Common Goldfish Diseases

Written By Lewis German  |  Disease  |  0 Comments

2 goldfish

Goldfish have been popular family pets for many years. They can thrive in a large aquarium or garden pond, come in many beautiful, unusual varieties, and will live for ten years or more if properly cared for.

However, there are some health conditions that can affect these typically hardy fish. 

Read this guide to learn how to diagnose, treat, and prevent the most common goldfish diseases to keep your pets healthy and long-lived!

What diseases are goldfish prone to?

There are quite a few diseases that can affect your goldfish, including the following:

But what causes goldfish diseases?

Poor water quality

Poor water quality is by far the most common cause of health problems in goldfish.

Goldfish are messy creatures that spend their days scavenging on food scraps and algae, producing vast amounts of waste as a consequence. Overcrowded tanks and small, unsuitable goldfish bowls quickly cause the water quality to suffer, stressing the fish and leaving them vulnerable to disease and parasite outbreaks.

Goldfish of all varieties are large fish, especially long-bodied types like Comets and Shubunkins, which often reach over a foot in length. For that reason, you must provide plenty of swimming space for your pets.

Long-bodied goldfish are best kept in a garden pond, while Fancy goldfish must have a tank of at least 20 gallons to start with, preferably larger as they mature and reach their full size.

Keep your goldfish tank clean by performing partial water changes once a week, using an aquarium vacuum cleaner to remove organic waste from the environment, and keeping up to speed with filter maintenance.

Use a reliable aquarium water testing kit to check the water chemistry weekly. Ideally, the water should contain zero ammonia and nitrites, with under 30 ppm nitrates. 

The most common goldfish diseases

In this part of our guide, we look at the most common goldfish diseases and how to treat and prevent them.

Ich (White Spot Disease)

White Spot disease, or Ich, is an extremely common disease that affects all freshwater fish species, including goldfish. The Ichthyophthirius multifiliis parasite causes the disease, which has a wide range of symptoms, including the following:

  • Flicking or rubbing against solid objects in the tank
  • A rash of tiny white spots all over the fish
  • Loss of appetite
  • Inactivity

The disease doesn’t usually affect happy, healthy fish but manifests in stressed, weak specimens, often when the water quality is poor. You can treat Ich if you catch it quickly by dosing the tank with an over-the-counter product you’ll get from your local fish store or vet.

Swim bladder problems

Swim bladder problems are extremely common in round-bodied Fancy goldfish.

The swim bladder is a gas-filled organ in the fish’s abdomen that enables the creature to remain buoyant and manoeuvre itself up and down in the water. Swim bladder problems are often caused by constipation or bloating rather than a disease, although sometimes bacterial infections can cause them.

A goldfish with swim bladder issues cannot swim up to the surface or sometimes becomes trapped there, unable to descend. Often, the fish can’t swim on an even keel, tipping over, standing on its head, or lying on one side on the substrate.

If the problem is caused by overeating, you can usually cure it by offering the fish a shelled, cooked pea or fasting your pet for 24 hours before giving it some live or frozen meaty protein.

Fin rot

A bacterial infection caused by poor water conditions generally causes fin rot. Affected fish’s fins and tail start to appear white or cloudy around the edges. As the disease progresses, the dead tissue drops off, leaving the infected fins ragged and shredded.

The Aeromonas, Vibrio, or Pseudomonas bacteria are usually responsible for fin rot, although inappropriate water chemistry, overcrowding, incorrect feeding, stress, and incorrect water temperature are contributory factors.

You can treat fin rot successfully by dosing the tank with an appropriate over-the-counter fish medication from your vet or local fish store.

Hole-in-the-Head disease

Hole-in-the-Head disease (HITH) affects most freshwater fish species. HITH starts as a tiny black or red spot on the fish’s head that gradually spreads and deepens.

The cause of the disease is unclear, but the guilty party is thought to be a species of diplomonad bacteria such as Octomitus, Hexamita, or Spironucleus. Poor water conditions, stress, and nutritional deficiencies are also thought to be contributory factors.

Treatment with metronidazole antibacterial medication can be effective if you start using the medication early enough.


Again, poor water conditions are usually associated with ulcers, although parasites and trauma can also be responsible.

An ulcer is a large, open wound on the fish’s head or body, typically with a white centre surrounded by bloody tissues. If left untreated, ulcers can penetrate the fish’s skin and even the internal organs in severe cases, usually killing the victim.

Although poor water conditions, physical injury, and parasites can all cause ulcers, they’re usually caused by the Pseudomonas, Vibrio, or Aeromonas bacteria.

To treat the condition, put the fish in a salt bath and dose it with antibacterial medication. You could also spot-treat the ulcer with a Q-tip dipped in hydrogen peroxide if you can net the fish safely.

Popeye disease

Popeye disease (exophthalmia) is a condition that causes the goldfish’s eye to swell up and protrude from the socket. Sometimes, the eye appears discoloured if the cornea is ruptured.

This condition can affect both or one of the eyes and is caused when fluid leaks into the space behind the eyeball. Popeye is usually caused by a trauma to the eye, a parasite attack, bacterial infection, or poor water conditions.

The treatment for this condition depends on the underlying cause. 

  • If the eye is injured, treat the water with aquarium salt while the damage heals.
  • If the water chemistry is incorrect, take action to put it right.
  • Treat bacterial infections with suitable antibacterial medication.

The prognosis for Popeye is generally good. Even if the fish loses an eye, it will manage just fine without it once the creature adjusts.


Dropsy is more correctly called ascites or edema. This condition causes the soft tissues inside the fish’s body cavity to swell because of an accumulation of excess fluid.

Goldfish with this condition have a swollen abdomen and scales that stick up like a pinecone. The gills are pale, and the eyes bulge; the fish’s anus is red and swollen, and ulcers often develop along the lateral line. The abdominal swelling causes the fish’s spine to curve, the fins are clamped to its sides, and red patches develop on the skin and fins.

Finally, fish with dropsy are lethargic and have a poor appetite.

The common Aeromonas bacteria cause this condition, usually affecting weakened or stressed fish.

Treat dropsy by moving the affected goldfish to a quarantine tank. Add a teaspoon of aquarium salt per 1 gallon of water to the aquarium. Treat the fish with antibiotics, and check the water daily to ensure the correct chemistry. Sometimes, the fish will recover, but this condition often proves fatal.

Cloudy eye

Fancy goldfish are commonly affected by this condition. The eye changes color, often appearing bloodshot or milky.

An injury to the eye, poor water quality, incorrect diet, or cancer usually causes Cloudy eye, and usually, only one eye is affected.

If a poor diet or unsanitary water causes the condition, treat that problem first. If the eye is injured, use aquarium salt to treat the water, and the condition should clear up on its own.

Flexibacter Columnaris disease

A bacterial infection usually causes Columnaris or Saddleback disease, which can be acute, chronic, internal, or external.

The condition appears as white or grey patches on the head, fins, and gills. As the condition worsens, the lesions turn yellow or brown and extend down the fish’s back and sides.

Lesions around the fish’s mouth are mouldy or cotton-like, eventually eroding the tissue. The fins fray and split, and the gills eventually collapse, leaving the fish unable to breathe and causing suffocation. When the infection is internal, the fish eventually dies for no apparent reason.

Columnaris is usually stress-related and caused by prolonged exposure to poor water conditions. You can treat the infection with antibiotics, especially Terramycin, and adding aquarium salt to the tank can help the fish’s recovery.


Several species of external parasites can attack goldfish, finding their way into your tank on plants or infected fish. That’s why you should always quarantine newcomers for a couple of weeks before adding them to your main tank.

Trichodina are little external parasites that attach themselves to the fish’s skin, causing irritation that causes the fish to rub against objects in the tank. In severe infestations, the fish might stop eating and become lethargic.

The most effective treatment for Trichodina is potassium permanganate, and salt baths can also be helpful.

Anchor worms (Lernaea) are visible to the naked eye, protruding from the goldfish’s body or mouthparts and sticking out into the water.

You can usually get rid of Lernaea by treating the fish with a specific medication from your vet or local fish store.

Velvet is caused by a parasite called Piscinoodinium or Oödinium. The fish develops a yellow film over its skin, giving the creature a velvety appearance. The condition only becomes problematic when a fish is stressed, or water conditions are poor.

To treat Velvet, slightly raise the water temperature, dim the lights for a week, and treat the tank with copper sulphate and aquarium salt for ten days.

Fish Lice (Argulus) are tiny, flat brown spots that can be seen attached to the fish’s body. These parasites are usually associated with pond goldfish recently put into an aquarium.

You can treat lice with an appropriate antiparasitic medication and add aquarium salt to your tank.

Flukes (Gyrodactylus and Dactylogyrus) feed on the fish’s gills and skin, and infestations can be fatal when they occur in large numbers.

Although you can’t see Flukes with your naked eye, infected fish often flash and flick against the substrate and rub on decorations in their aquarium to try to get rid of the parasites. That often results in missing scales and damaged skin, allowing bacteria to enter and set up an infection.

Flukes often get into your aquarium on new fish or plants taken from infected aquariums or ponds.

It can be tricky to spot flukes as they often present with the same symptoms as other parasitic conditions. So, treating the water with different antiparasitic drugs is best until you find the right one.


Fungus is very common in goldfish and is usually linked to poor water conditions and traumatic injuries.

This disease appears as white or grey cotton-like growths on the fish’s body and fins, usually around its mouth and head. Left untreated, the fungus will spread into the fish’s muscle tissue, eventually killing it. Certain fungus forms, such as Branchiomyces, destroy gill tissue, causing the fish to suffocate.

Poor water conditions, excessive ammonia in the water, stress, overcrowding, and a weakened immune system generally cause fungus. As well as rectifying the above issues, you can treat the water with Malachite Green, Methylene Blue, Potassium permanganate, or copper sulphate. Salt baths can also be beneficial in treating mild cases of fungus.


Tumours are quite common in goldfish. Some are cancerous, while others are benign and simply unsightly.

Gonadal sarcomas are associated with the reproductive tract and are often mistaken for egg-binding. Sometimes, these tumours are dealt with surgically, as is often the case with highly valuable Koi. However, if left untreated, the tumour often kills the fish by crushing it from the inside out.

Neurofibromas are benign tumours of the nerve sheath that appear as small lumps on the body and head, which grow and fall off before growing back. These harmless tumours are not treatable.

Carp Pox Virus

This condition is a herpes virus that affects Koi and goldfish. The fish’s skin thickens, and small lesions develop that look like drops of candle wax.

Some fish can be latent carriers of this disease and never display any symptoms, although they pass it on to others. Unfortunately, that means if you spot one case of Carp Pox in your tank, it’s highly likely there will be other fish already infected.

There’s no cure for this disease, but keeping the tank clean and hygienic can help prolong the lives of your fish.


Lymphocystis causes the cells of the fish’s skin and fins to become massively enlarged. Infected fish develop pinkish or pale grey lumps of different sizes over the tail, body, fins, and tail. 

This is a viral disease that has no cure, although most goldfish eventually become resistant to it, and it doesn’t usually prove fatal.

Final Thoughts

Although goldfish of all varieties are pretty hardy creatures, they can be susceptible to some common fish diseases.

As you now know, the most common reason for poor health in goldfish is unsanitary water conditions. If the water has high levels of nitrates, the fish won’t thrive and will be more susceptible to disease outbreaks.

Be sure to perform weekly partial water changes, remove organic waste from the substrate with an aquarium vacuum cleaner, and maintain your filtration system correctly. 

Whenever you buy new fish or plants, you should keep them in a separate quarantine tank for at least two weeks to ensure they are disease and parasite-free before introducing them to your main display tank.

That way, your goldfish tank will stay clean and safe for your fish, making common goldfish diseases a thing of the past for your pets!