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

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.