Here's a little snippet of info on the life cycle of ick...
Life Cycle - Ich is most often introduced into an aquarium by a fish carrying trophonts. However, cross contamination from theronts or a tomont brought in on a coral/invert are other possibilities. Assuming we are dealing with a fish carrying trophonts, this is how the life cycle plays out:
1. A trophont will typically spend 3-7 days feeding on a fish, before dropping off to become a protomont.
2. The protomont crawls around for 2-18 hours, looking for a surface to encyst upon. Once it finds this, it sticks to the surface, and begins the encysting process. The parasite is now called a tomont.
3. It takes about 8-12 hours for the cyst to harden around the tomont. After this, the tomont goes into “reproductive mode” producing numerous daughter tomites. These tomites are then released into the water column as theronts. How long it takes for theronts to be released varies greatly, depending upon which strain of ich you are dealing with. The average time is 2 weeks, with 35 days usually being the maximum; however in at least one study (Colorni and Burgess 1997), it took 72 days for all the theronts to be released from a group of tomonts.
4. The now “free swimming” theronts seek out fish to feed on, thereby becoming trophonts, and the cycle starts all over again. A given strain will die out after 100 generations or so. Given the average life cycle of ich is 2 weeks, this could take almost 4 years (on average).
As you may have noticed, the timing for each stage to “move forward” to the next varies considerably. Therefore, ich is rarely in sync. For example, it is not unusual for a fish to be battling trophonts, while simultaneously theronts are swimming around looking for a host to feed on. This is especially true if your tank is plagued by more than one strain of ich. It’s this “perfect storm” that sometimes allows ich to overwhelm an immune system and the fish dies.
