Fungal infections in Goldfish are relatively common, but they always tend to represent the same thing. First, let’s talk about the clinical appearance of a fungal infection.
The gross visualization of what appears to be a fungal infection is an unreliable means of diagnosis. Fungal infections usually appear as small to large tufts of white cottony material in the skin and fins of affected fish. The diagnostic challenge is that columnaris bacterial infections and Epistylis infections are grossly inseparable from Fungal infections grossly [to the naked eye]. You need a microscope to differentiate the conditions from each other reliably. Therefore it is not surprising to note that less than 25% [twenty five percent] of infections diagnosed as “fungal” truly are.
There are several fungal organisms, which infect Goldfish. The most common fungal pathogen of the skin is Saprolegnia. Under the microscope it has a very characteristic appearance: Saprolegnia appears similar to coarse strands of hair, by the hundreds organized in clumps.
Fungal infections are clinically relevant because they occur under two circumstances. There are serious, advancing cases wherein Goldfish which have been poorly handled, chilled, and stressed develop large areas of fungal growth, which cause depression and lethargy. This kind of fungal attack is seen only in fish that have suffered such mal-handling that their immune system is depressed or completely annihilated. The fish isolate themselves and eventually die. Fish with fungal lesions and which are lethargic or obviously ‘sick’ should be treated with Methylene Blue or potassium permanganate at half dose. Half dose would mean 2 PPM [two parts-per-million].
The second relevant clinical syndrome with fungus is the relatively harmless development of fungal lesions at the site of previous trauma. In these cases the fish is decidedly energetic, eating, and the lesions are restricted ONLY to those areas which were previously damaged. These fish may benefit from direct topical application of Methylene blue, malachite green or potassium permanganate paste. However, repeated water treatments are not needed because this second manifestation of fungal attack is self-limiting.
Fungal lesions in Goldfish should be considered worldwide. Fungal organisms are ubiquitous [everywhere] in the Goldfish’s natural environment and in every aquarium in the world, no matter how clean they may be. Fungal infections are ONLY seen in fish which are immune compromised or in tissues which have been damaged and left open to attack.
Remedies for fungal infections really depend upon how the fish present. A few members of a community may be affected with minor fungal lesions and in spite of the presence of these gross lesions, they may be eating and acting normally. These fish will benefit most by minimal handling, impeccable water quality and a higher plane of nutrition.
Fish which are depressed or ‘sick’ with fungal lesions will do well in warmer water, [780F] given enticing foodstuffs such as crushed freeze dried krill, and treated with Furazone Green, Methylene Blue or Malachite Green. See the formulary for dosages on these common medications.