| Co-Investigator(Kenkyū-buntansha) |
NAKABO Tetsuji Kyoto University, The Kyoto University Museum, Professor, 総合博物館, 教授 (20164270)
YAMASHITA Yoh Kyoto University, Field Science Education and Research Center, Professor, フィールド科学教育研究センター, 教授 (60346038)
NAKAYAMA Kouji Kyoto University, Field Science Education and Research Center, Assistant Professor, フィールド科学教育研究センター, 助手 (50324661)
MASUDA Reiji Kyoto University, Field Science Education and Research Center, Associate Professor, フィールド科学教育研究センター, 助教授 (60324662)
UEDA Hiroshi Ehime University, Center For Marine Environmental Studies, Associate Professor, 沿岸環境科学研究センター, 助教授 (00128472)
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| Research Abstract |
We have investigated various ecological aspects of the Ariake temperate bass population in the Chikugo estuary, Ariake Sea, and also growth, maturation and larval fish distribution of the Chinese temperate bass around Uwajima area, which was revealed as one of parental species for the Ariake population.
Copepod distribution was separated by 2 groups : one is mainly composed of Ariake endemic species Sinocalanus sinensis which occupied low salinity area, particularly in 1 to 3 psu salinity. The other one is a group of multi-species like Acartia omorii, Oithona davisae, Paracalanus parvus and Pseudodiaptomus marinus. The former group was always found from the turbidity maximum. Major parts of gut contents of S.sinensis were composed of phaeo-pigment, while chlorophyll-a was dominantly detected from the gut contents of common coastal copepod species. These facts suggest that detritus food chain exists in the upper estuarine area.
Juvenile stages of the Ariake endemic fishes as Coilia nasus,
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Neosalanx reganius, Acanthogobius hasta, Trachidermis fasciatus preyed exclusively S.sinensis. In contrast, common coastal fishes like amchovy and rock fish which are distributed in the estuary higher than 15 psu in salinity preyed a large variety of copepod species.
Using the trophic enrichment value and half-life value determined under rearing experiments, δ ^<13>C of gut contents and muscle showed temperate bass juveniles immigrated into freshwater area in April, shifted to intermediate saline area in May to July, and finally emigrated to sea area in August.
Chinese temperate bass, which escaped from aquaculture-pen or were discarded, could grow faster than the Japanese bass and the gonad somatic index markedly increased in November and December. We supposed they could successfully reproduce in Japanese coastal waters, but we could not collect eggs, larvae and juveniles. DNA analyses demonstrated there are two local populations in southern and northern areas of Chinese, continent. We could not find Chinese temperate bass in Ariake Sea, and all Ariake temperate bass have both genes special for Japanese and Chinese temperate bass.
These results suggest that there is a unique ecosystem characterized by strong linkage of highly turbid brackish water- endemic copepod-endemic fish juveniles in the upper Chikugo estuary. It appears to be needed to conduct a same type of field research in a model field of Chinese or Korean estuary. Less
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