The public is being encouraged to eat more wild fish, such as mackerel, anchovies and herring, which are often used within farmed salmon feeds. These oily fish contain essential nutrients including calcium, B12 and omega-3 but some are lost from our diets when we just eat the salmon fillet, a study says.
Scientists found that farmed salmon production leads to an overall loss of essential dietary nutrients. They say that eating more wild “feed” species directly could benefit our health while reducing aquaculture demand for finite marine resources.
“What we’re seeing is that most species of wild fish used as feed have a similar or greater density and range of micronutrients than farmed salmon fillets,” said lead author, David Willer, Zoology Department, University of Cambridge. “While still enjoying eating salmon and supporting sustainable growth in the sector, people should consider eating a greater and wider variety of wild fish species like sardines, mackerel and anchovies, to get more essential nutrients straight to their plate.”
“Making a few small changes to our diet around the type of fish that we eat can go a long way to changing some of these deficiencies and increasing the health of both our population and planet,” said Willer.
Scientists calculated the balance of nutrients in edible portions of whole wild fish, used within pelleted salmon feed in Norway, compared to the farmed salmon fillets. They focused on nine nutrients that are essential in human diets and concentrated in seafood – iodine, calcium, iron, vitamin B12, vitamin A, omega-3 (EPA + DHA), vitamin D, zinc and selenium. The wild fish studied included Pacific and Peruvian anchoveta, and Atlantic herring, mackerel, sprat and blue whiting – which are all marketed and consumed as seafood.
They found that these six feed species contained a greater, or similar, concentration of nutrients than the farmed salmon fillets. Quantities of calcium were over five times higher in wild fish fillets than in salmon fillets, iodine was four times higher, and iron, omega-3, vitamin B12, and vitamin A were over 1.5 times higher. Wild species and salmon had comparable quantities of vitamin D.
Zinc and selenium were found to be higher in salmon than the wild feed species – the researchers say these extra quantities are due to other salmon feed ingredients and are a real mark of progress in the salmon sector.
“Farmed salmon is an excellent source of nutrition, and is one of the best converters of feed of any farmed animal, but for the industry to grow, it needs to become better at retaining key nutrients that it is fed. This can be done through the more strategic use of feed ingredients, including from fishery byproducts and sustainably-sourced, industrial-grade fish such as sand eels”, said Richard Newton of the Institute of Aquaculture, University of Stirling, whose team also included Dave Little, Wesley Malcorps and Björn Kok.
“It was interesting to see that we’re effectively wasting around 80% of the calcium and iodine from the feed fish – especially when we consider that women and teenage girls are often not getting enough of these nutrients”.
Willer said that “these numbers have been underacknowledged by the aquaculture industry’s standard model of quoting Fish In Fish Out (FIFO) ratios rather than looking at nutrients.”
Researchers would like to see a nutrient retention metric adopted by the fishing and aquaculture industries. They believe that if combined with the current FIFO ratio, the industry could become more efficient, and reduce the burden on fish stocks that also provide seafood. The team is building a standardized and robust vehicle for integrating the nutrient retention metric into industry practice.
“We’d like to see the industry expand but not at a cost to our oceans,” said Willer. “We’d also like to see a greater variety of affordable, convenient and appealing products made of wild ‘feed’ fish and fish and salmon byproducts for direct human consumption.”
Researchers found consuming one-third of current food-grade wild fish directly would be the most efficient way of maximizing nutrients from the sea. “Marine fisheries are important local and global food systems, but large catches are being diverted towards farm feeds. Prioritizing nutritious seafood for people can help improve both diets and ocean sustainability,” said senior author James Robinson, Lancaster University.
The research was funded by the Scottish Government’s Rural and Environmental Science and Analytical Services Division (RESAS), a Royal Society University Research Fellowship, a Leverhulme Trust Early Career Fellowship a Henslow Fellowship at Murray Edwards College and the University of Cambridge.
Reference:
Willer, D.F., Newton, R., Malcorps, W. et al. Wild fish consumption can balance nutrient retention in farmed fish. Nat Food 5, 221–229 (2024). https://doi.org/10.1038/s43016-024-00932-z
