Diel Rhythms of Oxygen Consumption and Activity Level of Juvenile Flounder Paralichthys olivaceus

抄録

The diel rhythms of oxygen consumption and activity level were measured over a 24-hr period in three size groups of starved juvenile flounder Paralichthys olivaceus by continuous-flow respiratory and video-observation analysis, respectively. In the small group (mean body weight ± SD, MBW: 3.3±0.9g), two peaks of oxygen consumption were observed at 03:00 and 17:00 hours, and the hourly metabolic rates were not significantly different between dark and light periods. In the medium group (MBW: 20.3±3.7g) and the large group (MBW: 58.5±7.1g), only a single peak was observed at 04:00 or 06:00 hours, and the hourly consumption rates were significantly higher in the dark than in the light. For all groups, the highest oxygen consumption rates occurred under conditions of weak light or darkness. The routine metabolic rate is described by the equation logM=0.643 log W -0.387, where M is the oxygen consumption rate (mgO₂/kg/hr) and W is body weigh (kg) at 20°C. The diel pattern in activity rate (duration of swimming per hour in minutes) was similar to the pattern of oxygen consumption; fishes were more active during the night (mean activity rate=5.0min/hr) than duringthe day (mean activity rate=2.2min/hr). The relation between rate of oxygen consumption and activity rate is discussed.