A tropical freshwater fish belonging to the minnow family. There are many advantages of using zebrafish to study human disease and development: Firstly, zebrafish are small in size, and are easy to keep and breed. They are more similar to humans than you think; many genes are shared between humans and zebrafish, including the genes used to make muscles. The genes of zebrafish can be modified, this means we can create mutations in genes which cause human diseases, such as muscular dystrophy. Importantly, zebrafish embryos are transparent, so we can easily observe their muscles developing. Finally, the embryos can be used too look for drugs which may prevent or slow the progression of a disease.