Comprehensive Guide To Goldfish Diseases

Goldfish are known for being fairly low-maintenance fish, and it’s uncommon for them to get sick once they acclimate to their environment. Most health problems can be avoided by maintaining proper water parameters, feeding your fish a high-quality diet, and protecting your pond from predators.

However, sudden or drastic changes in these environmental factors can weaken their immune systems and make your goldfish more susceptible to various types of illness. If left untreated, these diseases can infiltrate your pond and spread to other fish, which is why early detection and treatment is so important.

Knowing the causes and symptoms of common goldfish diseases can help you diagnose and treat problems more quickly. We’ve put together this goldfish disease guide to help you identify and treat common illnesses, as well as effectively prevent any future health issues.

Parasitic Diseases

Anchor Worms & Fish Lice

Though the name may be deceiving, anchor worms are not actually worms. Lernea 

cyprinacea, known as “anchor worm,” is a parasite that burrows itself into the body of fish and feeds on its nutrition. Similarly, Argulus foliaceus, commonly known as “fish lice,” is a mite-like crustacean that feeds on the flesh of fish.

Once these parasites have been introduced to your pond, they can spread quickly. The wounds and bacteria associated with these parasites also can cause a secondary bacterial infection.

Causes

Anchor worms and fish lice are usually brought into a pond by new fish that haven’t been properly quarantined. It is critical to follow standard quarantine procedures prior to introducing any fish to your established pond.

Sometimes, pond plants that have been previously kept with infected fish can carry these parasites. Since parasites need a host to survive, quarantining plants for several weeks before adding them to your pond can break the anchor worm life cycle and prevent them from infiltrating your pond.

Symptoms

Early symptoms of anchor worms and fish lice are flashing and scratching. Once they have attached to fish, both parasites are visible to the naked eye. The area where the anchor worm has attached will usually look like a small red sore or pimple in the early stages of an infestation, but eventually it will look like a greenish-white thread coming off of the fish. Fish lice are a greenish-brown color and have flat, disk-shaped bodies. The area where the parasites have attached to the fish may become red and inflamed or have ulcers.

Treatments

Though these parasites can be removed manually, this can be difficult to do and can cause excess stress to your goldfish. If you do decide to remove the anchor worm or lice, use tweezers and grab as closely to the entry point as possible. Make sure that the whole parasite has been removed and then disinfect the wound with hydrogen peroxide afterwards to avoid infection.

Whether or not you choose to manually remove the parasites, you’ll need to perform a water change and treat the entire pond. Common treatments include potassium permanganate, which helps weaken the anchor worm so it releases its hold on the fish, and dimilin, which kills larvae in the water and ends the life cycle. Salt baths can be used to prevent a secondary infection. Koi and Koi Ponds put together a table of recommended concentrations and duration of treatment.

Chilodonella

Chilodonella uncinata, commonly referred to as “Chilodonella,” is a microscopic protozoan parasite that can be deadly to goldfish and can spread very quickly once it is introduced to your pond. This parasite thrives in colder water. At lower temperatures, the immune system of your goldfish becomes more fragile and susceptible to illness, which is why this parasite is so dangerous to your pond ecosystem.

Causes

Chilodonella parasites can stay dormant for extended periods. An outbreak typically occurs when a goldfish has a weakened immune system, which is usually associated with stress brought on by poor water quality or other environmental factors. Younger fish are more susceptible, but Chilodonella can infect fish at any age.

A goldfish that has Chilodonella and is introduced to a pond without being properly quarantined can easily spread the parasite. Always quarantine new fish for at least two weeks prior to introducing them to an established pond.

Symptoms

Common symptoms of Chilodonella include labored breathing, gasping at the surface, flashing, excessive mucus secretion, clamped fins, loss of appetite, and fraying of the fins. The parasite is not visible to the naked eye, so it can only be properly diagnosed using a microscope. Chilodonella appears leaf- or heart-shaped under a microscope with tiny hair-like structures on the larger side. These defining characteristics will disappear when the organism dies, typically 5-7 minutes after a body scrape is done.

Treatment

There are several treatment options for Chilodonella. A salt bath or a salt dip can be successful for mild infestations. Potassium permanganate can break down the cells and tissues of the parasite. A mixture of malachite green and formalin is considered the most effective treatment. You can purchase these as topical creams that can be applied directly to fish or as a liquid that can be used as a bath.

Costia

Ichthyobodo necator, commonly known as “Costia,” is a microscopic protozoan flagellate that thrives in cold water. Costia can multiply quickly and may not cause symptoms immediately, making it one of the most serious parasites for goldfish. The parasite burrows itself into the top epidermal cells of goldfish, attaches to the skin and gill membrane, and feeds on the content. When Costia attacks the gills, it diminishes the goldfish’s oxygen supply and makes it more difficult for the fish to heal.

Causes

Costia is typically brought into a pond by a fish that has not been properly quarantined. Outbreaks are common when the immune systems of goldfish are weakened, such as when water quality is poor or in early spring when fish are coming out of winter hibernation.

Symptoms

Costia can be difficult to identify because its symptoms resemble those of other common goldfish illnesses. Some possible symptoms include slimy patches around the head and gills, spider web-like lesions, gasping for air at the pond’s surface, red patches, clamped fins, twitching, appetite loss, or sudden death.

Under a microscope, Costia will appear pear or comma shaped with two hair-like appendages (flagella). Because this parasite is so small, it can be difficult to identify even under a microscope. Using a high magnification (400x) when viewing the scrape sample may help with identification.

Treatment

Salt is the preferred treatment for Costia; however, some strains of Costia are resistant to salt. If salt does not work, the second best option is formalin. Praziquantel can be effective for less serious infestations.

Flukes

Flukes are microscopic parasitic flatworms known as trematodes. There are two types of flukes, gill and skin. These parasites have large hooks which they use to attach to fish and feed on blood and cells. They can destroy gills and deplete the protective mucus coating on goldfish, which can hinder oxygen supply and make fish more susceptible to bacterial infections.

Causes

Fluke outbreaks typically result from stress due to environmental issues such as poor water quality, improper diet, overcrowding, or high ammonia levels. New fish and plants that have not been properly quarantined can also introduce flukes to your pond.

Symptoms

Common symptoms of flukes include loss of color, flashing, twitching, excess mucus secretion, tattered or clamped fins, rapid or labored breathing, and red skin. To properly diagnose flukes, you’ll need to take skin and/or gill samples and view them under a microscope. Both types have a slim cylinder shape and a set of hooks. Gill flukes have dark spots on the head of the body that are not present in skin flukes. These spots are the easiest way to distinguish gill flukes from skin flukes.

Treatment

The most effective treatment for flukes is Praziquantel, which prevents and treats infections caused by flukes. Salt can also be used, but it does not eradicate eggs or larvae in the water.  When treating for flukes, it is important to remember that treatments will not be effective against any unhatched eggs. This means that multiple rounds of treatment are required to fully eradicate a fluke issue.

Ich

Ichthyophthirius multifiliis, commonly known as “Ich” or “white spot disease,” is a freshwater protozoan parasite that penetrates the skin of goldfish and feeds on blood and flesh. There are three stages in the life cycle of Ich: the feeding stage, the encapsulated dividing stage, and the free-swimming stage.

The signature small, white nodule or lump you see on your goldfish occurs during the feeding stage, which is when the parasite is attached to your goldfish. Once the parasite has finished feeding, it will leave the fish and become a tomont. The tomont will attach itself to the bottom of the pond, a plant, or another surface, form a cyst and begin the encapsulated dividing stage. During this stage, the tomont continuously divides to create hundreds of new parasites, called theronts. The theronts break through the cyst and begin the free-swimming stage, where they will look for a host to attach to and repeat the cycle.

Causes

Ich attacks when goldfish have lowered immune systems. Poor water conditions or a sudden change in temperature also can lead to an Ich outbreak.

Symptoms

The most common indication of Ich is the presence of small, salt-like specks on the body and fins of your fish. Other symptoms include flashing, heavy breathing, clamped fins, loss of appetite, and lethargy. Proper diagnosis of Ich requires a microscope; under magnification, it’s characteristic crescent- or horseshoe-shaped nucleus within a round body is visible.

Treatment

Treatment for Ich is only effective during the free-swimming stage. The life cycle of Ich is largely dependent on water temperature and can be sped up by raising the water temperature, which will also speed up the treatment process.

The most common method for treating Ich is by gradually warming the water to 75-80° F, increasing aeration, and adding pond salt—which will eradicate Ich in the free-swimming stage. Salt should be left in water for three days after all symptoms are gone to ensure the life cycle doesn’t continue, and then a 25-50% water change should be performed.  A combination of formalin and malachite green is an effective follow-up treatment.

Velvet

Velvet disease, also known as “rust” or “gold dust disease,” is a rare illness caused by the Oodinium parasite that attaches to fishes’ skin and gills. The parasite destroys your fish’s cells and feeds on its nutrients. If left untreated, velvet can be deadly.

Causes

Like other parasites, velvet is often brought into a pond by a new fish that has not been properly quarantined. However, an outbreak also can be the result of stress caused by poor water quality.

Symptoms

The most notable symptom of velvet is the presence of a whitish-yellow film or gold-colored specks of dust that resemble velvet over the body or gills of your koi. Though it may look similar to Ich, velvet is smaller and finer. Other symptoms include weight loss, clamped fins, labored breathing, heavy mucous secretion, and flashing.

Treatment

The best treatment for velvet disease is copper sulfate, but keep in mind that this can be lethal to pond plants. Since Oodinium parasites rely on photosynthesis, turning off lights in or around the pond can also be beneficial in eradicating velvet.

Bacterial Diseases

Columnaris

Columnaris is a bacterial infection caused by Flavobacterium columnare, which is present in all ponds. Under normal conditions, this bacteria is harmless to fish; however, if fish are stressed or their immune systems are weakened, the bacteria can flourish and cause serious damage. Also known as “Cottonmouth” or “Saddleback disease,” columnaris infections can spread quickly in warmer temperatures and have a high mortality rate.

Causes

Columnaris can enter fish through the mouth, gills, or open wounds. Infections occur both internally and externally and are common in high-stress environments. Some stress factors include pond overcrowding, low oxygen, high nitrate or ammonia concentrations, or unstable pH levels.

Symptoms

The first physical indication of a columnaris infection is typically a gray or white line around the lips that may resemble fungus as it progresses. Lesions and sores on the body are common, especially around the dorsal fin. The fish may also develop white or cloudy patches that look similar to a fungal infection. Other symptoms include discoloration, clamped fins, loss of appetite, lethargy, flashing, frayed or ragged fins, and labored breathing.

Treatment

A salt treatment can be effective for columnaris if the case is less severe. An antibiotic that treats gram-negative bacterial infections, like oxytetracycline or nitrofurazone, can also be used.

Ulcers

Ulcers are red body sores that result from a bacterial infection. The bacteria responsible is typically Aeromonas or Pseudomonas, which are always present in pond water but can cause illness when fish are stressed or their immune systems are weakened. If ulcers are left untreated, the infection can spread to the organs.

Causes

Ulcers are usually the result of an underlying problem. Environmental stressors, such as poor water quality, can lead to ulcers. Open wounds or injuries caused by parasites can also make fish more susceptible to bacterial infections.

Symptoms

Ulcers begin as small pimples or sores, and left unchecked can progress to open wounds in the fish. Ulcers on the body will typically be circular in shape and will have a white edge where the infection is decaying tissue. They can appear on the skin or mouth and may cause your fish to appear swollen in more advanced cases. Other symptoms include flashing, lethargy, loss of appetite, and missing scales.

Treatment

Before treating the ulcer, it’s important to determine and address the underlying cause. In most cases, poor water quality or parasites are to blame. Once the root issue has been addressed, the ulcers can be swabbed with hydrogen peroxide or potassium permanganate to heal.

Red Pest

Hemorrhagic septicemia, commonly known as “red pest,” is caused by Aeromonas entering your fish’s circulatory system. Once in the bloodstream, the bacteria can damage body tissue, blood vessels, and the heart. Red pest also can lead to internal bleeding and septic shock.

Causes

Red pest disease is often triggered by an ammonia spike due to poor water conditions, which stresses fish and weakens their immune system, making them more susceptible to illness. Pond overcrowding can also be a factor. Wounds caused by parasites also can become infected with Aeromonas. The disease can spread quickly by infected fish and contaminated water.

Symptoms

The most common symptom of hemorrhagic septicemia is red patches and ulcers on the body of the goldfish. As the disease progresses, these wounds deepen and destroy the skin and tissues. Other symptoms include labored breathing, erratic swimming, gasping at the surface, and swelling of the eyes and abdomen.

Treatment

Sick fish should be moved to a quarantine tank and treated with broad-spectrum antibiotics. Wounds and ulcers can be treated with topical antimicrobial solutions. A water change should be performed to improve water quality. It’s also a good idea to ensure that your pond is well oxygenated and that the filter is in good condition.

Viral Diseases

Carp Pox and Goldfish Herpesvirus

Cyprinid herpesvirus 1, better known as “carp pox,” and Cyprinid herpesvirus 2 better known as goldfish herpesvirus or GHV, are common viral diseases caused by a herpesvirus infection. Herpesvirus infections are some of the oldest diseases seen in fish, but they are usually not life-threatening like some of the more serious types of cyprinid herpesvirus that primarily affect koi.

Causes

Cyprinid herpesvirus 1 and Cyprinid herpesvirus 2 are very common among koi and goldfish, but, much like chicken pox in humans, the viruses can lay dormant within otherwise healthy looking fish for years.

Most goldfish populations carry the genetic code for both herpesvirus, but they don’t begin making the virus unless exposed to environmental stressors that weaken the fish’s immune system. Your fish may be in danger of developing Carp Pox or GHV any time the water drops below 70°F.

Symptoms

Carp Pox are characterized by soft, pink wart- or blister-like lesions on the goldfish’s skin. These blisters are delicate and can easily rupture if touched or wiped; however, removing them leaves openings in the skin that are susceptible to secondary parasite or bacterial infections.

The most common symptom of GHV is anemia, or low numbers of red blood cells, that results from the virus attacking the head and kidney tissue. Infected fish will often have white or pale gills rather than the rich red of a healthy fish. In some cases, the goldfish may lose the mucus lining covering its skin, causing it to feel rough or appear dull on the surface.

Treatment

There is currently no cure for carp pox or GHV, but neither infection is fatal. However, it may be possible to prevent herpes virus outbreaks by mitigating stressors and keeping fish immune systems healthy, which is often linked to higher water temperatures.

Should an outbreak of Carp Pox occur, lesions should not be removed, as doing so will not cure the virus and may make fish susceptible to secondary disease. Usually, symptoms will disappear when water temperatures rise or fish mature and their immune systems strengthen.

Lymphocystis

Lymphocystis is a viral infection that causes growths on the skin and fins of goldfish. Though the growths aren’t very aesthetically pleasing, lymphocystis does not cause any serious health problems.

Causes

The virus is typically brought into a pond by an infected fish. Properly quarantining new fish can reduce the risk of the virus being introduced to your pond and spreading to other fish.

Symptoms

Lymphocystis causes growths on the skin or fins that are usually pink or white in color and resemble cauliflower. This is typically the only symptom associated with lymphocystis. In extreme cases, a large number of growths could cause swimming difficulties.

Treatment

There is no cure for lymphocystis. Typically, if proper water parameters are maintained, the disease will resolve itself within a few weeks. Depending on the location of the growths, there may be a risk of secondary infection, so it’s important to monitor fish for any signs of bacterial, parasitic, or fungal infection.

Other Diseases

Cloudy Eye

Cloudy eye, also called “white eye,” is a condition that causes one or both eyes to appear cloudy or opaque. It isn’t really a disease itself, but rather a symptom of an underlying issue. Cloudy eye can be caused by a variety of things, including infection or injury.

Causes

Cloudy eye can be brought on by bacteria, viruses, fungi, poor water quality, or physical injury. However, poor water quality and bacterial infections are the most common causes.

Symptoms

Cloudy eye will cause one or both of your fish’s eyes to appear foggy or hazy, and the fish could lose its vision. Depending on the underlying cause of cloudy eye, other symptoms can include excess mucus production, difficulty swimming, irritated skin, weight loss, and scale damage or dullness.

Treatment

Treatment for cloudy eye depends on the root cause. Testing water quality and looking out for additional signs and symptoms can help you determine the underlying issue. If only one eye is cloudy, it’s likely a result of a physical injury, which should heal on its own. It’s a good idea to keep the affected fish in a quarantine tank until the source of the cloudy eye is discovered. Once the initial cause is determined, treat accordingly.

Dropsy

Dropsy refers to the ballooning or swelling of a fish’s body due to fluid buildup inside their body. Dropsy isn’t an illness itself, but a physical sign of an underlying condition, typically a bacterial infection of the kidneys.

Causes

Dropsy is the result of damage to the kidney, which can be caused by infectious and non-infectious issues. In most cases, a bacterial infection is to blame, but toxins or parasitic attacks are also possible causes.

Symptoms

The most common symptom of dropsy is a swollen belly and a pinecone appearance due to scales being pushed outward. Other symptoms include lethargy, loss of appetite, rapid breathing, gasping for air, and bulging eyes.

Treatment

Unfortunately, dropsy usually is untreatable by the time symptoms appear. However, depending on the underlying cause, you can attempt to treat the condition if caught early. Determining the root problem will help you decide the best treatment plan. The affected fish should be moved to a quarantine tank. Epsom salt baths can help draw out excess fluids. Antibacterial or antibiotic regimens may also be effective.

Pop Eye

Much like cloudy eye, pop eye is not a disease but rather a signal of an underlying condition. Pop eye is the result of fluid buildup behind the eye, which causes one or both eyes to protrude.

Causes

Pop eye can be caused by a variety of issues, including physical injury to the eye, parasites or bacteria, poor water conditions, and kidney failure. Unilateral pop eye (affecting only one eye) is typically the result of physical trauma to the eye, while bilateral pop eye (both eyes) is usually due to an underlying illness.

Symptoms

The most obvious symptom of pop eye is one or both eyes protruding or bulging outward from the head. Other symptoms may include cloudy eye, bloodstained eye, loss of vision, and lethargy.

Treatment

Treatment depends on what is causing the pop eye. If the issue is accompanied by dropsy, it’s likely due to a kidney infection or kidney failure. Treating the affected fish with epsom salt in a quarantine tank can help reduce swelling and pressure. Maintaining good water quality can help the recovery process. If a parasitic or bacterial infection is the suspected cause, treat accordingly.

Fungal Disease

Fungal disease, or “cotton wool disease,” is a fungal infection that attacks vulnerable fish. This disease is typically secondary to another health problem, such as a parasitic attack, bacterial infection, or injury.

Causes

Fungal growth can be triggered by stress, a weakened immune system, or poor water quality. Goldfish with open wounds, ulcers, or parasitic or bacterial infections are at higher risk of fungal attacks. Ich, flukes, and Costia are a few of the diseases that can lead to fungal infections.

Symptoms

Cottony, gray-white growths on the skin and fins are the most common symptom of fungal disease. These growths can become long and cover large areas of the fish.

Treatment

Fungus can grow quickly and be lethal if left untreated. The infected fish should be moved to a quarantine tank before treatment. Malachite green is considered the best treatment for fungal disease, but formalin, potassium permanganate, and salt treatments can also be effective. Maintaining good water conditions can prevent future issues.

No matter the disease, the most effective way to keep your goldfish healthy is by taking proactive steps to prevent illness. Stress and weakened immune systems make fish more susceptible to infections and outbreaks, which is why it’s important to keep their environment clean and stress-free. You can reduce the risk of illness by properly quarantining new arrivals, keeping your pond free of debris, performing routine maintenance tasks, maintaining water parameters and completing water changes regularly. With the right preventative measures and quick diagnosis and treatment of any issues that do arise, you can help ensure that your goldfish stay healthy for years to come.