中文摘要：

通过室内实验与海区现场实验相结合的方法,研究了10℃、18℃及20℃下3种不同规格（壳高：S：2.5cm;M：5.5cm;B：6.8cm）的长牡蛎耗氧率、排氨率及钙化率的日变化。实验结果表明,长牡蛎的代谢有一定节律性,其中,呼吸表现为昼夜节律,在水温10℃时为夜高昼低,夜间的耗氧率比白天平均高0.07mg/ind.h;水温20℃时,室内实验的呼吸率无明显节律。而现场实验则表现为昼高夜低,白天比夜间高0.08mg/ind.h。排氨率与耗氧率变化不一致,白天和夜间分别有相近的变化趋势,可能是受到潮汐节律的影响;长牡蛎的钙化则表现出复杂的变化,不同时间段间有显著差异（P〈0.05）,但没有明显的节律性。在进行牡蛎生理实验时,要避免取短时间的生理指标计算其代谢水平,应选择不同时段进行重复实验。

英文摘要：

The diurnal rhythm of respiration,excretion and calcification of Crassostrea gigas at three sizes（shell height：Small：2.5cm ;Middle：5.5cm ;Big：6.8cm）were studied in laboratory control（at 10℃and 20℃）and an experimental farming area（at 18℃）.A rhythm was found for the metabolism of oysters.Oxygen consumption（OR）showed a diurnal rhythm,with higher OR at night at 10℃in the experimental containers,and a reversed rhythm was found at 18℃in the sea area.The difference in OR between day and night was 0.07～0.08mg /ind.h under either situations.Meanwhile,OR at 20℃ was stable.The NH 3 excretion rate showed the same trend at day and night,which was different with the OR rate.It was considered that excretion of C.gigas may be affected by tidal rhythm.Calcification did not show an obvious rhythm,but it was significantly different between time periods（P 〈0.05）.Reasons for the difference in metabolism rhythm was discussed in this paper.It is suggested that calculating the level of metabolism by physiological indices gathered in a short interval should be avoided,and replicates at different time periods are needed.