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Swim Bladder

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What is a Swim Bladder?

Nature works its best in all its creatures and bestows organs in the body of all living beings, plants, animals, and humans that are necessary to survive. The swim bladder or also referred to as the air bladder is one such gas-filled organ that is part of the body of fish that helps it stay in the required state of buoyancy without floating up. It is present in the dorsal coelomic cavity of fish and also aids in many other air bladder function.

Location of the Swim Bladder

The swim bladder is made up of two sacs in some and one in other species of fish. It is surrounded by a tough outer membrane and located in the dorsal cavity lying just under the spinal cord in the coelomic cavity portion of the fish. According to the fluid pressure the swim bladder contracts and expands.

What is a Swim Bladder and How Does It Work?

The swim bladder works in a similar fashion to the way planes move in the air and helps the fish to freely move in any way it intends to. When any object or in this case fish is in water, the fluid nature causes the organisms to experience two states of force: the downward pull of gravity and the upward push of buoyancy. Due to the difference in the fluid pressure at every point, there is buoyancy. The weight of the fluid displaced by the fish is equal to the force of buoyancy on it. But if the density of the fish, that is the weight of the fish, is greater than water, the buoyancy force does not consider the fluid displaced and the fish will sink.

To remain without sinking by the fluid pressure, the fish with the help of the swim bladder increases its volume and not its density. A swim bladder is just an expandable sac, the mechanism of it can be considered to be like a human lung. Via the gills, the fish fills the bladder from the oxygen collected from the surroundings and in this way it reduces its overall density.

With this filling of the oxygen sac, the weight of the fish does not increase, rather only the volume gets higher. With an expanded bladder that is inflated more water is displaced and buoyancy helps it rise on the surface level and it sinks when the bladder is deflated.

Function of Air Bladder in Fishes

The functions of the air bladder in fishes are mentioned below:

  • Maintaining buoyancy is the primary air bladder or swim bladder function.

  • Helps the fish rise and sink and keeps it alive and going.

  • Helps the fish move side to side freely.

  • Other hydrostatic activities.

  • Sound producing or a resonating chamber can also be referred to as phonation in a few species with an evolved secondary modification.

  • Maintains equilibrium with the surrounding medium under varying pressures.

  • Helps in maintaining posture and aids in swimming.

Causes of Swim Bladder Inflation

The causes of swim bladder inflation include:

  • With floating, fishes tend to rapidly eat and gulp air, leading to overeating and constipation, which affects the swim bladder.

  • Low water temperature.

  • Enlargement of other organs that are in contact with the swim bladder when they enlarge due to cysts and then the swim bladder no longer has space to expand and slowly loses its ability to function.

  • Inflammation of the swim bladder due to bacterial and parasite infection.

  • Sometimes it is due to a genetic defect.

Symptoms of Swim Bladder Inflation

The symptoms of swim bladder inflation include:

  • Distended belly

  • Struggling to maintain a normal position or stay there for longer periods.

  • Curved back.

  • Sinks to the bottom.

  • Stays afloat.

  • Floating upside down.

  • Loss of appetite.

Treatment of Swim Bladder Inflation

The treatment of swim bladder inflation can be treated by:

  • If the problem is extreme one can hand feed the fish.

  • Reduce the water flow current.

  • Cleaning the water regularly.

  • Keeping the water temperature between 78 and 80 degrees Fahrenheit.

  • Reduce water level.

If the swim bladder disorder does not respond to the treatment in a reasonable period after it gets affected then chances of recovery are slim and one has to watch the fish die.

Prevention of Swim Bladder Disorder

To prevent the swim bladder disorder, there are certain factors that are to be checked upon. They are:

  • Avoid feeding frozen foods.

  • Soak the dried foods before feeding them to the fish.

  • The water temperature can be put a little higher.

  • Trying to sink the food into the fish so it does not come out for a bite and have to gulp air.

  • Keep the fish tank clean by washing it more frequently.


The swim bladder keeps the fish thriving even with so much fluid pressure. The swim bladder is an important part of the anatomy of fish but many fishes which stay on the ground level of the ocean and do not require a swim bladder. The swim bladder disorder can cause the fish a lot of harm so one must be careful and try to protect and prevent it.

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FAQs on Swim Bladder

1. Does the Fish Die If the Swim Bladder is Affected?

Depending on the effect of the disease the damage to the swim bladder can be temporary or permanent. Even with an affected swim bladder, the fishes can live a long life with the help of some modifications performed by the fish surgeon.

2. Is the Swim Bladder Present in All Kinds of Fishes?

There is an exception to every rule and even in the case of the presence of a swim bladder in the fishes, the cartilaginous fishes do not have a swim bladder. Some examples of cartilaginous fishes with no swim bladder are sharks and rays. They do not possess a swim bladder because they mostly stay afloat and underwater or under sea level; the shark’s pectoral fins work like the wings of a plane and help them swim.

3. Did the Swim Bladder Evolve from the Lungs Over a Period of Time?

According to Charles Darwin, the oldest living bony fishes possess lungs and there is a possibility to this developmental scenario. According to the research on molecular and developmental evidence, lungs evolved before swim bladders pointing to the reverse case of evolutionary adaptation. Certainly, more research and strong evidentiary support are required to figure out this dilemma and find the answers.

4. Is the Swim Bladder Disorder Contagious?

The important thing to remember is that swim bladder disorder is not a standalone disorder and many factors contribute to this disorder and when left untreated you may lose your fish. However, know that your other fishes will not be affected by the swim bladder disorder if one of them is affected since it is non-contagious.

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