betta fish tumor

Betta Fish Tumor: Causes, Cures, and More

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Most fish hobbyists have to cope with sick fish from time to time. That can be devastating, especially if the affected fish is your prized betta. The good news is that most common fish diseases can be cured. But what about betta fish tumors?

In this guide, we discuss how to identify a betta fish tumor, what treatment could save your fish, and what you can do to prevent more tumors from impacting your precious pet’s quality of life.

Key Takeaways

  • Identifying Lumps on Bettas: Lumps can be tumors but can be caused by common issues like abscesses, ulcers, dropsy, constipation, or swim bladder problems. Various treatments are available, depending on the diagnosis.
  • Tumor Treatment and Care: External tumors can sometimes be surgically removed, while benign growths can be managed with tank cleanliness and proper diet. Internal tumors often have a grim prognosis and mean a poor quality of life for your betta. So, in those cases, euthanasia might be the only option.
  • Prevention Tips: Ensure a healthy environment for bettas by sourcing your fish from reputable sources, keeping your tank clean, feeding your fish on quality diets, and isolating new or sick fish.

Betta Fish Tumors – At a Glance

Potential CauseSymptomsPossible TreatmentsPrognosisPrevention
Cancerous TumorsVisible lumps on the skin or under it, affecting swimming and eatingSurgical removal by a fish veterinary specialist; euthanasia if quality of life is affectedVariable; surgery has risks, and internal tumors have a poor prognosisSource from reputable breeders; avoid inbred fish
Benign Tumors/GrowthsBumps on the body, possibly affecting buoyancyManage with clean water and proper diet; surgery for external tumorsOften manageable unless they impair vital functionsKeep water clean, feed high-quality food, and avoid crowded conditions
AbscessesWhite lumps under the skin, may burst and cause open woundsQuarantine, keep water clean, use aquarium antibacterial productsGood if treated early; can be fatal if left untreatedPristine water conditions, treat any injuries promptly
UlcersLumps with reddened, sore-looking areas, lethargy, loss of appetiteQuarantine, frequent water changes, salt addition, aquarium antibacterial productsGood with early treatment; can lead to further complications if not treatedMaintain good water quality, and reduce stressors in the environment
Swim Bladder DiseaseLopsided swimming, buoyancy issues, swollen abdomenFasting, therapeutic fasting, over-the-counter treatmentsGood if treated early; usually not fatalAvoid overfeeding, provide a balanced diet
DropsyBloating, curvature of the spine, pinecone scalesAntibacterial water treatmentsPoor; often leads to renal failureKeep water clean, monitor for early signs of illness
Gill HyperplasiaLump on the gills, caused by damage or infectionDepends on the severity and cause of the gill damagePermanent in severe cases; minor cases can be resolved with proper carePrevent gill damage, and maintain water quality to avoid infections
ConstipationLumps on stomach, lethargy, lack of feces, swim bladder issuesFasting followed by live or frozen food, regular “fasting” daysExcellent with proper dietary managementProvide dietary variety, including regular fasting periods

How To Recognize a Betta Fish Tumor

If you notice growths or bumps on or under your betta fish’s skin, that’s most likely a tumor. Some growths can be tiny and barely noticeable, or they can be huge. Even benign tumors covering large areas of the fish’s body can cause problems with buoyancy and affect the fish’s ability to swim.

However, some tumors are internal, and the naked eye can’t see them. Internal tumors usually impact the fish’s ability to eat and swim, which causes a rapid decline in the fish’s health. Unfortunately, with these growths, there’s usually nothing you can do to save your pet, and his quality of life will be miserable.

In cases like that, the only course of action is to euthanize your betta humanely.

What Causes Tumors?

Some bettas are predisposed to developing cancerous tumors, just like some people do, and that’s the most common cause of this condition.

However, there are a few causes of benign tumors or growths in a previously healthy betta. These include a poor diet, unsanitary water, and viral infections, which can be introduced into the tank when new specimens are added.

Can You Treat Betta Fish Tumors?

External cancerous tumors can sometimes be removed from betta fish. However, this highly risky surgery should only be undertaken by a qualified, experienced veterinary surgeon who is a specialist in treating tropical fish. Of course, there’s no guarantee that the tumor will not recur in the future.

You can see a video of veterinary tumor removal from a betta fish by clicking this link.

When Is a Lump Not a Tumor?

However, there is some good news. Chances are, what you’re seeing is not a tumor. Cancerous tumors in betta fish are quite rare. If you see a lump or bump on your betta fish, it’s more likely to be an ulcer or an abscess, both of which can look like tumors at first glance.

Other causes of lumps that may be mistaken for tumors include fluid retention, swim bladder disease, and constipation.

One time, in my early days of fishkeeping, I noticed my gorgeous young betta had developed what appeared to be a huge lump on one side of his body. The poor guy couldn’t swim on an even keel and spent most of his time floating on his side at the water’s surface.

Of course, I went into full-scale panic mode, thinking my beautiful pet was dying. My greedy fish was just suffering from constipation caused by eating too much dried food. I fasted him for a day and then fed him a couple of live brine shrimp. Within 24 hours, the lump had disappeared, and my pet went on to live a long, happy life.

How To Recognize a Betta Fish Abscess

Bacterial infections cause abscesses. It could be that your betta has sustained an injury by catching himself on something sharp in the tank, or a nip from another fish may have caused the damage. Most times, injuries like that clear up on their own. But, if the tank water is not kept in pristine condition, bacteria can enter the wound site and set up an infection.

As the bacteria destroy the tissues surrounding their entry point, the decomposing matter forms pus. The pus collects beneath the fish’s skin, forming a white lump or abscess.

If left untreated, an abscess will continue to grow until the fish’s skin is no longer able to contain it, at which point the abscess will burst. Once the abscess has ruptured, the fish will be left with a large, open sore on his body, leaving him vulnerable to further attack by bacteria, and so the whole cycle begins again.

As Reddit contributor, bthewolf experienced with his betta fish, “My boy Smee had a tumor on his gill plate like this. He lived for months without seeming uncomfortable. Eventually, it ruptured once it got too large. He still didn’t seem bothered by it. I treated with kanaplex and methylene blue just in case it was an abscess but it didn’t help. Slowly he struggled to swim up to breathe and got less and less active. When he stopped eating reliably I purchased clove oil and euthanized him. I added diluted clove oil drop by drop until he stopped swimming and then I added pure clove oil and let him sit for 15 minutes to make sure he was gone. It was less traumatizing than I expected and he went peacefully.”

So, if an abscess causes your betta’s tumor, it might be best to expect the worst and be prepared for it.

How To Treat a Betta Fish Abscess

As soon as you notice what could be an abscess forming on your fish, remove him from the main tank and place him alone in a separate hospital or quarantine tank.

Keep the tank scrupulously clean, and carry out frequent water changes, especially once the abscess has burst.

Providing a cave or something similar in the quarantine tank is very important. A sick fish will become stressed if he has nowhere to hide while he’s feeling vulnerable. A smooth-sided, plastic plant pot set on its side and partially buried in the substrate makes a safe, affordable hideout for your betta.

Plants make a great place for fish to hide and recuperate. However, it’s better to use silk plants, rather than fresh ones, in your quarantine tank. Fresh plants could bring unwanted bacteria or parasites into the environment that could seriously harm an already sick fish.

If the abscess is not too big, your betta has a good chance of surviving. Treat the tank water with a suitable aquarium antibacterial product that you’ll find in good fish stores or online. Take care to follow the manufacturer’s instructions and be sure to use the correct recommended dose.

API FIN & BODY CURE Freshwater Fish Powder Medication 10-Count Box
  • Contains one (1) API FIN and BODY CURE Freshwater Fish Powder Medication 10-Count Box
  • Treats body slime, eye cloud, fin and tail rot, open red sores, gill disease, and hemorrhagic septicemia
  • Causes slight discoloration of water that can be fixed by adding activated charcoal

How To Recognize a Betta Fish Ulcer

Sometimes, betta fish develop ulcers, which manifest themselves as lumps on the skin. Ulcers are usually easily identifiable due to the sore-looking, reddened areas around the edges of the lump.

Fish affected by ulcers often appear lethargic and emaciated to the point that they stop eating completely.

Bacterial infections usually cause fish ulcers. Ordinarily, many bacteria are already present in a healthy aquarium and cause no harm to healthy fish. However, once the fish become stressed by adverse environmental conditions or poor water quality, they become vulnerable to attack by the bacteria, which may cause ulcers.

How To Treat a Betta Fish Ulcer

As soon as you suspect that your betta has developed an ulcer, remove him from the main aquarium and place him into your quarantine tank.

Even if the ulcer clears up, fungal infections frequently follow. So, you must carry out frequent water changes for two to three weeks following the successful treatment of the ulcers.

After the first water change, add salt to the tank water at one-quarter of an ounce per gallon. That should encourage wound healing by reducing the osmotic effect of water entering the ulcer and also having a mild disinfectant action.

Maintain the salt content of the water after each water change by adding 30% of the quantity of salt you originally added. You can monitor the salt levels in the water by using a hydrometer. You should also add an aquarium antibacterial product to the water.

Wait until the ulcer has completely healed before returning your betta to the main display tank.

Location, Location, Location!

Tumors can appear anywhere on your betta fish’s body. However, as we’ve already mentioned, these lumps might not be caused by tumors. Lumps on certain parts of your betta’s body are most likely not tumors at all.

Here’s a brief guide to help you work out what causes lumps to appear on particular areas of your betta’s body:

Lumps on Betta’s Head

One very common place to find lumps is on your betta’s head.

Although head tumors can occur in bettas, lumps in this location can also be caused by a bacterial infection. Columnaris is one common bacterial infection that causes lump-like lesions to form around the fish’s gills and mouth.

Lumps on Betta’s Side

Lumps on your betta fish’s side can be caused by a variety of things, most of which are treatable.

Swim Bladder Disease

Swim bladder disease can give your betta’s side a swollen, lumpy appearance.

Fish that are affected by the disease either sink to the bottom of the tank or float involuntarily at the surface. Sometimes, an affected fish will be unable to keep itself stable and will adopt a lopsided position while swimming. Also, the fish’s abdomen will appear swollen, and he will be more lethargic than usual.

Overfeeding or constipation usually causes these swim bladder issues. You can often treat swim bladder disease successfully by withdrawing food from the fish for a few days to allow its digestive system to process any food that’s still inside.

Swim bladder disease is not contagious, so there’s no need to isolate your betta. There are also some proprietary treatments that you can buy over the counter for the treatment of swim bladder disease that should sort out the problem pretty quickly.


Dropsy is a serious bacterial infection of the betta’s kidneys, causing fluid to accumulate, which eventually leads to renal failure. The condition is likely caused by unsanitary aquarium conditions.

Betta fish with dropsy appear bloated, have curvature of the spine, and, in the disease’s final stages, “pinecone” or protruding scales. Although you can try to treat dropsy with antibacterial water treatments, the prognosis is generally poor.

Bacterial Infections

Fish that have injured themselves or been nipped can develop bacterial infections, which often appear as lumps on the fish’s sides.

If you’re concerned that your tank is infected, you can try treating the water with an over-the-counter antibacterial product, which should clear things up relatively quickly. In the meantime, quarantine your fish in a separate tank.

Lumps on Betta’s Stomach

The final most common place to find tumors on your betta fish is on its stomach. Although these growths can be tumors, there are other likely culprits too. Dropsy, swim bladder disease, constipation, or bacterial infection can all manifest on the stomach in addition to the sides.


Constipation can cause bettas to develop lumps on their stomachs, stop eating, become lethargic, stop passing feces, and even develop swim bladder disease.

You can cure constipation by withdrawing food from your betta for a couple of days and then offering live or frozen food, such as bloodworms or mosquito larvae, rather than dry pellets or flakes. That’s usually enough to kickstart your fish’s system again and relieve the blockage.

By including one “fasting” day each week in your betta’s feeding regime, you can help prevent constipation from affecting your fishy friend.

Tumors in Betta’s Gills

If you notice a lump or tumor in your betta fish’s gills, it’s often a sign of gill hyperplasia.

Gill hyperplasia usually occurs following damage to the gills. A parasitical or bacterial infection, physical injury, or exposure to toxins, such as ammonia, nitrates, and nitrites, could cause that. Rather than healing properly, the new gill tissue grows over the damaged area, forming a lump that resembles a tumor. Over time, the lump grows bigger as more new skin forms.

In severe cases of hyperplasia, the lumps are permanent. However, in minor cases, the lumps disappear, and the gills return to normal.

How To Prevent Tumors in Bettas

In fish that are not predisposed to genetically inherited tumors, there is much you can do to prevent the likelihood of your betta being affected.

  • When buying a betta, always source your fish from a reputable breeder. Some fish stores inbreed their stock because that’s cheaper than importing or rearing bettas properly. Inbred fish are highly likely to come with a whole gamut of problems, including an increased risk of developing cancerous tumors and unsightly growths.
  • Keep your tank water in pristine condition by using and maintaining an efficient filtration system. Be sure to change 25% of the water every week to prevent bacteria from building up, which could potentially put your fish at risk of developing health problems.
  • Feed your betta only good quality food. Low-grade foods usually do not contain the high levels of protein and nutrients that your betta needs to stay in good health. Check out our guide to feeding your betta fish for the full low-down on the dos and don’ts of betta nutrition.
  • If any of the occupants of your betta setup become sick, be sure to remove the affected fish right away and put them in a quarantine tank. That way, you can treat the sick fish and hopefully prevent a contagious condition from spreading.

Final Thoughts

Although cancerous tumors appear in bettas, there are many other causes of lumps and bumps that you might notice on your fish’s body, many of which respond very well to correct and timely treatment.

Always buy your betta from a reputable fish shop. Feed your betta only the best quality food, keep your fish tank clean, and always quarantine new fish before adding them to your main tank.

Finally, always check the tank’s occupants every day for signs of injury or disease. Spotting a problem early can mean the difference between life and death for your precious betta.

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