Betta Fish Tumor – Symptoms, Causes, Treatments, & Prevention

    Betta fish tumor

    Betta fish can develop tumors, even if you do everything right and provide them with the best care. However, there are many health issues that can look like a betta fish tumor, so it’s possible that another ailment is affecting your fish’s body.

    If you’re unsure whether your betta has a tumor, examine your betta fish’s skin. A tumor appears as lumpy growth that can occur anywhere on the body, including your betta’s head, side, or stomach.

    Tumors are usually caused by genetics, but poor water quality, viral or bacterial infections, and a low-quality diet can also be factors.

    Knowing the difference between tumors and other illnesses/diseases in betta fish will help you choose the appropriate treatment method, which is what we’ll be covering below!

    What Is A Betta Fish Tumor? What Does It Look Like?

    A betta fish tumor is a lumpy lesion or growth that appears on your betta’s body. Tumors can be either external or internal, but the latter is much harder to spot.

    A tumor on your betta can vary in size, from being almost invisible to as big as your fish itself. Cancerous tumors usually develop under the skin, so they are typically the same color as your betta’s scales. They can appear anywhere on the body, including your betta’s stomach, gills, sides, and head.

    This video gives you a good idea on what a tumor looks like in betta fish:

    YouTube player

    What Causes Tumors In Betta Fish?

    There are several factors that cause tumors on a betta fish’s body, including poor diet, improper water parameters, viral infections, and genetics.

    Poor Diet

    An unbalanced or low-quality diet can increase the risk of your betta developing tumors, among other health issues. Poor nutrition will have a negative effect on your fish’s health and their immune system, so it’s important to feed your betta a nourishing, varied diet.

    Bettas are carnivorous and require high-protein, meaty foods to thrive. Some good betta food options include betta pellets and frozen or live bloodworms, mosquito larvae, brine shrimp, and daphnia.

    Improper Water Parameters

    Similarly to a poor diet, improper water parameters can contribute to betta fish tumors and other health problems. Unsanitary living conditions can lead to a parasitical or bacterial infection, as well as cause extreme stress in your fish.

    You should make sure you have an efficient filtration system in your betta fish tank to prevent the build-up of ammonia, nitrites, and nitrates. If you live in a cooler climate, an aquarium heater is also a must as bettas are tropical fish.

    Ideal water parameters for bettas are:

    • pH: 6.5-7.5
    • Water Hardness: 5-20 DH
    • Temperature: 72°F-82°F (22°C-27°C)

    Viral Infections

    A viral infection can wreak havoc in a betta fish tank, especially if your pet is kept with other fish. These types of infections are highly contagious and can make your fish very sick, as well as increase the odds of tumors forming.

    Clean water and stable water parameters can help keep illness and disease at bay, as can limiting stressors in your betta fish aquarium. For instance, unsuitable tank mates or an undersized aquarium can lead to stress in Siamese fighting fish.

    If you add any new fish or invertebrates to your betta tank, it’s a good idea to put them in a quarantine tank for at least two weeks so you don’t potentially introduce any viral, parasitical, fungal, or bacterial infections to your aquarium.

    Genetic Predisposition

    Like humans, some betta fish are genetically predisposed to cancerous tumors. This is the most common reason why a betta fish develops a tumor.

    In these cases, there is nothing you can do to prevent the tumor other than ensuring you only select healthy fish from good fish stores or a reputable breeder.

    Dragonscale bettas may be at a higher risk than other scale types of developing cancerous tumors, at least according to some betta fish owners. While there is not scientific evidence to support this claim, it may be worth keeping in mind.

    Betta Fish Tumor Vs Abscess

    Betta fish tumor vs abscess

    Abscesses and tumors in betta fish can look fairly similar as they both manifest as abnormal, lumpy growths on your betta’s body. However, there is a very clear difference between the two, and that’s the color of the bump.

    A betta fish abscess looks like a white lump on your betta’s body, whereas an actual tumor is normally the same shade as your fish’s scales as it develops under the skin. If your betta has a white tumor, then it’s likely an abscess and not a tumor at all!

    Abscesses in bettas and other fish are typically caused by a bacterial infection. Bettas with open cuts or injuries, such as those sustained by a fish nipping them, are at high risk of developing a parasitical or bacterial infection, so it’s important to keep your tank water pristine to keep your betta’s wounds clean.

    If bacteria enters the site of the injury, it will destroy the surrounding tissue, and the dead matter will turn into pus. Once the pus pools beneath your betta’s skin, an abscess or ulcer develops.

    Frequent water changes and an aquarium antibacterial medication like API Bettafix are your best bet to treat abscesses, especially if they are not too big. Unfortunately, if left to progress, abscesses and fish ulcers will only get larger until they eventually burst.

    Not only is a ruptured abscess extremely painful for your betta, but it will leave them with an open sore on their body, which is likely to become infected a second time.

    How Do You Know If A Betta Fish Has A Tumor? Signs & Symptoms

    Betta fish tumor symptoms

    There are several different signs and symptoms you should look out for when determining whether or not your betta has a tumor:

    • Lumps or bumps underneath the skin
    • Lethargy
    • Loss of appetite
    • Abnormal swimming pattern

    Lumps Or Bumps Underneath The Skin

    If your betta’s skin forms a lump or growth, it’s most likely to be a tumor, particularly if you’ve ruled out an abscess or ulcer. Abscesses are usually white and betta ulcers are normally red.

    Tumors, on the other hand, are more or less the same hue as your betta’s scales. They can form under the skin surface, on the outer scales, or even internally. However, internal cancerous tumors are difficult to detect as there will be no visible abnormal growths on your fish.

    Betta fish tumors can be either very small or extremely large. The bigger your betta fish’s cancerous tumor, the harder it will be for them to function normally, especially if the growth is in an area like the side of their head.


    A healthy betta is active and inquisitive, but if your fish has recently slowed down or started sitting at the bottom of the tank, it could indicate a health issue like a tumor. Depending on where the tumor is located, your fish may find it difficult to move around the tank.

    If your betta’s tumor is painful, they are also more likely to hide and find shelter. Any changes in your fish’s behavior should be examined as there is usually a reason behind it.

    Loss Of Appetite

    As many Siamese fighting fish owners will tell you, bettas have huge appetites and will shamelessly beg for food. A betta that has suddenly lost their appetite or is more picky than usual is uncharacteristic and may point to a sick fish.

    If your betta fish has a tumor near their mouth, it can interfere with their ability to eat or may make it impossible altogether.

    Abnormal Swimming Pattern

    Although conditions like swim bladder disease can cause your betta to swim abnormally, so can a cancerous tumor depending on its location and size. A large tumor on your betta could cause them to swim on their side or struggle to balance.

    Where Can Tumors Form On A Betta Fish?

    Here are some of the most common parts of the body where betta fish may develop tumors:

    • Head
    • Sides
    • Gills
    • Stomach
    • Tail/Fins
    • Internal

    Betta fish can develop tumors on any part of their body, including internally. However, most cancerous growths tend to form in the abdominal region.

    Betta Fish Tumor Treatment

    Betta fish tumor treatment

    Treating a betta tumor depends on its severity and whether it’s cancerous or non-cancerous. Some ailments like a fungus infection or betta fish abscess can cause tumor-like lesions but need vastly different treatment methods.


    Treating a betta fish with a cancerous tumor can be tricky as there is no cure other than surgery. Some aquarists attempt this procedure themselves, but it’s best to seek a veterinarian that specializes in aquatic animals unless you know what you’re doing.

    That being said, having your betta fish operated on is extremely risky and there is no guarantee that the tumor won’t return at a later date.

    If your fish appears healthy otherwise and the tumor is not interfering with their quality of life, it may be better to simply leave your betta alone to live out their final months. Continue to monitor their condition and provide them with the best care you can.


    If your betta fish’s tumor is causing them pain or they are no longer able to function properly, then it may be kinder to humanely euthanize them to end their suffering. This is a difficult choice, but if your betta is extremely sick, it may be the most ethical option.

    Additionally, if your betta develops an internal tumor, it’s likely that you won’t notice any changes in your betta fish until it is too late.

    There are several ways to humanely euthanize a betta fish with a cancerous tumor, including the use of clove oil and alcohol. However, if you have an experienced fish veterinarian close to where you live, it’s a good idea to ask them for advice and to recommend products.


    While there is no cure for cancerous tumors in bettas, if your betta’s tumor or lesion is non-cancerous and the result of a secondary ailment like a bacterial infection, the lesion on your fish’s skin may clear up on its own once the health issue has been resolved.

    Treatment for a non-cancerous tumor will differ based on the illness/disease that has caused it. For instance, swim bladder disease, a bacterial growth, or betta fish ulcer can be managed with good water quality and an aquarium antibacterial medication.

    If you’re not sure of the cause of your betta fish’s tumor, add aquarium salt to your main tank as it can be used to cure a vast number of illnesses/diseases, including ich, swim bladder disease, fluid retention, and mild bacterial and fungal infections.

    However, if your sick fish lives in a community tank, it’s best to move them to a quarantine tank to treat them until they are healthy enough to return to the main tank.

    Regular Water Changes

    Some common betta fish tumor symptoms like lethargy and an abnormal swimming pattern or are due to secondary health conditions, including swim bladder disease or a bacterial infection, both of which can be controlled with clean water and regular water changes (medication will also help).

    Good water quality can help speed up the recovery process and get your betta fish back on the mend.

    How To Prevent Tumors In Betta Fish

    Betta fish tumor prevention

    It can be hard to treat betta fish tumors, so your best cause of action is to prevent them from forming in the first place. Fortunately, there are a few things you can do to reduce the risk of tumor development and promote good health in your betta.

    Use A Quarantine Tank For New Fish

    Before you add new fish or invertebrates to your betta fish tank, you should house them in a quarantine tank for at least two weeks so you can treat them for any illnesses or diseases that may develop in that timeframe.

    This will help you prevent the spread of bacterial, viral, and fungal infections to your betta and maintain a healthy aquarium.

    In addition, if you’re introducing fresh plants to your tank, either quarantine them for around a week or clean aquarium plants using a bleach and water solution (3% hydrogen peroxide mixed with water will also work).

    Buy From A Reputable Betta Breeder

    Some betta fish are genetically predisposed to external and internal tumors, but you can lessen the chance of your betta developing tumor growths by purchasing them from a reputable breeder or a good local fish store.

    Inbred fish and those from poor stock are more likely to develop lumps or other health issues.

    Only buy specimens that look healthy and don’t show signs of sickness, such as lethargy, rapid breathing, dull coloration, torn fins/tail, lesions on the betta fish’s side, or inflammation on the fish’s gills.

    Offer A Nutritious And Healthy Diet

    Providing your betta fish with a well-balanced, protein-rich diet will help keep your pet protected from illness and disease, as well as strengthen their immune system. This can vastly reduce the risk of many betta fish tumor causes.

    Make sure you offer your betta a variety of freeze-dried, live, and frozen food like betta pellets, mosquito larvae, daphnia, and bloodworms. You can also feed them peas every now and again to ease constipation, prevent swim bladder disease, and keep their digestive system healthy.

    Keep Your Tank Water Clean

    Many issues are tied to poor water quality and a dirty tank, including swim bladder infection, gill hyperplasia, and certain betta fish tumor causes like bacterial infections.

    Gill hyperplasia, which can cause tumor-like growths on your betta’s gills, is often caused by parasites, bacterial infections, or unsanitary living conditions. Fish with gill hyperplasia will have difficulty breathing properly and, in severe cases, it can be fatal.

    The best way to counteract issues with betta fish gills and other health conditions is by keeping your tank water clean with frequent water changes.

    Most fish keepers perform weekly water changes, though the size and bio-load of your tank will need to be considered. Smaller, overstocked tanks will need more maintenance than larger, understocked ones.

    Treat Other Health Issues Swiftly

    The last measure you can do to prevent tumors from developing on your betta’s fish skin is to treat other health issues quickly. Swim bladder disease, bacterial infections, parasites, ich, velvet, and other common betta fish ailments should be managed with an appropriate medication before they get worse.

    When a fish’s immune system is already weakened by an illness, they are more at risk of developing further complications or secondary health problems. Affected fish should be treated in a quarantine tank if there are other inhabitants in the main aquarium.


    Although some cases of tumors in betta fish are unavoidable, there is still a lot you can do to minimize the risk. Some conditions like abscesses and ulcers can look similar to tumors, so make sure you examine your betta carefully before you make a diagnosis.

    Good water quality, a healthy diet, stable water parameters, quarantining new fish in a separate tank, and dealing with other health issues quickly can all help keep your fish healthy and prevent the chance of tumors developing on your fish’s skin.


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