Ayu

This article is about the fish. For other uses, see Ayu (disambiguation).

Ayu
Conservation status
Not evaluated (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Osteichthyes
Class:	Actinopterygii
Subclass:	Neopterygii
Infraclass:	Teleostei
Superorder:	Protacanthopterygii
Order:	Osmeriformes
Suborder:	Osmeroidei
Superfamily:	Osmeroidea
Family:	Plecoglossidae
Genus:	Plecoglossus Temminck & Schlegel, 1846
Species:	P. altivelis
Binomial name
Plecoglossus altivelis (Temminck & Schlegel, 1846)

Ayu feeds on algae that accumulates on the rocks, scraping it off the rocks with their saw-shaped teeth

The ayu (アユ, 鮎, 年魚, 香魚) or sweetfish, Plecoglossus altivelis, is an amphidromous fish, the only species in the genus Plecoglossus and family Plecoglossidae. It is a relative of the smelts, and is placed in the order Osmeriformes. Native to the Palearctic ecozone, it occurs in rivers, lakes, and coastal waters of western Hokkaidō in Japan southward to the Korean Peninsula, China, and Hong Kong. The species has become extinct in Taiwan since 1967, although there are populations of re-introduced Japanese stocks in some of the northern streams.

The name "sweetfish" is due to the sweetness of its flesh. In reference to its typical one-year lifespan, it is also written as 年魚 ("year-fish"). The ayu is the prefectural fish of Gunma Prefecture and Gifu Prefecture.

Subspecies

Three subspecies are currently recognized, but their status is questioned and species may be monotypic:

• P. a. altivelis (Temminck & Schlegel, 1846) (ayu, sweetfish)
• P. a. chinensis Y. F. Wu & X. J. Shan, 2005
• P. a. ryukyuensis M. Nishida, 1988 (Ryukyu ayu-fish)

Ecology and uses

An omnivore, the ayu feeds on algae, crustaceans, insects, sponges, and worms. They are also very territorial animals. 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.

Ayu is an edible fish, mostly consumed in East Asia. Its flesh has a distinctive, sweet flavour with "melon and cucumber aromas". It is consequently highly prized as a food fish. The main methods for obtaining ayu are by means of fly fishing, by using a fish trap, and by fishing with a decoy which is known as ayu-no-tomozuri in Japan. The decoy is a living ayu placed on a hook, which swims when immersed into water. It provokes the territorial behavior of other ayu, which assault the "intruder" and get caught.

Japanese fishers also catch it using a traditional method, cormorant fishing (鵜飼 ukai). On the Nagara River where Japanese cormorants (Phalacrocorax capillatus) are used by the fishermen, the fishing season draws visitors from all over the world. The Japanese cormorants, known in Japanese as umi-u (ウミウ, "sea-cormorant"), are domesticated birds trained for this purpose. The bird catches the ayu, stores it in its crop, and delivers it to the fishermen.

Ayu is also fished commercially, and captive juveniles are raised in aquaculture before being released into rivers for sport fishing.

A common method of preparing ayu and other small fish in Japan is skewering the fish in such a way as to form a wave, as if they are swimming upriver, and then roasting them over a fire or charcoal.

• 

  Ayu no shio yaki
  (Ayu grilled with salt)

• 

  Ayu being grilled with salt in Japan

Further reading

• Gadsby, Patricia (2004): The Chemistry of Fish. Discover Magazine November 2004: 50-57. HTML fulltext
• Takeshima, Hirohiko; Iguchi, Kei-ichiro & Nishida, Mutsumi (2005): Unexpected Ceiling of Genetic Differentiation in the Control Region of the Mitochondrial DNA between Different Subspecies of the Ayu Plecoglossus altivelis. Zool. Sci. 22(4): 401–410. doi:10.2108/zsj.22.401 (HTML abstract)
• World Conservation Monitoring Centre (WCMC) (1996). Plecoglossus altivelis ssp. ryukyuensis. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 31 January 2008.

External links

• Froese, Rainer, and Daniel Pauly, eds. (2004). "Plecoglossidae" in FishBase. October 2004 version.
• Froese, Rainer, and Daniel Pauly, eds. (2004). Species of Plecoglossus in FishBase. October 2004 version.
• Froese, Rainer, and Daniel Pauly, eds. (2004). Plecoglossus altivelis altivelis in FishBase. October 2004 version.
• Froese, Rainer, and Daniel Pauly, eds. (2004). Plecoglossus altivelis ryukyuensis in FishBase. October 2004 version.