Ayu sweetfish

{{Short description|Species of fish}} {{Use dmy dates|date=March 2020}} {{Speciesbox | image = Sweetfish, Plecoglossus altivelis.jpg | status = DD | status_system = IUCN3.1 | status_ref = <ref name="iucn status 18 November 2021">{{cite iucn |author=Huckstorf, V. |year=2012 |title=''Plecoglossus altivelis'' |article-number=e.T62222A3110058 |doi=10.2305/IUCN.UK.2012-1.RLTS.T62222A3110058.en |access-date=18 November 2021}}</ref> | parent_authority = Temminck & Schlegel, 1846 | genus = Plecoglossus | species = altivelis | authority = (Temminck & Schlegel, 1846)<!-- Was it really placed in another genus first and revised to a monotypic genus less than 12 months later by the same authors? Yes, Plecoglossus was originally described in genus Salmo as a subgenus. --> | synonyms = {{Specieslist | Salmo altivelis | (Temminck & Schlegel, 1846) | Plecoglossus altivelis altivelis | (Temminck & Schlegel, 1846) | Plecoglossus altivelis ryukyuensis | (Nishida, 1988) | Plecoglossus ryukyuensis | (Nishida, 1988) | Plecoglossus altivelis chinensis | (Wu & Shan, 2005) }} }} The '''ayu sweetfish''' ('''''Plecoglossus altivelis'''''), {{nihongo|'''ayu'''|アユ, 鮎, 年魚, 香魚}} or '''sweetfish''', is a species of bony fish. It is the only species in the genus ''Plecoglossus'' and family Plecoglossidae. It is a relative of the smelts and other fish in the order Osmeriformes.

Native to East Asia, it is distributed in the northwestern Pacific Ocean along the coast of Hokkaidō in Japan southward to the Korean Peninsula, China, Hong Kong and northern Vietnam. It is amphidromous, moving between coastal marine waters and freshwater lakes and rivers. A few landlocked populations also exist in lakes in Japan such as Lake Biwa. Original wild populations in Taiwan became extinct in 1968 due to pollution and present extant populations were reintroduced from Japan in the 1990s.<ref name="iucn status 18 November 2021" /><ref>{{Cite web |last=TVBS |title=盤點台灣淡水魚 原生種香魚已滅絕│TVBS新聞網 |url=https://news.tvbs.com.tw/life/724260 |access-date=2022-11-08 |website=TVBS |language=zh-tw}}</ref>

The name "sweetfish" was inspired by the sweetness of its flesh. In reference to its typical one-year lifespan, it is also written as {{nihongo2|年魚}} ("year-fish").<ref name=kikko>[http://www.kikkoman.com/foodforum/thejapanesetablebackissues/11.shtml Queen of Freshwater Streams.] {{Webarchive|url=https://web.archive.org/web/20140425004349/http://www.kikkoman.com/foodforum/thejapanesetablebackissues/11.shtml |date=25 April 2014 }} Food Forum. Kikkoman Global Website.</ref> Some individuals live two to three years.<ref name="iucn status 18 November 2021" /> The ayu is the prefectural fish of Gunma Prefecture and Gifu Prefecture.<ref>[http://www.pref.gifu.lg.jp/foreign-languages/English/info/gifu/3.html Symbols of Gifu Prefecture.] Gifu Prefectural Government.</ref>

== Subspecies == Two<ref>Froese, R. and D. Pauly, Editors. [http://www.fishbase.org/identification/SpeciesList.php?genus=Plecoglossus ''Plecoglossus''.] FishBase. 2015.</ref> to three<ref>Shan, X., Wu, Y., & Kang, B. (2005). [http://adsabs.harvard.edu/abs/2005JOUC....4...61S Morphological comparison between Chinese Ayu and Japanese Ayu and establishment of Wu & Shan subsp. nov.] ''Journal of Ocean University of China'' (English Edition), 1(4), 61–66.</ref> subspecies are recognized by some authors. Others do not distinguish the subtaxa.<ref name=fishbase>Froese, R. and D. Pauly, Editors. [http://www.fishbase.org/summary/SpeciesSummary.php?ID=251&genusname=Plecoglossus&speciesname=altivelis+altivelis ''Plecoglossus altivelis altivelis''.] FishBase. 2015.</ref>

Subspecies include: * ''P. a. altivelis'' <small>(Temminck & Schlegel, 1846)</small> (ayu, sweetfish) * ''P. a. chinensis'' <small>Y. F. Wu & X. J. Shan, 2005</small> (Chinese ayu) * ''P. a. ryukyuensis'' <small>M. Nishida, 1988</small> (Ryukyu ayu-fish) – endangered<ref>{{cite iucn |author=World Conservation Monitoring Centre |date=1996 |title=''Plecoglossus altivelis'' ssp. ''ryukyuensis'' |volume=1996 |article-number=e.T17595A7151908 |doi=10.2305/IUCN.UK.1996.RLTS.T17595A7151908.en |access-date=18 November 2021}}</ref>

== Biology == thumb|A school of ayu|left|218x218px An omnivore, the ayu feeds on algae, crustaceans, insects, sponges, and worms. It feeds on algae that accumulates on the rocks, scraping it off the rocks with their saw-shaped teeth.<ref name=kikko/><ref>{{cite web |title=Rock Fishing in Tokushima, Japan |publisher=USA Today |url=http://traveltips.usatoday.com/rock-fishing-tokushima-japan-101712.html }}</ref> Adults typically maintain a feeding territory,<ref name=Hooper2005>Hooper, R. (21 September 2005). [http://www.japantimes.co.jp/life/2005/09/21/environment/ayu-sweetfish/#.WKI2fKjcCf0 Ayu sweetfish.] The Japan Times. Retrieved 13 February 2017.</ref> but the form restricted to lakes and associated streams is schooling.<ref name=Shirakihara2001>Shirakihara, Yoshids, Nishino, Takao and Sawada (2001). Acoustic evaluation of the vertical distribution of dwarf ayu Plecoglossus altivelis altivelis in Lake Biwa. Fisheries Science 67: 430–435.</ref>thumb|Scrape marks left by ayu feeding on algae when the rock was submerged|leftMost populations of this species are amphidromous and breed in the lower part of rivers during the autumn, laying their eggs in small pits they dig in the gravel.<ref name="iucn status 18 November 2021" /><ref name=Lucas2001>Lucas, M., and E. Baras (2001). Migration of Freshwater Fishes, p. 187. Blackwell Science. {{isbn|0-632-05754-8}}</ref> The eggs hatch shortly after and the larvae are carried downriver to the sea.<ref name=Otaka1998>Otake and Uchida (1998). Application of Otolith Microchemistry for Distinguishing between Amphidromous and Non-amphidromous Stocked Ayu, Plecoglossus altivelis. Fisheries Science 64(4): 517–521.</ref> They overwinter in coastal regions, staying there until the spring where the young fish typically are about {{convert|6|cm|in|abbr=on|round=0.5}} long and move back to the rivers. Here they reach {{convert|15|-|30|cm|in|abbr=on|0}} by the summer.<ref name=Otaka1998/> They reach maturity by the autumn and move down to the lower part of rivers to breed.<ref name=Lucas2001/> Some die after breeding and only live one year, but others return to live in the ocean and may spawn up to three times, each time moving into the lower part of rivers in the autumn.<ref name="iucn status 18 November 2021" /><ref>Shimizu, Uchida, Udagawa, Inoue, Sato and Katsura (2007). Multiple spawning and related variations in female reproductive parameters of amphidromous type ayu. Fisheries Science 73(1): 9–18.</ref> In Japan, some populations live their entire life in freshwater, only moving between lakes and the associated streams where they breed. These have a more variable migration pattern, moving upstream from the lakes in the spring, summer or autumn.<ref name=Lucas2001/> Although their larvae mostly stay within freshwater, some are carried downstream with the current to the sea and become part of the amphidromous populations.<ref name=Lucas2001/> The freshwater-restricted populations typically reach an age of two or three years.<ref name="iucn status 18 November 2021" /><ref name=fishbase/> During the breeding season the amphidromous and freshwater-restricted forms may occur together.<ref name=Otaka1998/> Ayu are also stocked in reservoirs.<ref name="iucn status 18 November 2021" /> [[File:Plecoglossus altivelis altivelis ayu.jpg|thumb|Lake Biwa ayu]] Although there are reports of ayu up to {{convert|70|cm|ft|abbr=on}} long,<ref name=fishbase/> a more typical maximum size for the species is about {{convert|30|cm|ft|abbr=on|0}}.<ref name=Hooper2005/><ref>FAO Fisheries and Aquaculture Department: [http://www.fao.org/fishery/species/2124/en Plecoglossus altivelis (Temminck & Schlegel, 1846).] Retrieved 13 February 2017.</ref> The form restricted to freshwater is considerably smaller than the amphidromous form.<ref name=Shirakihara2001/> The freshwater-restricted ayu of Lake Biwa that migrate into their spawning streams in the spring can reach up to about {{convert|15|cm|in|abbr=on|0}} in length, but those that migrate later in the year, primarily in the autumn, only grow to {{convert|10|cm|in|abbr=on|0}}.<ref name=Lucas2001/><ref name=LakeBiwaMuseumAquarium>Lake Biwa Museum: [https://www.biwahaku.jp/english/exhibits/aquarium.html Aquarium]. Retrieved 10 May 2019.</ref> This is caused by differences in the availability of food.<ref name=LakeBiwaMuseumAquarium/>

== Human uses == [[File:Ayu sweetfish total production thousand tonnes 1950-2022.svg|thumb|Capture (blue) and aquaculture (green) production of Ayu sweetfish (''Plecoglossus altivelis'') in thousand tonnes from 1950 to 2022, as reported by the FAO<ref>{{Cite web |title=Fisheries and Aquaculture - Global Production |url=https://www.fao.org/fishery/en/collection/global_production?lang=en |access-date=2024-05-06 |website=Food and Agriculture Organization of the United Nations (FAO)}}</ref>]]

The ayu is highly prized for its flavour, mostly consumed in East Asia. Its flesh is distinctively sweet, with "melon and cucumber aromas".<ref>{{Cite web |last=Gadsby |first=Patricia |last2=Eschliman |first2=Dwight |date=November 25, 2004 |title=The Chemistry of Fish |url=https://www.discovermagazine.com/2004/nov/chemistry-of-fish |archive-url=https://web.archive.org/web/20150412093749/https://www.discovermagazine.com/2004/nov/chemistry-of-fish |archive-date=12 Apr 2015 |website=Discover Magazine}}</ref> 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.<ref name=Waldman>{{cite book|last=Waldman|first=J.|title=100 Weird Ways to Catch Fish|year=2005|publisher=Stackpole Books|location=Mechanicsburg, PA|isbn=0-8117-3179-0|pages=[https://archive.org/details/100weirdwaystoca0000wald/page/6 6–7]|edition=1st|url-access=registration|url=https://archive.org/details/100weirdwaystoca0000wald/page/6}}</ref>

thumb|Ayu being grilled with salt in Japan; note the wave-like "swimming" shape of the skewered fish

The ayu is also caught by cormorant fishing. The practice on the Nagara River, where Japanese cormorants (''Phalacrocorax capillatus'') are used, 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.<ref>[http://www.gifu-rc.jp/ukai/u_main.html Cormorant-Fishing on the Nagara River.] {{Webarchive|url=https://web.archive.org/web/20140119040006/http://www.gifu-rc.jp/ukai/u_main.html |date=19 January 2014 }} Gifu Rotary Club.</ref>

Ayu is also fished commercially, and captive juveniles are raised in aquaculture before being released into rivers for sport fishing.{{Cn|date=January 2021}}

In Japanese cuisine, a common method of preparing ayu (among other small fish) is to fold their bodies in a wave-like "swimming" shape, then skewer. The fish is then grilled with salt over charcoal to preserve the natural flavor of the fish.<ref>[http://hirokoskitchen.com/2010/08/no-2ayu-fish/ No. 2: Ayu fish.] Hiroko's Kitchen. 10 August 2010.</ref>

== Gallery == <gallery> File:Plecoglossus altivelis altivelis 釣れた稚鮎.jpg|Young ''P. a. altivelis'' File:Ayu no Shioyaki.jpg|''Ayu no shio yaki'' <!-- 鮎の塩焼き --><br/>(Ayu grilled with salt) File:Naturalis Biodiversity Center - RMNH.ART.464 - A very inaccurate picture of Plecoglossus altivelis - Yūshi Ishizaki - Cock Blomhoff Collection - pencil drawing - water colour.jpg|Watercolor illustration File:Ayu TamagawaChofu 0403241c.jpg|Swimming up a dam File:CWD Plecoglossus altivelis altivelis.jpg|With cold water disease. File:Ayuikedukuri.jpg|As sashimi File:Ayu (Sweetfish) tempura.jpg|As tempura File:Plecoglossus altivelis-01.jpg|Farmed ayu </gallery>

== See also == * Tai Ho Stream

== References == {{reflist}}

== Further reading == * 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. <small>{{Doi|10.2108/zsj.22.401}}</small> (HTML abstract)

== External links == {{Commons category|Ayu}} {{Cookbook|Sweetfish}} * ''[https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=162027 Plecoglossus altivelis]''. Integrated Taxonomic Information System (ITIS).

{{Authority control}} {{Taxonbar|from=Q642906}}

Category:Fauna of Hong Kong Category:Freshwater fish of Japan Category:Plecoglossidae Category:Fish of Korea Category:Taxa named by Coenraad Jacob Temminck Category:Taxa named by Hermann Schlegel Category:Fish described in 1846