著者

早川 洋一 小林 牧人

出版者

日本比較内分泌学会

雑誌

日本比較内分泌学会ニュース (ISSN:09139044)

巻号頁・発行日

vol.2004, no.114, pp.114_17-114_22, 2004 (Released:2004-09-01)

参考文献数

12

著者

小林 牧人

出版者

公益社団法人 日本水産学会

雑誌

日本水産学会誌 (ISSN:00215392)

巻号頁・発行日

vol.76, no.1, pp.72-75, 2010 (Released:2010-05-13)

著者

中尾 遼平 入口 友香 周 翔瀛 上出 櫻子 北川 忠生 小林 牧人

出版者

一般社団法人 日本魚類学会

雑誌

魚類学雑誌 (ISSN:00215090)

巻号頁・発行日

vol.64, no.2, pp.131-138, 2017-11-25 (Released:2018-06-19)

参考文献数

28

被引用文献数

2

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Genetic disturbance in Japanese wild medaka populations (Oryzias latipes species complex) has resulted mainly from artificial introductions from geographically distinct populations or of commercial varieties, especially an orange-red body color variety (himedaka). Because the extent of genetic introgression within a single water body has remained unclear, the genetic population structure of wild minami-medaka Oryzias latipes in the Nogawa River, a tributary of the Tamagawa River system in Tokyo, Japan, was surveyed using three DNA markers (cytb and ND2 genes on mitochondrial DNA and b-marker on nuclear DNA) to evaluate the extent of introgression throughout upper and lower reaches. Genotypes originating from himedaka were detected at all sites surveyed. Although different genetic composition of introgressed mitotypes among some sampling sites suggested multiple introductions of non-native populations, high dispersal rates of introgressed genes could not be rejected as a cause of wide-spread introgression. Based on this study, appropriate management strategies for the genetic conservation of wild medaka populations are discussed.

著者

上出 櫻子 清水 彩美 小井土 美香 信田 真由美 小南 優 吉澤 茜 小山 理恵 早川 洋一 小林 牧人

出版者

公益財団法人 平岡環境科学研究所

雑誌

自然環境科学研究 (ISSN:09167595)

巻号頁・発行日

vol.29, pp.31-39, 2016 (Released:2020-01-12)

参考文献数

12

被引用文献数

2

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The Japanese medaka is designated as an endangered species because of its decreasing population, and conservation of the medaka is an urgent concern. In the present study, in order to obtain basic information for conservation of wild medaka, we observed the reproductive behavior of female medaka (Oryzias latipes, orange-red variety and wild fish) in experimental aquaria under various environmental conditions. Female medaka normally deposited eggs on aquatic plants or aquatic mosses which were solid with a soft surface in experimental aquaria. However, the fish did not deposit eggs but discarded eggs in aquaria provided with sand, floating aquatic plants, and no substrate, and in an aquarium lined with concrete. These results indicate that a suitable substrate is essential for successful egg deposition of medaka, and suggest that maintaining suitable vegetation in natural environments is important for conservation of wild medaka.

著者

小林 牧人 頼経 知尚 鈴木 翔平 清水 彩美 小井土 美香 川口 優太郎 早川 洋一 江口 さやか 横田 弘文 山本 義和

出版者

日本水産學會

巻号頁・発行日

vol.78, no.5, pp.922-933, 2012 (Released:2013-10-08)

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本邦の絶滅危惧種にも指定されているメダカを保全するためには,その生息環境だけでなく繁殖生態についても知見を得ることが重要である。本研究では屋外池で自然繁殖している野生メダカを対象に繁殖生態を調べた。メダカでは,雌が産卵後に卵をしばらく腹部に保持し,それらを基質に産み付ける。今回の観察で,野生下において「産み付け行動」の初の観察・記載に成功し,数種の基質を特定した。基質の特定および存在場所は,今後のメダカの保全において,繁殖場所の確保という点で重要な知見になると考えられた。

著者

早川 洋一 瀧田 真平 菊池 一也 吉田 彩夏 小林 牧人

出版者

一般社団法人 日本魚類学会

雑誌

魚類学雑誌 (ISSN:00215090)

巻号頁・発行日

vol.59, no.2, pp.111-124, 2012-11-05 (Released:2014-12-02)

参考文献数

39

被引用文献数

2

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The importance of olfaction in spawning of medaka Oryzias latipes was established for the first time by observation of spawning behavior by fish subjected to an olfactory blockage. Experimental fish were prepared by (1) covering the nostrils on both sides (bilateral treatment), thereby excluding all olfactory stimuli, and (2) covering nostrils on one side only (unilateral treatment), thereby giving partial exclusion. A control group comprised untreated (intact). Experiments conducted for both males (bilateral male-intact female, unilateral male-intact female and intact male-intact female) and females (bilateral female-intact male, unilateral female-intact male and intact female-intact male) resulted in no spawning by intact females paired with bilateral males, whereas spawning occurred in intact females paired with both unilateral and intact males. Spawning also occurred when intact males were paired with intact, unilateral or bilateral females, indicating that olfactory stimuli were necessary for males to complete spawning, but not so for females. Spawning acts exhibited from pairing started by bilateral males-intact female pairs included “following” (initial act of following female), “positioning” (lateral courtship display), and “quick circle” (turning in front of female), but they did not include “contact” (bodies in contact posteriorly prior to gamete release), “wrapping” (male embracing female using their dorsal and anal fins during gamete release). On the other hand, intact and unilateral males participated in all of the above spawning acts, indicating that olfactory stimuli are indispensable for behavior concerning emitting semen.

著者

小林 牧人 黑栁 仁志 大友 明香 早川 洋一

出版者

公益財団法人 平岡環境科学研究所

雑誌

自然環境科学研究 (ISSN:09167595)

巻号頁・発行日

vol.32, pp.7-13, 2019 (Released:2020-01-07)

参考文献数

18

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Construction of artificial river and lake banks changes the aquatic environment, and these changes are known to cause decreases of aquatic plants in shallow waters. We conducted experiments to examine the involvement of aquatic plants in spawning behavior of goldfish, Carassius auratus, and cruicuan carp, Carassius buergeri subsp.2. The spawning behavior was induced by injecting prostaglandin F2α into females. Pairs of male and female goldfish or crucian carp were placed in experimental tanks with or without aquatic plants made of acrylic yarn. Both goldfish and crucian carp spawned actively onto the aquatic plants whereas the behavior significantly decreased without the aquatic plants. The present experiments demonstrate that aquatic plants are essential as spawning substrates for performance of spawning behavior of these species. It is critical for conservation of fish species that use aquatic plants as spawning substrates to maintain aquatic plants on river and lake banks.

著者

森脇 俊尚 小林 牧人 会田 勝美 羽生 功

出版者

公益社団法人 日本水産学会

雑誌

日本水産学会誌 (ISSN:00215392)

巻号頁・発行日

vol.57, no.1, pp.41-43, 1991-01-25 (Released:2008-02-29)

参考文献数

12

被引用文献数

8 9

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Changes in plasma gonadotropin (GtH) and steroid hormone levels were investigated during ovulation induced by human chorionic gonadotropin (HCG) in female goldfish. Sexually mature female goldfish maintained at 20°C under 14L10D (lights on at 0430hr) were injected with HCG at a dose of 10IU/g BW at 2100hr. Twenty-one fish out of 28 ovulated between 9 and 18 hours (0600 to 1500hr) after injection. In ovulatory fish, there was neither a significant increase nor surge in plasma GtH levels after the injection, whereas plasma testosterone and 17α, 20β-dihydroxy-4-pregnen-3-one levels showed changes similar to those occurring in spontaneous ovulation. These results suggest that injected HCG acts directly on the ovary without accelerating endogenous GtH secretion, and therefore induces ovulation in a similar manner as does the ovulatory GtH surge in spontaneous ovulation.

著者

上出 櫻子 木村 恵美 小林 牧人

出版者

公益財団法人 平岡環境科学研究所

雑誌

自然環境科学研究 (ISSN:09167595)

巻号頁・発行日

vol.33, pp.1-4, 2020 (Released:2020-12-28)

参考文献数

11

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Japanese medaka (Oryzias latipes) is known to deposit fertilized eggs on aquatic substrates in shallow waters. In order to examine the influence of water depth on embryonic development of fertilized eggs of an orange-red variety and wild medaka, we observed fertilized eggs for 18 days and compared the hatching rate and the hatching time at different water depths of 5, 30, and 65 cm. The hatching rate was lower at 65 cm depth than at 5 cm depth and the hatching time was longer at 65 cm depth than at 5 cm depth with both the orangered variety and the wild medaka. These results indicate that deep water is not suitable for the embryonic development of medaka and suggest that preservation of natural conditions in shallow waters of rivers and ponds is important for conservation of wild Japanese medaka.

著者

上出 櫻子 小南 優 小林 牧人

出版者

公益財団法人 平岡環境科学研究所

雑誌

自然環境科学研究 (ISSN:09167595)

巻号頁・発行日

vol.30, pp.1-4, 2017 (Released:2020-01-07)

参考文献数

12

被引用文献数

1

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The present study examined the preference in water depth for egg deposition of female, orangered variety medaka Oryzias latipes in order to obtain basic information for conservation of wild medaka. Substrates for egg deposition were set at various depths in experimental aquaria and male and female medaka were kept in the aquaria for seven days to observe spawning. The number of eggs and the egg deposition depth were recorded every day. The female medaka deposited eggs on the substrates at various depths but notably a significantly large number of eggs were deposited at shallow depths. These results indicate that female medaka gives a preference to shallow water depths for egg deposition.