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Common Fish Diseases

Common Fish Diseases

Just like humans a fish's immune system can also weaken from stress, environmental factors such as poor water quality and poor nutrition, making them susceptible to common fish diseases. There's nothing sadder than a sick fish--particularly when it's your friendliest koi or goldfish. Learn what to look for and how to care for your finned friends.

Warning Signs

Lack of appetite, open sores, flashing, rubbing, or gasping at the surface are all warning signs that your fish are under the weather. Inspect your fish for red sores on fins or mouths, these are signs of a bacterial infection. White spots or a cottony appearance are signs of a parasite or fungal infection. Also watch for your fish gasping at the pond's surface indicating signs of stress from a lack of oxygen.

Common Parasites

When present in the water, parasites, like anchor worm, ich and fungi, can attach to the body of the fish and cause irritation. Fish can be seen "flashing" or rubbing against objects and can have a sunken appearance.

  • Anchor Worm: These white string-like worms and their larvae can be introduced to your pond when adding new fish or aquatic plants. Once the worms have attached to the body of the fish red sores or inflammation may appear at the point of attachment. Tweezers are often used to remove the worms followed by a treatment like KnockOut Plus or Microbe-Lift Anchor Worm.
  • Ich: Also known as the white spot disease, often infects fish when they are under a lot of stress caused by pH fluctuations or rapid temperature changes. Along with flashing, fish can be seen at the surface gasping for air with clamped fins and pinhead white spots that look like white grains of sand all over. CrystalClear KnockOut Plus can treat the initial pond fish disease, while Pond Salt or MelaFix are often used to prevent a secondary infection or when treating new fish in an isoloation tank before being introduced to the pond.
  • Fungus: Inspect your fish for gray or whitish fungus growths on the scales give the fish cotton like appearance. If only one fish shows signs of fungus, place them in an isolation tank and treat with a fungus medication like KnockOut Plus.

Bacterial Infections

Bacterial infections are usually a symptom of a bigger issue. Parasites, predators, and poor water conditions can lead to common infections like fin rot and mouth rot and dropsy.

  • Fin/Mouth Rot: Look for color fading and ragged or decaying tissue around the mouth or fins. The first step is to test the water and do partial water change because this is only seen when water conditions are poor. Next, treat with WipeOut or other bacterial medications.
  • Dropsy: Dropsy causes the kidneys to retain fluid and is very hard to treat. Look for signs of protruding scales or bloating. Dropsy often occurs as a secondary pond fish disease when the immune system has already been compromised so prevention is key. Place infected or new fish into an isolation tank with warm water (about 70-75ºF) with pond salt, MelaFix and vigorous aeration for treatment or prevention.

Other Diseases

Here are some other common fish illnesses and symptoms to watch for.

  • Gill Disease: Often caused by poor water conditions and high ammonia levels, fish will have sunken eyes, loss of appetite, gasping for air at the surface and will often lay at the bottom of the pond for long periods of time. Treatment will include an isolation tank with vigorous aeration and a mix of pond salt with MelaFix. After treatment it is a good idea to keep ammonia levels down with aeration, partial water changes and testing the water often.
  • Oxygen Deprivation: Seen in ponds without a sufficient aeration kit, chemical overdose or overcrowding. Ponds with low levels of oxygen may cause fish to gasp for air at the surface often or hang out by the waterfall. To prevent this from happening add a bottom diffused aeration kit to circulate the entire pond.
  • Pop Eye: Eyes can become cloudy or reddish in color, but the most common sign is when the eyes start to bulge out of the sockets. Poor water conditions and trauma are common causes, but in rare cases it can also be caused by nutritional deficiency. To treat, isolate the infected fish with pond salt and vigorous aeration.

Reevaluate Your Routine

The majority of common fish diseases can be prevented with routine maintenance such as partial water changes, water testing, filtration, aeration and of course population control. We recommend to allow no more than 1-2 koi or 2-3 goldfish per 200 gallons of water for the best ecosystem.