GASTROINTESTINAL MICROBIOTA AND IMMUNOLOGICAL RESPONSES OF RAINBOW TROUT Oncorhynchus mykiss FED MODIFIED SOYBEAN MEAL INGREDIENTS

Timothy J. Bruce*, Regg D. Neiger, Michael L. Brown
 
Missouri Department of Conservation
Lost Valley Fish Hatchery
Warsaw, MO 65355
tim.bruce@mdc.mo.gov
 

Alternative plant-based protein sources are of economic interest to aquaculture feed manufacturers and producers, in an effort to replace expensive marine-derived protein in feeds. Traditionally, high-levels inclusions of soybean meal have been found to present metabolic and health issues resulting in reduced growth performance. Advanced soybean meal processing methods may allow higher inclusions in salmonid aquafeed formulations but effects on gastrointestinal histology and microbiota require further investigation.

Two 60-day juvenile rainbow trout (Oncorhynchus mykiss) feeding trials were conducted to compare the effects of fishmeal (FMC), defatted soybean meal (SBM), bioprocessed soybean meal (BSBM, two levels), and commercial soy protein concentrate (CSPC) ingredients on intestinal histology, innate immunity, and microbiota profiles.  The first feeding trial investigated intestinal morphology, lysozyme levels of intestinal homogenate, and intestinal leukocyte phagocytosis (13.70±0.18 g fish weight). Results indicated no significant differences in intestinal immunoglobulin concentrations (P=0.41) or gut leukocyte phagocytosis at day 15 samplings (P=0.41).  Intestinal lysozyme content was found to be highest at day 60 in the BSBM treatment group (P<0.01).  No significant differences across treatments were observed in histological profiles at day 0 (P=0.75), day 15 (P=0.08), and day 60 (P=0.22).  

The second trial evaluated the intestinal microbiota, incorporating 16s rRNA analyses (42.30±0.26 g fish weight).  ANOSIM analysis for microbiota beta diversity showed differences among all dietary treatment groups, with the exception of the high and low levels of BSBM (P=0.40).  There were also differences observed in the alpha diversity ratios, with significant differences in gut communities among dietary treatments as demonstrated by Chao-1 (P<0.01) and Shannon indices (P=0.02).

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.  Definition, development and maintenance of beneficial gut microbe communities in rainbow trout fed soy ingredients requires additional study.