To investigate the role of epigen,a member of epidermal growth factor,in flounder Paralichthys olivaceus during metamorphosis stage,we characterised the epigen gene,which is cloned from the cDNA library of metamorphosing Paralichthys olivaceus.The epigen gene encodes 162 amino acids with a signal peptide,a transmembrane helix and a EGF-like domain.EGF-like domain contains six cysteines and three disulfide bonds,and is conserved between Paralichthys olivaceus and other species.Fluorescent real-time qRT-PCR was used to analyse the change of epigen gene expression during metamorphosing stage.From pro-metamorphic stage(17DAH,day after hatching) to pre-metamorphic stage,the expression level of epigen gene increased by 136.3%.Then,the expression level decreased by around 80% from pre-metamorphic to metamorphic climax.There was no significant change from metamorphic climax to post-metamorphic stage,and the expression of epigen gene kept at a relatively low level.The expression pattern of epigen gene during metamorphosing stage indicates that the epigen might be involved in the developmental events in pre-metamorphosing flounder,but not at metamorphic climax or post-metamorphosis stage.