If farmed salmon receive the minerals in their feed in organic forms, they need smaller amounts. As a result, less of these minerals enter the environment. That is one of the main conclusions of a four-year research project at the Institute of Marine Research.
“Currently it is normal to add minerals to the feed given to farmed fish, but generally in inorganic forms, as metal salts. These tend to bind to the salt in the sea water, which means they are less available to the fish. Consequently, they enter the environment instead”, explains project manager Antony Philip.
“One alternative is to add minerals in organic forms. That allows the fish to absorb more of the minerals, with less entering the environment”, he explained.
The aquaculture industry adds minerals to feed to help the fish grow bigger, stronger and healthier. This has become particularly necessary as a result of the transition to more plant-based feed. “The minerals found in plant ingredients are less available to the fish than the ones in fish meal. You can compensate for this by using more mineral supplements, but that also increases pollution”, said research group leader Erik-Jan Lock.
“Large quantities of minerals like zinc, selenium and copper can be harmful to marine environments. That can be seen, for instance, from the sediment that collects under fish cages”, explains Lock. “This is becoming more and more of an issue, because we’re beginning to look at sediment as an unexploited resource. High zinc levels limit the usefulness of sediment in fertilizers, for example.”
Researchers believe that the industry can reduce this pollution by using minerals in organic forms in feed supplements. Organic minerals, such as those bound to essential amino acids, are more available to the fish. This makes it possible to reduce the total amount of minerals added to the feed – without losing out on the benefits to the health and growth of the fish. Researchers have carried out experiments involving zinc, selenium and manganese and have looked at the amount of these minerals available as nutrients to fish in various chemical compounds in fresh and sea water.
In the case of selenium and manganese, they found a clear improvement if organic forms of the mineral are used. The results for zinc are less conclusive, but in principle the researchers believe that the same effect should apply to zinc and other metals.
“Increasing the availability of minerals in fish feed, particularly in sea water, must be a priority area of focus for future research and development. We are also looking at other strategies to achieve this”, said Antony Philip.