Microspectrophotometry studies show that zebrafish (Danio rerio) possess four cone photopigments. The purpose of this study was to determine the cone contributions to the zebrafish photopic increment threshold spectral-sensitivity function. Electroretinogram (ERG) b-wave responses to monochromatic lights presented on a broadband or chromatic background were obtained. It was found that under the broadband background condition, the zebrafish spectral-sensitivity function showed several peaks that were narrower in sensitivity compared to the cone spectra. The spectral-sensitivity function was modeled with L − M and M − S opponent interactions and nonopponent S- and U-cone mechanisms. Using chromatic adaptation designed to suppress the contribution of the S-cones, a strong U-cone contribution to the spectral-sensitivity function was revealed, and the contributions of the S-cones to the M − S mechanism were reduced. These results show that the b-wave component of the ERG receives input from all four cone types and appears to reflect color opponent mechanisms. Thus, zebrafish may possess the fundamental properties necessary for color vision.

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The XOPS-mCFP transgene causes selective degeneration of rods without secondary loss of cones in animals up to 7 months of age. This raises important questions about the significance of rod-cone interactions in zebrafish and their potential as a model of human inherited retinal degenerations.

Anatomical studies of the developing zebrafish retina have shown that rods approach maturity at about 15 days postfertilization (dpf). Past work has examined the photopic spectral sensitivity function of the developing zebrafish, but not spectral sensitivity under darkadapted conditions. This study examined rod contributions to the dark-adapted spectral sensitivity function of the ERG b-wave component in developing zebrafish. ERG responses to stimuli of various wavelengths and irradiances were obtained from dark-adapted fish at 6-8, 13-15, 21-24, and 27-29 dpf. The results show that dark-adapted spectral sensitivity varied with age. Spectral sensitivity functions of the 6-8 and 13-15 dpf groups appeared to be cone dominated and contained little or no rod contributions. Spectral sensitivity functions of the 21-24 and 27-29 dpf groups appeared to have both rod and cone contributions. Even at the oldest age group tested, the darkadapted spectral sensitivity function did not match the adult function. Thus, consistent with anatomical findings, the rod contributions to the ERG spectral sensitivity function appear to develop with age; however, these contributions are still not adult-like by 29 dpf, which is contrary to anatomical work. These results illustrate that the zebrafish is an excellent model for visual development.

The zebrafish has become an important vertebrate model in developmental neuroscience because it is a useful model for embryology, developmental biology, and genetic analysis. The similarities of its visual system to that of other vertebrates also make this animal a valuable model in vision science. The anatomical, physiological, and behavioral components of zebrafish visual processing have been studied in adult and in developing zebrafish. Its retinal anatomy continues to develop following hatching, providing an opportunity to correlate the development of retinal structure with visual physiology and behavior. In addition, a number of genetic mutations have been developed which are used to examine the contributions of genetics to visual development and function. This article will provide an overview of studies of zebrafish anatomical, physiological and behavioral processing, and the effects if genetic and environmental manipulations on visual development.

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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.

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