The skin and gills become discolored, taking on an opaque, bluish-white to gray coloration. The area between the head and dorsal fin is generally the most severely affected. In advanced cases skin begins to swell, eventually shredding and falling off in strips. Gills are also affected and may be completely destroyed. Clamped fins, listlessness, hanging at the surface and gasping may also be seen. The fish may rub or scrape against objects in the aquarium in an attempt to relieve irritation.
Cause:
The ciliate Chilodonella cyprini. These heart-shaped parasites, at a size of 40 to 60 microns, are not visible to the naked eye. The parasites are able to swim freely, spreading easily from fish to fish. Reproduction occurs by asexual division.
Treatment:
Highly infectious and able to kill in great numbers, Chilodonella may very well be the most dangerous skin parasite there is. Overcrowding increases the risk of infection. Acriflavin Plus, Malachite Green, Paraform, Quick Cure or Formalin are the drugs of choice for Chilodonella. All fish as well as the aquarium they inhabit should be treated.