Project Year 2016

New feed beats discolouration

 Nutrition and feed technology  

Each year fish farmers lose vast sums of money because of dark spots in salmon fillets. Leaner, protein-rich feed may offer a solution.

Dark spots – melanin pigmentation – in salmon fillets were first noticed more than 20 years ago.

Recently there has been a marked increase in these dark spots, and they now pose a serious quality problem. The increase coincided with significant changes in salmon feed, combined with more frequent outbreaks of pancreas disease (PD) and heart and skeletal muscle inflammation (HSMI).

Nofima has previously found that changes in feed can halve mortality from natural outbreaks of PD and HSMI. But could changes in the salmon’s diet also reduce the incidence of melanin spots in the fillet?


“Melanins are naturally occurring, useful pigments with an antioxidant effect that protect various types of tissues and are thus an important part of the salmon’s immune system. Since a lean, protein-rich test feed was found to improve disease resistance, we investigated whether this feed could also prevent the formation of melanin spots. Salmon were fed with the test feed or ordinary feed before, during and after a natural outbreak of disease with co-infection of the viruses PRV and SAV3. 2,600 fillets were examined,” says the head of the research project, senior scientist Turid Mørkøre.

The findings are very convincing:

The change in the feed reduced melanin spots from 26% to 16%. And perhaps even more importantly: the occurrence of large spots, which are difficult to cut away, was reduced to one third.

Major financial savings

“The change in diet also improved the salmon’s outward appearance. In the test group, 91% of the salmon were classified as ‘superior’, compared with 79% in the group that received ordinary feed,” says Mørkøre. The costs that companies report related to discolouration vary, but collected amount to several hundred million kroner a year. “Even a modest reduction in dark spots in fillets will lead to major financial savings for companies,” Turid Mørkøre points out.

Blom Fiskeoppdrett and Sotra Fiskeindustri

The Fishery and Aquaculture Industry Research Fund (FHF)

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