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Betta Fish Tumor: Symptoms, Causes, & Treatment

It’s possible to think that each lump on your betta fish is cancerous and fatal when some are not. It can be scary to fishkeepers when their betta fish develops a tumor that causes poor health or even leads to death. It can also be equally dangerous to stick to similar treatments for every lump you find on your betta fish.

In this guide, we’ll discuss betta fish tumors, their symptoms, causes, treatments, and how to prevent the tumors from occurring. 

What is a Betta Fish Tumor?

A betta fish tumor is a lumpy skin growth that can be external or internal. Surface tumors are the simplest for betta fish owners to identify because they’re visible on the exterior of your betta fish’s scales. They can also look like a bump or spot.

Internal tumors are frequently invisible, especially if they’re small. As a result, you’ll have to rely on observing your betta’s behavior to determine if something is wrong with them.

Tumors range in size from so small that you can’t see them with the naked eye to so large that your betta appears to be growing another fish on them.

What Causes a Betta Fish Tumor?

Betta Fish are vulnerable to a variety of health issues. If a lump appears on your betta fish, it’s not necessarily a fatal cancerous tumor, as those are incredibly rare.

Much like humans, a betta fish will develop certain illnesses if the parameters necessary for its care aren’t met. A lump on your betta fish could be a symptom of an illness like swim bladder disease, constipation, and other conditions. Common causes of these lumps include the genetic disposition of the fish, poor water parameters, low-quality diet, and viral infections.

Cancerous tumors on betta fish can develop despite pristine conditions and are typically a result of the genetic predisposition of the betta fish. Scientists have also linked the likelihood of cancerous tumors in betta fish to carcinogen-contaminated water.

causes and prevention of betta fish tumor

How Do I Know a Tumor Is Cancerous?

Cancerous tumors are rare in betta fish, and lumpy growths are usually a symptom of another illness. Cancerous tumors can also be identified by lumpy growths in single or multiple areas on the fish, but they typically come with other symptoms like;

  • Lack of energy
  • Inability to swim well
  • Loss of appetite
  • Breathing issues
  • Sickly appearance

To ensure you’re dealing with a cancerous cell, visit a reputable aquatic veterinary clinic for a consultation.

Can Cancerous Tumors Be Treated in Betta Fish?

Cancerous tumors can be removed surgically by an aquatic veterinary doctor; however, the process can be expensive, and there is no guarantee that the tumor will not re-appear. The procedure is also incredibly uncomfortable for your fish, and the success rates are slim.

Betta fish have a life span of two to five years. With a low success rate of surgery and the possibility the cancerous tumor will reoccur, it can be best to let the betta fish live only as long as it’s comfortable and then consider euthanization.

The best way to euthanize your betta fish is with the approval of a reputable aquatic veterinarian.

Non-Cancerous Tumors in Betta Fish

It’s essential to note that physical growths like swelling and lumps on your betta fish aren’t always a sign of a cancerous tumor. They can signify other issues like abscesses, ulcers, swim bladder diseases, and other conditions we will explore in this article.

Betta Fish Abscess

A whitish lump on the body of your betta fish is likely an abscess instead of a cancerous tumor.

Your betta fish can be injured by something sharp in the tank or the damage caused by a nip from another fish. In most cases, such injuries heal on their own;however, if the tank water isn’t kept clean, bacteria can enter the wound site and cause an infection. Bacterial infections cause abscesses.

Pus is created as a result of the bacteria destroying the tissues near their place of entry. Under the fish’s skin, the pus gathers and hardens, creating an abscess or lump.

Untreated abscesses will enlarge until they can no longer be contained by the fish’s skin, at which time they will rupture. The fish will be left with a sizable open sore on his body once the abscess has popped, making him susceptible to further bacterial infection, and the cycle will start again.

Treatment of Abscesses in Betta Fish

When you notice an abscess on your betta fish, please remove it from the main tank and isolate it in a quarantine tank.

A quarantine tank is simply a tank with the fish’s ideal water quality, a sound filtration system, heating, lighting, and a hiding place. Keep the tank spotless and perform frequent water changes, especially if the abscess has burst.

A smooth-sided, plastic plant pot on its side and partially submerged in the substrate provides a safe, low-cost hiding place for your betta. Including a cave or something similar in the quarantine tank is critical. If a sick fish has nowhere to hide while feeling vulnerable, it’ll become agitated.

Plants are an excellent place for fish to hide and recover. In your quarantine tank, however, it’s preferable to use silk plants rather than fresh ones. Fresh plants may introduce unwanted bacteria or parasites into the environment, endangering an already sick fish.

Use an appropriate aquarium antibacterial agent, which you can get in reputable fish stores or online, to treat the tank water. Ensure you use the prescribed dose according to the manufacturer’s recommendations.

Betta Fish Ulcers

Lumps on the skin can be a symptom of ulcers in betta fish. If the edges of the lump are reddened and sore looking, you’re likely dealing with an ulcer. 

Fish with ulcers frequently appear listless and emaciated to the extent they stop eating altogether.

Bacterial infections are typically the cause of fish ulcers. Usually, a healthy aquarium already has a lot of bacteria that don’t endanger healthy fish; however, once the fish undergoes stress due to unfavorable environmental factors or low water quality, they’re more susceptible to bacterial infection, which can result in ulcers.

Treatment of Ulcers in Betta Fish

When you notice your betta fish has developed an ulcer, remove it from the main tank and isolate it in a quarantine tank.

The ulcer may heal, but fungal infections usually follow. Therefore, you must perform frequent water changes for two to three weeks after the ulcers have been adequately treated.

After the initial water change, add one-quarter of an ounce of salt per gallon to the tank water. That should accelerate wound healing by lowering the osmotic effect of water entering the ulcer and acting as a moderate antiseptic.

Use a hydrometer to check the water’s salt content. Keep the water’s salt level constant by adding 30% more salt than you initially did after each water change. The water should also contain an aquarium antibacterial agent.

Plakat Betta

Swim Bladder Disease

Swim bladder disease develops when a fish’s swim bladder becomes infected. A swim bladder is a gas-filled sac found in fish that aids buoyancy and swimming. The disorder causes the fish to swell and become sluggish and can give betta’s side a lumpy appearance.

Swim bladder disease is typically caused by overeating and constipation. The affected fish will involuntarily sink to the bottom or float to the water’s surface. At times, the fish will struggle to stay upright in the tank. It may have to adopt a crooked swimming posture to move around the aquarium.

Treatment of Swim Bladder Disease 

Swim bladder disease is not transmissible, so you don’t need to isolate your betta fish. You can treat the disorder by starving your fish for a few days because its digestive system requires time to process the remaining food and return to routine operation.

Over-the-counter medications also provide faster relief from the swim bladder problem. You can treat the infection by following the dosage instructions on the product.

Dropsy in Betta Fish

Dropsy is an accumulation of fluid in the betta fish’s body, giving it a swollen appearance. It’s a severe bacterial infection that affects the kidney of betta fish due to poor living conditions. 

Dropsy causes the fish to retain fluid and bloat, eventually leading to renal failure. Furthermore, the fish’s spine would become curved, and the fish would have protruding scales in the final stages of the dropsy disease. It’s possible to cure dropsy in betta fish, but the chances of death are extremely high.

Treatment of Dropsy in Betta Fish

A key to treating dropsy in your betta fish is early discovery. If you notice your betta has stopped eating, avoids other fish, and tends to hide in the corner, these may be early signs of dropsy. These signs can also signify stress in your betta fish, so confirm it’s dropsy before beginning treatment. You can do this by taking the fish to an aquatic vet.

Once you can detect dropsy in your fish early enough, isolate it in a quarantine tank. Fill the quarantine tank with conditioned water, a heater to keep it warm, and a bubbler or airstone to keep it oxygenated. Add some aquarium salt to the tank. Follow the instructions that come with the salt.

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Use a strong antibiotic like amoxicillin to treat your betta fish, and remember to change the tank water and add the salt and antibiotic daily.

The treatment can only work when dropsy is discovered in its early stages. Once your betta fish starts to have protruding scales, it might be better to euthanize it with the approval of an aquatic vet.

Constipation in Betta Fish

Bettas can develop lumps on their stomachs as a result of constipation. It’s a widespread condition that affects bettas, but fortunately it’s simple to treat. Constipated fish typically stop eating, become sluggish, don’t excrete, and may develop swim bladder disease.

Treatment of Constipation in Betta Fish

Constipation is treated by withholding food from your betta for a few days and then offering live or frozen food, such as bloodworms or mosquito larvae, instead of dry pellets or flakes. That should be enough to restart your fish’s system and clear the blockage.

You can help your Betta avoid constipation by incorporating one “fasting” day per week into its feeding schedule.

Gill Hyperplasia in Betta Fish 

A lump or tumor in your betta fish’s gills is typically a sign of gill hyperplasia. Gill hyperplasia is caused mainly by gill damage. It could be due to a parasitic or bacterial infection, physical injury, or toxins like ammonia, nitrates, and nitrites. Instead of healing correctly, new gill tissue grows over the damaged area, forming a lump that resembles a tumor. As more new skin forms, the lump grows bigger over time.

The lumps are permanent in severe cases of hyperplasia. In minor cases, however, the swelling disappears, and the gills return to normal.

Gill Hyperplasia Treatment

Take your betta fish to the vet as soon as you notice the inflammation in its gills, as gill hyperplasia can lead to death if left untreated.

Use a water conditioner that contains ammonia removers to remove the ammonia from your betta fish tank. Our guide on water conditioner can help you choose the best one. Increase the tank’s water temperature with a water heater and aerate it with an air stone. Check out our guide on air stones to choose the right one for your fish.

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Ensure you give your Betta fish the antibiotic prescribed by the vet in the recommended doses and keep the tank water clean by changing it at least once a week.

Visual Cues of Tumors in Betta Fish

Your betta fish will typically have certain body disorders and display certain behaviors when dealing with tumors. Although these cues are general, a proper examination will determine if the tumors are cancerous or non-cancerous lumps.

  •  A hard lump or bump protruding from the body
  •  Difficulty swimming
  •  The continuous growth of the lump
  •  Discoloration and abnormal swelling
  •  Loss of appetite
  •  Scale loss
  •  Lethargy

Tumor Prevention in Betta Fish

There might be little you can do in cases where your betta fish is genetically predisposed to tumors, but where that’s not the case, apply the following tips to prevent tumors on your betta fish.

Buy From a Reputable Breeder

When purchasing a betta, always buy from a reputable breeder. Some fish stores inbred their stock because it’s less expensive than importing or rearing bettas correctly. Inbred fish are more likely to have various issues, including an increased risk of developing cancerous tumors.

Tank Conditions 

Use and maintain an efficient filtration system to keep your tank water in pristine condition. Make sure to change 25% of the water each week to prevent bacteria from growing and potentially jeopardizing your fish’s health.


Feed only high-quality food to your betta fish. Low-quality foods typically lack the high levels of protein and nutrients that your betta requires to stay healthy. 


If your betta fish becomes sick, remove it from the main tank and isolate it in the quarantine tank. It will stop the contagion from spreading and help you monitor the isolated betta fish in optimal conditions. If you betta is a singleton, you won’t need to isolate, unless you have aquarium plants. Also, if your betta has a non-contagious condition, you don’t have to separate him from his tankmates,

Frequently Asked Questions

Can Fish Tumors Go Away?

Most fish tumors and cancers have no cure or treatment. Internal tumors are hard to diagnose until much later in their advancements. Even when detected early, the tumor’s size and location often makes it operable.

Can Fish Develop Tumors?

Yes! Unfortunately, fish can develop cancerous and benign tumors. As with all other species, some tumors are treatable, while some are not.

What Is the White Thing on My Betta Fish?

An ick, or white spot, is an external parasite that latches onto a betta, causing irritation and uneasiness. The parasite can stay on the fish for up to five days before dropping off, reproducing, and latching back on.

Why Does My Fish Have a Lump Under Its Head?

If your betta fish has a lump under its head, then it could be a bacterial infection. One of the most common infections is columnaris, and it can cause tumors to grow around your betta’s mouth and gills.

Treat Tumors Accordingly 

You don’t have to fret when your beloved betta fish shows signs of a lump because now you know how to identify the tumors and the measures to take for treatment. Since cancerous tumors are so rare, the chances are slim that the lump you’re seeing is that heartbreaking one that makes you euthanize your betta fish.

We hope the recommendations provided in this article prove helpful, and we would love to hear your questions and contributions!
If you’re new to betta fish keeping, read our complete care guide for betta fish to learn how to care for them.

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