This study was conducted to investigate the effects of Clostridiumautoethanogenum protein (CAP) replacement for fish meal (FM) on growth performance, digestive enzyme activity, humoral immunity and liver and intestinal health in large yellow croakers (Larimichthys crocea). Four experimental diets were formulated by replacing FM with CAP at different levels—0% (CAP0), 15% (CAP15), 30% (CAP30) and 45% (CAP45). Triplicate groups of juveniles (initial weight = 11.86 ± 0.13 g) were fed the test diets to apparent satiation two times daily for eight weeks. There was no significant difference in final body weight (FBW), weight gain rate (WG) and feed efficiency (FE) between CAP0 and CAP15. However, compared to the CAP0, CAP30 and CAP45 significantly reduced FBW, WG and LDR (p < 0.05), while CAP45 significantly reduced FE and PDR (p < 0.05). The whole-body moisture was significantly increased by CAP replacement of FM while crude lipid content was decreased (p < 0.05). No significant difference in crude protein, ash and liver crude lipid was observed among all groups (p > 0.05). Compared to CAP0, CAP30 and CAP45 significantly reduced serum C4 concentration (p < 0.05), and CAP45 significantly reduced serum AKP activity (p < 0.05) but significantly increased LZM activity (p < 0.05). Serum C3 concentration was significantly increased by CAP15 (p < 0.05). In terms of intestinal histology, CAP addition significantly increased the thickness of intestinal villus (p < 0.05), and CAP15 and CAP45 significantly increased the thickness of intestinal muscular (p < 0.05). The addition of CAP significantly reduced serum DAO and D-lactate concentrations (p < 0.05), indicating the intestinal physical barrier was improved. The results of 16S rRNA gene sequencing showed that the intestinal microorganisms of large yellow croakers are dominated by organisms from Proteobacteria, Bacteroidetes and Firmicutes. The addition of CAP reduced the relative abundance of Ralstonia and Christensenellaceae and increased the relative abundance of Paenibacillus. Overall, the optimum level of CAP replacement FM in large yellow croakers feed is 15%, which helps to improve humoral immunity and intestinal health with no adverse effects on growth. However, the 30% and 45% substitution levels adversely affect the growth and humoral immunity of large yellow croakers.

中文翻译：

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用源自工业规模气体发酵的细菌蛋白（Clostridium autoethanogenum 蛋白）替代鱼粉：对幼年大黄鱼 (Larimichthys crocea) 生长和肠道健康的影响

本研究旨在研究自产乙醇梭菌蛋白(CAP) 替代鱼粉 (FM) 对大黄鱼 ( Larimichthys crocea ) 生长性能、消化酶活性、体液免疫以及肝脏和肠道健康的影响。通过用不同水平的 CAP 替代 FM 来配制四种实验日粮——0% (CAP0)、15% (CAP15)、30% (CAP30) 和 45% (CAP45)。一式三份的幼鱼组（初始体重 = 11.86 ± 0.13 克）每天两次喂食测试饲料至明显饱食，持续八周。CAP0 和 CAP15 在最终体重 (FBW)、增重率 (WG) 和饲料效率 (FE) 方面没有显着差异。然而，与 CAP0 相比，CAP30 和 CAP45 显着降低了 FBW、WG 和 LDR（p < 0.05)，而 CAP45 显着降低 FE 和 PDR ( p < 0.05)。CAP替代FM显着增加全身水分，同时降低粗脂质含量（p <0.05）。各组粗蛋白、灰分、肝粗脂比较差异无统计学意义（p > 0.05）。与CAP0相比，CAP30和CAP45显着降低血清C4浓度（p <0.05），CAP45显着降低血清AKP活性（p <0.05）但显着提高LZM活性（p <0.05）。CAP15显着增加血清C3浓度（p< 0.05)。肠组织学方面，CAP添加显着增加肠绒毛厚度（p < 0.05），CAP15和CAP45显着增加肠肌层厚度（p < 0.05）。添加 CAP 显着降低血清 DAO 和 D-乳酸浓度 ( p< 0.05)，表明肠道物理屏障得到改善。16S rRNA基因测序结果表明，大黄鱼肠道微生物以变形菌门、拟杆菌门和厚壁菌门的微生物为主。添加 CAP 降低了 Ralstonia 和 Christensenellaceae 的相对丰度，增加了 Paenibacillus 的相对丰度。总体而言，大黄鱼饲料中 CAP 替代 FM 的最佳水平为 15%，有助于提高体液免疫和肠道健康，且对生长无不良影响。然而，30% 和 45% 的替代水平会对大黄鱼的生长和体液免疫产生不利影响。