Effects of feeding level and water temperature on growth, nutrient and energy utilization and waste outputs of rainbow trout (

A study was carried out to determine the effect of feeding level and water temperature on growth and feed efficiency, nutrient and energy utilization and waste outputs of rainbow trout. A practical diet was fed to near-satiation to groups of fish reared at 6, 9, 12 and 15 °C. At each temperature, the feed intake of other groups of fish was restricted to about 85 % or 70 % of the amount of feed consumed in the previous week by the fish fed to near-satiation. Total feed intakes over 12 weeks were, on average, 76 % and 65 % of total feed intake of the near-satiety group for R1 and R2, respectively. Reducing the feed allocation resulted in significantly (P < 0.05) lower weight gains compared to feeding to near-satiation regardless of the rearing temperature. Feeding level and water temperature had no significant (P < 0.05) effect on feed efficiency, carcass composition or efficiencies of digestible nitrogen and digestible energy retention. Increasing temperature resulted in an increase in the apparent digestibility of dietary dry matter, nitrogen and energy (P < 0.05). The increase in digestibility of dry matter and nitrogen with increasing temperature resulted in higher estimated total solid and solid nitrogen waste outputs per kg fish produced (P < 0.05) at lower water temperatures. Estimated dissolved nitrogen and phosphorus waste outputs (g/kg fish produced) were not affected by the feeding level or water temperature. A highly significant (P < 0.01) linear relationship was observed between metabolizable energy (ME) intake above basal metabolism and recovered energy. The efficiency of ME utilization for growth (Kpf) was 0.61 and this coefficient was not affected by feed intake or water temperature. Protein and lipid were deposited in a constant ratio (1 kJ protein gain: 1.4 kJ lipid gain) regardless of ME intake or water temperature.