A comparison of constant acceleration swimming speeds when acceleration rates are different with critical swimming speeds in Chinese bream under two oxygen tensions.

To investigate the effect of acceleration rates on the constant acceleration test speed (U cat) and to compare U cat with the critical swimming speed (U crit) in Chinese bream (Parabramis pekinensis), the U cat test at acceleration rates of 0.05, 0.1, 0.2, 0.4 and 0.8 cm s(-2) and the U crit test in juvenile fish at 20 °C in either normoxia (>90 % saturation oxygen tension) or hypoxia (30 % saturation) were compared. The lactate concentration ([lactate]) of white muscle, liver and plasma and the glycogen concentration ([glycogen]) of white muscle and liver were also measured to identify whether tissue substrate depletion or tissue lactate accumulation correlated with exhaustion. The U cat decreased with the acceleration rate, and there was no significant difference between U crit and U cat at lower acceleration rates. Hypoxia resulted in lower U cat and U crit, and the difference increased with decreased acceleration rates of the U cat test, possibly due to the increased contribution of aerobic components in U crit or U cat at low acceleration rates. Hypoxia elicited a significant decrease in muscle [glycogen] and an increase in muscle and liver [lactate] in resting fish. All post-exercise fish had similar muscle [lactate], suggesting that tissue lactate accumulation may correlate with exercise exhaustion. Unlike hypoxia, exercise induced an increase in muscle [lactate] and a significant increase in plasma [lactate], which were worthy of further investigation. The similar swimming speed and biochemical indicators after exercise in the U crit and U cat groups at low acceleration rates suggested that U cat can be an alternative for the more frequently adopted protocols in U crit in Chinese bream and possibly in other cyprinid fish species.