Ayu

Ayu, in ichthyology, refers to Plecoglossus altivelis, commonly known as the sweetfish. It is a small to medium-sized migratory freshwater fish in the family Plecoglossidae and is valued as a food fish in parts of East Asia. The species is native to rivers and coastal waters in the region and is known for its delicate flesh and seasonal runs.

Ayu is anadromous, living in both freshwater and marine environments. Juveniles inhabit rivers and estuaries, migrating downstream to the sea as they mature and returning to rivers to spawn. They are generally semelparous, often dying after spawning. Spawning typically occurs in autumn in gravelly sections of rivers, where eggs adhere to the substrate.

Distribution and habitat: The fish ranges across Japan, the Korean Peninsula, eastern China, and the Russian Far East. It favors clear, well-oxygenated waters and is commonly found in rivers and estuaries, with spawning migrations tied to seasonal changes.

Description and diet: The body is slender with a silver to bronze coloration and a forked tail. Common lengths are around 15–25 cm, with larger individuals possible in favorable conditions. Diet shifts with life stage: juveniles feed on algae and detritus, while adults consume aquatic invertebrates and zooplankton.

Cultural and economic significance: In Japan and Korea, ayu is a seasonal delicacy often prepared as salt-grilled “ayu no shioyaki.” The Nagara River cormorant fishing tradition in Japan is historically associated with ayu fishing. The species is also cultured and harvested in fisheries across its range, and management practices aim to protect spawning runs and river health.

Other uses: The term Ayu also appears as a female given name in Indonesian and Malay contexts, meaning beauty or cherished one in some languages.