Immunomodulation in Rainbow Trout (Oncorhynchus mykiss) and Yellow Perch (Perca flavescens) Fed Bioprocessed Soy-Based Diets

The use of plant-based proteins to replace marine-derived fish protein (MDFM) has gained momentum with the potential for reducing feed cost and exploitation of wild fish stocks.  Bioprocessed plant-based feedstuffs may also provide immunostimulatory enhancements, producing additional fish health benefits.  Feeding trials evaluated immunological performance in juvenile rainbow trout (Oncorhynchus mykiss) and yellow perch (Perca flavescens) fed experimental plant-based diets. Formulated diets contained a converted soy concentrate (BSPC) or fermented soybean meal (FSBM) for comparison to a fishmeal reference.  Fish were sampled at prescribed intervals to measure innate immunological responses.  In 90-day rainbow trout study, the fishmeal control exhibited the greatest respiratory burst activity (RBA) in head kidney leukocytes (OD₆₂₀=0.603) and was found to be comparable to the BSPC (OD₆₂₀=0.462; P=0.69). The greatest plasma lysozyme concentrations were observed in BSPC (18.75U/mL) and FSBM (33.75U/mL). Yellow perch were found to show no significant difference in RBA compared to the FM reference (P=0.25), following completion of a 115-day trial. Bioconversion optimization and mineral supplementation to soy-based diets will further characterize immune changes in perch. Continued assessment of novel plant-based formulations will provide a better understanding of production performance and potential for enhanced immunoprotection.