A commercial diet enriched with synthetic antioxidants (butylated-hydroxytoluene and ethoxyquin (diet I) was fed to coho salmon (Oncorhynchus kisutch) and its effects were compared to two diets enriched with natural antioxidants, tocopherol-rich mixture (diet II), tocopherol-rosemary extract mixture (diet III). Once sacrificed, individual fishes were kept frozen at -18 degrees C for up to 18 months and then analyses were carried out on the frozen salmon muscle. The feeding of diet II led to frozen samples showing higher contents of sarcoplasmic proteins and gamma- and delta-tocopherols when compared to their counterparts previously fed with diet I. No effect of dietary antioxidant profile could be detected on proximate composition, alpha-tocopherol and astaxanthin contents or color (L*, a*, b*) parameters. Concerning the fatty acid composition, the fish samples corresponding to diet II showed higher C22:6 omega 3 and monounsaturated contents, but lower C20:5 omega 3 and saturated contents when compared to their counterparts from diet I.