Wild fish consumption can balance nutrient retention in farmed fish

Global seafood demand is rising and aquaculture is expected to contribute substantially to supply and to alleviating micronutrient deficiencies. While freshwater aquaculture supports food security, demand for marine-fed carnivorous species like Atlantic salmon continues to grow, particularly among affluent consumers. Salmon efficiently converts feed to food but relies heavily on finite marine ingredients (fishmeal and fish oil), now largely consumed by aquaculture. As many wild fish species used in salmon feeds (for example, herring, mackerel) are also edible, feeding them to salmon may reduce the total nutritious seafood available to people. Prior metrics such as FIFO and FFDR assess dependence on wild fish but do not capture micronutrient retention to humans. This study asks: how effectively are key dietary micronutrients in edible feed fish retained in farmed salmon for human consumption, and what reallocation scenarios could improve overall nutritious seafood supply?

The paper situates its work within assessments of feed efficiency in aquaculture, including FIFO, FFDR, and economic allocation approaches (eFIFO) that avoid double-counting and highlight fish oil as a limiting ingredient. Prior research shows increasing aquaculture dependence on marine ingredients (around 70% consumed by aquaculture) and declining inclusion rates of fish oil leading to lower omega-3 in farmed salmon. Metrics such as marine nutrient dependency ratio assess macronutrient conversion but overlook species-specific micronutrient flows. The authors identify a gap in quantifying edible micronutrient retention from wild feed fish to farmed salmon available for human diets and propose an edible nutrient retention metric to address this.

Design: A mass-balance assessment of edible nutrient retention from edible, commercially marketed (ECM) feed fish to Norwegian farmed Atlantic salmon in 2020, plus simulations reallocating ECM feed fish to direct human consumption while maintaining salmon production. Data sources: 2020 Norway salmon production (1,467,655 t), fish oil (203,597 t) and fishmeal (239,711 t) usage; species-specific fishmeal/fish oil yields from whole fish and trimmings; species composition of fishmeal/fish oil from a major feed producer (Skretting); nutrient composition of ECM feed fish and salmon from Norwegian food composition tables; UK NRVs for adult women for intake comparisons; UK National Diet and Nutrition Survey for consumption context. Whole fish requirement: Using species-specific yields and assuming fish oil is the limiting ingredient, the authors estimated whole fish reduced to marine ingredients required to supply Norway’s salmon sector in 2020, allocating additional fishmeal needs and noting 64,621 t of spare fishmeal not analyzed further. Total whole fish reduced was 2,111,283 t, with ~40% ECM species. Edible nutrient retention metric: For each of nine nutrients (calcium, iodine, iron, selenium, zinc, omega-3 EPA+DHA, vitamins A, D, B12), edible nutrient retention (%) = (nutrient in salmon fillets produced)/(sum over ECM feed species of (nutrient concentration in edible portion × edible whole-fish mass used for feed)) × 100. Salmon production and ECM feed fish masses were corrected by edible portions (salmon edible yield 58–88%, midpoint 73%). Only whole-fish-derived fishmeal/oil from ECM species (anchovies, herring, mackerel, sprat, blue whiting, Pacific/Peruvian anchoveta) were included; species with negligible direct consumption (sand-eel, menhaden, pout) were treated as inedible for this analysis. Dietary contribution visualization: Portion sizes needed to meet NRVs and contributions of a standard 140 g portion were estimated for ECM species and salmon using UK guidelines (WHO/FAO for EPA+DHA 0.25 g d−1). Scenario simulations: The authors simulated reallocating 0–100% of ECM whole fish (currently used for fish oil) to direct human consumption by species, tracking changes in edible nutrient retention, total edible seafood produced (salmon + forage fish), fish oil deficits (to be met by additional by-products or novel oils), and new by-products generated from processing edible fish (trimmings, heads, skin, bones). Salmon production was held at 2020 levels; salmon by-products were not allowed back into salmon feed. Analyses used R 4.3 and code/data are available on GitHub.

- Marine ingredient inputs: Producing Norway’s 2020 salmon required 2,111,283 t of whole fish reduced to fish oil/meal; ~40% were edible, commercially marketed (ECM) species. Peruvian anchoveta (~600,000 t, used entirely for oil) was the largest single contributor, followed by European sprat, Atlantic herring, and Atlantic mackerel. - Edible nutrient retention (business-as-usual): For 6 of 9 nutrients, salmon fillets retained less than 100% of nutrients present in ECM feed fish: - Calcium ~18% retention (~>5× more calcium in ECM fish than in salmon). - Iodine ~25% retention (~>4× more iodine in ECM fish). - Iron, omega-3 (EPA+DHA), vitamin B12, vitamin A each <75% retention (~>1.5× more in ECM fish). - Vitamin D retention comparable (~≈100%). - Zinc and selenium >100% retention, indicating additional supply from non-marine feed ingredients. - Nutritional equivalence/advantages of ECM fish: A 140 g portion of average ECM feed fish and Atlantic salmon each provided substantial intakes of selenium (>30% NRV), vitamin B12 (>90%), vitamin D (>78%), and omega-3 (>100%). ECM fish met NRVs for iodine, omega-3 (EPA+DHA), and vitamin B12 at smaller portion sizes and had higher concentrations of iodine, calcium, iron, and vitamin A than salmon. - Reallocation scenarios: Direct human consumption of 27–51% of ECM fish used in 2020 salmon feed raised edible nutrient retention above 100% for vitamin A, vitamin B12, omega-3 (EPA+DHA), and iron, and improved retention for calcium and iodine. Selenium, zinc, and vitamin D—already >100% at baseline—exceeded 300% retention when 46–66% of ECM fish were consumed directly. - By-product and oil implications: Redirecting 100% of ECM fish to direct food would create ~600,000 t of by-products suitable for marine ingredients but require ~69% additional fish oil from by-products or novel alternatives to maintain salmon output. For mackerel, processing would still yield 47,321 t of by-products to partially replace marine ingredients. - Consumer/market context (UK): In 2019, salmon consumption (~80,000 t) far exceeded mackerel (~20,000 t) and herring/anchovy/whiting (<3,000 t each). Reallocating one-third of mackerel currently used in Norwegian salmon feed to UK human consumption could increase UK mackerel consumption by ~66%, whereas doing so for herring and anchovy would vastly exceed current consumption (2,351% and 39,349% of 2019 consumption, respectively). - FIFO/FFDR context: Reported historical Norwegian salmon metrics were FIFO (combined) ~2.46 and FFDR (combined) ~2.39; oil components dominated (FIFO oil ~1.9; FFDR oil ~1.87), reflecting fish oil as the limiting ingredient.

From a food-systems perspective, using edible wild fish as feed for salmon reduces the overall availability of several key micronutrients to humans; business-as-usual salmon farming is a net consumer of nutrients contained in edible forage fish. Many ECM species (for example, mackerel, herring, anchovies) offer higher concentrations of omega-3, iodine, calcium, iron, and vitamin A than farmed salmon and can meet dietary recommendations at smaller portions. Reallocating a modest fraction of these edible feed fish to direct human consumption, while upcycling the resulting processing by-products into feed ingredients and supplementing fish oil with novel alternatives (for example, algal oils), can raise edible nutrient retention above 100% for multiple nutrients, increase total seafood produced for people, and reduce pressure on whole-fish marine ingredients. Realizing these gains requires overcoming consumer preference barriers, improving product formats and affordability, and adapting trade policies to support local consumption of ECM species. The approach reframes aquaculture performance to include micronutrient efficiency, complementing existing FIFO-type metrics and guiding interventions toward sustainable, nutritious, and diverse seafood supplies.

Assessing edible nutrient retention from feed fish to farmed seafood reveals that current salmon aquaculture practices underutilize the micronutrient potential of edible wild fish. Redirecting a portion of ECM feed fish to direct human consumption, coupled with efficient by-product upcycling and adoption of novel omega-3 oil sources, can increase total nutritious seafood available without increasing wild catch. To operationalize improvements, the industry should develop and adopt life-cycle ‘nutritional FIFO’ (nFIFO) metrics that track nutrient flows, invest in by-product infrastructure, scale sustainable fish oil alternatives (for example, algal, yeast, or GM plant oils), and innovate consumer-friendly ECM fish products. Future research should generalize nutrient retention analyses across species and regions, integrate economic allocation (eFIFO) with nutrient accounting (nFIFO), and evaluate trade-offs across nutrition, environment, and markets.

- Scope limited to Norwegian salmon in 2020; results may not generalize to other species, regions, or years. - Mass-balance back-calculation does not capture all nutrient flows (for example, ‘spare’ fishmeal use beyond salmon feed, broader livestock feed flows) and treats fish oil as the limiting ingredient without full system substitution dynamics. - Only whole-fish-derived marine ingredients from ECM species were included; nutrients in by-product-derived fishmeal/oil were excluded by design. - Nutrient retention estimates depend on edible yield assumptions (58–88% for salmon) and food composition table values. - Consumer demand and market acceptance of ECM species vary widely; modeled reallocations may be constrained by preferences, trade, and processing infrastructure.