Zebrafish embryo.

False-coloured scanning electron micrograph of a zebrafish embryo. The zebrafish, Danio rerio, is a tropical freshwater fish originating from eastern Asia and is a member of the minnow family. The zebrafish embryo has gained ground as a disease model, an assay system for drug screening and is used in cancer research. Zebrafish have many characterisics which make them suitable for biomedical rersearch. The embryos develop quickly, from a single cell in a fertilized egg to something that resembles a tiny fish in 24 hours. Zebrafish are vertebrates, meaning they are more closely related to humans than commonly used invertebrate models such as insects and worms. In addition, the embryos can be genetically manipulated and are inexpensive compared to other vertebrate models.