Discus are freshwater perciform fish, peculiar cichlids native to the Amazon River basin. There are two recognized species, both within the genus Symphysodon: the red discus or common discus (Symphysodon discus) and the blue discus (Symphysodon aequifasciatus). The two species are very similar and may interbreed, producing a number of hybrid strains. Details regarding the precise number of subspecies have not been finalised. Discus are most closely related to the genus Heros.

The first special characteristic of the discus is its flattened body shape. It is compressed from the sides to a dish or discus shape. Although patternation varies, most are showily coloured in shades of green, red, and blue. The height and length of the grown fish are both about 20–25 cm (8–10 in).

The second special characteristic of the discus is its care for the larvae. Like all cichlids, the parents care for the young but the discus has a unique way of doing so: the parents produce a secretion through their skin, off which the larvae live during their first few days. The young can be seen grazing off their parents.

The discus are shy and peaceful aquarium inhabitants. They are sensitive to stress and disturbance or lack of protection. The best cohabitants may be angelfish and small characides like tetras. The Uaru is another preferred tank-mate of the discus. However, small fish may be intimidated by the big discus fish or even eaten.

Generally, discus are considered to be difficult to care for and breed. Some breeders and owners use tap water while others claim that it is necessary to prepare the water in a very thorough way, for example by reverse osmosis. There are a lot of different breeds available with a wide range of colorations.

The popularity of the discus has given it its nickname among aquarists: the King.

S. discus

The Red Discus prefer very soft, acidic water with a 4.2–6.2 pH, a water hardness of 0.0–1.0 dGH, and a temperature range of 26–30°C (79–86°F). Their native diet consists of a combination of worms, insects, crustaceans, and plants. They originate from the Negro River where it drains into the Amazon River and from the Trombetas and Abacaxis Rivers.

S. aequifasciatus

The Blue Discus prefer soft, acidic water with a 6.0–8.0 pH, a water hardness of 0.0–12.0 dGH, and a temperature range of 26–30°C (79–86°F). Their native diet consists of a combination of insects and invertebrates. Besides their popularity among aquarists, the fish are sometimes grown for food in subsistence fisheries. The fish is natively found among rock crevices and roots. They are a schooling fish except during the breeding season when the become territorial. The Blue Discus originates from the Solimões River to the Tocantins River basin.

See also: List of freshwater aquarium fish species

References

• "Symphysodon aequifasciatus (http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=11185)". FishBase. Ed. Ranier Froese and Daniel Pauly. April 2004 version. N.p.: FishBase, 2004.
• "Symphysodon discus (http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=11186)". FishBase. Ed. Ranier Froese and Daniel Pauly. April 2004 version. N.p.: FishBase, 2004.
• "Symphysodon" (TSN 170023) (http://www.itis.usda.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=170023). Integrated Taxonomic Information System. N.p.: Integrated Taxonomic Information System, 2004. Accessed on May 11, 2004.