| Ayu sweetfish | |
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Osmeriformes |
| Family: | Plecoglossidae |
| Genus: | Plecoglossus Temminck &Schlegel, 1846 |
| Species: | P. altivelis |
| Binomial name | |
| Plecoglossus altivelis | |
| Synonyms | |
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Theayu sweetfish (Plecoglossus altivelis),ayu (アユ, 鮎, 年魚, 香魚) orsweetfish, is a species ofbony fish. It is the onlyspecies in thegenusPlecoglossus andfamily Plecoglossidae. It is a relative of thesmelts and other fish in the orderOsmeriformes.
Native toEast Asia, it is distributed in the northwesternPacific Ocean along the coast ofHokkaidō inJapan southward to theKorean Peninsula,China,Hong Kong and northernVietnam. It isamphidromous, moving between coastal marine waters and freshwater lakes and rivers. A few landlocked populations also exist in lakes in Japan such asLake Biwa. Original wild populations inTaiwan became extinct in 1968 due to pollution and present extant populations were reintroduced from Japan in the 1990s.[1][2]
The name "sweetfish" was inspired by the sweetness of its flesh. In reference to its typical one-year lifespan, it is also written as年魚 ("year-fish").[3] Some individuals live two to three years.[1] The ayu is the prefectural fish ofGunma Prefecture andGifu Prefecture.[4]
Two[5] to three[6]subspecies are recognized by some authors. Others do not distinguish the subtaxa.[7]
Subspecies include:
Anomnivore, the ayu feeds onalgae,crustaceans,insects,sponges, andworms. It feeds on algae that accumulates on the rocks, scraping it off the rocks with their saw-shaped teeth.[3][9] Adults typically maintain a feeding territory,[10] but the form restricted to lakes and associated streams isschooling.[11]
Most populations of this species areamphidromous and breed in the lower part of rivers during the autumn, laying their eggs in small pits they dig in the gravel.[1][12] The eggs hatch shortly after and thelarvae are carried downriver to the sea.[13] They overwinter in coastal regions, staying there until the spring where the young fish typically are about 6 cm (2.5 in) long and move back to the rivers. Here they reach 15–30 cm (6–12 in) by the summer.[13] They reach maturity by the autumn and move down to the lower part of rivers to breed.[12] 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.[1][14] 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.[12] Although their larvae mostly stay within freshwater, some are carried downstream with the current to the sea and become part of the amphidromous populations.[12] The freshwater-restricted populations typically reach an age of two or three years.[1][7] During the breeding season the amphidromous and freshwater-restricted forms may occur together.[13] Ayu are alsostocked in reservoirs.[1]
Although there are reports of ayu up to 70 cm (2.3 ft) long,[7] a more typical maximum size for the species is about 30 cm (1 ft).[10][15] The form restricted to freshwater is considerably smaller than the amphidromous form.[11] The freshwater-restricted ayu ofLake Biwa that migrate into their spawning streams in the spring can reach up to about 15 cm (6 in) in length, but those that migrate later in the year, primarily in the autumn, only grow to 10 cm (4 in).[12][16] This is caused by differences in the availability of food.[16]
The ayu is highly prized for its flavour, mostly consumed inEast Asia. Its flesh is distinctively sweet, with "melon and cucumber aromas".[18] The main methods for obtaining ayu are by means offly fishing, by using afish trap, and by fishing with a decoy which is known asayu-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.[19]
The ayu is also caught bycormorant fishing. Thepractice on the Nagara River, whereJapanese cormorants (Phalacrocorax capillatus) are used, draws visitors from all over the world. The Japanese cormorants, known in Japanese asumi-u (ウミウ, "sea-cormorant"), are domesticated birds trained for this purpose. The bird catches the ayu, stores it in itscrop, and delivers it to the fishermen.[20]
Ayu is also fished commercially, and captive juveniles are raised inaquaculture before being released into rivers for sport fishing.[citation needed]
InJapanese cuisine, a common method of preparing ayu (among other small fish) is to fold their bodies in a wave-like "swimming" shape, thenskewer. The fish is then grilled with salt over charcoal to preserve the natural flavor of the fish.[21]
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Authority control databases: National |
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