Spawning frequency of the Tsushima Current subpopulation of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> off Kyushu,Japan |
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| Authors: | Tetsuro Shiraishi Suvarna D Ketkar Yoshiki Katoh Mitsuo Nyuji Akihiko Yamaguchi Michiya Matsuyama |
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| Institution: | (1) Laboratory of Marine Biology, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan;(2) Present address: Seikai National Fisheries Research Institute, Fisheries Research Agency, Nagasaki 851-2213, Japan;(3) Present address: National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama 236-8648, Japan |
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| Abstract: | Female Japanese chub mackerel Scomber japonicus of the Tsushima Current subpopulation were collected during the spawning season from March to May 2001. A total of 137 adult
females were caught between midnight and daybreak. A considerable number of fish displayed new postovulatory follicles (POF),
whereas there was no evidence of germinal vesicle breakdown or hydrated oocytes in any of the fish collected. This suggests
a daily spawning synchronicity toward midnight. To estimate the spawning frequency (S), the female reproductive state was classified into four criteria based on the degenerative stage of the POFs and the developmental
stage of the oocytes. To stage the POFs according to age and determine the stage duration, ovaries from S. japonicus were induced to spawn in the laboratory and were sampled 0–72 h after ovulation at appropriate intervals. The average S, which is evaluated from four different indices, was 16.9%, corresponding to the average female chub mackerel spawned every
5.9 days (8.5 times) during the 50 days. |
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| Keywords: | Chub mackerel Postovulatory follicles Scomber japonicus Spawning frequency Tsushima Current subpopulation |
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