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SummaryA 12-week feeding trial was conducted to determine the optimum dietary protein requirement of brook trout, Salvelinus fontinalis, at 15 and 19°C. Twelve iso-energetic (22 MJ Á kg À1) and iso-lipidic (23%) diets (36-58% protein at 2% increments) were prepared. Fish (29.45 AE 3.25 g Á fish À1 ) were fed 2% of body weight per day, divided into two equal rations. The specific growth rate (SGR, % Á day À1 ), feed efficiency ratio (FER), productive protein value (PPV), productive lipid value (PLV) and productive energy value (PEV), apparent digestibility of diet (AD DM ) and protein (AD CP ) were significantly higher at optimum temperature (15°C). Increasing PPV with increasing dietary carbohydrate and with decreasing dietary protein content was due to the protein-sparing effect of carbohydrates. A piecewise regression (broken line) model between the SGR and digestible dietary protein level revealed that the digestible dietary protein requirement of brook trout was 44 and 40% at 15 and 19°C, respectively. When PPV (digestible protein retention basis) was modelled with a broken line, the digestible protein requirement of brook trout was 39 and 35% at 15 and 19°C, respectively. A reduction in dietary protein content balanced by increased gelatinised carbohydrate might be useful for improving the protein utilization efficiency for growth at 15 and 19°C; however, the growth and feed efficiency was lower at the elevated temperature.

The digestible protein (DP) and digestible energy (DE) requirements for maintenance and growth of brook trout (Salvelinus fontinalis) were determined using a factorial model at either optimum (15°C) or elevated temperature (19°C). Several key parameters of the factorial model were measured using a series of inter-related studies. The maintenance requirements for DP and DE were 0.10 gDP kg À0.69 day À1 (15°C) and 0.31 gDP kg À0.78 day À1 (19°C), and 34.86 kJDE kg À0.84 day À1 (15°C) and 46.14 kJDE kg À0.86 day À1 (19°C). The total requirements for DP were 0.10 gDP kg À0.69 day À1 + 2.14PG (protein gain) (15°C) and 0.31 gDP kg À0.78 day À1 + 1.98PG (19°C). The total requirements for DE were 36.86 kJDE kg À0.84 day À1 + 1.58EG (energy gain) (15°C) and 46.14 kJDE kg À0.86 day À1 + 1.64EG (19°C). The partial efficiencies for growth were 0.47 (15°C) and 0.51 (19°C) for protein, and 0.63 (15°C) and 0.61 (19°C) for energy. Nutrient gain was lower at the elevated temperature; however, feed formulation for brook trout should be adjusted to match changes in nutrient requirements at different culture temperatures. The protein and energy requirements model will be useful for developing commercial feeds and feeding charts for brook trout.

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