Danio rerio commonly known as the Zebrafish is a tropical fish belonging to the minnow family (Cyprinidae), commonly kept in aquaria and used for scientific research. Zebra Danios are of no economic importance in commercial fisheries as a food fish, but very commonly known and popular in the aquarium trade. Zebra Danios serve as a common and useful model organism for studies of vertebrate development and gene function because they reproduce very easily, passing from the egg to the larvae stage in less than three days. For genetic research groups, the zebrafish is an excellent test subject and is used in many labs to replace or to supplement higher vertebrate models, such as rats and mice. Danio rerio is one of the few species of fish to have been flown into space. The zebrafish is a special animal to biologists because its body is transparent. Aided by the transparency of the embryo, if researchers modify the fish's genotype at the egg stage they can see resulting changes in organ shape or dynamics barely three days later. The arrival of zebrafish as a major model for studying developmental biology coincided with a large scale mutagenesis screen (commonly referred to as the Tübingen/Boston screens).