Temporal changes in texture, gaping, composition and copper status of Atlantic salmon (Salmo salar, L) fed moist feed or extruded dry feed

Temporal development in product quality and copper status was investigated in Atlantic salmon (initial weight 2.3 kg) fed alginate-based moist feed (MF) or commercial extruded dry feed (DF). The fieldwork was conducted from January to May in sea-cages (800 m³) off the Norwegian west coast. The dry matter content (DM) in the muscle of the MF group was stable at about 32% throughout the experiment, while the DM of DF group increased linearly from 32% to 35%. Salmon were sampled for analyses of Cu status, fillet gaping, texture and pH in March and April. The serum Cu content of the MF group was highest in March, but no significant effect of dietary treatment was observed on Cu status of muscle or liver. The Cu level in serum and muscle decreased from March to April in both fish groups, but the hepatic Cu level showed no temporal changes. Gaping incidence and pH were higher in the MF group in April compared with the DF group and, for both fish groups, fillet gaping was higher and hardness was lower in April than in March. Variation in serum Cu level explained 32% of the variation in fillet hardness, and serum and muscle Cu level related negatively with gaping. At the end of the experiment the condition factor, and fillet and visceral fat contents were higher in the DF group, while sensory evaluated hardness and tastiness were similar for both dietary treatments. In conclusion, sampling time had a greater impact on Cu status, texture and gaping than dietary treatment during springtime in adult Atlantic salmon. Dietary treatment significantly affected body shape, and fat and dry matter contents.