Not evaluated (IUCN 3.1)
Temminck & Schlegel, 1846
(Temminck & Schlegel, 1846)
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 in 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, Taiwan and Hong Kong.
The name "sweetfish" is due to the sweetness of its flesh. In reference to its typical one-year life span, it is also written as 年魚 ("year-fish"). The ayu is Gunma Prefecture's prefectural fish.
There are currently three subspecies recognized, however their status is questioned and species may be monotypic:
- Plecoglossus altivelis altivelis (Temminck & Schlegel, 1846) (Ayu sweetfish)
- Plecoglossus altivelis chinensis Y. F. Wu & X. J. Shan, 2005
- Plecoglossus altivelis 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 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 anglers 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 birds catch the ayu, store it in their crop, and deliver it to the fishermen.
Ayu is also fished commercially in large numbers, 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.
- Froese, Rainer and Pauly, Daniel, eds. (2012). "Plecoglossus altivelis" in FishBase. February 2012 version.
- Gadsby (2004)
- Waldman, John (2005). 100 Weird Ways to Catch Fish (1st ed.). Mechanicsburg, PA: Stackpole Books. pp. 6–7. ISBN 0811731790.
- Cormorant Fishing "UKAI". Version of May, 2001. Retrieved 2008 January 30.
- "THE INTIMATE PLEASURE OF THE IZAKAYA". The Economist Newspaper Limited.
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.
- 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.
- "Plecoglossus altivelis". Integrated Taxonomic Information System. Retrieved 20 December 2004.
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