Muscle is the complex and heterogeneous tissue, which comprises the primary edible part of the trunk of fish and mammals. Previous studies have shown that dietary isoleucine (Ile) exerts beneficial effects on growth in aquatic animals. However, there were limited studies regarding the benefits of Ile on fish muscle and their effects on flesh quality and muscle growth. Thus, this study was conducted to explore whether dietary Ile had affected flesh quality and muscle growth in hybrid bagrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂). A total of 630 hybrid fish, with an initial average body weight of 33.11 ± 0.09 g, were randomly allotted into seven experimental groups with three replicates each, and respectively fed seven diets with 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile/kg diets for 8 weeks. In the present study, we demonstrated that Ile significantly: (1) increased muscle protein and lipid contents and the frequency distribution of myofibers with ≤ 20 μm and ≥ 50 μm of diameter; (2) improved pH value, shear force, cathepsin B and L activities, hydroxyproline content, resilience, cohesiveness, and decreased cooking loss, lactate content, hardness, springiness, gumminess, and chewiness; (3) decreased reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl (PC) contents, GCLC and Keap1 mRNA levels, and up-regulated CuZnSOD, CAT, GPX1a, GST, and Nrf2 mRNA levels; (4) up-regulated the insulin-like growth factor 1, 2 (IGF-1, IGF-2), insulin-like growth factor 1 receptor (IGF-1R), proliferating cell nuclear antigen (PCNA), Myf5, Myod, Myog, Mrf4, and MyHC mRNA levels, and decreased MSTN mRNA level; (5) increased muscle protein deposition by activating AKT-TOR-S6K1 and AKT-FOXO3a signaling pathways. These results revealed that dietary Ile improved flesh quality, which might be due to increasing nutritional content, physicochemical, texture parameters, and antioxidant ability; promoting muscle growth by affecting myocytes hyperplasia and hypertrophy, and muscle protein deposition associated with protein synthesis and degradation signaling pathways. Finally, the quadratic regression analysis of chewiness, ROS, and protein contents against dietary Ile levels suggested that the optimal dietary Ile levels for hybrid bagrid catfish was estimated to be 14.19, 12.36, and 12.78 g/kg diet, corresponding to 36.59, 31.87, and 32.96 g/kg dietary protein, respectively.

中文翻译：

---

膳食异亮氨酸可改善杂交鲢鱼 (Pelteobagrus vachelli♀ × Leiocassis longirostris♂) 的肉质、肌肉抗氧化能力以及与 AKT/TOR/S6K1 和 AKT/FOXO3a 信号相关的肌肉生长


肌肉是复杂且异质的组织，构成鱼类和哺乳动物躯干的主要可食用部分。先前的研究表明，饮食中的异亮氨酸（Ile）对水生动物的生长具有有益的影响。然而，关于 Ile 对鱼肌肉的益处及其对肉质和肌肉生长的影响的研究有限。因此，本研究旨在探讨膳食异亮氨酸是否影响杂交鲢鱼（Pelteobagrus vachelli♀×Leiocassis longirostris♂）的肉质和肌肉生长。将630尾杂交鱼，初始平均体重为33.11±0.09 g，随机分为7个实验组，每组3个重复，分别饲喂5.0、7.5、10.0、12.5、15.0、17.5和7种饲料。 20.0 g Ile/kg 饮食，持续 8 周。在本研究中，我们证明Ile显着：（1）增加肌肉蛋白质和脂质含量以及直径≤20μm和≥50μm的肌纤维的频率分布； (2)改善pH值、剪切力、组织蛋白酶B和L活性、羟脯氨酸含量、弹性、内聚性，并减少蒸煮损失、乳酸含量、硬度、弹性、粘性和咀嚼性； (3)降低活性氧(ROS)、丙二醛(MDA)和蛋白质羰基(PC)含量、GCLC和Keap1 mRNA水平，上调CuZnSOD、CAT、GPX1a、GST和Nrf2 mRNA水平； (4)上调胰岛素样生长因子1、2(IGF-1、IGF-2)、胰岛素样生长因子1受体(IGF-1R)、增殖细胞核抗原(PCNA)、Myf5、Myod、 Myog、Mrf4 和 MyHC mRNA 水平，以及 MSTN mRNA 水平降低； (5)通过激活AKT-TOR-S6K1和AKT-FOXO3a信号通路增加肌肉蛋白沉积。 这些结果表明，膳食 Ile 改善了肉质，这可能是由于营养成分、理化、质地参数和抗氧化能力的增加；通过影响肌细胞增生和肥大以及与蛋白质合成和降解信号通路相关的肌肉蛋白质沉积来促进肌肉生长。最后，咀嚼度、ROS和蛋白质含量与膳食Ile水平的二次回归分析表明，杂交鲢鱼的最佳膳食Ile水平估计为14.19、12.36和12.78 g/kg饲料，对应于36.59、31.87、和 32.96 克/千克膳食蛋白质。