7 Common Goldfish Diseases

Three goldfish in a tank with plants and rocks

HowardOates/Getty Images

Goldfish are susceptible to many freshwater diseases. If you are a goldfish owner, there are some diseases and conditions you should pay particular attention to:

Poor Water Quality

Although not technically a disease, poor water quality is the most common cause of disease in goldfish. Goldfish are messy critters and create a lot of waste and foul water quickly. Inappropriate environments, such as antiquated bowls or severely overcrowded systems, can contribute to chronic stress through poor water quality. A fish unable to escape a toxic system will become chronically stressed, with decrease in growth, immune function, and reproductive capability.

It is critical to make sure your goldfish have enough space for a healthy life. For comet and other long-bodied goldfish, they will require 20 gallons per fish to start. You will likely need close to 50 to 75 gallons per fish as they mature. Goldfish can grow up to 14 to 16 inches, so plan on that size, not 2 to 3" inches No fish deserves to live in a filthy bowl. All fish require filtered tanks, but goldfish do not require heaters.

Test your water quality regularly and be sure to correct any abnormalities. Feeding high protein flake food can be a big problem in many goldfish tanks. Always try to feed a pelleted diet in an appropriate size for your fish. If you are having trouble keeping your water quality within range, contact your aquatic veterinarian for additional support.


Bringing a fish home from the pet store is the highest risk point in a fish's life for coming into contact with a parasite. In pet stores, fish from many sources and exposures are mixed in different systems and most parasites can travel in water and on equipment.

Clinical signs of parasites in goldfish include missing scales, flashing, bruising, lethargy, and/or sudden death. The most common goldfish diseases include:

The best prevention of parasites is a strict quarantine protocol. There is no "one size fits all" treatment for parasites, so a definitive diagnosis from an aquatic veterinarian is critical to ensure proper treatment. Just guessing and throwing a bunch of OTC medications at your fish is a recipe for death.


Goldfish with neurofibroma on dorsal ridge

Dr. Jessie Sanders

These "lumps" are common in comet goldfish, particularly those kept outdoors. Neurofibromas form from neural tissue deep within skin layers and are nearly impossible to treat. They can commonly form a "stalk" and fall off, only to grow back again. Some fish may have one or two localized lumps or disseminated throughout the fish's body.

Treatment is not warranted due to recurrence. Multiple modalities utilizing surgery and cryotherapy have not been successful. It is not worth putting your fish through difficult treatment that will not resolve the issue. Since these benign tumors arise from neural tissue, there is no treatment currently available that can target these types of tissues specifically.

Buoyancy Disorders

Goldfish may are prone to both negative and positive buoyancy disorders. Being physostomous fish, they have a pneumatic duct between their esophagus and swim bladder, allowing them to swallow air to inflate their swim bladder. A separate gland, called the oval, is responsible for removing excess air.

Positive buoyancy disorders occur most commonly after feeding. Goldfish, the golden retrievers of the fish world, who feed vigorously at the surface, will commonly suck in too much air. It will either end up in the GI tract or the swim bladder. After the excess air is removed, the fish goes back to normal. Malfunction of the oval has been known to occur, resulting in permanent positive buoyancy disorders. Surgery is often required to correct these issues.

Negative buoyancy disorders are most common secondary to stress or poor diet. Simply put, your fish doesn't have the inclination or energy to swim. Once you alleviate the stress and give your fish a proper diet, they will revert to normal behavior. External "wheelchair" floats are extremely dangerous and can seriously hurt your fish.

Polycystic Kidney Disease

Goldfish necropsy with polycystic kidney disease

Dr. Jessie Sanders

Goldfish are prone to a disease that forms cysts in their kidneys, which cause malfunction and serious tissue damage. Unfortunately, the cause of this disease is unknown and there is no treatment. Once the kidneys have been damaged, as in many other species, they do not recover.

Clinical signs of polycystic kidney disease mostly look like your fish swallowed a baseball, softball or even volleyball. Fish can act normal despite an abnormal external appearance. Ultrasound is required for diagnosis. Do not attempt to squeeze your fish! This can cause serious organ damage and will not help your fish in any way.

Cloudy Eyes and Popeye

Cloudy fish eyes are common secondary to poor water quality, trauma, and secondary disease. Some fish may have eyes that poke out more than their counterparts, especially some fancy varieties, making them more prone to trauma.

Popeye is a common internet disease for which there is no one treatment. Eyes can become distended from many secondary issues and you should consult with an aquatic veterinarian to get to the root cause quickly and develop an effective treatment plan before the eyes are lost.

Red Streaks on Skin and Fins

Red streaks on skin and fins are common symptoms of stress and poor water quality. If you see these on your fish, it is important to check your water quality as soon as possible. If it is off, correcting it can resolve these streaky issues.

If your water quality is within range and no major changes have been recently made, it is critical to identify the stressor and remove it from your system.

Non Diseases

There are a few diseases out there on the internet that are technically not diseases. They are symptoms of many common fish diseases.


Koi with "dropsy" or skin edema

Dr. Jessie Sanders

This describes the clinical condition when fluid collects between the scales of a fish and they look like a pinecone. It is a clinical sign of kidney or gill malfunction and is not a disease.

"Swim Bladder"

Yes, your fish has a swim bladder. "Swim bladder" disease can be many different things and requires a consultation from an aquatic veterinarian. There is no one cause of buoyancy disorders.

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  1. Sirri, Rubina, et al. "Ultrasonographic and pathologic study of schwannoma in a Goldfish (Carassius auratus)." Veterinary clinical pathology 44.4 (2015): 586-591.

  2. Overfield, E. M., and J. A. Kylstra. "The volume and rate of volume change of the swimbladder of the goldfish." Respiration physiology 13.3 (1971): 283-291.