Koi fungus diseases usually start by attacking a cut or other wound on the fish's body. Most often associated with dirty water conditions, koi fungus can be difficult to treat once it takes hold. Courses of treatment need to be directed not only on the fungus itself, but also at the root cause of the problem.
Facts
The most common koi fungus is called saprolegnia, and it can affect other pond fish as well. Fungus is particularly viable in koi in spring and autumn, on either side of natural inactivity periods. Fungal growths are not contagious, but they do go deep into the infected fish, making the visible symptoms only part of the problem. As the fungus grows, it not only eats away at dead tissue around a sore, but also attacks living tissue. Fungus can spread across a koi's entire body.
Identification
Fungus is noted by hyphae--cottony, wool-like strands hanging from koi. These strands may turn green in color as a result of algae growth on the fungus. The thread-like hyphae contain digestive juices that are released on a koi's tissue. If fungal growth occurs in the gills, it could be difficult to spot. The visible symptom may be a koi that hangs near the surface of the pond and gasps for air.
Pond Conditions
A dirty pond could be the result of overcrowding, insufficient water filtration, or simply a lack of proper care and cleaning. These problems need to be corrected to eliminate future fungus issues with koi and help any infected koi recover.
Treatment
Fungal infections can be especially difficult to treat when the disease is in its advanced stages. For individual fish, a daily salt bath can help remove the fungus. A solution of 1 to 3 grams of aquarium salt per liter of water will help restore minerals lost to the disease. Pond treatment requires the addition of malachite green to the water, and an increase in pond aeration. Knowing the volume of the pond is vital in determining correct dosages. Under-dosages can stress koi further, while not being effective enough to eradicate the fungus. Too large a dose could also be harmful to fish. Calculate volume by multiplying pond length, width and depth. Once the fungus is eliminated, treat the cut or sore as well.
Warning
An accurate diagnosis is important before beginning any fungal treatment. A bacterial disease known as flexibacter, and commonly referred to as cotton-wool disease, looks very similar to fungus on koi. But, since it is bacterial in nature, an entirely different treatment course is necessary.
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