Largemouth bass (Micropterus salmoides, a carnivorous fish native to North America) prefers to utilize amino acids as energy sources rather than glucose and fatty acids. However, little is known about the nutritional regulation of substrate oxidation in the fish. Therefore, this study was conducted to determine whether the oxidation of glutamate, glutamine, glucose and palmitate in its tissues might be influenced by dietary protein intake. Juvenile largemouth bass (initial weight 18.3 ± 0.1 g) were fed three isocaloric diets containing 40%, 45% and 50% protein for 8 weeks. The growth performance, energy retention, and lipid retention of juvenile fish increased with increasing dietary protein levels. The rate of oxidation of glutamate by the intestine was much greater than that of glutamine, explaining why increasing the dietary protein content from 40% to 50% had no effect on the serum concentration of glutamate but increased that of glutamine in the fish. The liver of fish fed the 50% protein diet had a higher (P < 0.05) rate of glutamine oxidation than that in the 40% and 45% protein groups. In contrast, augmenting dietary protein content from 40% to 45% increased (P < 0.05) both glutamine and glutamate oxidation in the proximal intestine of the fish and renal glutamine oxidation, without changes in intestinal or renal AA oxidation between the 45% and 50% protein groups. Furthermore, the rates of glucose oxidation in the liver, kidney, and intestine of largemouth bass were decreased in response to an increase in dietary protein content from 40% to 45% and a concomitant decrease in dietary starch content from 22.3% to 15.78%, but did not differ between the 45% and 50% protein groups. The rates of oxidation of glucose in skeletal muscle and those of palmitate in all tissues (except for the kidney) were not affected by the diets. Collectively, these results indicate that the largemouth bass can regulate substrate metabolism in a tissue-specific manner to favor protein and lipid gains as dietary protein content increases from 40% to 50% and have a lower ability to oxidize fatty acids and glucose than amino acids regardless of the dietary protein intake. 

大口黑鲈（Micropterus salmoides，一种原产于北美的食肉鱼）更喜欢利用氨基酸作为能量来源，而不是葡萄糖和脂肪酸。然而，人们对鱼体内底物氧化的营养调节知之甚少。因此，本研究旨在确定其组织中谷氨酸、谷氨酰胺、葡萄糖和棕榈酸的氧化是否可能受膳食蛋白质摄入量的影响。幼年大口黑鲈（初始体重 18.3 ± 0.1 克）被喂食三种含有 40%、45% 和 50% 蛋白质的等热量饮食，持续 8 周。幼鱼的生长性能、能量保留和脂质保留随着日粮蛋白质水平的增加而增加。肠道对谷氨酸的氧化速度远大于谷氨酰胺，解释了为什么将膳食蛋白质含量从 40% 增加到 50% 对谷氨酸的血清浓度没有影响，但会增加鱼中谷氨酰胺的浓度。喂食 50% 蛋白质饮食的鱼的肝脏具有更高的 (磷 < 0.05) 谷氨酰胺氧化率高于 40% 和 45% 蛋白质组。相比之下，将日粮蛋白质含量从 40% 增加到 45% 会增加（P < 0.05）鱼近端肠中的谷氨酰胺和谷氨酸氧化以及肾谷氨酰胺氧化，而在 45% 和 50 之间，肠或肾 AA 氧化没有变化% 蛋白质组。此外，当日粮蛋白质含量从 40% 增加到 45% 以及膳食淀粉含量从 22.3% 减少到 15.78% 时，大嘴黑鲈肝脏、肾脏和肠道中的葡萄糖氧化率降低，但在 45% 和 50% 蛋白质组之间没有差异。骨骼肌中葡萄糖的氧化速率和所有组织（肾脏除外）中棕榈酸酯的氧化速率不受饮食影响。总的来说，