Swim Bladder Disease in Fish: Causes, Symptoms, and Treatment

Swim bladder disease is a condition that affects a fish’s ability to control its buoyancy, making it difficult to swim normally or maintain position in the water.

The swim bladder is a gas-filled organ that helps fish stay balanced at different depths. When it doesn’t function properly, fish may float, sink, or swim abnormally.

What Is a Swim Bladder?

The swim bladder is an internal organ that helps fish maintain neutral buoyancy.

It works by holding gases that allow fish to stay suspended in the water without constantly swimming. This helps conserve energy and maintain proper posture.

Download a PDF of this swim bladder diagram.

Fish can be grouped based on how their swim bladder functions:

• Physostomous fish fill their swim bladder by gulping air at the surface, which travels through a tube to the organ
• Physoclistous fish regulate gas levels internally using a specialized gland connected to their bloodstream

The swim bladder is located just beneath the spine within the body cavity and is protected by a durable outer membrane.

In addition to helping with swimming and posture, some fish use the swim bladder for sound production and detection, making it an important organ for both movement and communication.

Because of its role in maintaining balance and function, any disruption to the swim bladder can significantly affect a fish’s health.

What Causes Swim Bladder Problems?

Swim bladder disorders are most often caused by stress, environmental issues, or underlying health conditions that affect a fish’s ability to regulate buoyancy.

One of the most common and overlooked causes is poor water quality. When water conditions are unstable, fish experience stress, which disrupts normal body functions and can interfere with how the swim bladder works.

Other contributing factors may include:

• Dietary issues (such as excess air intake or improper feeding)
• Infection or inflammation
• Organ dysfunction
• Physical deformities or injury

If your fish shows signs of abnormal swimming or floating, testing water conditions and correcting if needed should be your first step.

What Do Swim Bladder Disorders Look Like?

Swim bladder disorders are most often recognized by changes in how a fish swims or maintains its position in the water.

Healthy fish are neutrally buoyant, meaning they can move up and down the water column easily without floating or sinking.

When the swim bladder is not functioning properly, fish may become either positively buoyant or negatively buoyant.

• Positively buoyant fish tend to float at the surface and struggle to swim downward. They may also display abnormal posture, such as floating upside down or on their side.
• Negatively buoyant fish remain near the bottom of the tank and have difficulty rising. They may also lie on their side or appear unbalanced.

In both cases, affected fish often show poor control of movement and unusual body positioning, which are key signs of a buoyancy disorder.

How Veterinarians Diagnose Swim Bladder Disorders in Fish

Swim bladder disorders are typically diagnosed using imaging and a review of the fish’s environment and symptoms.

If your fish needs veterinary care, it’s important to work with a veterinarian experienced in aquatic animals. Specialized organizations, such as the American Association of Fish Veterinarians or the World Aquatic Veterinary Medical Association, can help you find qualified professionals.

The most effective way to evaluate the swim bladder is through X-rays. Imaging allows veterinarians to clearly assess:

• The size and shape of the swim bladder
• Its position within the body
• The presence of abnormal fluid or displacement

These findings help determine whether the issue is caused by structural changes, infection, or another underlying condition.

Swim Bladder Disorders in Different Fish

Goldfish

Swim bladder disorders are especially common in goldfish, particularly in “fancy” varieties with rounded bodies and curved spines. These structural traits can place pressure on the swim bladder, making buoyancy issues more likely.

Goldfish are physostomous fish, meaning their swim bladder is connected to the digestive tract. This allows excess air swallowed during feeding to enter the swim bladder, sometimes leading to buoyancy problems.

In mild cases, switching to a sinking or neutrally buoyant diet may help reduce excess air intake. However, not all cases improve with diet changes alone.

Avoid using floats, weights, or other devices unless directed by a veterinarian, as these can damage the fish’s skin and protective mucus layer.

Koi

Koi are also susceptible to swim bladder issues, particularly when affected by spinal deformities or neurological conditions.

Over time, the swim bladder may change in size or shape to compensate for reduced mobility. These adaptations can help the fish survive but are often permanent.

Cichlids

Cichlids can experience both positive and negative buoyancy disorders, depending on the underlying cause.

As with other species, proper diagnosis—including imaging and environmental evaluation—is important to determine the cause and guide treatment.

Swim Bladder Treatment

Treatment for swim bladder disease depends on the underlying cause and whether the condition is temporary or permanent.

Management typically focuses on supporting the fish’s buoyancy and improving its environment, with adjustments made based on whether the fish is floating or sinking.

Positively Buoyant Fish

Fish that float at the surface may have parts of their body exposed to air, which can lead to drying and irritation.

To help manage this:

• Keep water conditions stable and clean
• Avoid lowering oxygen levels—do not cover the tank to force the fish underwater
• Consult your veterinarian about safe ways to protect exposed skin

Negatively Buoyant Fish

Fish that sink to the bottom often struggle to move and may rest on their side or belly.

To reduce injury and stress:

• Use a smooth, non-abrasive substrate (such as glass stones)
• Maintain excellent water quality
• Ensure the tank is kept especially clean

Because treatment varies widely depending on the cause, working with a veterinarian is the best way to develop an effective care plan.

Preventing Swim Bladder Disorders

Preventing swim bladder disorders starts with maintaining a stable, low-stress environment for your fish.

Because these conditions are often linked to environmental factors, the first and most important step is to monitor and maintain proper water quality. Poor water conditions are one of the most common and overlooked causes of buoyancy problems.

For species prone to swallowing excess air—such as physostomous fish—feeding a sinking or neutrally buoyant diet can help reduce the risk of swim bladder issues.

If your fish begins to show signs of abnormal swimming, address water conditions immediately and monitor closely. If symptoms persist, consult an aquatic veterinarian for further evaluation, which may include imaging such as X-rays.

While some swim bladder disorders cannot be fully reversed, many fish can continue to live healthy lives with proper care and adjustments to their environment.