At 14.5±0.5℃,the oxygen consumption and ammonia excretion rate of the Brook Trout(Salvelinus fontinalus)(mean body weight 26.5±2.0 g,n=260)were measured in satiation and starvation stage.The results indicated that the standard oxygen consumption and ammonia excretion rate were 175.00±8.49 mg/kg·h and 2.91±0.40 mg/kg·h respectively.The postprandial changing patterns in oxygen consumption and ammonia excretion were similar:after feeding,both rates increased drastically,and reached their maximum levels(375.93±9.73 mg/kg·h and 16.01±0.37 mg/kg·h,n=130)in a short time(6.0±0.3 h and 7.0±0.5 h,n=130),then decreased slowly towards their standard levels.The duration for the postprandial changes were 23.0±1.5 h and 23.0±2.0 h,the increased magnitude of oxygen consumption and ammonia excretion were respectively 2 641±137 mg and 164±10 mg compared with the standards.This study suggests that the response in the rate of ammonia excretion in satiation should be closely related to that in the oxygen consumption,and 18.8%±1.2% of energy expenditure for the specific dynamic action(SDA)of the brook trout in postprandial metabolism might be due to protein catabolism.