Astaxanthin is a carotenoid found in marine environments, usually in the tissues, skin, feathers, and ovaries of various fish and birds, as well as in algae and fungi. It provides an orange to red color for fish tissues, presents grayish-blue in the live shrimp and lobsters of exoskeletons, and turns pink when cooked. Since crustaceans and fish cannot synthesize astaxanthin themselves, they acquire it through the food chain from carotenoids produced by plants, bacteria, and fungi, which are transferred up the food chain. In aquaculture, when natural pigments are insufficient for tissue coloration, astaxanthin must be added to the feed.