Involvement of steroid hormones in the preovulatory gonadotropin surge in female goldfish |
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| Authors: | Makito Kobayashi Katsumi Aida Isao Hanyu |
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| Institution: | (1) Department of Fisheries, Faculty of Agriculture, University of Tokyo, Bunkyo, Tokyo 113, Japan;(2) Present address: Department of Zoology, University of Alberta, Edmonton, Canada, T6G 2E9 |
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| Abstract: | Goldfish,Carassius auratus, spawn several times within a spawning season. A gonadotropin (GtH) surge occurs at the time of ovulation in this cyprinid
species. This ovulatory GtH surge mediates the processes of final oocyte maturation and ovulation, and occurs at the end of
each spawning cycle. Within a cycle, there is a shift in the predominant plasma steroid from estradiol to testosterone, and
finally 17α, 20β-dihydroxy-4-pregnen-3-one at the time of the ovulatory GtH surge. High levels of testosterone were always
observed before ovulation. When ovariectomized or sexually regressed female goldfish were implanted with testosterone, they
exhibited a GtH surge which was similar to those normally observed at ovulation. These results strongly suggest that elevated
plasma testosterone is an important physiological requirement for the occurrence of the GtH surge. |
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| Keywords: | gonadotropin ovulation multiple spawning fish ovulatory cycle steroid feedback environmental factors |
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