Discus fish

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Discus fish
Symphysodon aequifasciatus

Symphysodon aequifasciatus

Systematics
Ovalentaria
Order : Cichliformes
Family : Cichlids (Cichlidae)
Subfamily : Cichlinae
Tribe : Heroini
Genre : Discus fish
Scientific name
Symphysodon
Heckel , 1840

Discus fish or discus cichlids ( Symphysodon ) are a genus of freshwater fish in the family of cichlids from the Amazon river system in tropical South America .

Appearance

Discus fish differ from all other cichlids (with the exception of the closely related angelfish ) by their strongly compressed and high-backed physique. Together with the non-elongated, rounded dorsal and anal fins , which can hardly be put on due to their strong scaling, the long, rounded forehead profile and the very short snout with a small mouth and bulging lips, they offer the appearance of the eponymous discus disc. The transparent, relatively large pectoral fins that reach up to the middle of the body are also rounded. In contrast, the narrow and long ventral fins taper to a point. The respective body drawing continues in the unpaired and pelvic fins. There is always a wide vertical stripe over the dark brown to bright red eye. A total of seven to nine further transverse strips are distributed over the body; the last one is always due to the also strongly scaled tail fin base . Depending on the type or occurrence, these bands appear more or less intensely depending on the mood. Again differently according to type or occurrence, blue and wavy horizontal stripes of different intensity appear. Sometimes only on the forehead or in the head area, sometimes just below the dorsal fin, but also spread over the whole body. Few populations have reddish speckles between the high lateral line and the anal fin. Discus cichlids have a significantly reduced dentition of the pharynx. But the symphysis, the interface between the two jaws, has few single-pointed teeth. The scientific generic name refers to this special anatomical feature . The size of adult animals in the wild is usually between 12 and 16 centimeters, but can also be up to 20 centimeters when bred or under optimal environmental or housing conditions.

Occurrence

Symphysodon aequifasciatus

Its previously known, very large area of ​​distribution in the Amazon extends from the Peruvian city ​​of Iquitos in the west to the beginning of the Amazon delta off the Brazilian Atlantic coast . From the main stream, the so-called Solimoes , discus cichlids have opened up the lower reaches of all major Amazon tributaries. Within this vast area, close to the equator , the deposits are not closed. They are close together, but remain predominantly island-like. This has led to the formation of very differently drawn and colored populations and to the scientific description of several species and subspecies .

ecology

The ecology of the natural habitat of the discus cichlids has been very thorough and careful studies by the Freiburg limnologist and fishery biologist Rolf Geisler since the 1960s . Geisler found that discus cichlids colonize all types of water (white, clear, black and mixed water) in the Amazon. But the milieu is always relatively hostile to life, i.e. very warm (at least 29 to 34.2 ° C), in the acidic range ( pH values between 4 and 6.5) and largely free of dissolved minerals and organic pollution ( electrical conductivity <30 µS / cm, total hardness <1 ° dGH, total ammonium content <0.5 mg / l).

Discus cichlids live in the bank and floodplain areas of their residential waters, but not on shallow banks, but only on steep banks with a water depth of at least 1.5 m. Their habitats are usually free of vegetation, but are structured by roots, dead wood, thick layers of fallen leaves or flooded land vegetation and are therefore rich in cover. Occasionally floating plants and floating islands cover their biotopes . Discus cichlids are also found over rugged and sharp-edged lava reefs and in rocky, niche-rich shore zones.

According to the results of gastric examinations that Geisler carried out on discus cichlids from different populations, they mainly feed on zooplankton , insect larvae , small bristle worms , small freshwater shrimp and plant detritus . Mayflies , mosquitoes and tufted mosquitoes make up a particularly large proportion of the diet . Food that is hidden in the ground or under plant-based substrate is exposed by blowing on with a targeted water jet and then absorbed. Apparently all discus cichlids are infested with parasites . Intestinal flagellates and gill worms in particular are found to be regular companions. However, they do not constitutionally harm healthy host animals .

Reproduction

Discus cichlids reach sexual maturity between seven and twelve months. They live in more or less large social associations, in schools , from which pairs are formed. The laying tube of the female, which protrudes clearly during courtship , is the only reliable feature for distinguishing the sexes . According to Geisler, fertility is related to the availability of certain nutritional animals (freshwater shrimp of the genus Macrobrachium ), which influence the hormonal balance of the fish. After only a few hours of ritualized pre-baling, a spawning substrate is selected, which is always an animate (plant part) or inanimate (wood, stone) vertical surface. The selected spawning site is thoroughly cleaned by the pair with the mouths. The larvae hatch after about two and a half days from the up to 300 eggs (average length 1.4 mm, width 1.17 mm), which adhere to the substrate with short adhesive processes. Both parents support the hatching process by chewing the larvae out of the egg shell. Then the larvae, which also have organs of attachment, are again attached to a vertical surface in a grape-like manner. Until they swim free, they are reburied several times by both parents. About four days after hatching, the larvae swim free and immediately start feeding. According to Blüm & Fiedler, brood care behavior is controlled by the male sex hormones testosterone and androsterone until the actual spawning process , while spawning and larval care is controlled by the pituitary hormone prolactin . The prolactin not only has an ethological effect on the brood care and social behavior of the discus cichlids, it also leads to a slight swelling of the epidermis and stimulates the reproduction of mucous cells. This is important because the larvae feed on their parents' epidermis: they bite tiny particles from the parental epidermis , in which carbohydrates and fats accumulate during the brood care period . This type of larval feeding has also been observed in other cichlids ( Pterophyllum altum , Australoheros facetum and Astronotus sp. ), But it is only so unique in the discus cichlids. When feeding young fish, the parents regularly take turns, stimulating their offspring to change through movement and color stimuli. From about the fourth day of life, the discus larvae begin to eat other food, but are dependent on the parent's skin as their basic food for at least four weeks.

Systematics

On November 2, 1833, the Austrian explorer Johann Natterer caught the only type specimen of the cichlid genus first described by Johann Jakob Heckel in 1840 as the Symphysodon on the lower Rio Negro in the area of ​​the Brazilian city ​​of Manaus . The specimen is also the holotype of the so-called Real Discus Symphysodon discus Heckel, 1840.

Subsequently, other species and subspecies were scientifically described, but their reliability was always questioned and hotly debated. The reason for this is that the classic metric and meristic (countable) determination criteria (for example, the survey of the fin rays, vertebrae and scale numbers) do not lead to clear delineations in discus cichlids. These characteristics are so variable within the genus, within the described species and within the huge range that they apply simultaneously to all described species.

Symphysodon discus

Also by Michael Kokoscha and Hartmut Greven 1996 at the Heinrich-Heine University in Dusseldorf undertaken isoenzyme electrophoresis only led to a surprising result: it "speaking not mind all the discus with the older name of S. discus to name."

There are currently three to five species:

Symphysodon Heckel 1840.

with the species

  • Symphysodon aequifasciatus Pellegrin 1904. Syn .: Symphysodon discus var. Aequifasciata Pellegrin 1904, Symphysodon aequifasciata aequifasciata Schultz 1960. Brown phenotype; Amazon east of the Rio Negro estuary.
  • Symphysodon tarzoo Lyons, 1959. Syn .: Symphysodon discus tarzoo Lyons 1959, green phenotype; western Amazon.
  • Symphysodon haraldi Schultz 1960. (Bleher et al.) Syn .: S. aequifasciata haraldi Schultz 1960, S. aequifasciata axelrodi Schultz 1960, or Symphysodon sp. 1 (Amado et al.), Blue phenotype; central Amazon.

Importance to humans

In the Amazon, freshwater fish are the most important source of animal protein for many people . Discus cichlids are also fished for this purpose, harpooned or caught with nets. However, their share in the total amount of freshwater fish caught for consumption does not play a significant role. But for a relatively large number of families, live catches are an important source of income for the aquarium hobby and often the only livelihood.

Discus cichlids from nature, so-called wild-caught fish, have been very popular and dearly traded aquarium fish for around sixty years. The wish of many aquarium enthusiasts to care for and even breed discus cichlids has had a decisive influence on this hobby as a whole. Since these cichlids need particularly clean, almost germ-free and acidic water and their successful care depends on the management and prophylaxis of numerous bacterial and parasitic diseases, they have decisively stimulated the further development of aquarium filter technology, water treatment, feed production and fish pharmacy, for example. Most studies on the biology and ecology of their habitats are based predominantly on the aquaristic interest in these fish. A dreaded highly contagious disease in aquariums is the discus disease .

Breeding form "Leopard Snakeskin"

With the development of artificial breeding methods, selective shape and color breeding began in the 1970s . Numerous cultivated forms have imaginative names such as "Ghost", "Blue Diamond", "Marlboro Red" or "Tangerine Dream", are already showing clear signs of domestication and are evaluated according to their appearance in international competitions in Europe, the USA and Southeast Asia. Only one of these cultivated forms is inherited : “Pigeon Blood”, which is based on a genetic defect associated with massive tissue deformations of the epidermis.

swell

  • H. Axelrod: Fishes of the sacred Rio Unini, Brazil. In: Trop. Fish hobby. 38 (10), 1989, pp. 38-57.
  • M. Blanc: Catalog des types de Poissons de la famille des Cichlidae en collection au Muséum national d'Histoire naturelle. In: Bulletin du Muséum National d'Histoire Naturelle. (Series 2) v. 34, no. 3, 1962, pp. 202-227. 69 (suppl. B), 1962, pp. 200-211.
  • V. Blüm, K. Fiedler: Prolactin-sensitive structures in the fish brain. In: Fortschr. Zool. 22, 1974, pp. 155-166.
  • WE Burgess: Studies on the family Cichlidae: 10. New information on the species of the genus Symphysodon with the description of a new subspecies of S. discus Heckel. In: Trop. Fish hobby. 29 (7), 1981, pp. 32-42.
  • PL Fuller, LG Nico, JD Williams: Nonindigenous fishes introduced into inland waterways of the United States. (= American Fisheries Society Special Publication. 27). 1999.
  • T. Hrbek, M. Villar Amado, I. Pires Farias: Evolutionarily significant units and species of the Amazonian discus fish ( Symphysodon. Cichlidae) and their names. In: DCG information . Special issue 7, September 2011.
  • SO Kullander: Cichlid fishes of the Amazon River drainage of Peru. In: Swedish Museum of Natural History. 1986, ISBN 91-86510-04-5 .
  • H. Ortega, RP Vari: Annotated checklist of the freshwater fishes of Peru. (= Smithsonian Contributions to Zoology. No. 437) 1986, OCLC 831060514 . (German)
  • RE Reis, SO Kullander, CJ Ferraris, Jr .: Check list of the freshwater fishes of South and Central America. CLOFFSCA, 2003, ISBN 85-7430-361-5 .
  • C.-P. Steinle: The king is dead ...! Thoughts on the discus cichlid. In: D. Aqu. u. Terr. Z. 35, 1982, pp. 361-364, 416-419.

Individual evidence

  1. ↑ a b c R. Geisler, S. Rönsch: The current state of our knowledge about the discus fish Symphysodon aequifasciata axelrodi. In: D. Aqu. u. Terr. Z. (DATZ) 14, 1961, pp. 228-232, 260-264, 292-295, 324-328.
  2. ↑ a b c R. Geisler: The current state of our knowledge about the discus fish Symphysodon aequifasciata axelrodi. In: D. Aqu. u. Terr. Z. 23, 1970, pp. 9-13, 40-44, 75-78, 131-133, 171-174, 196-198.
  3. ↑ V. Blüm, K. Fiedler: The influence of prolactin on the brood care behavior of Symphysodon aequifasciata haraldi LP Schultz (Cichlidae, Teleostei). In: Naturw. 51, 1964, pp. 149-150.
  4. ↑ M. Kokoscha, H. Greven: Is there only one kind? Isoenzyme electrophoresis in discus fish. In: D. Aqu. u. Terr. Z. special issue “Diskus”, 1996, pp. 20-21.
  5. ↑ JS Ready, EJ. Ferreira, SO Kullander : Discus fishes: mitochondrial DNA evidence for a phylogeographic barrier in the Amazonian genus Symphysodon (Teleostei: Cichlidae). In: J. Fish Biol. 69, Suppl. B, 2006, pp. 200-211. doi: 10.1111 / j.1095-8649.2006.01232.x
  6. ↑ Discus fish on Fishbase.org (English)
  7. ↑ a b Manuella Villar Amado, Izeni P. Farias, Tomas Hrbek: A Molecular Perspective on Systematics, Taxonomy and Classification Amazonian Discus Fishes of the Genus Symphysodon. In: International Journal of Evolutionary Biology. Volume 2011, Article ID 360654. doi: 10.4061 / 2011/360654
  8. ^ Heiko Bleher , Kai N. Stölting, Walter Salzburger, Axel Meyer : Revision of the genus Symphysodon Heckel, 1840 (Teleostei: Perciformes: Cichlidae) based on molecular and morphological characters. In: aqua, International Journal of Ichthyology. v. 12, no. 4, 2007, pp. 133-174.
  9. ↑ a b J. J. Heckel: Johann Natterer's new river fish from Brazil, described according to the discoverer's observations and reports (First Section, The Labroids). In: Annals of the Vienna Museum of Natural History. v. 2, 1840, pp. 325-471, Pls. 29-30.
  10. ^ J. Pellegrin: Contribution à l'étude anatomique, biologique et taxinomique des poissons de la famille des cichlidés. In: Memoires Societe Zoologique de France. v. 16, no. 2-4, 1904, pp. 41-400, Pls. 4-7.
  11. ^ E. Lyons: Symphysodon discus Tarzoo. New blue discus electrify aquarium world. In: Tropicals Magazine. v. 4 and cover, 1959, pp. 6-8, 10.
  12. ↑ LP Schultz: A review of the pompadour or discus fishes, genus Symphysodon of South America. In: Trop. Fish hobby. 8 (10), 1960, pp. 5-17.

Web links

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