| Project/Area Number |
08456100
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
General fisheries
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| Research Institution | University of the Ryukyus |
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Principal Investigator |
TAKANO Kazunori University of the Ryukyus, Tropical Biosphere Research Center Professor, 熱帯生物圏研究センター, 教授 (30001605)
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| Co-Investigator(Kenkyū-buntansha) |
TACHIHARA Katsunori University of the Ryukyus, College of Science Associate Professor, 理学部, 助教授 (70264471)
TAKEMURA Akihiro University of the Ryukyus, Tropical Biosphere Research Center Associate Professo, 熱帯生物圏研究センター, 助教授 (40222103)
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| Project Period (FY) |
1996 – 1997
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| Project Status |
Completed (Fiscal Year 1997)
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| Budget Amount *help |
¥5,300,000 (Direct Cost: ¥5,300,000)
Fiscal Year 1997: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 1996: ¥3,600,000 (Direct Cost: ¥3,600,000)
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| Keywords | Ryukyu-ayu / Flagtail / Tilapia / reproduction / sea water adaptability / diadromy |
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| Research Abstract |
This study was carried out to clarify the physiological and ecological characteristics of some selected diadromous fish inhabiting sround the island of the Ryukyus.
1.Ryukyu-ayu (Plecoglossus altivelis ryukyuensis) : The structure of mature spermatozoon of this species was characterized by a symmetric nucleus and asymmetric arrangement of two centrioles unlike Ayu, P.altivelis. Scales, comb-like teenth, alimentary canals and skeleton developed earlier than Ayu. Upstream migration also occurred earlier (February-March) and smaller in size (av. 32.3 mm) than Ayu.
2.Flagtail (Kuhlia marginata) : Based on the histological observations and gonad-somatic index, it was estimated that females spawn repeatedly during the spawning period from April to September. Number of ovarian eggs varied between 70,000 to 360,000 with an increase of BL.After young migrated from sea to rivers at av. 20mm BL,during March to July, females grew faster than males. The average longevity of female and male was estimated 6 and 2, respectively, and the ratio of female to male resulted in 3 : 1. The change in plasma Na and C1 after trasfer to sea water revealed that the fish have the high ability of tolerance to environmental salinity.
3.Tilapia (Oreochromis mossambicus) : The species O.mossambicus is the dominant fish occupying the estuaries of Okinawa Island. The average fertile span of this fish was estimated to be 2-9 years. Annual spawing period lasts from May through September, and females may spawn several times during this season. Although the analysis of the verious physiological parameters such as oxygen consumption rates, plasma constituents and plasma hormone levels under the different salinity conditions showed that sea water may be favorable environment to the fish, they might selsct estuaries as their habitat on the basis of the causes of reproductive strategy of the species.
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