20 Common Goldfish Diseases: Causes And Treatments

Tankarium is reader-supported. We may earn a small commission through products purchased using links on this page.

Goldfish are relatively hardy fish that usually live for over ten years in captivity, although some specimens have even been known to survive happily in a home fish tank for 30 years!

That said, there are some goldfish illnesses that can affect these much-loved family pets and dramatically shorten that life expectancy.

So, what goldfish parasites are there? What is goldfish Ich? And can any goldfish diseases be caught by humans?

Read this comprehensive guide to 20 common goldfish diseases to learn how to prevent and treat them.

20 Common Goldfish Diseases

Bacterial Infections

There’s a broad range of bacterial infections that can affect goldfish, but fortunately, most are treatable.

1. Hole-in-the-Head Disease

Hole-in-the-Head Disease (HITH) affects the fish’s head and most often occurs in freshwater species.


HITH often starts as a small red dot or black spot that gradually becomes deeper and larger. As the disease takes hold, pale, eroding holes appear all over the goldfish’s head.


It’s not entirely clear what causes HITH, but the main culprit is thought to be a species of diplomonad bacteria such as Hexamita, Octomitus, or Spironucleus. 

Nutritional deficiencies, stress, and poor water conditions are also thought to be contributory factors.


Antibacterial medication that contains metronidazole as an active ingredient generally has the highest chance of success.

2. Fin Rot/Tail Rot

Fin rot is usually associated with dirty tanks and poor water conditions.

Although it’s generally a very treatable disease, the damaged fins sometimes never grow back properly, and it can take many weeks to eradicate the disease completely.


The symptoms of fin rot can be subtle and go unnoticed at first. Initially, the edges of the fins appear white or cloudy. As the disease takes hold, the edges of the fins start to fray as the tissue dies off.

The fins gradually get shorter and shorter as the dead tissue falls away, leaving the infected area inflamed and red. Sometimes, bloody areas appear, potentially allowing other bacterial or fungal infections to take hold.


Fin rot is caused by either the Aeromonas, Vibrio, or Pseudomonas bacteria.

However, the condition is commonly associated with poor water quality, incorrect water temperature, overcrowding, incorrect feeding, and stress.


Fin rot can be treated successfully with antibiotics or a fin rot-specific medication. However, to eradicate the disease and prevent the condition from recurring, you first need to address issues of tank hygiene, water quality, and diet.

3. Ulcers

Ulcers are usually associated with poor water conditions, attacks by parasites, and physical trauma.


Ulcers generally appear as large, open sores on the fish’s body or head, often with a white center and blood around the edges of the wound.

Sometimes, ulcers extend into the muscle tissue under the fish’s skin or even penetrate the internal organs in severe cases. If left untreated, ulcers can kill your fish.


Ulcers are usually caused by either the Aeromonas, Vibrio, or Pseudomonas bacteria.

However, the condition is commonly associated with poor water quality, attacks by parasites, physical injury, or stress.


The success of treatment depends on addressing the cause of the ulcer. 

Start by ensuring that the water in the tank is clean and within the correct parameters for your goldfish. If parasites are present in the tank, they must be removed before you treat the ulcer.

Place the fish in a salt bath and then administer antibacterial medication. If possible, net the fish and spot-treat the ulcer with a Q-tip dipped in hydrogen peroxide.

4. Popeye Disease

Popeye disease (exophthalmia) causes the fish’s eye to swell and protrude from its socket.


Popeye can affect one or both eyes. 

  • Swelling caused by fluid leaking into the space behind the eyeball
  • Cloudy or discolored eye if the cornea is ruptured

Popeye can be caused by:

  • Physical trauma or injury to the eye(s)
  • Some kind of bacterial infection or attack by parasites
  • Poor water conditions

It’s thought that too many oxygen bubbles in the water can cause gas to accumulate inside the fish’s eyeball, causing it to swell.


The treatment for this disease depends on the underlying cause. 

In the case of injury to the eye, you can treat the water with aquarium salt while the eye heals. If water tests show that the water chemistry is incorrect, you’ll need to take action to rectify that through partial water changes or pH adjustment. Bacterial conditions should be treated using appropriate antibacterial medication.

5. Dropsy

Dropsy is an old medical name for a condition that’s more correctly called edema or ascites. The condition causes swelling of the soft tissues inside the fish’s body cavity due to an accumulation of fluid.


Fish with dropsy exhibit the following symptoms:

  • Swollen abdomen
  • Scales that protrude, giving the fish a pinecone-like appearance
  • Bulging eyes
  • Pale gills
  • Red, swollen anus
  • Pale, stringy feces
  • Ulcers along the lateral line
  • Curved spine
  • Clamped fins
  • Red patches on the fins or skin
  • Lethargy
  • Loss of appetite
  • Swimming at the surface

Dropsy is generally caused by the common Aeromonas bacteria and generally affects fish that already have a compromised immune system due to stress. Common causes of that stress include:

  • Poor water quality
  • Ammonia spikes
  • Temperature shock
  • Transportation 
  • Incorrect nutrition
  • Other diseases
  • Aggressive tank companions

Usually, fish that have been exposed to stress for prolonged periods are most susceptible to dropsy.


First, treat the underlying problem that’s causing the fish to become stressed.

  • Move the fish to a quarantine tank
  • Add 1 teaspoon of aquarium salt per 1 gallon of water to the tank
  • Feed only high-quality foods
  • Treat the fish with antibiotics either in the water or food
  • Check the tank water every day to ensure that the parameters are correct

6. Cloudy Eye

Fancy goldfish are one of the most common fish species to be affected by Cloudy Eye.


The fish’s eye changes color, sometimes appearing milky or bloodshot.


Cloudy Eye is generally caused by one of the following:

  • Trauma to the eye
  • Poor water quality
  • Cancer
  • Incorrect diet

Usually, only one eye is affected.


If the condition is related to poor water quality or diet, treat the underlying problem first. 

If the eye has been damaged by a traumatic injury, treat the water with aquarium salt. The condition should clear up on its own.

7. Flexibacter Columnaris Disease

Columnaris disease is caused by a bacterial infection and can be internal or external, acute or chronic. Sometimes, the condition is mistaken for a fungal infection due to the mold-like lesions that the bacteria present.


Columnaris disease initially presents as white or grayish patches on the fish’s head, gills, and fins. 

As the disease progresses, the lesions become brown or yellowish in color, extending down the back and sides, giving the condition its common name of “saddleback disease.” Lesions around the mouth are cottony or moldy, gradually eating away the tissue. The fish’s fins become frayed, and the gills eventually disintegrate, leaving the fish unable to breathe and eventually causing death.

In cases of internal infections, the fish gradually sickens and dies from no obvious external cause.


Columnaris is generally stress-related and can be triggered by long-term exposure to poor water conditions.


Columnaris can be treated with antibiotic medication, especially Terramycin, and the addition of aquarium salt to the tank can also help in some cases.

Goldfish Parasites

There are several external and internal parasites that can attack tank and pond-kept goldfish. Parasites generally find their way into your aquarium via new fish, attached to plants, or in live foods.

8. Trichodina

Trichodina are tiny external parasites that live on the fish’s skin. Although they don’t harm the fish, these creatures can be extremely irritating to the fish if they appear in large numbers.


These tiny, flying saucer-shaped parasites attach themselves to the fish’s skin via a sucking disc.

The irritation that the parasites cause results in the fish flicking and rubbing against solid objects in the tank in an effort to get rid of the creatures.

In severe infestations, the fish may stop eating, become lethargic, and clamp its fins.


Trichodina are usually associated with overcrowded tanks and poor water conditions.


Sometimes, over-the-counter antiparasitic medication is effective. However, potassium permanganate has a better cure rate. Salt baths can be useful when treating one or two fish.

9. Anchor worm (Lernaea)

Anchor worms can be seen by the naked eye, protruding from the fish’s skin and extending into the water.

In fact, the “worm” that you can see is actually the reproductive parts of the female parasite.


You’ll notice short, white worm-like structures sticking out from under the fish’s scales. You sometimes see the worms in the fish’s mouth, where they dangle down, appearing like the baleen that you see in whales.

You may also notice patches of fibrosis or hemorrhage where the worm has fallen off.


Anchor worms usually get into the tank on new fish, plants that have been kept with fish, or with live foods.


If your goldfish has Anchor worms, don’t be tempted to pull the worms off the fish! Sometimes, an over-the-counter Anchor worm treatment may be effective. If that fails, you need to ask your vet for a suitable medication to deal with the problem. 

10. Velvet

Velvet is also called rust or gold dust and is caused by a tiny parasite called Oödinium or Piscinoodinium.


Fish with Velvet disease exhibit some or all of the following symptoms:

  • Rubbing or scratching against objects in the tank
  • Lethargy
  • Poor appetite and weight loss
  • Labored or rapid breathing
  • Clamped fins
  • Fine rusty or yellow-colored film over the skin, giving the fish a velvety appearance 

When the disease is advanced, the fish’s skin begins to peel off.


The Oödinium parasite is present in many aquariums but only becomes a problem when the fish are stressed, or water conditions are poor.

  • Raise the water temperature
  • Turn off the lights or dim them for a few days
  • Treat the water with aquarium salt
  • Treat the tank with copper sulfate for ten days

Throughout the course of treatment, remove your carbon filter. Invertebrates and snails should also be removed as they are highly sensitive to copper.

11. Fish Lice (Argulus)

Fish Lice can be seen by the naked eye, attached to the fish’s body.


Fish lice appear as tiny, flat, brown/green spots crawling or attached to the fish’s skin. Red spots often appear on the skin due to the irritation that the lice cause.

Fish with lice are restless and irritable, scratching against hard structures within the tank in an attempt to get rid of the annoying parasites.


Fish lice are typically associated with pond fish that have been moved to an aquarium setting.


You can treat lice with an appropriate antiparasitic medication that you add to your fish tank. 

If the fish has any visible wounds, you should add aquarium salt to the water.

12. Flukes (Gyrodactylus and Dactylogyrus)

Gill flukes (Dactylogyrus) and skin flukes (Gyrodactylus) are common fish parasites that feed on the external skin and gill tissues. When they occur in large numbers, fluke infestations can be fatal. 


Flukes are not visible to the naked eye. Fish with an infestation of flukes usually “flash” and flick against objects in the tank in response to the irritation caused by the parasites on their skin.

Sometimes, you’ll see bruising to the fish’s skin or missing scales where the fish has rubbed against something and sustained a minor injury.


Flukes usually get into your tank on new fish or plants that have been kept in the same aquarium as infected fish.


Unfortunately, flukes present with the same symptoms as other parasitic infections, making this condition rather difficult to diagnose. So, you may need to treat the water with various antiparasitic medications until you find one that is effective.

13. Costia

Costia or Costiasis is a freshwater ciliated protozoan parasite that’s more correctly known as Ichthyobodo necatrix or Ichthyobodo pyriformi. The parasites latch onto the gills or skin of fish, where they feed on the fish.


Costia infestation causes the following symptoms:

  • Excess mucus production
  • Lethargy
  • Clamped fins
  • Respiratory distress
  • Resting on the gravel
  • General debilitation

Since these parasites feed on the fish’s gills, they can quickly kill a fish by depriving it of oxygen. Also, due to the skin damage that the Costia parasite causes as it feeds, secondary bacterial and fungal infections can also be a problem.


Costia moves from fish to fish as it reproduces, spreading rapidly within an aquarium. These parasites usually get into your tank attached to new fish.


You can treat Costia with commercially prepared aquarium treatments, such as Malachite Green, Acriflavine, and potassium permanganate. Strong salt baths can also be effective.

14. Chilodonella

Chilodonella is widely regarded as one of the most dangerous fish parasites, largely because it’s extremely difficult to detect. Consequently, serious tissue damage may occur before you’re even aware that there’s a problem.

  • Labored breathing
  • Flashing or rubbing against objects in the aquarium
  • Lethargy 
  • Clamped fins
  • Resting on the tank bottom
  • Hanging at the water surface

If the fish develops lesions, it may also suffer from a secondary bacterial infection.


Like many aquatic parasites, Chilodonella usually gets into your tank on new fish or with live foods.


You can treat Chilodonella with commercially prepared aquarium treatments, including:

  • Malachite Green
  • Acriflavine
  • Potassium permanganate
  • Formalin
  • Copper

Salt baths can also be effective, especially if the fish has sustained abrasions from rubbing against objects in the tank.

15. Ich (Whitespot)

White Spot disease or Ich is probably the most common disease that goldfish fans see. The condition is caused by the Ichthyophthirius Multifiliis parasite.

  • Fish flashing against solid objects in the aquarium
  • Lethargy
  • Poor appetite
  • Bloody streaks and red patches on the body
  • A sprinkling of tiny white bumps like grains of salt across the body, fins, and gill covers

In advanced cases, the fish may develop lesions and secondary bacterial infection. If the condition is left untreated, the fish’s gills may become so congested that it cannot breathe and suffocates.

Red, white, brown goldfish / comets, coldwater, freshwater aquarium fish tank

The Ich parasite is often present in the aquarium but goes unnoticed until fish are weakened by stress or poor water conditions.


Provided it’s detected and caught early, Ich is relatively easy to treat. 

Because of the parasite’s life cycle, you need to continue treatment for ten to 14 days to be sure that the problem won’t recur.

  • Elevate the water temperature slightly for three days.
  • Treat the water with an over-the-counter White Spot medication.

Throughout treatment, carry out partial water changes every few days, following the directions on the medication packaging.

Goldfish Fungal Diseases

16. Fungus

Fungus is a very common disease in goldfish that’s often associated with poor water conditions and fish that are injured.


Fungus appears as grayish or white cottony growths on the fish’s fins and body, typically around the head and mouth.

In advanced cases, the condition will spread from the skin into the fish’s muscle tissue, and the fish will eventually die.

Branchiomyces fungus destroys the gill tissue. Eventually, the gill membrane is severely damaged, and the fish will suffocate.


Fungus is usually associated with:

  • Poor water conditions
  • High levels of ammonia in the water
  • Overcrowding
  • Fish that are weakened by disease
  • Stress
  • Poor immune system

There are various treatments for fungus, including:

  • Malachite Green
  • Copper Sulphate
  • Potassium permanganate
  • Methylene Blue

A salt bath can also be beneficial in some cases.

Goldfish Viral Diseases

17. Tumors

Tumors in goldfish are relatively common and can be benign or cancerous.


Neurofibromas are commonly associated with goldfish. These are benign tumors of the nerve sheath and cause small, localized lumps. The lumps grow and then drop off before regrowing. 

These tumors don’t harm the fish and are not treatable.

Gonadal Sarcomas are reproductive tumors that can be mistaken for “egg-binding.” The tumors are difficult to detect, as they can’t be seen externally until the lump has grown very large. These tumors can be surgically dealt with, as often happens with very valuable Koi. However, if left untreated, the tumor will usually crush the fish from the inside out. 


Tumors are generally hereditary, although some can be caused by certain viruses.


Treatment depends on the nature of the tumor and its location on the fish.

In the case of very valuable fish, it is possible for a vet to surgically remove the tumor, and often such procedures are very successful, as you can see in this video. However, if an internal tumor is not discovered until it has grown very large, the prognosis is generally poor.

18. Carp Pox Virus

Carp Pox Virus is a herpes virus that can affect goldfish and Koi. 


The most common signs of Carp Pox are thickened skin and small lesions that resemble drops of candle wax.


Like herpes viruses in other species, there are latent carriers that never show any symptoms of the virus while still passing it onto others. So, by the time you spot Carp Pox on one fish, the chances are that the others are already infected.


Carp Pox has no cure. 

However, you can manage the condition by ensuring that the water quality is pristine and feeding your fish a nutritious, correct diet. Slightly warmer water is known to ease the symptoms of the disease in some sufferers.

Sometimes, the skin damage that the virus causes can predispose the fish to bacterial infections, so you need to be alert to that risk and treat that accordingly.

19. Lymphocystis

Lymphocystis affects the fins and skin, causing the fish’s cells to become grossly enlarged.


Infected fish develop irregular lumps over the head, body, tail, or fins. Those lumps can be tiny white spots or large cysts that cover a large part of the body.

The lumps can be pale gray or pinkish in color, giving the name its common name of “Cauliflower Disease.”


Lymphocystis is a viral disease that’s caused by an iridovirus. 


Like most viruses, Lymphocystis has no cure. However, most fish eventually develop their own resistance to the virus.

Digestive Disorders

20. Swim Bladder Disorder

Swim Bladder Disorder is the term used to refer to a collection of issues that affect the fish’s ability to swim normally. In goldfish, fancy, round-bodied varieties are especially vulnerable to this condition.


Fish with Swim Bladder Disorder are unable to swim upright or on an even keel. Often, affected fish float to the water surface or sink to the bottom, apparently unable to control their buoyancy. You might even see your poor goldfish upside down and unable to right itself.

Other signs include a distended belly and a curved spine, depending on the cause of the condition.


Swim Bladder Disorder occurs when the swim bladder becomes compressed. Possible causes include:

  • Overeating
  • Constipation
  • Gulping air
  • Eating a diet of dried foods
  • Bacterial infection
  • Trauma

Sometimes, birth defects can cause swim bladder problems, but these fish tend not to survive.


Swim Bladder Disorder can usually be successfully treated by starving the fish for two or three days and then offering a diet of frozen food or a blanched, skinned pea. Warming the tank water by a few degrees can also help to get things moving again.

If the condition has been caused by a bacterial infection, a broad-spectrum antibiotic can often help.

Goldfish Diseases

Although goldfish are pretty robust creatures, they are quite sensitive to poor water conditions and environmental factors within their tank or pond. 

So, sometimes, if your goldfish looks sick, it could simply be that there’s a problem with conditions in your aquarium.

Environmental Factors

Goldfish are quite dirty creatures that produce a lot of waste. If you don’t keep on top of your tank maintenance regimen, that waste can quickly accumulate and pollute the aquarium water, causing an ammonia spike that can be deadly for your goldfish.

To keep the tank clean and safe for your goldfish, you need to carry out weekly partial water changes of between 10% and 20%. Use an aquarium vacuum to deep-clean the gravel so that you remove solid fish waste, uneaten food, and decomposing plant debris before it has a chance to degrade.

Young man changing water in aquarium using siphon.

Every few weeks, you’ll need to remove the filter media and wash it in dirty tank water to remove any sludge that could clog the media and prevent water from flowing through it. You also need to change spent media from time to time in line with the manufacturer’s recommendations.


Although goldfish are highly social creatures that do best when kept in groups or pairs, it’s crucial that you don’t overcrowd your tank.

The minimum tank size for a goldfish is 15 gallons. That might seem like quite a large tank, but remember that these fish can grow to measure 6 inches long or more. For each extra fish, you need to allow 1 gallon of water per 1 inch of fish, factoring in the fishes’ growth rate.

Water Parameters 

Use an aquarium water testing kit to test the water in your goldfish aquarium every week to make sure that the water parameters are within acceptable levels as follows:

  • Ammonia – zero
  • Nitrites – zero
  • Nitrates – 20ppm or less
  • pH – in the range of 6.0 to 8.0
  • Water hardness – 5 to 19 dGH

Goldfish are coldwater fish, and they can suffer from temperature shock if the water in the aquarium becomes too warm. The ideal temperature for goldfish is between 65° F to 72° F.

These fish need a tank with well-oxygenated water. A long tank with plenty of surface area is the best choice for goldfish, and you should also include an air stone or bubbler in your setup.

In Conclusion

I hope you enjoyed this guide to 20 of the most common goldfish diseases.

You will have noticed that one of the most common causes of outbreaks of diseases is poor water conditions. So, be sure to perform weekly partial water changes, vacuum the gravel, and manage the filter media correctly so that conditions in the tank are safe for your fish. Keep parasites out of your aquarium or pond by quarantining new fish and plants, and feed your goldfish a correct, nutritious diet.

Please remember to share this guide with other goldfish fans if you found it helpful.

Alison Page has been an avid fish keeper for over 35 years and has owned many different species of freshwater tropical fish including bettas. Currently Alison has two large freshwater tanks. The first tank has two huge fancy goldfish who are almost ten years old and still looking as good as ever. In the other, she has a happy community of tiger barbs, green tiger barbs, corydoras catfish, platys, and mollies.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.