In order to assess electrophysiological responses of fish, a recording of Electroretinogram (ERG) was made on the dark-adapted eyes of anesthetized jack mackerel Trachurus japonicus in the strobe-flash frequency range of 1.7~25 Hz and in the intensity range of 56~415 lx.s. The amplitude change of the ERG is highest at the moment when the strobe light is irradiated and becomes weakest soon after, then gradually increases and becomes stable. The amplitude of the ERG by strobe flash frequencies looked stable tendency after about 12~17 minutes elapsed. During the test duration of 30 minutes, the maximum of amplitude change and stimulation amount over all the tested frequencies was found at 10 Hz. The reduction of the flash intensity caused the decrease in the amplitude and stimulation amount.