Immune and Endocrine Modulations Associated with Enhanced Plant-Based Protein Diets Within Freshwater Fish Species

The incorporation of bioprocessed soybean meals (BSBMs) as a protein replacement for marine-derived fish meal (MDFM) has gained momentum with the potential for aquafeed cost reduction, improved growth performance, and reducing exploitation on wild fish stocks. Further, potential health benefits and optimized production performance resulting from bioprocessed feed ingredients have led to research on the nutraceutical benefits of plant-based ingredients. A novel proprietary MBBM has been developed using a microbial conversion of carbohydrates into digestible protein and additional cellular components that have immunogenic potential. A series of five finfish feeding trials were conducted to investigate immunomodulation induced by the BSBM ingredients or dietary immunostimulants in yellow perch (Perca flavescens) and rainbow trout (Oncorhynchus mykiss), two domestically cultured species. Nonspecific immune components were characterized by trials incorporating graded inclusion levels of polysaccharides and minerals. A 1-1.5% inclusion of a commercial exopolysaccharide (EXOP) with the BSBM provided enhancement to the phagocytic capacity and superoxide production of yellow perch head-kidney macrophages. Analysis of respiratory burst activity (RBA) after 46 days of treatment were found to be significantly different across dietary treatments (PFlavobacterium psychrophilum (17830), a major salmonid pathogen in commercial aquaculture operations. At 10 days postchallenge, mortality rates were found to be lower in diets containing a base BSBM (47.91%), BSBM with 1% EXOP (49.55%), and BSBM with 0.1% b-glucans (40.47%), in comparison to the MDFM control diet (59.45%). At day 46, the macrophage RBA of the fish fed supplemented (EXOP and b-glucans) BSBM variants were greater than the FM control diet(P=0.009 and P=0.002, respectively). Lysozyme levels were found to have significant differences among diets at day 46 (PF. psychrophilum challenge (P=0.695). Two 60-day feeding trials with juvenile rainbow trout (Oncorhynchus mykiss) 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. Intestinal lysozyme content was found to be highest at day 60 in the BSBM treatment group (P-1) and unstressed groups (0.47±0.28 ng mL-1) had a significant difference in group means (P-1) and unstressed (0.36±0.12 ng mL-1) groups (