Diseases in Fish

Kalojen sairaudet

White spot disease

White spot disease is caused by a unicellular parasite called Ichthyophthirius multifiliis which is often known fearfully as ‘ich.’ The parasite bores right into the mucous membrane of the fish and implants itself there. An infestation can be seen clearly from the outside due to the slightly elevated, white spots. If the disease is in its more advance stages, the small dots can unite to form gray spots. The skin of the fish forms more mucous and begins to loosen. If affected fish are not treated, the disease is fatal. It is important to spot the symptoms early on, so you can act accordingly.


  • Hesitant or irregular swimming pattern.
  • Fins flat on the body.
  • Rubbing the skin on stones, roots and other aquarium decorations by swimming in a curved movement.
  • Possible loss of appetite.
  • When the gills are also infested, the fish can have difficulty breathing or might breathe quickly and often hang just below the water’s surface and gasp for air.


  • Treatment takes place in the aquarium because the parasites settle in the ground as well as infesting the fish.
  • You can raise the temperature to 28°-30° but be careful as not all fish and plants can tolerate higher temperatures. You should research this beforehand.
  • Change the water – at least 30%.
  • Remove debris as the parasites also settle there.
  • Turn off the light when using Malachite Green or substances that contain Malachite Green as it is photosensitive.

Treatments should last for 14-20 days because the parasites only cause problems in a specific stage of their lives. They can be caught at the swarmer stage with medication.

Fungal infection

This fungal disease is commonly known as ‘cotton wool disease’ and is caused by the types of fungus Saprolegnia and Achyla. Usually, only fish that have a weakened immune system due to other factors get this illness. Injury, fights among fish, low water temperature and a badly maintained aquarium can all put a strain on a fish’s immune system and cause it to be affected by fungus. The fungus is a low-level pathogen. In weakened or injured fish, the pH of the mucous membrane is changed just enough to create ideal conditions for the fungus. Skin, eyes, fins and gills can all be affected.

As with every disease, it is vital to spot the symptoms early on.


  • A cotton-wool-like covering on the affected area which disappears straight away when you take the animal out of the water.
  • Listlessness.
  • Loss of appetite.
  • Usually the fish will swim around very little or will stop all together and remain in a dark corner of the aquarium.


  • Move the fish to clean water or change at least 50% of the water.
  • Slightly increase the temperature.
  • Bathe in a saline solution (around 1 teaspoon of salt in 1 litre of water) for 10-15 minutes or in potassium permanganate solution (1g in 100ml water) for around 30 minutes. It is important that the bathing does NOT take place in the aquarium but in a separate container.
  • Give vitamins to strengthen their immune system.
  • Treatment with a remedy for fungal infections and primary bacterial infections.

As the saying goes, prevention is better than cure. Good quality water and fish care are the key to healthy fish and a beautiful aquarium.

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