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ALL ABOUT ICH
Common name: White spot disease, "Ick", Ich
Scientific name: Ichthyopthirius multifilis
Ich is a ciliated protozoan parasite that infests freshwater tropical fish, goldfish, koi, and other gamefish species. Ich is a relatively large protozoan, up to one mm in diameter. Ich infestations can wipe out an entire tank of fish or pond if left untreated.
The most common symptom is the appearance of white spots on the fish. The spots can be seen on fins, the body, and eyes of the fish. Infested fish may not immediately show the characteristic white spots. Ich infests the gills, feeding on cells and fluids. Gill tissue suffers extensive damage, leading to suffocation of the fish. Ich also infests the body and fins and can lead to secondary bacterial and fungal infections. In the early stages of infection fish may be seen scratching on ornaments, rocks, or gravel. In the later stages fish are often seen hanging near power filter outlets, pumping their gills, in an attempt to get oxygen. Some fish may sit of the bottom of the aquarium or pond. Infested fish often will not eat.
Ich parasites burrow just under the skin of fish, causing the characteristic "white spot" or trophont stage. At maturity, the adult parasite, called a tomont, detaches from the fish and swims freely for about six hours. The trophozite eventually settles to the bottom of the aquarium. The parasite then secretes a protective membrane. The "cyst" now undergoes many divisions, producing 1,000 or more offspring, called theronts. When the cyst breaks open, up to 1000 theronts emerge in search of a fish host. Theronts invade their fish host by burrowing into the skin with their cilia and digestive enzymes. The tomites feed on fish cells and tissue fluids until mature, starting the cycle over again. Tomites especially devastating to delicate gill tissue. The gills are destroyed by the destructive feeding action of the parasites, causing the fish to suffocate.
Considering that each trophozite releases about 1000 infective theronts, it is easy to see how fish can quickly succumb to an Ich outbreak. Water temperature controls the speed of the Ich life cycle. At 21° -24° C (70° -75° F) it takes about three days for a complete cycle.
Ich parasites can only be killed when they are in the free-swimming
theront stage. Medications do not kill the parasites attached to the
fish (white spot) or when the parasites are encysted in the gravel.
Disappearance of the white spots simply means that the parasites have
advanced to the cyst stage. In a few hours or days, depending on water
temperature, thousands of infective theronts will burst out in search
of a fish host. It is precisely at this point that the medication does
its job. Since not all the Ich parasites "hatch out" at the
same time, it is necessary to treat the aquarium or pond for several
days to insure control. When one fish has ick, all fish in the aquarium
or pond will be infected. All fish must be treated. Ich parasites are
easily transferred to other aquaria or ponds by nets, hands, boots,
etc. Quarantine the infested fish. Do not add or remove fish from the
infested aquarium or pond. Begin treatment immediately.