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Ayu Sweetfish

Plecoglossus altivelis (Temminck & Schlegel 1846)

Lifespan, longevity, and ageing

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Maximum longevity: 3 years Observations: Animals commonly die after first spawning (Patnaik et al. 1994).
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Benefits

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Most important species in Japanese freshwater fisheries, highly esteemed as food and game fish. Propagated commercially everywhere in western Japan. The total catch reported for this species to FAO for 1999 was 11 380 t. The countries with the largest catches were Japan (11 380 t). Marketed fresh and consumed fresh, fried and broiled.

Brief Summary

provided by FAO species catalogs
Typical amphidromous. Adults spawn in the spring, in the lower reaches of rivers. After spawning, some adults die while others return to the sea. Larvae enter the sea immediately after hatching and remain there during winter, feeding on plankton.In springtime, the young (5-7 cm) move upstream to the middle reaches of rivers to feed on algae. Those that are ready to spawn (about 20 cm of total length) move downstream to the lower reaches as well. Some fish spawn two or three years in succession, others only once.

Size

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To about 30 cm; usually 20 cm.

Distribution

provided by FAO species catalogs
Western Pacific Ocean; from western Hokkaido southward in Japan, the Korean Pen., Taiwan, and China.

Diagnostic Description

provided by FAO species catalogs
Body elongate. Scales small and cycloid; lateral line complete with 145-169 scales. Mouth large; teeth on both jaws small and conical in juveniles; movable, broad, lamelliform (placoids) and 11 to 14 in number on each side in adults. First arch branchial with 46-49 gillrakers. Dorsal fin high, with 10-11 rays; adipose fin present. Anal fin with 14-15 rays. Pectoral with 14. Pelvic fin base below middle of dorsal fin. Vertebrae 59-63.

References

  • Araga, C. - 1984 Plecoglossidae. In: H. Masuda; K. Amaoka; C. Araga; T. Uyeno; T. Yoshino (eds.). The Fishes of the Japanese Archipelago. Tokai. Univ. Press. 33-34.
  • Azuma, M. - 1977Specific problems on the "Ayu" fish of Lake Biwa. The Freshwater Fishes, (3): 78-85.

Diseases and Parasites

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Aeromonosis. Bacterial diseases
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Diseases and Parasites

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Yellow Grub. Parasitic infestations (protozoa, worms, etc.)
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Life Cycle

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During spawning some fish go up the river and some fish spawn on the river shoreline above pebbles. Spawns at night and excavates a 10cm (diameter or depth?) pit. Eggs are around 1 mm in size and adhere to the sand or pebbles for 14 to 20 days before hatching. This fish is semelparous and releases eggs many times over a short period each time releasing ~10,000 eggs. Sometimes females that want to spawn but cannot, save their strength, and go to a deep stagnant pool. These females wait until spring before going up the river with young fish. After hatching, the larvae are 6 mm and flow with the water current eating plankton. Juvenile fish will come again to the river in spring. These live in schools. When schools of Plecoglossus altivelis return to their river they guard their territory and eat food (Ref. 12218).Reproductive mode varies between semelparity and iteroparity. Large females spawn once, while smaller females spawn twice during a two-week interval (Ref. 76896).
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Migration

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Amphidromous. Refers to fishes that regularly migrate between freshwater and the sea (in both directions), but not for the purpose of breeding, as in anadromous and catadromous species. Sub-division of diadromous. Migrations should be cyclical and predictable and cover more than 100 km.Characteristic elements in amphidromy are: reproduction in fresh water, passage to sea by newly hatched larvae, a period of feeding and growing at sea usually a few months long, return to fresh water of well-grown juveniles, a further period of feeding and growing in fresh water, followed by reproduction there (Ref. 82692).
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Morphology

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Dorsal spines (total): 0; Dorsal soft rays (total): 10 - 11; Analsoft rays: 14 - 15; Vertebrae: 60 - 63
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Trophic Strategy

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Occurs in the upper to middle reaches of rivers, lakes, and reservoirs, but also in estuaries. Usually in pools, riffles with rock base and pebbles (Ref. 41299). Feeds on cladocera, rotifer, diatom, green and blue algae (Ref. 45563).
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Diagnostic Description

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Pyloric caeca 350-400.
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Biology

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Typical amphidromous fish; appears in near shore from late autumn to spring (Ref. 11230). Found in lakes and rivers, preferring clean river water and can be found the entire river long, from the head to the mouth (Ref. 12218). Ascends the river during March when the temperature is around 10°C (Ref. 12218). Adults spawn in the spring, in the lower reaches of rivers. After spawning, some adults die while others return to the sea. Larvae enter the sea immediately after hatching and remain there during winter, feeding on plankton. In springtime, the young (5-7 cm TL) move upstream to the middle reaches of rivers to feed on algae. Fish (about 6-9 cm) start schooling at the river mouth and are insectivores and eat algaeoff small pebbles (Ref. 12218); this is assisted by small leaf-like teeth which are loosely attached to the jaw with two ligaments (Ref. 45181). Those that are ready to spawn (about 20 cm TL) move downstream to the lower reaches of the river. Spawning adults from the sea migrate upstream to the lower reaches as well. Some fish spawn two or three years in succession, others only once (Ref. 9987 & 559). River forms live usually only one year whereas lake forms can live two or three years (Ref. 12218). Reaches maturity at 30-40 cm (Ref. 12218). Highly esteemed food fish. Marketed fresh and consumed fresh, fried and broiled (Ref. 9987).
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Importance

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fisheries: highly commercial; aquaculture: commercial; gamefish: yes; price category: unknown; price reliability:
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分布

provided by The Fish Database of Taiwan
分布於西北太平洋區域,包括中國、日本、韓國及臺灣均有產。臺灣原產於濁水溪以北及花蓮三棧溪以北的各溪流,其中以淡水河流域的香魚最為有名。但在1950年代後因為污染、棲地迫害及濫捕等原因,原生族群已遭滅絕,現在溪流中發現者,則是由日本所引入發眼卵而放流的。
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利用

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新鮮的香魚會有一股似哈密瓜般香甜的濃郁芬芳氣息,所以有「溪流之王」的美譽,是海鮮店內受歡迎之魚種。人們利用香魚的領域強之特性,發明「友釣法」的釣魚方法,即利用活的香魚去靠近原佔有領域的香魚,引誘原領域內的香魚去撞擊餌魚而誤觸魚鉤,這是一種高難度的釣魚技巧。
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描述

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體延長,稍側扁,略呈紡錘狀。頭小。吻中長,向前傾斜,而形成吻鉤。口裂大;上頜末端有一枚向下彎曲成鉤狀的門齒,上下頜另具寬扁之板狀細齒。體被極細小之圓鱗,側線沿體側中央直走。背鰭位於身體的中央,起點在腹鰭起點稍前,在靠近尾柄處另有一小的脂鰭;胸鰭狹長;尾鰭分叉。體呈橄欖綠色,腹部為白色,新鮮魚體的胸鰭後方,有一個鮮黃色斑塊,當魚受到驚嚇或死亡時,黃色斑塊則會變得非常暗淡。
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棲地

provided by The Fish Database of Taiwan
典型的河海迴游魚類。喜歡棲息在清澈乾淨的冷水溪流或湖泊。可分陸封型,即終生在淡水中生活者,可產卵2-3次,年平均壽命2-3年;降海型,在每年秋冬之際會順流到河川的下游地區產卵,產卵完後大部分的香魚就會死亡,其壽命約1年,故有「年魚」之稱。孵化後的仔魚會游至河口地區棲息,而後隨著成長的各階段,小魚會順著河川逆流而上。成長後的香魚會以附著在岩石上的藻類及水生昆蟲為食。具強烈的領域性,強壯的成魚會佔領一塊長滿藻類的大礫石,不准其它的香魚靠近,如果有外來的香魚侵入其領域,則會用身體去撞擊外來的香魚,將其趕出領域範圍。
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Ayu sweetfish

provided by wikipedia EN

The ayu sweetfish (Plecoglossus altivelis), ayu (アユ, 鮎, 年魚, 香魚) or sweetfish, is a species of 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 Biwa. Original wild populations in Taiwan 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 of Gunma Prefecture and Gifu Prefecture.[4]

Subspecies

Two[5] to three[6] subspecies are recognized by some authors. Others do not distinguish the subtaxa.[7]

Subspecies include:

  • P. a. altivelis (Temminck & Schlegel, 1846) (ayu, sweetfish)
  • P. a. chinensis Y. F. Wu & X. J. Shan, 2005 (Chinese ayu)
  • P. a. ryukyuensis M. Nishida, 1988 (Ryukyu ayu-fish) – endangered[8]

Biology

Scrape marks left by ayu feeding on algae when the rock was submerged
A school of ayu

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.[3][9] Adults typically maintain a feeding territory,[10] but the form restricted to lakes and associated streams is schooling.[11]

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.[1][12] The eggs hatch shortly after and the larvae 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 also stocked 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 of Lake 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]

Human uses

Ayu is an edible fish, mostly consumed in East Asia. Its flesh has a distinctive, sweet flavour with "melon and cucumber aromas".[17] It is consequently highly prized as a food fish. 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.[18]

Japanese fishers also catch it using cormorant fishing. 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 bird catches the ayu, stores it in its crop, and delivers it to the fishermen.[19]

Ayu is also fished commercially, 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 to skewer it in such a way so that its body forms a wave, making it look as though it is swimming.[20]

Gallery

References

  1. ^ a b c d e f g Huckstorf, V. (2012). "Plecoglossus altivelis". IUCN Red List of Threatened Species. 2012: e.T62222A3110058. doi:10.2305/IUCN.UK.2012-1.RLTS.T62222A3110058.en. Retrieved 18 November 2021.
  2. ^ TVBS. "盤點台灣淡水魚 原生種香魚已滅絕│TVBS新聞網". TVBS (in Chinese (Taiwan)). Retrieved 8 November 2022.
  3. ^ a b Queen of Freshwater Streams. Archived 25 April 2014 at the Wayback Machine Food Forum. Kikkoman Global Website.
  4. ^ Symbols of Gifu Prefecture. Gifu Prefectural Government.
  5. ^ Froese, R. and D. Pauly, Editors. Plecoglossus. FishBase. 2015.
  6. ^ Shan, X., Wu, Y., & Kang, B. (2005). 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.
  7. ^ a b c Froese, R. and D. Pauly, Editors. Plecoglossus altivelis altivelis. FishBase. 2015.
  8. ^ World Conservation Monitoring Centre (1996). "Plecoglossus altivelis ssp. ryukyuensis". IUCN Red List of Threatened Species. 1996: e.T17595A7151908. doi:10.2305/IUCN.UK.1996.RLTS.T17595A7151908.en. Retrieved 18 November 2021.
  9. ^ "Rock Fishing in Tokushima, Japan". USA Today.
  10. ^ a b Hooper, R. (21 September 2005). Ayu sweetfish. The Japan Times. Retrieved 13 February 2017.
  11. ^ a b 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.
  12. ^ a b c d e Lucas, M., and E. Baras (2001). Migration of Freshwater Fishes, p. 187. Blackwell Science. ISBN 0-632-05754-8
  13. ^ a b c 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.
  14. ^ 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.
  15. ^ FAO Fisheries and Aquaculture Department: Plecoglossus altivelis (Temminck & Schlegel, 1846). Retrieved 13 February 2017.
  16. ^ a b Lake Biwa Museum: Aquarium. Retrieved 10 May 2019.
  17. ^ Gadsby, P. The chemistry of fish. Discover Magazine 25 November 2004.
  18. ^ Waldman, J. (2005). 100 Weird Ways to Catch Fish (1st ed.). Mechanicsburg, PA: Stackpole Books. pp. 6–7. ISBN 0811731790.
  19. ^ Cormorant-Fishing on the Nagara River. Archived 19 January 2014 at the Wayback Machine Gifu Rotary Club.
  20. ^ No. 2: Ayu fish. Hiroko's Kitchen. 10 August 2010.
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Ayu sweetfish: Brief Summary

provided by wikipedia EN

The ayu sweetfish (Plecoglossus altivelis), ayu (アユ, 鮎, 年魚, 香魚) or sweetfish, is a species of 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 Biwa. Original wild populations in Taiwan 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 年魚 ("year-fish"). Some individuals live two to three years. The ayu is the prefectural fish of Gunma Prefecture and Gifu Prefecture.

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