Tetrachromatic color vision in the goldfish becomes trichromatic under white adaptation light of moderate intensity.

Spectral sensitivity of the goldfish was measured under white room light of 5 lx and 1.5 lx illuminance, using a behavioral training technique. Compared with the result obtained under 25 lx (Neumeyer, 1984), the functions differed remarkably in the mid- and longwave spectral ranges. Under 1.5 lx, the longwave maximum was absent, and wavelength discrimination was impossible in the mid- and longwave range (between 555 and 663 nm). This indicates that the longwave cone type does not contribute to color vision in these conditions. Since discrimination ability was not affected in other spectral ranges, we conclude that color vision is trichromatic then, being subserved by the ultraviolet, the short- and the midwave cone types only. Under 5 lx, the longwave cone type contributes to color vision, but, as shown in color mixture experiments, to a lesser extent.