Research has shown that adult zebrafish have a complex visual system, with two possible opponent mechanisms. Anatomically, zebrafish retina develops in a sequential manner and is immature at hatching. The purpose of the present study was to assess zebrafish retinal development using the electroretinogram (ERG). ERG responses to visual stimuli were obtained from 4-5, 6-8, 13-15, and 21-24 days postfertilization (dpf) zebrafish. Individual waveforms were assessed and compared across the four age groups. Spectral-sensitivity functions were calculated for the a- and b-wave components of the ERG response. Results showed that the ERG waveforms and spectral-sensitivity functions varied with age. While the 21-24 dpf subjects had an ERG waveform that was similar to that of adults, the younger subjects did not. Although there were modest differences in the a-wave spectral sensitivity, substantial differences were found in the b-wave spectral sensitivities across the ages. There was a consistent strong response to ultraviolet wavelengths, while across the remaining parts of the spectrum, there was a gradual increase in sensitivity with age. Also, the 21-24 dpf subjects appear to have adult-like U- and S-cone functions, but were missing the L-M and the M-S opponent mechanisms found in the adult. These results support the findings of the anatomical studies and demonstrate that the zebrafish is a useful model for examining the development of retinal function.