Classroom Explorations: Zebrafish Development
The zebrafish, Danio rerio, breeds year-round and produces hundreds of clear-shelled eggs with the developing embryos easily visible inside. The embryos develop from single cells to 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.
Swimming adult zebrafish
Zebrafish (Danio rerio) are common in household aquariums. They reach maturity at about 3 months.

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