Nofima proposes new zinc delivery method to improve uptake in salmon feed

NORWAY – Researchers at Nofima have developed a new method of adding zinc to salmon feed that could improve mineral uptake, reduce environmental emissions and support compliance with tightening EU regulations, the institute said. 

The approach involves shifting zinc supplementation from the premix stage to the coating process, allowing more of the mineral to be absorbed by the fish while reducing losses into the environment.

Zinc is an essential mineral in salmon diets, playing a key role in functions such as wound healing and overall health. 

However, current feeding practices result in low retention, with a significant proportion of zinc passing through the fish and entering the aquatic environment.

According to Antony Philip, researcher at Nofima, the solution lies in improving how zinc is delivered in feed rather than increasing inclusion levels. 

He said the industry should change the way zinc is added to feed to improve digestibility and reduce waste.

This comes as the European Food Safety Authority has proposed lowering the maximum zinc level in salmon feed from 180 mg/kg to 150 mg/kg, aligning it with limits already set for other fish species. 

The proposed reduction reflects growing regulatory pressure to limit mineral emissions from aquaculture.

From premix to coating

Traditionally, zinc is added to feed as part of a premix before extrusion, a high-temperature, high-pressure process used to produce pellets. 

While minerals can withstand heat, this process can bind zinc within rigid protein structures, reducing its availability for absorption in the fish gut.

Nofima’s approach shifts zinc addition to the coating stage, where pellets are treated under vacuum with oils after extrusion. 

This method is typically used for heat-sensitive additives, but researchers found it can also enhance the release and uptake of minerals such as zinc.

Philip, who has spent more than a decade studying mineral nutrition in salmon, said zinc bound during extrusion is less available for digestion. 

Moving supplementation to the coating phase helps avoid this limitation and increases bioavailability.

Trials conducted at Nofima’s Feed Technology Centre on post-smolt salmon weighing between 200 and 280 grams confirmed the benefits of the method.

Triple win for fish health and environment

Results showed that zinc digestibility increased by up to 15 percentage points when added during coating. 

At the same time, zinc levels in faeces were reduced by up to 25 per cent, indicating lower environmental discharge.

The findings suggest a threefold benefit. Improved uptake may support fish health. Reduced excretion lowers the environmental impact around fish farms. 

Lower zinc levels in aquaculture sludge could also enhance its reuse potential and value creation.

The research is now being expanded through the TOP-zinc project, which will evaluate long-term effects in sea-cage trials and identify optimal supplementation strategies. 

The project involves partners including the Institute of Marine Research, Akvaplan-niva, Mowi Feed AS, Huvepharma NV and NIVA, with funding from the Norwegian Seafood Research Fund.

Renate Johansen, R&D Director at the Norwegian Seafood Research Fund, said excess zinc can negatively affect microscopic life around fish farms, adding that stricter environmental requirements are increasing the urgency to reduce emissions.

Researchers say feed producers and farmers may benefit from testing the approach early, particularly in smolt facilities, as regulatory and operational pressures around mineral efficiency continue to grow.

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