Wild salmon get their pink or reddish flesh color through their diet of krill, plankton, and other small organisms. These organisms contain astaxanthin, which is a natural antioxidant in the same family as the beta-carotene found in carrots. Astaxanthin and beta-carotene are classified as carotenes, which are a subclass of carotenoids, and are the pigments responsible for the red, orange, and yellow colors found in foods and nature. Similarly to wild-caught salmon, farm-raised salmon are provided color through their diets by ingesting these same carotenes, primarily astaxanthin and a similar compound canthaxanthin. These compounds, which are added to salmon feed, are approved by the U.S. Food and Drug Administration (FDA) for use as color additives in food. Currently, most of the astaxanthin and canthaxanthin used in salmon feed is synthetic, although research is being done to improve the process of natural synthesis using microorganisms.
Salmon and trout have the unique ability to retain carotenes in their flesh. A white flesh fish species, such as catfish, does not have this ability and it is not necessary to include these compounds in the diet of farm-raised catfish. In order for farm-raised salmon and trout to be acceptable to consumers, their color must be similar to the wild-caught fish consumers are familiar with. Recently, it is required to label farm-raised salmon as ‘color added’ because of the addition of carotenes in their feed, seafood companies do not add dyes directly to the flesh of the fish.