Does anti-androgen, flutamide cancel out the in vivo effects of the androgen, dihydrotestosterone on sexual development in juvenile Murray rainbowfish (Melanotaenia fluviatilis)?

• Treatment with DHT reduced the body-length of both male and female fish, an effect which was canceled out by low and high concentrations of flutamide.
• The E2 levels were reduced only in female fish after exposure to DHT but returned to normal after treatment with Flu-high.
• DHT increased the levels of 11-KT and decreased the E2/11-KT ratio in both sexes. Flu-high, but not Flu-low, could nullify these effects.
• Both DHT and flutamide (low or high) induced VTG production and this effect persisted when both chemicals were co-administered.
• Treatment with DHT did not affect gonadal cell development in the testes.

The aim of the present study was to investigate if the effects of the androgen, dihydrotestosterone (DHT) on the sexual development in juvenile Murray rainbowfish (Melanotaenia fluviatilis) are canceled out by the anti-androgen, flutamide. Fish (60 days post hatch) were exposed to 250 ng/L of DHT, 25 μg/L of flutamide (Flu-low), 250 μg/L of flutamide (Flu-high), DHT + Flu low and DHT + Flu high. After 35 days of exposure, lengths and weights of the fish were measured and the condition factor (CF) calculated; vitellogenin (VTG) concentrations were measured in tail tissue; sex steroid hormones (17β-estradiol [E2] and 11-keto testosterone [11-KT]) were measured in the head tissue and abdominal regions were used in histological investigation of the gonads. Treatment with DHT reduced the body-length of both male and female fish, an effect which was canceled out by low and high concentrations of flutamide. However, flutamide (low or high) could not nullify the DHT-induced reduction in the CF in either sex. The E2 levels were reduced only in female fish after exposure to DHT but returned to normal after treatment with Flu-high. DHT increased the levels of 11-KT and decreased the E2/11-KT ratio in both sexes. Flu-high, but not Flu-low, could nullify these effects. Both DHT and flutamide (low or high) induced VTG production and this effect persisted when both chemicals were co-administered. Treatment with DHT did not affect gonadal cell development in the testes. However, the female fish treated with DHT contained ovaries in early-vitellogenic stage in comparison to the pre-vitellogenic ovaries in control fish. Co-treatment with flutamide (low or high) resulted in oocyte atresia. The results from the present study suggest that treatment with Flu-high could cancel out DHT-induced effects only on the hormonal profile and body-length in both male and female fish. Juvenile fish co-treated with DHT and flutamide (low or high) had high VTG levels and low CF. In addition, the ovaries in female fish were atretic. These data represent potential adverse effects on the ability of the fish to reproduce successfully.