IMMUNOMODULATION IN FRESHWATER SPECIES FED BIOPROCESSED SOYBEAN MEAL

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

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 improved production performance resulting from bioprocessed feed ingredients have led to research on the immune-enhancing properties of plant-based ingredients. A series of four finfish feeding trials were conducted to investigate immunomodulation induced by BSBM or immunostimulant ingredients 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. Study results indicate a variation in short-term innate immune responses as a result of feeding mineral (zinc and selenium) and polysaccharide (β-glucans and EXOP) supplemented to BSBM diets.

In additional trials, rainbow trout fed BSBM-based diets were challenged with Flavobacterium psychrophilum (17830), a virulent salmonid pathogen found in hatchery operations, and we determined innate immune responses.  Macrophage respiratory burst activity (RBA) was found to be significantly different at day 46 (P=0.004) and post-challenge 10 (P<0.001), indicative of immunomodulation due to diet.  Following the 10d challenge, a BSBM diet supplemented with β-glucans had the lowest mortality rate (40.47%). In another trial where rainbow trout were fed soy-based diets, physiological changes (plasma cortisol, plasma ion concentration, hematocrit, and macrophage activity) were evaluated following acute production stressors. Day 30 RBA values were different among dietary treatments in the stressed (P=0.004) trout and the day 60 unstressed trout (P<0.001). There appeared to be some secondary stress modulations between

unstressed and stressed treatment groups at day 30 (P<0.001) and day 60 (P<0.001), but no apparent dietary effects on the acute cortisol concentrations.

Continued development and assessment of novel plant-based ingredients, with a target of stress reduction and immune enhancement, 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 (non-antibiotic) the fish immune system and aspects of stress physiology.