The life cycle of ich goes something like this:
There are 4 stages to the life cycle.
The parasitic stage where you actually see the white spots on the fish is the Trophonts and lasts between 3--7 days.
After this, they are considered mature. At this stage, they drop off the fish and are free-swimming in the water column. Usually not more than 12--24hrs.
After the free-swimming stage, they settle to the bottom, in the sand bed or on rocks. At this stage they are reproducing inside the cyst. At this stage they are called Tomonts. This stage lasts between 3--28 days. Extremely variable on the time frame and it can only be attributed to tank conditions and particular strain of the parasite.
After the reproductive stage, the cysts burst open and release the new generation. These are called Theronts. They are free-swimming in the water between 24--48hrs. There is some argument that they can be free-swimming up to 72hrs at this stage, but it is very rare. This is the time when they seek a new host fish. If they do not find a host fish to infect, they are most certainly dead after 72hrs.
Okay, now we have a background on the parasite. How do you treat it?
The methods are debatable. As has been suggested already, it can range from isolation in a QT tank and treatment with copper, to hyposalinity, to simply letting the fish fight it on their own.
It's been suggested that certain species of fish can develope an immunity to reinfection after 2 or 3 infections. I wouldn't want my fish to go through 2 or 3 infections just so they might possibly develope their own immunity to the parasite. It's quite possible they wouldn't survive long enough to actually develope an immunity. How would you like to get the flu 3 times in a month just so that you could be immune to it for the rest of a season? :shock:
Hyposalinty really doesn't work. Research has been done where fish were dipped in freshwater for up to 18hrs and the Trophonts dropped off as normal and went onto the mature stage and successive Theront stage to reinfect another host. Obviously, the host fish died after 18hrs in fresh water, but the experiment shows that hyposalinity doesn't work. It doesn't work because the Trophonts are burrowed so deep into the fish's tissue, that the lower salinty has no effect. The theory is a good one. The lower salinity of freshwater will cause the cysts to explode, just as a copepod or saltwater nudibranch will do in lowered salinty or 100% freshwater. In reality, it doesn't work to treat ich and simply stresses an already sick and stressed fish.
Copper based medications can work, but again, they create stress in the fish. Itr can be used to treat the ich parasite, but must be used with extreme caution to avoid killing the fish. You should ALWAYS monitor copper saturation levels with a reliable test kit. Keep in mind that this is a SHORT TERM medication and you must not expose the fish to this for more than 48hrs at one time. The proper way to use copper medication for ich treatment is first to QT the fish. Now dose the copper medication into the water. Using a test kit, be sure you have the copper introduced at appropriate levels. After 48hrs. 50% of the water must be changed in the QT tank. And again in 24hrs after that--again 50% of the water must be changed to drop the copper levels in the water. The fish should be treated again 24-48hrs AFTER the second water change. Bring copper levels up to appropriate levels and allow the medication to work for 48hrs. The water must then be changed. 50% and again another 50% 24hrs later. At this point, water changes must be made every 24-48hrs to bring copper levels down to where they are undetecable. Leaving a fish exposed to high levels of copper for more than 48hrs can be lethal.
The fish should now be cured. But it is NOT ready to be introduced back into the tank.
The infected tank must be left without a single fish for as little as 6 weeks and as much as 8--10 weeks to ensure that all remaining parasites in the tank have died.
It has been suggested that a single strain of ich parasite should be dead after 11 months. That equates to about 34 life cycles. If you choose NOT to treat your fish in a QT tank and simply let them fight off the infection on their own--that particular strain of ich will be dead in 11 months. There is cell degradation with each successive life cycle. After 34 life cycles, there is so much cell degradation that the strain simply cannot continue to reproduce. So, if you HAVE ich, and you can keep it from killing your fish--it should go away in 11 months if you decide to just leave the fish in the tank and do nothing. NOT an option I'd ever consider.
If you can completely cure your fish in QT, and then wait the required 6--10 weeks before reintroduction into the tank, the ich cycle should be broken. You now have an ich free tank. That is, until you introduce another fish with ich. :shock:
