| Summary: | Superficial discolored spots on Atlantic salmon fillets is a serious problem for the farming industry. Fillets with large dark stained spots are downgraded by the processing industry while smaller spots are removed, requiring extra labour. The main aim of the present study was to investigate the effect of diet on appearance, location and size of dark stained spots. The fish used were Atlantic salmon (Salmo salar L.) fed a standard commercial feed (Control) or the same feed added antioxidants (vitamin C, E and selenium) (Antioxidant). The experiment was carried out from 7th January to 13th March 2015. The results showed that the supplementation of antioxidants had no significantly effect on growth (average body weight 4 kg) or other biometric traits, but improved the fillet quality. Significantly lower occurrence of spots (31% vs. 45%), lower number of dark stained muscle segments (1.4 vs. 2.3), smaller fillet spot size (0.6 vs. 2.2 score) and lower fillet gaping score (0.8 vs. 1.0) were found of the Antioxidant group as compared to the Control group. Results showed that the melanin (40%) and a combination of melanin and scar (25%) were dominating the visual appearance of spots. Colorimetric analysis of the dark stained spots of the Antioxidant group revealed paler (higher L* value), less redness (lower a* value) and less yellowness (lower b* value) as compared to the Control group. Colorimetric characteristics of the dark spots were stable during one week of ice storage. Image analysis showed significantly higher lightness (higher L* value), less yellowness, larger area and wider width of myocommata of the Antioxidant group compared with the Control group. It is concluded that dietary supplementation of antioxidants reduced fillet gaping, occurrence of dark spots, spots size and number of dark stained muscle segments significantly. M-AA
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