“Should avoid rancid feeds”

More than 300 fish and shellfish species are farmed on a global basis. Marine feed ingredients are an extremely valuable source of protein and fatty acids for most farmed species. However, marine raw materials and ingredients are exposed to oxidation (rancidification) because of a high content of unsaturated fatty acids.

The best known consequences of oxidation are loss of valuable nutrients and reduced exploitation of amino acids. Oxidation also leads to the formation of noxious substances in the feed.

Oxidised feed causes anaemia, discolouration and damage to the gills, liver and kidneys, including tumours. Oxidised feed is also utilised more poorly by the fish. As some farmed species cannot distinguish between lightly oxidised and oxidised feeds, it is both ethically and economically important to avoid using such feeds.

Synthetic antioxidants – not only good

Affordable synthetic antioxidants are added to the feed to prevent oxidation. The use of these is currently regulated and takes into account both safe transport and consumer health, but not the biology of the aquatic organisms. The vast majority of synthetic antioxidants used in aquaculture today are probably calculated from trials on land animals.

Studies carried out on aquatic species at amongst other places the National Institute for Nutrition and Seafood Research (NIFES) in connection with Bohne’s Doctoral project show firstly that:

  • biological disposition of synthetic antioxidants in salmon is different from that in land animals (rats and mice)
  • biological disposition of different synthetic antioxidants are unique in the same farmed organism
  • biological disposition of the same type of synthetic antioxidant varies between farmed species

The trials also show that:

  • synthetic antioxidants or combinations of these have a growth reduction effect on farmed shrimps
  • some synthetic antioxidants cause more extensive tissue damage in farmed shrimps than others and are consequently more noxious
  • some synthetic antioxidants are transferred from the feed to the brain in salmon, and can cause enlargement of the heart and liver in salmon (such effects were not reported in land animals)
  • unfavourable choice of synthetic antioxidants can influence the quality of the feed and the health of the animal and in doing so reduce the farming efficiency

Entire supply chain must contribute

“The increasing demand among consumers for utilisation of marine raw materials to high value products, total utilisation of the raw material and increased negative focus on the use of additives in aquaculture demands new thinking concerning the use of antioxidants,” says Victoria Bohne, a scientist at Nofima Ingrediens.

The choice of antioxidants in early phases of production of marine raw material and ingredients should cover all links in the supply chain – from the catch of pelagic species from both the fisheries and aquaculture industries. Bohne believes that the approach should be holistic, interdisciplinary and knowledge-based concerning for example:

  • seasonal variations in chemical composition in pelagic species
  • the biology of the farmed species and the effects of antioxidants in feeds
  • increased production efficiency associated with the correct choice of antioxidants
  • animal health and welfare related to antioxidants in feeds
  • development of new products from traditional and new marine raw materials, including by-products

“The connection between the type of synthetic antioxidant, reduced growth and the health of farmed organisms has not been in focus previously and should be studied more closely and parallel with the development of new feed types, perhaps particularly with a view to new species in aquaculture or species which have not been farmed successfully,” says Bohne.

Talking about feed quality in Vietnam

Nofima Ingrediens was invited to participate as a key-note speaker at the prestigious course “Aquaculture Feed Extrusion, Nutrition and Feed Formulation”, which was held in Ho Chi Minh City in Vietnam on January 25-26. More than 600 participants from 320 different companies and 50 different countries have participated in such courses since they started in 2004. Victoria Bohne was the only key-note speaker from Norway. Bohne’s address was entitled “Aquafeed quality: Lipid Oxidation and Stabilisation Strategy”.

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