Relationship between Serum Sex Hormone Concentrations and Histology of Seminiferous Tubules of Captured Baleen Whales in the Western North Pacific during the Feeding Season

  • WATANABE Hiroyuki
    Department of Animal Production Science, Obihiro University of Agriculture and Veterinary Medicine
  • MOGOE Toshihiro
    The Institute of Cetacean Research
  • ASADA Masatsugu
    Department of Animal Production Science, Obihiro University of Agriculture and Veterinary Medicine
  • HAYASHI Kengo
    Department of Agricultural and Life Science, Obihiro University of Agriculture and Veterinary Medicine
  • FUJISE Yoshihiro
    The Institute of Cetacean Research
  • ISHIKAWA Hajime
    The Institute of Cetacean Research
  • OHSUMI Seiji
    The Institute of Cetacean Research
  • MIYAMOTO Akio
    Department of Agricultural and Life Science, Obihiro University of Agriculture and Veterinary Medicine
  • FUKUI Yutaka
    Department of Animal Production Science, Obihiro University of Agriculture and Veterinary Medicine

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The present study was conducted to obtain new information on relationships among serum testosterone (T), estradiol-17 β (E2), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) concentrations and histology of seminiferous tubules in captured common minke and Bryde’s whales during the feeding season. Blood samples and testes were collected from common minke (n=39 for blood samples, n=15 for testes) and Bryde’s (n=14 for blood samples, n=7 for testes) whales captured from May 2001 to August 2001 in the Western North Pacific. Serum T concentrations, in 35.9% of the common minke and 57.1% of Bryde’s whales, were below the detection limit (< 2.5 pg/ml). There were no significant differences in the serum concentrations of E2, FSH, and LH among immature, mature common minke and Bryde’s whales except that LH levels of immature Bryde’s whales was higher than those of common minke whales. In most seminiferous tubules of mature whales, only a single-layer of spermatogonia was observed. However, spermatozoa were observed in seminiferous tubules in 2/13 of mature common minke and 4/4 of mature Bryde’s whales with the low or undetectable T levels. These results indicate that the low serum T concentrations reflect the inactivity of spermatogenesis in both baleen whales, and that it is not possible to assess gonadal activity in either common minke or Bryde’s whales using serum sex hormone concentrations during the feeding season.<br>

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