Replacement of fishmeal with soybean meal affects the growth performance, digestive enzymes, intestinal microbiota and immunity of Carassius auratus gibelio♀ × Cyprinus carpio♂

Abstract

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).