Feed and feeding. The fish were fed NUTRA commercial trout diets manufactured by TROUVIT (Nutreco Aquaculture, Holland). Three granulate sizes were used during the experiments – NUTRA 0 (0.6–1.4 mm), NUTRA 1 (1.7 mm),
NUTRA T (2.2 mm). The feed type was switched during a three-day adaptation period when a 50:50 mix of feeds was used. According to the manufacturer’s data, the feed contained 54% protein, 18% fats, 8% carbohydrates, and digestible energy
19.5 MJ/kg. The feed was delivered with an automatic band feeder (4305 FIAP, Fish Technic Gmbh,Germany).