The aim is the molecular characterisation of fish genes. A constitutive promoter of a viral gene has been linked to the reporter genes lacZ or luciferase and was tested by means of transient and stable transgenesis. The max. of transient DNA replication and enzyme expression was observed between 8 and 24 h after injection of the embryo. The Mendelian inheritance of the introduced fusion gene was shown. In a series of parallel experiments the conditions for the cloning of African catfish have been established (gynogenesis).