Effects of a multistrain probiotic on the growth, immune function and intestinal microbiota of the tongue sole Cynoglossus semilaevis

This study evaluated the effects of a dietary multistrain probiotic (Bacillus subtilis, B. licheniformis and Lactobacillus plantarum) on the growth, immune function and intestinal microbiota of the tongue sole Cynoglossus semilaevis. Fish in three groups were fed for 21 days: the control group (BG), which received with basal feed; the high-dose group (HG), which received basal feed supplemented with the probiotic at a dose of 2 × 109 CFU/kg feed; and the low-dose group (LG), which received basal feed supplemented with the probiotic at a dose of 5 × 108 CFU/kg feed. After feeding for 21 days, the weight gain rate was higher in HG and LG than in BG, whereas the feed conversion ratio was lower in HG and LG (P < 0.05). Among the three groups, HG had the highest lysozyme, acid phosphatase, and alkaline phosphatase activities and complement C3 concentration. The analysis of the diversity and species abundance of the fish intestinal microbiota revealed that HG had a higher Simpson index than LG at days 7 (P = 0.0238) and 21 (P = 0.0077). The HG samples at day 21 formed a distinct cluster that was separate from the other samples. At the phylum level, the relative abundance of Firmicutes was significantly higher in HG than in the other two groups at day 21 (P < 0.05). The 10 most abundant genera were not significantly different between BG, LG and HG at any time point. Linear discriminant analysis (LDA) effect size (LEfSe) analysis indicated that Firmicutes (phylum), Desulfovibrionaceae (family), Lachnospiraceae (family), and Desulfovibrio (genus) were representative biomarkers in HG at day 21. Overall, the higher dose of the multistrain probiotic was more effective than the lower dose in improving the growth performance, immune function, and intestinal microbiota of tongue sole.