Many inexperienced fish caretakers may attribute odd swimming behaviors to their pet’s quirkiness or inherent charm. Though a goldfish that seems to be doing somersaults and tricks in the water may come across as “cute”, this behavior is more likely to signify health-related issues. Unless it is done by an aquatic species known for naturally swimming in an inverted manner to search for prey, to communicate, or to thermoregulate, swimming sideways or upside down is caused by serious underlying issues.

Healthy goldfish, when raised in appropriate conditions, will always explore the tank or pond right side up. Their ability to maintain an upright position in the water is regulated by an organ called the ‘swim bladder’. Present in most bony fish species, this specialized organ typically serves as a gas pocket. Oxygen is pumped into or out of the bladder as the fish attempts to maintain its buoyancy at a specific depth.

In domesticated goldfish, the swim bladder is associated with a whole host of diseases. When its structure or its ability to retain or expel gas is compromised, the fish may either sink uncontrollably, remain afloat on the water’s surface, or swim upside down. Goldfish may live with minor swim bladder disorders, but those that impede their ability to feed or detect dangers are usually fatal.

How Does a Goldfish's Swim Bladder Work?

Fish specialists often compare the swim bladder to an elastic balloon, which can be inflated or deflated. In a fluid space, an inflated balloon is more likely to float upwards due to an increase in gaseous volume. As the swim bladder expands with oxygen, its volume increases and displaces more water. This causes it to be pushed upwards toward the surface.

For goldfish to maintain their buoyancy or their depth position in the water, they must displace a volume of water that is equal to or greater than their own mass. By expelling more gas from their swim bladder, thereby reducing the volume they displace, they tend to sink. The amount of air entering and exiting the swim bladder is usually well-regulated depending on the needs of the fish. Unfortunately, some types of domesticated goldfish are likely to develop swim bladder disorders due to their body shape, organ conformation, and diet.

Based on the means by which goldfish fill their swim bladders, they are considered “physostomous” fish. This means that the oxygen they take up from the water’s surface passes through a pneumatic air duct, which is linked to the esophagus, and directly into their swim bladder. This connection between the swim bladder and esophagus tends to increase the chances of buoyancy complications.

Swim Bladder Disorders

Swim bladder complications are more common in fancy goldfish breeds with a rounded body shape, a markedly curved back, or protruding organs (e.g. bubble eyes). The non-streamlined form affects their swimming ability and compounds the symptoms of having excess air in the swim bladder. As more oxygen enters the bladder, their bodies may flop to the side or become fully reversed, causing them to float upside down at the water’s surface.

Common causes of swim bladder disorders include a poor diet, poor dissolved oxygen conditions, the presence of pathogens and disease-causing parasites, as well as overfeeding. One or a combination of these may quickly cause the swim bladder to become deformed, twisted, or abnormally distended. The specific ways in which they can compromise the survival of your goldfish are outlined below.

• A poor diet: The use of dry pellets, frozen foods, or poorly made fish feeds can cause issues such as bloating and stomach complications. As dry food becomes enlarged upon contact with moisture, it can take up more space in the stomach than a serving of fresh, pre-moistened treats. A distended stomach may push on the swim bladder, preventing the gas from being distributed evenly. While a single instance of the stomach pushing on the bladder may be reversible, prolonged or repetitive issues may affect the overall health of the fish.

• Low dissolved oxygen conditions: Poor oxygen conditions may force your goldfish to stay close to the surface. Their tendency to gulp atmospheric air increases as they attempt to make up for the low oxygen content in the water. Swallowing too much air, a portion of which is likely to make its way into the swim bladder, may affect the fish’s buoyancy. Poor oxygen conditions also lead to compromised immunity.

• Overfeeding and constipation: Poorly formulated goldfish feeds can lead to constipation, which can irritate the digestive organs. Blocks in the digestive tract may either cause the stomach to push on the bladder or infect the surrounding organs. While any blockages may be temporary, they may have long-term consequences on the health of your fish.

• Pathogenic infections: Dangerous strains of bacteria and viruses may proliferate in the swim bladder or in nearby organs. These can compromise the capacity of the bladder to take up or release air, resulting in the fish’s inability to swim normally. If an infection isn’t treated in due time, the swim bladder disorder can become permanent.

• Sudden changes in water parameters: A drastic or abrupt change in the water chemistry and dissolved oxygen conditions of a goldfish pond or tank is one of the leading causes of fish stress, especially for fancy goldfish breeds. Large alterations in water temperature or in the concentration of nitrates may have an adverse effect on the amount of gas taken up by the swim bladder. Keep in mind that the volume of gases and the flow of water may be affected by properties like temperature and nutrient saturation.

• Heredity: Unfortunately, swim bladder disorders may also have a genetic basis. Thus, a goldfish can be born with a faulty organ. In some cases, the affected fish may live out a decent lifespan with the disease, swimming in a lopsided manner throughout its life. The disease may also be the result of developmental malformations that occurred in the egg or when the fish was just a hatchling.

How to Treat Swim Bladder Diseases

Before deciding on a specific treatment or mode of action in the attempt to get your goldfish to swim in an upright manner, you’ll have to determine the cause of the swim bladder issue. Oftentimes, this means double-checking the water parameters, switching out floating fish feeds for higher-quality sinking pellets, or consulting a local fish expert. Aim to determine the cause soon after the fish begins to display abnormal swimming behavior as an early diagnosis may help reverse or alleviate the severity of the disorder (if it is non-permanent).

If you’ve found that the cause of the disorder may simply be poor water conditions, a water change followed by frequent parameter checks and routine maintenance should improve your fish’s conditions in a few days. The source of impurities in the water, including fish waste, should be efficiently cycled or removed by your tank or pond system. If a change in your goldfish’s diet leads to signs of recovery, aim to invest in higher-quality feeds or fresh food.

Will My Goldfish Swim Upside Down Permanently?

Sometimes, even when water conditions and a feeding regimen have been optimized, goldfish may still show signs of swim bladder problems. If this is the case, it would be prudent to quarantine your fish before any other pond or tank mates are infected.

Do not attempt to correct your fish’s position by attaching foreign structures to their body or by installing a tank cover to force them down. A fish vet’s services may be required, as the most effective means to correct swim bladder problems require anesthesia and the removal of excess air (from the bladder) with the use of a needle and a tube.

If you’re able to have your fish checked by a local expert or veterinarian, they may suggest that you either treat the quarantine tank with a specific or broad-spectrum antibiotic. If the disorder was caught early, the antibiotic treatment may help reverse the swim bladder disorder. Swim bladder disorders that are spotted at a late stage may not be reversible. Whatever the outcome of the treatment, taking extra measures to ensure that your fish is kept comfortable should help prolong its lifespan.

Preventing Swim Bladder Disorders in Goldfish

Swim bladder disorders are usually prevented by maintaining a clean tank, feeding your goldfish just the right amount of high-quality feeds, regularly monitoring water parameters, and removing any sources of stress before they can harm your fish. Going the extra mile to keep your fish happy and healthy should ensure that they can swim and feed properly throughout the duration of their lives. Some simple measures to help reduce your fish’s risk of developing swim bladder issues are listed below.

• Use high-quality, sinking pellets to prevent your goldfish from gulping excess air at the water’s surface.
• Do not overfeed your fish. Create a feeding schedule and remove any uneaten feeds before they can sink to the bottom and pollute the tank/pond.
• Consider pre-soaking dry fish feeds to prevent them from expanding in your goldfish’s stomach.
• Regularly perform water changes.
• Regularly monitor the water parameters and dissolved oxygen concentrations in your pond or tank.
• Keep the water temperature within the range favored by your fish. When conducting water changes, make sure the temperature does not change drastically.
• Always quarantine new fish before introducing them into a stocked pond or tank.
• Unless you have lots of experience rearing ornamental freshwater fish, avoid investing in highly sensitive fancy goldfish breeds. Stick to the hardier varieties.