Dolly Varden - Oshoro Koma

A fish of the genus Salvelinus, order Salmoniformes, family Salmonidae. It is found along the coast of the North Pacific Ocean from the northern part of the Korean Peninsula through the Bering Strait and the Aleutian Islands to California in North America. In Japan, it is found mainly in mountain streams in central Hokkaido, and also in small streams in the Shiretoko Peninsula, the foot of Mt. Yotei, and the Shakotan Peninsula, the upper reaches of the Chiwase River in Minami Shiribeshi, and on Rishiri and Rebun islands, all of which live in the headwaters of the rivers where the water temperature is low. The white spots on the back are tiny and small, and the crimson spots on the sides of the body are bright and vivid. Those found in the north are anadromous (marine) type, and become smolts (silver hairs) that go down to the sea and migrate quite far offshore. Miyabei char, which lives in Lake Shikaribetsu in the Tokachi region, is considered to be an offshoot of Dolly Varden based on the characteristics of its hemoglobin and the number of projections called gill rakers on the inside of its gill arches, but it is considered to be an anadromous type due to its good body growth and high degree of silvery hair. The body length of Dolly Varden reaches 30 cm for river types and over 40 cm for marine types. It matures in 2 to 3 years and spawns in flat streams upstream. The Arctic char (alpine char), which is widely distributed from northern America to northern Europe, is thought to be a closely related fish species. It is also highly valued as a target for mountain stream fishing.

[Tatsuro Kubo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

硬骨魚綱サケ目サケ科イワナ属の魚。朝鮮半島北部からベーリング海峡、アリューシャン列島を経て北アメリカのカリフォルニア州に及ぶ北太平洋沿岸に分布する。日本ではおもに北海道中央部の山岳地帯の渓流に分布し、また知床(しれとこ)半島、羊蹄(ようてい)山麓(さんろく)、積丹(しゃこたん)半島の小流、南後志(みなみしりべし)の千走(ちわせ)川上流および利尻(りしり)島と礼文(れぶん)島にも生息し、いずれも水温の低い源流域にすむ。背部の白点は細小、体側の朱紅色点は鮮麗。北方に分布するものはアナドロマス型（海洋型）でスモルト（銀毛化）となり、降海してかなり沖合いにまで回遊する。十勝(とかち)地方、然別(しかりべつ)湖にすむミヤベイワナは、ヘモグロビンの特性や鰓弓(さいきゅう)（えらの弓状の一片をいう）の内側にある鰓耙(さいは)とよばれる突起の数からオショロコマの分派とされるが、よい体成長と高い銀毛化の度合いからアナドロマス型のものとみられる。オショロコマの体長は河川型で30センチメートル、海洋型で40センチメートルを超す。2～3年で成熟し上流の平瀬に産卵する。アメリカ北部からヨーロッパ北部にかけて広く分布するホッキョクイワナ（アルプスイワナ）はきわめて近縁の魚種と考えられる。渓流釣りの対象としても価値が高い。

［久保達郎］

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