Discus (fish)
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 Symphysodon aequifasciatus
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Symphysodon aequifasciatus |
Discus (Symphysodon spp.) are a genus of three species of freshwater cichlid fishes native to the Amazon River basin[1]. Discus are popular as aquarium fish and their aquaculture in several countries in Asia is a major industry.[2][3][4][5]
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[edit] Taxonomy
Discus belong to the genus Symphysodon, which currently includes three species: : The common discus (Symphysodon aequifasciatus), the Heckel discus (Symphysodon discus), and a new species which has been named Symphysodon tarzoo [1]. A further investigation published in August 2007 [2], suggested that the genus held three species: S. aequifasciatus, S. haraldi and S. discus.
[edit] 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).
[edit] 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.
[edit] Diet
In the wild they are opportunistic omnivores and their diet consists of invertebrates and plants. The waters from which discus hail are typically slow-moving, soft and slightly acidic (1 - 5 dGH, pH 4.0 – 6.7). Temperature of the water in their natural habitat varies from 25 – 33 C ( 82-88 F). When discus fish eat, they appear to mouth the food and spit it out before recapturing it and swallowing it.
[edit] 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.
[edit] In the Aquarium
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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.
[edit] Aquarium water chemistry
Aquariums for discus should be kept within a temperature range of 26-31 C; a temperature of 29 C (84 F) is thought ideal for adults. Babies and young fish should be maintained at 31 C (88 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.
Some Aquarists believe that the water must be changed regularly, but this may not be necessary in a very well planted tank, that has adequate lighting, and small fish to clean up after the messy eating discus, in this case a "top up" with one third tapwater mixed with RO water will suffice.
Captive bred fish adapt very well to harder water with a pH up to 6.8 except when attempting to breed, in which case soft and acidic water is best. Recently there are several captive bread Discus that can be purchased at Local Fish Stores(LFS's) that have been tanked raised in water with a PH of around 7.5 and although they prefer acidic water, they can survive and even thrive in hard water around 7.5PH. Actually, maintaining acidic water is always beneficial to these fish because the ever threatening ammonia which is an ever present danger in contained fish living quarters is unable to form in a pH under 6.5. At that Ph and lower it converts to ammonium, which is a form more easily tolerated by the fish. A Ph in this low (down to about 5.1) range protects from the poison of toxicity while allowing the fish to exist in conditions that more closely mimic the water conditions that they evolved in. Studies in the Amazon River Basin where they evolved and are naturally found range most consistently between a Ph of about 5.1 and 6.6.
Frequent water changes are necessary to maintain the water quality of a discus tank. In their native environment heavy rains purify the water naturally, and it is probably this constant flushing alongside the acidic water which is this species greatest defense against water borne pathogens and parasites. As it is always best to simulate natural conditions when containing captive animals, the discus fish keeper needs, first and foremost, to address the water conditions of their fish. In a home setting the chemical, sodium bisulfate, easily and inexpensively acquirable from a swimming pool supplies dealer, will serve the purpose well. Using a water holding drum as may be found in a clean, converted, sturdy plastic trash barrel, the fish keeper may experiment with both aging and conditioning the water.
When changing the Ph of water, however, it is imperative that one wait at least 24 hours until a "bounce back" effect occurs because the buffers naturally found in water will fight against the Ph change and the aquarium keeper will need to readjust with a further application of the chemical a second time. Though this process may prove demanding and complicated at first, repetition will, as with most things, allow it to become as simple as anything else we do frequently. The increased health of the fish will be the initial reward, while the comparative absence of disease in the captive schools of fish will actually make the process less demanding and time consuming over the life of the fish.
When discus fish breed the water parameters must become even more exacting, and it will usually be necessary for the keeper to process a percentage of the water through an R.O. filter. Never use pure R.O. water or distilled water as some “salts” are necessary (ie;calcium,magnesium, etc) 100 ppm GH is average. A lack of salts in the water can results in disease outbreaks. 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.
[edit] 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 coloration and quick growth. Pork heart has also been used to achieve a similar effect. 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. Discus delight in small live prey, which is the best option for them in the long term. Black worms, bloodworms, brine shrimp and mosquito larvae are all eagerly eaten by discus. Care must be taken when feeding discus live food though, for bacteria and parasites can be present. For this reason it is advisable to buy live food from aquarium retailers. Live tubifex worms should not be fed to discus AT ALL because it is practically impossible to remove all of the bacteria from them. It is safe however to feed discus freeze dried tubifex cubes as the bacteria and/or parasites have been removed in the process. If live food is unavailable, the best artificial food for discus is a high quality granulate food. Flakes are also a good option but granules retain vitamins, minerals and other trace elements better than flakes. They love frozen blood worm.
[edit] Lighting
It is a myth that discus prefer low lighting. They are often pictured in dark aquariums as this is the best way to show their colours, however discus do not require any special lighting. They will quite happily live in a well lit aquarium just as most other tropical freshwater fish.
[edit] 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.
[edit] 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.) 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.
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[edit] Breeding discus fish:
A bare bottom twenty or twenty-seven gallon tall tank is ideal for breeding discus. Discus lay their eggs in the same manner as angels, and so a vertical surface should be provided for them to deposit their eggs on. An inverted ceramic flower pot, but discus aren’t picky and will use whatever surface is available. A potted plant or two can be added to the breeding tank if so desired, and will provide some shelter for the pair, but this is not essential. As far as filtration goes, a sponge filter should be used to handle the biological load along with an outside power filter to pick up any debris that may be in the water.
Discus come from the warm, soft, acidic waters of the Amazon River and thrive when these conditions are replicated in the home aquarium. For both general maintenance and breeding of discus the pH should be kept at 6.5 and the temperature around 86 F. Any alterations that need to be made to the water chemistry should always be done prior to the water being added to the tank. For general maintenance water changes should be performed weekly. However in the breeding tank, a small water change should be done every day, or every second day. Frequent water changes increase appetite and promote mating activity in discus. It’s no coincidence that discus will often spawn after a water change.
If good water quality is maintained the discus will have large appetites and should greedily accept any food offered to them. Spawning discus should be fed frozen blood worms, beef heart, Tetra Color Bits, frozen or live brine shrimp, or live white worms. If feeding beef heart, one must be careful that none is left over because it will foul the water very quickly. Live tubifex or black worms should never be fed to discus at any time, as they will introduce parasites to the tank. A breeding pair will lay eggs as often as every week, as many as fifteen times. They will usually go through two of these spawning cycles in a year. The eggs take 48 hours to hatch, and are free-swimming another 72 hours later. Immediately upon becoming free-swimming the fry will move to their parents’ sides, and start feeding off the mucous secretion that are produced by the parents during this time. The fry will feed off their parents’ sides for as long as you leave them together, but they should be offered newly hatched brine shrimp after being free-swimming for five days.
The fry should be removed between two and three weeks after reaching the free-swimming stage, as leaving them with the parents any longer may be hazardous to the parents’ health. The youngsters will actually reach a point where they can start ripping off scales and bits of flesh from the parents. Once the fry are removed the pair will spawn again in short order. The fry, now in a tank of their own, should be fed six or more times a day. The best foods to give the fry are newly hatched brine shrimp and chopped blood worms. For the first few weeks there is noticeable daily growth. In the fry tank it is important to do a partial water change every night after the last feeding.
[edit] See also
[edit] External links
- Discus (fish) at the Open Directory Project
- Breeding Discus Fish Information On Breeding Discus Fish
[edit] References
- ^ Froese, R. and D. Pauly. Editors.. Genera reference: Symphysodon. FishBase. Retrieved on 2006-11-08.
- ^ Loiselle, Paul V. (1995). The Cichlid Aquarium. Germany: Tetra Press. ISBN 1-56465-146-0.
- ^ Sands D (1994) A fishkeepers guide to Central American cichlids. Tetra Press. Belgium pg 59-60.
- ^ Mills D (1993) Aquarium Fish Harper Collins ISBN 0-7322-5012-9
- ^ Chong K, Ying TS, Foo J, Jin LJ, Chong A (2005) Characterisation of proteins in epidermal mucus of discus fish (Symphysodon spp.) during parental phase Aquaculture 249:469–476.
