| To investigate the effects of exhaustive chasing training and detraining on swimming performance of fish, the darkbarbel catfish (Peltebagrus vachelli Richardson) , one of the most abundant fish species inhabiting in the Three Gorges Reservoir of China, was used as an experimental model in our study at 25±1℃. Three hundred juvenile experimental fish (2.09±0.80g, 4.74±0.47cm) were averagely divided into five groups (Initial group: before the beginning of the experiment; Training group: trained with exhaustive chasing for 2 weeks; 2 weeks without training group: not trained for 2 weeks;. Detraining group: 2 weeks of exhaustive chasing training followed by 1 week of detraining; 3 weeks without training group: untrained for 3 weeks). We assessed critical swimming speed (Ucrit), oxygen consumption rate (VO2), heart and gill indexes, body composition, food consumption and food conversion rates, and condition factor in all fish.The results as follows:1. Exhaustive chasing training resulted in a significant increase in Ucrit (8.09 BL·s–1) compared with the initial group (6.21 BL·s–1) and the non-trained group (6.89 BL·s–1). The Ucrit of the trained group (7.25 BL·s–1) returned to a value similar to the untrained group (7.19 BL·s–1) after 1 week of detraining.2. Training caused significant increases in VO2 max and the scope of VO2 compared with the non-trained groups and the initial group. Detraining resulted in significant decreases to levels similar to those of the initial and non-trained groups in VO2 max and scope of VO2. There were no significant differences on VO2 rest and EPOC in each group.3. Training caused a significant increase in the heart index from 0.93~1.06‰to 1.45‰, and detraining resulted in a significant decrease to level (0.99‰) similar to that of the non-trained group (1.13‰). Training caused a significant increase in the gill index (30.71‰) compared with the non-trained group (27.81‰), and detraining resulted in a significant decrease to level (26.64‰) similar to that of the non-trained group (25.01‰).4. Training resulted whole-body lipid content significantly decreased from 8.69~9.02 % to 7.28 %, and energy content significantly decreased from 6.71 ~7.02 % to 6.27 %. The lipid and energy content of the trained group increased to values similar to the untrained group after detraining. No significant differences in moisture and protein content among different groups. Moisture content varied from 75.52 % to 76.61 %, and protein content varied from 13.91 % to 14.64 %.5. During 2 weeks initially, food consumption rate, food conversion rate and weight gain in trained fish were 4.62 % body mass, 4.57 %, 0.69 %·d–1 respectively, all less than those of non-trained fish. During the third week, food consumption rate, food conversion rate and weight gain in trained fish were 6.83 % body mass, 2.26 %, 0.83 %·d–1 respectively, also less than those of non-trained fish. However, condition factor (0.39~0.42 g·cm?3%) remained constant throughout the experiment.The indications as follows:1. This is one of the first study to show that only 2 weeks of daily exhaustive chasing can cause a significant increase in aerobic swimming performance (Ucrit), compared with non-trained fish. But anaerobic metabolism capacity (EPOC) did not increase with exhaustive chasing training.2. The training-induced increase in aerobic swim performance (Ucrit) was thought to be closely related to a higher cardio-respiratory capacity (VO2 max and the heart, gill index).3. Trained darkbarbel catfish might use stored lipids to compensate for the extra energy expenditure during exhaustive chasing training.4. exhaustive chasing trained darkbarbel catfish would consume less food and grow slowly due to the exercise or handling stress.5. all observed effects of training on darkbarbel catfish were lost during the 1 week detraining period, which suggests the great flexibility of the locomotory performance in this fish.
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