Betta Fish Tumors – Identification, Causes, and Treatment

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As a devoted betta fish owner, you love your beautiful pet, but if he suddenly develops a lump on his side, does that mean your betta has cancer?

Fish tumors are usually a symptom of an underlying health problem. You can often treat betta fish tumors easily and successfully if you spot the issue early and treat it appropriately.

So, how do you identify a tumor on a betta fish? What can you do to treat a betta fish tumor? And can tumors be prevented?

Read this guide to learn how to correctly identify, treat, and prevent a tumor on your betta buddy.

Can My Betta Fish Get Cancer?

Although betta fish can get cancer, that’s really quite rare. If you spot a lump on your pet, it’s more likely to be caused by an injury or a disease than by cancer.

Essentially, anything that looks like a swelling or lump can easily be mistaken for a tumor. That can include bloating, constipation, or even swim bladder disease. Bacterial infections can sometimes turn into abscesses or ulcers that resemble a tumor, and sometimes, small cotton-like fungal growths can look like lumps to the naked eye.

Sometimes, poor water conditions can cause lumps to develop on fish that look like tumors, or a nip from a feisty tank mate could also cause a lump to form on your fishy friend’s body.

Betta Fish Tumor Treatment

Sometimes, an external cancerous tumor can be removed from a betta fish. However, that’s an extremely risky surgery that should only be taken on by a qualified, experienced veterinary surgeon with experience treating tropical fish. Of course, just like cancer in people, there’s no guarantee that the tumor won’t return.

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How To Recognize a Betta Fish Tumor

As previously mentioned, there are quite a lot of things that can be mistaken for tumors on a betta fish.

A simple bump, nip, or spot could be a tumor. Tumors can grow under the skin on the outside of the betta’s body or out of sight internally on your pet’s vital organs and body tissues. If your fish doesn’t have a visible lump on the outside of his body, there are other symptoms to watch out for.


White growths on betta fish are usually abscesses, which are typically caused by a bacterial infection rather than cancer.

Bacterial infections can be caused by injuries, such as nips from other fish or collisions with tank decorations. However, fish with conditions like Ich can sustain injuries by deliberately flashing and flicking against the substrate and other objects in their tank.

Usually, minor injuries and wounds self-heal over time without intervention or treatment. However, poor water conditions allow bacteria to enter the wound, triggering an infection that results in an abscess.

These tumor-like growths usually grow larger and larger until they burst, leaving the betta fish with ragged fins or a large ulcer on its side.


Fish ulcers often manifest as white lumps on the betta’s body, often progressing into open, bloody sores. Those wounds can provide an entry point for fungus or bacteria and usually cause permanent damage to the scales in that area.

Fortunately, most bacterial and fungal infections can be successfully dealt with by treating the fish with antibiotics or a disease-specific medication that you’ll get from your local pet store.

Fungal Infection

A fungal infection typically appears as a cottony growth or discolored scales. Sometimes, the fungus can look like a lump or abscess and might be mistaken for a tumor.


Columnaris is a severe fish illness that can cause lumps and bumps around the fish’s head that often resemble tumors at first glance.


Constipation is similar to Swim Bladder disease in that it affects the betta’s ability to swim on an even keel and can manifest as a swelling on one side of the fish’s belly.

You can often cure constipation by starving betta for 24 hours and then feeding him a shelled, blanched pea or some frozen meaty foods.

Gill Hyperplasia

Gill hyperplasia causes the betta’s gills to shrink and leaves them permanently deformed as they slowly heal. The deformity is often mistaken for a tumor at first glance.


Parasites can damage the betta’s tissues, causing lumps on the betta’s body or around its head.

Swim Bladder Disease

Swim bladder problems often cause an affected fish to develop a large lump on one side of its abdomen, which is easily mistaken for a tumor.

Where Are Tumors Usually Located?

Betta Fish Tumors

Lumps, bumps, and tumors can be found pretty much anywhere on your betta’s body. For example, on the fish’s head, body, tail, fins, belly, and gills.

Usually, internal tumors are malignant and untreatable. However, most of the lumps that appear elsewhere on your fish are usually caused by other factors, as mentioned above, and are not cancerous.

What Causes Betta Fish Tumors?

Unfortunately, some bettas are more likely to develop cancer than others, so you can do nothing to prevent that.

However, a few other factors can cause tumors to develop.

For example, dirty tank or pond water sometimes contains external carcinogens and can weaken your betta’s immune system. A low-quality diet leads to general poor betta health, leaving your pet open to attack by viral infections that could eventually cause a tumor.

Treatment Options

Unfortunately, if your betta buddy does develop a cancerous tumor, there’s no cure. In that case, you must take a deep breath and carefully consider your fishy friend’s quality of life.

If your betta is behaving normally and is able to feed, you might want to let him enjoy his life for a bit longer. However, if your pet is not eating, is disinterested in patrolling his tank, and no longer seems to enjoy his life, it’s time to consider euthanizing him.

When Should You Euthanize Your Betta?

Unfortunately, if your betta develops a tumor that you can’t cure, the kindest thing to do is humanely euthanize him.

Plenty of ideas exist on the web about how to humanely put a fish to sleep. However, from personal experience, I recommend using Fin-Quel or a similar product you can buy from fish stores or your vet.

These products are fish sedatives; however, an overdose quickly and peacefully ends the fish’s life with minimal stress. However, we recommend consulting your veterinary surgeon before you euthanize your pet.

How To Treat an Abscess

Treatment is relatively straightforward if you’re sure your betta’s lump is an abscess, not a tumor.

To treat an abscess, remove your betta fish from its main tank and put it into a separate hospital tank. The water here should be pristine to prevent bacteria from infecting the wound when the abscess ruptures.

Sick bettas get very stressed, so the hospital tank should have lots of silk plants and a cave where your betta fish can hide and rest. Although bettas love fresh plants, silk ones are a better option because they don’t harbor bacteria and parasites like live plants can.

Take a trip to your local pet or fish store and buy an over-the-counter broad-spectrum antibacterial treatment product. Treat the water following the manufacturer’s dosage directions carefully, and complete the entire course of treatment.

Ulcer Treatment

Ulcers are usually easily treatable!

Start by setting up a hospital tank as described above, and carefully transfer your pet from his regular tank. To keep bacteria and fungal infections at bay, you’ll need to keep the hospital tank scrupulously clean by carrying out several partial water changes every week.

Aquarium salt works as a mild disinfectant and also helps to accelerate the healing process. So, following the initial water change, use ¼ ounce of aquarium salt per gallon of water to treat the hospital tank. Following each water change, add 30% of the quantity of salt you previously added.

In addition, I recommend using a broad-spectrum antibacterial medication to protect your betta from secondary infections and other complications. Again, follow the manufacturer’s directions throughout treatment, and once the ulcer has completely healed, you can return your fishy friend to his tank.

Can You Prevent Betta Fish Tumors?

To a large extent, the likelihood of your betta fish developing a tumor is governed by genetics. That said, you can take some positive steps to reduce the likelihood of your pet developing a tumor or some other kind of lump.

Use a Reputable Breeder

Most people buy their betta fish from a local fish store, so their fish’s genetic makeup is unknown. However, if you choose a local breeder or an online one with a good reputation, you have more chances of buying a fish that’s free from genetic health issues.

Breeders that produce betta fish for the trade often inbreed their fish since that’s less expensive than researching the breeding stocks’ genetics and producing healthy fish. The inbreeding and lack of genetic screening cause many problems in bettas, such as physical deformities and a higher chance of cancerous tumors.

Clean Water

Your betta’s tank should always be kept immaculate!

Bettas are pretty hardy fish, but dirty water and an inefficient filter system are virtually guaranteed to lead to disease outbreaks in your betta fish tank. These fish are highly sensitive to water conditions and water temperature, and if you don’t keep up to speed with filter maintenance, water changes, and tank cleaning, you will stress your betta fish.

When a betta is stressed, his immune system doesn’t work as efficiently as it should, and that leaves your pet vulnerable to attack by parasites, fungal infections, and bacteria.

So, the levels of ammonia and nitrites in the water must always be zero, and nitrates should be 20 ppm or lower if possible. In addition, bettas are labyrinth breathers, and the labyrinth organ can be damaged if the ambient and water temperatures are massively different.

High-Quality, Varied Diet

Wild betta fish enjoy a varied diet of meaty proteins and a small amount of plant matter and algae. In the tank environment, you must replicate that diet as closely as possible by feeding your fish high-quality betta pellets, frozen meaty foods, and freeze-dried treats.

A balanced, high-quality diet will keep your betta healthy and strong, enabling him to fight off diseases and possibly be less likely to develop cancerous tumors.

Treat Disease Immediately

If you notice that your betta fish is sick, take steps to treat him immediately. The longer you wait to treat your pet, the less likely he is to recover fully, and he might even die.

In fact, the risk of your fish developing a tumor is thought to be increased by the stress of being sick, so it can protect your betta if you treat other diseases promptly.

Keep a Healthy Aquarium

Some chemicals are known to cause cancer in pet fish. So, check to see that whatever you’re adding to your tank is safe and doesn’t contain anything carcinogenic.

Final Thoughts

I hope you enjoyed our guide to identifying, treating, and preventing tumors in betta fish. If you found the information helpful, please take a moment to share the article.

Fortunately, malignant tumors are pretty rare in betta fish, but if your fishy friend does get cancer, it’s unlikely he can be treated successfully. However, bettas commonly develop lumps and bumps that are caused by accidental traumas and other common fish diseases, which are usually treatable.

Was your betta fish unlucky and suffered from a tumor? How did things work out for your pet? Tell us in the comments box below.

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