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.

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

Effect of relative meal size (0.6–24%) on specific dynamic action (SDA) was assessed in southern catfish juveniles (48.2±3.2 g) at 27.5℃. Cutlets of freshly killed loach species were used as test diet. Energy expended during SDA was linearly correlated with relative meal size (r =0.949, p＜0.001, N =47). There was no significant difference in SDA coefficient (energy expended on SDA quantified as a percentage of the energy content of the meal) among different relative meal size groups. Factorial metabolic scope increased from 1.47 to 4.08 when the relative meal size increased from 0.6% to 24%. The peak VO2 increased with meal size, but levelled when relative meal size gradually increased to the maximum. SDA duration showed a S-type (slow-fast-slow) increase course with increased meal size. The results of this study suggest that the high postprandial factorial metabolic scope and a trapezoid SDA curve might be the adaptation strategy of warmwater sitand-wait fish under the natural selection of evolution related to long-term food resources.

The ability of juvenile carnivorous southern catfish (Silurus meridionalis Chen) to use different levels, kinds and physic state (glucose, raw cornstarch and precooked cornstarch) of dietary carbohydrate was evaluated in term of growth performance. All diets contained 100 g kg-1 lipid and 16 kJ metabolizable energy. Three isonitrogeneus (400 g kg-1) diets were formulated to contain 150 g kg-1 raw cornstarch, precooked cornstarch and glucose. Another three isonitrogeneus (300 g kg-1) diets were formulated to contain 300 g kg-1 raw cornstarch, precooked cornstarch and glucose. A control diet was formulated with no carbohydrate containing 500 g kg-1 protein. Each experimental diet was fed to four tanks of 10 fish (28.3 ± 0.5 g) for 8 weeks at 27.5 ℃. Specific growth rate (SGR) of 300 g kg-1 glucose diet was significantly lower than those of other diets (P < 0.05). Feeding rates (FR) of 300 g kg-1 glucose and control diets were significantly lower than those of the other diets (P < 0.05). Feed efficiency (FE) was significantly decreased with increased dietary carbohydrate level (P < 0.05). Feed efficiency of the 300 g kg-1 glucose diet was significantly lower than those of the 300 g kg-1 raw and precooked cornstarch diets (P < 0.05). The protein efficiency ratio (PER) was significantly increased with dietary carbohydrate level except that of the 300 g kg-1 glucose diet, which was lowest among all diets (P < 0.05). The results suggested that both dietary starch and glucose were utilized for energy in southern catfish and had a protein-sparing effect. At 150 g kg-1 inclusion level, the utilization of raw and precooked cornstarch and glucose did not vary significantly, but a higher dietary glucose level (300 g kg-1) had a markedly detrimental effect on growth in southern catfish.

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.