Fish Fungus

Updated April 21, 2020
Author: Sabi - Fishlore member
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Fish fungus is another common disease that affects fish. Most fish fungus infections are connected to water moulds from the class Oomycetes. From the many different types of fungi, saprolegnia is most commonly known to affect fish.

Saprolegnia is a filamentous fungi that can prove to be fatal if it is not treated in the early stages. As with all common moulds, it feeds by secreting digestive enzymes onto its surrounding area. These enzymes break down the cells and tissues on the surrounding object. The fungi then absorbs nutrients such as proteins and carbohydrates.

Fish Fungus Photo Credit: anike13

Water moulds are saprotrophs. Saprotrophs are organisms that obtain their nutrients from non-living organic matter, which in this case, will be fish waste, uneaten food, dead fish etc. However, they are opportunistic parasites that will take advantage on stressed or weakened fish.

Water moulds are made of a tangled group of filaments called hyphae. As the group of hyphae grows, it becomes compressed tufts that are collectively called mycelium. This mass of fungi filaments can be seen clearly without the aid of a microscope. The moulds reproduce by releasing thousands of spores into the water. Spores of fungi are always present in aquariums and ponds and cannot be eliminated.

This disease more often comes as a secondary infection. Occasionally it may act as a primary pathogen infecting fish that have not been suffering recently from any infection, mistreatment etc.

Fish that are handled roughly: their outer skin can be scraped off. When the skin's protective layer is damaged or removed it enables fungus to move in. Keep in mind that poor water parameters enable diseases to break out fast. Low temperatures, too, are primary causes.

Fish fungus also affect fish eggs, usually the unfertile ones, however if not treated soon enough it will spread to the fertile eggs as well.

The fungus appears as grey or white patches on the fish. Generally at first, saprolegnia establishes as small infections in a specific area and thereafter spreads rapidly over the body and gills of the fish. Sometimes there may be inflammation but unless there is an underlying bacterial infection it is not common.

Never under-estimate the danger of fish fungus. The danger with saprolegnia comes from the speed at which it spreads and the area that is damaged, in which case protein and serum is lost.

Fungus can be somewhat difficult to treat, however, our recommendation in treatment would be Maracyn or Rid Fungus. A 50% water change should be made before the dosage is applied as partial water change cannot be done during the time in which treatment is in process as it weakens the medication. When the treatment is complete, a 50% water change should be done again to help remove the medication.

Useful products to treat fish fungus:

Fungus Cure
Fungus Clear

About the Author:

Sabi is from South Africa and started fish keeping with goldfish five years ago. There after the hobby slowly but surely grew. I've kept Goldfish, Koi, Malawis and now tropical freshwater fish. I currently have two running tanks, a 67 gallon and a 2 gallon. The 67 gallon aquarium is a community tank consisting of Angelfish, Tetras, Rasboras, Plecos, gourami and corys and the in the 2 gallon I may add a betta. I one day hope to breed either Discus or Angelfish.