Increasing concern regarding estrogenic environmental contaminants highlights a need for the development of laboratory screening assays to measure estrogenic response. An in vivo screening method for natural and environmental estrogens using the Japanese medaka (Oryzias latipes) is being developed. Medaka fish exposed to 17-estradiol (17-E) during early life exhibit disruption of normal gonadal development. Some fish display inter-sex appearance when fully mature and the proportion of females to males is higher than expected. Newly hatched medaka fry with undifferentiated gonads (60/group) were exposed to sublethal concentrations of 17-E (1.25, 2.5, and 5µg/L) for 48 hours in water at 25ºC. There were two control groups: spring water and acetone carrier. After two weeks, 50% of the surviving fry were killed and processed for histopathological analysis. The remaining 50% of fry were evaluated after four months. The mortality rates ranged from 26-38% and there were no statistically significant differences among groups. After two weeks, testis-ova (hermaphroditism) were observed in all groups including the spring water control (8%). A dose-response trend for hermaphroditism was observed but was not statistically significant (p>0.05). In the four month grow-out groups, the majority of fish developed into females, some were sexually immature, and hermaphroditism was not observed. Secondary sexual characteristics such as fin shape usually clearly identify the gender of the fish, but we found that the gender of fish smaller than 2 cm in size was not easily identified. The estrogenic potency of xenoestrogens can be determined by comparing their dose response curve with 17-E dose response.
Learning Objectives: The goal of this research is to develop a toxicological model using the Japanese medaka for rapid evaluation of environmental estrogens and/or reproductive toxins. A dose response curve is developed for 17 -estradiol in the medaka as a positive control for estrogenicity
Keywords: Environmental Exposures,
Presenting author's disclosure statement:
Organization/institution whose products or services will be discussed: None
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.