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Thursday, April 22, 2004


Amago salmon

* Japanese name: Amago
* Scientific name:Oncorhynchus masou ishikawa
* Description:Salmon are handsome fish with streamlined silver bodies. The scientific name means "hooked nose," and you will understand why if you see one. There are seven species of Pacific salmon, two of which occur in Asia. In Japan there are a number of subspecies which vary in the markings on the body (the amount of black and vermilion dots on the back and sides), and in their distribution. The species shown in the photo is called sakuramasu ("cherry trout") since the adults return to their native rivers from March to May, at the same time as cherry trees bloom across Japan. They grow up to 25 cm long. Amago salmon may also show parr marks, dark vertical stripes on the bodies of the fish.
* Where to find them: On the Pacific Ocean side of Japan, from Hokkaido through Honshu, Shikoku and Kyushu. Amago are commonly found in mountainous rivers and streams because they like cold water (below 20 degrees). Amago are active during the day; they spawn from October to November.
* Food:Amago feed on crustaceans and other fish. In coastal waters, sand lance and sand eel are commonly eaten.
* Special features:Most amago subspecies remain in rivers for the entire life cycle, but some migrate to the ocean. Unlike other species of salmon, though, most amago don't stray far, remaining in bays and inlets. Juveniles migrate to the sea in autumn, and return to their home streams the following spring. Although they spend less than six months as ocean-going fish, amago undergo physiological changes to adapt to salt water, and are able, remarkably, to return to the same mountain streams where they were spawned. They achieve this feat by smell (the fish follow a steadily increasing gradient of chemicals that match those of their home stream) and by the Earth's magnetic field. Salmon don't feed on their homeward journeys, relying on stored body fat. When the fish finally reach the stream where they were hatched, the female digs a nest (a "redd") in the stream bed and lays 2,500 to 7,000 eggs. The male then covers the eggs in milt (sperm) to fertilize them. Both sexes, exhausted, then die.

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