Diverse coloration and color patterns are one of the features of the family Salmonidae, and a particularly remarkable feature of several genera in this family, including the genus Salmo to which the Atlantic salmon belongs, is the pinkish-red coloration of their fl esh. The primary sources of this color are naturally occurring carotenoid pigments in crustacean prey items (Norris and Cunningham 2004). Carotenoids are conjugated double-bond pigment molecules synthesized by plants, bacteria, algae and fungi. In addition to being a source of pigmentation, they are known to act as vitamin A precursors, and have also been associated with other biological functions including improving intercellular communication, enhancing immune responses, and acting as antioxidants in vivo (Goodwin 1986; Demmig-Adams et al. 1996). Carotenoids are extremely widespread throughout the animal kingdom, and in aquatic species are found in the fl esh of fi shes, exoskeleton and muscular epithelium of shrimps, carapaces of lobsters and other crustaceans, integuments of red and yellow fi shes, and gonads and hepatopancreas of mollusks (Bjerkeng 2000). However, of all the marine or freshwater fi sh species in the Northern Hemisphere, only the genera Oncorhynchus, Salvelinus, Salmo and Parahucho in the family Salmonidae possess characteristic pinkish-red fl esh coloration (Rajasingh et al. 2007). The uptake of carotenoids and carotenoid dynamics are particularly interesting in salmonids, as many other sympatric species that prey on similar food items do not deposit carotenoids in the muscle and have non-pigmented fl esh, despite having similar uptake and metabolism patterns. The distinct fl esh and skin pigmentation within these four genera suggests that there may be a unique evolutionary scenario accounting for the emergence and maintenance
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