The prevailing theory is that they are mutation of Amago or Yamame. The habitat of Amago is in the Pacific Ocean side of south of Sakawa River in Kanagawa Prefecture, all over Shikoku, north of Ono River in Oita Prefecture and in the rivers around the Inland Sea of Seto. Yamame live in all over Hokkaido, the Pacific Ocean side of north of Sakawa River, all over the Japan Sea, the East China Sea of north of Kumamoto Prefecture and south of Bansho River in Oita Prefecture. Besides Japan, their home is East of Korean Peninsula, the Far Eastern Russia and the Sea of Okhotsk. But the habitats of Amago and Yamame are not clearly separated now because of artificial planting.
Main habitat are upper streams because they like cold water.
They like light and open streams as shallows when the temperature of the water is the most suitable for them. And they stay near the surface in the pool. Their active time is during the daytime. But they don't actively catch bait at the daytime of fine weather because they are very cautious. Their action is easily influenced by environment.