An eight week 3 × 2 two-factorial experiment was conducted to investigate the interaction between carbonate alkalinity levels at 0 and 15 mmol/L, and dietary protein levels at 310, 340 and 370 g/kg on the growth rate, digestive ability and the intestinal immunity, physical barrier function and microflora of Songpu mirror carp (Cyprinus carpio songpu). Fish at an initial average weight of 17.86 ± 0.19 g were randomly allotted to 18 aquariums each with 30 fish. Results revealed that weight gain rate (WGR) significantly decreased as carbonate alkalinity levels increased (p < 0.05), whereas the feed conversion ratio (FCR) of fish significantly increased (p < 0.05). Amylase activity in the intestine significantly decreased with increasing carbonate alkalinity levels (p < 0.05). A carbonate alkalinity of 15 mmol/L significantly reduced the superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) activities, elevated the malondialdehyde (MDA) contents in the intestine and hepatopancreas and decreased the contents of Complement 3 (C3), Complement (C4) and Ig M (p < 0.05). The relative expressions of occludin, claudin3, claudin7, myosin light chain kinase (MLCK) and interleukin 10 (IL-10) in the intestine were significantly down-regulated with increasing carbonate alkalinity levels (p < 0.05), whereas the relative expressions of interleukin 6 (IL-6), interleukin 8 (IL-8) and tumor necrosis factor (TNF-α) in the intestine were significantly up-regulated (p < 0.05). The Proteobacteria abundance significantly increased with increasing carbonate alkalinity level (p < 0.05). The WGR significantly decreased as dietary protein levels increased (p < 0.05). The MDA contents in intestine and hepatopancreas also showed a significant rise with increasing dietary protein levels (p < 0.05). Increments in dietary protein levels significantly reduced the C3 and C4 contents of fish intestine (p < 0.05). Fish in the 370 g/kg diet protein level group showed a significantly lower relative expression of occludin and TNF-α (p < 0.05). There was an effect on the C3 content, the relative expression of occludin, the abundance of Firmicutes and Firmicutes: Bacteroidetes ratio between carbonate alkalinity and dietary proteins over time (p < 0.05).

In summary, under the long-term carbonate alkalinity stress of 15 mmol/L, dietary protein level for Songpu mirror carp should be controlled below 310 g/kg, which could effectively weaken the oxidative damage produced by carbonate alkalinity stress and further strengthen the growth and intestinal immune response of fish.

进行了为期八周的 3 × 2 双因素试验，研究了 0 和 15 mmol/L 的碳酸盐碱度水平与 310、340 和 370 g/kg 的日粮蛋白质水平之间的相互作用对生长速度、消化能力和松浦镜鲤（Cyprinus carpio songpu）的肠道免疫、物理屏障功能及微生物区系。将初始平均重量为 17.86 ± 0.19 克的鱼随机分配到 18 个水族馆，每个水族馆有 30 条鱼。结果表明，随着碳酸盐碱度水平的增加，体重增加率（WGR）显着降低（p  < 0.05），而鱼的饲料转化率（FCR）显着增加（p < 0.05)。肠道中的淀粉酶活性随着碳酸盐碱度水平的增加而显着降低（p  < 0.05）。15 mmol/L 的碳酸盐碱度显着降低了超氧化物歧化酶 (SOD) 和总抗氧化能力 (T-AOC) 的活性，增加了肠道和肝胰腺中丙二醛 (MDA) 的含量，并降低了补体 3 (C3) 的含量，补体 (C4) 和 Ig M ( p  < 0.05)。肠道中occludin、claudin3、claudin7、肌球蛋白轻链激酶（MLCK）和白细胞介素10（IL-10）的相对表达随着碳酸盐碱度水平的增加而显着下调（p < 0.05），而肠内白细胞介素6（IL-6）、白介素8（IL-8）和肿瘤坏死因子（TNF-α）的相对表达显着上调（p  < 0.05）。的变形菌门丰度随碳酸盐碱度水平（显著增加p  <0.05）。随着日粮蛋白质水平的增加，WGR 显着降低（p  < 0.05）。肠道和肝胰腺中的 MDA 含量也随着日粮蛋白质水平的增加而显着增加（p  < 0.05）。日粮蛋白质水平的增加显着降低了鱼肠的 C3 和 C4 含量（p < 0.05)。370 g/kg 饮食蛋白质水平组的鱼表现出 occludin 和 TNF-α 的相对表达显着降低 ( p  < 0.05)。随着时间的推移，对 C3 含量、occludin 的相对表达、厚壁菌门和厚壁菌门的丰度有影响：碳酸盐碱度和膳食蛋白质之间的拟杆菌比 ( p  < 0.05)。

综上所述，在15 mmol/L的长期碳酸盐碱胁迫下，松浦镜鲤日粮蛋白质水平应控制在310 g/kg以下，可有效减弱碳酸盐碱胁迫产生的氧化损伤，进一步加强生长。和鱼的肠道免疫反应。