Immunoreactive changes in pituitary FSH and LH cells during seasonal reproductive and spawning cycles of female chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> |
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| Authors: | Mitsuo Nyuji Tetsuro Shiraishi Sethu Selvaraj Vu Van In Hajime Kitano Akihiko Yamaguchi Kumiko Okamoto Shizumasa Onoue Akio Shimizu Michiya Matsuyama |
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| Institution: | (1) Laboratory of Marine Biology, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan;(2) Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Saiki 879-2602, Japan;(3) National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama 236-8648, Japan;(4) Present address: National Broodstock Center for Mariculture in Northern Vietnam, Haiphong, Vietnam |
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| Abstract: | The physiological functions of pituitary gonadotropins (GtHs) are well established in higher vertebrates, whereas those in
teleosts are still poorly understood. To describe the role of GtHs during gonadal development of female chub mackerel Scomber japonicus, changes in follicle-stimulating hormone (FSH) and luteinizing hormone (LH) cells were investigated immunohistochemically
during the seasonal reproductive and spawning cycles. FSH and LH cells were identified in the different cell types of the
proximal pars distalis (PPD); FSH cells were located in the central PPD, whereas LH cells were localized along the border
of the pars intermedia. To examine changes in FSH and LH cells, the percentage of FSH or LH cell-occupying area in the PPD
was evaluated and represented as FSHβ-immunoreactive (ir) or LHβ-ir levels, respectively. FSHβ-ir levels increased significantly
from immature to the completion of vitellogenesis, whereas LHβ-ir levels were maintained at high levels from early vitellogenesis
to post-spawning. During the spawning cycle, which consisted of four stages from just after spawning to the next oocyte maturation,
both FSHβ-ir and LHβ-ir levels showed no significant changes among different stages; however, LHβ-ir levels remained relatively
high, and FSHβ-ir levels were constantly low. These results suggest that both FSH and LH may be involved in vitellogenesis
and LH may act at final oocyte maturation in female chub mackerel, although the role of FSH during the spawning cycle is still
unclear. |
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