|- valign=top |Genus:||P. altivelis The ayu (Plecoglossus altivelis) is a amphidromous fish, the only species in its genus, Plecoglossus Temminck & Schlegel, 1846, and in family Plecoglossidae (order Osmeriformes). Native to the Palearctic ecozone, it occurs in rivers, lakes, and coastal waters of northern Hokkaido in Japan, the Korean Peninsula, China, and Taiwan.

Omnivorous, the ayu feeds on algae, crustaceans, insects, sponges, and worms. The adults ascend from coastal waters into the lower reaches of rivers to spawn in the spring. The larvae descend to the sea immediately on hatching and winter there before returning to fresh water again in the spring. Most but not all individuals die after their first spawning.

The flesh of the ayu has a distinctive, sweet flavour with "melon and cucumber aromas" (Gadsby). It is consequently highly prized as a food fish. Japanese anglers catch it with live lures as well as by a traditional method whereby captive cormorants catch the ayu and regurgitate the fish for human consumption (Akimichi). It is also fished commercially in large numbers, and captive juveniles are raised in aquaculture before being released into rivers for sport fishing.

P. altivelis is also known as the sweetfish (for the sweetness of its flesh) or, in reference to its typical one-year life span, nen-gyo (year-fish).

Subspecies

The Ryukyu ayu-fish (P. altivelis ryukyuensis), is a subspecies of ayu, endemic to the Ryukyu Islands, which reaches a maximum total length of only about 14 cm (5.5 in). IUCN classifies the Ryukyu ayu-fish as Endangered on the basis of declining and highly fluctuating population and limited and declining range and habitat.

References

• Akimichi, Tomoya. "Queen of Freshwater Streams". Kikkoman Soy Sauce Food Forum. Accessed on 21 December 2004.
• Gadsby, Patricia. "The Chemistry of Fish". Discover, November 2004, 50–57.
• "Plecoglossus altivelis ryukyuensis". FishBase. Ed. Ranier Froese and Daniel Pauly. October 2004 version. N.p.: FishBase, 2004.