Q: Why is salmon pink?
The pink colour of salmon flesh, wild or farmed, results from the retention of carotenoids in the fish flesh. Carotenoids are a naturally occurring group of pigments, imparting colour to the tissues of a variety of organisms. More than 600 naturally occurring carotenoids have been identified in plants and animals. They are responsible for the colours of many fungi, fruits (tomatoes, paprika, citrus fruits), flowers (marigold), insects (ladybirds), birds (flamingos), fish (salmon, goldfish) and they produce the colours of the autumn leaves. Carotenoids found in fish belong to a group known as xanthophylls and include astaxanthin. Astaxanthin is the major carotenoid naturally found in wild salmon and crustaceans (shrimp, lobsters) and is responsible for their pink-red pigmentation.
Nature-identical synthesized pigments are used commonly in a variety of animal feeds as standard practice, including salmon feeds. Feeds for layer hens contain a variety of xanthphylls to produce consistent yolk coluoration, broiler chickens for a yellow skin and meat colour, ornamental birds for feather colour and dog and cat feed for antioxidant and health reasons.
Crustaceans and krill contain carotenoids that are absorbed by the salmon and deposited mainly in the muscle but also in the skin and in the eggs. The prime role of astaxanthin is as a potent antioxidant. Astaxanthin can also be a pro-vitamin A source. These two functions can help to protect tissues against oxidative damage, stimulate the immune system, and improve fertility and growth.
Salmon cannot make their own astaxanthin, and must consume it via their diet. The wild salmon diet includes krill, zooplankton, small fish and crustaceans. The main source of astaxanthin used by the aquaculture industry is synthesised, yielding a molecule that is identical to that found in wild salmon. Synthesised astaxanthin has the same structure, appearance and biological function as that found in wild salmon.
As female salmon prepare for breeding, the xanthophylls are transported to the ovaries where they improve the maturation rate of the oocytes. The pigments become part of the yolk sac. 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 also been shown to increase the growth rate and survival of juvenile fish, in starter feeds and at the fingerling stage.
Astaxanthin is approved for addition to the diet of farmed salmon and trout in all relevant markets. No markets have set an ADI (Acceptable Daily Intake) for astaxanthin and thus no MRL (Maximum Residue Limit) has been set. Astaxanthin has been declared safe for the human consumer by the exacting standards of the European Panel on Additives and Products or Substances used in Animal Feed (FEEDAP).
What is astaxanthin and why is it used in salmon feed?
Salmon naturally has a red/pink colour, due largely to a pigment called astaxanthin. It is produced in natural waterways by algae, yeast and bacteria. The pigment is passed on to crustaceans, such as shrimp or krill, when they eat these primary producers. Salmon then eat the crustaceans and retain the astaxanthin that they receive through their diet in the flesh and skin, where it provides vital antioxidant protection and improves robustness. It is also essential to the salmon natural reproductive cycle and can function as a provitamin, being converted to vitamin A. Salmon are unable to make astaxanthin themselves, needing a dietary supply for these vital functions.
It is now possible to make the pigment directly, without the need to harvest wild crustaceans or cultivate organisms that produce astaxanthin. This form of the pigment is identical to that found in the wild food chain, and provides the same benefits to the fish. The ability to make an identical version of this nutrient increases the ability of the industry to sustainably grow without impacting other industries or depleting naturally occurring, but limited, resources.
Is astaxanthin a chemical?
The term ‘chemical’ can be applied to anything with a known composition, including water. The term ‘chemical’ is commonly misused to make something appear ‘unnatural’ because of negative connotations related to chemical additives that are unrelated to natural substances and may be considered harmful. All substances of known composition are chemicals, including water, proteins, fatty acids, minerals and carbohydrates that make up the majority of living organisms.
Astaxanthin is a chemical with a known composition, like water, and can be synthesised. Synthesised astaxanthin has the same chemical composition as the astaxanthin found in wild salmon flesh, is approved for use as a feed additive, and has been declared safe for the human consumer by the exacting standards of the European Panel on Additives and Products or Substances used in Animal Feed (FEEDAP).
Is astaxanthin harmful to humans?
No. In fact, there is a growing body of medical research that highlights astaxanthin as a valuable antioxidant for human health, and it is now included directly in neutraceutical products.
What colour would a salmon fillet be if astaxanthin is not included in the feed?
Given its health benefits in salmon feed, it is poor practice to make feeds for this species without astaxanthin, and it is not natural for salmon to be depleted of this nutrient. Salmon are not naturally white fleshed and thus farmed salmon are not naturally white fleshed. Salmon have experimentally been depleted of astaxanthin and the fillet appears similar to white-fleshed fish.