The project leader for multiple projects focused on research and development of soybased aquaculture feeds is Dr. Mike Brown, Natural Resource Management Department, South Dakota State University. This summary was prepared by Rosie Nold, SDSU Extension Agriculture and Natural Resources Program Director. This article focuses on a summary of the project “High Value Protein Replacers for Aquaculture Feeds from Defatted Soybean Flakes” which was made possible by the support of the South Dakota Soybean Research and Promotion Council.
Commercial aquaculture production of fish and shellfish is one of the fastest growing segments of U.S. animal agriculture. The primary constraint of this industry is the availability of high-quality, cost- competitive protein ingredients for inclusion in feeds. The primary focus of this project is to develop high value, soy protein products which would replace marine-derived protein (i.e. fish meals) which are the traditional protein source in aquaculture feeds, particularly food fish grower diets. Investigation is needed because the quality of current soy protein concentrates is not adequate to fully replace aqua-based feeds in fish species with high nutritional requirements. Thus, the approach is to investigate various thermal, mechanical, chemical, and enzymatic pretreatments, along with microbial conversion processes, to enhance nutrient composition and reduce anti-nutritional factors in soybeans. In addition to protein content, a limiting factor in the quality of soy based products is naturally occurring compounds which inhibit absorption of some amino acids. Thus, protein content must be increased and inhibitor activity decreased to achieve the goal of this and similar projects.
In the past year, studies of white flakes, soybean meal, and low fat, low sugar non-genetically modified (GM) soybean flake were conducted. Extrusion of the products resulted in higher protein levels and lower levels of trypsin inhibitors in white flake trials, but not in soybean meal. However, trypsin inhibitor levels were lowered in the non-GM soybean meal trials. Protein levels ranged from 56-66% on a dry matter basis. Two large- scale trials were used to generate high protein meal that was commercially processed into fish feed (42% protein, 9% lipid) for use in a feeding trial with a commercial fish producer, which is currently underway.
The digestibility of six different products is also currently being studied. Those products include microbially converted extruded and un-extruded white flake, GM, and non-GM soybean meal. Studies on yellow perch have been completed, with similar trials with rainbow trout in process. Overall, digestibilities for protein, essential amino acids, and energy were higher for converted GM and non-GM soybean meals, as compared to converted white flake.
Following digestibility trials, the next step is to conduct feeding performance trials using the same type of products – microbially converted extruded and non-extruded GM and non-GM white flake and soybean meal. These trials will determine relative performance of fish, including growth, survival, feed consumption, protein and feed efficiencies, along with intestinal and immune responses to the various types of protein. Many steps must be done before and during the feeding performance trials to obtain accurate results that can be used to advance the knowledge needed in this industry. Composition of feed (protein, lipid, and amino acid and fatty acid profiles) must be determined in advance and then evaluated against the nutritional requirements of the fish species. Further decisions must be made about supplements (vitamins, minerals, enzymes) that may be needed. And because feeding these products is new research, all this is done in the context of not fully knowing how different species may respond to other factors in the feeds including inhibitors or other antinutritional factors.