On the contrary, other
prebiotics such as mannanoligosaccharides (MOS) increased species
richness and diversity of the gut microbiota of gilthead sea
bream [44], but no significant histological differences were found.
However, the dietary administration of MOS to rainbow trout (O.
mykiss, Walbaum) reduced species richness and increased the
similarity of bacterial populations of intestinal microbiota, and
improved gut morphology and epithelial brush borders