[Beverly]

From this webpage, Marine "Ich":

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

Is "Ich" always present in our aquaria?

There is a widely held belief in the marine aquarium hobby that "Ich" is always present in our aquaria and this belief is often repeated on marine bulletin boards. There is much information in the scientific literature that contradicts this belief.

C. irritans is an obligate parasite (Burgess and Matthews, 1994; Dickerson and Dawe, 1995; Yoshinaga and Dickerson, 1994). Obligate means the parasite can not survive without infecting its host, in this case, fish. Theronts have been shown to die if a suitable host is not found within the required time. Yoshinaga and Dickerson (1994) found that few theronts (0.34%) were viable 12.5 hours after excystment and Burgess and Matthews (1994) found that no theronts were viable 18 hours after excystment. Colorni (1985) found that some excysted tomites (=theronts) were observed to be moving weekly after 48 hours. While the life span of the theronts appears variable, it is limited and all will die without finding a suitable host.

If an aquarium has no fish in it, and there are no additions of fish, or anything else that could be carrying trophonts, tomonts, tomites or theronts for a period of 6 weeks or longer, all parasites will have died. An aquarium such as this is an obvious exception to "Ich" always being present.