Exploring Soy-Derived Alternatives to Fish Meal: Using Soy Protein Concentrate and Soy Protein Isolate in Hybrid Striped Bass Feeds

Many protein sources, including soybean meal (SBM), have been investigated as alternatives to fish meal (FM) in aquaculture feeds. However, FM replacement in feeds for carnivorous fishes is limited by problems with feed intake, growth rate, and overall health associated with the reduced digestibility of SBM and the antinutritional factors (ANFs) it contains. Processing strategies can reduce the effects of ANFs and can improve protein utilization. We conducted two trials to examine the possibility of further FM replacement in SBM- maximized feeds for hybrid striped bass (white bass Morone chrysops x striped bass M. saxatilis) by using two refined soy products: soy protein concentrate (SPC) and soy protein isolate (SPI). Diets were formulated to maximize FM replacement, beginning with a basal diet containing 10% FM and 65% SBM. Further reductions in FM were made by using SPC or SPI to spare FM- derived protein. Refined soy protein- based feeds were evaluated in feeding trials with juvenile hybrid striped bass that were cultured in recirculating aquaculture systems. Although reducing dietary FM below 10% by using SPC or SPI resulted in decreased production performance, this appears to be due to a reduction in palatability rather than to negative biological effects (e.g., changes in gut histology, major shifts in carcass proximate composition) associated with ANFs or other dietary effects. A moderate reduction in growth associated with administering the SPC- based feeds corresponded with a moderate reduction in feed intake, whereas dietary inclusion of SPI resulted in severe feeding reluctance, starvation, and cannibalism. Although SPC and SPI may vary in their suitability as FM alternatives, the differential performance observedmay also be related to the fact that younger, smaller fish were used in the SPI trial than in the SPC trial. Refined soy proteins can be used in conjunction with SBM to spare FM, but the cost of these products and their acceptability to juvenile carnivorous fish will determine the extent of their utilization in aquafeeds.