Shao Ming, Liang Hualiang, Xu Gangchun, Zhu Jian, Li Songlin, Ren Mingchun
Wuxi Fisheries College, Nanjing Agricultural University, Wuxi, 214081, China.
Key Laboratory of Integrated Rice-Fish Farming Ecology, Ministry of Agriculture and Rural Affairs, Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, Wuxi, 214081, China.
Fish Physiol Biochem. 2024 Feb;50(1):331-347. doi: 10.1007/s10695-022-01126-9. Epub 2022 Sep 29.
An 8-week growth experiment was conducted to investigate the effects of dietary leucine on growth performance, body composition, and gene expression of hepatic nutrient metabolism in the largemouth bass (Micropterus salmoides). Six isonitrogenous (49.87%) diets with graded leucine levels (2.62, 3.07, 3.60, 3.87, 4.20, 4.71% of dry diet) were fed to triplicate groups with 20 juvenile fish (20.00 ± 0.13 g). The results revealed that the specific growth rate (SGR) and weight gain (WG) increased significantly with increasing dietary leucine levels, reached their maximal value in the Leu-4.20% groups, and then decreased slightly. Although the feed conversion ratio (FCR) showed decreasing trends, no significant difference was detected. Leucine supplementation significantly improved the content of body protein and total plasma protein (TP). Additionally, a higher expression level of target of rapamycin (TOR) and ribosomal protein S6 (S6) mRNA was observed in the Leu-3.87% and Leu-4.20% diets, whereas the GCN2 (general control nonderepressible2 kinase) and AFT4 (activating transcription factor 4) mRNA expression levels were suppressed. The lipid content of the body was not influenced by leucine levels, whereas the content of total triglyceride (TG) first decreased significantly with increasing dietary leucine levels from 2.62 to 3.87% and then increased with increasing leucine levels (4.20% to 4.71%). The total cholesterol (TC) and low-density lipoproteins (LDL) trended in a similar direction but did not achieve statistical significance (P > 0.05). The expression of insulin receptor substrate 1 (IRS-1) was significantly elevated by dietary leucine levels, while protein kinase B (AKT) and phosphatidylinositol 3-kinase (PI3K) expression was inconsistently upregulated. Furthermore, leucine supplementation decreased plasma glucose and hepatic glycogen contents, and the expression levels of glucokinase (GK), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6pase) were significantly inhibited at 4.20% and 4.71% leucine diets. Analyses of the change in SGR and FCR using the quadratic regression model estimated that the optimum dietary leucine requirement of juvenile largemouth bass was 4.42% and 4.63% of the dry diet (8.86% and 9.28% of dietary protein), respectively.
进行了一项为期8周的生长实验，以研究饲料中亮氨酸对大口黑鲈（Micropterus salmoides）生长性能、身体组成以及肝脏营养物质代谢基因表达的影响。将六种等氮（49.87%）且亮氨酸水平呈梯度变化（占干饲料的2.62%、3.07%、3.60%、3.87%、4.20%、4.71%）的饲料投喂给三个重复组，每组20尾幼鱼（20.00 ± 0.13 g）。结果显示，特定生长率（SGR）和增重（WG）随着饲料中亮氨酸水平的升高而显著增加，在亮氨酸含量为4.20%的组中达到最大值，然后略有下降。虽然饲料转化率（FCR）呈下降趋势，但未检测到显著差异。补充亮氨酸显著提高了鱼体蛋白质和血浆总蛋白（TP）的含量。此外，在亮氨酸含量为3.87%和4.20%的饲料组中，观察到雷帕霉素靶蛋白（TOR）和核糖体蛋白S6（S6）的mRNA表达水平较高，而一般控制非抑制性2激酶（GCN2）和激活转录因子4（AFT4）的mRNA表达水平受到抑制。鱼体的脂质含量不受亮氨酸水平的影响，而总甘油三酯（TG）的含量首先随着饲料中亮氨酸水平从2.62%增加到3.87%而显著下降，然后随着亮氨酸水平的进一步升高（从4.20%到4.71%）而增加。总胆固醇（TC）和低密度脂蛋白（LDL）的变化趋势相似，但未达到统计学显著水平（P > 0.05）。饲料中的亮氨酸水平显著提高了胰岛素受体底物1（IRS-1）的表达，而蛋白激酶B（AKT）和磷脂酰肌醇3激酶（PI3K）的表达上调情况不一致。此外，补充亮氨酸降低了血浆葡萄糖和肝糖原含量，在亮氨酸含量为4.20%和4.71%的饲料组中，葡萄糖激酶（GK）、磷酸烯醇式丙酮酸羧激酶（PEPCK）和葡萄糖-6-磷酸酶（G6pase）的表达水平受到显著抑制。使用二次回归模型分析SGR和FCR的变化估计，大口黑鲈幼鱼的最佳饲料亮氨酸需求量分别为干饲料的4.42%和4.63%（占饲料蛋白质的8.86%和9.28%）。
