Caratinoids are widespread and important pigments and contribute characteristic quality criteria, especially color, to meet consumer demands from aquaculture products. In the diets of fish for which pigmentation is important, synthetic and natural carotenoid sources are included to address this. They contribute to the yellow, orange and red colors found in the skin, shell or exoskeleton of several important fish and shellfish species.
Plant-based carotenoids are mainly derived from microalgal pigment. The freshwater microalgae, Haematococcus pluvialis is commercially exploited for aquaculture primarily due to its rapid growth and high astaxanthin content and the biflagellate algae Dunaliella salina, is a source of β-carotene and used as a natural food coloring agent in the aquaculture feed industry. Among microorganisms, the yeast Phaffia rhodozyma is probably the most important as it contains astaxanthin as its main carotenoid, which makes up 85 percent of its total pigments.
Crustacean processing discards (shrimp, krill and crabs) are also an important carotenoid source. However they can vary in pigment concentration, and a high ash and chitin content reduce their digestibility for fish, which can severely limit the rate of inclusion in diet formulations.
Other land-based feed ingredients such as yellow corn, corn gluten meal and alfalfa are also used as sources of carotenoids in aquaculture feed formulation, as are marigold meal and red pepper extract.
Carotenoids are assumed to be essential for reproduction in aquatic animals. As an example, astaxanthin supplementation in cultured salmon and red sea bream increases ovary development, fertilization, hatching and larval growth. Dietary supplementation of carotenoids can improve the flesh color of various fishes, and the skin color and the market value of ornamental fishes. here is controversy on the role of carotenoids in fish growth, with several studies reporting a positive influence whereas others did not find any effect. In Atlantic salmon fry and juveniles, the inclusion of synthetic astaxanthin and canthaxanthin also enhanced survival.
Carotenoids, especially astaxanthin, are strong antioxidants that probably play roles in protecting broodstock nutrient reserves and developing embryos from oxidation. They reportedly act as pigment reserves in embryos and larvae for the development of chromatophores and eyespots, and as a vitamin A precursor. Carotenoids also enhance egg quality, perhaps by protecting against the damaging effects of UV radiation or other environmental pro-oxidants.
Author: Amit Ranjan PhD. Read the full article in Global Aquaculture Advocate here.
