We describe a series of Stages for development of the embryo of the ze
brafish, Danio (Brachydanio) rerio. We define seven broad periods of e
mbryogenesis-the zygote, cleavage, blastula, gastrula, segmentation, p
haryngula, and hatching periods. These divisions highlight the changin
g spectrum of major developmental processes that occur during the firs
t 3 days after fertilization, and we review some of what is known abou
t morphogenesis and other significant events that occur during each of
the periods. Stages subdivide the periods, Stages are named, not numb
ered 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 embr
yo with the dissecting stereomicroscope. The descriptions also fully u
tilize the optical transparancy of the Live embryo, which provides for
visibility of even very deep structures when the embryo is examined w
ith the compound microscope and Nomarski interference contrast illumin
ation. Photomicrographs and composite camera lucida line drawings char
acterize the stages pictorially. Other figures chart the development o
f distinctive characters used as staging aid signposts. (C) 1995 Wiley
-Liss, Inc.