The cotton-like growth/tuft is generally an actual fungus (Saprolegnia) (Ill. 107-114),
but in some cases the symptoms may have been caused by parasites, Stalked Ciliates
These symptoms usually occur after damage or after infections caused by parasites or bacteria.
See also WHITE PATCHES ON THE SKIN:
- Ill. 35: Oranda with a white head caused by fungus following a bacterial infection?
- or Ill. 34: Guppy with a white head caused by the Tetrahymena parasite.
See also SPOTS, Ill. 99 White fin edges on Scatophagus caused by a virus (Lymphocystis).
The latter is easily mistaken for fungal infection.
Tip: Whitish cotton-like growths on the skin or fins are not always fungal infections.