Treatment & Prevention of Cotton Wool Disease

Cotton wool disease, also known as black-patch necrosis, fin-rot, as well as saddleback, these are all descriptive terms for similar bacteria, columnaris ( or Flavobacterium columnare). This bacteria is often confused with a fungus because of its pale color and swollen appearance. It can affect all kinds of freshwater fish, but is typically secondary to a primary aggressor. Certain strains are more dangerous as well as contagious in comparison to others.

What is Cotton Wool Disease in Freshwater Fish?

This cotton wool disease is caused by the bacteria Flavobacterium columnare. It is not a fungus even though it has an appearance like a fungus. It is able to infect the gills, skin and gills. It is crucial for the commercial aquaculture industry. It is less common within the pet fish community. It is usually an opportunistic disease that is able to take advantage of stressed fish that has a weak immune system. There are a variety of strains within the species, and some are much more deadly and are more easily spread.

What Causes White Growth on Fish (Cotton Wool Disease)

Fish health issues are common in aquariums, but the main cause is poor conditions in the water, which is easily avoidable. The fundamental rule is safe water, clean and contented aquatic friends.

Of all the diseases that can be attributed to fungal diseases, they are among the most frequent and appear to be constantly lurking in aquariums, possibly because fungal spores exist throughout tank conditions, even after impeccable maintenance.

Fortunately, fungal diseases usually are not invasive, so they’re easy to detect even for people who do not have any experience. They have a distinctive light, fluffy appearance hence commonly known as cotton wool disease.

Yet, the growth of cotton wool disease is sometimes misinterpreted as a bacterial infection known as cottonmouth (Columnaris) that is also affecting tropical fish. It manifests as the form of greyish white spots.

Another condition that displays white growth, and could be the cause is Lymphocystis virus. Small white-pin-prick-like growths can be seen on fin or skin of a fish in the beginning stages, and eventually clump to form cauliflower-like masses on the mouth, coat or flippers and, occasionally, the gills.

Cotton Wool Disease Symptoms in Freshwater Fish

The most frequent symptom of cotton wool disease is a small, swollen patch on the skin of your fish. It could be everywhere on the body including the fins and face. Lesions typically display the appearance of a fluffy appearance similar to fungal growth. In certain instances, it may be spread to the gills leading to fatigue, difficulty swimming and a loss of appetite. In some cases, the gill tissue may appear necrotic or pale upon examination.

What are the Causes of Cotton Wool Disease in Freshwater Fish

Columnaris bacteria are commensal bacteria that are naturally found on healthy fish. When a stressed-out host or a particularly harmful strain of bacteria is when the fish show symptoms of clinical. It is most likely to enter healthy systems when the fish are infected without the proper quarantine. It is essential to keep a watch on the tank’s temperature because columnaris bacteria prefer warm waters (around 80F) and will cause issues faster than cooler water.

Cotton Wool Disease Diagnosis in Freshwater Fish

It is crucial to distinguish columnaris species from fungal infection. In order to determine this your doctor will collect a tiny sample from a fish that has been sedated and then place it under a microscope. If the condition is cotton wool disease, the bacteria rods will morph into tiny haystacks. However, fungus does not, and the hyphae of each individual may be distinct.

Further testing could be necessary by sending a sample of swabs to a laboratory to determine the strain of bacteria and to determine the antibiotics are most efficient. Don’t “guess” with antibiotic treatment. You could end up wiping the biological filtration as well as using an wrong dosage or product, creating more resistant strains to your body.

Cotton Wool Disease in Aquarium Fish

It is also known as the cotton wool disease is a general term that is used by aquarists for the presence of one or more commonly-occurring fungal infections that can affect the skin, mouth, finns or fins.

The most frequent fungi that cause problems for aqua fish include Saprolegnia and Achlya however they aren’t the only two. Be aware that it is possible to find several species at the spot of the illness on the body of a fish.

Typically it is the growth that appears white fungus usually infests areas that have had prior infections, parasites or even injuries.

In this way, cotton wool disease is common in tanks that have injured fish due to nippings or tail and fin ammonia burns or injuries that are not related to infection and nippers like heater burns.

Fish that are stressed or sick are also more prone to cotton wool diseases (fungal infection) as well as poor water quality can exacerbate the condition even in healthy fish.

The infection begins as white marks on a fish’s damaged area, and then it spreads into a white-fluffy , cotton-like growth. Based on the circumstances there could be other symptoms such as swelling and reddened ulcers around the body or frayed fins.

Cotton Wool Disease Treatment in Freshwater Fish: How do you treat fish fungus at home?

Fish that show symptoms should be kept in the hospital tank. The veterinarian can prescribe an antibiotic that is in the fish’s water or offer injectable treatment. Injectable antibiotics are not harmful to the effectiveness of your biological filter and provide a more effective treatment alternative. Do not attempt to inject your fish by yourself.

The fish you catch may require different antibiotics even if there isn’t a sample taken for culture or test for sensitivity. A complete account of your fish’s history, as well as the treatment options that have been tried is crucial to determine the best antibiotic for your specific situation.

Fish that are severely sick, such as those that have >50% of the gill tissue affected, might require euthanasia. It is extremely difficult to heal a fish from an extreme disease. If your fish’s gills developed an infection, it’s crucial to give them oxygen help through an airstone.

As it is a secondary intruder the fish’s ecosystem should be examined for any possible stresses. This means conducting a test of the quality of your water chemistry, reviewing your fish’s diet as well as comparing fish compatibility with any recent additions to your decor or fish. If you fail to eliminate the main reason, your fish could become sicker after the treatment.

Treating cotton wool disease in aquarium fish is baths with aquarium salt or treating your fish using a commercially-available antifungal treatment like Api Fungus Cure.

If you are considering the salt bath route, it is recommended that you research the way in which your species of ornamental fish you have handles saline water.

Fishes such as mollies, platies, and even guppies are able to endure high salinity levels and endure a long salt bath, but other (most) freshwater tropical species such as goldfish and betta, will only take a brief and gentle dip.

Make your salt bath for your fish by adding four teaspoons of salt into an unclean bucket and gradually adding the gallon of the water in the fish tank while swirling the vessel until the salt is completely dissolved.

After the salt has completely dissolved, you can dip your fish into the bucket for between 5 to 30 minutes, be sure to keep track of the amount of time you need to give the species of fish you own.

If just one or a couple of your fish are affected, transferring them to the quarantine tank is recommended to ensure that the fish’s mates are healthy.

It is also possible to address other problems that cause fungus diseases, such as an underlying condition, nippings, and burns. Make sure that the levels of ammonia inside the tank are at 0ppm and keep any nippers from the other fish.

Make use of API Melafix or Furan 2 to treat the bacterial infection, repair Fins, ulcers as well as open cuts to stop secondary infections like fungus.

Cotton Mouth Disease in Fish

The bacterium known as cottonmouth causes a disease of fish. The condition is commonly confused with it being a fungus disease due to the white, fluffy mildew-like lesions. But unlike fungal ones, Columnaris can be external or internal, and is more likely to develop a chronic as well as acute course.

The condition can be caused due to it being caused by the gram-negative, aerobic, rod-shaped bacteria known as Flavobacterium columnare, which enters the body of a fish through mouth, gills, as well as small cuts.

As I said that the infection could be both internal and external however, it usually manifests on the outside, appearing initially as grayish or white spots on the head as well as around the fins and gills.

Symptoms: A prime indication for cottonmouth among fishes is the shade of the lips of the fish. They shift from their usual color to grey or white and white-hair-like growths can be seen.

Patches tend to be more obvious on fish that are less luminous or on parts of a fish’s body which do not have the same natural glow as the whole frame.

The affected areas typically turn yellow or brown and the skin around could be red. Lesions occur in chronic cases are slow to progress and can last for a long time before reaching the point of death.

Other signs that are typical for affected fish are white lines that line the mouth, clamped fins , thinned slime coats as well as rotting flesh and, eventually, premature death.

The basic idea is that in the end, Columnaris bacteria are most likely to be a problem for fish stressed due to conditions like poor quality of water or a poor diet or stress due to transportation and handling.

It is important to note that in contrast to fungus, cottonmouth disease is extremely contagious and could spread through infected containers, nets, and even food items. So, sterilize the items and if it is possible, quarantine the affected person and then cleanse your aquarium. tank.

How do you treat cottonmouths in fish?

A variety of treatments are used to deal with the cotton mouth disease that affects fish. The use of salt, such as salt baths and the addition of aquarium salt in your water is very effective, particularly when it comes to fighting minor illnesses.

The addition of salt to your aquarium can treat every fish within the tank and the saline baths as well as salt rubs are best for people who have been affected.

Make use of 1 to 4 teaspoons of salt per gallon of water you want to include in your fishing tank or soak your catch for a few minutes. Be cautious when handling delicate fishes like catfish.

Livebearer will benefit from the extra salinity of the tank, baths, and rubs.

Infections can be treated using antibiotics or chemicals in water or both. Terramycin as well as Aureomycin are excellent for baths and also when employed to treat food items for internal infections.

Copper sulfate, Acriflavine, and Furan are also effective as do an 5 percent Silver Mercury solution directly on the affected regions.

However, be aware that some of these chemicals can be harmful to fish, snails and shrimp, as well as scaleless fish, therefore be careful and only in the instances where it is necessary.

Lymphocystis Virus

Lymphocystis is the final of three ailments of aquarium fish that can manifest as white cotton wool-like substances that appear on the body of a fish.

It is however the most rare of the three mentioned in this article.

The condition manifests on infected fish in the form of some white or beige-colored sands or wart-like nodules that are typically seen on the skin, fins or gills. Other tissues can be affected as well.

Most of the time, Lymphocystis may also be the reason behind pop-eye in fish. It results in the eye being forced to grow out when the virus infects the tissues in the area behind it.

In general, the virus found within fish can cause cells to expand several times the size they normally are and, after approximately 4 weeks, it may burst and explode in the water and spread to other fish within the tank.

We are happy to inform you that the treatment for Lymphocystis is exactly the same as other contagious illnesses in fish tanks. If you take the proper precautions, care and treatment for the affected fish, they are likely to recover, and other fish within your tank aren’t affected.

How to Prevent Cotton Wool Disease? Or, How do you get rid of cotton wool disease?

As with all diseases that are a part of the human body, cotton wool disease can be avoided by the proper quarantine. This requires a separate system, with distinct filtration as well as other tools to last for 4-6 weeks. 2 weeks isn’t enough and keeping the right temperature is vital.

Keep an eye on your fish throughout this time and be aware of any changes to their look or behavior. If you observe something that isn’t right it’s crucial to identify the issue quickly and properly to ensure that it does not become a major issue. If you keep your pet in isolation and away from the rest of your fish, you can guard your entire system from getting infected.

It is essential to ensure that your fish are healthy in a calm environment. It is essential to ensure that your fish are provided with plenty of space with a good quality diet and a good water chemistry.


Can humans catch cotton wool disease?

The illness is extremely contagious and the result can be fatal in some cases. It is not zoonotic at all.

Why is there cotton in my fish tank?

The health of fish is a major concern in aquariums. However, the primary reason is the poor quality of the water. This is easily averted.

Is fish fungus contagious?

Fungal infections are extremely contagious, so infected fish should be treated as soon as possible by taking anti fungal medicine.

What causes white fungus in fish tanks?

The bacteria “Flavobacterium Columnare” causes Cotton Wool Disease in fish.

How does salt cure fish fungus?

Sodium chloride (NaCl) is one of the top comprehensive “medications” on the market that works for fighting off bacteria fungus in addition to external parasites.

How long does it take to cure fish fungus in a fish tank?

API Fungus Cure fish remedy prevents the spread of the infection and is effective for up to 48 hours to clear up symptoms.

How long does it take for cotton wool disease to go away?

To heal the cotton wool disease completely it takes on average 4-6 weeks


Dibyajyoti Bordoloi is the creator and author of, a third-generation experienced fish keeper and owner of a successful pet breeding farm. He is also a member of the Center for Wildlife Rehabilitation And Conservation (Assam), the Marine Aquarium Societies of North East India, and the Kaziranga Nature Conservancy of Assam.

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