Gut histology, immunology and the intestinal microbiota of rainbow trout, Oncorhynchus mykiss (Walbaum), fed process variants of soybean meal

Processed soybean meal ingredients have become an emerging plant-based protein used in aquafeed formulations and have been shown to influence gastrointestinal health and microbiota in cultured species. Two 60-day feeding trials with juvenile rainbow trout (Oncorhynchus mykiss, Walbaum) were conducted to compare the effects of fishmeal (FMC), defatted soybean meal (SBM), bioprocessed soybean meal (BSBM) and commercial soy protein concentrate (CSPC) ingredients on intestinal histology, innate immunity and microbiota profiles. Results indicated no significant differences in intestinal immunoglobulin concentrations (p=.41) or gut leukocyte phagocytosis at day 15 samplings (p=.41). Intestinal lysozyme content was found to be highest at day 60 in the BSBM treatment group (p<.01). No significant differences across treatments were observed in histological profiles at day 0 (p=.75), day 15 (p=.08) and day 60 (p=.22). ANOSIM analysis for microbiota beta diversity showed differences among all treatment groups, with the exception of the high and low levels of BSBM (p=.40). There were also differences observed in the alpha diversity ratios, with significant differences in gut communities among dietary groups as demonstrated by Chao-1 (p<.01) and Shannon indices (p=.02). The incorporation of processed soy-based proteins alters the microbial community composition within the distal intestine, and modulates lysozyme concentrations within the distal intestinal tissues.