Effects of dietary glycinin on the growth performance, digestion, intestinal morphology and bacterial community of juvenile turbot, Scophthalmus maximus L.

This study was run to investigate effects of dietary glycinin on the growth performance, digestion, intestinal morphology and bacterial community of juvenile turbot (Scophthalmus maximus L.). Graded levels (0%, 3%, 6% and 12%) of purified glycinin were added to the basal diet to formulate four experimental diets containing 0%, 2.18%, 4.17% and 8.31% immunologically active glycinin, respectively. Triplicate groups of 30 fish were fed to apparent satiation twice daily for 12 weeks. Dietary inclusion of glycinin did not affect feed intake, feed efficiency ratio or weight gain of turbot, however, fish fed 12% glycinin showed a significant decrease in the apparent digestibility of dry matter and protein, as well as the whole-body lipid content. Meanwhile, slightly increased infiltration of mixed leukocytes in the lamina propria was observed in turbot fed 12% glycinin, so was specific IgM against glycinin in the serum. Sequencing of bacterial 16s rRNA V4 region showed that Proteobacteria (90.64%), Bacteroidetes (6.01%) and Firmicutes (1.73%) were the dominant bacteria in the intestine of turbot. Dietary inclusion of glycinin had no significant effect on the overall structure of bacterial community but dramatically reduced the relative abundance of the Vibrio genus, one of the core microbes, in a dose-independent manner. Our results suggest that turbot can tolerate a relatively high level of immunologically active glycinin (8.31%) in the diet without showing notable impairments of growth performance and gut function.