Mechanical handling alters salmon fillet colour

The measures salmon farmers take to reduce parasite infestations are contributing to variances in fillet colour, according to a Norwegian study. Fish farmers can also artificially vary pigmentation to suit different market preferences - Japanese customers tend to prefer a more red fillet compared to consumers in some European countries.

The study found repeated mechanical delousing alters fillet colour. Slaughtering fish at a lower weight to avoid infestations has a further negative effect on colour.

The period of the year in which smolt are transferred to salt water is also important, with autumn smolts having a slightly more vibrant pink fillet colour in the survey than smolts transferred to seawater in spring.

The study was based on a questionnaire sent to Norwegian farmers. This revealed variations in the lowest acceptable colour for their salmon on the SalmoFan scale, which measures fillet colour by shades of pink – from a lighter, paler pink to a more vibrant reddish pink – on a scale of 20 to 34. The lowest acceptable colour farmers reported ranges from 24 to 27 on the scale.

Additionally, farmers disagree on how much astaxanthin should be in salmon fillets. Astaxanthin is an antioxidant wild salmon naturally eat in their diets. Farmed salmon eat synthetic astaxanthin through carefully composed feed that gives them their pinkish hue. The low end of their acceptable range is between 5 and 7 milligrams per kilogram per fillet.

Read the full report in Seafood Source, 16 August 2024.