The role of astaxanthin (Ax) and canthaxanthin (Cx), in flesh pigmentation of salmonids is widely recognized. The retention of these carotenoids in flesh is low (5-20%) and is affected by genetic factors, the efficiency of absorption, transport, tissue uptake, stages of growth, development, metabolism and excretion. Although nutritional strategies have been developed to effectively utilize synthetic and natural sources of Ax and the application of carotenoid dynamic models for different strains and species of salmonids by the aquaculture industry, the progress in research to better understand the molecular basis of carotenoid metabolism in fish has been slow. In recent years, research has been focused on the biochemical mechanisms involved in Ax absorption, transport, cellular uptake and metabolism, muscle binding with protein and the molecular basis of Ax and Cx breakdown by carotenoid cleaving enzymes in Atlantic and Pacific salmon. Beyond flesh pigmentation, Ax and Cx have also been shown to have other physiological functions e.g., provitamin A, antioxidant, reproduction, immunity and health. Astaxanthin is considered an effective biological antioxidant that prevents stress disorders, which are linked to the primary cause of certain diseases in humans and experimental animals.
In this presentation, a brief review of current knowledge of Ax metabolism and the bottlenecks involved in its low absorption and retention will be discussed. The progress made to date in molecular mechanisms involved in carotenoid metabolism in other vertebrates may be useful to examine the problems associated with absorption and to better define the role of Ax in oxidative stress related diseases and fish health.