We investigated the effects of temperature changes on the oxygen consumption rhythm in Japanese eels, Anguilla japonica, using an automatic intermittent flow respirometer (AIFR). The endogenous rhythm of the oxygen consumption rate (OCR) in the eels (n = 18; 44-74 cm, 145-690 g), freshly collected by bag net from estuaries, was nearly synchronous with the tidal pattern of the estuarine collection site. The magnitude of mean OCR (mOCR) of eels showed variable range of 82.2 - 116.5 ml O2 kg-1 ww h-1 under constant conditions. In case of increasing temperature from 25 to 38℃, the OCR of eels exhibited a gradually increasing trend with a rhythmic pattern until 36℃. Above 36℃, the rhythms of the OCR dampened and the OCR decreased rapidly at around 36 - 37℃. The OCR of the eels exhibited the maximum value at 38℃, and then it sharply decreased. The results suggested that the critical thermal maximum (CTM) regarding the endogenous rhythms of the eels was at around 36 - 37℃ when water temperature increased at 0.5℃/14 h following the acclimation at 25℃. In case of decreasing temperature (0.5℃/14 h) from 25 to 0℃, the OCR of the eels displayed a abrupt decrease up to 23℃, and between at 23 and 20℃, there was an agitation which showed a slight increase in the OCR with a duration of 1-2 days. Below 9℃, the OCR rhythm of the eels showed a constant state regardless of temperature decreasing. These results suggest that the Japanese eel has an upper incipient lethal temperature at 36℃, with a lower thermal limit at 9℃. The biochemical aspects of the eels influenced by water temperature need to be further studied.

Abstract
 1. Introduction
 2. Materials and methods
 3. Results
  3.1. Experiment I : Constant temperature similar tothe collection site
  3.2. Experiment II : Exposure to increasing watertemperature (25 → 38℃)
  3.3. Experiment III : Exposure to decreasing watertemperature (25 → 0℃)
 4. Discussion
 References

• Jong Wook Kim(Marine Ecosystem & Conservation Research Division, Korea Ocean Research & Development Institute)
• Tae Won Lee(Department of Oceanography, Chungnam National University)
• IL Noh(Division of Marine Environment & Bioscience, Korea Maritime University)
• Wan Soo Kim(Marine Ecosystem & Conservation Research Division, Korea Ocean Research & Development Institute) Corresponding Author