Although 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene (p,p0-DDE), the major and most persistent metabolite of dichlorodiphenyltrichloroethane
(DDT), was continually detected in wild fishes that showed abnormal gonad development such as intersex, little
is known about the impact of p,p0-DDE exposure on gonad development in fishes. To survey the e ects of p,p0-DDE on gonadal
development and gene expressions, male juvenile (20-d post hatch) Japanese medaka (Oryzias latipes) was exposed to 1, 5, 20, and
100 mg/L p,p0-DDE for two months. Increased hepatosomatic index (HSI) and decreased gonadosomatic index (GSI) were found in the
p,p0-DDE-treated groups. Intersex was found in 100 mg/L p,p0-DDE exposure group, as well as 100 ng/L 17 -ethynylestradiol (EE2)
group. By quantitative real-time RT-PCR, it was found that gene expressions of vitellogenins (VTG-1, VTG-2), choriogenins (CHG-H,
CHG-L), and estrogen receptor (ER- ) in the liver of the fish were significantly up-regulated by p,p0-DDE exposure. VTG-1 and VTG-
2 were recommended as the preferred biomarker for assessing anti-androgenic p,p0-DDE because they were the highest up-regulated
among the genes and showed good dose-response relationship. The up-regulated ER- suggested that a potential synergetic e ect would
occur when p,p0-DDE coexists with other ER- -binding endocrine-disrupting chemicals (EDCs).