[cheeks69]

What is Black Spot Disease?
Also referred to as Black Ich, this saltwater fish disease is caused by a small parasitic turbellarian flatworm in the genus Paravortex that takes up residence in the aquarium substrate. The adult worm attaches to a host for about six days, falls off into the substrate, then in about five days the adult body ruptures releasing a new population of young worms and the cycle begins again. It normally does not show up in the larger numbers as with other forms of Ich (Whitespot Disease and Coral Fish Disease) and is not nearly as dangerous. It is a disease that is fairly common with Yellow Tangs and Angelfishes, but can effect other fish species as well.

http://saltaquarium.about.com/cs/com...a/aa041701.htm

It should be noted that anemonefish may develop black spots on their skin through contact with corals, corallimorphs, zoanthids and anemones with which they are not familiar. These spots tend to be larger and less uniform than those from turbellaria.

http://www.petsforum.com/personal/tr.../blackich.html