Co-treatment with the non-steroidal anti-androgen drug, flutamide and the natural estrogen, 17β-estradiol does not lead to additive reproductive impairment in juvenile Murray rainbowfish (Melanotaenia fluviatilis).

Abstract

The aim of this study was to investigate if the anti-androgen, flutamide, and the estrogen, 17β-estradiol work together to feminize juvenile Murray rainbowfish (Melanotaenia fluviatilis). Fish (60 days post-hatch) were exposed to 25 ng/L 17β-estradiol (E2), 25 µg/L flutamide (Flu low), 250 µg/L flutamide (Flu high), E2 + Flu low and E2 + Flu high. After 35 days of exposure, concentrations of sex steroid hormones, 17β-estradiol and 11-keto testosterone (11-KT), were determined in the head; and vitellogenin (VTG) concentration was measured in the tail. The abdomens were used for histological investigation of the gonads. Treatment with E2 + Flu high resulted in reduction in body weights and lengths in males and condition factor in females. Intersex was noted in Flu high and E2 + Flu high treatments. Exposures to E2 and/or Flu (low and high) resulted in precocious oocyte development but inhibited sperm development. The 17β-estradiol levels decreased significantly in the heads of both sexes after exposures to E2 and/or Flu (high and low). Flu high and E2 alone increased the 11-KT levels in both sexes. However, E2 + Flu low decreased 11-KT levels in males and increased them in females. Flutamide (low and high) induced VTG protein in the tails of both sexes. In males, VTG was not induced in the tail after exposure to E2. No significant effect of flutamide on E2-induced VTG concentration was noted. We conclude that co-treatment with flutamide and 17β-estradiol does not lead to additive reproductive impairment in juvenile Murray rainbowfish.