Androgen disruption of early development in Qurt strain medaka (Oryzias latipes)

Androgen disrupting chemicals (ADCs) are widespread in the aquatic environment, where they may pose a risk to aquatic organisms during critical periods of development. In this study, static renewal 96-h toxicity tests were followed over a 3-month growth period to investigate the endocrine disrupting effects of the androgen 11-ketotestosterone (11-KT), and the antiandrogen flutamide (FLU) on 1-week-old Qurt strain medaka larvae. The measured endpoints included: survival, growth performance (i.e., body weight, body length, condition index), and histopathology. There was no significant acute mortality, except for males treated with the highest FLU concentration (96 h-LC(50)=1.92 mg/l). Gender-specific effects in growth were identified after 11-KT and FLU treatments. Histopathological alterations including thyroid follicular hypertrophy (TFH), germ cell necrosis (GCN), ovarian atresia (OA), and testis-ova (TO) were observed in medaka at 90-day post-exposure. We observed TFH in all 11-KT treatment levels. The incidence of TFH in males was double that in females 11-KT or FLU treatment. Females showed GCN at lower 11-KT concentrations (0.01, 0.1mg/l) than males (1.0mg/l). Severe OA was observed at low (0.01 mg/l) and high (1.0mg/l) 11-KT concentrations in females. Flutamide induced TO (0.32, 1.0mg/l), ovarian cell necrosis (0.32 mg/l), and disrupted spermatogenesis (3.2mg/l) in males. The lowest observed effective concentration (LOEC) for TO induction in Qurt medaka males was 0.32 mg/l. The present study underscores the importance of fish early life stage tests for detecting the interaction of ADCs with the reproductive and thyroid glands in both genders.