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 GFP
This movie, shown in real time, shows the heartbeat of a normal 48-hour-old zebrafish embryo. This embryo is expressing a gene for Green Flourescent Protein (GFP) in the cells lining its circulatory system.
Live GFP-bearing zebrafish embryos were mounted in fresh water between a slide and coverslip with a silicon spacer. The image was taken on a fluorescent dissecting microscope equipped with a GFP filter set, 5x objective, and digital camera.