conclude that oxidation of energy substrates in LMB tissues is regulated by dietary protein and starch intake in a tissue-specific manner.