Molly Fish Swim Bladder Disease: Causes, Symptoms & Treatment

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I won’t forget the moment I caught my molly fish showing signs of a swim bladder disorder. My fish looked awful – it was bloated, sunk to the bottom, and couldn’t swim straight.

Fortunately, by searching online, I was able to identify what was going on with my fish and solved the issue.

In this article, I will cover everything there is to know about swim bladder disease – the causes, the symptoms, and some preventive measures.

So, without further ado, let’s get started.

An image of a Molly fish suffering from swim bladder disorder, struggling to maintain its position

Swim Bladder Disorder in Molly Fish: Quick Overview

Molly fish with swim bladder disorder experience a malfunction in their internal organ responsible for buoyancy control.

This condition leads to irregular swimming behaviors, such as struggling to ascend, descend, or maintain a stable position in the water.

Swim bladder disorder is frequently attributed to various factors, including bacterial or parasitic infections, physical traumas, or underlying health conditions.

Also Read: 15 Molly Fish Diseases & Their Treatments

Causes of Swim Bladder Disorder in Molly Fish

There is a wide range of reasons that might have caused your molly fish to suffer from a swim bladder disorder, including:

1. Physical Trauma

Physical injuries to a molly fish can directly impact the swim bladder, leading to disorder. These injuries can be from aggressive tank mates, accidents, or mishandling:

  • Aggression: Molly fish that share their habitat with aggressive fish are often physically harmed, causing injuries that can disrupt the swim bladder.
  • Accidents: Molly fish can be injured accidentally during tank cleaning or if they collide with sharp objects in their tank.
  • Mishandling: Mishandling during transfer can cause undue stress and physical harm to the molly fish, which can negatively affect the swim bladder.

2. Gastrointestinal Complications & Constipation

A low-quality diet and excess feeding can trigger constipation in molly fish, leading to a disrupted swim bladder function due to the pressure exerted on it:

  • Inadequate diet: Molly fish consuming substandard, monotonic food can suffer digestive complications, impacting the swim bladder.
  • Excessive feeding: Overfeeding molly fish can cause constipation, which can compromise the function of the swim bladder.
  • Insufficient fiber: A diet lacking in fiber can induce constipation, which adversely affects the swim bladder.
Bloated molly fish

3. Environmental Tension

Alterations in water conditions, including pH and temperature variation, can generate stress potentially resulting in swim bladder disorders in molly fish:

  • pH alterations: Rapid variations in pH can stress molly fish, which might lead to swim bladder complications.
  • Temperature variation: Abrupt shifts in water temperature can trigger stress, thereby affecting the function of the swim bladder.
  • Substandard water quality: Poorly maintained tanks with elevated nitrate and ammonia levels can contribute to swim bladder problems.

4. Newborn Fish Vulnerability

Freshly hatched molly fish are susceptible to swim bladder disorder due to the immature and nonfunctional nature of their swim bladder:

  • Incomplete development: Freshly hatched molly fish may have a not fully developed swim bladder, posing potential disorder risks.
  • Nutritional inadequacy: Insufficient nutrition during early life stages can cause underdevelopment of the swim bladder.
  • Environmental fluctuations: Swift changes in the environment can harm the evolution of a fully operational swim bladder in newborn molly fish.
Molly fish fry

5. Reduced Water Temperature

Cool water can decelerate the metabolism of molly fish, leading to digestive problems that can unfavorably affect the swim bladder:

  • Metabolic reduction: Cold water can slow down the metabolism of molly fish, possibly causing constipation, which can interfere with the swim bladder.
  • Poor digestion: Lower temperatures can decrease digestive efficiency, potentially causing swim bladder issues.
  • Limited movement: Chilly temperatures can induce sluggishness, making it harder for molly fish to maintain their buoyancy and swim efficiently.

6. Infections from Parasites & Bacteria

Infections from parasites and bacteria may lead to inflammation, which can in turn interfere with the proper functioning of the molly fish’s swim bladder:

  • Inflammation: Invading parasites and bacteria can cause the swim bladder to swell, thus jeopardizing its normal operation.
  • Tissue damage: Such infections can cause harm to the swim bladder tissue, leading to difficulties with its performance.
  • Spread of disease: Infections may travel from other parts of the body to the swim bladder, causing it to malfunction.

7. Issues Related to Pregnancy

Molly fish that are pregnant face a greater likelihood of experiencing swim bladder problems due to the physical changes and stress associated with pregnancy:

  • Physical changes: As the belly of a pregnant molly fish grows, it may place pressure on the swim bladder and potentially lead to problems.
  • Hormonal shifts: The swim bladder’s functionality can be affected by the hormonal changes that occur during pregnancy.
  • Stress: Pregnancy-related stress may increase the vulnerability of molly fish to swim bladder issues.
Pregnant molly fish

8. Other Organ-Related Complications

Diseases and complications affecting other organs in the molly fish, like the kidneys or liver, can indirectly affect the swim bladder:

  • Kidney disease: Diseases such as kidney stones can exert pressure on the swim bladder, affecting its function.
  • Liver disease: Liver diseases can affect the overall health of molly fish, indirectly causing swim bladder disorders.
  • Tumors: Abnormal growths or tumors in adjacent organs can exert pressure on the swim bladder, leading to its malfunction.

Symptoms of Swim Bladder Disorder in Molly Fish

Fortunately, identifying swim bladder disorder in molly fish is pretty straightforward, as there are many symptoms that are typical of this situation. Consider the following:

1. Buoyancy Difficulties and Impaired Swimming

Molly fish with swim bladder disorder may have trouble maintaining buoyancy and demonstrate unusual swimming patterns:

  • Inability to dive: Molly fish may struggle to dive, indicating an inflated swim bladder.
  • Erratic swimming: Molly fish may swim erratically due to the imbalance caused by a deflated swim bladder.
  • Difficulty rising: A deflated swim bladder could make it hard for molly fish to rise to the water’s surface.

2. Upside-Down Swimming

Molly fish with swim bladder issues may occasionally swim upside down due to buoyancy problems:

  • Loss of control: Upside-down swimming indicates a loss of control over buoyancy.
  • Disorientation: Molly fish may seem disoriented, which can cause them to swim upside down.
  • Difficulty righting: Molly fish with a swim bladder disorder may struggle to right themselves when they roll over.

Also Read: Why Is My Molly Swimming Upside Down?

Upside-down molly fish

3. Swollen Abdomen

A bloated abdomen in molly fish can indicate constipation or a physical issue with the swim bladder:

  • Visible swelling: A visibly swollen abdomen can be a sign of constipation or swim bladder problems.
  • Scale protrusion: The scales may protrude outward, creating a ‘pinecone’ appearance due to a swollen abdomen.
  • Discomfort: Molly fish may show signs of discomfort, such as reduced activity, due to a bloated belly.

Also Read: Why Is My Molly Fat?

4. Struggles in Maintaining Position

Molly fish afflicted with a swim bladder disorder may have difficulty holding their place in the water because of disrupted buoyancy management:

  • Continual swimming: To preserve their water placement, Molly fish might need to swim without pause.
  • Challenge in remaining at the base: A bloated swim bladder may cause them to have trouble staying at the tank’s bottom.
  • Surface struggle: If Molly fish find it hard to remain submerged, it suggests a buoyancy problem.

5. Loss of Appetite

Molly fish suffering from swim bladder disorder might experience a decrease in appetite, potentially due to discomfort or internal complications:

  • Diminished eating: If Molly fish consume less than the norm, it could signal underlying health concerns.
  • Ignoring meals: An outright dismissal of food by Molly fish is a critical warning of health issues.
  • Weight reduction: An extended loss of appetite could cause noticeable weight decrease in Molly fish.

6. Manifestation of Lethargy

Molly fish with swim bladder disorder might demonstrate signs of lethargy or a decrease in their usual activity levels:

  • Limited movement: Molly fish may show a decrease in mobility or remain stationary at either the top or bottom of the tank.
  • Limited engagement: They might have less interaction with their environment or other fish.
  • Slow response: A delay in responding to external stimuli such as the introduction of food or changes in lighting could be observed in Molly fish.

7. Consistently Hiding

Molly fish battling swim bladder disorder might prefer solitude, a sign of discomfort or stress:

  • Preference for isolation: Molly fish might habitually seclude themselves behind tank decorations or plants.
  • Avoidance of companions: Their avoidance of other fish could be an indication of potential discomfort.
  • Continuous hiding: Remaining hidden even during meal times could signal serious discomfort.

8. Unusual Vertical Swimming

Molly fish might demonstrate vertical swimming behaviors due to a swim bladder that is either deflated or inflated:

  • Nose-down swimming: A deflated swim bladder may cause Molly fish to swim nose-down.
  • Nose-up swimming: If they swim with their nose up, it might indicate an inflated swim bladder.
  • Trouble with horizontal orientation: Struggling to stay horizontal could signify a swim bladder disorder.

Also Read: Molly Fish Swimming Vertically

Molly fish swimming vertically, nose down

9. Floating on the Water’s Surface

Molly fish with an inflated swim bladder may end up floating at the water’s surface, unable to dive:

  • Persistent floating: Persistent floating on the surface can indicate a buoyancy problem.
  • Struggling to dive: Molly fish may appear to struggle when trying to dive.
  • Remaining at the surface: Remaining at the surface even during non-feeding times can signal a potential swim bladder issue.

Also Read: Why Is My Molly Fish Floating At The Top?

Treatment Options for Molly Fish with Swim Bladder Disorder

Treating swim bladder disorder in molly fish depends on the underlying issue. Here, I will focus on:

  • Overfeeding/constipation
  • Environmental shock
  • Infections

Here are some instructions:

1. Managing Disorder Caused by Overfeeding/Constipation

A swim bladder disorder caused by overfeeding or constipation can often be managed with changes in diet and feeding practices:

  • Fasting: A short period of fasting (up to 48 hours) can help alleviate constipation in molly fish.
  • Peas: Feeding them cooked, deshelled peas can act as a laxative, helping relieve constipation. This works in approximately 70% of cases.
  • Reduced feeding: Reducing the amount of food can help prevent overfeeding, which is a common cause of swim bladder disorders in molly fish.
  • High-fiber diet: A high-fiber diet can help prevent constipation in molly fish, improving swim bladder function.
  • Feeding intervals: Spacing out feeding times can allow the molly fish’s digestive system to process food more efficiently, reducing the likelihood of constipation.

Also Read: Molly Fish Constipation

2. Handling Environmental Shock-Induced Disorder

Swim bladder issues in molly fish stemming from environmental shock can be dealt with by enhancing and maintaining stable aquarium conditions:

  • Maintain a steady water temperature: A consistent water temperature, ideally within 72-78°F (22-26°C), aids in molly fish recovery.
  • Enhance water quality: Routine water replacements (25-50% weekly) better the water quality, lowering molly fish stress.
  • Assess water parameters: Regular analysis of pH, ammonia, nitrite, and nitrate levels helps in tracking and preserving perfect conditions for molly fish.
  • Apply water conditioner: The use of a water conditioner assists in eliminating harmful water chemicals, decreasing molly fish stress. My recommendation: Tetra AquaSafe (link to Amazon).
  • Gradual modifications: Implement all alterations to the aquarium environment slowly to prevent additional shock to the molly fish.

3. Dealing with Bacterial/Parasitic Infection-Related Swim Bladder Disease

Swim bladder problems in molly fish because of bacterial or parasitic infection can be managed with suitable medication:

  • Antibiotics: Antibiotics can aid in addressing bacterial infections in molly fish, possibly enhancing swim bladder function. My recommendation: API MELAFIX (link to Amazon).
  • Anti-parasitic drugs: Anti-parasitic drugs can be useful in treating parasitic infections impacting the swim bladder. My recommendation: Hikari Prazipro (link to Amazon).
  • Isolation: Isolate the affected molly fish to stop infection spread to other aquarium mates.
  • Medicated feed: Supplying medicated feed ensures the molly fish gets the medication, boosting recovery probabilities.
  • Watch recovery: Continually observe the molly fish during therapy to assess recovery and adjust treatment if required.
Molly fish infected with Columnaris

How to Prevent Swim Bladder Disease in Molly Fish

Obviously, preventing is always better than treating. When it comes to a swim bladder disorder in mollies, there are a few preventive measures you can take:

1. Supplying Quality Fish Food

Top-tier food ensures that molly fish get all necessary nutrients, decreasing swim bladder disease chances:

  • Nutrition-packed food: Feed molly fish a nutrition-packed diet to boost overall health and fend off diseases.
  • Food variety: Providing an assortment of food types helps guarantee balanced nutrition for molly fish.
  • Avoid subpar food: Eschewing low-quality food can lower digestion issues risk, which may cause swim bladder disease.

2. Maintaining a Nutritious Diet

Feeding molly fish a nutritious diet is critical for their overall health and wellness:

  • Varied meals: Offer a mix of dry, freeze-dried, and live foods to provide molly fish a well-rounded diet.
  • Plant-based food: Integrate plant-based food into the molly fish’s diet, as they’re omnivores that thrive on a balanced diet.
  • Appropriate serving sizes: Regulating serving sizes can help avoid overfeeding and consequent swim bladder issues.

3. Avoiding Excessive Feeding

Feeding too much can cause digestive troubles, potentially leading to swim bladder disease in molly fish:

  • Multiple small feedings: Instead of one big meal, give molly fish small servings several times a day.
  • Brief feeding times: Keep feeding times to approximately 2-3 minutes to prevent overconsumption.
  • Watch feeding habits: Monitor the molly fish’s eating routines and tweak the feeding timetable as needed.

4. Ensuring Optimum Water Quality

Preserving top-notch water quality is essential in preventing various diseases, including swim bladder disorder in molly fish:

  • Routine water replacements: Perform regular water replacements (25-50% weekly) to maintain excellent water quality.
  • Monitor water parameters: Regularly review water parameters (pH, ammonia, nitrite, and nitrate levels) to ensure they’re in the acceptable range. My suggestion: API FRESHWATER MASTER TEST (link to Amazon).
  • Use of water conditioners: Apply a water conditioner to neutralize harmful substances in tap water.

5. Maintaining Stable Water Temperature

A consistent water temperature can help mitigate stress and related swim bladder issues in molly fish.

  • Stable temperature control: Maintain a steady water temperature, preferably between 72-78°F (22-26°C), for molly fish.
  • Use of aquarium heater: Utilizing an aquarium heater can assist in maintaining the right temperature. My recommendation: Orlushy Submersible Aquarium Heater (link to Amazon).
  • Avoid sudden changes: Stay clear of abrupt temperature shifts as these can shock molly fish, potentially leading to swim bladder disease.

6. Removing Threatening Tank Mates and Dangerous Decorations

Threatening tank mates and sharp decorations can physically harm molly fish, possibly resulting in swim bladder disorder:

  • Use safe decorations: Employ smooth, safe decorations that won’t injure molly fish.
  • Provide ample space: Make sure the tank provides enough room for molly fish to swim without collision risk.
  • Choose peaceful tank mates: Opt for peaceful tank mates for molly fish to avoid injury and stress.

Here is a list of peaceful tank mates that can live with mollies:

  • Neon Tetra (Paracheirodon innesi)
  • Harlequin Rasbora (Trigonostigma heteromorpha)
  • Cherry Barb (Puntius titteya)
  • Honey Gourami (Trichogaster chuna)
  • Corydoras Catfish (Corydoras spp.)
  • White Cloud Mountain Minnow (Tanichthys albonubes)
  • Celestial Pearl Danio (Danio margaritatus)

On the other hand, I would avoid aggressive tank mates like:

  • African Cichlids (various species from the genera Malawi, Tanganyika, and Victoria)
  • Tiger Barb (Puntigrus tetrazona)
  • Red Devil Cichlid (Amphilophus labiatus)
  • Jack Dempsey (Rocio octofasciata)
  • Green Terror (Andinoacara rivulatus)
  • Flowerhorn Cichlid (Hybrid species)
  • Convict Cichlid (Amatitlania nigrofasciata)
Tiger Barb (Puntigrus tetrazona)


For those of you who are short on time, here is a quick overview of what I discussed earlier:

  • Swim bladder disorder in molly fish can have various causes, including physical trauma, gastrointestinal complications, and environmental tension.
  • Recognizing symptoms like buoyancy difficulties, swollen abdomen, and loss of appetite is crucial in identifying swim bladder disorder in molly fish.
  • Treatment options for molly fish with swim bladder disorder involve managing overfeeding/constipation, handling environmental shock, and addressing bacterial/parasitic infections.
  • Preventing swim bladder disease in molly fish requires supplying quality fish food, maintaining a balanced diet, keeping water quality high, and ensuring stable water temperature.
  • By taking preventive measures and providing appropriate care, swim bladder disorders in molly fish can be minimized, promoting their overall health and well-being.