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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Still Image:
Zebrafish embryos expressing GFP
These two-day-old zebrafish (Danio rerio) embryos are expressing a gene for Green Fluorescent Protein (GFP) in cells lining their circulatory system. This causes the embryo's circulatory system to glow green when exposed to light of a certain wavelength.
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.