| Project/Area Number |
12575023
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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 | 海外学術 |
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| Research Field |
General fisheries
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| Research Institution | Nagasaki University |
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Principal Investigator |
ISHIMATSU Atsushi Nagasaki University, Faculty of Fisheries, Professor, 水産学部, 教授 (00184565)
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| Co-Investigator(Kenkyū-buntansha) |
TAKEDA Tatsusuke Kyushu University, Faculty of Agriculture, Associate Professor, 農学部, 助教授 (30091367)
SOYANO Kiyoshi Nagasaki University, Faculty of Fisheries, Associate Professor, 水産学部, 助教授 (80260735)
TAKITA Toru Nagasaki University, Faculty of Fisheries, Professor, 水産学部, 教授 (30039721)
KAWAGUCHI Sadao Kyushu University, Faculty of Agriculture, Associate Professor, 農学部, 助教授 (20091366)
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| Project Period (FY) |
2000 – 2002
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| Project Status |
Completed (Fiscal Year 2002)
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| Budget Amount *help |
¥15,400,000 (Direct Cost: ¥15,400,000)
Fiscal Year 2002: ¥5,100,000 (Direct Cost: ¥5,100,000)
Fiscal Year 2001: ¥4,700,000 (Direct Cost: ¥4,700,000)
Fiscal Year 2000: ¥5,600,000 (Direct Cost: ¥5,600,000)
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| Keywords | Intertidal flats / Mudskippers / Oceania / Fish physiology / Fish Ecology / Chloride cell / Periophthalmus minutus / Osmoregulation / 潮間帯 / Periophthalmus minutus / オセアニア / 魚類生態学 / 魚類生理学 / マングローブ / 窒素循環 / 土壤微生物 |
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| Research Abstract |
The Australian mudskipper, Periophthalmus_minutus, inhabits high intertidal mudflat areas that experience seawater inundation only during the high water spring tides. Our study site remained emerged usually for 7-12 days during neap tides in one tidal cycle, throughout a year. As a result, burrow water salinity increased from 33 ± 5 psu in March (end of the rainy season) to 84 ± 7 after an extended period of emersion in August (dry season). P.minutus remained inside its burrow during these long emersion periods. Experimental exposure to either freshwater (FW) or 200% SW did not affect the chloride cell density, of P.minutus. However, apical pits of the chloride cells were rapidly closed in response to FW, but not to 200% Sw, exposure. Chloride cell size significantly increased after 9-14 day exposure to 200% SW. Plasma sodium concentration did not change by the exposure to 200% SW but decreased significantly after 5 days in FW. No mortality occurred during exposure to 200% SW, whereas 50% of FW-exposed fish died within 4 days. These results demonstrate that the exceptionally high salinity tolerance of P.minutus is made possible by the high density and adaptive hypertrophy of the opercular chloride cells. This allows P.minutus to effectively regulate ion concentrations of the body fluids during the extended burrow confinement during which concentrated seawater is the only source of water supply to the fish.
The gonads of P.minutus were immature throughout the dry season, but rapidly grew with time during the rainy season, attaining the largest size in January to February. Subsequently, the gonadal size decreased at end of the rainy season (March). Spawning occurred in neap tides in February. These results demonstrated that gonadal maturation is triggered by the advent of the rainy season, and that spawning takes place in a semi-lunar cycle.
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