Supplementation of salmon (Salmo salar) diets with Ulva rigida (UR; 0, 5, 10, and 15% UR) or synthetic astaxanthin (positive control, PC) for 19-weeks preslaughter on quality indices of fresh (raw) salmon fillets was examined. Susceptibility of salmon fillets/homogenates to oxidative stress conditions (cooking/iron-ascorbate induced oxidation) was also measured. In salmon fillets stored in modified atmosphere packs (MAP; 60% N-2:40% CO2) for up to 15 days at 4oC, U. rigida increased surface -a* greenness and b* yellowness values in a dose-dependent manner resulting in a final yellow/orange flesh color. Proximate composition, pH, and lipid oxidation (fresh, cooked, and fillet homogenates) were unaffected by dietary addition of U. rigida. On Day 12, 5% UR psychrotrophic bacterial growth was lower than controls. Salmon fed 5% UR did not influence eating quality sensory descriptors (texture, odor, oxidation flavor, and overall acceptability) in cooked salmon fillets compared to 0% UR. Higher levels of dietary U. rigida (10 and 15% UR) were negatively correlated with color and overall acceptability descriptors. Results indicated that dietary U. rigida, at a level of 5%, may prove to be a functional ingredient in salmon feed to enhance salmon fillet quality.