We investigated chromatic processing in the outer retina of
the cichlid fish Aequidens pulcher. Intracellular
recordings from cone-specific horizontal cells (CHCs) revealed
that the two morphologically identified types (H1 and H2) also
have different spectral responses. H1-L cells hyperpolarize
to all wavelengths (“luminosity”). H2-Cb cells
depolarize to long wavelengths and hyperpolarize to short
wavelengths (“chromaticity”, biphasic). Furthermore,
we verified by immunocytochemistry that H2-Cb cells of A.
pulcher predominantly contact the middle-wavelength-sensitive
(MWS) members of double cones. Developmental plasticity in the
cone–CHC networks was induced by rearing fish under
conditions of spectral deprivation and different levels of white
light. H1-L spectral responses were unaffected by the rearing
conditions. Different intensity levels of white light and
deprivation of long wavelengths during rearing both induced
changes in the spectral responses of H2-Cb. Deprivation of short
and middle wavelengths had no effect. Our results indicate that
spectral processing in the outer retina of fishes can be modulated
in response to different visual experiences and suggest that
developmental fine tuning of the color-vision system occurs
at early levels of visual processing.