Symphysodon, colloquially known as discus, is a genus of cichlids native to the Amazon river basin in South America. 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. Symphysodon are highly social, typically occurring in groups that may number many dozens of individuals, which is unique among cichlids of the Americas.[17] When breeding, the pair moves away from the group, possibly to reduce the risk of cannibalism of the young.[17] As for most cichlids, brood care is highly developed with both the parents caring for the young. Additionally, adult discus produce a secretion through their skin, which the larvae live off during their first four weeks.[19] During the first two weeks, the parents stay near their young allowing them to feed easily. In the last two they swim away, resulting in the young being gradually "weaned off" and starting to fend for themselves.[19] Although rare in fish, more than 30 species of cichlids are known to feed their young with skin secretion to various extent,[19] including Pseudetroplus and Uaru species.[20] Sexual maturity is reached in one year.[17] Symphysodon primarily feed on algae, other plant material and detritus (periphyton), but also eat small invertebrates. 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.[17] Unlike more predatory cichlids, Symphysodon have relatively long intestines typical of a herbivore or omnivore Symphysodon species inhabit the margins of floodplain lakes and rivers in the lowland Amazon basin,[17] where it is part of the highly diverse Neotropical fish fauna. S. discus is restricted to blackwater habitats, but periodically these may experience brief floods of whitewater.[10] S. tarzoo is found in both black[10] and whitewater,[7] and S. aequifasciatus also occurs in clearwater.[10] Because of their preference for lentic habitats such as floodplains and flooded forests, whitewater inhabited by discus contain little suspended material (unlike main sections of whitewater rivers).[13] 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.[7] In contrast the distribution of S. discus appears to be limited to the lower reaches of the Rio Negro, upper Uatumã, Nhamundá, Trombetas and Abacaxis Rivers.[7][13] The Nanay River in far western Amazonas is outside the native range; discus in this river were introduced from stock originating in the Tefé area by an aquarium exporter more than 30 years ago