Real discus
| Real discus | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Common discus cichlid ( Symphysodon discus ) |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Symphysodon discus | ||||||||||||
| Heckel , 1840 |
The real discus , real discus cichlid or Heckel discus and, more rarely, pompadur fish ( Symphysodon discus ), is one of currently three species in the discus cichlid genus from the Amazon river area in tropical South America .
features
All species of the genus Symphysodon are distinguished by their unmistakable and eponymous disc or disc-like body shape. The real discus cichlid differs from the other two species only in its coloration and pattern. The most striking features are a dark, often bluish, wave-like line drawing that covers both sides of the body and a wide, dark brown vertical band that extends from the dorsal to the anal fin at the beginning of the rear half of the body . Several less pronounced and slightly lighter vertical stripes, the first of which is above the eye, are also typical of the species.
Classical metric and meristic distinguishing features to the sister species do not exist. Symphysodon discus has lower scale counts than many populations of Symphysodon aequifasciatus and Symphysodon haraldi . But the range of variation in these taxonomic features is so great in all three species that many congruent or overlapping diagnoses occur.
distribution
While the genus occurs from the Peruvian jungle town of Iquitos to the Amazon delta along the entire main stream (Rio Solimões and Rio Amazonas), the distribution of the real discus cichlid is clearly limited. Its habitats are in the lower reaches of the Rio Negro , Rio Trombetas and the Rio Abacaxis . The Swedish ichthyologist Sven. O. Kullander found that although the common discus cichlid lives within the large range of its two sister species, it has not been found syntopically with Symphysodon aequifasciatus or Symphysodon haraldi anywhere .
ecology
According to the studies of the American biologist and publisher Herbert R. Axelrod and the Freiburg limnologist and fishery biologist Rolf Geisler , Symphysodon discus is not a black water inhabitant . All Amazonian tributaries in which real discus cichlids have been detected carry a mixture of white and clear water with water temperatures between 28 and 30 ° C, pH values of 4.2 to 6.2, and an electrical conductivity of up to a maximum of 25 µS / cm a total hardness of less than 0.5 ° dGH. The total nitrogen content does not exceed 0.5 mg / l. The milieu is therefore poor in nutrients and relatively hostile to life. Aquatic plants cannot exist in such conditions. That is why real discus cichlids hide in the bank areas, alluvial land and floodplain areas between roots, dead wood and flooded land vegetation.
Their main diet is made up of zooplankton , insect larvae , small bristle worms , small freshwater shrimp and vegetable detritus . Mayflies , mosquitoes and tufted mosquitoes make up a particularly large proportion of the diet . Nourishing animals that hide in the ground or under plant-based substrate are exposed by blowing on with a targeted water jet and then taken in.
Reproduction
The reproductive behavior is the same for all Symphysodon species: They reach sexual maturity between seven and twelve months of age. They live in more or less large social associations, in schools , from which pairs are formed. The laying tube of the female, which clearly protrudes during courtship, is the only reliable feature for differentiating 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 common discus cichlid Symphysodon discus Heckel, 1840.
The type locality is not precisely defined. Natterer writes "" Barra do Rio-negro ", which Kullander 163 years later defines as" "somewhere on the lower Rio Negro. The not fully grown holotype is under the collection number 35612 in the Natural History Museum Vienna and has a standard length of 98.6 millimeters. The true discus cichlid can only be distinguished from its sister species by the pattern of living specimens preserved in formalin. All classical criteria for differentiating between species and even modern methods of isoenzyme electrophoresis suggest that all known discus cichlids belong to only one species, namely Symphysodon discus .
In the Rio Canuma and Rio Abacaxis, Axelrod found a population of the common discus cichlid , which Burgess described in 1981 as the subspecies Symphysodon discus willischwartzi . However, Kullander showed that the number of flank scales used to distinguish them lie within the counts of the primary species and put the subspecies in the synonymy of the nominate form . Again Axelrod presented a differently colored form of the real discus cichlid from the Rio Unini, which has a very striking blue color on the head. It turned out, however, that this characteristic of the fish called “Cabeca azul” (“Blue-headed discus”) depends on the mood.
At the moment one follows this not final representation after Kullander:
- Symphysodon discus Heckel 1840.
Synonym : Symphysodon discus willischwartzi Burgess 1981.
Importance to humans
In Brazil , all freshwater fish are the most important sources of animal protein for many people . Real discus cichlids are also caught, harpooned or caught with nets for this purpose. However, their share in the total amount of freshwater fish caught for consumption plays a very minor role. But for a relatively large number of people, live catches are an important source of income for aquaristics and often the only livelihood. Real natural discus cichlids, so-called wild-caught fish, have been in great demand for around sixty years and are still dearly traded today.
Aquaristics
Keeping and care
Discus should be kept in the largest possible, high aquariums with light planting and a few root stocks. There must be enough free swimming space and the lighting should not be too bright. The animals form territory during the spawning season, otherwise they are very peaceful towards other fish. The species does not root. Live feed of any kind can be offered as feed, flake feed is not always accepted.
Legal regulation in Austria
In Austria, the minimum requirements for keeping fish are defined in Regulation 486 in Section 7 and its Annex 5. See also the Wikipedia entry ornamental fish .
Especially for discus, the following applies: The fish should be kept together with other fish so that they show their typical behavior. In addition to these by-fish, at least five animals of this species (each pair) must be kept together. In addition, the following limit values must be observed:
| value | annotation | |
|---|---|---|
| Minimum size of the aquarium | 120 × 40 × 50 | Length × width × height in [cm] |
| Area for the water temperature | 26 - 31 | Degrees Celsius [° C] |
| Area for the water hardness | 0-15 | Degree of German total hardness [⁰dGH] |
| PH range | 5.0 - 7.0 | Acidity |
| Maximum value of nitrate | 50 | [mg / l] |
swell
- H. Axelrod: Fishes of the sacred Rio Unini, Brazil. In: Trop. Fish hobby. 38 (10), 1989, pp. 38-57.
- 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.
- 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.
- R. Geisler: The current state of our knowledge about the discus fish Symphysodon aequifasciata axelrodi. In: D. Aqu. u. Terr. Z. (DATZ) 23, 1970, pp. 9-13, 40-44, 75-78, 131-133, 171-174, 196-198.
- JJ Heckel: Johann Natterer's new river fish from Brazil described after the discoverer's observations and reports (first section, Die Labroiden). In: Annals of the Vienna Museum of Natural History. v. 2, 1840, pp. 325-471, Pls. 29-30.
- M. Kokoscha, H. Greven: Is there only one kind? Isoenzyme electrophoresis in discus fish. In: D. Aqu. u. Terr. Z. (DATZ). Special issue “Diskus”, 1996, pp. 20–21.
- SO Kullander: Cichlid fishes of the Amazon River drainage of Peru. Swedish Museum of Natural History, 1986, ISBN 91-86510-04-5 .
- SO Kullander: Another overview of the discus fish, genus Symphysodon Heckel. In: D. Aqu. u. Terr. Z. (DATZ). Special issue "Diskus", 1996, pp. 10-19.
- JS Ready, EJG Ferreira, SO Kullander: Discus fishes: mitochondrial DND evidence for a phylogeographic barrier in the Amazonian genus Symphysodon (Teleostei: Cichlidae). In: Journal of Fish Biology. 2006.
- RE Reis, SO Kullander, CJ Ferraris, Jr .: Check list of the freshwater fishes of South and Central America. Porto Alegre 2003, ISBN 85-7430-361-5 .
- C.-P. Steinle: The king is dead ...! Thoughts on the discus cichlid. In: D. Aqu. u. Terr. Z. (DATZ) 35, 1982, pp. 361-364, 416-419.
- V. Blum, K. Fiedler: Harmonic control of some reproductive behavior in some cichlid fish. In: Gen. Compo Endocrinol. 5, 1965, pp. 186-196.
Web links
- Real discus on Fishbase.org (English)
Individual evidence
- ^ Rüdiger Riehl, Hans A. Baensch: Aquariums Atlas . Ed .: Hans A. Baensch. 15th edition. tape 1 . Mergus, Melle 2006, ISBN 3-88244-227-1 , pp. 772 .
- ↑ BGBl 486., 2nd Animal Husbandry Ordinance. Retrieved February 9, 2019 .
- ↑ a b BGBL II No. 486 Annex 5, minimum requirements for keeping fish. Retrieved February 9, 2019 .