A fishmeal-free diet for post-smolt Atlantic salmon in RAS

Authors: DAVIDSON, JOHN - Freshwater Institute; SUMMERFELT, STEVEN - Freshwater Institute; Barrows, Frederic; KENNEY, BRETT - West Virginia University; GOOD, CHRISTOPHER - Freshwater Institute; SCHROYER, KAREN - Freshwater Institute

Submitted to: Hatchery International Magazine
Publication Type: Trade Journal
Publication Acceptance Date: 2/14/2017
Publication Date: 5/1/2017
Citation: Davidson, J., Summerfelt, S., Barrows, F., Kenney, B., Good, C., Schroyer, K. 2017. A fishmeal-free diet for post-smolt Atlantic salmon in RAS. Hatchery International Magazine. 19(3):35.

Interpretive Summary:

Technical Abstract: Rising costs and static supply of ocean-harvested fishmeal have spurred decades of research to identify sustainable feed ingredients for salmon diets. There has been substantial progress. The amount of fishmeal and fish oil used in commercial diets has declined and there is now a long list of alternative ingredients. And these advances in nutrition have been central to securing a more sustainable future for the salmon industry. Meanwhile, a new storyline has been quietly unfolding - adoption of state-of-the-art recirculating aquaculture systems (RAS). Salmon farmers around-the-world are now producing smolts and post-smolts in large land-based RAS, and a few facilities have begun to raise salmon to market-size in these systems. The convergence of these trends has spurred research into the culture requirements of Atlantic salmon raised in RASs and has led to the development of diets that simultaneously meet the needs of the fish and the production setting. Considering these trends, researchers from the Conservation Fund's Freshwater Institute (TCFFI), the USDA Agricultural Research Service, and West Virginia University collaborated to study a novel fishmeal-free diet fed to post-smolt Atlantic salmon in RAS. In the diet, nut meal, corn protein concentrate, and poultry meal proteins were used to replace fishmeal, and oil was sourced from a fisheries by-product. Performance attributes of Atlantic salmon fed the fishmeal-free diet were compared with those of salmon fed a commercial-type diet containing fishmeal and menhaden oil. Resulting water quality, waste discharge, and salmon fillet quality were also studied. According to the researchers the fishmeal-free formulation, developed by recently-retired USDA/ARS nutritionist Rick Barrows, provided exceptional results. Salmon performance metrics were nearly identical for each diet. The fish grew from 0.28 to 1.72 kg in 6 months, feed conversion ratios were less than 1.0, survival was greater than 99 %, and histopathology data indicated normal health. The authors report that to their knowledge this was one of the first published studies to demonstrate uncompromised health and performance in an RAS of Atlantic salmon fed a diet without fishmeal. Water quality ideal for salmon health was maintained, but the fishmeal-free diet resulted in 4 times more dissolved phosphorous in the tank water and greater total suspended solids, and higher biochemical oxygen demand and phosphorous concentration in the effluent. Depending on local discharge regulations, elevated phosphorous could be a problem for land-based fish farmers. For example, in states with strict discharge standards, expensive waste treatment technologies could be required to mitigate high phosphorous levels. On the positive side, high phosphorous concentrations could be an important nutrient if the effluent was used for aquaponics. In either case, the authors note that they are confident that excreted phosphorus could be managed by fine-tuning the amount of dicalcium phosphate included in the fishmeal-free diet. Less could be added to match the biological requirement of the fish and thereby limit phosphorous excretion or more could be added to produce extra phosphorous for aquaponics. The fishmeal-free diet also resulted in similar fillet quality attributes to that of the standard fishmeal diet. No differences were found in fillet yield, composition, texture, or color. The fillet fatty acid profile was also similar, indicating that omega-3 fatty acids, such as EPA and DHA that are important for human health were maintained. The fishmeal-free diet also resulted in a fish-in to fish-out ratio (FIFO) of 0:1 and a “best choice” sustainability score, as per Monterey Bay Aquarium's Seafood Watch criteria, due to its fishmeal-free status and use of fisheries byproduct for oil. This research was published in Aquacultural Engineering, Vol. 7