Some of the favourable physical and genetic cha racteristics of the zebrafish are discussed in this article, the equivalent char acteristics to the mouse which is another popular system for studies in vertebra te genetics are also listed. Then the advantages and disadvantages of the zebraf ish and mouse are compared. In addition, the fact is introduced that zebrafish a re experiencing an exponential increase in popularity as a model system for stud ying the genetic control of embryo development.