Wild fish consumption can balance nutrient retention in farmed fish, research finds

Eating more wild fish such as mackerel, anchovies and herring could benefit our health while reducing aquaculture demand for finite marine resources, a new study has found.

Researchers analysed 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 8 – but increased levels of selenium and zinc.

Most wild 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.

Optimise nutrients

Dr Wesley Malcorps of the University of Stirling’s Institute of Aquaculture (IoA), who was involved in the research, said: “It is crucial to develop a better understanding of the interlinkages between aquaculture and capture fisheries and how we can optimise nutrient availability for the global population.”

Dr Richard Newton of the IoA, who was also part of the research team, said: “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 more strategic use of feed ingredients, including from fishery by-products and sustainably sourced, industrial-grade fish such as sand eels.”

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.  

The researchers found consuming one-third of current food-grade wild feed fish directly would be the most efficient way of maximising nutrients from the sea.

The study, Wild fish consumption can balance nutrient retention in farmed fish, was published in the journal Nature Food.

Wider variety

Lead author, Dr David Willer, of the Zoology Department at the University of Cambridge, said: “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.

“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.”

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 as the farmed salmon fillets. Quantities of calcium were over five times higher in wild feed fish fillets than salmon fillets, iodine was four times higher, and iron, omega-3, vitamin B12, and vitamin A were over 1.5 times higher. Wild feed 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.

Reduce burden

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 are building a standardised and robust vehicle for integrating the nutrient retention metric into industry practice.

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.