The Effects Of Hypoxia On Critical Swimming And Constant Accelerate Swimming Performance And Biochemical Mechanism In Juvenile Parabramis Pekinensis

To investigate the effects of hypoxia on the capacity of steady swimming and unsteady swimming, we focus on juvenile Chinese bream(Parabramis pekinensis), raising in water 1 month with saturated dissolved oxygen under 20±1℃. We measured the following:(1) critical swimming speed(Ucrit), tail beat frequency(TBF) and tail beat amplitude(TBA) under 3 mg O2 L-1 and 8 mg O2 L-1 respectively;(2) setting five accelerations(0.05, 0.1, 0.2, 0.4 and 0.8 cm s-2),measured constant accelerate swimming speed(Ucat) and endurance under normoxia and hypoxia respectively;(3) biochemical parameters: contents of lactate, glucose and glycogen in white muscle and liver, concentration of lactate in plasma before and after exhaustive swimming.The results are as follows:1. The Ucrit, TBA and TBF were significantly affected by hypoxia(p<0.05). The Ucrit was significantly reduced under hypoxia(p<0.05). TBA and TBF were increased with the increased water speed. In the condition of low water speed, the TBF of the fish under hypoxia was higher than that under normoxia. However, in the condition of high water speed, the TBA of the fish under hypoxia was higher than that under normoxia(p<0.05).2. The biochemical parameters of the fish were significantly altered after sustained swimming. The white muscle [lactate], plasma [lactate] and liver [glucose] were significant increased after the determination of Ucrit(p<0.05). Additionally, the white muscle [glycogen] and liver [glycogen] under hypoxia were found significantly decreased than that under nomoxia after the determination of Ucrit(p<0.05).3. Both hypoxia and acceleration affect Ucat significantly(p<0.05). The Ucat was showed a tendency of increase and the endurance decreased significantly(p<0.05) with the acceleration increase. Ucat with low acceleration under nomoxia were significant higher than that under hypoxia(p<0.05), but not high acceleration.4. After the determination of Ucat with a range of accelerations, the biochemical parameters of the fish changed to some extent. There were a tendency of the white muscle [lactate], plasma [lactate] and liver [lactate] increased after Ucat measurement. Liver [glucose] decreased with acceleration increased, the white muscle [glycogen] and liver [glycogen] increased with acceleration increased. And there was no significant change in the white muscle [glucose] with acceleration increased.The indications as follow:1. Hypoxia limits the capacity of aerobic locomotion in juvenile Parabramis pekinensis. The fish in hypoxia environment showed significant behavioral response mode.2. Hypoxia limited the performance of constant accelerate swimming in juvenile Parabramis pekinensis. The Ucat with low acceleration was close to Ucrit, indicates there was a larger proportion of aerobic metabolism, so the Ucat with low acceleration was more sensitive to hypoxia environment. There was a larger proportion of anaerobic metabolism with high acceleration swimming, so the effect of hypoxia on Ucat was not significant.3. Both sustained swimming and constant accelerate swimming lead to shorten of endurance in hypoxia environment. With the white muscle [glycogen] and liver [glycogen] decreased, the white muscle [lactate] increased after exhaustive swimming. Plasma [lactate] increased after exhaustive swimming, it indicates “Lactate leaking”.