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Rainbow trout with initial body weight 1144 g were fed two diets with high (feed A) or low (feed B) water stability for 6 weeks. During the last 2 weeks either stable or fluctuating oxygen saturation, salinity and temperature was introduced. High water stability of the feed was associated with harder pellets, less dust formation and less broken pellets compared to feed with low water stability. During the first 4 weeks, feed intake was 23% higher in trout fed diet B than in those fed diet A. Fluctuating environment resulted in a severe drop in feed intake for both dietary groups. At termination of the trial, stomachs of trout fed feed B contained mashed pellets and free water and oil. Stomachs of trout fed feed A contained more intact pellets and little fluid. The apparent digestibility of protein, starch, dry matter and energy was highest in feed A. The apparent digestibility of P and Zn was highest at stable environment, and the absorption of P was highest from feed A. In conclusion, physical quality affected the nutritional value of the feeds, and differences in nutritional value at stable or fluctuating environment appeared to be related to feed intake.

1 2For the development of commercial scale semi-closed sea systems for farming post-smolt 3 Atlantic salmon (Salmo salar), further knowledge is required on the interaction between fish 4 density, farming conditions and fish welfare. In this experiment post-smolts (115.0 g 13.6) 5 were stocked at 5 different densities (25, 50, 75, 100 and 125 kg m -3 ), and kept at these 6 densities for 8 weeks. All treatments received an equal specific flow rate of 0.6 L kg fish -1 7 min -1 of flow-through seawater (fully oxygenated, salinity 34 ‰ and temp. 9.3°C) and water 8 oxygen (O2), pH, carbon dioxide (CO2) and total ammonia nitrogen (TAN) levels were 9 monitored in the outlet and kept within recommended limits. Over the 8 week period, specific 10 growth rate (SGR %) was significantly reduced in stocking densities of 50 kg m -3 and above.