The effect of feeding a novel multistrain yeast fraction on European seabass (
 Dicentrachus labrax
 ) intestinal health and growth performance

Fish were fed a single-strain yeast fraction (SsYF; 2 g/kg) or a multistrain yeast fraction (MsYF; 0.8 g/kg) for 10 weeks. The results demonstrated significant ( p ≤ 0.03) elevations in weight gain, specific growth rate, protein efficiency ratio, and feed conversion ratio in fish fed the yeast fraction-supplemented diets. In the distal intestine, a significant elevation in microvilli density was observed after 5 and 10 weeks of dietary supplementation with MsYF and SsYF, respectively, compared to control fed fish ( p < 0.001). A significant elevation ( p = 0.02) in the perimeter ratio was observed in fish fed diets supplemented with the yeast fractions. After 10 weeks of feeding on the experimental diets, Rt-qPCR demonstrated a significant downregulation ( p < 0.05) in the stress response genes, heat-shock protein 70 ( hsp70 ) and proliferating cell nuclear antigen ( pcna ), in fish fed diets supplemented with the yeast fractions. Significant ( p < 0.05) elevations in interleukin 1-beta ( il1 β ) and interleukin-10 ( il10 ) gene expression were observed in fish fed diets supplemented with the MsYF compared to the other dietary groups. These findings suggest that feeding an MsYF specifically at a lower incorporation rate < 1 g/kg, compared to a commercial SsYF at 2 g/kg, is effective in improving the intestinal health status and growth performance of European seabass. Tapia-Paniagua Specific investigations on the effect of feeding different yeast cell wall fractions from different yeast species or strains is an emerging field in teleost fish 2013; We hypothesize that there could be a benefit to localized immune responsiveness and intestinal integrity of combining different yeast fractions obtained from distinct yeast strains specifically selected for their contrasting cell wall architecture and molecular structure. The present study aimed at investigating the effects of feeding a novel multistrain yeast fraction (MsYF) consisting of two strains of S. cerevisiae and one strain of Cyberlindnera jadinii and comparing this to a commercially available single-strain yeast fraction (SsYF) on intestinal health and growth performance of one of the most developed aquaculture species in the Mediterranean, the European seabass ( Dicentrachus labrax ) (Food and Agriculture Organization, 2008). This study was designed as a preliminary assessment of an MsYF concept combining Saccharomyces and non-Saccharomyces yeast strains prior to further mechanistic studies. through chemiluminescence. Differences in the cell wall glycosylation of a specific yeast species was measuring the extension of glycoproteins at the yeast cell surface. To do so, the cell surfaces of each strain were probed with Concanavalin A using an Atomic Force Microscope according to Schiavone et al. (2017). The presence of the specific yeast species composing MsYF is shown by identification using ITS-PCR followed by DNA digestion using restriction enzymes Cfo I, Hae III, and Hinf I. DNA extraction was performed directly on the sample dry biomass after Schiavone et al. (2017).