ABSTRACT

Modified from: Kimmel et al., 1995. Developmental Dynamics 203:253-310. Copyright © 1995 Wiley-Liss, Inc. Reprinted only by permission of Wiley-Liss, a subsidiary of John Wiley & Sons, Inc.

We describe a series of stages for development of the embryo of the zebrafish, Danio (Brachydanio) rerio. We define 5 broad periods of embryogenesis - the zygote, cleavage, blastuIa, gastrula, segmentation, pharyngula, and hatching periods. These divisions highlight the changing spectrum of major developmental processes that occur during the first three days after fertilization, and we review some of what is known about morphogenesis and other significant events that occur during each of the periods. Stages subdivide the periods. Stages are named, not numbered as in most other series, providing for flexibility and continued evolution of the staging series as we learn more about development in this species. The stages, and their names, are based on morphological features, generally readily identified by examination of the live embryo with the dissecting stereomicroscope. The descriptions also fully utilize the optical transparancy of the live embryo, which provides for visibility of even very deep structures when the embryo is examined with the compound microscope and Nomarksi interference contrast illumination. Photomicrographs and composite camera lucida line drawings characterize the stages pictorially. Other figures chart the development of distinctive characters used as staging aid signposts.

Key words: Zebrafish, Danio rerio, Morphogenesis, Embryogenesis, Zygote, Cleavage, Blastula, Gastrula, Segmentation, Pharyngula, Hatching

ACKNOWLEDGEMENTS During the past 20 years a very large number of our colleagues at the University of Oregon have been most generous in sharing their findings, and insights, that have helped immeasurably in our being to assemble this series. Walter K. Metcalf, Eric Hanneman, and Rachel Warga did the first staging work at Oregon at particular periods of embryogenesis. Many others, including Cosima Fabian, Robert Kelsh, Beth Morin-Kensicki, Mark Fishman, Beatte Schmitz, J. P. Trinkaus, and Rachel Warga have shared unpublished information, and Monte Westerfield criticized several versions of the text. Jerry Gleason and Greg Kruse helped technically, and Pat Edwards located many of, and entered all of the references. Reida Kimmel made the photographic prints, and helped in multitudinous other ways including giving her unfailing encouragement throughout the project. The more recent work and the writing were supported by NIH grants HD22486 and 5T32 HD07348.