Family: Cichlidae, Subfamily Cichlasomatinae
Common Name: Discus, Heckel Discus
Origin and Habitat: Lowermost parts of the Rio Negro, Rio Abacaxis and Rio Trombetas. Inhabits very quiet streams thick with aquatic plants and flooded forest.
Compatibility/Temperament: Should always be kept in a group of 5 or more except for breeding. Very peaceful, but will become territorial during all stages of spawning. A very sedate fish, that should never be maintained with active, boisterous or aggressive fish. Suitable companions are small catfish, characins (hatchetfish, larger pencilfish and splash tetras, medium tetra), rasbora (Trigonostigma sp), dwarf cichlids. Should not be kept with angelfish or gourami.
In nature, feeds on insects, worms, crustaceans and plant matter. In the aquarium: prepared foods other than flake, especially one of the specific discus preparations; frozen daphnia, artemia (brine shrimp), bloodworms, beef heart, squid; live blackworms, mosquito larvae, daphnia and artemia. Make sure to feed beef heart and worms sparingly to minimize chances of the discus getting intestinal parasites. As varied a diet as possible will ensure better health.
Attains 8 inches (20 cm).
Minimum Tank Suggestion
48 inches in length, 75 gallons.
Water parameters for Heckel Discus
Soft (< 2 dGH), acidic (pH 4.2-6.2) water, temperature 26-30C/79-86F. Hardness and pH ranges are for wild-caught fish; tank-raised fish bred locally will likely be adapted to local water parameters. This species is more demanding than S. aequifasciatus with respect to water conditions.
The subject species is one of two very closely related [see discussion below]; the other, S. aequifasciatus has a separate profile.
Symphysodon aequifasciata is smaller at maturity than S. discus. The two nominal species currently recognized can be distinguished by colour pattern. S. discus has a distinct pattern of dark undulating lines covering the sides and a dark vertical bar across the middle of the side much more intense than the other vertical bars. S. aequifasciatus has all vertical bars similar in width and intensity; horizontal stripes do not show in preserved specimens except occasionally on nape and on anal fin base [Kullander].
Gender can be ascertained externally only during spawning; the papillae of the male is pointed, and that of the female rounded and blunt. Like many other cichlids, discus form socially monogamous pairs and undertake bi-parental care of their broods (Matthaeus, 1992). Symphysodon and Uaru are unique among fishes in producing nourishing mucus that the newly hatched fry graze on. This mucus, known as 'discus milk', is exuded from the hypertrophied skin of both parents and is apparently essential for larval growth (Hildemann, 1959) [from Crampton, 2008].
This species was described by J.J. Heckel in 1840. In 1981, W.E. Burgess described the subspecies S. discus willischwartzi but Kullander determined this was not a valid subspecies and the name is now deemed a synonym (invalid) of the subject species.
Symphysodon derives from the Greek symphysis [=grown together] and odous/odon [=tooth], referring to the few teeth situated where the two jaw halves meet. The species epithet discus comes from the Greek discos [=discus, a circular disk used in athletics] and refers to the circular disk-shape of the fish.
The number of discus species has been a subject of disagreement for some time. Schultz (1960) published the first revision of the genus, and recognized two species on the basis of pigmentation: S. aequifasciatus and S. discus. He also divided S. aequifasciatus into three subspecies based on pigmentation: S. aequifasciatus aequifasciatus ('green' discus), S. a. haraldi ('blue' discus) and S. a. axelrodi ('brown' discus). Kullander (1996) determined the subspecies were invalid. Bleher et al. (2007) considers Symphysodon haraldi as a distinct species [see following].
Ready et al. (2006) proposed that the genus contains two distinct lineages corresponding to the species S. aequifasciatus [the eastern range fish] and a new species S. tarzoo [the western range fish]; the latter corresponds to the subspecies "described" by Lyons in 1959 as S. discus tarzoo. Ready et al. note that they found no significant genetic differences between the two existing eastern species S. discus and S. aequifasciatus, which suggests the species are either very closely related or they may be a single variable species. Without further examination of specimens, they are not proposing to synonymize S. aequifasciatus with S. discus, i.e., the two distinct species remain for the present. The result is there are three recognized species, S. discus (the Heckel Discus), S. aequifasciatus (the Blue Discus) and the new S. tarzoo (the Green Discus).
Bleher et al. (2008) also recognizes three species, though differing in the names: S. discus (the Heckel Discus), S. aequifasciatus (the Green Discus) and S. haraldi (the Blue Discus). In both Ready and Bleher the "brown" or "common" discus is the same as the Blue Discus. And both studies used mitochondrial DNA sequence data.
Bleher, H., K.N. Stolting, W. Salzburger and A. Meyer (2007), "Revision of the genus Symphysodon Heckel, 1840 (Teleostei: Perciformes: Cichlidae) based on molecular and morphological characters," Aqua--International Journal of Ichthyology, Vol. 12, No. 4, pp. 133-174.
Crampton, William G.R. (2008), "Ecology and life history of an Amazon floodplain cichlid: the discus fish Symphysodon (Perciformes: Cichlidae)," Neotropical Ichthyology, Vol. 6, No. 4.
Kullander, S.O. (1996), "Eine weitere Ubersicht der Diskusfische, Gattung Symphysodon Heckel," DATZ Sonderheft Diskus: pp. 10-16.
Ready, J. S., E.J.G. Ferreira and S.O. Kullander (2006), "Discus fishes: mitochondrial evidence for a phylogeographic barrier in the Amazonian genus Symphysodon (Teleostei: Cichlidae)," Journal of Fish Biology (2006) 69 (Supplement B), pp. 200-211.
A Guide to Choosing Discus:
1. Size of their eyes
The size of the eyes should be small in proportion to their body. If they seem bigger, then there is a sign that the discus are already stunted. Stunted fish tend to have enlarged eyes and will die prematurely.
They shouldn't look like the shape of a football which again signals a sign of stunted growth. Consider also their finnage, are the fins round-looking? Round appearance of the fins indicate the fish are healthy and don't have deformed fin formation.
When the discus are young(below 4 inches), their colors aren't fully developed. However if you see discus with bright colors at a size of below 4 inches, then the discus may have been injected with hormones. The use of hormones to improve coloration is rather impractical.
Does the discus look healthy? Discus with very dark coloration(depending on the strain) are probably sick or severely stressed. Check their anus. Are there white stringy poo? They are a sign of the presence of intestinal parasites.
When buying discus, it is recommended to buy the biggest you can afford. Anything smaller than 4 inches can be difficult to keep alive as their immune systems are not fully developed making them rather vulnerable to diseases. Young discus should receive three to four small feedings per day taking care to remove what isn't eaten within 30 minutes.
If at all possible, always buy fish raised by a local breeder. These fish will be adapted to your water parameters. And local breeders will likely be far more helpful with advice.
A lot of pet stores sell "pairs" of discus. This is not a wise practice as discus tend to be choosy of their partner in nature. It is better to have a group of 5 or more and let the fish select their mates.
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