Effects of fish meal replacement by soybean meal with supplementation of functional compound additives on intestinal morphology and microbiome of Japanese seabass (Lateolabrax japonicus)

A 15-week trial was carried out to estimate the effects of functional compound additives (FCA) on intestinal morphology and microbiome in Japanese seabass, Lateolabrax japonicus, fed diets with soybean meal (SBM) partially replacing fish meal (FM). The formulation of FCA was the mixture of antioxidant, immunopotentiator and Mintrex((R)) trace elements. Four isonitrogenous (45%) and isolipidic (11%) diets, including FM42 (the control group without FCA), FM35 (15% FM protein substitution level with FCA), FM21 (50% FM protein substitution level with FCA) and FM21-N (50% FM protein substitution level without FCA) were formulated. Quadruplicate groups of seabass (initial average weight 125.65 +/- 0.60g) were randomly handfed each diet twice daily in seawater floating cage. No significant differences were found in microvillus height (HMV) and muscular thickness (MT) of distal intestine among fish fed FM42, FM35 and FM21, whereas the HMV, MT and fold height (HF) in seabass fed FM42 were significantly higher than those of seabass fed FM21-N (P<0.05). Seabass fed FM21-N had more obvious enteritis parameters such as tissue disruption, wider lamina propria and less mucosal fold than those in seabass fed FM21. High-throughput sequencing technology of gut flora showed that Proteobacteria was the most dominant bacteria at phylum level among groups. There was no significant difference in relative abundance and composition of gut microflora among groups. In conclusion, supplementation of FCA might partially eliminate SBM-induced enteritis, but the composition and relative abundance of intestinal microflora were not affected by dietary treatments.