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Role of endogenous steroid hormones on gonadal sex differentiation in fish
Nakamura, M.; Kobayashi, T.; Yoshiura, Y.; Nagahama, Y. (2000). Role of endogenous steroid hormones on gonadal sex differentiation in fish, in: Norberg, B. et al. (Ed.) Proceedings of the 6th International Symposium on the Reproductive Physiology of Fish, Bergen, Norway, July 4-9, 1999. pp. 247-249
In: Norberg, B. et al. (Ed.) (2000). Proceedings of the 6th International Symposium on the Reproductive Physiology of Fish, Bergen, Norway, July 4-9, 1999. Department of Fisheries and Marine Biology, University of Bergen: Bergen. ISBN 82-7461-048-2. 499 pp., more
In: International Symposium on the Reproductive Physiology of Fish. Museo Nacional de Ciencias Naturales, more

Available in Authors 
    VLIZ: Proceedings [4226]

Keyword
    Marine

Authors  Top 
  • Nakamura, M.
  • Kobayashi, T.
  • Yoshiura, Y.
  • Nagahama, Y.

Abstract
    To clarify the role endogenous estrogen plays in sex differentiation in fish, we examined the effects of aromatase inhibitor (AI) on genetically controlled, all-female tilapia. Three different treatment protocols caused fish to develop testes: AI at 200 µg/g diet, AI at 500 µg/g diet, and methyltestosterone (MT) from 8 days after hatching (DAH) for 22 days. In contrast, all fish that received a diet containing both AI 500 and estradiol-17 beta 250 µg/g had normal ovaries. Therefore, we conclude that AI effectively masculinizes genetic females. A corollary conclusion is that endogenous estrogen plays an important role in ovarian differentiation in tilapia. We also established immunohistochemically the presence of aromatase (arom) and 3 beta -hydroxysteroid dehydrogenase (3 beta -HSD) in the gonads of fish. Immunopositive cells for arom-antibody (AB) were present in the testes of fish treated with AI, but not in the testes of fish treated with MT. In contrast, positive cells for 3 beta -HSD were present in the testes of specimens treated with either AI or MT. These differences suggest that the mechanisms by which AI and MT affect the differentiation of steroid-producing cells and the expression of aromatase are different, despite both AI and MT being powerful masculinizing agents.

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