Scanning electron micrograph (SEM) of a zebra fish (Danio rerio) egg. Developmental biologists trigger mutations in zebra fish by using viruses, chemicals, or radiation to identify the genetics of a developing vertebrate embryo. Zebra fish are used because the hardy fish can produce in large quantities and the embryos are transparent. This transparency allows researchers to watch deep tissue interactions during development. Magnification: unknown. Enhancement of [9l0304].