While many fish diseases have similar symptoms, diagnosing goldfish pond fungus is not difficult. If your fish have new protrusions on their bodies that have a fluffy appearance and are colored white or grey, chances are good a fungal infection is to blame. As fungal infections generally are considered secondary diseases, it is important to turn the tide against this invader so you can address whatever other conditions are affecting your fish.
What Is It?
Goldfish pond fungus is somewhat misnamed in that the fungus actually is on the fish. Practical Fishkeeping describes it as a white-grey, cotton wool-like growth projecting from the body surface. Fins, skin, eyes or gills can be affected. In the beginning stages, the fungus may affect only one specific part of the body. If left untreated, it will spread to other body parts.
What Causes It?
Scientifically speaking, this goldfish fungus is called Saprolegnia. Fish Channel tells us that three aquatic fungi culprits are to blame: Saprolegnia, Achlya or Dictyuchus. While in taxonomy terms each of these fungi are slightly different, their basic characteristics are virtually identical. Fish Channel claims that even fungi specialists have trouble sorting them out and advises aquarium enthusiasts simply to view them as a single invader in terms of treatment.
Conditions That Make Fungus Thrive
This fungus infection is most common in koi or goldfish that are either too cold or too stressed, according to the website Pond Crisis. Fish that already are weakened due to a compromised immune system are more likely to have goldfish pond fungus develop on their bodies. Practical Fishkeeping advises that this fungus rarely attacks healthy and unstressed fish. This means it is recommended to investigate the cause of the fungus versus simply treating it. Some possibilities include dirty water conditions, overcrowding in the pond, skin injuries from debris in the pond, improper diet and water temperatures below the long-term tolerance level for that species. Fish Channel suggests checking water quality, pH, temperature and oxygen levels. Also, check for residual chlorine and high ammonia and nitrate levels.
Pond Crisis advises not to treat a fish with fungus if itstill is schooling with the rest of its pond-mates. This is true especially if the fish still is eating. Monitor this fish for changes and take action if the fungus infection becomes worse. Aquarium Knowledge suggests trying to treat the entire pond before isolating individual fish. If it become necessary to treat fish singularly, Pond Crisis directs separating the infected individual and raising the water temperature in the treatment tank by one degree per hour until reaching 76 to 78 degrees Fahrenheit.
Use of Malachite Green
Fish Channel advises treating infected fish by bathing them in water treated with malachite green. While not legal for use in fish raised for food in the United States and Canada, it is allowed for treating ornamental species, such as goldfish. This synthetic dye frequently is used to color silk, wool, jute, leather, cotton and paper, and it also is found to be extremely effective in controlling the Saprolegnia fungi most commonly the cause of goldfish pond fungus.
Amy M. Armstrong is a former community news journalist with more than 15 years of experience writing features and covering school districts. She has received more than 40 awards for excellence in journalism and photography. She holds a Bachelor of Arts in communications from Washington State University. Armstrong grew up on a dairy farm in western Washington and wrote agricultural news while in college.