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Keeping your Fish Healthy

Signs of illness in fish are gasping for air, lethargy (reluctant to swim), spots, red skin and fins, weight loss, abdominal enlargement and inflamed gills.  A lot of fish health problems are related to water quality but fish can develop diseases and our guide will help you to recognise the symptoms.

Water quality problems

If you spot your fish gasping at the water's surface this could be a sign that your fish are struggling to breathe.  Your fish will be at the surface as oxygen concentration is highest where air and water meet.  Other signs of respiratory problems are lethargy, swimming sluggishly and inflamed gills.

  • Your aquarium could have too much ammonia or nitrite in the water.  Elevated ammonia levels inflame the fish's gills and nitrite poisoning prevents red blood cells from transporting oxygen. The presence of chlorine and pH levels that are too high or too low will also make fish gasp at the surface.  
  • Test your aquarium water for ammonia, nitrite and pH imbalances. Our staff can  test a water sample for you - we can test for Ammonia, Nitrite, Nitrate and pH in store. We test for all four and will advise you on the best course of action based on the results.  
  • Check that your heater, filter and air pump are working properly and siphon debris from the gravel to improve biological filtration.  
  • A water change is usually recommended  but the amount that should be changed depends upon the quality of the water and the frequency of the changes.  If in doubt of the amount of water you should change ask our staff for help and advice.

Whitespot /Ich

Whitespot or Ich (Ichthyophthirius multifiliis) is caused by a protozoan parasite and is very contagious. It can be triggered by poor water quality and stress.  Symptoms are small white spots – about the size of a pin head - on the fish, scratching against hard objects and lethargy.  Whitespot is very common and is easy to treat but you must catch it early as fish can become too ill to recover.  In advanced stages fish can suffer from gill damage and be seen gasping for air.  There are effective liquid treatments available which you add to your tank water.

Columnaris / Cotton Mouth

Columnaris is often mistaken for a fungal infection but is actually a common bacterial infection.   Symptoms are greyish white patches on the mouth, edges of scales, and fins that resemble fungus.  Sores may appear on the body and the gills can become affected.  It is highly contagious and can be triggered by poor water quality or stress.  Anti-bacterial medications are available and should be used promptly.

Fin Rot / Tail Rot

Fin Rot or Tail Rot is a common disease and is caused by several different bacteria.  The symptoms are opaque, fraying and ragged fins and/or tail that become eroded away until the fish dies.  The disease is usually triggered by poor water quality or where fin damage has occurred – often caused by fin-nipping fish.  It's important to catch this disease early and there are antibacterial treatments available.


Fungal spores are always present in the aquarium, and an outbreak of fungal disease usually occurs after damage to the fish and as a secondary infection.  Symptoms are cotton wool like growths on the body.  Anti-fungal remedies are available that can destroy the fungus and prevent it from spreading.

Velvet / Rust / Gold Dust Disease

Velvet (also known as Rust or Gold Dust Disease) is a common disease and is caused by the protozoan parasite Oodinium.  Symptoms are a fine greyish gold to white dust on the body of the fish, rapid gill movement, weight loss and scratching or rubbing the body against hard objects as the fish tries to remove the parasite. Oodinium is usually triggered when the fish are stressed by poor quality water, changes in the water temperature, or being transported.  Medication is available and should be used as soon as possible as Velvet is highly contagious.