iPhoneOgraphy – 16 Oct 2016 (Day 290/366)
Symphysodon, colloquially known as discus, is a genus of cichlids native to the Amazon river basin. Due to their distinctive shape and bright colors, discus are popular as freshwater aquarium fish, and their aquaculture in several countries in Asia is a major industry. They are sometimes referred to as pompadour fish.
Discus are fish from the genus Symphysodon, which currently includes the above species. However, another review of the genus published in August 2007 suggested that the genus held these three species: S. aequifasciatus (the green discus), S. haraldi (the blue/brown/common discus), and S. discus (the Heckel discus). 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. aequifasciatusby FishBase.
Other (sub) species 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. aequifasciatusremains to be determined; if valid it is widespread but it might just be a color morph.
Like cichlids from the genus Pterophyllum, 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. The height and length of the grown fish are both about 20–25 cm (8–10 in).
Symphysodon species inhabit the margins of floodplain lakes and rivers in the Amazon Basin of lowland Amazonia, where it is part of the highly diverse Neotropical fish fauna.
The three species of Symphysodon have different geographic distributions. S. aequifasciatus occurs in the Rio Solimões, Rio Amazonas and the Río Putumayo-Içá in Brazil, Colombia and Peru. In contrast the distribution of S. discus appears to be limited to the lower reaches of the Abacaxis, Rio Negro and Trombetas rivers. S. tarzoo occurs upstream of Manaus in the western Amazon.