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20 Goldfish Diseases You Can Treat and Prevent

Brooke Billingsley

Goldfish have the potential to live very long lives, sometimes in excess of 30 years! The key to keeping them alive for the longest amount of time is by providing them the healthiest life possible by carefully managing everything from water quality to diet. If you have a goldfish that lives for more than a couple of years, it’s almost certain that at some point, your goldfish will experience some type of illness. Some illnesses are more serious and deadly than others, so it’s important to your goldfish’s wellbeing that you learn what diseases your goldfish might experience, how to identify them, and how to treat them. Here are some of the most common, and some less common, diseases your goldfish may experience and information on how to treat and prevent them.

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How Can I Determine if My Goldfish is Even Sick?

If your goldfish appears to be experiencing any symptoms of an illness, either in appearance or behavior, your first course of action is extremely simple: check your water parameters. Preferably, check them correctly but quickly using a trustworthy test kit. Follow the directions for each specific test within the kit because some require different numbers of drops, length of time shaking, and length of time until test result should be read.

As a quick reminder, here’s what your water parameters should look like:

  • pH: 6.5-7.5
  • Ammonia: 0
  • Nitrite: 0
  • Nitrate: up to 20-40

Also make sure your water temperature is staying in the 64-74°F range, give or take. Water that is too cold may cause your goldfish to enter torpor, which is a semi-hibernation state that causes the metabolism to drop significantly, which means your goldfish will become less active and eat less. Water that is too warm may lead to stress, which can lead to a depressed immune system. Warm water also has less dissolved oxygen present, which can make it more difficult for your goldfish to breathe properly.

Problems with the water quality in the goldfish’s environment is the most common cause of illnesses and abnormal behaviors. Increased ammonia and nitrite can lead to poisoning, which can cause symptoms like fin damage, color changes, and lethargy. Problems with the water parameters can also increase stress and cause physical changes like a decrease in slime coat, both of which can increase the risk of developing infections. Poor quality water can quickly become a breeding ground for parasites and bacteria as well.

sick goldfish
Image Credit: mrk3PHOTO, Shutterstock

What Diseases Can My Goldfish Get That I Can Treat and Prevent?

1. Ich

This parasitic infection is caused by a parasite called Ichthyophthirius multifiliis that attaches itself to the body of the fish, causing the appearance of salt grains scattered across the body and fins of the fish. These parasites cause itching and irritation to the fish and can eventually lead to secondary infections and death if left untreated. Ich parasites drop egg packets into the water where they hatch, creating free-swimming parasites that search for a host.

There are multiple treatments for ich, including medications, heat therapy, salt therapy, and some alternative treatment options. Ich is contagious, so catching and treating it early will prevent a full-blown outbreak in the tank or pond. Quarantining new fish and plants and ensuring you don’t introduce water from pet stores into your tank can help prevent ich. Maintaining good water quality will also help you ensure ich parasites are not able to take hold in your tank.

goldfish with ich
Image Credit: Zay Nyi Nyi, Shutterstock

2. Velvet

Velvet is a parasitic infection that is uncommon in goldfish, but it does show up from time to time. Velvet, also called Gold Dust Disease or Rust, is easy to spot because it will leave your goldfish looking like it was sprinkled with gold or reddish-brown dust. Like ich, your fish will likely begin showing symptoms like flashing and clamped fins. These parasites attach themselves to the fish’s skin, creating a significant amount of irritation and itching. The fish begins overproducing slime coat in response to the presence of the parasites.

Velvet is highly treatable with antiparasitic medications like copper. Take note that copper is deadly to invertebrates, like snails and shrimp, and can stay in the water for a long time since it is a heavy metal. Velvet is more deadly than ich, so make sure you are quarantining new plants and fish for 1-2 weeks before adding to the main tank.


3. Fungus

Sometimes called Cotton Wool disease, fungal infections create fluffy, white patches on the fish. These can be concentrated around the mouth but may also be seen on various parts of the body and fins. You may see flashing or rubbing against structures in the tank.

Fungal infections can be treated with tea tree oil and bay tree oil based water treatments. Some ich treatments, like Ich-X, can be effective against fungal infections. The best prevention of fungal infections is by keeping the water quality high and not keeping the water temperature too high. Warm temperatures often stimulate the growth of fungi.


4. Anchor Worms

Anchor worms are creepy parasites that attach themselves to the skin of the goldfish and feed off the goldfish, creating irritation and bleeding around the bite location and creating an opening for bacterial infections to enter the skin and bloodstream. These worms are visible to the naked eye and can be seen sticking out from between scales on the fish. They’re highly contagious and dangerous to your fish. 

If you spot anchor worms on your goldfish, you should manually remove them carefully with a pair of tweezers and then gently clean the area with a cotton swab soaked in hydrogen peroxide if you are able. Potassium permanganate is an effective treatment against anchor worms and can be used as a tank treatment or a bath. Other treatments, like Microbe-Lift, are also effective at treating the fish and the tank.


5. Flukes

These microscopic parasites can infect the skin and gills of goldfish. They attach to the fish, feeding off its blood, eventually leading to secondary infections and death. Goldfish with flukes may be seen flashing or clamping its fins. If gill flukes are present, you may see redness around the gills and rapid breathing or difficulty breathing.

Flukes are treatable with antiparasitic medications, but they are contagious and should be treated as soon as you suspect them. They are common, especially in fish that come from large breeding operations, like pet store goldfish, so make sure you quarantine and prophylactically treat any fish you bring home before adding it to your tank. 


6. Fish Lice

These parasites are visible to the naked eye as disc-shaped, green flecks that visibly move about on the fish. Severe cases will cause red or bloody areas on the fish’s skin, but you’re more likely to see symptoms like flashing and clamped fins. Fish lice are more common in ponds than they are in aquariums, so you’re unlikely to spot them in your aquarium unless you’ve brought a fish in from an established pond.

Fish lice can be difficult to treat but are usually susceptible to the same treatments as anchor worms, so potassium permanganate and Microbe-Lift are great options. They are usually resistant to salt treatments. To prevent fish lice, quarantine any new fish before adding them to the new tank. This is especially important when bringing in fish from outdoor environments.


7. Chilodonella

This is a microscopic parasite that attaches itself to goldfish, causing irritation and stress. Chilodonella can stay dormant for extended periods of time, only taking hold when a stressed goldfish has a depressed immune system. Symptoms include clamped fins, lethargy, red areas on the skin, excess slime coat production, and air gulping occurs in the end stages of this infection. 

The best treatment for this infection is aquarium salt baths or water treatments. Formalin and potassium permanganate can also be used in lieu of salt. The best prevention for this is quarantining new plants and animals before adding them to your tank. New animals are often stressed and may begin to show symptoms of illness while in quarantine.


8. Trichondia

While these parasites aren’t dangerous for your goldfish, they are extremely irritating to the skin and can lead to flashing and rubbing against the substrate or décor in the tank. Trichondia parasites don’t feed on goldfish; rather, they attach to the goldfish, using the goldfish as a place to live while the parasites consume bacteria. Your goldfish may develop red, raw spots from rubbing against items. 

Trichondia is treatable with salt baths, salt treatments for the tank, potassium permanganate, and antiparasitic medications. These parasites will enter your tank via infected fish, plants, or water. Ensure you properly quarantine anything you’re adding into your tank.


9. Ulcers

Ulcers are open wounds on the surface of the skin. They are typically caused by bacteria that take advantage of decreased immunity. The earliest symptoms of ulcers are redness that continues to worsen over time. The scales may raise and will likely fall off in the area of the ulcer. Ulcers open up a pathway for internal infections to occur, so treat them as early as possible.

Most ulcers can be treated by improving the water quality to keep the wound clean while it heals. You can treat with antibacterial medications as well, which will help keep the wound clean and clear of bacteria. If your fish will let you, you can clean the wound with a cotton swab dipped in hydrogen peroxide. Don’t do this on a daily basis, though, as hydrogen peroxide can kill healthy cells that are trying to heal. Salt baths or salt treatments in the tank may help with healing as well.

goldfish with ulcer
Image Credit: Zay Nyi Nyi, Shutterstock

10. Black Spot

This is not actually a disease, but it is indicative of elevated ammonia levels in the water. Usually, black spots will appear while the fish is healing as ammonia levels decrease, but long-term exposure to elevated ammonia levels can lead to black spots while the ammonia is still elevated as the fish’s body attempts to heal itself. Some goldfish change colors with age, so if you notice black spots developing, there isn’t necessarily a problem, but it’s a good idea to check your water parameters to verify your ammonia levels aren’t elevated.


11. Bacterial Gill Disease

This infectious disease affects the gills, gill covers, and area around the gills. Fish with bacterial gill disease will have redness and swelling in and around the gills that will continue to worsen with time. As time goes on, the gills will begin to fuse to the body, eventually closing them completely. Even with treatment, the gills will not come apart on their own and require human intervention. Fish with this disease will have rapid breathing, difficulty breathing, lethargy, and lack of appetite. 

This disease is uncommon in goldfish and usually occurs in large-scale breeding operations of food fish, like salmon, but it can occur in goldfish kept in overstocked environments with poor water quality. Ensure your water quality is high and treat with antibiotic medications like kanamycin, neomycin, and tetracycline, or antibacterial medications like nitrofurazone.

group of sick goldfish
Image Credit: Suphakornx, Shutterstock

12. Mouth Rot

Mouth rot can be caused by parasites or bacteria and is an extremely deadly infection if allowed to enter later stages. Catch it early by watching for your fish rubbing its mouth on items in the tank or redness in and around the mouth. Mouth rot will cause the external structures of the mouth, including the lips, to rot away, leaving nothing but a large, open hole behind. Fish that have reached this point are often unable to eat or have great difficulty and may require hand feeding.

Prevent mouth rot by maintaining your water quality and monitoring your fish closely for symptoms. In the early stages, you can treat mouth rot at home with antibiotics like kanamycin and antibacterials like nitrofurazone. As this disease advances, it may require veterinary intervention and antibiotic injections to save the fish’s life.


13. Fin Rot

This bacterial infection causes the fins to slowly tear and dissolve until the fin is down to the nub. You may notice a cloudiness in the fins, jagged or shredded appearance, or pieces of the fins slowly peeling or rotting off. Once the fins have rotted all the way down, it’s unlikely they will grow back.

Products containing tea tree oil, like Melafix, can be effective against fin rot. Antibiotics, like kanamycin or sulfamethoxazole, are very effective but can be hard on your fish. The addition of Stress Coat or another product to protect and stimulate the slime coat can help reduce stress and prevent further damage. To prevent fin rot, ensure your water quality is high and your parameters are where they should be.


14. Hole in the Head Disease

This disease is caused by a parasite and is not as common in goldfish as it is in other fish, like cichlids, but it does still occur. Hexamita parasites are usually opportunistic and will cause infections when your goldfish’s immune system is depressed because of stress or other illness. This disease often goes hand in hand with a secondary bacterial infection. Hexamita causes a pitting ulcer, usually on the face and head, that creates a deep hole. Eventually, this leads to a systemic bacterial infection and can cause death. 

The first step in treatment is to check your parameters and do whatever is necessary to improve your water quality. Goldfish cannot heal from this infection in a tank with poor water quality. If you are able, gently clean the wound with a cotton swab dipped in hydrogen peroxide. Do not do this more than once because hydrogen peroxide can kill healthy tissue. You will need to treat your fish with antibiotics, like metronidazole, and antiparasitic medications.


15. Pop Eye

Some fish are prone to losing an eye, like telescope and bubble eye varieties of goldfish, but pop eye is a bacterial infection that can cause this. Pop eye is a dangerous systemic infection that is recognizable by swelling or fluid pouches around the eyes or even the eyes themselves bulging out. This increases the risk of losing an eye significantly.

Pop eye can be treated with salt treatments and a powerful antibiotic, like kanamycin. It’s important to try to catch this early to prevent your fish from losing one or both of its eyes. Pop eye isn’t completely preventable but keeping your water parameters in check and your water quality high can significantly decrease the risk of its occurrence.

black pop-eyed goldfish
Image Credit: haireena, Shutterstock

16. Cloudy Eye

This isn’t a specific disease, but it’s an indicator that an injury has occurred on the surface of the eye that has led to an infection. Telescope and bubble eye goldfish are at an increased risk of this. You will see a hazy or cloudy look to one or both eyes. Cloudy eye can be caused by ammonia burns or injuries that allowed bacteria to enter the eye.

Treatment of cloudy eye revolves around improving water quality to help the eyes heal. Salt baths or tank treatments can be useful in treating this condition. Antibiotics or antibacterials may be useful, but they do not always make a difference. Keep your tank free of sharp or jagged edges if you are keeping fish with protruding eyes.


17. Carp Pox

This disease appears like warts on your goldfish’s scales or fins. Thankfully, it looks much worse than it actually is. Carp pox do not injure the fish and typically do not cause pain or irritation. It is caused by a herpes virus, though, so once your goldfish has carp pox, they will always have it. It may appear to heal but will usually reoccur later. There is not a good prevention for carp pox except to purchase your goldfish from environments where they have not had these symptoms occur before.


18. Tumors and Growths

Just like other animals, goldfish can develop tumors and growths. They are not always cancerous or malignant, but they can become uncomfortable. If you notice an unusual lump on your goldfish, you can monitor it closely for changes. If it continues to grow or begins to interfere with normal activities, like swimming or eating, then euthanasia is usually the kindest choice. Some veterinarians are equipped to remove tumors from goldfish, so this is always an option you can explore. There is no known prevention for tumors except maintaining water quality to decrease the chance of their occurrence. 


19. Lymphocystis

This virus is similar to carp pox in that it is not dangerous, and it usually reoccurs. It’s characterized by cauliflower-shaped growths on the fish. These growths are usually pink in appearance. This disease has no treatment and is self-limiting, which means it will clear up on its own. Preventing lymphocystis is accomplished by keeping your goldfish in a stress-free environment. Stressed fish with decreased immunity are at risk for developing lymphocystis. It may or may not reoccur if your fish is kept in a low-stress environment.


20. Dropsy

Dropsy isn’t a disease on its own, but it is a symptom of a serious problem inside the goldfish. Dropsy is a collection of fluid within the abdomen of the fish, causing noticeable swelling. When this swelling occurs, the fish will often “pinecone”, which means the scales begin to stick out from the body, similar to the way a pinecone looks.

Dropsy isn’t fully preventable because it can be associated with multiple medical problems. Poor water quality, sepsis, organ failure, and even a diet that isn’t nutritionally sound can all lead to dropsy occurring. Once dropsy symptoms develop, the fish is already seriously ill. You can attempt to treat dropsy with strong antibiotics, like kanamycin, salt baths, and improvements in water quality. Dropsy is usually fatal, though, and sometimes, euthanasia is the kinder choice for seriously ill fish.

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In Conclusion

This isn’t a fully comprehensive list of diseases and infections your goldfish can get, but these are the most likely to occur. Keeping your water quality high is your best defense against all of these diseases. Quarantining new plants and animals can help to keep your tank safe and allow you to catch any diseases your new fish may have early. Early identification and quick treatment of these diseases is the key to helping your goldfish heal and get back to good health. Keeping a low stress tank and feeding a balanced diet are an important piece of the puzzle as well.

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Featured Image Credit: dien, Shutterstock

Brooke Billingsley

Brooke Billingsley spent nine years as a veterinary assistant before becoming a human nurse in 2013. She resides in Arkansas with her boyfriend of five years. She loves all animals and currently shares a home with three dogs, two cats, five fish, and two snails. She has a soft spot for special needs animals and has a three-legged senior dog and an internet famous cat with acromegaly and cerebellar hypoplasia. Fish keeping has become a hobby of Brooke’s and she is continually learning how to give her aquarium pets the best life possible. Brooke enjoys plants and gardening and keeps a vegetable garden during the summer months. She stays active with yoga and obtained her 200-hour yoga teacher certification in 2020. She hosts a podcast focusing on folklore and myth and loves spending her free time researching and writing. Brooke believes that every day is an opportunity for learning and growth and she spends time daily working toward new skills and knowledge.