A six‐week growth trial was conducted to evaluate the optimum dietary isoleucine requirement of juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Seven isoenergetic (3,400 kcal/kg of dry matter), isoproteic (496 g/kg of dry matter) and isolipidic (70 g/kg of dry matter) diets were formulated to contain graded Ile levels (7.3, 11.3, 15.7, 19.6, 23.5, 26.8 and 30.8 g/kg, dry‐matter basis). Each experimental diet was fed to triplicate groups of 12 hybrid grouper juveniles (average initial body weight: 6.00 ± 0.01 g/fish). Experimental fish were randomly distributed into 21 glass tanks (L 60 × W 45 × H 50 cm) connected to mechanical and biological water filters as a recycling system. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. After the sampling of the growth trial, the remaining fish in each group were fed their corresponding diets for 2 d and then exposed to 4 mg Cu²⁺ · L⁻¹ water for 24 hr. Results showed that growth performance and feed utilization were significantly affected by different dietary Ile levels (p < .05). Weight gain percentage (WG%), protein productive value (PPV), protein efficiency ratio (PER) and feed efficiency (FE) were increased as dietary Ile level increased, reaching a peak value at 19.6 g/kg dietary Ile, and thereafter, these four parameters declined as dietary Ile level continued to increase. Daily feed intake (DFI) showed an opposite tendency of variations as FE. The quadratic regression analysis of WG%, PPV, PER and FE against dietary Ile levels indicated that the optimum dietary Ile requirement for hybrid grouper was estimated to be 19.8, 20.8, 19.4 and 19.1 g/kg dry matter, respectively. Among all experimental treatments, fish fed 19.6 g/kg dietary Ile had the highest expression of growth and protein synthesis‐related genes, including growth hormone (GH) in pituitary, insulin‐like growth factor 1 (IGF‐1), growth hormone receptor 1 (GHR1), target of rapamycin (TOR) and S6‐kinase 1 (S6K1) in liver. Gut micromorphology was significantly influenced by dietary Ile levels. After the exposure to 4 mg Cu²⁺ · L⁻¹ water for 24 hr, fish fed 19.6 g/kg dietary Ile had the highest survival and the best immunologic manifestation among all experimental treatments. Generally, the optimum dietary Ile requirement for maximum growth of hybrid grouper was estimated to be 19.8 g/kg dry matter, corresponding to 39.9 g/kg dietary protein.

中文翻译：

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少年石斑鱼的最佳饮食异亮氨酸需求量（Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂）

进行了为期六周的生长试验，以评估少年杂交石斑鱼（斑节对虾×斑节对虾）的最佳饮食异亮氨酸需求量）。配制了7种等量能量（3,400 kcal / kg干物质），等蛋白（496 g / kg干物质）日粮和等脂（70 g / kg干物质）日粮，以包含分级的Ile水平（7.3、11.3、15.7、19.6， 23.5、26.8和30.8 g / kg，以干物质计）。每种实验饮食都喂入12个杂种石斑鱼幼鱼一式三份（平均初始体重：6.00±0.01 g /鱼）。将实验鱼随机分配到21个玻璃罐（L 60×W 45×H 50 cm）中，该玻璃罐与机械和生物滤水器相连，作为回收系统。每天两次（08:00和16:00）给鱼喂食，使其明显饱食。在对生长试验进行采样后，将每组剩余的鱼饲喂相应的饲料2 d，然后暴露于4 mg Cu 2 ⁺  ·L ^-1水24小时。结果表明，不同日粮中Ile水平对生长性能和饲料利用率有显着影响（p <.05）。体重增加百分比（WG％），蛋白质生产价值（PPV），蛋白质效率比（PER）和饲料效率（FE）随着日粮Ile水平的增加而增加，达到19.6 g / kg日粮Ile的峰值，此后，随着饮食中Ile水平的持续升高，这四个参数均下降。每日采食量（DFI）与FE的变化趋势相反。WG％，PPV，PER和FE对饮食中Ile水平的二次回归分析表明，混合石斑鱼的最佳饮食Ile需求估计分别为干物质19.8、20.8、19.4和19.1 g / kg。在所有实验处理中，饲喂19.6 g / kg膳食Ile的鱼的生长和蛋白质合成相关基因的表达最高，包括垂体中的生长激素（GH），胰岛素样生长因子1（IGF-1），生长激素受体1（GHR1），雷帕霉素（TOR）和肝S6激酶1（S6K1）的靶标。肠道Ile水平显着影响肠道形态。暴露于4 mg铜后在所有实验处理中，使用2 ⁺  ·L ^-1水持续24小时，喂食19.6 g / kg膳食Ile的鱼具有最高的存活率和最佳的免疫学表现。通常，杂种石斑鱼最大生长的最佳饮食Ile需求估计为19.8 g / kg干物质，相当于39.9 g / kg饮食蛋白质。