From The Aquarium Wiki
Astaxanthin is a food additive which is a carotenoid. It is used to give essential minerals to aquatic animals and aids full development of the animals body and fin colours.
It is a colourful, fat/oil-soluble pigment (EU dye E161) and a powerful antioxidant; it is 10 times more capable than other carotenoids.
- It is an expensive additive and therefore usually only found in high quality aquatic animal diets.