Dou Xiaomei, Liu Yu, Cao Yixiong, Zhang Yumeng, Fu Xinlangji, Deng Junming, Tan Beiping
College of Fisheries, Guangdong Ocean University, Zhanjiang 524088, China.
Guangdong Engineering Technology Research Center of Aquatic Animals Precision Nutrition and High Efficiency Feed, Zhanjiang 524088, China.
Aquac Nutr. 2023 Jun 3;2023:1017222. doi: 10.1155/2023/1017222. eCollection 2023.
An 8-week feeding trial was conducted to evaluate the effects of dietary lysine level on growth performance and protein metabolism of juvenile leopard coral grouper () and thereby obtained the optimal dietary lysine requirement of . Six isoproteic and isolipidic experimental diets were formulated to contain 1.10%, 1.69%, 2.30%, 3.08%, 3.56%, and 4.36% lysine of diets, respectively. Each diet was assigned at random to triplicate groups of 25 juveniles (initial mean weight is 10.57 g) per tank in a flow-through mariculture system maintained at 27-30°C. Dietary inclusion of 2.30-3.08% lysine improved the weight gain rate (WGR) and specific growth rate and decreased the feed conversion ratio (FCR) of juveniles ( < 0.05). The intestinal digestive enzyme (trypsin, amylase, and lipase) activities were overall enhanced by dietary inclusion of 3.08-3.56% lysine ( < 0.05). The mammalian target of rapamycin (mTOR) signaling pathway was activated in fish fed diets with 1.69-2.30% lysine by upregulating the relative expression levels of hepatic TOR and S6K1 (p70 ribosomal protein S6 kinase 1) but downregulating the relative expression level of hepatic 4E-BP2 (eIF4E-binding protein 2). Conversely, the amino acid response signaling pathway was inhibited in fish fed diet with 2.30% lysine by downregulating the relative expression levels of hepatic GCN2 (general control nondepressible 2), ATF3 (activating transcription factor 3), ATF4a (activating transcription factor 4a), and ATF4b (activating transcription factor 4b). Additionally, dietary 1.69-3.08% lysine enhanced the plasma total protein level and hepatic lysine -ketoglutarate reductase activity but depressed the blood urea nitrogen level and hepatic adenosine monophosphate deaminase activity ( < 0.05). Moreover, dietary 3.08% lysine increased the contents of whole-body crude protein and total amino acids, while 1.69%-4.36% lysine depressed the whole-body lipid content ( < 0.05). These results indicated that optimal dietary lysine increased the digestive enzyme activities, promoted protein synthesis but depressed protein degradation, and thereby improved the growth performance of . Based on the second-order polynomial model, the optimal lysine requirement of juvenile for WGR, FCR, and lysine deposition was 2.60%-2.97% of diets (4.91%-5.60% of dietary protein).
进行了一项为期8周的饲养试验，以评估日粮赖氨酸水平对豹纹鳃棘鲈幼鱼生长性能和蛋白质代谢的影响，从而得出豹纹鳃棘鲈幼鱼的最佳日粮赖氨酸需求量。配制了六种等蛋白、等脂肪的实验饲料，其赖氨酸含量分别为日粮的1.10%、1.69%、2.30%、3.08%、3.56%和4.36%。在温度保持在27-30°C的流水式海水养殖系统中，每个水族箱随机分配每种饲料，每组25尾幼鱼（初始平均体重为10.57 g）。日粮中添加2.30%-3.08%的赖氨酸可提高幼鱼的增重率（WGR）和特定生长率，并降低饲料系数（FCR）（P<0.05）。日粮中添加3.08%-3.56%的赖氨酸可总体提高肠道消化酶（胰蛋白酶、淀粉酶和脂肪酶）活性（P<0.05）。在饲喂含1.69%-2.30%赖氨酸日粮的鱼中，通过上调肝脏TOR和S6K1（p70核糖体蛋白S6激酶1）的相对表达水平，但下调肝脏4E-BP2（eIF4E结合蛋白2）的相对表达水平，激活了雷帕霉素靶蛋白（mTOR）信号通路。相反，在饲喂含2.30%赖氨酸日粮的鱼中，通过下调肝脏GCN2（一般控制非抑制性2）、ATF3（激活转录因子3）、ATF4a（激活转录因子4a）和ATF4b（激活转录因子4b）的相对表达水平，抑制了氨基酸反应信号通路。此外，日粮中添加1.69%-3.08%的赖氨酸可提高血浆总蛋白水平和肝脏赖氨酸-α-酮戊二酸还原酶活性，但降低血尿素氮水平和肝脏腺苷酸脱氨酶活性（P<0.05）。此外，日粮中添加3.08%的赖氨酸可提高鱼体粗蛋白和总氨基酸含量，而添加1.69%-4.36%的赖氨酸可降低鱼体脂肪含量（P<0.05）。这些结果表明，最佳日粮赖氨酸可提高消化酶活性，促进蛋白质合成但抑制蛋白质降解，从而改善豹纹鳃棘鲈幼鱼的生长性能。基于二次多项式模型，豹纹鳃棘鲈幼鱼对于WGR、FCR和赖氨酸沉积的最佳赖氨酸需求量为日粮的2.60%-2.97%（占日粮蛋白质的4.91%-5.60%）。
