Astaxanthin is the most commonly occuring red carotenoid in marine and aquatic animals, and thus occurs naturally in certain human foodstuffs, most importantly in salmon and rainbow trout, to which it imparts a characteristic pink color when present at sufficient levels (Torrissen and Christiansen 1995). Astaxanthin also occurs in shellfish (e. g., lobsters and shrimps), in fish eggs (e. g., salmon roe), and in some other fish species (e. g., red sea bream) (Mera Pharmaceuticals 1999).

Salmon and trout, like other animals, cannot synthesize astaxanthin themselves and must obtain it from their diet--in the wild, from zooplankton (which presumably feed on the microalgae that are the original producers of the carotenoid), or, in the case of commercial fish feeds used for pen-raised fish, from intentionally added astaxanthin. It has been shown that in fish and crustaceans, astaxanthin is essential for growth and plays a vitamin-like role, and, in fact, astaxanthin is absorbed and deposited in fish flesh more efficiently than are other similar xanthophylls (oxygenated carotenoids) such as canthaxanthin, lutein, or zeaxanthin (Torrissen and Christiansen 1995).

Astaxanthin is thus commonly used world-wide to supplement fish feeds, and is approved in the United States as a safe additive to salmonid fish feed (at up to 80 mg per kg feed) in order to obtain the desired pink to orange-red color (Code of Federal Regulations 21 CFR 73.35). Apart from imparting an attractive color, astaxanthin has been shown to prevent the oxidation of fats in rainbow trout during frozen storage, thus preventing rancidity (Jensen et al. 1998).

Astaxanthin levels in the flesh of Atlantic salmon range from about 4 to 10 mg per kg, whereas levels in wild Pacific salmon can be much higher, with a recent FDA study reporting an average of about 14 mg per kg in coho salmon and about 40 mg per kg in sockeye salmon (Turujman et al. 1997). Thus, a reasonable serving portion of 4 ounces (one-fourth of a pound, 113.4 g) of farmed Atlantic salmon would contain from 0.5 to 1.1 mg of astaxanthin, whereas the same amount of sockeye salmon would contain 4.5 mg of astaxanthin.

Jensen, C., Birk, E., Jokumsen, A., Skibsted, L, H., and Bertelsen, G. (1998) Effect of dietary levels of fat, alpha-tocopherol and astaxanthin on colour and lipid oxidation during storage of frozen rainbow trout (Oncorhynchus mykiss) and during chill storage of smoked trout. Zeitschrift f. Lebensmittel-Untersuchung u. Forschung A, 207(3):189-196.

Torrissen, O. J. and Christiansen, R. (1995) Requirements for carotenoids in fish diets. J. Appl. Ichthyol., 11:225-230.

Turujman, S. A., Wamer, W. G., Wei, R. R., and Albert, R. H. (1997) Rapid liquid chromatographic method to distinguish wild salmon from aquacultured salmon fed synthetic astaxanthin. J. AOAC Int., 80(3):622-632.