CHEEK, A.O.*; BROUWER, T.H.; CARROLL, S.; MANNING, S.; MCLACHLAN, J.A.; BROUWER, M.: Experimental evaluation of vitellogenin as a predictive biomarker for reproductive disruption

Vitellogenin (VTG) synthesis in male oviparous vertebrates is used as an indicator of environmental estrogen exposure, yet the reproductive consequences of exposure are unknown. To examine whether VTG expression predicts reproductive impairment, we exposed medaka fry (Oryzias latipes) for 2 or 8 weeks post-hatch to 0, 0.5, 1.0, 2.5, and 7.5 ppb of the environmental estrogen o, p’ DDT. Fish were sampled 2, 4, and 8 weeks after hatch to examine gonad histology and VTG expression. After exposure, fish were transferred to clean water, grown to sexual maturity, and placed in mating pairs. Eggs were collected for 7 days and scored for fecundity, fertility, and hatching success. Two week exposure had no effect on VTG expression, while all doses induced VTG after 8 weeks. The highest doses of DDT caused a female-skewed sex ratio in adults. Gonadal feminization appeared to be progressive – some ovotestes appeared after 2 and 4 weeks exposure to the two highest doses, but the proportion of ovaries increased after 8 weeks. Both two and eight week exposure significantly reduced fertility and hatching success at all doses, but lower doses had a greater effect after longer exposure. Fertility and hatching success were more sensitive to estrogenic disruption than was VTG synthesis. Therefore, VTG expression may be interpreted as a warning of reproductive consequences, but absence of expression cannot be interpreted as absence of developmental and reproductive disruption.