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Betta Tumor Guide: Symptoms, Treatments & Prevention

Sarah Psaradelis

By Sarah Psaradelis

closeup sick betta fish

Bettas (also known as Siamese fighting fish) are beautifully colored fish considered as the jewels of the aquarium world.

Tumours are a dreaded yet common occurrence in betta fish. It is unpleasant to wake up one morning and eagerly peer into your betta’s tank to let it know its times for feeding, only to find a large bump protruding from its body. This happens quite often in betta fish and is typically unavoidable. Understanding tumors in bettas is important for all betta fish enthusiasts because they can occur at any stage of a betta’s life.

This guide will help inform you on tumors in betta fish and how you can prevent and treat them!

Types of Tumors in Betta Fish

Tumors or abscesses are inevitable to certain low-quality bred betta fish and there is rarely a direct cure. The type and size of the tumor are what makes them harmful or not.


This is a non-cancerous lump that can swell to large sizes. This type of tumor rarely spreads to other parts of the body and is typically low risk. Large benign tumors can become too heavy for a betta fish to comfortably swim, and an aquatic veterinarian should have it removed.


A more worrisome form of tumor contains cancerous cells. This can quickly spread to major organs of the body and cause problems. Most of the time these tumors cannot be successfully removed from every part of the body and the fish may have to be euthanized with the approval of an aquatic veterinarian.

A closeup shot of sick betta fish in aquarium tank
Image credit: Wirestock Creators, Shutterstock


These are lumps filled with pus that look like tumors. They are typically caused by an injury from a scratch or poke from rough aquarium decoration. They can easily become infected from dirty aquarium water, and this can cause them to swell to extreme sizes. The only viable treatment for abscesses is to have an aquatic veterinarian drain the pus.


A bloated betta can appear as if it has a tumor. A large lump appears underneath their head where their stomach is located. This can occur if your betta fish eats plant matter or if the water temperature is too cool. The swelling should go down within a few days.


The Main Causes of Tumors in Betta Fish

  • Poorly bred bettas: Bettas that have been thrown together to breed can lead to poorly bred lines. This makes them more susceptible to different disorders and illnesses. Inbreeding can also pose a risk to their health and shorten their lifespan. This typically occurs in a fish breeding mill setting.
  • Genetics: Tumours are commonly caused by genetics. If one of the parents or ancestors in the betta’s family tree has a history of tumors, then the offspring is most likely going to develop one at some time during its life.
  • Pet-store bettas: These bettas are generally poorly bred and have a higher risk of developing tumors. It is very common for pet-store betta fish to develop a cancerous tumor during old age. Unlike ethically bred bettas from a breeder which has better genetics and is healthier.
  • Chemicals and toxins: Low-quality aquatic medications or foods can have cancer-causing ingredients in them. Over time, these toxins can build up in a bettas system and cause tumors to grow. Certain cancerous medications are carbon, aquatic plant fertilizers, off-brand foods, or water conditioners. It is also common for painted aquarium decorations to leach off chemicals into the water and cause health issues.
sick red betta fish
Image Credit: Yasin Fadlilah, Shutterstock

Common Symptoms

Determining the symptoms of a tumor in betta fish is classified by three or more of the following symptoms with the inclusion of an abnormal bump or lump forming on the bodily area of the betta fish. Loss of appetite, lethargy and the inability to swim is usually present in severe stages. The tumor may grow to a certain point where it is too heavy for the betta fish to swim with. The result of this is poor oxygen intake since the betta is unable to swim to the surface to refill its labyrinth organ and the betta will eat away at its fins to make itself lighter in the hopes of being able to swim.

  • Protruding hard lump or bump on the body
  • Struggling to swim
  • The bump continues to grow
  • Discoloration
  • Abnormal swelling
  • Constipation
  • Loss of appetite

  • Lethargy
  • Inability to swim in the last stages
  • Scale loss
  • Dull coloration
  • Torn fins
  • Gasping

sick betta fish
Image By: yin8003211, Pixabay

Treating Betta Tumors

Tumours are hard to treat in fish and there are no cures for benign or cancerous tumors. Benign tumors can be cut out by a professional while the fish is under anesthesia. There are no medications to treat tumors and prevention is more effective than cure.

If a betta is deemed to have a poor quality of life while having a tumor, then it should be euthanized to end its suffering. Bettas who struggle to swim, develop lethargy, or have a loss of appetite are generally not feeling well and they will most likely not die as a direct result of a tumor, but rather succumb to their symptoms.

How to Prevent Tumors in Betta Fish

You can start by purchasing a betta fish from a reliable source. This means a qualified betta fish breeder who breeds their bettas for quality rather than quantity. They will most likely have a better genetic heritage. Although this does not mean the betta will not develop a tumor, it will lower the chances.

Always use good medications and high-quality foods. Avoid using foods that are poorly made or use low-quality ingredients with fillers. If you want to use high-tech in a planted aquarium, do not overdose on the usage amount and avoid using it at night when the plants will not take in the nutrients. This helps prevent the water from being contaminated with the chemicals which can be absorbed through your betta’s gills and into their bloodstream.

fish divider


Although tumors are prevalent in bettas, every type of fish can develop a tumor. The only advantage other fish have is being bred less because there is low demand in the aquarium trade when compared to betta fish. Goldfish are the next type of fish that are prone to developing benign or cancerous tumors.

We hope that this guide has helped you understand tumors in betta fish better!

Featured Image Credit: Wirestock Creators, Shutterstock

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