Discus belong to the genus Symphysodon, which currently includes three species: : The red discus or common discus (Symphysodon discus), the blue discus (Symphysodon aequifasciatus), and a new species which has been named Symphysodon tarzoo.
Appearance
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).
Reproduction and sexual dimorphism
Another characteristic of Symphysodon species are their care for the larvae. 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, off which the larvae live during their first few days. This behaviour has also been observed for Uaru species. Diet
In the wild they are opportunistic omnivores and their diet consists of invertebrates, small fish and plants. The waters from which discus hail are typically slow-moving, soft and slightly acidic (1 - 5 dGH, pH 4.0 – 6.5). Temperature of the water in their natural habitat varies from 25 – 30 C ( 82-86 F).
Distribution
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.
Discus are shy and generally peaceful aquarium inhabitants. They are sensitive to stress and disturbance or lack of protection. The best cohabitants may be angelfish (although some aquarists claim that keeping them together with angelfish will introduce parasites and/or diseases) and small characides like tetras. Uaru species are also suggested cohabitants for discus. It is noteworthy, however, that small fish may be intimidated or eaten by the discus. Catfish with sucker mouths are less than ideal cohabitants for discus since they sometimes attach themselves on the sides of discus and eat their mucus membranes.
Many aquarists consider discus to be finicky and not particularly hardy. They often become susceptible to disease and die if not kept in optimal conditions.
Aquarium water chemistry
Aquariums for discus should be kept within a temperature range of 26-31 C ( 82-86 F); a temperature of 29 C (84 F) is thought ideal for adults. Babies and young fish should be maintained at 31 C (86 F) degrees. The water should be very soft and slightly acidic; a pH of 5.5 - 6.5 is considered good for wild caught discus.
Captive bred fish adapt very well to harder water and to pH up to 7.2, except when attempting to breed, in which case soft and acidic is best, although it is preferred by the fish anyway. VERY clean water with frequent large volume water changes is necessary for the health of these fish. Never use pure R.O. water or distilled water as some "salts" are necessary.(ie;calcium,magnesium, etc) 100 ppm GH is average. Discus need plenty of space, and 150 litres is recommended as the minimum tank size for one single Discus. New fish should be quarantined for a minimum of 4-6 weeks in a separate room, separate tank, and separate water changing equipment to eliminate the possibility of bringing in an infection to established fish.It is generally accepted that new fish should be added after "lights out" or during normal feeding.
Water quality must be very high, as discus do not tolerate pollution of any sort very well. A good tank will be equipped with a high capacity biological filter and be fully cycled (which usually takes a month or more.) Ammonia and nitrites should be kept at 0 ppm. Nitrates should also be kept as low as possible. Weekly water changes are important, except in the case of a very heavily planted tank with high nitrogen compound grounding capacity and a very small biological load.
Feeding
Feeding discus is sometimes a challenge. They have no unique nutritional requirements; they can be raised on just about any high-protein fish food. However, discus are often extremely cautious about new foods; it is not unusual for them to go for weeks without food before accepting a new type of food. (Therefore, when purchasing discus it is a good idea to ask what they are being fed.) After starving for a month discus will almost always accept a new food, but this may stunt the growth of younger fish.
It is not advisable to use the starving method for weening discus off of one food for another. Instead, mix the new food with the discus' preferred food. Over time, the discus will begin to accept the new food, and the old can be removed.
Beef heart is often fed to discus in order to promote good colouration and quick growth. However, concern over the long-term consequences of feeding discus a diet high in mammalian protein has prompted some hobbyists to switch their discus to a diet of krill, a shrimp-like crustacean.
Lighting
Discus prefer low lighting. They are often skittish in the home aquarium, so low lighting together with profuse aquatic vegetation may help them to feel more comfortable in their environment.
Common Colour Varieties
There are three layers of colour on discus: The base colour (which usually ranges from cream to red-brown), the secondary colour (a metallic colour, usually a blue or green colour) and the black pigment that makes up the black vertical bars and allows the fish to darken and lighten at will.
Most discus strains have either a golden or reddish base colour. The secondary colour is often striped down the sides of the fish, although many strains (such as 'solid cobalt' or 'blue diamonds') have secondary colour that eventually covers most or all of the fish's body.
There are no rules or authorities on what constitutes a unique colour variety or what to call it. A particular form may or may not breed 'true' (with offspring very closely resembling the patterns of their parents.) Generally all of the common, established forms breed true[citation needed]. The exact patterning of the secondary (blue/green) colour is like a fingerprint; it develops chemically rather than being set precisely by genetics[citation needed]. The offspring of two 'spotted' discus will likely have spots, but not in the exact same size/position as their parents.
Notable colour varieties:
- Brown: The most common colour form in the wild; these fish have a brownish base colour with minimal stripes of secondary colour only along the head and fins.
- Blue/Green: Similar to the Brown, but with more secondary colour (either bluish or greenish.)
- Royal Blue: The secondary colour forms stripes across the entire body, with a golden base colour. These splendid fish are the basis of many of the developed colour strains, and are primarily responsible for the early fame of discus. Royal Blues can usually be readily distinguished from selectively bred colour forms by their less even base colour, with the golden colour becoming a brighter yellow around the breast area.
- Red Spotted Green: A reddish base colour with greenish secondary colour with 'holes' in it (producing spots of the red base colour showing through.) This handsome colour form is extremely rare in the wild, but is produced by several breeders.
- Heckel: Possibly a separate species, Heckels are identifiable by two vertical black bars that are much thicker than the others.
Common Bred forms:
- Red Turquoise: A red-brown base colour with stripes of blue-green secondary colour, normal black pigmentation (bars).
- Solid Cobalt: Golden or light brown base colour, but when fully mature covered with a blue secondary colour. Black pigmentation may be normal or incomplete (some vertical bars missing.)
- Blue Diamond: Essentially a 'solid cobalt', but the black bars have been completely removed through selective breeding. The reduction in black pigment gives these fish a bright, lighter blue colour than most 'solid' discus.
- The Pigeon Blood mutants: These fish have a gene that disrupts the distribution of the black pigment. As a result, they lack vertical black bars (but often have 'pepper'). The lack of black pigment makes their base colour much lighter and brighter; as a result, discus with this mutation may show brilliant red or yellow (or even pale cream) primary colour. Most of these strains are no longer called 'pigeon bloods' per se, but are easily identifiable by the bright base colour, pepper, and lack of black vertical bars. All pigeon bloods are the descendant of a single fish found in Eastern Asia in the 1980s. Since the trait is dominant and appears to be controlled by a single gene, fish bearing this mutation can be crossed with any other colour strain to produce novel new 'pigeon blood' types. Pigeon bloods do have one drawback: They cannot darken at will (as normal discus can). This can make it difficult for them to raise fry, which are attracted to their parents by seeking out a dark object. (Normal discus darken when spawning or stressed.) The fish shown at the top of this document is a pigeon blood. (High quality pigeon blood types have few or no 'pepper'.)
- Snake-skins: These fish have a mutation that makes their patterning 'tighter'; as a result, they have about twice as many black vertical bars, but also have tighter, finer secondary colour patterns than normal discus.
Breeding
Spawning
Discus like to choose their own partner. This makes breeding a little more difficult and a lot more expensive. Discus should be kept in groups of at least six. If the water parameters are good and they are well fed they will spawn.
The discus will choose a site that is near vertical. They will clean the site. They may even lay their eggs on the bottom or side of the tank.
Laying And Fertilization
The female's egg tube will protrude a few mm when she is laying the eggs. This will make her passes in an upward direction laying the eggs against the surface. The male will follow after her and fertilize the eggs.
Egg Care
The parents will both protect their eggs, chasing away all the fish that come near. They will even eat one at a time so the eggs are not left vulnerable. They will continually fan their eggs. It is not uncommon for young parents to eat the eggs one at the time. White eggs are infertile.
