The visual system couverts the distribution and wavelengths of photons entering the eye into patterns of neuronal activity, which then drive motor and ersdocdrse behavioral responses. The gene products important for vîsuai processing by a living and behaving vertebrate anima! have not beers identified in an unbiased fashion. Likewise, the genes that affect development of the nervous system to shape visual! function later ira life are îargely unknown. Here we have set oyt to caose this gap in our understanding by using a forward genetic approach m zebrafish. Moving stimuli evoke two initiate reflexes in zeforafish larvae, the optomotor and the optokinetie response, providing two rapid arid quantitative tests to assess visual function in wild-type (WT) and mutant animals. These behavioral! assays were used 1rs a high-throughput screen, encompassing over half a million fish. Sn almost 2,öOÖ F2 families mytagersized with ethyanitrosoisrea, we discovered S3 recessive mutations art 41 gerses. These new mutatsoras have generated a broad spectrum of phenotypes, which vary in specificity and severity, bist can be placed into only a handfy! of classes. Deveiopmenta! phenotypes include compîeîe absence or abnormal morphogenesis of photoreceptors, and deficits in ganguort ce!! differentiation or axon targeting. Other mutations evidently ieave newona! circuits intact, but disrupt phototransduction, Sight adaptation, or behavior-specific responses. Almost all of the mutants are morphologicaily indistinguishable from WT, and many survive to adulthood. Gersetic linkage mapping and initiai molecular analyses show that our approach was effective in identifying genes with functions specific to the visual system. This coîlection of zebrafash behavioral mutants provides a rsovef resource for the study of normal vision and its genetic disorders, Copyright ©2005 Muto et al.