In biology, any substance that can impart colour to the tissues or cells of animals or plants can be called a pigment. The term carotenoid is the generic name for one of the most common groups of naturally occurring pigments found in the animal and plant kingdoms. To date, over 600 have been identified in nature, varying in colour from yellow to red. For example, those who are responsible for the colours of autumn leaves. Coloration is not the only role of pigments, they also :

• can function as a provitamin A source ;
• are potent antioxidants ;
• enhance the immune response system ;
• are required for normal reproduction in cattle and therefore possibly other animals.
  

Carotenoids need to be supplied in the of animals, including humans, as they cannot make carotenoids from simpler molecules. They are totally dependent on the amounts supplied in their feed. In this respect, carotenoids are like vitamins; if intakes are inadequate, health and survival may be compromised.
The pink colour of salmon flesh, wild or farmed, is caused by the presence of carotenoid pigments. These are also known to be important in both salmon and human nutrition; as an example, they are important antioxidants.

Crustaceans and krill contain carotenoid pigments that are extracted by the salmon and deposited in skin, organs and in the eggs. The intensity of the colour varies between fish and does not seem to have an effect on the taste but it does enhance attractiveness to the consumer. There is evidence to show that there are several health benefits from the pigments for salmonid fish.

The group of carotenoids found in fish are known as xanthophylls.

As salmon are unable to synthesise these pigments, they must take them in as part of their diets. To meet the consumer preference for a pink colour, the two xanthophyll pigments, astaxanthin and canthaxanthin, are employed. The pigments may come from crustaceans or, more usually, from nature identical products - both approved for addition to the diet of farmed salmon and of trout.

Fish health benefits

In the wild salmon it seems that pigments have benefits in camouflage and in sexual attraction.

As female salmon prepare for breeding, the xanthophylls are transported to the ovaries where they improve the rate of the ovocytes.  When the eggs are released, the pigments have two further functions, protecting the eggs from damage by light and helping the male to find them. Carotenoids in the diet have been shown to increase the rate and survival of juvenile fish.

Acceptable intakes

Because of the past use of canthaxanthin in the cosmetics/beauty industry, expert committees of the World Health Organisation, in June 1997, set an Acceptable Daily (ADI*) of 0.03mg/kg bodyweight for the canthaxanthin . In February 1998, the UK Advisory Committee concluded that the use of canthaxanthin in salmon feed did not give rise to any food safety concerns.

Even well pigmented salmon flesh contains extremely low levels of carotenoid pigment, measured in parts per million (or mg/kg). The flesh of salmon that have been fed diets containing canthaxanthin will typically contain a maximum of five parts per million of the pigment. A 70kg  could consume 420g of salmon every day without exceeding the ADI.

*ADI = the amount of a substance that can be consumed by an individual each and every day without any danger  to the health of the individual.