People are encouraged to include more wild fish like mackerel, anchovies, and herring in their diets. These oily fish are key components in farmed salmon feed and are rich in essential nutrients such as calcium, B12, and omega-3 fatty acids, which are often underrepresented in our diets.
Scientists have discovered that the production of farmed salmon results in a net loss of vital dietary nutrients. They suggest that consuming wild ‘feed’ species directly could improve our health and decrease the demand for limited marine resources in aquaculture.
Researchers analyzed the flow of nutrients from the edible species of wild fish used as feed, to the farmed salmon they were fed to. They found a decrease in six out of nine nutrients in the salmon fillet – calcium, iodine, iron, omega-3, vitamin B12, and vitamin A, but increased levels of selenium and zinc.
Most wild ‘feed’ fish met dietary nutrient recommendations at smaller portion sizes than farmed Atlantic salmon, including omega-3 fatty acids which are known to reduce the risk of cardiovascular disease and stroke.
Health Benefits of Diversifying Fish Consumption
“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, Dr. David Willer, Zoology Department, University of Cambridge. “Whilst 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.”
In the UK, 71% of adults have insufficient vitamin D in winter, and teenage girls and women often have deficiencies of iodine, selenium, and iron. Yet while, 24% of adults ate salmon weekly, only 5.4% ate mackerel, 1% anchovies, and just 0.4% herring.
“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.
The researchers found consuming one-third of current food-grade wild-feed 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 Dr. James Robinson, Lancaster University.
This approach could help address global nutrient deficiencies say the team of scientists from the University of Cambridge, Lancaster University, University of Stirling, and the University of Aberdeen. The study was published in the journal, Nature Food.
Comparison of Nutrient Levels in Fish
The 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-feed 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. Wildfeed 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 by-products and sustainably-sourced, industrial-grade fish such as sand eels,” said Dr. Richard Newton of the Institute of Aquaculture, University of Stirling, whose team also included Professor Dave Little, Dr. 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 “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.
The 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 by-products for direct human consumption.”
Reference: “Wild fish consumption can balance nutrient retention in farmed fish” by David F. Willer, Richard Newton, Wesley Malcorps, Bjorn Kok, David Little, Anneli Lofstedt, Baukje de Roos and James P. W. Robinson, 20 March 2024, Nature Food.
DOI: 10.1038/s43016-024-00932-z
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.