Southern catfish juvenile (37.6–65.9 g) were fasted for two weeks and fed with cutlets of freshly killed loach species at 2% body mass per meal twice daily (06:00 and 18:00) for four days at 27.5℃. Metabolic rates were measured during the fasting and feeding periods and all metabolic rates were adjusted to a standard body mass of 1 kg using an exponent of 0.75. The aim of this study was to investigate the effect of fasting and repeat feeding on the resting metabolic rate and the feeding metabolic rate. The results demonstrated that the standardized value of the resting metabolic rate gradually decreased from 69.6±2.7 (means±S.E.) to 42.8±2.3mgO2 h-1 during the two weeks of fasting. The peak feeding metabolic rate and average metabolic rate of each feeding (12 h) gradually increased with repeat feeding before leveling off. The results of this study suggest that southern catfish can regulate digestive function and gradually alter the characteristics of metabolism according to the availability of a food resource.

The effect of dietary macronutrient composition on specific dynamic action (SDA) in southern catfish Silurus meridionalis Chen juveniles (39.0

etabolic response was investigated in southern catfish Silurus meridionalis at 27.5℃. The results showed that there was no significant difference in the specific dynamic action (SDA) coefficient among the groups of different feeding levels (P >0.05). The duration increased from 26.0 to 40.0 h and the peak metabolic rate increased from 207.8 to 378.8 mg O2 kg-1 h-1 when the feeding level was increased from 0.5 to 4%. The relationship between the peak metabolic rate (RP, mg O2 kg-1 h-1) and FL could be described as: RP =175.4 t 47.3 FL (r2 = 0.943, n = 40, P < 0.001). The relationship between the SDA duration (D, h) and FL could be described as D=30.97FL0.248 (r2=0.729, n=40, P < 0.001).

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℃; 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=0.0000432I2+0.140I+2.12. The lowest value of SDA coefficient appeared at 2% body mass group.

In previous growth experiments with carnivorous southern catfish (Silurus meridionalis), the non-fecal energy lose was positively related to dietary carbohydrate level. To test whether metabolic energy expenditure accounts for such energy loss, an experiment was performed with southern catfish juveniles (33.2–71.9 g) to study the effect of dietary carbohydrate level on fasting metabolic rate and specific dynamic action (SDA) at 27.5 ℃. The fasting metabolic rate in this catfish was increased with dietary carbohydrate level, and the specific dynamic action (SDA) coefficient (energy expended on SDA as percent of assimilated energy) was not affected by dietary carbohydrate level. The results suggest that in southern catfish, carbohydrate overfeeding increases metabolic rate to oxidize unwanted assimilated carbohydrate. A discussion on the poor capacity of intermediate metabolism for adapting dietary carbohydrate in carnivorous fish and its possible relationship with facultative component of SDA was also documented in this paper.