Effects of temperature changes on the endogenous rhythm of oxygen consumption in the Japanese flounder Paralichthys olivizceus

Abstract

The effects of temperature changes on the endogenous rhythm of oxygen consumption in the Japanese flounder Paralichthys olivaceus which were acclimated to 3, 14 or 20 degrees C in advance were investigated. The oxygen consumption rate (OCR) of individuals (total length > 28 cm) that were acclimated to 3 degrees C, maintained a relatively low value of 6.9 +/- 2.3 mL (mean +/- SD) O-2/kg ww (wet weight)/h till 5.8 degrees C, which is considered a 'minimum' rate. Thereafter, the OCR gradually increased up to 18.7 mL O-2/kg ww/h at the temperature of 10.6 degrees C. The OCR of individuals acclimated to 14 degrees C stabilized with 124.2 +/- 24.1 mL O-2/kg ww/h, when tested at the relatively constant temperature of 14.4 +/- 0.17 degrees C. Maximum entropy spectral analysis revealed that the peak OCR occurred at 23.9 h intervals, which could be a circadian rhythm. The mean OCR showed a peak at 06.00-08.00 hours. For the temperature above 25 degrees C in which the fish were acclimated to 20 degrees C, the rhythmic patterns of OCR were observed until the experimental temperature reached 26.4 degrees C. For the temperature above 28.4 degrees C, the metabolic activity rhythm of the OCR was dampened and then the OCR abruptly rose again. It is assumed that the oscillator of the endogenous rhythm, lost the governing of normal metabolic activity in Japanese flounders above 28.4 degrees C. These results suggest that the temperatures of around 5.8, 26.4 and 28.4 degrees C are the 'lower limit temperature', 'upper incipient lethal temperature', and the 'critical thermal maximum', respectively, for the endogenous rhythm of oxygen consumption in the Japanese flounder.