EFFECTS OF FEEDING LEVEL AND WATER TEMPERATURE ON GROWTH, NUTRIENT AND ENERGY-UTILIZATION AND WASTE OUTPUTS OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

A study was carried out to determine the effect of feeding level and w ater temperature on growth and feed efficiency, nutrient and energy ut ilization 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 degrees C. At each temperature, the feed intake of other groups of fish was r estricted 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 ov er 12 weeks were, on average, 76 % and 65 % of total feed intake of th e near-satiety group for R1 and R2, respectively. Reducing the feed al location resulted in significantly (P < 0.05) lower weight gains compa red to feeding to near-satiation regardless of the rearing temperature . Feeding level and water temperature had no significant (P > 0.05) ef fect on feed efficiency, carcass composition or efficiencies of digest ible nitrogen and digestible energy retention. Increasing temperature resulted in an increase in the apparent digestibility of dietary dry m atter, nitrogen and energy (P < 0.05). The increase in digestibility o f dry matter and nitrogen with increasing temperature resulted in high er estimated total solid and solid nitrogen waste outputs per kg fish produced (P < 0.05) at lower water temperatures. Estimated dissolved n itrogen and phosphorus waste outputs (g/kg fish produced) were not aff ected by the feeding level or water temperature. A highly significant (P < 0.01) linear relationship was observed between metabolizable ener gy (ME) intake above basal metabolism and recovered energy. The effici ency of ME utilization for growth (K-pf) was 0.61 and this coefficient was not affected by feed intake or water temperature. Protein and lip id were deposited in a constant ratio (1 kJ protein gain:1.4 kJ lipid gain) regardless of ME intake or water temperature. (C) Ifremer/Elsevi er, Paris.