sweetfish

The sweetfish, Plecoglossus altivelis, is a medium-sized freshwater fish native to East Asia and widely known by its common name ayu, especially in Japan. It is valued for its delicate flesh, which is said to have a sweet flavor. The species inhabits rivers, estuaries, and coastal waters, and many populations migrate between freshwater and saltwater as part of their life cycle.

In appearance, ayu has a slender, laterally compressed body, typically 20 to 30 centimeters long, with a pale silver body and a bronze-gold back; individuals up to about 40 centimeters have been reported. They feed on zooplankton and small invertebrates as juveniles, while adults consume plankton and occasional aquatic invertebrates. Ayu are migratory; adults move from seawater into rivers to spawn during warmer months, whereas juveniles descend to the sea before returning upstream to mature and reproduce.

Culinary use: In Japan, salt-grilled ayu (shioyaki) is a traditional seasonal dish; in Korea and China, the fish is also consumed fresh or salted. Commercial fisheries and aquaculture supply markets; there are annual catch limits and seasonal protections in some regions to protect spawning runs.

Conservation: River damming, habitat alteration, and overfishing have affected some stocks by blocking migratory routes and reducing suitable spawning habitat. Management measures include riverine habitat restoration, hatchery releases, and fishing restrictions. The sweetfish remains an important cultural and ecological component of East Asian freshwater systems.