三重県三国谷のイワメとアマゴにおける形態比較

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  • ミエケン ミクニ ダニ ノ イワメ ト アマゴ ニ オケル ケイタイ ヒカク

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イワメ markless masu trout に関する研究は Kimura and Nakamura（1961）が Oncorhynchus　iwame として新種記載を行って以来，Ito et al.（1973）と名越（1981）の報告があるが，その分類学的位置は明確になっていないのが現状である。宮地，川那部，水野（1976），水野，山内，住野（1980）及び名越（1981）は，イワメとアマゴSalmo (Oncorhynchus） masou macrostomus との相異点はパーマークと朱点の有無だけであるとし，イワメをアマゴもしくはヤマメの突然変異型と位置付け，とくに宮地ら（1976）は型（form）としても疑問であると述べている。　 本稿は，三重県三国谷に生息するイワメとアマゴの形態についての比較を行い，その結果としてイワメはアマゴとは別種であるという見解は不適であるとする宮地ら（1976）などに従うものである。しかし，本研究は彼らが述べたイワメの位置付けに関し少々異なる見解を示し，その理由を若干言及する。

The markless masu trout (Iwame) and the red-spotted masu trout (Amago), Salmo (Oncorhynchus) masou macrostomus, coexist in Mikuni-dani stream of Inabe river system, Mie Prefecture. Morphological characteristics of the markless and red-spotted masu trouts were examined. These masu trouts,heretofore, have been regarded as different species, Oncorhynchus iwame KIMURA et NAKAMURA and O.rhodurus (Salmo(O.)masou macrostomus in this paper). The two masu trouts differ in numbers of pectoral fin ray,ventral fin ray,gill raker and pyloric coeca. However, such differences are not so remarkable for taxonomic character as they are attributed to different species. Moreover, since significant differences are not between the two masu trouts in other meristic and measurable characteristics and there is no evidence of ecological isolation as far as our observations, those differences are intraspecific variations rather than are reflected specific criteria. Consequently, these are no remarked differences between the two fishes except for the color patterns of parr marks and red spots,and then it is insufficient that they are considered separate biological species by only aspects of colouration.Therefore,the markless masu trout is considered a variation form (a kind of albinism?) from the red-spotted masu trout. In addition,similar form pairs exist in some steams in Kyushu,Shikoku and Honshu Islands but, at present, the morphological and genetical relationships between the form pairs in these regions are almost unknown, and zoogeographical problem also remains to be proved.

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