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Mekong Giant Catfish

Pangasianodon gigas Chevey 1931

Biology

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A migratory species, the giant catfish is thought to move from the Tonle Sap Lake in Cambodia from October to December each year and into the Mekong River from which it progresses upstream into northeastern Cambodia, Laos or Thailand to spawn (1). The giant catfish eats the vegetation growing on the river bed (3).
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Conservation

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The giant catfish has been listed on Appendix I of the Convention on International Trade in Endangered Species since 1975 when it first became apparent that it had seriously declined. It occurs in a Biosphere Reserve and a RAMSAR site (for wetlands of international significance), but both fail to provide active protection. In Cambodia and Thailand it is illegal to catch the giant catfish but this legislation is not enforced. In Laos it is protected, but again, this has no practical effect (1). Artificially spawned individuals have been released into the River Mekong since 1985, and captive breeding has been taking place since 2001 (1). The Mekong Fish Conservation Project works in cooperation with the Cambodian Department of Fisheries to conduct research and educate the public. This project has released 20 catfish into the river system since 2000 (5). Studies have provided evidence that it spawns in areas that will be impacted by the Mekong Navigation Improvement Project which plans to dredge long stretches of river and blast away areas with rapids that obstruct the passage of large ships. The project was partially underway before the reliability of the Environmental Impact Report was questioned, and the project was put on hold (6).
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Description

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The giant catfish is the world's largest freshwater fish (1). It has a whitish underside and the back and fins are grey. The eyes are located low on the head and point downwards. Whilst juveniles have barbels, adults can be distinguished from other large catfish by their reduced barbels and lack of teeth (4).
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Habitat

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Inhabits freshwater rivers and lakes (1).
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Range

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The giant catfish is endemic to the parts of the Mekong River basin that run through Cambodia, Laos, Thailand, Viet Nam and possibly Burma and China. It is primarily found in the Tonle Sap River, the Tonle Sap Lake and the Mekong River (1).
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Status

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The giant catfish is classified as Critically Endangered (CR A4bcde) on the IUCN Red List 2004 (1). It is listed on Appendix I of the Convention on the Conservation of Migratory Species of Wild Animals (2) and on Appendix I of CITES (3).
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Threats

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The giant catfish has been subject to over-fishing for many years. Catches at the beginning of the 20th century were in the thousands each year but declines have been so severe that less than ten are now caught per year (1). Habitat loss and degradation as a result of damming and the clearance of flooded forest near the Tonle Sap Lake (1) have disrupted the giant catfish's migration, spawning, eating and breeding habits (5).
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Diagnostic Description

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Body without stripes; posterior nostril located near anterior nostril; 7 branched dorsal-fin rays; gill rakers rudimentary or absent; fins grey, never black (Ref. 12693). The center of the eye above the horizontal line through the mouth angle in juveniles; eye totally below the level of mouth angle in subadults and adults. The maxillary and mandibulary pairs of barbels well developed in juveniles; mandibulary barbels become rudimentary in subadults and adults (Ref. 9448). Gigantic size; oral teeth and gill rakers present in small juveniles, absent at about 30-50 cm SL; dorsal, pelvic and pectoral fins without filamentous extensions (Ref. 43281). Distinguished from other large catfish in the Mekong by its lack of teeth and the almost complete absence of barbels (Ref. 2686)
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Recorder
Rodolfo B. Reyes
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Migration

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Potamodromous. Migrating within streams, migratory in rivers, e.g. Saliminus, Moxostoma, Labeo. Migrations should be cyclical and predictable and cover more than 100 km.
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Morphology

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Dorsal spines (total): 2; Dorsal soft rays (total): 7 - 8; Analsoft rays: 35; Vertebrae: 48
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Trophic Strategy

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Feeds heavily on fruit in high water when it enters the flooded forest.
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Biology

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A migratory species (Ref. 37772) which occurs in medium to large-sized rivers (Ref. 12975). Feeds on detritus and algae on the bottom (Ref. 58784); feeds only on vegetation in the river but takes other food in captivity; little is known on its general pattern of life and migratory journeys for spawning (Ref. 2686). Shows one of the fastest growth rates of any fish in the world, reaching 150 to 200 kg in 6 years (Ref. 12693). Cited in the Guinness Book of Records as largest freshwater fish (Ref. 6472). Marketed fresh (Ref. 12693). Maximum length of 300 cm needs confirmation. Threatened due to over harvesting and habitat loss (Ref. 58490).
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Importance

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fisheries: commercial; aquaculture: experimental
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Mekong giant catfish

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 src=
Illustration of a Mekong giant catfish at a Buddhist temple in Chiang Khong.

The Mekong giant catfish (Pangasianodon gigas; Thai: ปลาบึก, RTGS: pla buek, pronounced [plāː bɯ̀k]; Khmer: ត្រីរាជ /trəy riec/; Vietnamese: cá tra dầu), is a large, critically endangered species of catfish (order Siluriformes) in the shark catfish family (Pangasiidae), native to the Mekong basin in Southeast Asia and adjacent China. It is considered critically endangered due to accelerating habitat loss.

Description

Grey to white in colour and lacking stripes, the Mekong giant catfish is distinguished from other large catfish species in the river by the near-total lack of barbels and the absence of teeth.[2] The Mekong giant catfish once held the Guinness World Records' position for the world's largest freshwater fish in 2005.[3][4] Attaining an unconfirmed length of 3 m (9.8 ft), the Mekong giant catfish grows extremely quickly, reaching a mass of 150 to 200 kg (330 to 440 lb) in six years.[2] It can reportedly weigh up to 350 kg (770 lb).[2] The largest catch recorded in Thailand since record-keeping began in 1981 was a female measuring 2.7 m (8 ft 10 in) in length and weighing 293 kg (646 lb). This specimen, caught in 2005, is widely recognized as the largest freshwater fish ever caught (although the largest sturgeon species can far exceed this size, they are anadromous). Thai fisheries officials stripped the fish of its eggs as part of a breeding programme, intending then to release it, but the fish died in captivity and was sold as food to local villagers.[4][5][6] Juvenile fish wear barbels that shrink as they age.[7] Numbers of young fish are declining. Spawning fish in upper Cambodia are being over harvested. Larval fish are threatened by habitat fragmentation due to construction of dams which are becoming increasingly common.[8]

Distribution and habitat

The Mekong giant catfish is a threatened species in the Mekong, and conservationists have focused on it as a flagship species to promote conservation on the river.[3][9] Although research projects are currently ongoing, relatively little is known about this species. Historically, the fish's natural range reached from the lower Mekong in Vietnam (above the tidally influenced brackish water of the river's delta) all the way to the northern reaches of the river in the Yunnan Province of China, spanning almost the entire 4,800 km (3,000 mi) length of the river.[10] Due to threats, this species no longer inhabits the majority of its original habitat. It is now believed to only exist in small, isolated populations in the middle Mekong region.[3] Fish congregate during the beginning of the rainy season and migrate upstream to spawn.[3] They live primarily in the main channel of the river, where the water depth is over 10 m (33 ft),[11] while researchers, fishermen and officials have found this species in the Tonle Sap River and Lake in Cambodia, a UNESCO Biosphere Reserve. In the past, fishers have reported the fish in a number of the Mekong's tributaries. Today, however, essentially no sightings are reported outside of the main Mekong river channel and the Tonle Sap region.

Understanding of the species’ migration pattern is incomplete.[12] The fish are thought to rear primarily in the Mekong and Cambodia's Tonle Sap lake and migrate hundreds of miles north to spawning grounds in Thailand.[12][7] Spawning fish in the upper Cambodia are being over harvested. Fragmentation caused by infrastructure development of dams are becoming increasingly common posing threats to larval fish and reducing breeding abilities.[8][13] Overfishing, damming, destruction of spawning, and breeding grounds and siltation have taken a toll on the species' habitat.[7]

Feeding

As fry, this species feeds on zooplankton in the river and is known to be cannibalistic.[14] After approximately one year, the fish becomes herbivorous, feeding on filamentous algae, probably ingesting larvae and periphyton accidentally. The fish likely obtains its food from algae growing on submerged rocky surfaces, as it does not have any sort of dentition.[14] The Mekong giant catfish are toothless herbivores who lives off of the plants and algae in the river.[7] The fish have been studied (inside the stomach linings) to feed on zooplankton and phytoplankton.[15]

Conservation

Endemic to the lower half of the Mekong River, this catfish is in danger of extinction due to overfishing, as well as the decrease in water quality due to development and upstream damming.[12] A 2018 study suggests that the Mekong stocks could fall up to 40% as the result of dam projects.[16] The current IUCN Red List for fishes classes the species as Critically Endangered; the number living in the wild is unknown, but catch data indicate the population has fallen by 80 percent in the last 14 years.[1][17] It is also listed in Appendix I of CITES, banning international trade involving wild-caught specimens.[18]

In The Anthropologists' Cookbook (1977), Jessica Kuper noted the importance of the pa beuk to the Lao people and remarked, "In times gone by, this huge fish, which is found only in the Mekong, was fairly plentiful, but in the last few years, the number taken annually has dwindled to forty, thirty or twenty, and perhaps in 1976 even fewer. This is sad, as it is a noble fish and a mysterious one, revered by the Lao."[19] In 2000, fishers hauled out 11 giant catfish. In 2001 they caught seven. In 2002 they caught just five.[20]

Fishing for the Mekong giant catfish is illegal in the wild in Thailand, Laos, and Cambodia, but the bans appear to be ineffective and the fish continue to be caught in all three countries.[1] However, in recognition of the threat to the species, nearly 60 Thai fishermen agreed to stop catching the endangered catfish in June 2006, to mark the 60th anniversary of Bhumibol Adulyadej's ascension to the throne of Thailand.[21] Thailand is the only country to allow fishing for private stocks of Mekong giant catfish. This helps save the species, as lakes purchase the small fry from the government breeding programme, generating extra income that allows the breeding program to function. Fishing lakes, such as Bueng Samran (บึงสำราญ) in Bangkok, have the species up to 140 kg (310 lb). The most common size landed is 18 kg (40 lb), although some companies specialise in landing the larger fish.

The species needs to reach 50–70 kg (110–150 lb) to breed, and it does not breed in lakes. The Thailand Fisheries Department has instituted a breeding programme to restock the Mekong River. From 2000 to 2003, about 10,000 captive-bred specimens were released by the Thai authorities.[1] Specimens are released into reservoirs rather than the Mekong River itself.[1]

The Mekong giant catfish is described as a contemporary example of overharvest.[12] Millions of tons of fish are harvested in Cambodia every year, with spawning fish being over-harvested. Fragmentation caused by dams increasingly poses threats to larval fish.[8] Trends in water use, energy production, consumption and associated environmental degradation are projected to continue rising in southeast Asia. The Mekong giant catfish are highly migratory requiring large stretches of river for seasonal journeys and specific environmental conditions in their spawning and breeding areas.[7]

The World Wide Fund for Nature (WWF) works in partnership with other organizations including the Mekong River Commission and the Asian Development Bank which aims to ensure that environmental and social impacts are considered in developments of hydropower infrastructures. It also implements projects dedicated to conservation, research, monitoring and raising awareness of the Mekong giant catfish.[13]

In culture and art

In Thai folklore, this fish is regarded with reverence, and special rituals are followed and offerings are made before fishing it.[22] The species is represented as ancient art along the Mekong river.[7]

References

  1. ^ a b c d e Hogan, Z. (2011). "Pangasianodon gigas". IUCN Red List of Threatened Species. 2011: e.T15944A5324699. doi:10.2305/IUCN.UK.2011-1.RLTS.T15944A5324699.en.
  2. ^ a b c Froese, Rainer and Pauly, Daniel, eds. (2014). "Pangasianodon gigas" in FishBase. July 2014 version.
  3. ^ a b c d Hogan, Z. S. (2004). "Threatened Fishes of the World: Pangasianodon gigas Chevey, 1931 (Pangasiidae)". Environmental Biology of Fishes. 70 (3): 210–210. doi:10.1023/B:EBFI.0000033487.97350.4c.
  4. ^ a b Mydans, Seth (2005-08-25). "Hunt for the big fish becomes a race". The New York Times. Retrieved 3 March 2013.
  5. ^ Owen, James (2005-06-29). "Grizzly Bear-Size Catfish Caught in Thailand". National Geographic News. Retrieved 2006-06-29.
  6. ^ "Fish whopper: 646 pounds a freshwater record". NBC News. 2005-07-01. Retrieved 2006-06-29.
  7. ^ a b c d e f The Elusive Giant Catfish (Television production). National Geographic. July 20, 2009.
  8. ^ a b c Searching for Giant Catfish Babies on the Mekong (Television production). National Geographic. September 4, 2018. Retrieved 9 March 2019.
  9. ^ MGCCG, 2005
  10. ^ Lopez, Alvin, ed. (2007). "2.3 Focal species". MWBP working papers on Mekong Giant Catfish, Pangasianodon gigas (PDF). Mekong Wetlands Biodiversity Conservation and Sustainable Use Programme.
  11. ^ Mattson, Niklas S.; Buakhamvongsa, Kongpheng; Sukumasavin, Naruepon; Tuan, Nguyen; Vibol, Ouk (2002). "Mekong giant fish species: on their management and biology" (PDF). Mekong River Commission technical paper (3): 14.
  12. ^ a b c d Eva, Bellemain; Harmony, Patricio; Thomas, Gray; Francois, Guegan; Alice, Valentini; Claude, Miuad; Tony, Dejean (July 13, 2016). "Trails of river monster: Detecting critically endangered Mekong giant catfish Pangasiadon gigs using environmental DNA". Global Ecology and Conservation: 148–156. doi:10.1016/j.gecco.2016.06.007.
  13. ^ a b "The giant of the Mekong". World Wildlife Fund for Nature. Retrieved 26 March 2019.
  14. ^ a b (Pholprasith, 1983 as cited in Mattson et al. 2002)
  15. ^ Yamagishi, Y.; et al. (2004). "Study on feeding habits of Mekong giant catfish in Mae peum Reservoir, Thailand" (PDF). Proceedings of the International Sym posium on SEA STA R2000 and Bio-logging Science (The 5th SEA STA R2000 Workshop): 105–109.
  16. ^ Lovgren, S. (2018). "Southeast asia may be building too many dams too fast". National Geographic. Retrieved 19 April 2019.
  17. ^ "Giant Catfish Critically Endangered, Group Says". National Geographic News. 2003-11-18. Retrieved 2006-06-29.
  18. ^ "CITES Appendices I, II and III". CITES. 2006-06-14. Archived from the original on 2007-02-03. Retrieved 2006-06-29.
  19. ^ Kuper, Jessica (1977). The Anthropologists' Cookbook. Universe Books. p. 167.
  20. ^ Roach, John (2003-05-15). "Big Trouble for Asia's Giant Catfish". National Geographic News. Retrieved 20 February 2018.
  21. ^ "Giant Mekong catfish off the hook". BBC News. 2006-06-10. Retrieved 2006-06-29.
  22. ^ "Pla Buek: The Giant Catfish of the Mae Khong River Chiangrai". Archived from the original on 2013-01-21. Retrieved 2012-10-05.

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Mekong giant catfish: Brief Summary

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 src= Illustration of a Mekong giant catfish at a Buddhist temple in Chiang Khong.

The Mekong giant catfish (Pangasianodon gigas; Thai: ปลาบึก, RTGS: pla buek, pronounced [plāː bɯ̀k]; Khmer: ត្រីរាជ /trəy riec/; Vietnamese: cá tra dầu), is a large, critically endangered species of catfish (order Siluriformes) in the shark catfish family (Pangasiidae), native to the Mekong basin in Southeast Asia and adjacent China. It is considered critically endangered due to accelerating habitat loss.

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