The ayu sweetfish, ayu or sweetfish, is a species of fish. Wikipedia

Species of fish Wikidata

A sweetfish, an amphidromous fish of East Asia, the only member of its genus and family, Plecoglossus altivelis, named and prized for its sweet-tasting flesh. It is a game fish and is also subject to extensive aquaculture. Wiktionary

Amphidromous fish. Wiktionary (translation)

An amphidromous fish, the ayu of East Asia (Plecoglossus altivelis), the only member of its genus and family Plecoglossidae, named and prized for its sweet-tasting flesh, especially in Japan, as a game fish, and is also subject to extensive aquaculture. Wiktionary