Effects of green light on circadian rhythm of the olive flounder Paralichthys olivaceus anaesthetised with clove oil

We measured the induction and recovery time of anaesthetised olive flounder Paralichthys olivaceus with two concentrations of clove oil (25 and 50 mu L/L), under the fluorescent lamp or green-wavelength light. In addition, we investigated their effects on the circadian rhythm after recovery from anaesthesia. We found that with the increase in anaesthesia concentration, induction time decreases and recovery time increases, in both light conditions. However, when anaesthetised with the same concentration of clove oil, induction time remained the same, but the recovery time was significantly decreased under green-wavelength light. The circadian rhythm was evaluated by quantifying the transcript levels of clock genes [period 2 (Per2) and cryptochrome1 (Cry1)] and activities of melatonin for 42 h. In the anaesthesia experimental group, the expression of the clock genes and activities of melatonin were significantly lower than that in the control group, and it was further lowered as the concentration of clove oil was increased. However, the anaesthetised group under green wavelength did not show a significant difference in circadian parameters compared to the control group, over time. This study provides the critical information on the use of clove oil anaesthesia in flounders and shows the effective recovery after anaesthesia upon exposure to green-wavelength light.