Fungus on Goldfish

goldfish image by martin schmid from

Fungus-related diseases are one of the leading causes of death in goldfish both directly and indirectly. Fungus is present at different levels in tanks at all times, but the amount of fungus present and the health condition of a goldfish will determine whether the fish gets infected or not.

Luckily, fungus is easy to prevent and treat in cases where it is diagnosed in the earlier stages.


Fungus rarely becomes a problem with goldfish if their tanks are well-maintained. Dirty water often brings on the growth of saprolegnia and achlya, which are the two most common fungal organisms in tanks. Healthy goldfish are usually strong enough to fend off the effects of the fungus, but those whose health has been compromised are susceptible to fungal growth. Once infected, the fungus feeds by using enzymes to digest the fish's flesh and it releases spores into the water to reproduce, thus repeating the cycle if left untreated.


Symptoms of a fungal infection on a goldfish are very apparent and visible unlike other diseases. The fungus often presents itself as a white fluffy growth on the skin or gills but can vary slightly in colour to greyish hues. If the fungus is left untreated, it may turn into a slimy material that will encompass the entire goldfish body. In addition to the unsightly symptoms, goldfish may become lethargic and exhibit additional symptoms related to other underlying diseases.

Related Diseases

Fungus is often associated or linked to other diseases or conditions in goldfish. One of the most common related causes is an injury. The fungus will begin to grow near the wound and slowly spread across the body. Finrot is another situation that may bring on a fungal infection. This disease is caused by bacteria eating at a fish's fins, which ultimately gives the fish the appearance of rotting away. Fungus in a dirty tank may take this opportunity to infect the site of rot.


Fungus is easy to treat in its earlier stages. Most pet stores and veterinary clinics sell anti-fungal solutions, such as methylene blue, for fungus treatment. This is added to the water in small amounts to kill the fungus present. Fish that are really bad off should be isolated from other fish and kept in clean water until it is fully recovered. In some cases where treatment is unsuccessful, the goldfish may be infected with another condition such as cotton-wool disease and should be treated accordingly.


Tank maintenance is the number one step in preventing fungal infections from occurring. A clean tank will not only keep the fungus levels in the water at a minimum, but also prevent the other conditions that may contribute to fungus. A tank that is cleaned weekly should adequately prevent fungus and waste build-up in the water.