Effects of pentachlorophenol (PCP) on the oxygen consumption rate of the river puffer fish Takif ugu o bscurus 'Marine Biotechnology Lab., and 'Chemical Oceanography Division. Korea Ocean Research & Development Institute, Ansan. PO Box 29. Seoul 425-600. Korea ABSTRACT: Laboratory bioassays were conducted to determine the effects of pentachlorophenol (PCP) on the oxygen consumption of the river puffer fish Takifugu ohscnrus. Oxygen consu.mption of 6 to 9 mo old puffer fish was measured with an automatic intermittent-flow-respirometer (AIFR). Oxygen consumption rate was s~gnificantly increased by exposing fish to concentrations of 50, 100, 200 and 500 ppb PCP Follow~ng exposure to 50 or 100 ppb PCP, the instantaneous rate of oxygen consumption was considerably increased. T obscurus exposed to 200 ppb PCP, however, exhibited a breakdown in the biorhythm of oxygen consumption presumably due to a strong physiological stress caused by the higher PCP concentrations. River puffer fish exposed to 500 ppb PCP died in 10 h.