Endogenous circadian rhythm in the river puffer fish Takifugu obscurus

Abstract

Oxygen consumption rate of 8 to 12 mo old river puffer fish Takifugu obscurus was determined using an automatic intermittent-flow-respirometer (AIFR). During the experiments, the fish were not fed and were kept in constant darkness and at constant temperature to avoid any extrinsic disturbances. It was clearly demonstrated that this species has a strong endogenous circadian rhythm in its instantaneous rates of oxygen consumption, although there were weak minor peaks of 11.4 to 11.7 h intervals. This endogenous rhythm appeared to be independent of the number of fish in the experimental chamber. The endogenous rhythm in the oxygen consumption rate observed in the present study may have profound implications for the physiological processes and biological rhythms of this species, and could also be a good reference in determining the oxygen consumption rates of other aquatic organisms.