(July 1998 Version)

Dionigi Maladorno






Many aquarists in the hobby do not have access to the laboratory techniques that would allow a specific diagnosis and a targeted treatment of fish diseases. In most cases, symptoms are discovered during routine tank clean-up or fish feeding, and someti mes this leads to inappropriate use of medications that compound the problem. The following document is intended as a support and orientation tool focused on helping the aquarist with few practical recommendations for a first-line treatment of some commo nly found discus diseases. Alternative treatments may be used as well, and in some situations different therapeutic criteria may be required.




A symptom-based approach to the treatment of diseases means that the medications or the procedures used to attempt to cure the disease are chosen on the basis of the type of behavior and physical appearance of the fish, as opposite to decisions made on the basis of diagnostic tests.

It should be however emphasized that the aquarists may discover that obtaining and using a microscope is much easier than what they originally thought. For example, friends or club members may associate to purchase one, or a complacent student, doctor, pharmacist or veterinarian may be available to provide some help. Several hobbyist-grade books2,3,4 provide very useful information on the use of this instrument, which may contribute to save a lot of money and fish lives.

An effective empirical treatment of some fish diseases is often possible, but it still requires a good knowledge and understanding of the basics of fish physiology and diseases. For this reason, it is extremely important that the hobbyist reads and un derstands a good book on this subject. Several excellent choices are available1,2,3,4,7,11 and they represent the best investments in time and money for the discus keeper.





The cornerstone of disease prevention is the creation and maintenance of excellent water conditions. The proper physical parameters of the water for a discus aquarium may be somewhat different on the basis of the type of fish being kept, and on the bas is of the area of interest of the aquarist. For example, wild-caught Heckel discus have the reputation to be more sensitive to organic waste than aquarium-raised strains, and they also prefer very warm, peaty, soft and acidic water. On the contrary, discu s strains obtained by selective breeding are known to have occasionally spawn in relatively harder water conditions, which is considered just fine for simple keeping, without spawning intentions. As a general recommendation, one of the basic disease preve ntion measures is to conscientiously follow the aquarium set-up and maintenance schedules contained in most books on South American cichlid care5.

These books contain in most cases also recommendations on quarantine procedures that should be followed with newly acquired fish. Quarantine is an extremely important concept since it helps to avoid several serious problems, mainly related to infectiou s diseases . The term quarantine originally indicated an isolation period of 40 days, and for our purposes it can be defined as a six weeks period of segregation away from the final destination tank. The following table provides a overview of its benefit s:


Beneficial Effect of Quarantine


Evaluation of the health condition of the new fish

Diseases in stage of incubation may become manifest days or weeks after a apparently healthy fish is acquired.


A quarantine tank allows a more effective observation of the fish than a community tank

Reduction of disease transmission risk to pre-existing fish

Although pathogens may be transmitted to other tanks by contaminated equipment (nets, etc.) or even by air-borne particles, most bacteria and parasites remain contained to the quarantine tank until proper treatment eliminates them

More gradual acclimatization of the new fish

A community tank is often a highly competitive environment where new fish are at disadvantage

Administration of drugs is convenient

Quarantine/hospital tanks are often smaller than the community tank, and less drug is needed (if dissolved in water)


Less organic material that may inactivate the active drug is present


It should, however, be made very clear that while quarantine procedures greatly reduce the problems associated with the acquisition of new fish, there is no guarantee that the problems will be eliminated completely. Some diseases may have an incubation period so slow, that it takes months before symptoms appear. In other cases, a new fish may simply be an healthy or sub-clinical carrier of an infectious disease. In other words, infection is not always associated with disease. This means that the carrie r does not show signs of the infection although a potential pathogen is present, and the quarantine is completed with no problems. However, other fish later on infected by the same agent in the community tank may start to manifest symptoms. This type of s ituation is for example encountered with Ichthyophthirius multifiliis ("Ich") infestations. It can go even the other way around, with newly introduced (and quarantined) healthy fishes being infected by pre-existing ones whose immune system was a ble to keep the parasite under control4.


The risk of parasite infestation is higher in wild-caught fish than in animals obtained directly from a reputable breeder. Fish purchased from stores may be in good shape, but because of the promiscuity with wild-caught or otherwise sick specimens, the y should be considered at high risk of carrying potential pathogens. Some hobbyists do not routinely disinfest the fish coming from known and reliable sources, using the quarantine period just for observation. On the contrary, high risk specimens are ofte n preventively disinfested. A discussion of the pros and cons of these procedures however goes beyond the purposes of this document. One of the possible preventive treatment schemes is however presented at the end of this paper, in treatment the schemes s ection.


When setting up a quarantine (or hospital) tank, it is important to consider the following recommendations:


1) The filtration system used should be able to cope with the ammonia produced by the fish. In other words, the filter must have been cycled , otherwise a procedure designed to improve the health of the fish becomes more like the execution of a death sentence!

Since relatively few people can continuously maintain a spare tank running, the hobbyist should always have extra filtration material available from other established tanks in order to "seed" the filter of a newly setup quarantine tank. Filte r "booster" preparations are commonly available in aquarium stores, and many users report good results with them. Since however controversies exist on exactly which bacteria are responsible for de-nitrification 6, in the opinion of th e Author it is uncertain that the product will contain what really is needed to accelerate the maturation of the filter. The availability of a kit for ammonia and nitrites is also a very useful tool to make sure that there is no accumulation of these toxi c compounds before (if previously running filters and or water from other aquaria were used) and after introduction of the fish. The tank should be understocked in order to provide the best possible water quality for the fish.


2) Quarantine tanks are normally bare, with just a few plastic plants and/or plastic driftwood if the fish requires cover to prevent or reduce stress (although the Author considers this point very important, it is a fact that many experienced discus k eepers disagree and achieve excellent results with bare tanks). With or without plastic plants, these tanks are intrinsically more unstable than an established tank, and the importance of daily and adequate water changes is extreme, unless contraindicate d by the medication schemes being used. As a general indication, daily 25% water changes should be considered a bare minimum for a mildly understocked tank (for example, two discus in a 30 gal tank). The walls and bottom of the tank should be kept as clea n as possible: even apparently minor slime coating of the glass can hide massive amount of microorganisms which are able to dramatically decrease the oxygen content of the water (it happened to the Author!!) and give the fish respiratory and neurological problems.


3) A reliable and adequately powered heater with easy-to-adjust temperature settings should be used, and an airpump with airstone may help to maintain the water well-oxygenated.


4) Nets, vacuuming equipment, buckets and any other equipment used in the quarantine tank should not be utilized, as a precaution against transmission of diseases, for any other tank. Procedures for equipment sterilization are explained in the above-m entioned fish health books.





Medications have an expiration date beyond which they may loose their effectiveness. Light, moisture and elevated temperatures are factors that may dramatically accelerate the rate of degradation of drugs. Unfortunately, many remedies available in aqua rium stores do not carry any expiration date, nor are kept under acceptable storage conditions. Warm temperatures, moist environment, display on racks under full light are factors normally affecting the commercial preparations sold in the hobby. Other tim es it is the hobbyist himself who decides to use old products just to clean up the medicine cabinet!

These situations should be avoided. Here are some useful tips to consider on the subject of purchasing and keeping medications:


1) Unless you are planning to acquire several new fish in a short period of time, or you have a very large number of aquaria, do not buy medications "just in case". Few treatable conditions require an immediate use of medications, and in most cases it is better to start with water changes, temperature adjustments, home remedies like salt or just careful observation. Wait another 24 hours until stores are open and buy a fresh package of the specific drug you need.


2) Buy medications from a store that has a high volume of sales and that keeps them in acceptable conditions. Stay away from dusty or moisture-stained packages. An airtight sealed container is preferable to boxes or bottles that can be easily opened an d contaminated.


3) Formulations with an expiration date and a clear label explaining contents and concentrations are much more reliable than those with unknown or poorly described content.


4) Store what you bought in a dark, cool and dry place. If you opened an airtight container, it is unlikely that after a few months the content will still be viable, and you should dispose of it in a safe manner.


5) Keep you aquarium medications out of the reach of other pets or children.





The medications most commonly used to treat diseases in ornamental fishes are antibacterial, antifungal and antiparasitic drugs. It is important that the aquarist understands that each category of pathogens has different types o f targets on which these medications work , and that therefore a "magic bullet" does not exist.

Even within the same category of pathogens, say for example bacteria, there are major differences in the susceptibility to each antibiotic, which therefore should be chosen on the basis of a careful selection of the most active compound. The effectiven ess of any compound on a given target is an intrinsic characteristic, but it may be influenced by the dose used, by the frequency of administration and by the duration of use. In addition, sometimes adverse effects occur as a result of toxicity occurring not only on the target organism, but also on the host. Sometimes some characteristics of a drug (for example, the ability to diffuse to all body tissues and fluids) are very desirable because they make it more efficacious, but unfortunately this increased efficacy is also related to increased toxicity. This is not however always the case, and the commonly heard statement that "potent" drugs are more toxic is quite misleading. There are in fact some antibiotics that are quite toxic and not effect ive at all, and others that are very well tolerated and very effective!


On the market several "cocktail" preparations are available, which contain a mix of different drugs which are hoped to cover the desired target. This is sometimes perceived from the aquarist as an excuse for not trying to learn and understand what type of disease is affecting the fish. The use of single preparations that are (erroneously) believed to cover every problem is commonly called the "shotgun" approach! The downside of this idea is that in most situations the majority of th e array of chemicals given to the sick fish are useless in terms of efficacy, since they are not targeted on the desired pathogens. This may "mask" the characteristics of the disease and it can cause unnecessary toxicity problems which could hav e been easily avoided by selecting only the proper compound. In addition, other problems such as avoidable selection of resistant pathogens may occur as well. These cocktail preparations are particularly dangerous when they contain mixed antibiotics activ e on bacteria, which in most cases achieve the only result of very effectively kill the "good bugs" that degrade ammonia and nitrites in the filter. In addition, bacterial infections are very often secondary to injuries or parasite infestations, and once the primary cause is taken care of, they may resolve with just clean and healthy water conditions.

Therefore, there are plenty of reasons to use medications with caution and following specific criteria.










The Author does not assume any responsibility on possible negative effects related to the use of the medications and treatment schemes mentioned in this paper. The ultimate decision on what to do is in the hands of the owner of the aquaria, which is encouraged to decide on his actions after having reviewed the available literature and, if necessary, obtained help from qualified professionals. Several ornamental fish magazines carry advertisements of companies providing advice on fish health problems, and many veterinarians may be available to give professional advice.

The Author has no financial or personal interest in any of the companies marketing the products recommended in this paper.





In general, before a medication is introduced in the aquarium, it is necessary to:


  1. Carefully clean the tank, making sure however not to disrupt biological filtration cleaning the filter with excessive enthusiasm! Organic compounds accumulated mainly at the bottom and in the filter may inactivate some medications1.
  2. Remove, if present, any activated carbon or other filtration resins. Discontinue the use of any water additive (slime coat protectors, detoxifiers for heavy metals, etc.) that may inactivate the drugs being administered. Inert filtration mater ial such as foam blocks, filter floss, ceramic beads are OK.
  3. Start keeping a log, which by the way should be kept regardless of disease outbreaks! It will help to remember the correct dates and dosages used.
  4. If medications that are toxic to snails will be used (these will be indicated in the following text), as many snails as possible should be removed. Decaying snails may be dangerous to the fish. Manual removal after baiting with lettuce or fish food ( in a container with holes large enough for the snails, but not for the fish) is reasonably effective. In extreme cases, a remedy not toxic for snails (or the complete tear-down of the aquarium) should be considered.
  5. Inactivate the UV sterilizer, if one is being used, since it may make some medications less effective.
  6. During treatment, feed the fish very lightly, in order not to overload the bacterial filtration at such a critical moment.
  7. If treatments require the calculation of drug concentrations and volumes/weight of medication to use, ask a friend to review it for possible errors.


Once treatment is completed:


  1. Make good-sized water changes (approximately 30%) daily for several days.
  2. Introduce in the filter a nylon mesh bag with activated carbon, in order to remove the medication. Remove the bag after 1-2 days.
  3. Resume normal water change and feeding procedures after you are sure the nitrification process is working efficiently.
  4. Observe the fish very carefully for several days, in order to determine if the treatment had any effect and whether any further intervention is necessary.








When the fish loses weight there are several explanations that the aquarist should consider3. Weight loss may or may not be associated with abnormal feces or aspecific symptoms such as color darkening, and it is often the only symptom initia lly noted by the fish keeper. In other cases, an otherwise apparently normal fish produces long, stringy and whitish feces, which are often deemed to be one of the tell-tale signs of infestation with Hexamita, Spironucleus or other flagellates3,4,11< /SUP>. From a practical standpoint, either sign, weight loss or abnormal feces, is an indication of possible gastrointestinal problems, and the treatment recommendations that are given in this paper are the same.


The following tables are a summary of some of the most common primary causes of this type of problem. For a comprehensive list see the above-mentioned references about fish disease books:




Poor appetite due to external causes

Competition from more dominant fishes

New environment

Inappropriate/poorly accepted food

Inappropriate chemical/physical water parameters

Temperature, pH, ammonia, nitrites, nitrates, toxic compounds, low dissolved oxygen

Other chronic/acute diseases

Cancers, genetic defects and malformations


While in the last case intervention is very difficult, the first two causes can be managed successfully if properly recognized. Re-arrangement of the aquarium and of its decor, provision of hide-outs, live foods and feedings targeted to the weaker fish often eliminate hunger strikes due to stress. A careful evaluation of the water parameters, followed by water changes and other chemical and physical manipulations is in most cases followed by complete recovery of the fish, unless major organ damage has already occurred.






Unicellular parasites with one or more "filaments" (flagella). Often associated with whitish and stringy feces.

Tapeworms (Cestodes)

Large intestinal worms, in most cases segmented

Nematodes (roundworms, pinworms, threadworms)

Round worms (in cross-section) ranging from microscopic size to several millimeters long. Capillaria is one of them.

Other intestinal infections

Bacteria (including fish tuberculosis), viruses, other parasites

Skin and Gill parasites (Flukes, Ciliates, Dinoflagellates)

The fish stops eating in the late stages of the disease and the parasites rob nutrients from the fish


Several of these organisms have complex life-cycles which include forms such as eggs or cysts which are not easily attacked by many drugs.

Even if the adults are killed by a first antibiotic treatment, the surviving resistant forms may mature and continue the infective process. This is a factor which can easily lead to improper use of some medications, which in some cases must be given in repeated cycles in order to definitely interrupt the life-cycle of the pathogen.


Several different types of pathogen may be simultaneously present in a diseased fish, and in the absence of accurate laboratory diagnostic criteria, it is preferable to administer carefully chosen drugs that cover both flukes and tapeworms, possibly ne matodes also.


Because of this multiplicity of possible causes, a multiplicity of possible solutions obviously exists! What follows is a type of approach that has been used successfully by the Author in case one or more fish in a tank manifest weight loss and/or abno rmal feces:


1) EXCLUDE NON-INFECTIVE CAUSES: in case of weight loss alone or with other aspecific symptoms such as color changes, the compatibility of the affected fish with its tankmates should be carefully re-evaluated. In addition, several critical water par ameters should be checked immediately (temperature, pH, ammonia, nitrites, nitrates). Even in old and established tanks some unpredictable and undetected event (malfunctioning of a heater or of a filter, unnotified change by the water company of the tapwa ter chemical parameters, etc.) may occur.

If any abnormality is found, it should be corrected and a period of observation of several days should follow. If no cause of abnormality is found, then:


2) HYPOTHESIZE AN INFECTIVE CAUSE: in this case, the likelihood of generalized infestation of all the fish in the tank is very high, even if only one shows some symptoms. It will therefore be necessary to treat the entire community tank. Severely w eakened fish may be moved to a hospital tank for rest and protection, but this is not strictly necessary and may in fact be more stressful to the fish than simply leaving them alone.

Because of the possibility of involvement of different types of pathogens, a broad-spectrum and well tolerated treatment should be chosen in order to break quickly and efficiently the life cycles of the potential pathogens. The goal is to prevent infec tions of new fishes as well as re-infection of the one originally sick. A simple and generally very effective scheme of treatment is the following:


a) Treat first for flagellate infestation using:




b) Treat then for other common intestinal parasites not covered by metronidazole:


Various options exist (choose one only).





The above-mentioned treatment proposals do not cover the situations when the Discus quits eating because of skin infestations with ciliates or flagellates like Oodinium. If the previous two steps of treatment have failed to produce a response, a temper ature increase may be attempted in order to eliminate certain possible protozoan infections of the skin and gills, which sometimes may cause weight loss without any typical skin lesions. See the section on lesions of the skin for more information.


Some Discus owners attempt force-feeding with needless syringes fishes that have quit eating. This procedure is highly stressing for the fish, often ineffective since most of the food ends up being expelled through the gills, clogging them, and most of all does nothing on the primary cause of the lack of appetite. In general, it is to be avoided.








Wounds, Scratches w/ or w/out infection

Aggressive tankmates, sudden escape movements, sharp objects, shipping.


Chronic incurable diseases or poor water conditions. Sometimes due to a bacterial infection, which may be treated with a broad-spectrum antibiotic.


Aging, trauma, infections, poor water conditions


Congenital or infective causes


The most common eye problems encountered in Discus are, in the opinion of the Author, superficial wounds or scratches with subsequent bacterial or fungal superinfection. The eye often appears partially or totally off-white and opaque, and often a cotto n-like growth covers it. It is a situation that looks extremely serious but luckily very often it is possible to obtain a complete recovery.


The remedy is very simple:


1) Attempt to understand how the problem occurred: sharp edges of aquarium decor, aggressive tankmates (especially in situations of overcrowding), careless handling during netting attempts are some of the primary causes, which need to be eliminated in order to proven further episodes. In the direct experience of the Author, attack from other fishes (including other Discus) is the most frequent culprit, and it should lead to a critical re-evaluation of the fish density and availability of space and s helter for everyone in the tank.


2) The traditional home remedy of kitchen (or aquarium) salt is extremely effective, and the frequently recommended antibiotic courses should be considered only as second-line treatment if salt does not work. See the treatment scheme with salt at th e end of this paper.


Concerning the other possible eye lesions, several different causes may be at the root of the problem. On a case-by-case basis, a check of the water parameters and a review of the descriptions and explanations given by a book on fish diseases may help to understand the situation. In the absence of a valid explanation, it is better to just focus on maintenance of good water quality, and refrain from using medications empirically.










Fin Rot

Often initiated by a physical cause or poor water quality, which opens the way to an infection. White patches may be present.

White dots

Infection due to parasitic unicellular organisms

Fin clamping/shaking

Possible early sign of stress or disease.


Fin rot is a common problem, due most often to poor water quality or physical damage during transportation and fights with other fishes. Often fungi and bacteria may infect the lesions, producing a whitish edge. In addition to the obvious need to remov e the primary cause of the problem, several reference books recommend antibiotic treatments. The Author did not have much success with that, but simple addition of kitchen salt proved to be extremely effective, stimulating complete regeneration of the los t tissue. See the treatment scheme with salt at the end of this paper.


Concerning the first of the remaining two groups of abnormalities, fin clamping is a very aspecific behavior which indicates some form of distress and that should simply alert the aquarist to carefully observe the fish for the presence of other, more s pecific problems. It may be due to skin parasites, but also to internal diseases. It becomes a real concern when it is a persisting problem, especially when it occurs in conjunction with other aspecific symptoms, such as darkening of the skin. A treatmen t should however be initiated only after a presumptive specific cause for the fin clamping has been identified.


White spots on the fins are basically due to the same group of pathogens (ciliated or flagellated protozoans) that cause similar lesions on the skin. See the section on lesions of the skin for details.













Sometimes respiratory problems are very evident, such as when fishes gasp for air by the water surface or when only one gill is functional, while the other stays close over an extended period of time. The gill tissue may be swollen, and partially protr ude from the gill cover. Other times the symptoms may be more subtle, since they are evidenced only by the increased frequency or, on the contrary, by the absence of the gill movements. In other cases the abnormalities are limited to one side only. It is important to verify that the increased breathing rate persists over a prolonged period of time. Normal fish may in fact ventilate very fast, sometimes for several minutes, during feeding, fights or other moments of excitation. Juvenile discus breath faste r than adults, and it may be difficult to suspect gill infections until mortality problems occur. Breathing abnormalities in most cases occur either for water quality problems, or for infectious diseases.





Low Oxygen

Poor water surface movement, excess of organic matter (food, waste), bacterial bloom, overstocked tank, filter failure


Inadequate biologic filtration, chloramine in the tapwater, filter failure


pH crash, chlorine, certain medications, other toxic substances


Non-infective causes should be suspected first, and a careful evaluation of the water quality conditions should be the immediately performed. Even before a possible cause is identified, the best response is massive (at least 50%) and frequent (even sev eral times a day) water changes, unless the problem is originated by poor quality of the tapwater itself (water companies sometimes change the composition of the water without warning the customers). The water changes should be continued until all symptom s are gone. On the market it is possible to easily find various types of neutralizers and special filter materials which inactivate various toxic substances. They can be used in addition to water changes, not as a substitute.


If ammonia is suspected, the simplest way to inactivate most of it is to keep the pH below 7, for example 6-6.5, so that the much less toxic ammonium is formed (many ammonia testing kits will still be positive, since they read the total of ammonia+ammo nium). A pH much lower than that may severely impair biological filtration, compounding the ammonia problem.


Kits for the measurement of oxygen levels may be expensive, but they can be extremely useful. The normal oxygen levels of the aquarium should be known, so that moderate decreases causing no symptoms can be detected. In the experience of the Author, lev els of O2 around 2-3 mg/l are associated with major respiratory problems of discus fishes. A simple airstone gives an immediate relief, until the primary cause is identified and eliminated.


As usual, if no water quality problems are found or suspected, it is acceptable to presume an infective cause.




Extremely small, transparent worms (less than 1 mm in most cases). Some are livebearers, others are egg-layers.

Protozoans (Ciliates and Dinoflagellates such as Ich, Oodinium, etc.)

Unicellular parasites with one or more "filaments" (flagella or cilia). Oodinium (the cause of "velvet") is particularly frequent and dangerous. Often associated with skin infections (dark color, white dots of various s ize and number, white patches) and weight loss.

Other gill infections

Bacteria, viruses, fungi, other parasites


In adult Discus, gill flukes often do not cause symptoms. When clinically evident, they normally progress in severity at a constant, but not too rapid, pace. Therefore, there is often time to choose and find the proper treatment. The same is not true f or fry, which die very rapidly and sometimes without showing any obvious warning symptom. In such emergency case, see the following option 3) for a preliminary, emergency intervention.


In general, one reasonable approach to the presumptive treatment of gill infections is:


1) The most common agents of gill infections in Discus are egg-laying flukes2,3, and they should be considered the most likely cause of a newly occurred infection. Some valid treatment options in decreasing order of preference (choose one o nly) are:

- Praziquantel

- Flubendazole

- Fluke-Tabs

They are all described in the Treatment Schemes section. If used correctly, the symptoms should resolve. When however the tank contains substrate such as gravel, it is sometimes very difficult to completely eradicate the infection, since the mulm at th e bottom may protect the eggs from the action of the medication.


2) If there is no response to the treatment for flukes, or if signs of a skin ciliate or flagellate infection are present (for example, white dots on the skin or the fins) it may be presumed that one of those organisms, and not flukes, are at the base of the problem.

In this situation it is preferable to administer an elevated temperature treatment (see directions at the end of this paper). However, in community tanks, many fishes other than Discus may not tolerate it. In such situations, when the temperature treat ment is not a viable option, the exact symptoms should be evaluated very carefully, and a specific treatment regimen chosen from one of the fish health books available on the market. Among the others, possible choices are copper, methylene blue, acriflavi n, quinine chloridrate.


3) In life-threatening situations (for example, for fry affected by high mortality or if the fish is unable to eat anymore), when it is difficult to choose between a suspected fluke infection, or a protozoan infection, administer two or three doses of formalin+malachite green (see treatment scheme at the end of this work). This should produce at least a temporary relief of the symptoms. Then, proceed with a more specific treatment as indicated in the two preceding points.






A careful observation of the conditions of the skin is one of the most important parameters for an effective monitoring and evaluation of the general health condition of the fish. Minor scratches and rare missing scales are a quite common finding, in m ost cases due to the expression of dominance behavior between discus fishes. They normally resolve spontaneously within a few days. Following are some of the changes suggestive of health problems:

- Persistent dark color

- Discolored patches

- Whitish dots

- Increased skin mucus

- Bumps, sores, open wounds

- Raised scales


In general, as for other body areas, skin problems may be due to non-infective or infective causes. Following is an overview of the most commonly findings described in fish health books, observed by the Author in Discus fishes or reported to the Discus -L e-mail list12.





Low pH (approx. below 4.5)

Ammonia or Nitrite Poisoning

Dark color, increased skin mucus, infected skin patches, frayed fins, abnormal swimming, rapid breathing


With or without signs of infection

Skin or deep tissues cancers

Bumps, possibly ulcerated.

Holes in the Head

Possibly associated with intestinal parasites, but primarily due to deficient nutrition


As usual, the best remedy for the skin conditions related to poor water quality is the prompt correction of the abnormal chemical parameters. Some kitchen salt (see dosages at the end of the paper) may help accelerating the healing. At most, a mild wat er disinfectant such as methylene blue may be used instead. Although some people may disagree, it is the opinion of the Author that the antibiotics often advocated in these cases are mostly unnecessary, and potentially dangerous for the negative effects t hey have on biological filtration. Once the right water conditions are re-established, the immune defenses of the fish are in most cases adequate to heal the existing lesions. In severe cases, the damage may not be reversible despite water changes or anti biotic usage.


A similar approach may be followed for skin wounds, for which in addition an explanation for the cause should be found and corrected.


In most cases, skin or deep tissues cancers are not treatable.


Hole-in-the-Head (HITH) is a relatively common problem in Discus fish. The onset is quite slow, with small, pin-size holes appearing most often near the nostrils, on the gill plates or near the eyes. These holes gradually increase in size and number, u ntil large portions of the cranial area are destroyed. The fish ultimately dies of malnutrition and infections. Various theories on its cause exist, and in some cases intestinal infections due to Hexamita (Spironucleus) may be associated. Since however th e problem may occur even without any concomitant parasitic infection, it seems that the primary cause is a vitamin and/or mineral deficiency. In general, dry foods are often inadequate to prevent HITH, while when using fresh foods or vitamin supplementati on it is possible that it occurs more rarely. Some discus keepers never experience this problem, while others encounter it regularly, even if both provide apparently well balanced diets. Many books recommend a treatment cycle with metronidazole (see expl anations at the end of this work). Although this is most certainly beneficial and necessary, in the direct experience of the Author feeding chopped red compost earthworms is at the same time the best treatment and the best prevention of this condition. Qu ite amazingly, 100% cure rates can be achieved within a few weeks after initiating daily administrations of chopped earthworms, with or without concomitant metronidazole treatment. Afterwards, administrations once or twice weekly are sufficient to complet ely prevent the disease.

Red composting worms can be easily cultured following the instructions provided on various Web sites (such as the FAQ on live foods). Starter cultures are available from advertisements on aquarium or organic gardening magazines.


Several of the infectious agents affecting the skin have already been briefly described in previous sections of this work on different body systems. In the following table therefore the most common and typical symptoms they cause at the level of the s kin are briefly summarized.






Scratching against objects, dark color

Protozoans (Flagellates and Ciliates such as Oodinium, Ich, Costia, Chilodonella, etc.)

Dark color, white dots of various size and number, increased mucus, white patches, scratching, fin clamping, weight loss (in advanced cases)

Bacterial Infections

Dark color, white patches, scratching, fin clamping, laying in a corner or at the bottom. Often seen in

recently shipped juveniles.

Discus Plague

Large patches forming a reticular pattern


Initially, for several skin infections the first signs noted by the aquarist are rather aspecific, such as rubbing against objects and dark color. If no other symptoms are noticeable after careful observation, it is reasonable to think that flukes may be involved. If however excessive mucus, patches or white dots are present as well, chances are that a protozoan is involved. These however are not absolute rules, but rather reasonable possibilities which might in some cases not be correct. A microscopic examination of skin swabs would provide more reliable guidance.


Skin flukes cause in most cases relatively slow progressing infections, often facilitated by overcrowding. In these conditions, the livebearing type of skin flukes may be transmitted from one fish to another simply by direct contact11. See the section on weight loss for instructions on the possible therapeutic options (praziquantel, or flubendazole, or Fluke-Tabs).


Skin protozoan infections may be due to several different agents, and to describe them in detail goes beyond the purposes of this work. The Author strongly recommends to the readers to carefully review this topic on a fish health book. In this paper it should be sufficient to say that they may be rapidly fatal and highly contagious (both from fish to fish within the same tank, and towards other tanks, via infected equipment). Separate sets of aquarium tools for each tank will help to reduce the risks o f disease transmission.

There are several types of proprietary or generic drugs indicated for some, or many, of the skin protozoans. Some of them may be highly effective when used properly, while others may not be too efficacious. To increase the temperature to 93 deg. Fahren heit is beneficial particularly when white dots are present or after a treatment for flukes has failed (because of the possibility of ich or velvet; see instructions at the end of this paper). Fishes other than Discus may not tolerate such temperature inc rease, and die. Therefore, medications are often the only option available for community tanks. Two of the chemical compounds that cover most of the possible agents in this group of diseases are :


- Formalin+malachite green (see treatment guidelines below).


- Copper (see treatment guidelines below). It is contraindicated when plants and invertebrates (snails) are present or in very soft water conditions (however, calcium salts can be added to increase hardness).


If you can not administer an increased temperature treatment, administer one or the other, making sure that the appropriate drug concentrations in the water are achieved. The response may occur quite slowly (over several days) or it may be only partial , with only a temporary improvement of the symptoms. Because ich and some other protozoans are not susceptible to medications during portions of their life cycles, treatment must be continued for a week or more.


Bacterial skin infections are particularly common and serious in juveniles that just underwent shipment or in fishes that suffered from pH and temperature shock after introduction to a new tank, although infections may occur in adults too. In such spec ific cases, commonly used broad spectrum antibiotics, particularly those belonging to the family of the furans, could be used as per the manufacturer’s instructions. The Author has a direct (and positive) experience only with the nifurpirinol formulation sold in the US under the commercial name of Furanace, and used as directed.


The Discus Plague is a disease of unspecified infectious origin, characterized by rapid progression, high infectivity (even through contaminated equipment or to tanks in nearby rooms) and frequently lethal outcome. The most characteristics signs are i ncreased skin mucus production, and a reticulated pattern on the skin. Although frequently mentioned in fish health books, it is quite rare.








Sometimes it is difficult to distinguish between abnormal or impaired swimming ability due to organic diseases, versus aspecific signs of nervousness. In fact, while events such as persistent headstanding or laying flat are quite obviously pathological , darting and hiding for cover may occur in perfectly normal fish. When in doubt, careful observation of the dominance hierarchy in the tank, and a critical re-assessment of the aggressivity of other species in the tank, may provide possible explanations. Some experienced discus keepers have observed that, paradoxically, bare tanks that do not provide any cover force the fish to be less shy and nervous, while the availability of hiding places invites the fish to hide and react more nervously to movements in front of the tank 12 . This however has not been directly observed by others, including the Author, suggesting that this event may occur in some cases, but not others, for unknown reasons.


Following is a table summarizing some of the most common causes of abnormal swimming:




Headstanding, laying flat

Water quality problems, drug side effects, swimbladder infection, intestinal obstruction, late stage of infectious diseases


Water quality problems, skin parasites, drug side effects, stray voltage in the tank

Swimming by the surface

Lack of oxygen


As the reader can see, these symptoms are generally related to problems previously discussed in this paper, and the reader is referred to the appropriate sections for further details.


Stray voltage may be generated by poorly insulated electrical equipment, and it can be detected with a tester of appropriate sensitivity. It is unclear to the Author whether or not grounding the tank eliminates the problem, but common sense should sugg ests replacing the defective equipment before more serious failures occur.


Intestinal obstruction with bloating may affect the swimbladder functionality. This problem is associated with overfeeding, or use of dry foods that have not been previously hydrated, that then expand in the stomach of the fish. The problem is often self-limiting (no more food should be administered until resolution), but if it does not resolve within a few days, two teaspoons of Epsom salts each ten gallon of aquarium water often clear the intestinal tract of the fish within a few more days.


Swimbladder infections are not extremely common, but they do occur and are in most cases of bacterial origin. Headstanding, laying flat or just poorly coordinated swimming are possible signs. In the opinion of the Author, a swimbladder infection may be suspected with higher likelihood once water quality problems and intestinal obstruction have been ruled out, since the latter occur more frequently. Several reports17 seem to suggest that an antibiotic for human or veterinary use, trimethopri m-sulfamethoxazole, is very effective. If it can not be purchased (a veterinarian may however help), an aquarium formulation of nifurpirinol or the Tetra medicated food for parasites (containing a compound similar to trimethoprim-sulfamethoxazole) may be tried instead. Flagellates are occasionally responsible for swimbladder infections and may be treated with metronidazole.















To prevent the emergence of drug-resistant pathogens, it is important to follow dose instructions exactly. Do not decrease the length of treatment or the strength of the medication, even if the fish appears to recover fully. If the fish react adversely to a given medication, it is better to try a different one, than to reduce dose or duration.

The following treatment schemes should not be applied to fishes intended for human consumption, since some of the compounds discussed are not approved for such use and could be potentially harmful.






Use at 250 mg/10 gallons of water8 or 7 mg/liter1. Three administrations every other day, with a 20% water change before each dose is given. Pre-dissolve the compound in a cup of aquarium water, and then pour it in th e aquarium.




The recommended dose is 1 tablet/10 gallons of water10. Pre-dissolve the compound in a cup of aquarium water, and then pour it in the aquarium. After 48 hours, change 30% of the water (siphoning well the deposit of powder left a t the bottom), and introduce activated carbon in the filter. Even if one single treatment is quite active on a number of different pathogens (mainly flukes, including their eggs, arthropods and tapeworms. Some nematodes may be covered as well), the Autho r thinks it is possible to administer a second treatment a week later if the diseased fish has shown signs of partial, but not satisfactory, improvement or even just as an additional precaution. The hobbyist should however be aware that quite frequently o ne of the components of this product may cause neuro-muscular symptoms in the treated fish, such as uncoordinated swimming, headstanding or difficulties in the mouth muscle movements necessary to ingest food. These events seem to be more frequent at doses higher than recommended, or after multiple treatments. If such situations occur, the aquarist should not panic, since these problems are usually reversible within a few days, at most weeks, once the medications are removed. Just make an immediate water change and introduce activated carbon. In the opinion of the Author the benefits provided by this product still outweigh the risks of temporary negative drug effects.

It is very unfortunate that the manufacturer’s customer service refuses to provide information on the concentration of the individual components of this preparation, since this would most likely help to understand the causes of this problem and possibl y optimize the efficacy to risk ratio for the soft water conditions peculiar of Discus tanks.

The Author does not recommend to use this product at half the usual dose, since this procedure does not offer any guarantee that adequate efficacy will be preserved.

If there is a very high concern about the side effects occasionally associated with this compound, the available alternatives should be considered.




It is available in the US only through prescription from a veterinarian (trade name: Droncitâ , 34 mg Canine Tablets). It is active primarily on tapeworms and flukes, while it is not active on nematodes. Since it does not kill fluke eggs, it is compulsory to administer it at least two times, at exactly a week interval9, in order to eli minate the individuals that may have developed from the eggs present when the first treatment was given, before they reach maturity and lay eggs themselves. A very practical mean of administration is to crush two and a half 34 mg tablet for each 10 gallon s9 of aquarium water and dissolve them in a separate cup of water, pouring it in the aquarium once the tablets are dissolved. The solubility of these tablets is low, and care must be given to have them dissolved as much as possible before intro duction in the aquarium. After 48 hours, change 30% of the water (siphoning well the deposit of white powder left at the bottom), and introduce activated carbon in the filter. Remember to repeat the treatment a week later, otherwise in terms of egg-laying flukes it was a complete waste of time and money!




Flubenol 5% (flubendazole), a white powder (at the time this article was written, it can be purchased in the US from Florida Tropical Fish Farms, Inc. 1-800-940-3833. Other sources may be available, and the Author does not know for how lon g the above-mentioned supplier will keep it in stock). FLUBENOL IS TOXIC TO SNAILS. Use at the dose of 1/2 teaspoon for each 30 gal, which roughly corresponds to the recommended dose of 200 mg/100 liters4. Pre-dissolve the compound in a contain er with some aquarium water, and then pour it in the aquarium. It is better to use a container with a watertight lid, so that it can be shaken to facilitate the dissolution process, which is quite difficult with this drug. After six days, change at least 30% of the water (removing the deposit of white powder left on the aquarium walls), and introduce activated carbon in the filter. Some experienced Discus keeper however repeat the treatment on a weekly basis for a total of three consecutive weeks, since the response to flubendazole occurs very slowly (after 10 days according to Untergasser4). Flubendazole is a very active antiparasitic drug, which with a single treatment should effectively kill tapeworms and flukes (including eggs). It is al so effective on nematodes (such as Capillaria), although the Author does not think that in this case one single treatment would always suffice.

Flubenol treatment failures may occur, and have actually been described by several experienced Discus keepers in cases of flukes. In such situations there is the option to treat again with praziquantel or Fluke Tabs.

The only problem experienced by the Author with this drug consisted in a sudden drop in dissolved oxygen levels (with severe respiratory and neurological symptoms of the Discus that were being treated), presumably due to bacterial proliferation on the film of deposits left by this preparation on the aquarium walls. Therefore, use of aeration during treatment and a thorough clean-up of the tank at the end of the treatment period (wiping off the sides with a sponge and siphoning the bottom) are absolutel y necessary.




The Author has successfully used doses of two tablespoons/ 10 gal. or 2g/10 liters of water. This should produce in the aquarium concentrations of approximately 0.2g/l. Maintain the concentration for seven or more days, replenishing the a mounts lost during water changes. Live plants may suffer some damage.



Two teaspoons of Epsom salts each ten gallon of aquarium water, will often clear within a few days the intestinal tract of the fish from food obstructions.



Several skin and gill protozoans (e.g. Ich, Oodinium or velvet, Costia) do not tolerate high temperatures2. The critical temperature to eliminate them varies according to the pathogen, but a temperature of 33-34 deg. Celsius (93 deg. Fahrenheit) maintained for a week, should eliminate all of them. Remember that the content of dissolved oxygen will decrease with higher temperatures, and an airstone will help to prevent problems. For Discus tanks, most (but not all) aquarium plant s will survive this temperature increase. Do not combine this procedure with other treatments, such as formalin, that cause drops in oxygen levels. Remember that fishes other than Discus may not tolerate such temperature increase, and die. For community t anks, a pharmacological treatment may be preferable.




Several premixed formulations are available on the market, but there is also the possibility to buy the two components separately and prepare a homemade mix. Some fishes may tolerate this treatment less well than others. The Author has dir ect experience with a ready-to-use formulation of formaldehyde 4.26% and malachite green 0.038% (Rid-Ich + by Kordon13). Since the optimal target concentration in the aquarium water is 25 mg/l of formalin and 0.1 mg/l of malachite green1< /SUP>, 7ml/10 gal or 9 ml/50 liters should be used. If different formulations than the one mentioned above are to be used, they should specify the concentration of the ingredients and the correct dose should be calculated by the aquarist. The aquarium lig ht should be well dimmed down or turned off, since malachite green is degraded by the light. The recommended dose needs to be administered on day 1,4,7,10, with water changes on and after day 13. At that point, adding carbon in the filter may help to acce lerate the removal of the medication. Water changes can also be performed, if necessary, just before each administration.

It is essential to increase aeration in the tank, since the oxygen levels will drop. An adequately sized airpump will effectively take care of the problem. Because of the decrease in oxygen levels, never use formalin while treating the tank with high t emperature.




This agent may be extremely effective, but also extremely toxic, particularly under the typical Discus soft water conditions. Some fishes may tolerate it less well than others. It is extremely toxic to plants and invertebrates such as sna ils. It should not be used with water hardness below 10 GH 2 or 50 mg/l of total alkalinity11 : hardness may be increased simply by adding over a period of a few days some Tanganyika or Malawi salts. Several different formulations of copper are available, and a simple approach is to ask a reliable aquarium store dealer which formulation he is familiar with, and then use it as per the manufacturer’s instructions. It is extremely important to monitor the copper levels with a test kit, initially every day, and then every two or three. The levels of non-chelated copper should be exactly between 0.15 and 0.20 mg/l11: if too low, there will be no therapeutic effect, and if too high toxicity may occur. It is better to maintain t he treatment for two or three weeks.




The following proposal is aimed at eliminating several of the pathogens that may be present on a newly acquired fish, before symptoms occur. It is important however to understand that it is impossible to cover all the possible causes of in fectious disease, and no thing such as complete "sterilization" exists. These procedures help to further reduce the risk of future problems, and to be completely effective and avoid re-infection they must have been applied to all fishes in a gi ven tank.

The dosages of the medications recommended have already been described, and they will not be repeated here. Newly obtained fish(es) should be placed in their own quarantine tank, and first well fed and conditioned with good water changes. After indica tively one week, the preventive treatment may start.


  1. Administer one cycle of metronidazole, to eliminate or at least reduce the numbers of flagellates that might be present. After several water changes:
  2. Administer either flubendazole or Fluke-tabs, which will target flukes, tapeworms and probably also nematodes. If nematodes are not a concern, praziquantel may be use instead. After several water changes:
  3. For situations where skin and gill ciliates or dinoflagellates may be a concern (or for those like the Author that suffered from a velvet epidemic which lasted several months, and that do not want to have such experience again), a week long temperatur e increase to 93 deg. F (33 deg. Celsius) or, less preferably, a prolonged bath with copper may be beneficial for preventing future problems.


Account for the fact that these procedures will require several weeks, and that time and dedication will be needed to maintain the quarantine tank in healthy conditions (regular and frequent water changes, water chemistry monitoring, vacuuming of the b ottom, etc.).







1. C. Andrews, A. Exell, N. Carrington (1988). The Manual of Fish Health. Tetra Press.


2. D. Untergasser (1989). Handbook of Fish Diseases. TFH, Neptune, NJ, U.S.A


3. D. Untergasser (1991). Discus Health. TFH, Neptune, NJ, U.S.A.


4. D. Untergasser (1991). Malattie dei Pesci d’Acquario. Primaris s.a.s., Milano, Italia


5. P.V. Loiselle (1994). The Cichlid Aquarium. 2nd Edition, Tetra Press


6. T. Hovanec (1997). Nitrifying Bacteria - Part Two. Aquarium Fish Magazine (January)


7. V. Zupo (1990). Le malattie dei pesci. Ed. Olimpia


8. Hex-A-Mitä , Dose Instructions (Aquatronics, P.O. Box 6028, Zuma Station, Malibu, CA 90265, U.S.A.)


9. Unknown Author (July 1995). Tropical Fish Hobbyist, page 151. TFH, Neptune,

NJ, U.S.A.


10. Fluke-Tabsä , Dose Instructions (Aquarium Products, Glen Burnie, MD 21061, U.S.A.)


  1. E.J. Noga (1996). Fish Disease, Diagnosis and Treatment. Mosby-Year Book, St. Louis, Missouri, U.S.A.

  3. Discus-L e-mail list: for subscription and other information see the Discus-L web page:


  1. Rid-Ich+Ò , Dose Instructions (Kordon Division of Novalek, Inc., Hayward, CA 94545, U.S.A.)



Many thanks to Kevin Conlin for the accurate review given to the manuscript and to Raffaele Bufo for the support and the patience he had with such a slow writer like me!

The Author would also like to thank the contributors to the Discus-L e-mail list for the information shared among the members.