Vitellogen (VTG) is a glucolipoprotein yolk precursor produced by all oviparous animals. This protein is female-specific and its expression is under hormonal control (estrogen). However, in the presence of Endocrine Disrupting Chemicals (EDC's), males can express the VgTG gene in a dose dependent manner. The use of VTG gene expression in male fish can be used as a molecular marker of exposure to estrogenic EDC's.