Nofima has mapped the current status and potential pigmentation challenges in salmon filets among Norwegian fish farmers. The mapping also provides insights into some solutions that can be pursued further.
The investigation reveals the negative impact that repeated mechanical delousing has on filet color. This effect has not been documented before and could be caused by several factors. It may be due to increased consumption of antioxidants like astaxanthin when fish are stressed. However, reduced feed intake could result in lower slaughter weight, which is crucial for filet color. If fish are slaughtered at a lower weight to avoid further delousing, this will have an additional negative effect on color.
The findings are based on questionnaires answered by Norwegian industry stakeholders in 2023, data on filet color from commercial productions between 2012 and 2023, and from Nofima’s R&D licenses. FHF – Norwegian Seafood Research Fund has funded the study, which has been carried out by Nofima senior scientist Trine Ytrestøyl and her colleagues.
“There is a high degree of correlation between what the fish farmers report in the questionnaire and what we observe affecting pigmentation in the data analysis, so there is reason to believe it provides a realistic picture of the situation,” said Ytrestøyl.
Variable scope of problems
Not all fish farmers perceive inadequate filet color as a problem. Some report a 2% reduction in pigmentation of slaughtered fish, while others indicate problems with 20-40% of the slaughtered fish. There is also variation in their target for the lowest acceptable color, ranging from 24-27 on the SalmoFan scale and between 5-7 milligrams of astaxanthin per kilogram of filet.
Historical data show that the color intensity of Norwegian salmon has decreased from 2012 to 2021, with a slight increase after this period. There is also more variation in filet color now than in the past, which supports the results of the questionnaire: some fish farmers struggle more with pigmentation than others.
Measures require planning and minimal lice
Almost all respondents have taken measures to improve pigmentation. There is now more astaxanthin in the feed (50-70 mg per kg) than before, and some fish farmers have also increased the amount of omega-3 fatty acids, such as EPA and DHA, as well as vitamins in the feed.
“This has had a positive effect, but it is expensive, and we have been trying to understand what causes inadequate pigmentation,” said Trine Ytrestøyl.
There are seasonal variations in pigmentation, which can be considered when planning production. A very rapid growth led to poorer pigmentation, while color improved with greater slaughter weight. There was also a clear negative effect from multiple mechanical delousing treatments. “This has not been shown before, although it has been mentioned as a possible cause of poor filet color,” said Ytrestøyl.
What surprised the scientists was the significant difference in color at slaughter between suppliers of hatchery fish. They want to investigate this further to determine what impact the hatchery phase has on pigmentation levels when the fish are slaughtered.
Download the report in the link below.
