Color Vision in Fishes and Its Neural Basis

Abstract

The neurons in the retina of fishes possess chromatic response properties that are found in primates only in the visual cortex. The retinae mainly of cyprinid and cichlid fish species are being intensively studied using electrophysiological and neuroanatomical techniques. On the other hand, behavioral experiments are performed to establish the overall properties of color vision and other visual functions. Many details of color vision are known in goldfish, which is an ideal subject because it is especially suited for training experiments using food reward. To establish the neural basis of color vision and other visual functions a neuropharmacological approach in combination with behavioral experiments yields promising results. They indicate that there is a parallel processing of “color” and high visual acuity on the one hand, and “motion,” “flicker,” and “brightness” detection on the other hand, which is similar to the situation in the visual system of primates. In goldfish, as the best-investigated fish species, the following properties of color vision are described: wavelength discrimination, spectral sensitivity, color constancy, color contrast, and color perception. The shape of the Δλ-function gave the first hint that goldfish color vision may be tetrachromatic, being based on four cone types. This was proven to be the case in additive color mixture experiments. Goldfish color vision includes the ultraviolet spectral range and is, therefore, perhaps more complicated than human color vision.