Amago - Amago

A fish belonging to the bony fish family Salmonidae. A mountain stream fish endemic to Japan, it is also known by local names such as Amenouo, Amego, Hirame, and Kin'enoha. Its original habitat is the Pacific coast south of the Sakawa River in Honshu, rivers along the Seto Inland Sea, rivers in Shikoku, and mountain streams along the Seto Inland Sea in Oita Prefecture, but as a result of transplantation for aquaculture, it has now spread to rivers on the Sea of ​​Japan side of Honshu and Kyushu. Its body shape is very similar to that of a young cherry salmon (yamame), with a greenish-brown back with small black spots, a silvery-white ventral side, and oval-shaped markings called par marks on the sides of the body that are unique to young salmon and trout. However, unlike the yamame, it has bright vermilion spots scattered above and below the lateral line, and the number and shade of these spots vary considerably depending on the region. In the upper reaches of rivers that flow into Ise Bay and the Seto Inland Sea, a phenomenon occurs in which the body color of the fish turns silvery white in late autumn (silvering or becoming smolts), and they take on the appearance known as whitebait, descending to the sea in early winter, migrating along the coast until early summer the following year, growing rapidly as mature trout, and migrating upstream before midsummer. In the middle and lower reaches of the Kiso River, they are called brook trout. The crimson spots do not disappear even when they reach the body shape of a mature trout.

Examples of species that live in lakes and marshes include the Biwa trout of Lake Biwa and the Ame trout of Lake Suwa. In the case of the Biwa trout, the crimson spots disappear as they grow, and the silvery fur of young fish develops extremely quickly. In addition, recent biochemical research has cast doubt on the idea that they are exactly the same species as the Amago. The Amago feed mostly on aquatic insects and fallen terrestrial insects, and they spawn mainly under the gravel of slow-flowing flat streams, with the peak in late October. They are highly valued as a target for stream fishing, and are also extremely delicious. In recent years, their farming technology has made remarkable advances, and many private companies are engaged in intensive farming. In particular, an increasing number of fishery cooperatives in the various rivers of Honshu are releasing Amago into the rivers along with Ayu and Yamame.

[Tatsuro Kubo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

硬骨魚綱サケ科に属する魚。日本特産の渓流魚で、アメノウオ、アメゴ、ヒラメ、キンエノハなどの地方名もある。その本来の分布生息域は本州では酒匂(さかわ)川以南の太平洋沿岸、瀬戸内海沿岸の河川、四国の河川および大分県の瀬戸内海沿岸の河川の渓流域であるが、現在、増養殖に伴う移殖の結果として本州、九州の日本海側の河川にも分布が広まっている。体形はサクラマスの幼魚（ヤマメ）とよく似ており、背部は帯緑褐色で小黒点があり、腹側は銀白色、体側にはサケ・マス類の幼魚特有の小判形のパーマークとよばれる斑紋(はんもん)をもつ。しかしヤマメと異なって側線の上下に鮮麗な朱赤点が散在し、この数や濃淡には地方によってかなり差異がある。伊勢(いせ)湾、瀬戸内海などに注ぐ河川の上流では、晩秋に体色が銀白化する現象（銀毛化またはスモルト化）がおこり、いわゆるシラメとよばれる姿となって初冬のころ降海し、翌年初夏まで沿岸域を回遊、急速な成長をして成熟したマスとなり、盛夏の前に溯上(そじょう)する。木曽(きそ)三川の中・下流では、これをカワマスとよぶ。なお成熟したマスの体形に達しても朱赤点は消失しない。

　湖沼生活型のものとして琵琶(びわ)湖のビワマス、諏訪(すわ)湖のアメがある。ビワマスの場合、成長に伴って朱赤点が消失し、また幼魚の銀毛化が著しく早い点、さらに近年の生化学的研究の結果などからアマゴとまったく同一の魚種とする考え方には疑問が出ている。アマゴの餌(えさ)の大部分は水生昆虫と落下陸上昆虫であり、10月下旬をピークとして、おもに流れの緩い平瀬の砂礫(されき)下に産卵する。渓流釣りの対象として価値が高く、またきわめて美味である。近年その養殖技術が著しく進み、民間企業でも集約的養殖をしているところが多い。とくに本州の各河川の漁業協同組合はアユ、ヤマメとあわせてアマゴの河川放流を行う所が増えている。

［久保達郎］

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