Mekong giant catfish

from Wikipedia, the free encyclopedia
Mekong giant catfish
Young animals in the Gifu World Fresh Water Aquarium

Young animals in the Gifu World Fresh Water Aquarium

Systematics
Cohort : Otomorpha
Sub-cohort : Ostariophysi
Order : Catfish (Siluriformes)
Family : Shark catfish (Pangasiidae)
Genre : Pangasianodon
Type : Mekong giant catfish
Scientific name
Pangasianodon gigas
( Chevey , 1931)

The Mekong giant catfish ( Pangasianodon gigas ) is the largest species of the shark catfish family (Pangasiidae) and one of the largest freshwater fish in the world. It occurs exclusively in the Mekong and is considered threatened with extinction due to overfishing and loss of habitat. In Southeast Asia it is used as a flagship species to convey the need to protect large fish in the Mekong. Mekong giant catfish are characterized by a very high growth rate and are therefore also grown in aquaculture programs ; To what extent artificial offspring are suitable for supporting wild populations is still unclear.

features

Mekong giant catfish, like all shark catfish, have no scales and an elongated, laterally flattened body. Adult animals are very strongly built and can reach a body length of three meters and a weight of over 300 kg. The females become longer and heavier than the males. Mekong giant catfish are silvery-gray with a pale white belly and have no markings. The fins are always gray. Young animals are darker with a silvery-shiny belly and have two stripes along the flanks. Their head makes up 14 to 21% of the standard length (head and trunk without the caudal fin) and is wider than that of the Pangasius ( Pangasianodon hypophthalmus ), but not as wide as that of the Pangasius sanitwongsei . The mouth is blunt or rounded and terminal, with a slightly protruding lower jaw. In young animals there is a pair of barbels on the upper and lower jaws and the eye is higher than in the other shark catfish. The lower and upper jaw and the ploughshare have small, conical and relatively blunt teeth. In older animals that have reached a length of about 30 to 50 centimeters, the teeth fall out and the barbels recede; the pair of barbels on the upper jaw is then only three to four millimeters long, the one on the lower jaw disappears completely in the fatty tissue. The eyes move down to below the corner of the mouth, which is not the case with any other species of shark. The gill arches have a very short upper arm and a greatly elongated lower arm. The upper arm has three gill spikes , the lower fourteen; even these are almost completely regressed in older animals.

The triangular dorsal fin has two hard rays, the first of which is very small and often imperceptible from the outside, as well as seven, rarely eight, branched soft rays. A small adipose fin is present. The pectoral fins have a hard ray and 10 to 11 soft rays, the ventral fins an unbranched and 7 or 8 branched soft rays, and the elongated anal fin 31 to 35 soft rays, of which the first six or seven are unbranched. Filamentous appendages are not present on any of the fins. The swim bladder is single-chambered and restricted to the abdomen . The number of vertebrae is 48.

genetics

The chromosome set of the species consists of 30 pairs (2n = 60). Sex determination is probably carried out using an XY / XX system , so males are characterized by the difference in the two sex chromosomes. The mitochondrial genome was completely sequenced in 2007 .

Occurrence

Location of the Tonle Sap in Cambodia

The Mekong giant catfish is endemic to the Mekong area. Originally, the distribution area probably included the entire Mekong and its tributaries in Laos , Thailand , Cambodia , Myanmar , Vietnam and southern China . Today the animals are almost only seen in the Tonle Sap lake and river and in the adjacent Mekong lower reaches. It is unknown whether the entire range is inhabited by one population or whether two populations exist in the upper and lower Mekong regions; the rarity of the animals prevents more precise examinations. The documented long migrations during the spawning season, however, indicate a single, coherent population. In the Mae Nam Chao Phraya ( Chao Phraya River ) as well as in some reservoirs in Thailand animals were released, but from this no self-sustaining populations have developed.

Way of life

Mekong giant catfish are pure freshwater fish that colonize medium-sized to large rivers and occur predominantly in water depths of 10 or more meters. They prefer stony or gravelly ground and are occasionally found in underwater caves. The animals are almost exclusively diurnal. Measurements with sound probes in a reservoir in Northern Thailand indicate that they are in significantly deeper water layers during the day and near the shore at night. This behavior could have something to do with the oxygen content of the water.

nutrition

After they have used up the yolk , juveniles feed on zooplankton , especially small crustaceans and phytoplankton, and are also prone to cannibalism . The gastrointestinal tract of the animals (including the anus) is very flexible and thus allows the ingestion of large amounts of food. Older animals are pure herbivores that feed primarily on trichal algae , which are likely to be ingested from the rocky soil. Occasionally, fist-sized stones and probably also periphyton and insect larvae are picked up.

Reproduction

Little is known about the reproduction of the Mekong giant catfish in nature. Young animals with a length of less than 50 centimeters were almost never caught, but this may have something to do with the animals' rapid growth. The spawning season begins in late April with the receding flooding and lasts until mid-May. The animals migrate up to several thousand kilometers upstream, whereby the fat stores are used up for the migration and the development of the gonads . It is believed that the spawning grounds are in the Mekong River in northern Thailand and possibly also in northern Cambodia. The eggs are yellowish and sticky and about 1.7 mm in diameter. Females one and a half to two meters long can lay around five hundred thousand to two million eggs, and 13.5 kilograms or around 11 million eggs were found in an animal weighing 175 kilograms. The juveniles are likely to be driven downstream and migrate to the floodplains in the next rainy season. The growth is extremely rapid. From a length of 3.8 millimeters when hatched, the animals grew to a length of 13.4 millimeters in captivity within a week. After four months a length of 40 centimeters and a weight of over 600 grams were reached; after three years the weight was over 100 kilograms. Measurements on wild animals suggest even higher growth rates. Sexual maturity is likely to be reached at 6 to 8 years of age.

Use and protection

The Mekong giant catfish has long been valued as a valuable food fish due to its size and meat . The meat is considered to be tastier after the spawning migration. In some areas, traditional hunting was limited to the period after spawning and was accompanied by festivities, which led to relatively gentle fishing of the stocks. From the 1950s onwards, fishing increased significantly and as a result the annual catches fell from a few hundred animals to just a few individual catches. It is believed that the population of free, adult animals has declined by over 80% and is now less than 2500 animals. The species is listed in Appendix I of the Washington Convention on Endangered Species and classified in the IUCN Red List as Critically Endangered . In addition to overfishing, the destruction of spawning grounds and migration routes through pollution and dam construction are also possible reasons for the decline in the species. Coordinated protective measures have now been implemented; they include bans on fishing in Thailand and Laos and a program to buy up and release caught fish in Cambodia. With the latter, however, the high death rate of the animals and the low willingness of fishermen to cooperate are problematic, especially since release without financial reward has been required by law since 2005. In addition, the hiking trails are explored using markings for caught fish and awareness-raising campaigns are intended to establish the Mekong giant catfish as a flagship species for the protection of the Mekong's fish stocks and thus raise the population's awareness of species protection.

The first attempts to keep the Mekong giant catfish in aquaculture were made in Thailand in 1967, as the species is considered to be very promising for commercial use due to its rapid growth. Artificial propagation has been successful since 1983; In her, sexually mature animals are brought to the release of sex products with the help of hormones. Captured wild animals were initially used for this purpose; Since 2005, animals from offspring have also reached sexual maturity. The annual production is currently over three hundred thousand animals. Some of the young animals obtained in this way were successfully introduced in Thailand in breeding ponds and in the Chao Phraya. Tens of thousands of animals were also released in the Mekong; However, it is not yet clear whether this had a positive impact on the wild population.

Systematics

The Mekong giant catfish is placed together with the pangasius ( Pangasianodon hypophthalmus ) in the genus Pangasianodon . Molecular biological studies confirmed that these two species are sister taxa . However, some authors classify them as part of the genus Pangasius or as a subgenus Pangasius (Pangasianodon) due to their great similarity with other shark catfish .

No subspecies are described.

literature

  • TR Roberts, C. Vidthayanon: Systematic revision of the Asian catfish family Pangasiidae, with biological observations and descriptions of three new species. In: Proceedings of the Academy of Natural Sciences of Philadelphia . tape 143 , 1991, pp. 97-144 (English).
  • Hogan, ZS: Threatened fishes of the world: Pangasianodon gigas Chevey, 1931 (Pangasiidae) . In: Environmental Biology of Fishes . No. 70, 2004, p. 210.

Individual evidence

  1. ↑ Ayanomiya Fumihito: Morphological Comparison of the Mekong Giant Catfish, Pangasianodon gigas, with Other Pangasiid Species . In: Japanese Journal of Ichthyology . tape 36 , no. 1 , 1989, pp. 113-119 , doi : 10.11369 / jji1950.36.113 (English).
  2. ↑ a b c d T. R. Roberts, C. Vidthayanon: Systematic revision of the Asian catfish family Pangasiidae, with biological observations and descriptions of three new species . In: Proceedings of the Academy of Natural Sciences of Philadelphia . tape 143 , 1991, pp. 97-144 (English).
  3. ↑ a b c Niklas S Mattson, Kongpheng Buakhamvongsa, Naruepon Sukumasavin, Nguyen Tuan, Ouk Vibol: Cambodia Mekong giant fish species: on their management and biology . In: Mekong River Commission (Ed.): MRC Technical Paper . tape 3 . Phnom Penh 2002 (English, PDF, 749kB ).
  4. ↑ J. Manosroi, K. Meng-Umphan, U. Meevatee, A. Manosroi: Chromosomal Karyotyping from Peripheral Blood Lymphocytes of the Mekong Giant Catfish (Pangasianodon gigas, Chevey) . In: Asian Fisheries Science . tape 16 , 2003, p. 241–246 (English, full text [PDF; 73 kB ]). Full text ( memento of the original from October 6, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.ist.cmu.ac.th
  5. ↑ Amnuay Jondeunga, Pradit Sangthonga and Rafael Zardoya: The complete mitochondrial DNA sequence of the Mekong giant catfish (Pangasianodon gigas), and the phylogenetic relationships among Siluriformes . In: Genes . tape 387 , no. 1-2 , 2007, pp. 49-57 (English).
  6. ↑ Hogan, ZS, Moyle, PB, May, B., Zanden, MJV, Baird, IG: The Imperiled Giants of the Mekong . In: American Scientist . No. 92, 2004, pp. 228-237. ( PDF ( Memento of the original dated August 16, 2009 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ) @1@ 2Template: Webachiv / IABot / genome-lab.ucdavis.edu
  7. ↑ a b c d A.F. Poulsen, KG Hortle, J. Valbo-Jorgensen, S. Chan, CKChhuon, S. Viravong, K. Bouakhamvongsa, U. Suntornratana, N. Yoorong, TT Nguyen, BQ Tran .: Distribution and Ecology of Some Important Riverine Fish Species of the Mekong River Basin . In: Mekong River Commission (Ed.): MRC Technical Paper . tape 10 . Phnom Penh 2004 ( PDF, 4.7MB ).
  8. ↑ Hogan, ZS: Threatened fishes of the world: Pangasianodon gigas Chevey, 1931 (Pangasiidae) . In: Environmental Biology of Fishes . No. 70, 2004, p. 210.
  9. ↑ Hiromichi Mitamura, Nobuaki Arai, Yukiko Yamagishi, Yuuki Kawabata, Yasushi Mitsunaga, Metha Khachaphichat, Thavee Viputhanumas: Habitat use and movement of hatchery-reared F2 Mekong giant catfish in the Mae Peum reservoir, Thailand, studied by acoustic telemetry . In: Fishery Science . tape 75 , 2009, p. 175–182 (English, full text [PDF; 345 kB ]). Full text ( memento of the original from October 17, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / bg66.soc.i.kyoto-u.ac.jp
  10. ^ A b Tim M. Berra: Freshwater Fish Distribution . The University of Chicago Press, Chicago 2007, ISBN 978-0-226-04442-2 , pp. 179 .
  11. ↑ Stephen R. Humphrey, James R. Bain: Endangered Animals of Thailand . CRC Press, 1990, ISBN 978-1-877743-07-8 .
  12. ↑ Guidelines for Application of IUCN Red List Criteria at Regional Levels: Version 3.0 . 2003, ISBN 978-2-8317-0738-9 , pp. 23 .
  13. ↑ JNCC Report No. 379: Checklist of fish and invertebrates listed in the CITES appendices and in EC Regulation No. 338/97 , Joint Nature Conservation Committee, 2005 ( PDF, 2.4MB )
  14. ^ Entry in the IUCN Red List
  15. ↑ a b A. Lopez (Ed.): MWBP working papers on Mekong Giant Catfish, Pangasianodon gigas . Mekong Wetlands Biodiversity Conservation and Sustainable Use Program, Vientianne 2006 (English, full text [PDF; 4.2 MB ]).
  16. ↑ L. Pouyard, GG Teugels, R. Gustiano, M. Legendre: Contribution to the phylogeny of pangasiid catfishes based on allozymes and mitochondrial DNA . In: Journal of Fish Biology . tape 56 , no. 6 , 2000, pp. 1509–1538 , doi : 10.1111 / j.1095-8649.2000.tb02161.x .

Web links

Commons : Mekong giant catfish ( Pangasianodon gigas )  - Collection of images, videos and audio files
This version was added to the list of articles worth reading on October 15, 2009 .