A 120-day feeding trial was conducted to assess the effect of dietary protein levels on growth performance, serum indexes, PI3 K/AKT/mTOR/S6 K signalling pathway and intestinal microbiota of abalone Haliotis discus hannai. Abalones (initial body weight: 15.88–16.54 g; initial shell length 41.70–42.40 mm) were fed nine isoenergetic (~16.08 kJ/g) and isolipidic (~42.0 g/kg) experimental diets with 93.5, 116.9, 151.1, 191.8, 230.3, 275.9, 320.3, 360.5 and 405.9 g/kg protein contents, respectively. Results showed that the optimal dietary protein level for H. discus hannai was determined as 259.4 g/kg through second-order polynomial regression analysis for weight gain rate (WGR). Serum TP and urea nitrogen levels were significantly increased when dietary protein levels were higher than 320.3 g/kg (p < .05). The highest gene expressions of phosphatidylinositol 3 kinase (PI3 K), target of rapamycin (mTOR) and ribosomal protein S6 kinase (S6 K) in muscle were found in the treatment with 275.9 g/kg of dietary protein. The excessive dietary protein level (405.9 g/kg) significantly decreased the gene expression of S6 K. Meanwhile, abalone fed with 275.9 g/kg of dietary protein exhibited the highest microbial diversity in intestine as measured by Chao richness and Shannon diversity index. In conclusion, dietary protein level reduced from 259.4 g/kg to 154.0 g/kg or increased from 259.4 to 323.0 g/kg, the WGR of abalone might be depressed with 5% likelihood. Over high (>360.5 g/kg) or low (<151.1 g/kg) dietary protein levels had negative effects on growth performance, serum indexes, PI3 K/AKT/mTOR/S6 K signalling and microbial diversity in intestine of abalone.

中文翻译：

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日粮蛋白质水平对鲍鱼生长性能、血清指标、PI3K/AKT/mTOR/S6K信号和肠道菌群的影响

A 120天的饲养试验以评估饮食蛋白质水平对生长性能，血清指标，PI3 K / AKT / mTOR的/ S6ķ信号通路和鲍鱼的肠道微生物群的影响皱纹盘鲍。鲍鱼（初始体重：15.88-16.54 克；初始壳长 41.70-42.40 毫米）用 93.5、116.9、151.81.8 和 9 种等能 (~16.08 kJ/g) 和等脂 (~42.0 g/kg) 实验饮食喂养蛋白质含量分别为 230.3、275.9、320.3、360.5 和 405.9 g/kg。结果表明，H的最佳日粮蛋白质水平。 铁饼通过体重增加率 (WGR) 的二阶多项式回归分析确定为 259.4 g/kg。当日粮蛋白质水平高于320.3 g/kg时，血清TP和尿素氮水平显着升高（p < .05）。在用 275.9 g/kg 膳食蛋白质处理时发现肌肉中磷脂酰肌醇 3 激酶 (PI3 K)、雷帕霉素靶标 (mTOR) 和核糖体蛋白 S6 激酶 (S6 K) 的最高基因表达。过量的日粮蛋白质水平（405.9 g/kg）显着降低了 S6 K 的基因表达。同时，根据 Chao 丰富度和香农多样性指数测量，饲喂 275.9 g/kg 日粮蛋白质的鲍鱼在肠道中表现出最高的微生物多样性。总之，日粮蛋白质水平从 259.4 g/kg 降低到 154.0 g/kg 或从 259.4 g/kg 增加到 323.0 g/kg，鲍鱼的 WGR 可能以 5% 的可能性被抑制。过高（>360.5 g/kg）或过低（<151.1 g/kg）日粮蛋白质水平对生长性能、血清指标、