Discus are native to the Amazon river basin, are a popular aquarium fish and belong to the genus Symphysodon, which includes the common discus and the Heckel discus
Discus cichlids have a laterally compressed body shape which is rounded. It is this body shape that gives them their common name, "discus". 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
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 can also be observed in Uaru.
In the wild they are opportunistic omnivores and their diet consists of invertebrates and plants. The waters that discus live in are typically slow-moving, soft and slightly acidic (1 - 5 dGH, pH 4.0 – 6.5). The temperature of the water in their natural habitat varies from 25 – 30 C ( 82-86 F).
Discus are shy and generally peaceful aquarium inhabitants. They are sensitive to stress and disturbance or lack of protection. The best cohabitants tetras, e.g., Rummynose or Neon. 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 difficult 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 discus adapt well to harder water and a pH up to 7.2, excluding attempting to breed, in which case soft, acidic conditions are better, and preferred by the discus. Clean water and frequent water changes is necessary for discus health. Do not use R.O. water or distilled water as some "salts" are necessary, i.e., calcium, magnesium, etc, 100 ppm GH is average. New fish should be quarantined for a minimum of 4-6 weeks in a separate tank, with separate water changing equipment to eliminate the possibility of bringing in an infection to established discus. New discus should be added when the lights are out or during feeding time.
Water quality must be kept high, as discus will not tolerate pollution very well. A fully cycled high capacity biological filter is necessary, which usually takes a month or more. Ammonia and nitrite levels should be kept at 0 ppm. Nitrates should be kept as low as possible. Weekly water changes are important, except in the case of a very heavily planted tank and a small biological load.
Feeding discus can be a challenge. They can be raised on just about any high-protein fish food. Discus can be cautious about new foods, and 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 to ween discus off of one food for another. A better approach is to 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, to promote good color 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.
their young with a secretion that might as well be called milk. The tiny fry
live off their egg-sacs for several days, and then migrate and attach themselves
to one of the parents, where they feed off the fish-milk.
Discus prefer low lighting. They are often timid in the home aquarium, so low lighting together with profuse aquatic vegetation may help them to feel more comfortable in their environment.
Common Color Varieties
There are three layers of color on discus: The base color (which usually ranges from cream to red-brown), the secondary color (a metallic color, usually a blue or green color) 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 color. The secondary color is often striped down the sides of the fish, although many strains (such as 'solid cobalt' or 'blue diamonds') have secondary color that eventually covers most or all of the fish's body.
There are no rules or authorities on what constitutes a unique color 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. The exact patterning of the secondary (blue/green) color is like a fingerprint; it develops chemically rather than being set precisely by genetics. The offspring of two 'spotted' discus will likely have spots, but not in the exact same size/position as their parents.
Notable color varieties:
• Brown: The most common color form in the wild; these fish have a brownish base color with minimal stripes of secondary color only along the head and fins.
• Blue/Green: Similar to the Brown, but with more secondary color (either bluish or greenish.)
• Royal Blue: The secondary color forms stripes across the entire body, with a golden base color. These splendid fish are the basis of many of the developed color strains, and are primarily responsible for the early fame of discus. Royal Blues can usually be readily distinguished from selectively bred color forms by their less even base color, with the golden color becoming a brighter yellow around the breast area.
• Red Spotted Green: A reddish base color with greenish secondary color with 'holes' in it (producing spots of the red base color showing through.) This handsome color 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 color with stripes of blue-green secondary color, normal black pigmentation (bars).
• Solid Cobalt: Golden or light brown base color, but when fully mature covered with a blue secondary color. 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 color 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 color much lighter and brighter; as a result, discus with this mutation may show brilliant red or yellow (or even pale cream) primary color. Most of these strains are no longer called 'pigeon bloods', but are easily identifiable by the bright base color, 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 color 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.)
• 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 color 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 4. If the water parameters are good and they are well fed they will spawn.
A discus guarding its eggs.
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 Fertilisation
The female's egg tube will protrude a few mm when she is laying the eggs. This makes her passes in an upward direction laying the eggs against the surface. The male will follow after her and fertilize the eggs.
The parents will both protect their eggs, chasing away all 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.