Diets supplemented with synthetic astaxanthin at concentrations of 0, 15, 30, 45, and 60 mg/kg were fed to groups of coho salmon ( Oncorhynchus kisutch) for 28 weeks. The mean initial and final weights were 50 and 379 g, respectively. Flesh color was determined by chemical, instrumental, and visual analysis of fillets from eight coho salmon per group at 50-g weight intervals. Chemical analysis indicated a linear relationship between dietary and flesh carotenoid concentrations after initial absorption. Overall carotenoid flesh retention efficiencies in relation to dietary carotenoid levels were 20.0, 17.4, 15.3, and 19.8% for fish fed diets containing 15, 30, 45, and 60 mg of astaxanthin/kg, respectively. The Huntcrlab tristimulus colorimeter showed that intensity of redness ( a *) and yellowness ( b *) increased with increasing carotenoid concentration in the flesh, while lightness ( L *) decreased. Carotenoid levels in the flesh were accurately estimated using ( a *) as a criterion. Visual assessment of flesh color using the Hoffman-LaRoche salmon color card scale correlated well with the chemical determination; however, due to its curvilinearity, values above 5 mg astaxanthin/kg flesh became visually indistinguishable. Data extrapolations suggest that an economical pigmented diet for pan-size coho salmon would contain approximately 15 mg of astaxanthin/kg and that it would be necessary to feed this diet throughout the production cycle, starting at an initial fish weight of 50 g.