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アリアケギバチPseudobagrus aurantiacus(Temminck and Schlegel)の地理的分布と生活史に関する研究

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タイトル: アリアケギバチPseudobagrus aurantiacus(Temminck and Schlegel)の地理的分布と生活史に関する研究
その他のタイトル: Geographical distribution and life history of Japanese bagrid,Pseudobagrus aurantiacusTemminck and Schlegel
著者: 溝入, 真治
著者(別表記) : Mizoiri, Shinji
発行日: 1998年 2月19日
引用: (1998-02-19)
抄録: Pseudobagrus aurantiacus which is confined to Kyushu, Japan, has beenconsidered to be declining drastically and threatened by environmentaldeterioration such as river improvements and water pollution. However thecurrent distributional range and ecological characteristics of the fish are unclear.Information on their exact range and life history is essential for conserving thefish. The present study on the geographical- distribution in Kyushu and lifehistory of P. aurantiacus was carried out in the Chikugo River, Kyushu from1993 to 1996 to clarify its living situation. The results obtained are as follows: 1. P. aurantiacus was observed in 27 reaches of 14 river systems, and wasfound in most of the localities ever known. However its habitats in most of thereaches appears to be in decline. Several populations were feared to have beendestroyed in several river systems. 2. The congener species P. nudiceps was also found to inhabit 11 riversystems in northeast Kyushu facing the Seto Inland Sea, and also in the KumaRiver., southwest Kyushu where it might have been introduced artificially fromLake Biwa. 3. Spawning season of the fish is during June to August, and nesting sitesare vacant spaces under boulders or roots of emerged plants located in rapids orsmall channels with densely vegetated banks. The fish seem to remove loosematerial from a vacant space to make the spawning bed. The developmentalpattern of the ovarian eggs is synchronous and therefore this type of spawningseems to occur once a season. 4. Spawned eggs were 2.0-2.4 mm in diameter and adhesive. 3 days afterspawning the eggs hatched. Just hatched larvae were 4.4 mm TL and reachedthe postlarval stage at 10.0 mm TL and juvenile stage at 13.0 mm TL. Theadipose fin of the juveniles separated from caudal fin at 20.5 mm TL and at thisstage the juveniles have almost the same external characteristics as the adultfish, From the size-frequency data, the wild juveniles begin to recruit from theend of July to the middle of August. 5. Age and growth were estimated based on the 6th vertebra as an agecharacter. Males are larger than females at the same age. The age of maturitywas estimated to be 1 year in males and the 2 years in females. The sex ratio ofthe fish in the Chikugo River seemed to be biased to the males. 6. Stomach contents of 11 specimens from 23.4 to 186.1 mm TL wereobserved to. clarify the feeding habits of the fish in the summer season. Allindividuals fed mainly on aquatic insects such as larvae of mayfly, caddis andmosquito. These prey seemed to be principal items for the fish. 7. In aquariums, males formed spawning beds under the shelters andinduced females there. Mating behavior on the spawning bed was carried outas follows. At first, the male and female chase each other. Then the male wrapshis body around the female's head. The male continued to hold the female for ten-odd seconds, and then the female spawns the eggs. Finally, female withdrew fromthe bed stirring eggs. These behavior were carried out repeatedly over 1 to 5hours, and females spawned a total of 500-4000 eggs by installments whichoccurred several tens of times. The mating system of P.aurantiacus appears tobe polygamous. Males care for the eggs, larvae, and juveniles by flapping,fanning and nest defense using aggressive behavior. These behaviors werecontinued until the juveniles disperse from the nest.8. P. aurantiacus was considered to be threatened, but the assessments toits vulnerability has discrepancy. Environmental Agency (1991) defined the fishas an Endangered Species, the most threatened category of theEnvironmental Agency's definition, while the Fisheries Agency (1996) definedthe fish as a Declining Species, the fourth rank of the Fisheries Agency'sdefinition. The discrepancy between the assessments the two agencies does notindicate the recovery of the habitat status, but confusion of the assessments dueto the lack of information and by the utilization of categories withoutquantitative criteria. In this study, the vulnerability of P. aurantiacus wasjudged to be Vulnerable based on the new categorization method given inthe Japanese Environmental Agency's Red Data Book. 9. Rapids and channels covered with natural vegetation, are important forthe spawning, feeding, and breeding sites of this species, while these areas aresusceptible to river improvements. We should maintain the rapids and channelswith the bank covered by emerged plant to conserve P. aurantiacus. 10. The ecology and habitat requirements in the non-reproductive seasonand inter-populations relationships of P. aurantiacus are unclear yet.Additionally/its living status seems to be different in each river system. It isnecessary to clarify the local habitats in each river system and to research thestructure and dynamics in each population to establish a comprehensiveconservation plan.
記述: 長崎大学学位論文 学位記番号:博(海)甲第131号 学位授与年月日:平成10年2月19日
URI: http://hdl.handle.net/10069/7278
資料タイプ: Thesis or Dissertation
出現コレクション:090 学位論文

引用URI : http://hdl.handle.net/10069/7278



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