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Farmed Atlantic salmon has become one of the most food commodities in the world, enjoyed for its versatility as much as for its health benefits. It has long been known that such as salmon is the best way to consume long-chain omega-3 fatty acids. These are essential for .

In salmon, omega-3 fatty acids must come from the fish's diet. For farmed fish, this means fishmeal and fish oil—so–called "marine ingredients" made from ground-up wild fish such as anchovy and fish by-products.

But the global supply of omega-3s is severely limited, whether from farmed or wild seafood. Many of the key fisheries supplying marine ingredients reached full exploitation in the . Since the growth of salmon aquaculture, increasing volumes of the limited have been taken up by fish farming.

This has raised concerns over sustainability and inflated the cost of these ingredients. The result has been a steady decline in the proportion of fish oil in farmed salmon diets, which has been replaced by plant oils. But these oils do not contain long-chain omega-3s.

In turn, the amount of omega-3s in a portion of salmon 2006 and 2015. However, the salmon industry increasingly as a for its product— of farmed Scottish salmon per week would meet the recommended intake for an adult at current levels.

If the salmon industry is to continue to grow and maintain the omega-3 targets, it must be more efficient. And the seafood industry as a whole must do more to prevent omega-3 losses through its value chains. Part of the efficiency journey has been to produce more fish oil.

This can be done by harnessing the value of fishery and aquaculture byproducts such as trimmings, skins and heads, so that more omega-3s are kept in the food (and feed) system.

There is a growing incentive to use the whole fish—consequently, there has been good progress in improving the use of byproducts. It is now estimated that around half of the global fish oil supply is sourced from fishery—and particularly aquaculture—processing sources. However, there is still a and logistical difficulties in storing and transporting .

Much of the industry incentive to use byproducts has been economic, as the global shortage of fish oil pushed prices above in 2024. Evidence from the past 20 years suggests that the overall use of wild fish in the European salmon industry has dropped (replaced by plant ingredients), while production has grown several-fold.

Despite improvements and reductions in the use of marine ingredients, the industry still comes under huge pressure from NGOs and conservation groups. They are concerned about the use of , which may damage public perceptions of the aquaculture industry.

To assess the use of fish as feed in aquaculture, the "fish in fish out" (Fifo) ratio was conceived, which measures the ratio of fish biomass included in fish feeds to the biomass of fish ultimately produced for consumption. The goal is for more fish to be produced for human consumption than is used as feed, and this would result in a .

New measure for nutrients

Certification bodies such as the and have adopted different forms of the Fifo metric. However, until now, Fifo has not addressed one of the fundamental reasons for including marine ingredients in aquafeeds—providing omega-3s to consumers. It has neither considered the omega-3 content within feed fish, nor in the final product.

Similarly, studies examining nutrient retention in salmon have only looked at that from feed to the farmed fish. The omega-3 lost in the process of turning the fish raw material into feed is not currently measured. By introducing our new measure, (nFifo), nutrients can be followed from wild fish capture, its separation into meal and oil, and through to the final product sold to consumers.

The method used in nFifo favors the use of byproduct resources over virgin raw materials, so that diets containing byproducts receive a lower nFifo. In theory, this should promote circular economy initiatives.

This is crucial in the marine ingredients industry. Seafood is highly perishable and the byproducts especially so. But they are also some of the richest sources of omega-3s, such as from herring or mackerel.

However, the cost of retaining, stabilizing, storing and transporting byproducts is often prohibitive. This is especially true on board fishing boats, where space is at a premium and byproducts are often dumped at sea.

Introducing metrics that prevent bioresources being wasted is essential for sustainable food production. Current salmon feed contains around 20% to 25% marine ingredients, but only around 5% is from byproducts. This results in a nFIFO of 2.17.

Incorporating only marine ingredients sourced from byproducts reduces that nFifo to below 0.5. Crucially, this still provides the same level of omega-3s to the consumer.

If the seafood industry is serious about sustainable production, it needs to become much more efficient with resources. The nFifo metric links the use of wild fish to omega-3s consumed in farmed salmon for the first time—but it could also be applied to other species and nutrients.

The methodology is similar to that used for environmental impact indicators for climate change, land or water use. It makes it possible to assess the trade-offs of including and substituting marine ingredients in fish diets at different points of production.

For example, while may raise concerns around their impact on fisheries, they have comparatively low carbon footprints and almost no land or water footprints compared to plant ingredients. This could potentially lead to more balanced and sustainable approaches to seafood production.

It is hoped that the nFifo metric and an accessible tool for calculating it (there is one provided on the website) will be adopted by certifiers. It could also lead to more complex sustainability indicators becoming mainstream, letting consumers make informed choices about the nutritional and environmental credentials of the products they buy.

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