HOME

TheInfoList



OR:

''Symphysodon'', colloquially known as discus, is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
cichlids Cichlids are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, the Labroidei, along with the wrasses ( Labridae), in the order Perciformes, but molecular studies have contradicted th ...
native to the
Amazon river basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Bolivi ...
in South America. Due to their distinctive shape, behavior, and bright colors and patterns, discus are popular as freshwater aquarium fish, and their aquaculture in several countries in Asia is a major industry.Sands D (1994) ''A fishkeepers guide to Central American cichlids.'' Tetra Press. Belgium pg 59-60. They are sometimes referred to as pompadour fish. The discus fish has attracted a cult following of collectors and has created a multimillion dollar international industry complete with shows, competitions, and reputed online breeders.


Species

Following a review published in 2006, three species are recognized by FishBase: * ''
Symphysodon aequifasciatus ''Symphysodon aequifasciatus'', the blue discus or brown discus, is a species of cichlid native to rivers of the eastern and central Amazon Basin downriver from the Púrus Arch. This discus is found in black-, clear- and whitewater, but its p ...
'' Pellegrin, 1904 (blue discus or brown discus) * '' Symphysodon discus'' Heckel, 1840 (red discus or Heckel discus) * ''
Symphysodon tarzoo ''Symphysodon tarzoo'', the green discus, is a species of cichlid native to rivers of the western Amazon Basin upriver from the Purus arch, although it occasionally occurs downstream. An introduced population in the Nanay River is based on st ...
'' E. Lyons, 1959 (green discus)


Taxonomy

Discus are fish from the genus ''Symphysodon'', which currently includes the species ''S. aequifasciatus'', ''S. discus'' and ''S. tarzoo'', based on a taxonomic review published in 2006. A review published in 2007 largely came to the same result, but differed in
nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally ag ...
, as the species called ''S. tarzoo'' in the 2006 study was called ''S. aequifasciatus'' in the 2007 study, and ''S. aequifasciatus'' in 2006 was ''S. haraldi'' in 2007. Further arguments have been made that ''S. tarzoo'' was not described in accordance with ICZN rules and thus should be considered invalid and replaced with ''S. haraldi'', currently considered a synonym of ''S. aequifasciatus'' by FishBase. Other species and subspecies have been proposed, but
morphometric Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...
data (unlike in ''
Pterophyllum ''Pterophyllum'' is a small genus of freshwater fish from the family Cichlidae known to most aquarists as angelfish. All ''Pterophyllum'' species originate from the Amazon Basin, Orinoco Basin and various rivers in the Guiana Shield in tropical ...
'', the freshwater angelfish) varies as much between individuals from one location as across the whole range of all discus fish species. ''S. tarzoo'' was described in 1959 and applies to the red-spotted western population. ''S. aequifasciatus'' and ''S. discus'', meanwhile, seem to hybridise frequently in the wild or have diverged recently, as they lack mitochondrial DNA
lineage sorting Incomplete lineage sorting, also termed hemiplasy, deep coalescence, retention of ancestral polymorphism, or trans-species polymorphism, describes a phenomenon in population genetics when ancestral gene copies fail to coalesce (looking backwards ...
but differ in color pattern and have dissimilar
chromosomal translocation In genetics, chromosome translocation is a phenomenon that results in unusual rearrangement of chromosomes. This includes balanced and unbalanced translocation, with two main types: reciprocal-, and Robertsonian translocation. Reciprocal translo ...
patterns. ''S. discus'' occurs mainly in the Rio Negro. Whether ''S. haraldi'' is indeed distinct from ''S. aequifasciatus'' remains to be determined; if valid it is widespread but it might just be a
color morph In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative ''phenotypes'', in the population of a species. To be classified as such, morphs must occupy the same habitat at the s ...
. A molecular study in 2011 found five main groups, which generally matched previously recognized
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
s. They recognized them as
evolutionarily significant unit An evolutionarily significant unit (ESU) is a population of organisms that is considered distinct for purposes of conservation. Delineating ESUs is important when considering conservation action. This term can apply to any species, subspecies, geo ...
s and species. Their assigning of scientific names to species differed to some extent from that used by earlier authors: Heckel (''S. discus''; Rio Negro, upper Uatumã,
Nhamundá Nhamundá is the easternmost municipality in the Brazilian state of Amazonas. Its population was 21,443 (2020) and its area is 14,106 km².IBGE The Brazilian Institute of Geography and Statistics ( pt, Instituto Brasileiro de Geografia e ...
,
Trombetas The Trombetas is a large river on the northern side of the Amazon River. Course The Trombetas is long, and is navigable by 500 ton vessels for a stretch of . The Trombetas river gives birth to very many rivers, including the Anamu river. It is ...
and Abacaxis), green (''S. tarzoo''; West Amazon drainages upriver from the
Púrus Arch The Púrus Arch ( pt, Arco do Purus) is a basement high in Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 mil ...
, blue (''S.'' sp. 1; central Amazon from Purus arch to the
Meeting of Waters The Meeting of Waters ( pt, Encontro das Águas) is the confluence between the dark ( blackwater) Rio Negro and the pale sandy-colored (whitewater) Amazon River, referred to as the Solimões River in Brazil upriver of this confluence. For th ...
), brown (''S. aequifasciatus''; East Amazon downriver from Meeting of Waters), Xingu group (''S.'' sp. 2; Xingu and
Tocantins Tocantins () is one of the 26 states of Brazil. It is the newest state, formed in 1988 and encompassing what had formerly been the northern two-fifths of the state of Goiás. Tocantins covers and had an estimated population of 1,496,880 in 20 ...
). The Xingu group currently lacks a scientific name, but it is possible that the correct name for the blue is ''S. haraldi''. This taxonomy with four described valid species, ''S. discus'', ''S. tarzoo'', ''S. haraldi'' and ''S. aequifasciatus'', has been adopted by the
Catalog of Fishes Catalog of Fishes is a comprehensive on-line database and reference work on the scientific names of fish species and genera. It is global in its scope and is hosted by the California Academy of Sciences. It has been compiled and is continuously u ...
. Some hybridisation occurs (or has occurred) between the brown discus and neighbouring forms, but overall they maintain their separate evolutionary trajectories. In addition to the wild discus, several captive variants achieved by
selective breeding Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant m ...
exist. Based on RAPD sequences, the captive variants popularly known as turquoise, pigeon, ghost, cobalt and solid red are derived from wild green, blue and brown discus (not Heckel discus).


Description

Like cichlids from the genus ''
Pterophyllum ''Pterophyllum'' is a small genus of freshwater fish from the family Cichlidae known to most aquarists as angelfish. All ''Pterophyllum'' species originate from the Amazon Basin, Orinoco Basin and various rivers in the Guiana Shield in tropical ...
'' (angelfish), all ''Symphysodon'' species have a laterally compressed body shape. In contrast to ''Pterophyllum'', however, extended finnage is absent giving ''Symphysodon'' a more rounded shape. It is this body shape from which their common name, "discus", is derived. The sides of the fish are frequently patterned in shades of green, red, brown, and blue. Some of the more brightly marked variants are the result of selective breeding by
aquarist An aquarist is a person who manages aquariums, either professionally or as a hobby. They typically care for aquatic animals, including fish and marine invertebrates. Some may care for aquatic mammals. Aquarists often work at public aquariums. They ...
s and do not exist in the wild. Discus typically reach up to in length, but captives have been claimed to reach . Adults generally weigh . No clear
sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
is seen for this fish, but males may reach a larger size than females. In breeding form varieties, solid red discus (red melon, red cover) females are generally redder than males.


Behavior

''Symphysodon'' spp. are highly social, typically occurring in groups that may number many dozens of individuals, which is unique among cichlids of the Americas. When breeding, the pair moves away from the group, possibly to reduce the risk of cannibalism of the young. As with most cichlids, brood care is highly developed with both the parents caring for the young. Additionally, adult discus produce a secretion through their skin, on which the
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
e live during their first 4 weeks. During the first two weeks, the parents stay near their young allowing them to feed easily. In the last 2 weeks, they swim away, resulting in the young being gradually "weaned off" and starting to fend for themselves. Although rare in fish, more than 30 species of cichlids are known to feed their young with skin secretion to various extent, including ''
Pseudetroplus The orange chromide (''Pseudetroplus maculatus'') is a species of cichlid fish that is endemic to freshwater and brackish streams, lagoons and estuaries in southern India and Sri Lanka.Pethiyagoda, R., Maduwage, K. & Manamendra-Arachchi, K. (2 ...
'' and ''
Uaru ''Uaru'' is a small genus of cichlids found in blackwater and whitewater habitats in the upper Orinoco and the Amazon basin. Etymology The name ''Uaru'' comes from the Amazon word for toad. Species There are currently two recognized species in ...
'' species. Sexual maturity is reached in a year. Research has shown that, through this unique parental care behaviour (discus parents feeding their progeny with skin mucus), discus fish parents transmit key microorganisms to their fry. This parent-to-offspring transmission of important microorganisms might explain the high survival rate of discus fry raised with their parents, compared to the low survival rate of progeny raised artificially by fish breeders (e.g. on egg yolk, brine shrimp, or other replacement foods). ''Symphysodon'' spp. primarily feed on algae, other plant material, and detritus (
periphyton Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs (German "surface growth" or "overgrowth") refers to the col ...
), but also eat small
invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...
. Invertebrates can make up 38% of the stomach content in wild ''S. aequifasciatus'' during the high-water season, but this decreases during the low-water season, and year-round it is generally lower in the other species. Unlike more predatory cichlids, ''Symphysodon'' spp. have relatively long intestines typical of a herbivore or omnivore.


Distribution and habitat

''Symphysodon'' species inhabit the margins of floodplain
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s and
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
s in the lowland Amazon basin, where they are part of the highly diverse Neotropical fish fauna. ''S. discus'' is restricted to blackwater habitats, but periodically these may experience brief floods of
white water Whitewater forms in a rapid context, in particular, when a river's gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that froths, making the water appear opaque and w ...
. ''S. tarzoo'' is found in both black and white water, and ''S. aequifasciatus'' also occurs in clearwater. Because of their preference for
lentic A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems (''lentic'' re ...
habitats such as floodplains and
flooded forest Freshwater swamp forests, or flooded forests, are forests which are inundated with freshwater, either permanently or seasonally. They normally occur along the lower reaches of rivers and around freshwater lakes. Freshwater swamp forests are found ...
s, white water inhabited by discus contains little suspended material (unlike main sections of whitewater rivers). The three species of ''Symphysodon'' have different geographic distributions. ''S. aequifasciatus'' occurs in the East Amazon downriver from the Purus arch and ''S. tarzoo'' in the West Amazon upriver from the Purus arch. In contrast, the distribution of ''S. discus'' appears to be limited to the lower reaches of the Rio Negro, upper Uatumã,
Nhamundá Nhamundá is the easternmost municipality in the Brazilian state of Amazonas. Its population was 21,443 (2020) and its area is 14,106 km².IBGE The Brazilian Institute of Geography and Statistics ( pt, Instituto Brasileiro de Geografia e ...
,
Trombetas The Trombetas is a large river on the northern side of the Amazon River. Course The Trombetas is long, and is navigable by 500 ton vessels for a stretch of . The Trombetas river gives birth to very many rivers, including the Anamu river. It is ...
,and
Abacaxis River The Abacaxis River is a river in the Amazonas state in north-western Brazil. It is located east of the Madeira River and these two are connected via the Paraná Urariá. Through the Paraná Urariá it is also connected to several other smaller ...
s. The
Nanay River The Nanay River is a river in northern Peru. It is a tributary of the Amazon River, merging into this river at the city of Iquitos. The lower part of the Nanay flows to the north and west of the city, while the Itaya River flows to the south an ...
in far western Amazonas is outside the native range; discus in this river were introduced from stock originating in the
Tefé Tefé, known in early accounts as Teffé, is a municipality in the state of Amazonas, northern Brazil. Location Tefé is located about 525 km by air or 595 km by river to the west of Manaus on the south bank of the Rio Solimões (th ...
area by an aquarium exporter more than 30 years ago. A significant number of discus now live in fish farms in
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainlan ...
. These discus go to home aquaria around the world.


Home aquarium

Discus are kept by fishkeepers in the home aquarium, where they are valued for their striking appearance. They are considered difficult to keep, due to strict requirements for water quality and the need to be kept in groups. Breeders have selected for individuals with more adaptability to tap water conditions. In home aquariums, discus live for an average of 10 years, but can live up to 15 years, and can grow up to 8 inches. Like many fish in the home aquarium, they will eat almost anything that fits within their mouth. Due to their size, they often require a minimum 55–75 gallon aquarium. Each year the World Discus Competition takes place in
Guangzhou Guangzhou (, ; ; or ; ), also known as Canton () and alternatively romanized as Kwongchow or Kwangchow, is the capital and largest city of Guangdong province in southern China. Located on the Pearl River about north-northwest of Hong Kon ...
, China. The North American Discus Association focuses on both supporting hobbyists and helping to support wild discus.


See also

* List of freshwater aquarium fish species * Project ''Piaba''


References


External links


Discus Society MalaysiaFanatik-Discus-International informations, pictures, videos about discus fish
{{DEFAULTSORT:Discus (Fish) Heroini Taxa named by Johann Jakob Heckel