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Related FAQs: FW Troubleshooting, Freshwater Disease, Freshwater Disease 2, Freshwater Disease 3, Toxic Situations, Infectious FAQs, Parasitic FAQs Ich/White Spot Disease, Worm Diseases, Freshwater MedicationsNutritional Disease, Goldfish DiseaseAfrican Cichlid Disease 1, Cichlid Disease

Related Articles: Freshwater Diseases Freshwater Maintenance, Freshwater Infectious and Parasitic DiseaseUnderstanding Bacterial Disease in Aquarium Fish; With a gallery of bacterial infections, a discussion of 'Fish TB', and a listing of major antimicrobial medications with examples available to fishkeepers By Myron Roth, Ph.D., Ich/White Spot Disease, Choose Your Weapon: Freshwater Fish Disease Treatment Options by Neale Monks,

Freshwater Aquarium, Livestock Disease Troubleshooting


© Neale Monks 2007


Freshwater fish can suffer from a variety of ailments, but only a relatively small number are commonly encountered. The key below will help you identify the most frequently seen freshwater fish health problems. Identifying the exact problem is important, because without knowing what you treating, you cannot choose the correct medication. Merely adding medications at random is unlikely to work.

In many cases, the disease itself is a symptom of a larger problem. Fishes with finrot may be suffering from a bacterial infection, but the reason they are sick at all is almost always problems with water quality. Similarly, the appearance of whitespot (ick) in an established aquarium typically follows on from adding new fish that haven't been quarantined first.

Keeping your fish disease-free is generally much easier than trying to identify and treat diseases once they happen. Choose fishes suited to the water conditions you have in your aquarium. Buy healthy fish from clean, well-run stores. Quarantine them carefully before adding them to your tank. Maintain proper levels of cleanliness in the aquarium. Perform regular water changes. Test the water chemistry and water quality regularly, especially with newly set-up aquaria. Avoid live foods that can transfer diseases (feeder fish and tubifex worms) or stick with frozen foods or dried foods. Many fish are omnivores and need algae or plant matter in their diet, so provide some. Isolate sick fish, and treat diseases immediately. Some diseases, such as finrot, start off easy to cure but can develop into lethal, difficult to cure problems when ignored.


Dwarf gourami (including artificial forms like neon gourami and powder blue gourami) lethargic, not eating properly, eventually with bloody sores or blisters on the skin.

Dwarf gourami disease (DGD). Sometimes caused by a bacteria, sometimes by a virus. Bacterial form may be treated at early stages with antibiotics; otherwise untreatable. Quarantine sick fish immediately as DGD is highly contagious. Provide optimal water conditions and hope for a natural recovery; otherwise destroy the fish painlessly. DGD is most easily avoided by not keeping dwarf gouramis, but instead opting for similar but resistant species such as Colisa labiosus and Colisa fasciata.


Not a dwarf gourami showing these symptoms

Go to 2a.


Neon tetra (and only rarely cardinal or other tetras) staying away from others in the school, hiding away, not eating, eventually losing colour and becoming listless.

Neon tetra disease (NTD) caused by the protozoan parasite Pleistophora. Essentially untreatable, even with antibiotics, and sick fish should be destroyed painlessly. Highly contagious, though apparently primarily through sick or dead fish being pecked at or eaten by other fish, hence removing sick fish is a major step in preventing infection of the other fish.


Not a neon tetra showing these symptoms.

Go to 3a.


Fish swollen, with scales protruding at an odd angle from the body, giving it a pine cone-like appearance.

Go to 4a.


Fish not notably swollen.

Go to 5a.


Lake Malawi or Tanganyika cichlid, showing classic signs of accumulation of fluid in the body cavity together with heavy breathing, odd behaviour, lack of appetite, and stringy faeces.

Malawi Bloat, precise causes unknown but a variety of factors have been identified. The use of marine or tonic salt in an attempt to harden the water is one consistent factor. Poor diet is another factor, especially the overuse of meaty foods with species that are primarily herbivorous in the wild. Stress and poor water quality may also be important factors. Once fish are visibly sick, the prognosis is poor, and treatments with antibiotics and commercial medications have had mixed results. Prevention is better than cure.


Body swollen due to accumulation of fluid in the body cavity. Often accompanied by other symptoms of ill-health such as listlessness, poor appetite, and odd swimming behaviour. Note that a few fishes have naturally protruding scales, notably male Pachypanchax playfairi at spawning time.

Dropsy, a symptom of a wide variety of diseases, almost always at a stage too late for treatment. Small fish like guppies with dropsy should be destroyed painlessly, and even treating larger fish like koi without veterinary assistance is very difficult indeed. Dropsy is not especially contagious, but it does seem to be common in tanks with poor water conditions or where the fish have been provided with an unhealthy diet. As such, reviewing aquarium maintenance is important to prevent other fish from becoming sick.


Fish bears off-white to brown lumps with a cauliflower-like texture, sometimes small but potentially large. These growths are commonly on the fins but may be elsewhere. Otherwise the fish seems healthy and happy.

Lymphocystis, a relatively benign, non-contagious viral condition. Generally uncommon in freshwater fishes and almost only ever seen on members of "advanced" taxa such as spiny eels, cichlids, pufferfish, etc. Apparently caused by poor environmental conditions. Untreatable, though vets may be able to cut away damaged tissue on large fish. Being a viral disease, antibiotics have no effect at all. Primarily a cosmetic problem, after a period of many months (even years) the growths may disappear by themselves. Tumours are superficially similar but are part of the fish and usually have a visible network of blood vessels. Often have a silvery or pearly appearance thanks to the stretched skin. Most are benign (like warts on humans) and may go away eventually by themselves. Exceptions are where the tumours block the mouth, gills, or anus, in which case the fish should be painlessly destroyed.


Fish does not have these growths.

Go to 6a.


One or both eyes protruding abnormally from the head. The fish seems otherwise healthy.

Pop-eye or exophthalmia is a condition that may be caused by water quality issues, physical damage to the eye, bacterial or parasitic infections, and metabolic disorders. It cannot be treated directly, but providing optimal diet and water conditions can help reverse the symptoms. Antibiotics may help in cases where infections are the cause. Not normally contagious, but frequently a sign that aquarium conditions or maintenance is faulty.


Eyes not protruding.

Go to 7a.


Eyes cloudy.

Cloudy eyes can be caused by a variety of problems. Poor handling when fish are netted is one common cause. Nutritional imbalance, fungal infections, and certain worms can also cause these symptoms. Treatment is difficult, and essentially comes down to providing optimal water conditions and the correct diet and waiting for the symptoms to go away. Eye flukes (cataract worms) in particular cannot complete their life cycle in an aquarium, and will eventually die off without being able to infect other fish.


Eyes not cloudy.

Go to 8a.


Mouth covered with of-white or grey growths, somewhat slimy in appearance. In advanced cases such growths may appear also on the body and fins. Infected fish often show odd swimming behaviours and loss of appetite.

Mouth fungus is caused by a bacterium (not a fungus) called Flexibacter columnaris. The root cause is almost always poor water quality or the wrong water conditions. Correct these underlying factors is critical to fixing the problem in the long term. Treatment of the symptoms can be obtained using commercial medications but advanced cases may require antibiotics.


Fish do not show these symptoms.

Go to 9a.


Sections of fin missing.

Go to 10a.


Fins do not have bits missing.

Go to 12a.


Fins have obvious, discrete bite-marks that seem to appear suddenly. At least initially, the fins show no signs of infection.

Fin-nipping is a behaviour of some fishes towards others, typically the victim being large, slow-moving, or having longer than normal fins. Notorious fin-nippers include serpae tetras, tiger barbs, black widow tetras, dwarf upside-down catfish, and certain pufferfish. Regular victims of fin-nippers include fancy guppies, angelfish, gouramis, bettas, and fancy goldfish. The immediate "treatment" is to separate the fin-nipper from the victim. Anti-fungus and anti-finrot remedy should also be used prophylactically to prevent damaged fins becoming infected.


Fins becoming gradually more damaged over time and across a large area of the fin.

Go to 11a.


Fin membranes "eaten away" leaving the fin rays largely intact. There is usually a noticeable whitish region where the fin is being eaten away. Can spread onto the body of the fish if left untreated, creating open, bloody sores and eventually damage to the internal organs.

Finrot is caused by a variety of bacteria such as Aeromonas and Pseudomonas. Essentially a reflection of poor aquarium conditions, though clumsy handling, fin-nipping, fighting, and the wrong diet are additional factors. Fancy goldfish are very sensitive to finrot when kept in too-cold water, for example in a pond that freezes over. Easily treated with commercial medications in its early stages, finrot will require antibiotics if allowed to develop into a more serious infection, septicaemia.


Fins ragged with both membranes and fin rays missing. Patches of thread-like fibres are clearly visible. Can spread onto the body if left untreated.

Fungus will usually set in where the fins have been damaged in some way, but it may also be caused by keeping the fish in appropriate water conditions. Maintenance of brackish water fish in freshwater conditions frequently leads to fungal infections. Readily treated in its early stages with commercial anti-fungus medications. Not contagious as such, but the conditions that cause fungus can allow more than one fish in the tank to develop the symptoms. Advanced cases of mouth fungus can also cause symptoms similar fungus, where the bacteria have spread from the face onto the body and fins (see 8a).


Body and fins dusted with small white or yellow spots.

Go to 13a.


Body does not have these spots.

Go to 14a.


Discrete small white spots on fins and skin. Each spot looks like a grain of salt. There may be only one or two spots at first, but dozens or hundreds in advanced cases. Fish often scratch themselves against structures in the aquarium, such as rocks. Ventilation of the gills is often more rapid than normal.

Whitespot disease, also known as ick, is caused by the protozoan parasite Ichthyophthirius. Very commonly seen in freshwater aquaria, often when new fish are introduced to an established tank. Also common when tropical fish are kept insufficiently warm or other environmental parameters are not conducive to their health. Most easily cured using commercial anti-whitespot/ick medications. Not fatal if treated quickly, but if left untreated eventually damages the gills irreversibly.


Fine off-white to gold powder on skin and fins. The individual spots are smaller than those of whitespot disease, and give the impression the fish was dipped in confectioner's sugar.

Velvet disease, caused by the protozoan parasite Oodinium. Relatively uncommon in freshwater aquaria. May be treated using commercial remedies; many anti-whitespot also treat velvet. Like whitespot, can cause damage to the gills if left untreated, eventually leading to death.


Large white, grey, or pink spots, irregular in shape, often clumped together to form phlegm- or wax-like masses.

Fish pox is a viral infection, and as such is essentially untreatable. Antibiotics, salt baths, and so on have no effect. Under good conditions it seems to fade away eventually though it may recur. Fish pox does not seem to be particularly contagious and doesn't seem to cause the fish any undue suffering. Very rarely seen in tropical fish, it is mostly an issue with goldfish and koi.


Fish does not show these symptoms.

Go to 15a.


Fish "treading water", rocking from side to side and clearly having trouble swimming normally.

The shimmies is a name used to describe this sign of damage to the nervous system. It can be a secondary symptom of a variety of diseases, but is most commonly observed with mollies kept in the wrong water conditions. Mollies do best in hard, alkaline, slightly brackish water. In soft and acidic water especially, they are prone to getting the shimmies along with finrot and fungus. There is no specific treatment to the shimmies, but transferring the fish to the appropriate water conditions will generally improve things quite rapidly. Other symptoms, such as finrot, will need to be treated as well.


Fish not behaving in this way.

Go to 16a.


Fish behaving in an odd manner, swimming in a peculiar way, but otherwise seem physically normal.

Go to 17a.


Fish not exhibiting such behaviour.

Go to 18a.


Fish gasping at the surface, breathing heavily, and swimming nervously, often rapidly darting about. They may try to jump out of the aquarium. Tiger barbs will swim head-downwards, while air-breathing fish like Corydoras will dash to the surface to gulp air more frequently than normally. Many species will adopt subdued or otherwise abnormal colouration.

Signs of distress such as these are warnings that something has changed in the aquarium making the water inhospitable. The most common problems are failure of the filtration system and sudden changes in the pH/hardness of the water. Toxic substances can cause similar symptoms, for example paint fumes and insecticide sprays. Identify the problem, and perform remedial action at once. Almost always, performing multiple, large-scale water changes will provide a useful "first aid" to such problems.


Fish attempting to swim normally but seem unable to maintain proper posture, rolling over or holding an unusual orientation.

Swim bladder problems can be caused by bacterial and viral infections but the most common cause is malnutrition. Feeding high-fibre foods (plant foods, such as tinned peas) will help in mild cases. Goldfish, particularly fancy goldfish, are most prone to swim bladder problems of this sort.


Small worm-like organisms stuck to the surface of the fish.

Flukes and fish lice are external parasites that commonly infest the skin and gills. Commercial treatments exist for external flukes and lice, but saltwater baths can also work very effectively. In severe cases, veterinarian help may be required. Relatively uncommon among commercially bred fish, flukes and lice are more characteristic of certain wild-caught fish, such as bichirs.


No such organisms visible.

Go to 19a.


Fish superficially normal, but rapidly losing weight.

Wasting diseases can be caused by intestinal parasites, bacterial infections, or viruses and tend to be difficult to identify without performing an examination of the body cavity. Very commonly introduced with certain live foods, particularly "feeder fish". The pathogens responsible are typically highly contagious, especially when recently deceased fishes are eaten by their tankmates but potentially through contact with faecal matter. Therefore any fish exhibiting these symptoms should be quarantined and either treated with anti-worm or antibacterial medications (probably both) or else painlessly destroyed.


Fish not losing weight.

Go to 20a.


Fish has strange deformities such as crooked spine or twisted fin not apparently associated with physical damage such as fighting or fin-nipping.

Congenital deformities are common in fish, and typically a few deformed fry will be found in every batch. Obviously such fish should not be bred from, and if suffering, painlessly destroyed.


Fish not showing these deformities.

Write to Wet Web Media for help!

 A note on antibiotics

Antibiotics are a powerful tool for treating bacterial infections. However, they are only available without prescription in the US; aquarists in Europe, Canada, and elsewhere will likely have to obtain them by prescription from a veterinarian surgeon. In the UK, such a prescription will cost around £20. Obviously this underlines the fact that prevention is better than cure! It is also important to recognise that antibiotics generally have no effect on diseases not caused by bacteria. Viral infections in particular generally cannot be treated with antibiotics and all you can do is provide optimal water conditions and a balanced diet and allow the fish's own immune system to deal with the problem.


Chris Andrews, Neville Carrington, Adrian Excell (1988), The Interpet Manual of Fish Health. Salamander Books, London & New York.

Neale's fish disease chart  5/23/07 Bob, <Neale> I'd been meaning to do this for a while. This article/chart is for  the page linked at below. http://www.wetwebmedia.com/FWSubWebIndex/fwdistrbshtart.htm The idea is that since we get a lot of the same queries again and  again, perhaps you can use this article to help people ID the  diseases their freshwater fish are suffering from. I hope it's  useful. It's attached as RTF and HTML, at least one of which should  work for you, I hope! Cheers, Neale <Outstanding! (as always)... Might I ask if you are the same Neale Monks who penned a piece re Mollienesia in captivity that ran in PFK recently? If so, would you sell the use of this work on WWM as well as this chart and spiffy dichotomous key to/for our use... for the grand sum of two hundred U.S. dollars (spend them while they're worth something... don't cry for me Argentina!)? BobF>

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