The colour of a salmon’s flesh, whether wild or farmed, is determined by its diet. Ranging from orange to ivory-pink, flesh coloration is a result of the levels of organic pigments, known as carotenoids, present in what the fish has eaten.
There are more than 600 naturally occurring carotenoids; they are what make carrots and pumpkins orange, daffodils and sweetcorn yellow and what produces the spectacular colour changes in autumn leaves.
For animals such as pink flamingos and through to the vibrant red sockeye salmon, which feed on crustaceans and plankton, the carotenoid responsible for their eye-catching colours is called Astaxanthin.
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Astaxanthin, which can be synthesised or biologically grown, is a powerful antioxidant and source of pro-vitamin A. These properties stimulate immune systems and can improve fertility and growth. In Scotland farmers use a organic, naturally sourced pigment, derived from the fermentation of a micro-organism and with no additives or preservatives.
Scottish Salmon farmers want to provide their fish with the best feed possible, closely aligned to a wild diet, but they also want to meet the expectations of consumers. The salmon farming sector therefore adds small quantities of Astaxanthin (between 20 and 60 milligrams per kilo of food) to salmon feed resulting in not only healthier fish but also the familiar ‘salmon pink’ colour of fillets.
What would salmon flesh look like if this important pigment was left out of their diets? As the picture above (of a salmon smolt fed a non-carotenoid diet) shows it would look much more like haddock, white with a pink hue.
In the wild, 1 in 20 Chinook (also known as King) salmon, found in the northwest Pacific, is unable to process Astaxanthin which results in its flesh staying white. Until recently the white-fleshed chinook salmon was considered less desirable.
It is also worth noting that Astaxanthin is widely available and used as a human health supplement due to its antioxident properties.