The effect of relative meal size (0.5-24% body mass) on specific dynamic action (SDA) was assessed in Chinese catfish (Silurus asotus Linnaeus) (30.90+/-1.30 g) at 25.0 degrees C; the cutlets of freshly killed loach without viscera, head and tail were used as a test meal. There was no significant difference in either SDA duration or peak oxygen consumption (VO2) among low meal size ranges. But both increased linearly as meal size increased from 2 to 24% without reaching a plateau. Factorial metabolic scope was 5.92 in fish fed with 24% body mass, the highest documented feeding metabolic scope value in fish till now. The Peak VO2 of satiated meal size groups (175.85+/-10.55 mg O2 h(-1)) was above 80% of maximum metabolic rate during locomotion recovery process (215.48+/-7.07 mg O2 h(-1)). The relationship between energy expended on SDA (E) and energy ingested (I) was described as: E=0.0000432I(2)+0.140I+2.12. The lowest value of SDA coefficient appeared at 2% body mass group.