Immune and endocrine modulations associated with enhanced plant-based protein diets within freshwater fish species

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<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). 16S rRNA microbiota analyses from collected fecal material indicated differences in alpha diversity among dietary groups, 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 rainbow trout gastrointestinal tract (GIT), and modulates lysozyme concentrations within the distal gastrointestinal tissues.;A 60-day feeding trial was conducted to evaluate physiological changes from acute stressors in rainbow trout (Oncorhynchus mykiss) fed soy-based diets. Experimental diets contained two BSBM levels or a CSPC while dietary controls included a FM reference and a SBM. On days 30 and 60, trout were subjected to 4 hours of acute stressors (low flow rate, decreased dissolved oxygen and handling stressors) or left unstressed as controls for respective diet treatments. Day 30 changes in macrophage RBA were significantly different among diet treatments in the stressed (P=0.004) groups and between the stressed and unstressed groups at Day 60 (P=0.004).. Plasma cortisol results indicate that there were no dietary treatment differences but day 30 stressed (11.481.51 ng mL-1) and unstressed groups (0.470.28 ng mL-1) had a significant difference in group means (P<0.001). Day 60 plasma cortisol levels following a similar trend, significance between stressed (7.221.48 ng mL-1) and unstressed (0.360.12 ng mL-1) groups (P<0.001). Continued assessment of novel plant-based ingredients to reduce stressors may benefit producers by allowing increased stocking densities and reducing losses due to fish transport, thus further contributing to the needs of a rapidly expanding domestic aquaculture market.;Small additions of immunostimulants and the incorporation of bioprocessed soybean meal appear to modulate the fish immune system, the distal intestine microbiota, and aspects of stress physiology. These findings corroborate current aquaculture immunology initiatives to create non-antibiotic approaches that enhance fish health and increase production stocks in the rapidly expanding aquaculture sector. (Abstract shortened by ProQuest.).