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

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

. It is the only

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

in the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

''Plecoglossus'' and

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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 (biology), order of ray-finned fish that includes the true or freshwater smelts and allies, such as the noodlefishes; they are also collectively called osmeriforms. They belong to the teleost superorder Protacanthopt ...

. Native to

East Asia East Asia is a geocultural region of Asia. It includes China, Japan, Mongolia, North Korea, South Korea, and Taiwan, plus two special administrative regions of China, Hong Kong and Macau. The economies of Economy of China, China, Economy of Ja ...

, it is distributed in the northwestern

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

along the coast of

Hokkaidō is the second-largest island of Japan 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 railway via the Seikan Tunnel. The ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

southward to the

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

n Peninsula,

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...

and northern

Vietnam Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about and a population of over 100 million, making it the world's List of countries and depende ...

. It is

amphidromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...

, 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 durin ...

. Original wild populations in

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

became extinct in 1968 due to pollution and present extant 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 landlocked Prefectures of Japan, 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 . Gunma Prefecture borders Niigata Prefecture and Fuk ...

and

Gifu Prefecture is a Prefectures of Japan, prefecture of Japan located in the Chūbu region of Honshu. Gifu Prefecture has a population of 1,910,511 () and has a geographic area of . Gifu Prefecture borders Toyama Prefecture to the north; Ishikawa Prefecture ...

Subspecies

Two to three

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

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 patrician, zoologist and museum director. Biography Coenraad Jacob Temminck was born on 31 March 1778 in Amsterdam in the Dutch Republic. From his father, Jacob ...

Schlegel Schlegel is a German occupational surname. Notable people with the surname include: * Anthony Schlegel (born 1981), American football player * August Wilhelm Schlegel (1767–1845), German poet, brother of Friedrich * Brad Schlegel (born 1968), C ...

, 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 Geography of Taiwan, Taiwan: the Ryukyu Islands are divided into the Satsunan Islands (Ōsumi Islands, Ōsumi, Tokara Islands, Tokara and A ...

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, inv ...

Biology

omnivore An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

, the ayu feeds on

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s, and

worm Worms are many different distantly related bilateria, bilateral animals that typically have a long cylindrical tube-like body, no limb (anatomy), limbs, and usually no eyes. Worms vary in size from microscopic to over in length for marine ...

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 the educational institution (and, in the case of in-person learning, the building) designed to provide learning environments for the teaching of students, usually under the direction of teachers. Most countries have systems of fo ...

.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.

Plecoglossus altivelis altivelis hami-ato1

Most populations of this species are

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 (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

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. It is 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 13 ...

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 sweetfish total production thousand tonnes 1950-2022

The ayu is highly prized for its flavour, mostly consumed in

. Its flesh is distinctively sweet, with "melon and cucumber aromas". The main methods for obtaining ayu are by means of

fly fishing Fly fishing is an angling technique that uses an ultra-lightweight lure called an artificial fly, which typically mimics small invertebrates such as flying and aquatic insects to attract and catch fish. Because the mass of the fly lure is in ...

, by using a

fish trap A fish trap is a animal trapping, trap used for fishing, catching fish and other aquatic animals of value. Fish traps include fishing weirs, lobster trap, cage traps, fish wheels and some fishing net rigs such as fyke nets. The use of traps ar ...

, 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. Charcoal broiled Ayu

The ayu is also caught by

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 China and Japan, as well as Greece, North Macedonia, and briefly, England ...

. The practice on the Nagara River, where

Japanese cormorant The Japanese cormorant (''Phalacrocorax capillatus''), also known as Temminck's cormorant, is a cormorant native to the east Palearctic. It is migratory, and has been observed to dive to significant depths for food. It has a black body with a wh ...

s (''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 A crop is a plant that can be grown and harvested extensively for profit or subsistence. In other words, a crop is a plant or plant product that is grown for a specific purpose such as food, Fiber, fibre, or fuel. When plants of the same spe ...

, 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. Nelu ...

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 roasting ...

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: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 is a Japanese cuisine, Japanese delicacy consisting of fresh raw fish or Raw meat, meat sliced into thin pieces and often eaten with soy sauce. Origin The word ''sashimi'' means 'pierced body', i.e., "wikt:刺身, 刺身" = ''sashimi'', whe ...

File:Ayu (Sweetfish) tempura.jpg, As

tempura is a typical Japanese dish that usually consists of seafood and vegetables that have been coated in a thin batter and deep-fried. Tempura originated in the 16th century, when Portuguese Jesuits brought the Western-style cooking method of ...

File:Plecoglossus altivelis-01.jpg, Farmed ayu

References

External links

*
Plecoglossus altivelis
'. Integrated Taxonomic Information System (ITIS). {{Taxonbar, from=Q642906 Fauna of Hong Kong Freshwater fish of Japan Plecoglossidae Fish of Korea Taxa named by Coenraad Jacob Temminck Taxa named by Hermann Schlegel Fish described in 1846 Edible fish