Zebrafish Staging In order to repeat a published experiment, or have someone else repeat yours, it is important to use the same materials. For developmental studies, that means knowing the precise point in development that the embryos have reached. The time of incubation gives only an approximation of the developmental age. For this reason, staging series based on morphologic criteria have been prepared. Zebrafish embryos are laid over approximately an hour and develop very rapidly. A given batch will contain embryos at a range of developmental stages. To obtain a reproducible group of embryos for experimentation, sort embryos after collection and maintain at a constant temperature. Zebrafish embryos are staged using a series prepared by M. Westerfield, The Zebrafish Book, or Kimmel et al., Develop. Dynam. 203:253-310.