Discus (fish) - WikiHQ

Symphysodon (colloquially known as discus or discus fish) is a genus of cichlids native to the Amazon river basin in Brazil. Due to their distinctive shape, calm behavior, many bright colors and patterns, and dedicated parenting techniques, discus are popular as freshwater aquarium fish, and their aquaculture in several countries in Asia (notably Thailand) is a major industry. 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 reputable online breeders.

Etymology

The genus name "symphysodon", which was coined in 1840 by Johann Jakob Heckel, refers to the unusual symphysis of the teeth (-odon from Greek ὀδών, tooth).

Species

Following a review published in 2006, three species are recognized by FishBase:

{| class="wikitable sortable"

!Image !! Name !! Distribution

|120px|| Symphysodon aequifasciatus Pellegrin, 1904 (blue discus or brown discus)||central Amazon Basin

|thumb||| Symphysodon discus Heckel, 1840 (red discus or Heckel discus)|| Amazon Basin

|120px|| Symphysodon tarzoo E. Lyons, 1959 (green discus)|| western Amazon Basin

Taxonomy

thumb|Symphysodon discus

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, 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 data (unlike in Pterophyllum, 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 but differ in color pattern and have dissimilar chromosomal translocation 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.

thumb|Two captive variants (orange and solid turquoise)

A molecular study in 2011 found five main groups, which generally matched previously recognized phenotypes. They recognized them as evolutionarily significant units 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, Trombetas and Abacaxis), green (S. tarzoo; West Amazon drainages upriver from the Purus Arch, blue (S. sp. 1; central Amazon from Purus Arch to the Meeting of Waters), brown (S. aequifasciatus; East Amazon downriver from Meeting of Waters), Xingu group (S. sp. 2; Xingu and Tocantins). Some hybridisation occurs (or has occurred) between the brown discus and neighbouring forms, but overall they maintain their separate evolutionary trajectories.

Description

thumb|alt=Red Turquoise Discus|Red turquoise discus

Like cichlids from the genus Pterophyllum (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 aquarists and do not exist in the wild. Discus typically reach up to in length, but captives have been claimed to reach . Adults generally weigh . Additionally, adult discus produce a secretion ("discus milk") through their skin, on which the larvae 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. Sexual maturity is reached in a year. 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).

Water quality and pH requirements

Discus fish are highly sensitive to water chemistry, with their ideal potential of hydrogen (pH) requirements heavily dependent on whether the individuals are captive-bred or wild-caught. Historically, wild specimens are native to the soft, highly acidic blackwater tributaries of the Amazon basin, where pH values frequently range between 5.0 and 6.0. In contrast, the vast majority of discus commercially available in the modern aquarium hobby are captive-bred strains. These domesticated fish exhibit significantly higher environmental plasticity and can be safely maintained in more neutral water chemistry, typically between 6.0 and 7.0 pH, though they can adapt to values as high as 7.5 provided the parameters remain stable.

Water stability is considered far more critical to the long-term health of the fish than achieving a specific numerical target, as rapid pH fluctuations can induce severe physiological stress, compromise the immune system, or lead to acute alkalosis or acidosis. During the reproductive and early life stages, water parameters must be tightly regulated. Research into the embryonic and larval development of the blue discus (Symphysodon aequifasciatus) indicates that a stable pH range between 6.3 and 6.6 is optimal for minimizing developmental stress and preventing skeletal deformities during the incubation period. They are considered difficult to keep, due to strict requirements for water quality and the need to be kept in groups.

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 – aquarium. The North American Discus Association focuses on both supporting hobbyists and helping to support wild discus.

References

External links

Discus Society Malaysia
Fanatik-Discus-International informations, pictures, videos about discus fish
Discus Care Guide