A 60-day feeding trial was conducted to evaluate the effects of different substitution levels (0 %, 20 %, 40 %, 60 %, 80 % and 100 %, named as G1, G2, G3, G4, G5 and G6, respectively) of fishmeal with soybean meal on growth, feed utilization, intestinal microbiota composition and immunity of Carassius auratus gibelio ♀ × Cyprinus carpio ♂ (13.2 ± 0.2 g). Quadratic regression analysis of fish responses including growth performance and feed utilization indicated that the maximum level of soybean meal inclusion varied significantly with the response being modeled. Generally, 95 %–100 % of most growth responses, i.e., weight gain rate and specific growth rate, could be obtained if substitution of fishmeal by soybean meal was limited to <38.52-41.81 % of the diet, 95 %–100 % of most feed efficiency could be achieved when soybean meal substitution was restricted to <40.75 %. Similarly, digestive enzymes activity (chymotrypsin, lipase and amylase) also significantly decreased with increasing dietary soybean levels, as did height of the fold (HF) and height of the microvillus (HMV) in hindgut. The catalase activity in G6 was the lowest, and the superoxide dismutase and lysozyme activity in G1 and G2 were the highest. With the dietary soybean meal increased, the gene expression of IL-6 and TNF-α were up-regulated, while Claudin-12 and Zo- were down-regulated; meanwhile, an increased trend was found in the proportion of Fusobacteria, Proteobacteria and Actinobacteria, but a decreased trend was found in the proportion of Firmicutes and Bacteroidetes. Higher substitution levels had harmful effects on the digestive enzyme activity, intestine morphology, immune response and intestinal health, eventually led to the weakened feed utilization and growth performance of crucian carp.

In conclusion, based on the results of the growth performance and feed utilization, <38.52-41.81 % substitution level of fishmeal by soybean meal was suggested in the diets of crucian carp (13.2 ± 0.2 g).

进行了为期60天的喂养试验，以评估不同替代水平（分别为G1，G2，G3，G4，G5和G6分别为0％，20％，40％，60％，80％和100％的影响） ）用大豆粉上生长，饲料利用，肠道微生物群的组成和免疫鱼粉鲫鱼鲫♀×鲤♂（13.2±0.2克）。对鱼类响应（包括生长性能和饲料利用率）的二次回归分析表明，随着模拟的响应，豆粕最大添加量变化显着。通常，如果将豆粕替代鱼粉的比例限制在日粮的<38.52-41.81％，即日粮的95％–100％之内，则可以达到大多数生长反应的95％–100％，即体重增加和特定生长率。当豆粕替代量限制在<40.75％时，可以达到最大的饲料效率。同样，随着日粮大豆水平的增加，消化酶的活性（胰凝乳蛋白酶，脂肪酶和淀粉酶）也显着下降，后肠的褶皱高度（HF）和微绒毛高度（HMV）也显着降低。G6中的过氧化氢酶活性最低，G1和G2中超氧化物歧化酶和溶菌酶活性最高。随着日粮豆粕含量的增加，IL-6和TNF-α的基因表达上调，而Claudin-12和Zo-的基因表达下调。同时，梭菌，Proteobacteria和放线菌的比例呈上升趋势，而Firmicutes和Bacteroidetes的比例呈下降趋势。较高的替代水平对on鱼的消化酶活性，肠道形态，免疫反应和肠道健康具有有害影响，最终导致feed鱼饲料利用和生长性能下降。梭菌，变形杆菌和放线菌的比例呈上升趋势，而硬菌和拟杆菌的比例呈下降趋势。较高的替代水平对on鱼的消化酶活性，肠道形态，免疫反应和肠道健康具有有害影响，最终导致feed鱼饲料利用和生长性能下降。梭菌，变形杆菌和放线菌的比例呈上升趋势，而硬菌和拟杆菌的比例呈下降趋势。较高的替代水平对on鱼的消化酶活性，肠道形态，免疫反应和肠道健康具有有害影响，最终导致feed鱼饲料利用和生长性能下降。

总之，基于生长性能和饲料利用率的结果，cru鱼（13.2±0.2 g）日粮中建议豆粕替代鱼粉的鱼粉含量低于38.52-41.81％。