| The aim of this study were, to determine the anaerobic to aerobic metabolism ratio under maximum sustainable swimming speed (critical swimming speed, Ucrit) of selected fish species, to examine at what swimming speed fish start to recruit its anaerobic metabolism, and hence to investigate the relationship among locomotion performance, energy supply characteristics and ecological habits of selected experimental animal. Juvenile darkbarbel catfish (Pelteobagrus vachelli Richardson) (w: 4.34±0.13g, l: 6.89±0.06cm), an economic fish species distributed widely in the Yangtze River and Pearl River, were chosen as the experimental animal. The critical swimming speed (Ucrit) of juvenile darkbarbel catfish was determined at 25±1℃. Based on the Ucrit data, we set 7 experimental groups: 2 control groups (resting control group and high-speed exhaustive control group) and 5 speed-manipulating groups, which were set following the gradient of mean Ucrit (20, 40, 60, 80 and 100% Ucrit). Fish of speed-manipulating groups were forced to swim for 20 minutes at its setting speed, during this period, the oxygen consumption rate was measured and the activity metabolic rate was calculated. The lactate, glycogen and glucose levels of muscle, blood and liver of fish in experimental treatment groups were determined immediately after forced swimming. The biochemical parameters and resting metabolic rate (only for resting control group) were also measured in two control groups. Revealed aerobic and anaerobic metabolism in response to different swimming speed, to provide basic information for the movement of fish physiology research.The results as follows:1. The critical swimming speed (Ucrit) of juvenile darkbarbel catfish was determined at 25±1℃. The absolutely critical swimming speed of juvenile darkbarbel catfish in this study was 48.28±1.02 cm/s and the relative critical swimming speed was 6.78±0.16 BL/s. From high-speed (130% Ucrit) to exhaustive swimming in juvenile darkbarbel catfish of the duration time only 2.81±0.33min.2. The oxygen consumption rate of juvenile darkbarbel catfish raised from 58.88 to 329.96 mgO2/h/kg, its significantly with the increasing of the swimming speed (0, 20, 40, 60, 80 and 100% Ucrit) (P <0.05).3. The muscle and blood lactate levels of fish underwent 100% Ucrit treatment were 7.25±0.70 umol/g and 9.25±2.66mmol/L while the lactate levles of muscle and blood samples were 5.31±0.43 umol/g and 3.44±0.25 mmol/L, respectively. The lactate levels of both muscle and blood samples of 100% Ucrit treatment group were significantly higher than those of 80% Ucrit treatment group (P <0.05) while the lactate level of liver showed no significant change (P> 0.05).4. As swimming speed increased, glycogen content of all three tissues showed a downward trend (P <0.05), of which liver glycogen content of 100% Ucrit group was significantly lower than that of 40% Ucrit level (P <0.05) while glycogen content of muscle showed no significant difference among all experimental treatment groups (P> 0.05). Glucose levels remained relatively stable.The indications as follows:1. The critical swimming speed (Ucrit) of juvenile darkbarbel catfish has a high level, comparing with the cold-water fish reported in the paper with the relevant information.2. Anaerobic metabolism starts its function when fish reaches around 80% of its Ucrit, comparing with other fish the start-up time was late. It showed that their swimming activity relied less on anaerobic metabolism.3. Calculated anaerobic metabolism to aerobic metabolism power ratio is 11.0% when juvenile darkbarbel catfish reaches the critical swimming speed, indicating that the main power came from aerobic metabolism path;4. This study indicates that juvenile Darkbarbel Catfish has strong aerobic capacity and the characteristics of energy metabolism in this fish species may be related to its higher survival fitness.
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