クニマスについて : 秋田県田沢湖での絶滅から70年

概要

論文の詳細を見る
Oncorhynchus kawamurae (Osteichthyes : Salmonidae) (Japanese name "Kunimasu"), a species endemic to Lake Tazawa, Akita Prefecture, Japan, was believed to have become extinct just before World War II. However, it was discovered in March and April, 2010 in Lake Saiko, Yamanashi Prefecture, one of the lakes to which eyed eggs of the species were introduced in 1935. The species is unique within Oncorhynchus in occurring normally in depths of 150-270m (water temperature 3.8-4.2℃), and spawning in 105-225m depth around September (3.8-4.5℃) and 15m depth (shallowest recorded) around February (3.0-4.6℃). Although Kunimasu shares the lake-spawning characteristic with the North American kokanee (O. nerka), no populations of the latter occur and spawn in such depths or temperatures. The specific distinctiveness of the black-coloured kunimasu from kokanee is here supported by morphological and biological characteristics recorded in pre-1941 literature. Because of the low temperatures tolerated during spawning, Kunimasu may have been derived from a population of "O. nerka" in the early Pleistocene (ca. 160 my BP), Lake Tazawa having become established at about that time. Subsequent climatic changes during the Pleistocene and Holocene resulted in the species necessarily moving into colder (deeper) water.
2011-02-20