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Species & Sports:
Officially, Discus comprise two cichlid species (Symphysodon discus (Heckel, 1840) and S. aequifascateus (Pellegrin, 1903)) and five subspecies (S. discus discus (Heckel 1840), S. discus willischwartzi (Burgess 1981), S. aequifasciatus aequifasciatus (Pellegrin 1903), S. aequifasciatus axelrodi (Schultz 1960) and S. aequifasciatus haraldi (Schultz 1960)) of fishes. Additionally there is a myriad of sport mutations, man-made varieties'¦ and a dizzyingly complex "lingua discae" describing them.
Some Discus Varieties Now!
Wild Discus distribution mapping can be found on the net at: http://www.aquaworldnet.com/dbws/biotope.shtml. A note re the current taxonomic status of Symphysodon species. There are those that contend (Al Klee, Marc Weiss et al.) that there is but one species of discus, and others (notably Heiko Bleher) that there are at least three and many more subspecies'¦ the jury is indeed "still out" (Please see Burgess 1991).
There are a few schemes for naming, describing discus varieties. Most are regional in scope and more useful for marketing the fish than descriptive. Just the same, names are important for placing exactly what we're all looking at and for and often can be a key to determining the source, place of the actual breeding colony.
About Buying Wild Discus:
If you can, don't! Wild fishes are far more likely to perish'¦ from the rigors of capture, holding, handling & shipping'¦ adjustment to captive conditions. Also, wild-collected specimens are very likely to be carriers of parasites. It is best to buy the most "local" source discus livestock you can, acclimated to your water conditions'¦ fed foods you are likely to be able to purchase and/or prepare. Captive-produced discus are outright better'¦ and more colorful than wild-caught. Unless you're bolstering your genetic stock, investigating the wild animals for some other purpose, do look to tank-bred sources.
If possible purchase your entire discus at the same time, of about the same size and introduce them to their permanent home simultaneously (the same day). This will reduce a great deal of inter-specific aggression and start the process of social adjustment for all on an even keel.
Investigate before you buy! Discus ARE expensive, for good reasons'¦ they take time, care, money to breed, raise to saleable sizes. Buy only from reputable sources. Ask around'¦ especially on the Internet'¦ re whose discus are quality, not "juiced" (treated with hormones to enhance their color'¦ temporarily), and of good value. Buy smaller fish in a good number, six or more, as some may well not "make it" and if you become interested in breeding them, this will provide a good possible mix for a match or two.
About Buying Discus Period:
The importance of knowing what you're looking at and carefully observing potential buys cannot be overstated. Do NOT buy fishes or from systems that contain fishes with clamped fins or dark body coloration. Torn fins will heal themselves in time with good care, but infected, parasitized specimens can often be observed as such and they and their tankmates avoided. Make sure the specimens are feeding, that they are alert and "bright-eyed". Do NOT buy fishes that are thin in the forehead region or have sunken stomachs. These fish may have nothing more wrong with them than that they've been starved for some time, but they may be parasitized or so far gone that they will not recover.
Purchasing discus of all sizes, varieties can be done through a retail outlet, breeder or etailer. The last two entail shipping costs and their inherent risks, but can be of considerable savings overall if purchasing a number of fish. The retail route is not often possible/practical for making a "group" purchase, as the vast majority of stores stock very few discus. If you are fortunate a "home breeder" may be located within driving distance (you can locate these folks through the Net, tropical fish societies) and you can "go to the source" in picking out specimens'¦ with the added bonus of their likely acclimation to local water conditions. If you're not quite so lucky, I suggest you try a "piggy-back" deal with your LFS in which they buy the fish with you (you put down a deposit against their purchase) and they use their suppliers, probably their systems to bring the fish in, and stabilize them ahead of your taking them home.
About Buying "Mated" Discus:
Buying "pairs" of discus of breeding size/age from any source other than a breeder you can personally trust is almost invariably a mistake. Real breeding pairs are and should be expen$ive'¦ Having taken time to develop, feed, and potentially making the owner a profit in their development and pairing. Too often what are promoted as "pairs" are not viable couples or even a male and female. My real advice is to buy young fish and grow them up yourself. Starting from very small this might take anywhere from ten months to two years'¦ so you will have to judge how much money you want to expend initially in your search for broodstock.
All "wild" discus, those that come from the Amazon or from overseas breeders should be quarantined, sequestered from other livestock and out of your main/display system. This protocol will prevent much head- and heartache in eliminating the introduction of parasitic and infectious disease, and affording the new livestock a chance to "rest up" from the rigors of collection and shipping.
Actual quarantine consists of two elements, the system and actual treatment. The quarantine tank can be as small as twenty gallons, but should allow for at least that many gallons per one medium to large individual. It should have a cover (to prevent jumping, reduce evaporation), a heater, and a biological filter (generally a box or sponge filter will do, but having a small inside power filter in your main system you can switch to the quarantine is very handy). Gravel should be dispensed with as it acts to accumulate detritus and may interfere with chemical treatments. It is strongly suggested that you coat or paint the bottom, sides and back of the quarantine tank to eliminate light and reflection. You do NOT want a light on this tank. The use of plastic plants is strongly encouraged as these serve to calm down the fish and will not affect medication concentrations.
Treatment varies by writer/opinion, but mine is borne out of many years in the trade and import of many hundreds, even thousands of discus. Some folks advocate a "wait and see" first approach and treat specifically per symptoms IF such arise. In the wholesale livestock business we tend to be much more pro-active and assume foreign livestock (caught or cultured) is likely carrying parasitic, bacterial and/or fungal pathogens and treat prophylactically. Almost all (actually all that I've tested) wild discus harbor gill and body Trematodes or flukes (Gyrodactylidea and Dactylogridea). Very often they are infested with "Costia" (now Ichthyobodo necatrix), a small flagellate of the skin, very often manifesting itself macroscopically as a "white patch" in appearance.
As if these external complaints weren't bad enough, there are a number of internal parasites to be expected in wild discus (or non-wild ones that have been exposed to them). Of particular note is intestinal Spironucleus (aka Octomitus, Hexamita); another flagellated protozoan, and a/the causative mechanism for "Hole in the Head" disease. Lastly, it is common to find nematode worms of the genus Capillaria and less commonly tapeworms (Cestodes) in wild-caught discus and these can become an important source of loss of vitality (even death) through gut-blockage, nutritional loss and general internal damage. Positive identification of these parasites requires some sampling (of skin slime, a sacrificed fish, fecal material) and a good microscope.
My recommended S.O.P. (standard operating procedure) is a preventative dip/bath in 200 ppm formaldehyde (with an airstone, you watching the animals all the while for signs of over-stress, for 10-15 minutes) on the way to quarantine (but after acclimation)'¦ UNLESS the animal/s are in so much duress that it makes more sense to acclimate and quarantine them for a few days to weeks first to assure their survival), and feeding with anti-protozoal and anti-worm food. For the former, Metronidazole, aka Flagyl, at the rate of 250 mg. is blended per four ounces of their food. And for nematode worms the use of Fenbendazole (Panacur tm) at the rate of 0.35 percent of the food mixture you make or buy. These two are administered sequentially, with the Metronidazole being given twice a day for six days and the Flubendazole for four days following.
The first line of such prevention is careful acclimation of new fish/es. Shipping water is tested for pH and hardness and matched in acclimation water and initial tanks. Almost always you'll find pH's that are very low and if you test for it, ammonia that is sky-high. One of the very important reasons you should match pH is to prevent ammonia "burn" and outright toxic poisoning. Coupling ammonia and high pH is a deadly combination that can kill newly arrived aquatic livestock outright.
Feeding new discus can be a trying ordeal. If at all possible try to find out what the fish were fed prior to your receiving them and offer the same or something similar. As most freshwater medications are of little use added straight to the water, introducing them into food is the best method of administration (injection being a last resort).
A quarantine period should be no shorter than two weeks. A month is about as long as one might benefit from isolating new stock. Do test regularly for ammonia and have pre-made water at the ready for change-outs. Keeping the new fish in a system that is stable, clean and as stress-free as possible can make the difference between success and dismal failure. Some discus aficionados suggest quarantining new fish at high temperature, in the ninety plus degree F. range. The thinking being that it's best to speed up the metabolism and appetite of the discus and that parasites do not do well at high temp. If you do this, do lower the temperature slowly (a degree or so per day) afterwards, and be on constant vigil for signs of low oxygen.
Discus can live for a decade or more given basic attention to proper set-up and adherence to a routine of regular maintenance. Most folks fail with Symphysodon from a lack of attention or commitment to providing a decent home for these fish from the get-go. Don't be one of them.
Water quality is the single most important aspect of success/failure with discus keeping. A basic routine of providing "about right" conditions will keep you in good stead, and a deviation from this practiced routine can easily spell ruin. What is required is a simple understanding of what your source water is made up of, what your fish desire/require, and an ongoing routine for making the first fit the second.
Discus of all kinds, wild and domestic do best in water of a pH between 6 and 7. Best in many ways not to try to match any lower value than 6.0, as most ways this is achieved leave little buffering capacity and a "slippery slope" to chemistry problems. Is your water of "moderate" hardness (up to 10 degrees of GH) right out of the tap and a pH between 6-7? Fine. I would store it in a container, heated, aerated and ready for use on an ongoing basis somewhere near the discus system. If it were of higher pH, too hard, you would do well to consider "blending" it with water of lower pH and hardness (perhaps made at home via an RO or DI device)'¦ maybe you could boil some peat moss, place this in a filter and run the new water through it for a few days. In extreme cases of very hard, alkaline water you may have to resort to chemical treatment.
And all this being written and understood, you don't want absolutely solute-free water for your discus. Without some mineral content for buffering pH for instance, the water will quickly become deleterious for their habitation. Hence the need to either not take out all mineral content, or to add some back if using reverse osmosis or other filtration that effectively removes all minerals. Some aquarists simply blend some source water back in with their purified, others avail themselves of commercial products that replenish or reconstitute mineral content.
Plan on getting, using and recording accurate and precise test kits for aspects of nitrogen cycling, pH, general (and possibly carbonate) hardness and pH.
Size does matter. Allow at least twenty gallons per medium/large discus, and thirty or more for very large specimens. Larger volumes are better for stability, reducing interspecific aggression and to give you leeway should there be an accident like a power outage, overfeeding or toxic event. Yes, smaller discus can be kept in smaller systems/volumes of water, but this is ill advised. One principal factor in Symphysodon health is the mal-effects of metabolite build-up, the accumulation of organic molecules from the discus themselves that reduce growth and vigor. It is much better to provide for dilution of metabolites through having larger systems.
Placement of the tank can be important, structurally and for the psychological well being of your discus livestock. The usual cautionary notes here re placing large, heavy objects on wooden floors'¦ near windows or drafty doorways, too close to walls. Additionally, discus do not appreciate much sudden motion outside their system, so placing their tank outside of much foot-traffic is called for.
Discus do not like "sudden movements", and so not only is placement of the aquarium important (so they can see you coming), but blocking out extraneous light is strongly advised. This is most easily accomplished by simply painting (water-based latex paint) a dark (blue or even black) coating on the bottom, back and if they're not going to be viewed through them, the sides of the tank.
Good biological filtration is absolutely required, with complete, though not overly brisk circulation to ensure all the water and wastes are being swept up and passed through the filter. Some folks use simple inside "wool" or sponge filters, but if you have a system of any size, with more than a few fish, an outside power filter (canister, and/or hang-on) is suggested. The use of undergravel filters is strongly discouraged. Not only are these difficult to maintain, they mal-affect the water too much for successful discus keeping and/or live plants if you keep them.
Discus greatly suffer for the presence of any detectable ammonia or nitrite and substantial (more than 10 ppm) of accumulated nitrates. Do be diligent about water testing, regular water change regimens, vacuuming, and careful attention to the care and feeding of biological filter media. Never place discus in a system that is not thoroughly cycled. In fact it should show no signs of nitrite and some accumulated nitrate for a good two weeks or more before introduction of these fishes.
Though undergravel filters are employed by some folks still who keep discus casually, most breeders employ sponge type filters, either in-tank or as media in outside power hang-on or canister filters. Best to plan on redundancy in these arenas, and have some biological filter media both in and outside your system, and take care to never change all of it within any given week. In actual practice it's actually best to have multiple sets/layers of media and to "cycle" out just some of it (the older) and replace it under the media that is to be changed next.
Circulation should be "complete" but not achieved by over-sized pumping. A turnover of one to two times per hour is advised in actual outside pump capacity, with "bubbling" from foam filters a bonus.
Unless you have a good deal of surface or overlying live plant growth, a diminished amount of light is recommended. Discus do NOT like bright lighting. For your viewing pleasure a full-spectrum (color rendering index in the 90 plus percent, temperature of 5,500 Kelvin plus) of a watt or so per gallon is about right. Remember, your discus are happy in almost complete darkness. The lighting is for your use. To enjoy their beauty, check them for health.
Some discus species, subspecies are found in water that drifts down to the upper seventies Fahrenheit in temperature, but all are best kept in the mid-eighties. This elevated thermal regime poses a challenge in that both metabolism is elevated and reciprocally, gas solubility reduced'¦ a deadly combination in situations like power outages and overfeeding incidents. To wit, some writers suggest much warmer water (upper eighties F., even into the nineties). I urge caution here and just setting your thermometers to the mid eighty ranges, and to use two, even three heaters of the total desired wattage rather than just one to prevent outright chilling through failure.
Plants & Decor
Discus in the wild are found amongst submerged wood, some plant material, in generally slow-moving water with diminished intensity filtered light. If you were dealing with wild-collected discus or ones just a generation or two from wild stock, you'd do well to try simulating this sort of setting. Captive-produced stock of many generations can be housed in very bare tanks. Indeed, many commercial breeders keep pairs in twenty and more gallon tanks with little more (or nothing more) than a box or sponge filter and a spawning substrate (typically a cone, clay flower pot or red brick). However, all discus show their best and are most comfortable in a more naturalistic setting'¦ of submerged wood, some live plants'¦ diminished lighting and current.
Bear in mind there are many downsides to keeping discus in planted settings. Many plants do not do well with low illumination, high temperature, soft, acidic water'¦ and your discus will tend to hide, be less visible with plants present. Planted tanks are harder to keep clean, harbor more parasitic problems and make for far more problems should you have to medicate. This being said there are is no denying that live plants add a great deal to an aquariums looks and to discus health'¦ if you want plants but want to avoid the troubles associated with keeping a substrate in the discus system there is always potted planting'¦
A related issue is whether to utilize substrates in discus systems. Gravel is attractive'¦ and of a necessity to planted aquariums, but is a bastion of waste accumulation and increased maintenance. My real advice: If you intend to have a "compromised" plant AND discus system, do use gravel of a minimum depth, otherwise plan on doing without it.
Plants that do well with discus are ones that live or tolerate similar water quality, temperature and low illumination. The many Swordplants of the genus Echinodorus, Java Ferns (Microsorium spp.), Crypts (Cryptocoryne spp.), my favorite, Water Sprite (Ceratopteris) floating at the top, and Bolbitis ferns are strongly recommended.
IMO and experience, no discus display (as opposed to earnest breeding set-up) is complete without the provision of sunken (and if your tastes align to it floating) "bogwood"'¦ There are many types of this natural sinking logs available'¦ and their use does so much to improve water quality, provide shade, and general beauty to the discus tank that you should seek out and place this wood in advance of your fish. In the wild all discus are found in association with sunken wood'¦ show yours with the same.
Some Recommended Plants for Discus Tanks:
Discus are social animals; they live in groups in the wild and are most at ease being kept as such in captivity. There is more to this than simply placing a given number of individuals in a tank however. Discus live in communities of individuals with a complex social arrangement'¦ a hierarchy of a dominant individual (usually the largest specimen) and successively less dominant individuals'¦ the latter arrayed progressively outward in a given habitat'¦ where they are more likely to fall prey to predation. You can draw a few insights from the above. One, your discus should be housed in a group'¦ with either starting them off small and allowing them to sort out their social hierarchy, or if starting with larger individuals (more than 2-3 inch diameter), allowing space for the development of social dynamics. And, if adding specimen/s at a later time, making sure there is room for them, that they are of substantially smaller size, and possibly screening them from the existing community such that they can see and smell each other, but not get to the new individual for a few weeks. If you are starting with even small fishes in a small system (under twenty gallons per individual), you should buy an odd number (3, 5) so that that the dominant individual (and sub-dominant) will not pick on a single lowest-subordinate conspecific.
Other fishes that mix well with Symphysodon include species that are sub-dominant AND less aggressive/adept at food competition. More bold fishes will outright intimidate discus into hiding, non-feeding. Faster, more-vigorous feeders will not only get to the food first, but also very likely scare your discus into isolation and subsequent starvation.
Though there are many other fish species that WILL co-habit with Symphysodon in terms of temperament, other aspects of behavior, water quality, I am a big fan of utilizing animals that might be found in their biotope. This includes a huge number of "ditherfish", smaller species, mainly Characoids ("tetras") that break up the environment, taking the discus "worries" away from their minds, as well as a few hundred species of catfishes, particularly Loricariids ("Plecos"), and Callichthyids (armored cats, "Corys").
Examples of Good Discus Tankmates:
Characins/Tetras to Consider:
Include such small characin/tetra fishes as Cardinals (Paracheirodon axelrodi), Black Neons (Hyphessobrycon herbertaxelrodi), and Lemon Tetras (Hyphessobrycon pulchripinnis'¦ Serpae, Bleeding Hearts'¦ of the Hyphessobrycon callistus -- H. serpae group). The small, dwarf Pencilfishes (family Lebiasinidae) of the genera Nannostomus and Nannobrycon can do well in a small school housed with discus if they're relatively large enough to avoid becoming meals. Another group to consider that spends its time at the surface are the Hatchetfishes (family Gasteropelecidae). An "oddball" characin that deserves consideration is the spotted Headstanders (Chilodus punctatus), an easygoing and a beauty in its own right.
Characins to Avoid:
Include types that are too nippy (most large Pencilfishes, family Anostomidae), even Black Skirts (Gymnocorymbus ternetzi) and Red-eyed Tetras (Moenkhausia sanctaefilmenae), fast-moving types like Buenos Aires (Hemigrammus caudovittatus) and Silver-Tips (Hemigrammus marginatus). Silver dollar species are out for both being too active and large. Many small characins simply can't "take the heat" so have to stay out of the (discus) water. Notable examples include the Black and Red Phantom Tetras (Megalamphodus melanopterus and M. sweglesi) and Flame Tetras (Hyphessobrycon flammeus). When/where in doubt re a prospective fishes requirements, use the Net: fishbase.org lists important life history information for many species.
About Keeping Discus With Other Cichlids:
Angels and Discus do not "play well together", with the former often bullying the latter, to their lack of feeding and ultimate demise. House them separately. I have seen many other Amazonian cichlid species kept with Symphysodon, notably Uarus, Festivums and Juraparoids. If you have a huge system (hundreds of gallons) this can be attempted, but your discus will suffer for having other large animals present. Best to select for easygoing, innocuous small species like Dwarf Cichlids to keep with them. Apistogramma species tend to "burn out" quickly at the higher temperatures that discus keepers keep their tanks at, but the Checkerboard Cichlid (Dicrossus filamentosus) and ever-popular "Ram" (Microgeophagus ramirezi) do very well in the same settings.
Catfishes in a Discus Tank:
Should be small, non-aggressive, slow-moving'¦ a group of Corydoras species is a delightful sight and a good way to keep the tank bottom tidy. A copy or two (if space and temperament allows) of a sucker-mouth catfish can likewise aid you in keeping sediment stirred and the tank sides clean.
Genus Panaque Plecos. Of the ten described species in this genus, only two are offered in the hobby, and never cheaply. The Royal Plecostomus, Panaque nigrolineatus (Peters 1877) and Blue-eyed Panaque, Panaque suttonorum (formerly P. suttoni) are collected mainly out of Columbia for the aquarium trade, though they are found in Brazil and Ecuador as well. These fishes grow respectively to at least sixteen and nine inches in length in the wild. (Images: A juvenile and adult Royal Pleco in captivity). I particularly like the "Plecos" of the genus Ancistrus and the many small Otocinclus spp. for discus tanks as well'¦ as these do not grow to the huge sizes of the more commonly offered sucker-mouthed catfishes.
And Though They're Not Catfishes: Siamese Algae Eaters
Other than water quality, the second most important aspect of discus keeping (well, vying with social arrangements) is nutrition. There are many do it yourself formulas for making formulated discus food'¦ calling for grinding, blending beef heart, gelatin, peas'¦ many more possible ingredients, as well as quite a few very good commercially prepared foods. These include frozen, freeze-dried, flake and even pellet varieties. Once you get your fish accustomed to whichever brand, format, it's best to stick with this.
Do take care in dealing with "live foods" of freshwater or even sewerage origins'¦ Worms (Blood, Black, Tubifex) can be trouble in particular. I do not endorse the use of live freshwater source foods period. Best to offer these freshwater source foods in frozen/defrosted formats, even ones that have been gamma-radiation zapped.
Know that discus do go on "hunger strikes" at times, often for no apparent reason. At these instances, it's always a good idea to check ones water quality, effect a good-sized water change, possibly raise the tank temperature, and offer some different variety of meaty foods.
Very small discus should be fed several times a day. Even the largest of discus should be fed at least twice daily. They can/will learn to take food from your hand, but initially, foods may best be accepted if they are sinking'¦ as discus feed from the bottom mostly in the wild.
With a bit of planning, a few specialized tools (a dedicated plastic trash can and lid, test kits, a pump or powerhead'¦) taking care of your discus tank/s can be reduced to a few minutes per week. The most important aspect of their regular maintenance is attention to preparing, storing and making requisite water changes. Symphysodon are particularly sensitive to an accumulation of their own (and others) wastes, and thus, in addition to providing plenty of volume (for dilution), careful feeding and filtration, frequent partial water changes are de riguer.
New water is vastly better having been made-up and kept in a separate container for their use. This is where the trash can and cover, pump, heater'¦ come into play. If at all possible, locate this menagerie near the tank for ease of use, develop and adhere to a system of "making" new water after using that which was stored previously. For some lucky folks with relatively "clean" tapwater, this might entail simply using a hose to dump water in their "water change bucket" for next weeks use'¦ But for most people some steps will need to be employed to lower overall solute concentration and lower pH. Again, depending on where you're starting from source-wise this can be a simple matter, perhaps just adding a pH depressing product or a box filter of boiled peat moss wedged between filter "wool". For folks with "liquid rock" tapwater of high hardness (more than 20 dH) and/or TDS (total dissolved solids) in the hundreds of ppm, you'll be best off investing in an inexpensive reverse osmosis or deionization system for making your change water.
Ideal set-ups for discus involve continuous "drip" water change mechanisms, but practically speaking, weekly change outs of fifteen-twenty percent are about prime for hobbyist systems.
Early attempts at discus breeding incorporated separating parents from their valuable eggs'¦ a mistake as the young feed on their parents prolactin-induced secretocytes (specialized cells) as an initial source of nutrition (not actually the parents body slime).
The author was fortunate to have a pair of wild blue Heckel discus spawn for him back in the mid-sixties, but most folks will take the far easier route of starting with tank-bred specimens. There are some general "rules" concerning sexing discus (females are rounder in body shape, males more elongate'¦), or you can try closely observing their interaction in groups, hoping to "guess" at a pair at your dealers, but it is strongly suggested to purchase and raise a goodly number (six or more) individuals at a small size (less than mature) and allow them to sort themselves out. "Pairs" in stores and home can be two females'¦ and often first spawnings are non-fertile even with a male and female. There are many variations on the theme of spawning discus commercially, with some folks/companies opting to separate eggs with wire mesh or totally from their parents, raising them with Methylene Blued water, an airstone'¦ even protocols for early foods other than parental slime (See Wattley's accounts).
Pairs of discus lay and fertilize their eggs on a vertical surface, a plant leaf, aquarium wall or purposeful spawning medium. At typical aquarium temperatures (low to mid-eighties F.) the young hatch out in about 3-4 days and are moved about by the parents. At six days or so they commence to "contact feed" on their parents sides and fins and continue to do so for about two weeks. After this time, numerous (several times per day) of small live food (often newly hatched brine shrimp) must be offered to sustain the young. For commercial purposes the young are separated from their parents, speeding up their time to next spawning (typically a week to two weeks).
Diseases of Discus:
Problems like too-bright lighting, poor/unsuitable water quality (generally not warm enough, too hard/alkaline) and too much human traffic about their system are often make that way-too-often a source of over-stress for captive Symphysodon. Even relatively "plastic" sports require low lighted, quiet settings with attention to warm, softer water conditions.
Many "disease" problems with discus can be solved via environmental manipulation. Lowering pH between 5-6, and raising temperature (to the upper eighties F.) will often affect a "cure" for ailing Symphysodon. Of course, you should look for and remedy any "root causes", such as poor water quality otherwise, a lack of maintenance or gear failure. Otherwise, the old saw, "when in doubt check water quality and effect a water change" applies to discus that for "no apparent reason" become secretive turns dark or refuses food.
Bacterial Diseases of Discus:
As with other captive aquatic life, bacterial infections are almost always "secondary" in nature, that is, resultant or consequent of other insults. Most common bacterial disease "causes" are damage in handling/shipping, starvation (in the process of shipping, collection they're rarely fed), netting'¦ Symphysodon do exhibit a "wasting syndrome" emaciation, swelling of the eyes, dropsical conditions) as a result of Mycobacterial infection. Positive identification is through microscopic examination of the liver, spleen or kidney (for nodules containing Mycobacterium). Not uncommon seasonally in discus imported from the Far East.
Septicemia is a term defined as "bacteria in the blood". In discus this is most often associated with Aeromonad and Pseudomonad infections. Typical symptoms include exophthalmia, distension of the abdomen (dropsy) and blotchy hemorrhages on the body and fins.
Fin rot or Columnaris disease is caused indirectly by a rod-shaped bacterium called Flexibacter columnaris. In severe cases, all fins are eroded to their nubs.
These bacterial complaints can largely be avoided by careful selection of new fishes, and attention to good care/maintenance of their systems. There is anecdotal evidence of the efficacy of using anti-microbials (e.g. Furan compounds) and oxidizing agents (e.g. potassium permanganate) in their "treatment", though it is my opinion that keeping the mal-affected fish in clean, high-quality water does about as much good.
External Worms (Trematodes/Flukes) and Protozoans:
These external complaints, evidenced by white patches, spots, opened inflamed gill areas, sometimes by darkened bodied, head-down, hiding behavior, are best dealt with through formaldehyde baths of 10-15 minute duration at 200 ppm concentration. Obviously the fish/es will need to be moved to other settings to prevent re-infestation, and the existing system either left fallow (w/o fish hosts) for a period of several weeks to months, or cleaned/disinfected before fish are reintroduced. Some writers endorse the use of organo-phosphate pesticide treatments (e.g. Masoten, Dylox, Trichlorofon'¦) for these complaints. I do not.
Discus are susceptible, particularly if chilled to White-Spot disease, Ichthyophthiriasis, and susceptible to treatment with therapeutic agents as other freshwater fishes. Additionally, the stalked protozoan Epistylis is common on wild-imported animals, forming a bloody scab at its point of attachment. It can likewise be eliminated with Malachite, Formalin and metal-salt treatments.
Internal Worm Infestations:
Distended or prolapsed cloaca (communal openings for sex and excretory products), white, trailing feces, actual microscopic examination of fecal material or the alimentary canal of a sacrificed fish might indicate roundworm (nematode) or tapeworm (cestode) infestation. These can be treated with Anthelminthics like Flubendazole or Piperazine laced foods.
About "Hole in the Head" Disease:
Though Metronidazole (aka Flagyl) is often sold to aquarists to "treat" for this neuromast destruction syndrome, and very often, improved water quality (large changes, lowered pH and hardness, elevated temperature) will affect a lasting cure. Yes, Spironucleus/Hexamita can be a co-causative organism here, but often they can be brought back into balance and eliminated by improved, favorable environment to their host.
General Malaise, Darkening, Wasting:
The causes of these observed syndromes are numerous, but I'd like to list one general "tonic" cure that has saved many discus: the use of the dye Acriflavine, sometimes coupled with formalin in fish remedies. If/when all else fails, I strongly encourage that you try this dye (in the absence of activated carbon) in your discus water.
Loss of discus from social causes is very common and almost always there is at least a social component to their captive mortality. First off in importance is the lack of regard for their social structure'¦ there are no "solitary" discus in the wild'¦ or even just natural "pairs". These animals live in groups, thus unless you're involved in a commercial breeding enterprise, your fish should be housed in a "colony" with other discus.
Starting with discus requires a good deal of forethought and commitment. Are you willing to provide a large enough (eighty gallons minimum) tank for their principal use? Do you have the resolution to prepare change water of adequate make-up and change it frequently? How about the costs associated with their feeding? In the west it is common for people to have an attitude of "I can afford'¦" and "they look neat so'¦" but discus deserve a much more thorough consideration than just an admiration of their beauty and requisite initial expense. Unless you can commit to "the total package" of their appropriate long-term care you are encouraged to seek out more forgiving, less touchy species. The "King" of aquarium fishes deserves respect.
Discus Breeders Website: http://www.aquaworldnet.com/dbws/
Diskus Brief: http://www.diskusdesign.net/
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Fairfield, Terry F. 1997. Iso-Med for wild caught discus. TFH 6/97.
Finley, Lee. 1991. Discus mania. If the number of books available is any indication, discus are more popular than ever. AFM 1/91.
Gargas, Joe. 1988. Trickling-bed nitrification in a discus hatchery. TFH 11/88.
Gargas, Joseph. 1990. Juvenile discus. FAMA 12/90.
Green, Woody. 1998. Discus, no black magic is needed. AFM 7/98.
Hayley, Art. 1979. Some mistakes with discus. FAMA 4/79.
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Herkner, Hugo. 1987. The discus fish. Still a problem fish? Today's Aquarium 2 & 3/87, 1/88.
Koehler, Horst W. 1991. Do discus pairs really form secretions. FAMA 9/91.
Lass, David. 1997. Discus are just fish. There are too many "rules" about keeping them. AFM 8/97.
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Loiselle, Paul V. 1999. Discus alone. Discus alone. Tankmates are fine, but it's better to be selective in your choices. AFM 6/99.
Middleton, Brian. 1999. Starting with discus. TFH 8/99.
Morfitt, Craig & Lee Newman. 2002. When discus don't adjust well to their new aquarium home. AFM 10/02.
Quarles, Jim E. 1993. Conditioning wild discus for spawning. 7/93.
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Wattley, Jack. 1985. Handbook of Discus. TFH Publications, NJ 111pp.
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Weiss, Marc, 1983. Food formula for the finicky discus. FAMA 5/83.
Weiss, Marc. 1995. Wasting away in discusville. Cichlid News 4/95.
Yat, Lo Wing, Sunny . 1986. Development of the turquoise discus, pt.s 1-4. FAMA 12/86, 1,2 & 3/87.
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