Why Is My Pond Goldfish Bloated? [Causes & Treatment]

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Why Is My Pond Goldfish Bloated?

Pond goldfish
Pond goldfish are more susceptible to parasites and diseases due to their exposure to outdoor elements. Elliott Brown / CC BY-SA 2.0

As live ornamental additions to outdoor ponds, goldfish are undeniably stunning and hypnotizing to watch. They can thrive in a pond environment, able to live for years, and grow into maximum lengths that are much longer than those of their counterparts in tanks. Hardy and tolerant of cool temperatures, many breeds are perfectly suited to pond life. That being said, exposure to outdoor elements can, unfortunately, make them more susceptible to parasites and diseases.

Goldfish bloating is a fairly common yet problematic issue with many potential causes. Pathogens, particularly bacteria or parasites, can cause their bellies to swell considerably. This condition, usually termed ‘dropsy’, may be reversible if it is treated in a timely manner. Diagnosing this ailment can be challenging as bloating can also be a symptom of obesity, reproductive issues, and tumors.

The best way to pinpoint the cause of bloating would be to, of course, consult a veterinarian or a local expert on pond fish. They should be able to help you determine the right course of action and treatment for your fish. If you intend to diagnose the condition yourself, however, you may use the information outlined below as a guide. Note that seeking professional help remains to be the most advisable first step in treating your fish.

Possible Causes of Goldfish Bloating

1) Dropsy

Goldfish with dropsy
One of the most telltale signs of dropsy is protruding scales, as seen here. Jakehicks

Dropsy, also known as ‘bloat’, edema, or ascites, is an umbrella term for many conditions and diseases that may cause a goldfish’s stomach or abdomen to enlarge. Some of the most telltale signs of dropsy, which make it easier to tell apart from other causes of bloating, are its rapid development and the occurrence of protruding scales. The victim’s abdomen can get so large that other body parts become somewhat displaced or pushed outward.

Dropsy is usually brought about by the accumulation of fluids due to underlying health issues and the presence of pathogens. A malfunctioning kidney or liver, for example, can cause normal metabolic and hormonal processes to become disrupted or stop taking place altogether. This compromises the fish’s immune system, allowing other environmental stressors to wreak havoc on the body. If your fish has some of the following symptoms, it should be treated for dropsy:

  • Markedly swollen abdomen or belly
  • “Pine cone scales” which point away from the skin on some or all parts of the body
  • Pale and distended gills
  • Exophthalmia (bulging eyes)
  • Swollen anus due to fluid buildup in the goldfish’s intestines
  • Ruptured blood vessels, causing redness in the skin or fins
  • Abnormal swimming behavior (in advanced stages)

If the cause of dropsy is a pathogenic infection, it can quickly spread to other fish in your pond. Dropsy infections are often caused by the presence of harmful bacteria and parasites in poor pond water. This is why goldfish ponds need to be maintained, with water changes taking place every few days.

Note that by the time fluid accumulation has caused the belly to distend considerably, the damage may be very difficult to reverse. Once the disease has done extensive damage to the body’s organ systems, the fish is unlikely to recover. It would be prudent to conduct a thorough water change and double-check your pond parameters even after the bloated goldfish has been removed from the pond.

2) Obesity

Goldfish feeding
Goldfish may become obese over time if they are overfed or have an improper diet. Conall / CC BY 2.0

Although they should be able to regulate their own food consumption, goldfish can indeed become overweight. The initial sign of obesity is a slightly enlarged belly. It is usually caused by an improper diet or overfeeding and takes place over time. Even healthy fish can become obese if they are fed with feeds that contain excess fats or have a poor nutrient profile. In contrast, dropsy may occur suddenly and is more likely to affect fish that already have health complications.

If you suspect that your goldfish is obese (with the possibility of egg production eliminated) due to overfeeding or a poor diet, switch out its food to a high-quality product purchased from a reputable merchant or pet store. Closely observe your fish during feeding times and make sure to feed them only with the amount that they are able to finish in a few minutes. Scoop out all excess feeds.

3) Development of a tumor

Goldfish tumor
Goldfish are not exempt from cancer and can eventually develop tumors. John Smith / CC BY 2.0

As fish are not exempt from cancer, which may be caused by genetic mutations and triggered by environmental conditions, they too can eventually develop tumors. The most common type of tumor in goldfish is the neurofibroma. Unlike cancerous tumors, neurofibromas are benign and seldom cause fatalities. They only become problematic when they significantly hinder a fish from breathing properly, being able to see, or swimming in a hydrodynamically balanced manner.

Tumors can also be malignant and may develop within the organs of the goldfish. If one is situated in the goldfish’s abdomen, it can push its organs until they rupture or are eventually stopped from functioning normally. Unfortunately, there are rarely any treatments for cancerous tumors in fish.

4) Presence of eggs

Goldfish full of eggs
Mature female goldfish may produce lots of eggs closer to the spawning season, which causes their abdomens to appear swollen. Amanda / CC BY-SA 2.0

If your bloated goldfish is a mature female and is surrounded by sexually mature males, it may simply be carrying eggs. Closer to the spawning season, female goldfish may produce more and more eggs, which causes their abdomens to become stretched out and appear swollen. The vent of a “pregnant” female becomes enlarged as well, so you can conduct a visual check to confirm that she is preparing to spawn.

If the female deems the pond unsuitable for spawning, she may become egg-bound. This means that the eggs are trapped in her abdomen. This condition, which may also be caused by hormonal imbalances, is quite dangerous as it can lead to an inflammatory reaction and be life-threatening in the long run. To accurately distinguish between an egg-bound female and one that has dropsy, it may be necessary to conduct invasive tests.  

Egg-bound females need to be treated in a timely manner as the degenerating eggs can cause bacterial infections and may exert too much pressure on the surrounding organs. Females need external stimuli to signify that it is safe to release their eggs. Spring conditions, such as warming water temperatures, longer daylight hours, and thriving vegetation (as spawning material) may be necessary to induce spawning. A gentle massage of the abdomen coupled with medication should aid in egg release.

Treatment for Bloated Goldfish

Goldfish quarantine
If your goldfish is visibly stressed or sick, it’s recommended to isolate them in a tank with controlled conditions. Tom Booth / CC BY 2.0

If you’ve just noticed that one of your pond goldfish has an unusually large abdomen, try to go over the possible causes for bloating and eliminate those which are highly unlikely. If it seems like the cause may be an infection and if the fish is evidently stressed or sick, it is advisable to isolate it in a tank with controlled conditions. As much as possible, it should be kept comfortable in quarantine.

If you’ve caught your goldfish in one of the early stages of bloating, the right medication may reverse its condition. Note that the treatment must target the underlying ailment that is causing the fish to bloat. The application of Epsom salt in tank water should help the fish osmotically release some of the accumulated fluids. Bringing the salinity up to 1 – 2 ppt should be enough to provide relief.

Check all of the important water parameters of your quarantine tank to make sure that the bloated goldfish is comfortable. If it’s possible to consult a veterinarian about your case, you should do so before adding any medication to the tank water. If not, you may consider using broad-spectrum antibiotics and medicated feeds. Again, if the goldfish is in the late stage of its health condition, it may not be possible to reverse the damage even if the bloating is somewhat relieved.

While the sick goldfish is undergoing treatment in its own tank, it would be prudent to check the quality of your pond water and conduct a water change. If poor water quality is one of the major reasons for your goldfish’s condition, this should help ensure that any remaining fish in the pond are less likely to become stressed or infected. If your bloated goldfish does recover, it should be returned to a well-maintained pond.

Preventing Goldfish Illnesses

Pond filter
To keep your pond in tiptop shape and prevent goldfish illnesses, you should regularly clean your pond filter. Carolyn from Pemberton Township, NJ, USA, CC BY 2.0, via Wikimedia Commons

When it comes to keeping your pond goldfish free of parasites and diseases, prevention is indisputably better than the cure. This applies to goldfish bloating as most cases are diagnosed too late and are unfortunately fatal.

Routine maintenance is absolutely essential because good water conditions are necessary for healthy and happy fish. You also need to have a basic understanding of goldfish behavior, metabolic patterns, and freshwater ecology to keep your pond and its inhabitants in tiptop shape. Listed below are some tips to prevent goldfish illnesses from occurring.

  • Clean your pond filter regularly and introduce beneficial bacteria if need be.
  • Feed your goldfish with the right amounts of high-quality fish feeds. Feeding frequencies and feed types should be adjusted according to your fish’s metabolic needs. This means taking into account the effects of seasonal temperatures on fish metabolism.
  • Do not overfeed your goldfish and collect any uneaten feeds.
  • Optimize water parameters to prevent pathogens and parasites from multiplying in the pond water.
  • For gravid females: make sure they have a suitable site for spawning and keep a close eye on them prior to, during, and right after the spawning period.
  • Conduct frequent water changes and monitor water parameters after every change.
  • Employ biosecurity measures to keep wild-sourced vectors of pathogens away from the goldfish pond.

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