Fish Diseases

Most fish diseases are easily recognized and successfully treated. However, the fishkeeper can do much by following a few simple guidelines, to ensure that his fishes do not contract diseases. External factors should also be considered. Fumes from paint, cigarette smoke and air sprays and furniture polish can all be carried into the aquarium through the air pump. Avoid using materials giving off strong vapors near the aquarium, and do not put hands recently washed with strong soap. Even apparently healthy additions to the aquarium should be quarantined. Isolate the new stock in a spare tank for 2-3 weeks, during which time any latent disease should manifest itself. Aquarium plants can also introduce unwanted guests and new plants should be thoroughly rinsed before use.

Aquarium nets can spread diseases from tank to tank, so each tank should be allocated its own net, which must be disinfected after each use. wherever possible, avoid any metal/water contact. Be sure to maintain correct water temperatures, clean filters regularly and make partial water changes a habit. These actions, together with a full varied diet, will ensure that your fishes remain at the peak of fitness.

Treatments for diseases range from individual baths to medication of the whole tank. In some cases, treatment can be administered internally by soaking the fish's food in the medication before feeding. Occasionally, a fish may be treated out of water, when dealing with a wound or a parasitic infection large enough to be treated this way.

Filters used in any tank that is to be treated should not contain carbon, as it will absorb the medication; and extra aeration should be used, because medications often reduce the level of oxygen in the water. Aquarium plants are sometimes adversely affected, and fine-leaved species suffer most.

At the end of any treatment, the fishes should be acclimatized gradually to normal water conditions by the partial replacement of medicated water with fresh clean water over a period of days.

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White Spot Disease

(Ichthyophthiriasis or "Ich") - This is the most common parasitic ailment and probably the easiest to diagnose. The fish's body is covered with tiny white spots, which extend to cover the fins. The disease is of a cyclic nature: the parasite leaves the fish's body to form cysts on the aquarium floor and upon hatching the parasite is then free-swimming, seeking a new host. It can be attacked by treatment at this stage. As the disease is likely to affect all the fishes in an aquarium, the whole tank should be treated.

Only repeated treatments will continually kill the juvenile tomites, preventing continuation of the infection. This process will be greatly accelerated if organic debris can be removed from the tank following treatment. Treatments should never be discontinued until all mortality from "Ich" has stopped. In general, copper sulfate, formalin, and potassium permanganate are all effective against "Ich" when applied at the correct concentration in a repetitive manner.


This disease is fairly easy to diagnose. The fish appears to be covered by a layer of fine golden dust, giving it a velvety look. The parasite responsible, Oodinium limneticum, has a similar cycle to that of the white spot disease parasite. O. pillularis is responsible for another "velvet" disease, where the color is more of a brown color. Both freshwater and marine fish are affected. There are many commercially available products to cure Velvet.

Fungus Saprolegnia

In this disease outbreaks of cotton-woll-like tufts appear on the fish's body, or it may be covered completely with a fine layer of cobwebby or dusty fungus. It is sometimes tinged green. The affected fishes can be easily spotted by erratic swimming, darting, and scratching against the aquarium hard surfaces. Often confused with body fungus is mouth fungus, which is caused by a slime bacterium, and may not be cured effectively by all treatments suggested for body fungus. Treat water with a medication containing methylene blue or malachite green.


Occasionally a fish's body becomes bloated to such a degree that the scales protrude outwards. This is due to the body cavitis filling with liquid. This condition is difficult to cure and can be contagious. The affected fish must be isolated until it recovers or has to be destroyed.



Finrot is degeneration of the tissue between individual rays of the fins caused by bacteria such as Aeromonas, Pseudomonas, or Flexibacter that abound in all aquatic environments. Damaged fins allow the bacterial infection to gain a hold on the injured fins. A general clean-up of the aquarium water is required, together with better aquarium management: avoid overcrowding, watch for parasites, maintain proper oxygen levels, remove aggressive fish from the community, maintain superior water quality etc.

Gill Flukes

Sometimes fishes scratch themselves on rocks or plants and have visibly gaping gills. Such fishes are infected with Dactylogyrus or Gyrodactylus parasites, which burrow into the skin or collect on the delicate membranes. The parasites may be removed by bathing the fish in well-aerated medicated solutions. The parasites cannot survive without a fish host, so if the aquarium is left uninhabited for a few days while the fish are being treated with medicaments, the parasites will be eliminated. Fishes panting at the surface may not be afflicted by parasites at all, but gasping for oxigen because of an excess of carbon dioxide in the water. Immediate relief can be provided by extra aeration.

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