Angelfish Diseases – Symptoms, Treatments & Prevention

A sick fish will be one thing that you are almost guaranteed to experience over the years as you keep freshwater angelfish. While these fish are hardy compared to other tropical fish, the potential for angelfish diseases is always there.

We have treated several types of diseases in our years of fishkeeping and would like to help you identify some of the more common variations you may see in your aquariums.

Angelfish diseases

Identifying and understanding these conditions will help you treat your angelfish and keep them alive. From poor water conditions to unintentional parasite introduction, keepers can often prevent issues if they know what to look for.

Some of the things we will broadly cover here include:

  • Common Bacterial Diseases
  • Common Parasites
  • Common Viral Diseases

Angelfish Bacterial Diseases

Cotton Wool Disease

The cotton wool disease appears to many keepers to be a fungus, but it is a bacterial infection. Its source is the bacteria Flavobacterium columnare (the source of cotton wool’s other name, Columnaris). What surprises most hobbyists is that this bacteria is constantly on their pets and aquarium water.

Also called cotton mouth by some, this disease creates cotton-like patches on the fins, mouth, and skin of your angelfish. Its appearance is fungal, giving rise to the mistake that it is a fungus growing on the fish. You’d need to look at the infected area under magnification to distinguish the cottony growth from a fungal patch.

Treatment will include using some form of anti-bacterial medication. You might read online that an anti-fungal is required, but we find these are less effective (it’s not a fungus, after all). The trick is that Columnaris is a secondary infection, so you must identify and remove the stress affecting your pet’s immune system.

Stress-related immune deficiency is the top cause of cotton wool disease, so maintaining a low-stress tank is your best form of prevention. Maintain ideal water parameters and reduce conflict to a minimum.

Fin Rot

Angelfish fin rot is often the result of damage to the fins from nipping or sharp decorations that results in a bacterial (or sometimes fungal) infection. The infection causes further damage resulting in color changes, edge damage, holes, increased tears, or loss of part/all of the fin.

If you are new to keeping freshwater angelfish, understand it is one of the more common diseases you may see. The negative-gram bacteria or fungal sources responsible for fin rot are often already in the water column. Fin damage or a reduced immune system allows infections to take hold and damage the fins more.

View fin rot as a secondary infection that requires you to identify the primary cause. Remove fin nippers and sharp decor from community tanks. Once you eliminate these sources, consider water temperature or poor water conditions as potential problems.

Treatment options include aquarium salt, methylene blue, or bacterial/fungal medications introduced through food. We suggest moving infected fish to a quarantine tank, especially if you plan to treat the water.

Remove stress factors, maintain good water quality, and feed your fish a proper diet to help prevent this common disease.

Mouth Fungus Disease

Mouth fungus is another bacterial infection that often gets mistaken for fungal growth due to its appearance. It appears and acts similar to columnaris but is listed separately here because other negative-gram bacteria like Aeromonas are the cause. This mouth fungus is also referred to as flexibacter by some.

It manifests as a section of white material on the lips or general mouth area of your freshwater angelfish. That patch can grow as the disease progresses. Mouth fungus disease will produce toxins in the infected area that erode the mouth tissue.

The damage can advance to the point that your pet can’t eat, resulting in suffering and death. That is why it is critical to treat it early using general antibiotics. Early treatment will allow you to place the medications in the food, providing a more concentrated dosage and better results (otherwise, you use water treatments that lack the same concentrations of antibiotics).

Providing a stress-free environment is the best form of preventative medicine. That includes frequent water changes, proper temperatures, ideal chemical balance, and a roomy aquarium with hiding spaces.

Popeye Disease

Popeye is not a disease but is the result of another condition. Most often, Popeye comes from a physical injury. We list it here as bacterial infections can also cause your fish to suffer from this problem.

Also called exophthalmia, this condition can affect one eye (unilateral) or both eyes (bilateral). If you observe unilateral exophthalmia, it is likely due to physical damage from another tank mate or running into something in the aquarium. Bilateral exophthalmia will indicate an underlying infection or unhealthy water conditions.

The most notable symptoms are body swelling, eye socket expansion, cloudiness in the eye, or ruptured eyeballs. Early non-trauma indicators can include clamped fins, loss of appetite, and listlessness.

Begin treatment by trying to identify sources of trauma and removing them. You can then check water parameters to eliminate this as a source. Only then should you move on to treating Popeye’s symptoms as a bacterial infection using a general antibiotic.

Prevention involves providing ideal water conditions and eliminating things that can physically harm your angelfish.

Swim Bladder Disease

Swim bladder disease is a catch-all phrase describing the inability of the swim bladder to function correctly in your freshwater angelfish. Causes can include environmental issues, physical problems with the digestive tract, an underlying disease or infection, and other undiagnosed conditions.

You may also find this being called swim bladder disorder in literature or online sources. It results in your angelfish sinking to the bottom of the tank, floating to the water’s surface, or swimming at an abnormal angle. The fish may struggle to remain upright, swim upside down or sideways, and have changes in appetite.

One of the most common causes of this condition is overeating or eating too quickly, causing the stomach to swell and preventing the swim bladder from operating normally. We place this in this section because bacterial infections (and sometimes parasites) can interrupt bladder function.

Start treatment by checking water temperature and water chemistry. You can stop feeding your fish or provide it with a laxative like cooked frozen peas if you suspect overeating or consuming food too quickly. General over-the-counter antibiotic treatments should help if the cause is determined to be a bacterial infection.

Prevention includes buying healthy fish, maintaining a clean tank with ideal water parameters, and avoiding overfeeding.

Healthy angelfish

Angelfish Parasite Diseases

Anchor Worms

These parasites are not worms but copepod crustaceans that will attach to your freshwater angelfish using large, hooked claws. The anchor worm will then ingest the blood of its host.

You will notice red-colored lesions and inflamed marks on the infected fish’s skin. Closer inspection with a magnifying glass lets you see the anchor worm’s body. It looks like a dark green thread against the skin.

Many keepers will notice something is wrong by the way their fish act. Infected angelfish will rub against tank decor and substrate to remove anchor worms from their body. These attempts are futile as the worms burrow under the skin through the initial wound.

You can pull the anchor worm out, but be gentle to prevent further damage or stress. A topical antibiotic can be placed on the wound to help prevent additional problems.

Poor water conditions and introduction through new fish or decor are the most common pathways anchor worms infest your tank. Isolating new specimens, disinfecting items, and maintaining proper water temperature and quality are the best forms of prevention.

Gill Flukes

Gill flukes are parasitic organisms, most commonly the fish flatworms known as Monopisthocotylea monogenea. These worms will attach to an angelfish’s gills, mouth, or skin. The worms can lay and fertilize up to ten of their eggs daily.

After hatching, free-swimming worms will find a new host to attach to. That makes gill flukes a contagious parasite, so early detection and treatments are crucial.

You may notice your pet acting strangely, including scratching against objects within the fish tank. A loss of appetite and low energy are associated with gill fluke infestation. Physical manifestations include redness around the gills, labored breathing, and increased mucus production.

Some keepers prefer to treat using aquarium salt, but you can also consult your veterinarian for all-in-one chemical treatments.

Poor water quality, live foods, and new fish that are infected are the common pathways into your aquarium. That makes prevention easy if you monitor water chemistry, perform scheduled water changes, avoid live foods, and use a quarantine tank for four to six weeks for new specimens.

Hexamita (Hole-in-the-Head Disease)

The hole-in-the-head disease is usually a result of an infestation of the single-celled Hexamita parasite, but symptoms can also arise from some viral infections. These creatures live in the digestive tract but only cause Hexamita when its immune system becomes weakened.

Initial symptoms can include subdued color changes, white stringy feces, and a loss of appetite. Reduced eating will lead to a thin appearance, and the specimen will develop lesions along its head and lateral line along the sides of the fish.

You can add over-the-counter hexamita medications into the food you feed your freshwater angelfish. The medicine is put into the water column if your fish is not eating.

Overcrowded tank conditions and diet may be factors in the development of hole-in-the-head disease. You can help prevent an outbreak by keeping fewer fish in the aquarium, providing a healthy diet, and maintaining water parameters to promote a healthy immune system.

Ich / Ick

Ichthyophthirius multifiliis is a common parasite found in the hobby and can be deadly if not treated quickly. It is also referred to as a white spot disease because the parasite creates white spots on the body of your angelfish as it burrows into the skin to eat, move, and reproduce. One parasite can generate 1,000 offspring, overwhelming the host and spreading rapidly to others.

Treatments can involve chemicals or aquarium salt. It can be hard to treat infected fish because the parasite burrowed into them, so the sooner you start treatments, the better. The first treatment targets infected fish and free swimming parasites in the water column, killing the current generation. A second treatment is required to remove the next generation of parasites that will develop a few days later.

Prevention involves isolating and cleaning anything you plan to add to your aquarium. Use a quarantine tank for four to six weeks with new arrivals, fish or live plants. Other decorations, filter media, and aquarium hardware should be cleaned and air-dried before incorporating them into your system.

Velvet Disease (Gold Dust Disease)

Gold dust or velvet disease results from an infestation by a small single-cell parasite called Piscinoodinium pillulare. It makes your angelfish look like it has a layer of dust covering it. That is a rusty-colored film on the top of the skin.

You may notice other symptoms, including clamped fins and labored breathing. In severe cases, the skin will peel off of your fish. Some specimens display lethargy, labored breathing, reduced appetite, and scratching movements against decor within the fish tank.

You need to treat the entire aquarium if velvet disease is suspected. Multi-stage applications are also necessary to kill off unhatched parasites unaffected by the first treatment.

Hobbyists increase water temperatures to speed up the parasite’s lifecycle and cover their tanks to weaken this photosynthesis-powered creature. You could use older methods like aquarium salt, but we suggest easy solutions like ready-made velvet medications. Stable water temperatures and proper water parameters are the two best preventative measures.

Angelfish Viral Diseases

Virus Infection

Viral diseases can be challenging to identify because symptoms often manifest in ways that would indicate other maladies like bacterial, fungal, or parasitic conditions. Another issue with viral infections is that most have no cure; currently, there are no available medications to treat fish-borne viral infections. You have to make living conditions the best you can for your pet and let the virus run its course.

Hundreds of piscine viruses display various symptoms, but some affect certain species more than others. One example you may want to watch for is the iridovirus Angelfish Virus. Common symptoms include clamped fins, listless behavior, swimming nose slightly up, more slime than usual, and isolating behavior.

There is no treatment for this three-week-long disease that is highly contagious. Removing the fish from your aquarium is critical to saving other specimens from this deadly virus. We suggest humanely putting the infected fish down to prevent suffering.

Your best preventative measure will be to isolate new arrivals for at least four weeks before introducing them into your community tank. If you suspect Angelfish Virus, immediately remove the sick fish and observe your other fish for the signs over the next three days.


Dropsy isn’t a disease; it is a secondary symptom that displays as a swelling of your pet’s body. The ballooning up will cause the scales on the fish to stand out and is best compared to a pinecone in appearance.

Things that cause dropsy in freshwater angelfish may include diet, poor water conditions, aggressive tank mates, tumors, bacteria, parasites, and viruses. The gills and kidneys struggle to remove additional water from the body through regular organ function. That causes water to collect in the skin beneath the scales, forcing them to protrude outward.

Treatment begins by examining water conditions and making adjustments if needed. Verify you are feeding your pets a proper diet and eliminate the possibility of aggressive tank mates. If these scenarios are covered, you can contact your vet about possible bacterial treatments (remember that viral sources are non-treatable).

While the prognosis for a specimen with dropsy is poor, prevention for most underlying causes is within your power. Provide a healthy diet and maintain a proper environment, including regular water changes.

If caught early enough, fish with dropsy can recover. We place this entry under viral diseases as dropsy caused by a virus is only identifiable through eliminating other sources and is non-treatable. Your angelfish might survive if internal organs do not die due to the condition.

Keeping Your Freshwater Angelfish Healthy and Happy

There are various diseases your pets can contract through bacterial infection, viral infection, parasite, or even a secondary infection resulting from another primary source. We hope you can now identify some of the more common diseases you might encounter in the hobby and what to do if you should.

The biggest takeaway here should be prevention. Most diseases are preventable by maintaining water quality through regular water changes and monitoring through test kits. Water temperature is crucial, so inspect equipment often and keep an extra thermometer and heater handy to cover emergencies.

Quarantine new fish for at least four to six weeks before you add them to your community tank. That applies to fish from trusted sources as well. Always clean and disinfect new or used decor before adding it to your tank, and avoid using live foods that might hold parasites.

Finally, observe your fish (this shouldn’t be hard because they are fun to watch). Look for behavior changes or unusual blemishes and wounds that may appear. As you probably concluded from the lists above, early identification and treatment are crucial for recovery.

We hope you and your freshwater angelfish continue to enjoy health and longevity. Make sure to leave a comment with your experiences with angelfish diseases, or ask questions that we can help answer!

Don’t forget to keep an emergency first-aid kit on hand to help with treatments. Some items you may want to include:


What diseases are angelfish prone to?

Your freshwater angelfish are susceptible to several bacterial, fungal, parasite, and viral water-borne diseases. Some of the more notable conditions that breeders, keepers, and veterinarians see regularly include Hexamita, Ich, and Cotton Wool Disease.

Many diseases your pet contracts are treatable if caught early, so knowing what to look for is crucial for survivability. Some may, however, prove to be fatal even if you apply appropriate treatment promptly.

How do you treat a sick angelfish?

Treating sick angelfish may require isolation, medications, water treatments, or procedures from a qualified vet. The type of treatment and its duration hinges on identifying the problem, including primary causes resulting in a secondary infection.

Water-borne illness in a community tank presents more challenges than treating a single specimen. You may have to perform water changes, treat all tank mates (even if they are not symptomatic), or remove components for disinfecting. That is why early identification is so critical for maintaining a healthy aquarium.

Should I put my sick angelfish down?

Consider euthanizing your freshwater angelfish when recovery is unlikely or when it has a highly-contagious illness that threatens other fish in a community aquarium. Weigh this decision against the suffering the fish appears to be going through, its quality of life after recovery, and your ability to treat and care for the fish after.

If you decide to put a sick fish down, use the most humane method possible. Contacting a vet can help you avoid stress for yourself and your pet. Avoid flushing your fish, boiling it, freezing it, suffocating it, or other inhumane forms of terminating its life.

Is there a medicine for sick fish?

There are several medications available online or through your veterinarian you can use to treat sick fish. These can be treatments added to food, placed on the fish, or put into the aquarium water column. Examples include Levamisole, Maracyn, Methylene Blue, and brand-name treatments like Tetra Lifeguard All-in-One Bacterial and Fungus Treatment.

The medicine used will depend on what you identify as the problem. A vet will often prescribe a specific medication, or you can use something like Methylene Blue if you suspect a fungal infection that warrants it. Generalized treatment products are ideal if you are unsure and lack the resources to seek a vet’s opinion.

Why is my angelfish dying suddenly?

Your freshwater angelfish may have suddenly died due to poor water quality, improper water temperature, stress from water changes or tank mates, parasites, bacterial or viral infections, age, or genetic conditions.

We suggest observing current tank conditions through a test kit, noting the water temperature, and looking for impurities tainting the water column. Be suspicious of anything new you recently added to the tank, including other fish. To limit surprise deaths, observe your fish continuously and familiarize yourself with the common diseases discussed here.

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