Neurogenesis in the visual system of embryonic and adult zebrafish (Danio rerio)

The zebrafish has recently assumed a central position in the study of verte brate development. Numerous studies of other fish have shown that their cen tral nervous systems, and especially their visual systems, continue to add new neurons throughout life, which is probably related to their abilities t o regenerate axons and whole nervous tissue. Retinal neurogenesis had not b een examined in adult zebrafish, and two reports concluded that the optic t ectum ceased neurogenesis early in life, so the question arose whether the zebrafish was anomalous in this regard. We labeled embryonic (24- and 48-h postfertilization) and adult zebrafish with the thymidine analog, bromo-deo xyuridine, and, after short and long survivals, examined the retina and bra in for labeled cells. They were abundant in both the optic tectum and the r etina. Although the rate of retinal growth slows considerably between embry onic and adult stages, the patterns of neurogenesis in both the embryo and the adult are similar to those described in other fish, so these "fish-spec ific" features of general interest can justifiably be studied in zebrafish.