The Most Common Diseases of Fish and Their Treatments

Aquarium Health Care

Just like people, aquarium fish can become sick. There are many diseases and parasites that can occur in freshwater aquariums, which is why it is important to quarantine any new fish prior to adding them to your aquarium. Nonetheless, even with a quarantine and properly caring for your fish they can still become sick. When this happens, it is important to quickly and properly diagnose and treat your fish. Remembering sometimes fish die of old age, or are too sick to recover.

Gold fish with areas selected

Recognizing Diseases:

Diseases and other aliments effect fish in many different ways. Therefore, it is important to know what a fish looks like when it is healthy so that any changes can be recognized and treated. Symptoms can present themselves as changes to behavior, such as feeding or swimming patterns, or can be physical signs on the fish body.  Behaviors to look out for include; refusal to eat, gasping for air, hectic movements, limited movement, or irregular swimming patterns. Physical symptoms to look out for affect the five main areas of the fish’s body.

The five areas to inspect for illness include:

  1. Head Area
  2. Gills
  3. Fins
  4. Scales
  5. Rear Fin Area

Inspecting these areas for irritation, parasites, abnormal growths, and other symptoms out of the ordinary on a regular basis allows aquarium owners to spot the early signs of aliments in the aquarium. This allows for early treatment and prevents the spread of disease to the entire tank.

Common Aliments, Their Causes, and Their Treatments

IchWhite Spots on Fins and Body, Loss of AppetiteIch (Ichthyophthirus multifiliis), a common parasite in aquariums that reproduces rapidly and can quickly infect an entire tankAdminister Ich medication to entire aquarium (See medication rules for aquarium dosages) and raise temperature around 4 degrees.
Swim Bladder DiseaseSwimming Upside-down, difficultly maintaining balance, swimming on sides, fish at the bottom or top of tank Swim Bladder Disease, Damage to the swim bladder can occur through mishandling or fish fighting, or bacterial infection from poor water conditionsImprove water quality, if only one fish is showing symptoms isolate to hospital tank and treat with antibiotics.
Anchor WormWhite worm protruding from agitated area on body, erratic swimming, scratching against tank objectsAnchor Worm (Lernaea), an adult form of the parasite that buries itself into a host fish. Commonly effecting pond fishRemove fish from tank and carefully remove worm using tweezers, treat with antibiotics.
DropsyFish grows fat and looks like its going to burst with its scales protruding outwardDropsy, Malawi Bloat, Ascites (Bacterial infection), Abdominal bloating caused by metabolic disease or overfeeding.Remove effected fish, reduce feeding and administer antibacterial. Increase oxygen content and temperature
ConstipationInactivity, resting on the bottom of the tank, abdominal swelling and bulging occurs. Constipation, caused by overfeeding or poor diet. Correct diet and dose tank with aquarium salt.
Fin RotFins missing parts or are shredding away, Fins become eaten away and inflamedFin Rot, caused by bacterial infection and poor water quality. Can also be caused by physical damage during handling or fin nippingImprove water quality. Remove effected fish and treat with antibacterial medications. If entire community is affected treat the whole tank.
FungusFluffy, cotton-like growths in patches across the body and fins, white in colorFungus, often occurs with other bacterial or parasite infections. Caused by poor water quality or open wound sitePerform a water change and correct any water issues. Treat entire tank with fungicide.
PoisoningColors fade, fish swim erratically, breathing accelerates Poisoning or unbalanced water conditions. Caused by metallic, chemical, or other water parameters being unsuitable for fish. Particularly noticeable after a large water change.Check environment for metal contamination. Complete an inspection of water change bucket and equipment. Test tap water and use distilled water for a water change and stress coat to protect fish.
VelvetYellowy-gold velvety covering on the body and fins. Sudden spots with a peppered fine powder look. More yellowish than whiteVelvet Disease (Piscinoodinium) Parasite that feeds on the skin cell roots. Administer Velvet treatment to the tank. Caution must be taken to avoid harm to aquarium invertebrates.
Gill WormsRapid breathing and colorless threadlike worms protrude from gills, eyes may have glazed appearanceGill worms, parasite, Infestation can occur from wild caught or non-quarantined fish. Raise oxygen content, treat with antibacterial medications and aquarium salt
Fish LiceScratching against tank environment, small disc-like parasites are visible and lay flat on skinFish Lice (Argulus), a parasite that attaches it self to fish. Females produce larvae that see out new hosts. Remove fish and pull off parasite with tweezers. Treat with antibacterials and aquarium salt. Dose tank to kill larvae

Aquarium Defense Arsenal

Once you have diagnosed your fish, choosing the right treatment is important to ensure quick remedy. Below we have listed the top products for each of the possible illnesses. The cure all-in-one are great to have for common illness that cannot be specifically diagnosed. For an aliment like Ich or Fungus, it is better to use a targeted medication like the ich treatment listed above or an antifungal displayed in the chart below.

Seachem ParaGuard<$15
API General Cure<$15
Tetra LifeGuard Tablets<$10
API Melafix<$10
API Furan-2<$10
API Pimafix<$10
API Fungus Cure<$10
Aquarium Salt
API Aquarium Salt<$10
Fish Coat Protector
Stress Coat Plus<$10

Treating a Sick Fish

Upon diagnosing an illness, it is essential to act quickly to minimize damage to aquarium fish. Keeping a supply of essential medications and chemicals on hand allows for a quick response to any signs of aliment. Furthermore, a quarantine tank can serve as a hospital tank for a sick fish; however, sometimes it’s better to treat an entire tank to kill any harmful bacteria or parasite.

We always recommend following the instructions provided with aquarium medications and chemicals. Most cases of illness can be treated with one or a combination of the following essentials plus a water change, filter media change, and potentially a temporary temperature raise.

Additionally, if you have tried all the above and followed the instructions on the medications we advise consulting with a local aquarium store. They will be able to test water and provide area specific causes that may be affecting your aquarium.

As with any pet, sometimes illness is not treatable. With fish often the most humane way to treat the illness is to remove the effected fish from the tank and euthanize it. Here we have attached a link. Finally, if you have tried several treatments and there is no remedy consult with a local fish expert, or message us directly. Sometimes the only solution is getting rid of the effected fish and completely starting fresh.


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