Goldfish fungus: Types of fungus, causes and treatments

Fungus grows on fish due to less than ideal conditions in the water and is the most commonly seen disorder in fish. It is seen as cotton-like growths on the gills, mouth, and face.

Fungal infections tend to appear because the fish has broken skin or a primary disease such as a parasite or bacteria. Broken skin can also happen due to sharp edges in the aquarium or fighting. If it is fighting, then it is imperative that the aggressor fish is moved out. If not treated quickly and appropriately, fungus can infect the internal organs of the fish and cause death.

There are several kinds of fungus that each require a little bit different treatment.

Stress and a lowered immune system will cause the fungus to grow more.

Different kinds of fungus

Saprolegnia fungus

Saprolegnia fungus infects fish and their eggs. This fungus will affect the internal organs and deeper tissues of the fish. It appears as a light gray, cottony growth on the skin, fins, gills, and eyes.

This type of fungus appears as a secondary infection, usually attacking sick or injured fish. This fungus enjoys eating dead material in the aquarium and the more detritus there is then the more of this fungus will be floating around.

Keeping a clean tank and performing regular maintenance of the water will help keep less fungus and the fish healthier.

If you suspect that this is the cause of the fungal growth, it will need to be diagnosed by an aquatic veterinarian. This fungus is non-responsive to antibiotics so treating the underlying issue is the best way to treat it.

Cotton fin fungus

Cotton fin fungus, otherwise known as cotton wool disease. This fungus takes a hold of sick or injured fish. It shows up as cotton like growths on the body wherever there is an injury or open wound. This open wound allows the fungus to grow better and if not treated in time can lead to health problems or death.

This fungus can also occur alongside a bacterium known as fin rot which can be caused by the same bacteria flavobacteria. Fin rot shows as frayed edges on the fins. Cotton fin fungus should be treated by a veterinarian diagnosis and can be treated in a whole tank or injections. It is imperative that the sick fish is in quarantine during the treatment and recovery to allow it to heal appropriately.

Egg fungus

Egg fungus is commonly seen in breeding tanks and grows on eggs that are infertile and will quickly spread to other healthy eggs. Once the fungus starts to spread then it will slowly kill off all the eggs.

Removing the affected eggs is one way to treat the infection, however, this can be hard to achieve.

Once the eggs are removed from the main tank and transferred to their hatching tank, you can rinse them in clean water to help remove any potential disease from the main tank that can harm the eggs and place them in their new tank. Methalyne blue is sometimes added to help prevent any fungus growth but this can sometimes be unnecessary. A quick rinse, proper aeration, and clean water is usually all that is needed to keep the eggs healthy.

Treating fungus

The first thing to do when treating for a fungal infection is to move the affected fish to its own enclosure or a quarantine tank to ensure that uninfected fish are not treated or harmed from the treatment.

Treatment of fungus depends on the type of fungus that is affecting your fish.

SaprolegniaI is treated by medicating the water with potassium permanganate. Fungal infections should start to clear up or be cleared up within two weeks of treatment and consistently clean water.

Cotton wool disease is treated with an additive anti-fungal to the water where the sick fish is being housed. You can also increase the salt content of the water but be careful to not over do the salt as this can also damage the fish if it’s too much for the fish.

You should always check with a veterinarian before starting to treat any potential disease. A veterinarian will prescribe an appropriate treatment and be sure to follow the directions.

How to prevent fungal infections

The best way to prevent fungal infections from occurring is to ensure that the tank or pond water is consistently cleaned and maintained. If there are any aggressive fish picking on other ones, then the aggressors should be removed to prevent further damage to the nonaggressive fish.

Clean water is imperative to prevent any disease and is good tank maintenance. Verify that all your water conditions are appropriate and kept in a healthy range for the fish you are housing.

It is easier to prevent fungus from occurring than treating and potentially losing fish to it. Clean water means healthy fish.

In conclusion

Fungal infections occur due to improper water conditions and sick or injured fish. Maintaining the water conditions and ensuring a healthy living condition will keep the fish in good condition to fight off disease better.

There are three fungal infections that are well known and should be diagnosed by a veterinarian and given proper antibiotics.

These are:

  • Saprolegnia
  • Cotton fin fungus
  • Egg fungus

Fungus is usually seen as a secondary illness because once the fish is in an unhealthy state then the fungus can take hold better. Bacteria, parasites, and broken skin are some common reasons for fungus to grow out of control.

The best way to prevent fungus from spreading is to keep the aquarium clean and properly maintained. If there are aggressive fish in the tank, then they will need to be removed promptly to prevent any further damage to other fish. It is always best to prevent a disease than try and treat it and risk losing fish.

1 thought on “Goldfish fungus: Types of fungus, causes and treatments”

  1. Great post, we lost a lot of fish this way and couldn’t work out why. It wasn’t until we moved the tank from the kitchen bench into the loungeroom that the problem went away. Guessing it was food particles from cooking that was the problem.


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