An initial evaluation of fishmeal replacement with soy protein sources on growth and immune responses of burbot (Lota lota maculosa)

Burbot (Lota lota maculosa) are the only freshwater member of the cod family (Gadidae) and potentially a new species for aquaculture production. This "freshwater cod" species could provide diversification for freshwater salmonid and other aquaculture operations, given its desirable fillet quality and growth potential. Burbot nutrition research is necessary to further define dietary requirements and the potential of this species to utilize sustainable plant-based proteins. A 91-day feeding trial and subsequent 28-day pathogen challenge was conducted with juvenile burbot (26.8 g mean weight) to assess growth performance, survival, and immune parameters. Dietary treatments included a fishmeal control (CTL), and 25% and 50% fishmeal replacement with soybean meal (SBM) soy protein concentrate (SPC), and bioprocessed soybean meal (BSBM). Growth results indicated a difference in percent gain (PG; P = 0.015) and thermal growth coefficient (TGC; P = 0.014) among dietary treatments, with the fish fed the SBM-25 and CTL performing higher than other diets except for the SPC-25. Analysis of distal intestine samples revealed no discernable differences in lamina propria thickness (P = 0.489) or cellularity (P = 0.944), and the amount of connective tissue of the submucosa was found to be similar (P = 0.988). Immediately following the feeding trial, burbot were challenged with a virulent strain of Aeromonas sp. (A141) while remaining on their respective dietary treatments. At day 28 post-challenge, no diet-related effects were found in cumulative percent mortality (P = 0.170) or serum lysozyme activity (P = 0.715). The respiratory burst activity of isolated head kidney-derived leukocytes did not show treatment differences at pre- and post-challenge sampling (P = 0.857), but activity decreased post-challenge (P < 0.001). Overall, results indicate that 25% FM replacements with SBM and SPC are suitable in burbot diets and long-term feeding of soy based proteins does not appear to cause distal enteritis, impair disease resistance, or affect innate immune function. Utilizing soy-based protein sources for commercial burbot culture will expand the use of sustainable plant ingredients in aquaculture and provide burbot producers with a cost-effective alternative to high fishmeal feeds.