Life through the lens
Introduction: Zebrafish
The zebrafish, Danio rerio, breeds year-round and produces hundreds of clear-shelled eggs with the developing embryo easily visible inside. The embryos develop from one cell to a swimming fish in about two days. The visibility and speed of zebrafish embryonic development allow scientists to observe the growth of organs in very young embryos.

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Normal zebrafish heartbeat
This movie, in real time, shows the heartbeat of a 48-hour-old zebrafish (Danio rerio) embryo.

Elapsed time 24 seconds.
A two-day-old zebrafish embryo was mounted in fresh water between a slide and coverslip using a silicon spacer. The movie was taken on an inverted compound microscope using a 20x DIC objective and digital video camera.