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We reproduce here, with their kind permission, the table of 9 common diseases of fish from Practical Fishkeeping Magazine's Good Health Guide (see Useful Links for their address).

Goldfish keepers should note that, although the table covers tropical and marine fish as well as coldwater fish, goldfish are susceptible to all these conditions. Notice the common theme - water quality - running through the Action column, and cross-refer this to our Golden Rules for keeping healthy goldfish.

Disease and Causes Symptoms Reason for Infection Action Treatment


Caused by Pseudomonas and Aeromonas bacteria

Pinky-white open wounds, often with a white edge and sometimes secondarily infected by fungi and other bacteria. Very poor water quality or an excessively high pH level. Minor scratches can become infected if conditions are poor. Also commonly affects newly imported Koi and goldfish. Test the water for signs of ammonia and nitrite. Conduct a large water change to reduce pollution levels. Fish lose salts quickly through open wounds, so add aquarium salt at a dose of 1-3g/litre. Use an anti-ulcer treatment. If treatment fails, a vet can prescribe stronger antibiotics.

Cloudy eye

Caused by poor water quality, poor diet, eye flukes, corneal damage, bacterial infection.

Entire surface or lens of eye takes on a cloudy, opaque appearance. There may be a build-up of mucus on the outer surface. Most commonly caused by poor water conditions. A lack of vitamins in the diet may also cause clouding. On rare occasions digenetic flukes, such as Diplostomum, can cause problems. Improve water conditions. Use a good quality food containing added vitamins. Improving water conditions usually cures cloudy eyes. Eye flukes are uncommon and can be difficult to accurately diagnose and treat.


Usually caused by bacterial infection. Viral infection, nutritional, metabolic and osmoregulatory problems can also be responsible.

Swelling of the body cavity due to a build-up of fluid. Scales become raised giving a pinecone-like appearance. One or both of the eyes may be protruded. Usually triggered by poor water quality, especially the presence of ammonia and nitrite. Often confined to individual fish. Test water and improve water conditions immediately. Aquarium salt at a dose of 1- 3g/litre can help to prevent salt loss. Can be difficult to treat. A broad spectrum anti- bacteria treatment is the best option in most cases.

White spot

Caused by Ichthyophthirius multifiliis parasite

Small white spots, about the size of a salt grain, on the skin, fins and gills. Stress related. Usually a consequence of poor or incorrect water conditions, fluctuating temperature and general poor husbandry. Sensitive species may develop white spot as a result of being introduced to a new aquarium. Ensure the water is free of pollution and isolate cause of stress. Treat promptly with an anti-parasite medication. It may be necessary to raise the water temperature to improve the effectiveness of the treatment. Wounds left by parasites may become secondarily infected.

Bacterial infection

Caused by Aeromonas and Pseudomonas bacteria

Reddening of the skin or fins; ragged fins with signs of infection, open sores. Common on many newly imported fishes. Often accompanied by other diseases, including fungi. Poor water conditions, especially the presence of ammonia and nitrite. Wounds resulting from poor handling, transport or fighting may become secondarily infected by these bacteria if conditions are poor. Improve water conditions, and treat promptly. Use a proprietary treatment as soon as possible. Aquarium salt at a dose of 1- 3g/litre can help prevent salt loss. Severe infections may require prescription medications from a vet.


Caused by Saprolegnia and Achlya

Fluffy growths affecting wounds on the skin and fins of freshwater fishes. Usually a secondary infection that invades wounds left by ulcers and parasites, including whitespot. Rarely a problem in tanks with good water quality. Improve water conditions and treat promptly. Standard anti-fungal medications, such as methylene blue, are usually very effective, but may affect filtration and water quality. When the disease occurs on open wounds, aquarium salt at a dose of 1-3g/litre can help reduce salt loss. Cotton-wool disease (Flexibacter) looks similar but is caused by bacteria and may require a different treatment.


Caused by Aeromonas, Pseudomonas or Flexibacter bacteria

Frayed fins, often with a pale pinky-white edge and some blood in the fin tissue. The bacteria are present on most fish. Stress from poor water conditions usually triggers an infection. Nipped fins may become secondarily infected if water is polluted. Some wounds may also be attacked by fungus. Improve water conditions. Isolate nippy fishes. Treat promptly with a finrot or anti-bacteria treatment to prevent the further spread of the disease. Consider adding salt (1-3g/litre) to reduce the loss of salt by the fish. Ensure that water stays free of pollution during treatment.

Swimbladder disorder

Caused by bacterial infection, incorrect diet, trapped gas, physical deformities.

Fish have difficulty swimming to the surface, or to the lower levels of the tank. Commonly affects egg-shaped fancy goldfish. Sometimes caused by poor water quality. Genetic problems in selectively-bred goldfish. Improve water conditions. Feed less dried foods, or pre-soak pellets and flakes so they don't swell the gut. Feed Daphnia, which acts as a laxative. Change diet and improve water conditions. Treat with a specialist anti-bacteria treatment. Fancy goldfish suffering from physical deformities will not recover.


Caused by an iridovirus

The virus causes crusty grey-white lumps to develop on the skin and fins. These may affect freshwater or marine fishes, and sometimes take on the colour of the underlying skin. These lumps are clusters of enlarged cells. The disease is viral, but may be triggered by stress, poor handling or poor water. Some fish may carry the virus without showing symptoms. The disease rarely kills, although lesions may become secondarily infected. Ideally, infected fish should be isolated. There is no known treatment. Some vets recommend the surgical removal of the lesions.

(We hope to provide photographs illustrating these conditons in due course).

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