The ayu sweetfish (''Plecoglossus altivelis''), or sweetfish, is a species of

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

. It is the only

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

in the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

''Plecoglossus'' and

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Plecoglossidae. It is a relative of the

smelts Smelts are a family of small fish, the Osmeridae, found in the North Atlantic and North Pacific Oceans, as well as rivers, streams and lakes in Europe, North America and Northeast Asia. They are also known as freshwater smelts or typical smelts ...

and other fish in the order

Osmeriformes The Osmeriformes are an order of ray-finned fish that includes the true or freshwater smelts and allies, such as the galaxiids and noodlefishes; they are also collectively called osmeriforms. They belong to the teleost superorder Protacanthopte ...

. Native to

East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...

, it is distributed in the northwestern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

along the coast of

Hokkaidō is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

southward to the

Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic o ...

n Peninsula,

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...

and northern

Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...

. 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

Biwa The is a Japanese short-necked wooden lute traditionally used in narrative storytelling. The is a plucked string instrument that first gained popularity in China before spreading throughout East Asia, eventually reaching Japan sometime duri ...

. Original wild populations in

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

became extinct in 1968 due to pollution and present extent populations were reintroduced from Japan in the 1990s. The name "sweetfish" was inspired by the sweetness of its flesh. In reference to its typical one-year lifespan, it is also written as ("year-fish").Queen of Freshwater Streams.
Food Forum. Kikkoman Global Website. Some individuals live two to three years. The ayu is the prefectural fish of

Gunma Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Gunma Prefecture has a population of 1,937,626 (1 October 2019) and has a geographic area of 6,362 km2 (2,456 sq mi). Gunma Prefecture borders Niigata Prefecture and Fukushima ...

and

Gifu Prefecture is a prefecture of Japan located in the Chūbu region of Honshu. Gifu Prefecture has a population of 1,991,390 () and has a geographic area of . Gifu Prefecture borders Toyama Prefecture to the north; Ishikawa Prefecture to the northwest, F ...

Subspecies

Two to three

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

are recognized by some authors. Others do not distinguish the subtaxa.Froese, R. and D. Pauly, Editors
''Plecoglossus altivelis altivelis''.
FishBase. 2015. Subspecies include: * ''P. a. altivelis'' (

Temminck Coenraad Jacob Temminck (; 31 March 1778 – 30 January 1858) was a Dutch aristocrat, zoologist and museum director. Biography Coenraad Jacob Temminck was born on 31 March 1778 in Amsterdam in the Dutch Republic. From his father, Jacob Temmin ...

Schlegel Schlegel is a German occupational surname. Notable people with the surname include: * Anthony Schlegel (born 1981), former American football linebacker * August Wilhelm Schlegel (1767–1845), German poet, older brother of Friedrich * Brad Schlege ...

, 1846) (ayu, sweetfish) * ''P. a. chinensis'' Y. F. Wu & X. J. Shan, 2005 (Chinese ayu) * ''P. a. ryukyuensis'' M. Nishida, 1988 (

Ryukyu The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yonaguni ...

ayu-fish) –

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inva ...

Biology

Plecoglossus altivelis altivelis hami-ato1

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...

, the ayu feeds on

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

s, and

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

s. It feeds on algae that accumulates on the rocks, scraping it off the rocks with their saw-shaped teeth. Adults typically maintain a feeding territory,Hooper, R. (21 September 2005)
Ayu sweetfish.
The Japan Times. Retrieved 13 February 2017. but the form restricted to lakes and associated streams is

schooling A school is an educational institution designed to provide learning spaces and learning environments for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is sometimes compuls ...

.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. Most 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.Lucas, M., and E. Baras (2001). Migration of Freshwater Fishes, p. 187. Blackwell Science. The eggs hatch shortly after and the

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e are carried downriver to the sea.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. They overwinter in coastal regions, staying there until the spring where the young fish typically are about long and move back to the rivers. Here they reach by the summer. They reach maturity by the autumn and move down to the lower part of rivers to breed. 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. 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. Although their larvae mostly stay within freshwater, some are carried downstream with the current to the sea and become part of the amphidromous populations. The freshwater-restricted populations typically reach an age of two or three years. During the breeding season the amphidromous and freshwater-restricted forms may occur together. Ayu are also stocked in reservoirs. Although there are reports of ayu up to long, a more typical maximum size for the species is about . The form restricted to freshwater is considerably smaller than the amphidromous form. The freshwater-restricted ayu of

Lake Biwa is the largest freshwater lake in Japan, located entirely within Shiga Prefecture (west-central Honshu), northeast of the former capital city of Kyoto. Lake Biwa is an ancient lake, over 4 million years old. It is estimated to be the 13th ol ...

that migrate into their spawning streams in the spring can reach up to about in length, but those that migrate later in the year, primarily in the autumn, only grow to .Lake Biwa Museum
Aquarium
Retrieved 10 May 2019. This is caused by differences in the availability of food.

Human uses

Ayu is an edible fish, mostly consumed in

. 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 Fly fishing is an angling method that uses a light-weight lure—called an artificial fly—to catch fish. The fly is cast using a fly rod, reel, and specialized weighted line. The light weight requires casting techniques significantly diffe ...

, by using a

fish trap A fish trap is a trap used for fishing. Fish traps include fishing weirs, lobster traps, and some fishing nets such as fyke nets. Traps are culturally almost universal and seem to have been independently invented many times. There are two main ...

, 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

fisher Fisher is an archaic term for a fisherman, revived as gender-neutral. Fisher, Fishers or The Fisher may also refer to: Places Australia *Division of Fisher, an electoral district in the Australian House of Representatives, in Queensland *Elect ...

s also catch it using

cormorant fishing Cormorant fishing is a traditional fishing technique in which fishermen use trained cormorants to catch fish in rivers. Historically, cormorant fishing has taken place in Japan and China, as well as Greece, North Macedonia, and briefly, England an ...

. On the

Nagara River The has its source in the city of Gujō, Gifu Prefecture, and its mouth in the city of Kuwana, Mie Prefecture, Japan. Along with the Kiso River and Ibi River, the Nagara River is one of the Kiso Three Rivers of the Nōbi Plain. Previously, ...

where

Japanese cormorant The Japanese cormorant (''Phalacrocorax capillatus''), also known as Temminck's cormorant, is a cormorant native to the east Palearctic. It lives from Taiwan, north through Korea and Japan, to the Russian Far East. The Japanese cormorant has a b ...

s (''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 A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydroponic ...

, and delivers it to the fishermen. Ayu is also fished commercially, and captive juveniles are raised in

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...

before being released into rivers for sport fishing. A common method of preparing ayu and other small fish in Japan is to

skewer A skewer is a thin metal or wood stick used to hold pieces of food together. The word may sometimes be used as a metonym, to refer to the entire food item served on a skewer, as in "chicken skewers". Skewers are used while grilling or roastin ...

it in such a way so that its body forms a wave, making it look as though it is swimming.No. 2: Ayu fish.
Hiroko's Kitchen. 10 August 2010.

Gallery

File:Plecoglossus altivelis altivelis 釣れた稚鮎.jpg, Young ''P. a. altivelis'' File:Ayu no Shioyaki.jpg, ''Ayu no shio yaki''
(Ayu grilled with salt) File:Charcoal broiled Ayu.JPG, Ayu being grilled with salt in Japan; note the wave-like "swimming" shape of the skewered fish File:Naturalis Biodiversity Center - RMNH.ART.464 - A very inaccurate picture of Plecoglossus altivelis - Kawahara Keiga - 1823 - 1829 - Siebold Collection - pencil drawing - water colour.jpeg, In watercolor

References

External links