Effects of long-term spectral deprivation on the morphological organization of the outer retina of the blue acara (Aequidens pulcher)

To investigate the developmental plasticity of colour vision, we reared fis h with a trichromatic cone system (Aequidens pulcher) under three near-mono chromatic lights, differentially stimulating each spectral cone type from t he larval stage to the ape of at least one year. Control conditions compris ed white lights of two intensities. The treatments did not affect the visua l pigments, but led to significant changes in cone outer segment lengths. F urther more, in the blue-reared group the density of single cones within th e retina was reduced by two-thirds after. 18 months of exposure, while no c hanges were observed in the other groups. The connectivity of cone horizont al cells with the single cones was influenced by the intensity and spectral composition of the rearing lights: H1 cells were more sensitive to the spe ctral component, whereas H2 cells responded to intensity cues. In the blue- light group the dynamics of horizontal cell synaptic spinule formation and degradation were severely compromised. These observations show that long-te rm spectral deprivation leads to significant morphological changes at the l evel of photoreceptors and horizontal cells. While the reactions of photore ceptors may be interpreted mostly interpreted mostly of compensation, the f unctional consequences of the changes observed on the horizontal cell level remain to be determined electrophysiologically.