1. Instead of the critical fusion frequency (Cff) of the flicker ERG, the frequency at which the amplitude becomes half of the maximum amplitude (FHMA) was adopted to investigate the nature of the flicker ERG in carp. 2. The FHMA of the light-adapted carp eye varies not only with the light intensity (Fig. 8) but also with the temperature (Figs. 5&6). 3. If the two relationships-FHMA-Temperature and FHMA-Light Intensity-are obtained in various fish species, they may be useful to compare the Cff or the ability of movement perception between the species.