Scientists highlight pigment problems

Norway’s farmed salmon are less pink than they used to be – and this could partly be due to sea lice treatments.

These are among the conclusions of a study by Nofima, the Norwegian food research institute.

The findings are based on questionnaires answered by Norwegian industry actors in 2023, data on fillet colour 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,” says Ytrestøyl.

Historical data show that the colour intensity of Norwegian salmon has decreased somewhat from 2012 to 2021, with a slight increase after this period. There is also more variation in fillet colour now than in the past, which supports the results of the questionnaire: some fish farmers struggle more with pigmentation than others.

The researchers believe the investigation reveals the negative effect that repeated mechanical delousing has on fillet colour. This effect has not been documented before and could be caused by several factors. It may be due to increased consumption of an antioxidant like astaxanthin when the fish are stressed.

However, it could also be that reduced feed intake results in lower slaughter weight, which is of great importance in relation to fillet colour. If fish are slaughtered at a lower weight to avoid more delousing, this will have a further negative effect on colour.

Almost all respondents had taken measures to improve pigmentation. There is more astaxanthin in the feed (50-70 mg per kg) than before and some fish farmers also have more of the omega-3 fatty acids EPA and DHA as well as vitamins in the feed.

Trine Ytrestøyl, Senior Scientist, Nofima

“This has had a positive effect, but it is expensive, and we have tried to find out what leads to inadequate pigmentation,” says Trine Ytrestøyl.

There are seasonal variations in pigmentation, and this can be taken into account when planning production. Very rapid growth resulted in poorer pigmentation, while the colour increased with greater slaughter weight. There was also a clear negative effect from many mechanical delousing treatments.

“This has not been shown before, although it has been mentioned as a possible cause of poor fillet colour.”

What surprised the scientists was the significant difference in colour at slaughter between suppliers of hatchery fish. Now, they are looking to investigate this further to determine what impact the hatchery phase has on pigmentation levels when the fish are slaughtered.