Abstract: The postprandial rates of oxygen consumption and ammonia excretion in the southern catfish (Silurus meridionalis Chen)were measured by a continuous2flow respirometer at 27.0±0.5℃The results showed that the standard oxygen consumption rate and ammonia excretion rate were 116.4±6.4 mgO2/kg/h and 6.9 ± 1.4 mgNH4+/kg/h,respectively1The postprandial changing patterns inoxygen consumption and ammonia excretion were similar eachother. After the testedfish ate itsfood the both rates increased drastically,and reached their maximum levels(358.8 ± 11.4 mgO2/kg/h and 76.1±2.5 mgNH4+/kg/h) in a short time(10.8±1.4h and 10.1±0.9 h),then decreased slowly towards to their resting levels1The durationfor the postprandial changes were 36.0±2.3h and 37.2±2.8h;the increased magnitud of oxygen consumption and ammonia excretion were 88.3±2.7 mgO2and 23.1±1.7 mgNH4+ compared with the standards,respectively1This study suggests that response in the rate of ammonia excretion to post2feeding should be relative closely to that in the oxygen consumption1And 79.4 % of energy expenditure for the specific dynamic action(SDA)in postprandial metabolism might be due to protein catabolism in the catfish