Fungal Infections in Fish

By PetMD Editorial on Aug. 1, 2008
Fungal Infections in Fish

Saprolegnia and Ichthyophonus Hoferi


Fungal infections in fish can cause damage to multiple body systems, such as the liver, kidney, and brain, and usually occur when the fish is in a weakened state, either due to injury or trauma. It can also develop if a fish is placed in poor living conditions (i.e., substandard water quality or an overstocked fish tank).


Saprolegnia and Ichthyophonus hoferi are two such fungi that can be found in fish, whether they are kept in tanks, aquariums or ponds.


Symptoms and Types

The Saprolegnia fungus infects fish (or its eggs), affecting its internal organs and deeper tissues. Symptoms include light gray, cottony growths on the skin, fins, gills, and eyes.


The Ichthyophonus hoferi fungus mainly infects older fish which are kept in aquariums. However, it is an uncommon fungal infection that typically occurs due to infected raw fish food. If left untreated, it may prove fatal for the fish. Symptoms are species-specific, but unlike Saprolegnia, it will present small black growth in the skin. This fungus also causes bulging eyes, loss of color, ulcers and cysts in internal organs, and sometimes causes fish to swim in abnormal circular movements.



The Saprolegnia fungal infection is caused by having an unclean environment containing dead and decaying organic matter.


The transmission and cause of the Ichthyophonus hoferi fungus is unknown, but keeping a clean environment for your fish is always a good practice.


Treatment of the Saprolegnia infection is accomplished by medicating the water with potassium permanganate, after removing skin pathogens. While increased salt levels, combined with good electrolyte and calcium levels in the water, are good treatment options for an Ichthyophonus hoferi infection, another possible measure is raising the water temperature to 82 degrees Fahrenheit (consult a veterinarian first), as the Ichthyophonus fungi are more virulent in colder waters.

It is important to thoroughly clean and sanitize the fish tank, aquarium, or fishpond for either of these injections.



Removing dead infected fish, sanitizing the environment, and not feeding your pets raw fish are all good ways to prevent either of these fungal infections.

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