TEMPORAL AND SPATIAL PATTERNS OF OPSIN GENE-EXPRESSION IN ZEBRAFISH (DANIO-RERIO)

In zebrafish, the first class of cone photoreceptor to become morpholo gically distinct is the ultraviolet-sensitive short single cone, at 4 days postfertilization, whereas the last class, the red- and green-sen sitive double cone, becomes distinct at 10 days postfertilization. We have examined the time course of visual pigment gene expression in zeb rafish using whole-mount in situ hybridization. Within the retina, ops ins may be detected as early as 40 h postfertilization with the ultrav iolet and rod visual pigments being expressed before the blue- (48 h) and red- (60 h) sensitive pigments. In the pineal, red-sensitive opsin is expressed at 48 h postfertilization.