Aquaculture, the farming of fish and other aquatic organisms, plays a crucial role in meeting the growing global demand for seafood products. As malnutrition remains a concern, both wild-caught and farmed fish offer essential nutrients such as iodine, iron, omega-3 fatty acids, and vitamins A, D, and B12. In particular, freshwater aquaculture has significantly improved food security in many regions.
However, there is also an increasing demand for carnivorous fish fed in the sea, such as Atlantic salmon. While salmon boasts efficient feed conversion rates (meaning less food waste), its high position in the food chain consumes many resources for its production.
A team of scientists from the University of Cambridge, University of Stirling, University of Aberdeen, and Lancaster University used fish input/output mass balance approaches to assess nutrient retention in salmon farming and identify scenarios that provide nutrient-rich foods to people.
The Challenge of Marine Ingredients
One of the main concerns of salmon farming is its reliance on wild-caught fish, primarily for fishmeal and fish oil in its feed. This raises sustainability concerns, especially when these wild fish are also consumed directly by humans (think herring and mackerel).
It’s worth noting that research on new inputs (insect meal, plant meals, single-cell protein, among others) to fully or partially replace them is underway. However, economically viable alternatives have yet to be achieved.
A New Metric: Edible Nutrient Retention
Scientists are exploring a new concept: edible nutrient retention to improve resource efficiency and optimize nutrition in seafood products. This metric evaluates the proportion of essential nutrients from wild fish used in salmon feed that are retained in farmed salmon’s edible portion.
Norwegian Salmon: A Case Study
Researchers used data from the Norwegian salmon industry to estimate the edible nutrient retention of nine essential nutrients commonly found in seafood. This analysis helps us understand how the salmon farming system contributes to overall dietary needs and identify pathways to increase the nutritional value of our seafood supply.
The scientists calculated nutrient balance in the edible portions of whole wild fish, used in pelleted salmon feed in Norway, compared to farmed salmon fillets.
They focused on nine nutrients essential in the human diet 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 Peruvian anchovy, Pacific anchovy, herring, mackerel, sprat, and Atlantic blue whiting, all of which are marketed and consumed as human food fish.
Salmon Production Leads to Nutrient Losses
Scientists found that farmed salmon production leads to an overall loss of essential dietary nutrients. They say that consuming more wild species as food directly could benefit our health while simultaneously reducing the demand for finite marine resources from aquaculture.
The researchers analyzed nutrient flow from edible wild fish species used as feed to farmed salmon they were fed to. They found a decrease in six of nine nutrients in salmon fillets: calcium, iodine, iron, omega-3, vitamin B12, and vitamin A, but higher levels of selenium and zinc.
Most wild fish met dietary nutrient recommendations in smaller portions than farmed Atlantic salmon, including omega-3 fatty acids, known to reduce the risk of cardiovascular diseases and strokes.
They found that these six feed species contained a concentration of nutrients higher or similar to that of farmed salmon fillets. Calcium amounts were 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 more than 1.5 times higher.
Wild species and salmon had comparable amounts of vitamin D.
Zinc and selenium were found to be higher in salmon than in wild feed species; researchers say these additional amounts are due to other salmon feed ingredients and are a real sign of progress in the salmon sector.
“Farmed salmon is an excellent source of nutrition and is one of the best food converters of any farmed animal, but for the industry to grow, it needs to improve on retaining key nutrients it feeds on. This can be achieved through a more strategic use of feed ingredients, including sustainably sourced, high-quality industrial fish, such as sand eels,” said Dr. Richard Newton from the Institute of Aquaculture, University of Stirling.
Importance of Fisheries for Local Food Systems
“Marine fisheries are important local and global food systems, but large catches are being diverted to aquaculture feeds. Prioritizing nutritious seafood for people can help improve both diet and ocean sustainability,” said lead author Dr. James Robinson from Lancaster University.
“What we’re seeing is that most wild fish species used as feed have a similar or higher density and variety of micronutrients compared to farmed salmon fillets,” said lead author Dr. David Willer from the University of Cambridge.
“While still enjoying eating salmon and supporting sustainable growth in the sector, people should consider eating a greater and broader variety of wild fish species like sardines, mackerel, and anchovies, to get more essential nutrients directly on their plate.”
Other studies have highlighted the competition between fishery resource use for aquaculture feed production and that for human consumption.
Fish Consumption in the UK
In the UK, 71% of adults have insufficient vitamin D in winter, and adolescents and women often have deficiencies in iodine, selenium, and iron. However, while 24% of adults ate salmon weekly, only 5.4% ate mackerel, 1% anchovies, and only 0.4% ate herring.
“Making some small changes in our diet around the type of fish we eat can go a long way in addressing some of these deficiencies and improving the health of both our population and the planet,” said Dr. Willer.
Researchers found that directly consuming one-third of currently food-grade wild fish would be the most efficient way to maximize marine nutrients.
This approach could help address global nutrient deficiencies, according to a team of scientists from Lancaster University, the University of Cambridge, the University of Stirling, and the University of Aberdeen.
Waste of Calcium and Iodine
“It was interesting to see that we’re effectively wasting around 80% of the calcium and iodine from fish feed, especially when considering that women and adolescents often don’t get enough nutrients,” Dr. Willer said.
“These figures have been underestimated by the aquaculture industry’s standard FIFO model instead of analyzing nutrients.
Researchers would like fisheries and aquaculture industries to adopt a nutrient retention metric. They believe that if combined with the current FIFO ratio, the industry could become more efficient and reduce the burden on fish populations that also provide seafood products. The team is building a standardized, robust vehicle to integrate the nutrient retention metric into industry practice.
“Aquatic foods must be sustainably produced, prioritizing species that can best contribute to a healthy diet. In the UK, we could eat more locally caught fish, such as mackerel, while simultaneously reducing the use of wild fish in farmed salmon feed,” Dr. Robinson said.
Conclusion
Scientists conclude that “reallocating one-third of food-grade wild fish for direct human consumption would increase seafood production and, at the same time, retain by-products for use as aquaculture feed, thus maximizing the utilization of marine nutrients.”
The research was funded by the Scottish Government’s Rural and Environmental Science and Analytical Services Division (RESAS), the Royal Society University Research Fellowship, the Leverhulme Trust Early Career Fellowship, the Henslow Fellowship at Murray Edwards College and the University of Cambridge
Contacto
David F. Willer
Department of Zoology, University of Cambridge, Cambridge, UK
Email: dw460@cam.ac.uk
Referencia (acceso abierto)
Willer, D.F., Newton, R., Malcorps, W. et al. Wild fish consumption can balance nutrient retention in farmed fish. Nat Food (2024). https://doi.org/10.1038/s43016-024-00932-z
