Incomplete Development of the Brain-Pituitary-Gonadal Axis May Underlie the Delay in the Initiation of Precocious Maturation in Male Sockeye Salmon

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  • Amano Masafumi
    Nikko Branch, National Research Institute of Aquaculture School of Fisheries Sciences, Kitasato University
  • Okumoto Naoto
    Nikko Branch, National Research Institute of Aquaculture
  • Aida Katsumi
    Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo

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  • Incomplete Development of the Brain-Pit

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Description

Precocious males first appear in the second year in sockeye salmon, whereas in masu salmon they appear in the first year. In underyearling male masu salmon, precocious maturation is accelerated under short photoperiod with an increase in salmon gonadotropin-releasing hormone (sGnRH) and pituitary gonadotropin subunit (GTH Iβ and GTH IIβ) contents, suggesting that the brain-pituitary-gonadal axis is already completed. In this study, the development of the brain-pituitary-gonadal axis in underyearling male sockeye salmon was investigated by manipulating photoperiod in order to clarify the relationship between its development and initiation of precocious maturation. Fish were divided into short (8L-16D) and long photoperiodic (16L-8D) groups in June and were reared for 4 months until October. sGnRH contents in the brain and pituitary, and GTH Iβ and GTH IIβ contents in the pituitary were measured. sGnRH contents in the hypothalamus and the pituitary, and GTH Iβ contents in the pituitary increased under short photoperiod, although gonadal maturation was notinduced under either photoperiod. However, pituitary GTH IIβ contents did not increase in either photoperiodic group. These results suggest that in contrast to masu salmon, the brain-pituitary-gonadal axis is not completed in underyearling male sockeye salmon. This species-specific difference in the development of the brain-pituitary-gonadal axis may underlie differences in the initiation of precocious maturation.

Journal

  • Fisheries science

    Fisheries science 63 (6), 873-876, 1997

    The Japanese Society of Fisheries Science

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