Improvement and possible commercialization of a home-made electroporation apparatus(home-made) were further tried to establish a simple and effective introduction of foreign gene into sperm followed by in vitro fertilization. Expressions of introduced pJJ9 and pNT plasmids were shown in all fertilized eggs with electroporated spermatozoa. In particular, with this gene transfer system all the fry showed a consistently transient expression in the syncytium of the yolk sac. This fact is important since some required, minute quantity of human proteins can be produced from the established transient expression on the yolk sac of all fry derived from in vitro fertilization with electroporated spermatozoa. To explore tissue-specific expression in fish, which we will use a similar system later, we targeted the nerve tissue to see whether tissue-specific promoter is working in fish properly. pNT plasmid containing a nerve cell-specific tubulin promoter gene demonstrated consistently exact targeted expressions among the developing nerve cells in later stages of embryos and hatched fry. Finally, liver-specific genes are now being cloned by using already selected primers for useful human protein gene fusion.