Betta Fish Tumors: How To Diagnose, Manage, And Prevent Them

Betta fish tumors appear as lumpy growths outside or inside of the body.

External tumors may grow anywhere on the betta. This includes the head, abdomen, and gills.

Internal tumors are usually smaller and only detectable by changes in your betta’s behavior.

Not all tumors on bettas are cancer. In fact, cancerous tumors rarely occur in bettas.

Some bettas have a genetic predisposition for tumor growth. Other causes of tumors include:

  • Poor water quality
  • Overcrowding
  • Exposure to toxins
  • Viral Infections

Early detection is crucial for determining a course of treatment.

Treating non-cancerous tumors in the early stages gives your betta a better chance of recovery.

Unfortunately, treatment for cancerous tumors in bettas has a low success rate.

The only option is the surgical removal of the tumor. Many times, the tumor grows back.

betta fish tumors

Types of Tumors in Betta Fish

Tumors in betta fish may grow small or large anywhere on the body.

If your betta has a lumpy appearance, this may seem very alarming.

But abnormal growths on your betta are not always a death sentence.

Understanding the types of tumors in betta fish helps you determine the correct diagnosis and treatment.


Benign tumors are not cancerous. These types of tumors do not spread to other organs and do not have a fatal diagnosis.

Many benign tumors have the appearance of a white bump.

Sometimes, these white lumps are mistaken for other diseases in betta fish, including:

  • Ulcers
  • Gill Hyperplasia
  • Parasites
  • Dropsy
  • Constipation
  • Swim bladder disease
  • Columnaris

Treatment for these tumor-like growths depends on the underlying cause.

Fish ulcers are the result of a bacterial infection. Antibacterial medications heal these bacterial growths.

Sometimes, fungal infections develop from ulcers.

Fungal infections look like cottony growths on a betta’s body. Antifungal treatments kill the fungus, and the white growths disappear.

Tumors or physical injury cause gill hyperplasia. As the gills heal, they shrink, and the cell buildup has the appearance of tumors.

Certain parasites cause abscesses and growths on a betta’s head. These head tumors may also be the result of columnaris.

Read about what columnaris is in betta fish in our article here.

Dropsy and constipation cause bloating, which often appears like a lumpy tumor on your betta’s stomach.

Swim bladder disease also causes bloating due to inflammation in the stomach.

Treatments for most of these secondary ailments involve over-the-counter medications. Once the diseases heal, the lumpy growths usually disappear.


Malignant tumors are cancerous growths and most commonly affect the internal organs.

Detecting these tumors is challenging when they occur inside the betta’s body.

If there are no visible lumps, the only signs of sickness are behavioral changes.

When internal tumors grow larger, the swelling becomes visible on the betta’s body due to fluid retention.

Malignant tumors usually happen in bettas with a genetic predisposition to them. Toxins, like carcinogens, also cause cancerous tumors.

You may notice changes in your betta, such as:

  • Loss of appetite
  • Lethargy
  • Difficulty swimming

The only treatment for cancerous tumors is surgical removal. This type of surgery is difficult, and in most cases, the tumor grows back.

Symptoms of Tumors in Betta Fish

Betta fish tumor symptoms present in different ways.

Besides physical symptoms, behavioral symptoms are similar to any sick fish’s.

If you notice any of these symptoms in your betta, seek treatment immediately.

Early detection and treatment can mean the difference between life and death for your betta.

Physical Symptoms

Physical symptoms vary according to the severity of the tumor.

Besides lumps, you may see changes in the color or texture of your betta’s scales.

Lumps or Growths on the Body

The most obvious symptom of tumors in bettas is the presence of small or large bumps on the body.

Lumps and abnormal growths usually appear on a betta’s head and stomach. This includes areas like the gills and sides of the body.

These tumors may start as small common bumps or grow into enormous lumps.

You may see single or several tumors all over the fish’s body.

Changes in Color or Texture

White tumors usually are not cancerous. These tumors are more likely abscesses caused by a bacterial infection.

Tumors caused by bacterial infections are a solid color.

When fungal infections cause tumors, there is usually scale discoloration. Fungal tumors also have a more porous appearance.

If these tumors go untreated, they burst open. This leaves a hole in the scales or causes ragged fins.

Behavioral Symptoms

Tumors on betta fish also cause behavioral symptoms.

These symptoms are like other common betta fish ailments.

Loss of Appetite

If your betta has a tumor, it may eat less or not at all.

Appetite loss occurs with most common fish diseases.

Without proper nutrition, your betta’s immune system weakens.


Large tumors on bettas make swimming challenging.

This makes your betta lethargic and may stay in one spot all day.

Bettas are normally very active swimmers. Lack of movement is a definite sign something is wrong.

Difficulty Breathing

Tumors in and around the gills cause breathing issues.

Your betta may also have difficulty breathing from internal tumors due to fluid retention.

If your betta has trouble breathing, you will notice a lot of gill movement. The betta may also swim to the surface and gasp for air.

Abnormal Swimming Habits

Large external tumors may cause a crooked swimming posture in your betta. The betta will likely have problems staying upright.

Internal tumors affect organs like the swim bladder. This might cause your betta to float or sink to the bottom.

Brain tumors may also cause an abnormal swimming pattern.

Causes of Tumors in Betta Fish

Several things can contribute to tumor growth in bettas.

Genetic factors causing tumors are beyond control.

Environmental factors are more variable.

Genetic Factors

Bettas with poor genetics are more prone to the development of tumors. These bettas may also have more health issues in general.

Selective breeding and inbreeding cause genetic mutations.

Some of these genetic mutations increase the development of cancer cells.

Dragon scale bettas seem more prone to cancerous tumors.

There is no scientific evidence behind this. But anecdotal evidence from betta fish owners supports this theory.

Bettas with marbling genetics also tend to develop tumors. This is largely due to their constantly mutating genes.

Inbred fish have a weakened immune system. Lifelong health issues increase the chance of tumors developing in these bettas.

Environmental Factors

External factors leading to tumor development in bettas are avoidable with some extra care.

Good fishkeeping practices prevent exposure to harmful environmental factors, which may cause tumors.

Poor Water Quality

Poor water quality is one of the biggest factors in tumor growth in bettas.

Harmful bacteria thrive in dirty water. These unwanted bacteria have the potential to infect your betta and cause tumors.

Improper water parameters like unstable temperatures and pH levels make your betta stressed.

Too much stress lowers a betta’s immune response. This makes the fish more susceptible to infections from parasites and fungi.

Many parasitic and fungal infections cause tumor formation in bettas.

This is especially true of gill flukes, which cause gill hyperplasia. In severe cases of gill hyperplasia, permanent tumors form due to the scarring of gill tissue.


Overcrowding in a community tank is dangerous for a couple of reasons.

If the tank is too small for the number of fish, the bioload produced is more than your filter can handle.

The excess fish waste also makes maintaining safe water parameters a challenge.

An overcrowded tank also increases the risk of fighting and injury among tank mates.

Small cuts and abrasions make your betta more vulnerable to bacteria. Once these exterior injuries become infected, lumps develop.

When these lumps turn into abscesses, your fish are prone to even more infections. Severe infections can become deadly without proper treatment.

Exposure to Toxins

Exposure to toxins like ammonia and chlorine can make your fish sick and stressed.

Any time your betta has a weakened immune system, it is more susceptible to diseases and tumors.

Carcinogen-contaminated water also increases the risk of cancer in fish.

Some fish medications contain carcinogenic ingredients like formalin and malachite green.

The likelihood of these ingredients causing tumors is low when you use the medication as directed.

But, overusing these types of medications may contaminate your tank water over time.

If you have concerns about using potentially carcinogenic medications on your betta, consult your veterinarian for natural alternatives.

Treatments like aquarium salt and Epsom salt effectively heal minor injuries and relieve constipation.

Severe infections and injuries need stronger medications, though. When used as directed, these medications are not harmful to your betta.

Frequent water changes help remove most cancer-causing toxins from your aquarium water.

Viral Infections

Viral infections in bettas are rare but can cause death without prompt treatment.

One of the most common viruses is iridovirus. This virus mainly affects dwarf gouramis and betta fish.

The iridovirus causes a disease known as lymphocystis.

Lymphocystis attacks the connective tissues, leading to raised nodules all over a betta’s body.

These nodules are infected cells called fibroblasts. Fibroblasts are full of virus particles, and when they burst, the virus spreads through the aquarium water.

Lymphocystis nodules may cover the body, fins, and gills. If there are a large number of nodules present, your betta may have trouble swimming and breathing.

Sometimes, betta owners mistake lymphocystis for ich.

The disease spreads through infected fish. Placing new fish in a quarantine tank for 4-6 weeks prevents the spreading of contagious diseases.

There is no cure for lymphocystis and most bettas recover after a few weeks. The major concern with this virus is a possible infection of the burst nodules.

Prevention and Management of Tumors in Betta Fish

Cancerous tumors have limited treatment in betta fish.

If the tumors result from an underlying illness, treatment helps your betta fully recover.

You may prevent tumors from developing in your betta in several different ways.

Buy Your Betta From a Reputable Breeder

Always buy your betta from a reputable breeder whenever possible.

This ensures you get a betta with healthy genetics, which reduces the risk of tumors.

Consider the possible health issues in bettas with dragon scale and marble genetics. The mutating genes in these betta types put your fish at risk of developing tumors.

Maintain Good Water Quality

Keeping the tank water clean prevents most diseases associated with tumor growth.

Ideal water parameters for bettas include a pH level close to 7.0 and water temperatures ranging from 78-80° degrees Fahrenheit (25.5-27° C).

Maintain stable water parameters with an aquarium heater and a proper filtration system.

Quarantine fresh plants for a week or two before adding them to the tank. Aquarium plants may contain bacteria or parasites.

Performing weekly water changes removes ammonia and other harmful toxins from your tank.

Add a water conditioner to clean water before adding it to the aquarium. This removes toxic chlorine and chloramine from tap water.

Provide a Balanced Diet

Bettas are carnivores and need a healthy diet of animal protein and essential nutrients.

Feed your betta high-quality foods like betta pellets and live or frozen foods.

Some excellent betta food options include:

  • Blood worms
  • Daphnia
  • Mosquito larvae
  • Baby brine shrimp

A healthy diet boosts your betta’s immune system. This makes your fish more resistant to bacterial and fungal infections.

If you’re unsure where to start, check out our list of the best foods for betta fish.

Regularly Check for Symptoms

Regularly check your betta for symptoms of tumors.

If you see abnormal lumps on your betta’s body or notice unusual behavior, seek treatment options immediately.

Cancerous tumors are rare in bettas. The symptoms you observe are more likely a treatable disease and your betta will fully recover.

Consult a Veterinarian for Diagnosis and Treatment

When your betta struggles with everyday activities, get help from an experienced fish veterinarian.

If the diagnosis is a malignant tumor, go over your options with a veterinary surgeon.

Surgical removal of tumors in bettas is risky due to the fish’s small size.

Even if surgery is successful, the tumor may grow back.

When a tumor does not affect your betta’s quality of life, the best course of action is to do nothing.

Many betta’s live with tumors throughout their life with no significant health issues.

The only option for a very sick betta with a tumor is euthanization.

Do not attempt euthanizing your betta on your own. Some fish keepers use clove oil or alcohol for euthanizing their bettas.

There is no evidence these methods do not cause suffering in betta fish.

Take your betta to a veterinarian for a more humane euthanization. 

Betta Fish Tumors Aren’t Always a Death Sentence

Lumps on your betta are usually due to an underlying disease caused by an injury or poor water quality.

Cancerous tumors in betta fish are rare but may happen in fish with a genetic predisposition for them.

Frequently check your betta for signs and symptoms of tumors and other illnesses.

Treating tumors in their early stages improves your betta’s quality of life and increases the chance of a full recovery.

There is no cure for cancerous tumors in bettas, and surgery is risky.

If a tumor affects your betta’s quality of life, humane euthanization is the best option.

For more on typical betta diseases, check out our list and guide at the link.

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Toni Tedescucci is a freelance writer who loves all animals, especially betta fish. When she isn’t busy writing for Betta Fish Bay, she’s spending time with her family or getting cozy with her cats and a good book.

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