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Ichthyophthirius multifiliis

Ichthyophthirius multifiliis is a species of ciliate protozoan which parasitizes freshwater fish; the disease it causes is usually called ich or white spot. It is probably the most common aquarium fish parasite and there are few Aquarists that have not met it on one or more occasions. "Ich" (the colloquially abbreviated form of the name) is the largest known parasitic protozoan found on fishes. Adult organisms are oval or round and measure 0.5 to 1.0 mm in size. The adult is uniformly ciliated and contains a horseshoe-shaped nucleus which can be seen in older individuals. The disease becomes especially serious in enclosed areas, where it spreads quickly from one fish to another. Ich is the disease responsible for the most fatalities in freshwater aquarium fish and can cause notable damage to aquaculture. Marine ich is caused by a different ciliate, Cryptocaryon.

After approximately one week of parasitism, mature trophozoites leave their host, settle to a substrate and secrete a cyst. The encysted cell, called a tomont, undergoes rapid division over approximately twenty-four hours to produce 600-1000 daughter cells called tomites. Once these reach maturity, they exit the cyst and develop into a theront stage, which is highly mobile. Theronts then infect new fish, digging their way into exposed parts, under the scales, or more commonly into its gill plate. The entire life-cycle takes about seven to ten days to complete.

Prevention

It is important to note that the Ich parasite is present in almost every tank. Prevention is key to avoiding an outbreak. Preventative measures against Ich include buying only healthy fish from reputable dealers, proper acclimatization techniques such as not transferring water from other aquariums, separating already-sick fish from healthy fish through quarantine, maintaining high water quality, and not overstocking.

Adding a small amount of aquarium salt according to the directions on the aquarium salt package may also help prevent Ich. However, beware that not all freshwater fish can handle salt in their water. Some "skin fish," like most loaches and some catfish, are very susceptible to burning from salt.

Predisposing factors

Ich outbreaks usually occur when new fish are introduced or during times of stress. Elevated ammonia or nitrate levels or sudden changes in temperature can also bring about a latent infection. A sudden chilling of the fish, which can easily occur when they are being transported, is often sufficient to take the parasite from its latent state to the reproductive phase.

Diagnosis

Typical behaviours of ich infected fish include:

Anorexia (loss of appetite, refusing all food, with consequential wasting)
Hiding abnormally
Flashing
Rubbing and scratching against objects

Tropical fish are vulnerable to a large variety of diseases. As such, ich treatment should not be applied unless one or more of the fish is exhibiting the characteristic white spots.

Skin

Ich infections are usually visible in the form of characteristic white spots on the side of the fish. The white spots are pockets of fish epithelia containing Ichthyophthirius cells called trophozoites or trophonts, which feed on the tissues of the host and may grow to 1 mm in diameter. A smear should show ciliates if white spot is present.

Fins

Fins are folded and show white spots about 1 mm in diameter.

Eyes

Eyes may appear cloudy or milky.

Gills

Gill infection will cause breathing at the surface and fast respiration. Gill examination may show numbers of such white spots. Wet mount of a Gill Biopsy may show I. mutifiliis trophozoites.

Treatment

Any treatment method must take into account the species of fish (some will not tolerate certain medications), how high the infection rate is, and the size and type of environment.

If it is detected before it becomes too serious, a number of different treatments can be applied. Only the free-swimming stage of the parasite is susceptible to treatment; neither the trophonts under the epithelium nor the tomont cysts can be killed.

Heat treatment

Heat treatment can be highly effective, and it can be combined with other treatments.

The three phases of the ichthyophthirius life-cycle (Adult, Cyst, Free swimming) take about 4 weeks at 21 °C (70 °F) to complete but only 5 days at 27 °C (80 °F). For this reason it is recommended that the aquarium water be raised to 28-30 °C (82-86 °F) for the duration of the treatment. Avoid fast temperature changes; water temperature should be raised or reduced gradually 0.5-1 °C (1-2 °F) per day. There are species of fish that will not tolerate the high end of temperatures needed to be effective. If the fish can stand it, raise the temperature even higher, up to 30 °C (86 °F). Raising the temperature also, presumably, reduces and kills the free swimming parasite. It is important to remember that raising the temperature higher, but not high enough so that the parasite is killed, should be used in conjunction with some sort of medication. The heat speeds up the life cycle of the ichthyophthirius, which is useful if the fish is being medicated, because otherwise the parasites simply reproduce at a faster rate, and kill the aforementioned fish quicker. Temperatures at or above 30 °C (86 °F) are generally considered to be fatal to ich

Salt

In small tanks, the most recommended method of treatment for ich consists of adding aquarium salt until a specific gravity of 1.002 g/cm³ is achieved, as the parasites are less tolerant of salt than fish. This is not practical in ponds because even a light salt solution of 0.01% (10 mg/L), would require large quantities of salt. Fish can be dipped in a 0.3% (300 mg/L) solution for thirty seconds to several minutes, or they can be treated in a prolonged bath at a lower concentration (0.05% = 50 mg/L). Salt at low concentrations (0.01 to 0.05% solution) is an excellent means of controlling "Ich" in recirculating systems without harming the biofilter. Care should be taken to avoid damaging aquatic plants and salt intolerant fish. In particular, do not use salt with sensitive soft water Tetras such as Neons, Cardinals and Glow-Lights or scaleless Catfish and Loaches (which can be easily burned if salt is not pre-dissolved) .

Salt treatment can be combined with heat treatment.

Chemical treatments

Chemical treatments include formalin, malachite green, chelated copper, copper sulfate, potassium permanganate and Quinine Sulfate. Because they can be harmed by these treatments, certain plants and invertebrates, such as snails, should be removed before application. There are also a large number of proprietary treatments available for the treatment of white spot, and the related Oodinium (velvet disease). Although based on the chemicals mentioned above, they are generally considered to be better for the safety of both the aquarist and fish than the pure chemical form of the treatment. All treatments target the free-living theronts and tomonts, which only survive about two to three days in the absence of a host fish, so treatment should be continued until a few days after the last white spot has disappeared from the fish. This will usually take about a week; 10 days is typical at 27 °C (80 °F) and 6 days at 29 °C (84 °F). But the best , quickest and most thorough treament and removal of ICK is Magnesium. Bring the level of Magnesium to 28 (parts per million), roughly 1 and 1/4 teaspoon for a 50 gallon tank. No temperature change, salinity change or isolation of any invertabrate, coral or fish is necessary. The ICH will start to disappear in 24 hours, gone in 3 days. After 1 week bring your Mag level back to normal for your tank size.

Fish transfer

Ich can be treated with a transfer method. Fish are moved daily into a different tank with clean, conditioned, warmed water. Parasites that fall off of the fish are left behind in the tank. After moving the fish daily for 7-10 days, the fish (presumably cured) can be put back into the main tank. The disadvantage of this method is that it stresses both fish and fishkeeper.

Gravel Vacuuming

Vacuuming the surface of the gravel with a siphon device can remove the parasite at cyst stage. Try not to stir up the water too much as it just blows the cysts all over.

Cautions

All medications, to some degree, are toxic not only to the parasite but also to the fish. Grossly weakened fish will not tolerate medication that more robust and less infected ones may. Bottom feeders such as catfishes, scaleless fish, and many tetras are adversely impacted by the use of malachite green.

Malachite green is hazardous to handle: it is known to cause blator problems, mutations, and is harmful to fetuses. Gloves and a protective mask should always be worn when handling the concentrated powder. Pregnant women should never handle this chemical. There are claims that malachite green might increase in toxicity to fish as the temperature increases. You may want to reconsider your decision to use malachite green if you intend to raise the temperature at the same time, or if you already maintain your temperature at a higher level than normal. Malachite green also tends to stain the plastic and silicone in the aquarium.

Prognosis

If the disease is diagnosed early and effectual treatment is applied, the outlook is excellent. However if the infestation is at an advanced stage, mortalities should be expected. Note that when a fish has been cured from Ich, it will usually form an immunity to the infection.