Effects Of Feeding Frequency And Body Mass On The Specific Dynamic Action Of The Snakehead(Channa Argus)

To study the effects of feeding frequency and body mass on the specific dynamic action (SDA) of the snakehead (Channa argus), two experiments were conducted. In experiment Ⅰ, SDA oxygen consumption and ammonia excretion were measured at feeding frequencies of 1 time/2 days, 1 time/1day, 2 times/ 1 day and 4 times/1 day at 25℃. In experiment Ⅱ, SDA oxygen consumption, ammonia excretion and digestive enzyme activities were measured at different body mass at 25℃The results were as follows:1. For each given feeding frequency, oxygen consumption rate peaked significantly after feeding, and then gradually decreased to pre-feeding level, and each feeding resulted in a peak. Feeding frequency did not significantly influence on energy expended on SDA (ESDA) and SDA coefficient (CSDA), while SDA duration markedly increased as frequency increased. Peak metabolic rate (Rpeak), ESDA, and SDA duration increased as the single feeding rate increased, but CSDA decreased.Postprandial ammonia excretion (TAN) showed the similar trends to oxygen consumption and also rose rapidly and then gradually decreased to pre-feeding level. TAN duration increased with the increasing feeding frequency. Fasting ammonia quotient (AQ) and percentage of protein respired pre-feeding increased with the increasing feeding frequency. There were no obvious differences in AQ during SDA and percentage of protein respired during SDA among feeding frequency groups. The percentage of protein respired during SDA (42-54%) was significantly higher than that respired pre-feeding (32-38%).2. Individual resting metabolic rate (RMR), Rpeak and ESDA showed increasing trend, but CSDA decreased with the increasing body mass. Postprandial ammonia excretion showed the similar trends to oxygen consumption. TAN duration, TAN magnitude, and percentage of protein respired during SDA increased with the increasing body mass.As body mass increased, gastric pepsin activities increased from 0.21 to 0.36U/g. Intestinal pancreatic trypsin activities were 1.10, 2.11, 2.56, and 2.61U/g, and aslo increased with increasing body mass. Intestinal amylase activities were 2.19,2.91,3.88, and 4.88U/g, and there were no obvious differences among body mass groups. Intestinal lipase activities were 0.28, 0.39, 0.53, and 0.58U/g, and increased with the increasing body mass.The conclusions suggested in this study were as follows:1. Feeding frequency does not significantly affect on ESDA and CSDA·It suggests that there is no difference in food energy utilization between feeding frequently on small meal and infrequently on large meal, indicating that the snakehead does not have to make a choice on the meal size. This study indicates that when the feeding frequency is higher (frequently on small meal), the single Rpeak reduces, which could leave enough power scope for other activities; when feeding frequency is low (infrequently on large meal), the SDA coefficient is low, suggesting a higher utilization of food energy. A trade-off may exist between metabolic scope and energy utilization in the fish under different feeding frequency.2. When feeding frequency is high, the snakehead post a single small meal showes shorter digestion time, faster ammonia nitrogen release, and easier ammonia nitrogen fluctuat; When feeding frequency is low, the snakehead post a single large meal, showes longer digestion time, which may be due to that the fish has not fully digest before next feeding, resulting ammonia nitrogen value remains high, without obvious fluctuation. In addition, with the increasing feeding frequency, the ammonia nitrogen excretion values do not appear superposition effect, which may be due to that the ammonia concentration of the blood rise after feeding, but cannot increase above its ammonia ceiling following next feeding. The percentage of protein respired SDA is significantly higher than the percentage of protein respired pre-feeding. It suggests that the energy source changes pre-feeding and post-feeding: fasting fish tends to use fat and sugar as fuels, while after feeding, protein is preferred.3. With the increasing of body mass, Rpeak and CSDA decrease, which suggests that the lager fish has higher utilization efficiency of food energy, allowing faster growth and other life activities. The smaller snakehead distributes more protein to amino exchange and then to growth, but the lager snakehead distributes more protein to metabolism. The digestive enzyme activities increase with increasing body mass, suggesting changes in digestive enzymes activities as fish grows, which may be due to increase in the mass of digestive organs and improvement of digestive system.