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Arapaima

The arapaima, pirarucu, or paiche (Arapaima) is a genus of bonytongue native to the Amazon and Essequibo basins in South America. They are the largest freshwater fish of South America, and among the largest freshwater fish in the world.[2]

Anatomy and morphology[edit]

Arapaima leptosoma shown at its full length

Arapaima can reach lengths of more than 2 m (6 ft 7 in), in some exceptional cases even more than 2.5 m (8 ft 2 in) and over 100 kg (220 lb). The maximum recorded weight for the species is 200 kg (440 lb), while the longest recorded length was 4.52 m (15 ft). As one of the most sought-after food fish species in South America, it is often captured primarily by handheld nets for export, by spearfishing for local consumption, and consequently, large arapaima of more than 2 m (6 ft 7 in) are seldom found in the wild today.

The arapaima is torpedo-shaped with large blackish-green scales and red markings. It is streamlined and sleek, with its dorsal and anal fin set back near its tail. Its local name, paiche, derives from the indigenous words for "red" and "fish".

Arapaima scales have a highly mineralised, very hard outer layer with a corrugated surface under which lie several layers of collagen fibres.[3] In a structure similar to plywood, the fibres in each successive layer are oriented at right angles to those in the previous layer for maximum toughness. The hard corrugated surface of the outer layer, the soft but tough internal orthogonal collagen layers, and the hydration of the scales all contribute to their ability to flex and deform while remaining strong—a solution that allows the fish to remain mobile while heavily armored.

The arapaima has a fundamental dependence on surface air to breathe. In addition to gills, it has a modified and enlarged swim bladder, composed of lung-like tissue, which enables it to extract oxygen from the air. This is an adaptation to the often hypoxic conditions of the Amazon floodplains, but requires the arapaima to surface for air every 5 to 15 minutes.[4] This tendency to stay at the surface makes it more vulnerable to attacks from spear fishermen.

Fishing[edit]

Skull from side and above

Commercial fishing of the arapaima has been banned by the Brazilian government due to its commercial extinction. Fishing is allowed only in certain remote areas of the Amazon basin, and must be catch-and-release, or harvesting by native peoples for consumption. Because the arapaima produces boneless steaks, it is considered a delicacy; some 7000 tons per year were taken from 1918 to 1924, the height of its commercial fishing. The demand for the arapaima has led to farming of the fish by the ribeirinhos (as Brazilians call those living on the riverbanks).[5]

Ecology[edit]

The diet of the arapaima consists of fish, crustaceans, and even small land animals that walk near the shore. The fish is an air-breather, using its labyrinth organ, which is rich in blood vessels and opens into the fish's mouth,[6] an advantage in oxygen-deprived water that is often found in the Amazon River. This fish is therefore able to survive in oxbow lakes with dissolved oxygen as low as 0.5 ppm. In the wetlands of the Araguaia, one of the most important refuges for this species, it is the top predator in such lakes during the low water season, when the lakes are isolated from the rivers and oxygen levels drop, rendering its prey lethargic and vulnerable.

Reproduction[edit]

Due to the geographic ranges arapaima inhabit, the animal's life cycle is greatly affected by the seasonal flooding. The arapaima lays its eggs during the months when the water levels are low or beginning to rise. They build a nest about 50 cm wide and 15 cm deep, usually in muddy-bottomed areas. As the water rises, the eggs hatch and the offspring have the flood season to prosper, during May to August. Therefore, the yearly spawning is regulated seasonally. The arapaima male is a mouthbrooder, like his relative, the Osteoglossum, meaning the young are protected in his mouth until they are older. The female arapaima helps to protect the male and the young by circling them and fending off potential predators.

In his book The Whispering Land, naturalist Gerald Durrell reported hearing the tale in Argentina that female arapaima have been seen secreting a white substance from a gland in the head and that their young have been noted seemingly feeding on the substance.

Evolutionary history[edit]

Fossils of arapaima or a very similar species have been found in the Miocene Villavieja Formation of Colombia.[7]

Importance to humans[edit]

Closeup of scales

The arapaima is hunted and used in many ways by local human populations. They are harpooned or caught in large nets, and the meat is said to be delicious. Since the arapaima needs to swim up to breathe air, traditional arapaima fishers often catch them by first harpooning them and then clubbing them dead. One individual can yield as much as 70 kg of meat.

The arapaima has also been introduced for fishing in Thailand and Malaysia. Fishing for this species in Thailand can be done in several lakes, where one often sees arapaima over 150 kg landed and then released.

Special care is needed when dealing with these fish, as since they are large, they can be hard to handle. With catch-and-release after the fish is landed, it must be held for five minutes until it takes a breath. The fish has a large blood vessel running down its spine and lifting the fish clear of the water for trophy shots can rupture this vessel, causing death. Arapaimas are also known to leap out of the water if they feel constrained by their environment or harassed.

It is also considered an aquarium fish, although it obviously requires a large tank and ample resources. In addition, this animal appears in the pet trade, although keeping an arapaima correctly requires a large tank and can prove quite difficult.

The tongue of this fish is thought to have medicinal qualities in South America. It is dried and combined with guarana bark, which is grated and mixed into water. Doses of this are given to kill intestinal worms. In addition, the arapaima's bony tongue is often used to scrape cylinders of dried guarana, an ingredient in some beverages, and the bony scales are used as nail files.

In the Amazon region, the locals often salt and dry the meat, rolling it into a cigar-style package that is then tied, and can be stored for a long time without rotting, which is very important in a region where few have refrigeration. This is often referred to as the "cod of the Amazon", and can be prepared in the same way as traditional salted cod.

In July 2009, some villagers who lived around Kenyir Lake in Terengganu, Malaysia, reported sighting Arapaima gigas. The "Kenyir monster", or "dragon fish" as the locals call it, was claimed to be responsible for the mysterious drowning of two men on 17 June.[8]

Conservation[edit]

The status of the arapaima population in the Amazon River Basin is unknown, hence it is listed on the IUCN red list as Data Deficient. It is difficult to conduct a population census in so large an area, and it is also problematic to monitor catches in a trade that is largely illegal. However, a 2014 study found that the fish was depleted or overexploited at 93% of the sites examined and well-managed or unfished in only 7%; the fish appeared to be extirpated in 19% of these sites.[9][10] Arapaima are particularly vulnerable to overfishing because of their size and because they must surface periodically due to their obligate air-breathing nature.

In popular culture[edit]

Arapaima depicted on a 1954 postage stamp of British Guiana

Gallery[edit]

See also[edit]

References[edit]

  1. ^ World Conservation Monitoring Centre 1996. Arapaima gigas. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1. <www.iucnredlist.org>. Downloaded on 04 October 2013.
  2. ^ Howard, B. C. (2013-10-13). "New Species of Giant Air-Breathing Fish: Freshwater Species of the Week". Water Currents blog. National Geographic. Retrieved 2013-10-15. 
  3. ^ "Engineers Find Inspiration for New Materials in Piranha-proof Armor". Jacobs School of Engineering, UC San Diego. Retrieved 8 February 2012. 
  4. ^ http://www.arkive.org/arapaima/arapaima-gigas/#speciesFactFile
  5. ^ River Monsters episode name: "Unhooked", Animal Planet, 16 July 2010 10AM PDT.
  6. ^ Ferraris, C.J. (2003). "Family Arapaimatidae". In Reis, R.E., Kullander, S.O., Ferraris, C.J. Check List of the Freshwater Fishes of South and Central America. Porto Alegre, Brazil: EDIPUCRS. pp. 582–588. 
  7. ^ Lundberg, J.G. and B. Chernoff (1992). "A Miocene fossil of the Amazonian fish Arapaima (Teleostei, Arapaimidae) from the Magdalena River region of Colombia--Biogeographic and evolutionary implications". Biotropica 24 (1): 2–14. doi:10.2307/2388468. JSTOR 2388468. 
  8. ^ Giant fish sighthings in Kenyir Lake
  9. ^ Castello, L.; Arantes, C. C.; Mcgrath, D. G.; Stewart, D. J.; De Sousa, F. S. (2014-08-13). "Understanding fishing-induced extinctions in the Amazon". Aquatic Conservation: Marine and Freshwater Ecosystems. doi:10.1002/aqc.2491.  edit
  10. ^ Gough, Z. (2014-08-13). "Giant Amazon fish 'locally extinct' due to overfishing". BC Nature. BBC. Archived from the original on 2014-08-14. Retrieved 2014-08-15. 
  11. ^ http://www.giantbomb.com/blanka/3005-1859/

Bibliography[edit]

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