Ichthyophthirius multifiliis
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The ciliate, Ichthyophthirius multifiliis, is an obligate parasite that affects all species of freshwater fish, causing the disease ichthyophthiriasis, which is commonly referred to as ich or white spot. I. multifiliis is one of the most prevalent protozoan parasites of fish and is an important pathogen of ornamental and farm-raised food fish species when reared under intensive conditions. Wild fish populations are also susceptible and outbreaks are occasionally seen. There are few aquarists that have not met it on one or more occasions[1]. The I. multifiliis life cycle consists of the free-swimming, highly motile infective theront, which is approximately 40-50 micrometres in length; the fish associated trophont, which grows up to 800 micrometres in diameter; and the reproductive trophont, which leaves the fish and secretes a gelatinous cyst, in which it undergoes 7-9 divisions to produce 800-1000 daughter tomites. Highly dependant on water temperature, the entire life-cycle takes approximately 7 days at 25 °C (77 °F) to 8 weeks at 6 °C (43 °F). Marine ich is caused by a different ciliate, Cryptocaryon. Like other ciliates, I. multifiliis cells have a transcriptionally inactive germline micronucleus and a transcriptionally active somatic macronucleus.
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[edit] Prevention
Preventing the introduction of infected fish into the aquarium or pond is the only way to avoid Ich. Infected fish may be either subclinically infected (showing no symptoms or white spots)or clinically infected. Preventative measures against Ich include buying only healthy fish from reputable dealers; using quarantine and treatment procedures for ALL new fish before their introduction to the main group; preventing introduction of tomites/theronts on plants and hardware like nets, filters and pumps. Newly acquired, subclinically infected fish introduced to a tank or pond without quarantine and is the most common cause of Ich outbreaks.
[edit] Predisposing factors
There is no dormant stage in the lifecycle. Ich does not lie in wait for a weakened fish to infect. However, any factor that reduces immunity like changes in water temperature and quality may, in a subclinically infected fish, accelerate an outbreak of Ich. The prescence of ammonia, nitrite and high levels of nitrate in water does not in itself cause clinical cases of Ich. However poor water quality will stress fish, allow an outbreak to spread rapidly and increase mortality rates in infected fish.
[edit] Diagnosis
Typical behaviours of clinically infected fish include:
- Anorexia (loss of appetite, refusing all food, with consequential wasting)
- Rapid breathing
- Hiding abnormally/ not schooling
- Resting on the bottom
- Flashing
- Rubbing and scratching against objects
A subclinically infected fish will not show any of these signs. For example, a healthy fish with a newly attached trophozoite will not yet have clinical disease. The trophozoite will not become visible to the naked eye until it has fed on the fish and grown to one or two millimetres. A trophozoite attached to the gills usually is not readily seen. A subclinically infected fish may initially only have a single trophozoite.
[edit] Skin
Visible Ich lesions are usually seen as one or several characteristic white spots on the body or fins of the fish. The white spots are single 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.
 This Siamese fighting fish developed spots characteristic of ich (including one between his eyes) upon arrival from a pet store. The symptoms disappeared after treatment with a parasite-preventing water additive. |
 This Cichlid is affected by the disease in further state. |
 Two juvenile clown loaches with ich. Characteristically, for this stage of infestation, both are hiding in an ornament. |
 Two juvenile clown loaches with ich. The second can be seen hiding in the ornament. |
[edit] Fins
Fins are folded and show white spots about 1 mm in diameter.
[edit] Eyes
Eyes may appear cloudy or milky.
[edit] 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.
[edit] 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.
[edit] 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 fish quicker. Temperatures at or above 30 °C (86 °F) are generally considered to be fatal to ich[2]
[edit] 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% (100 mg/L; pure water at Template:Convert/LoffAoffDorSoffT), would require large quantities of salt. Fish can be dipped in a 0.3% (3000 mg/L; pure water at 4 °C) solution for thirty seconds to several minutes, or they can be treated in a prolonged bath at a lower concentration (0.05% = 500 mg/L; pure water at 4 °C). Salt at low concentrations (0.01 to 0.05% solution) is an excellent[citation needed] 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)[citation needed] [2].
Salt treatment can be combined with heat treatment.
[edit] 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).
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.
[edit] 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.
[edit] Gravel vacuuming
Vacuuming the top layer of substrate with a siphon device will reduce the amount of organic matter in the aquarium. Organic matter reduces the activity of many Ich treatments. Gravel vacuuming is not effective in reducing parasite load.
[edit] Prognosis
When Ich is diagnosed early, effective treatment is used and stresses are minimised, mortality rates can be low. However if the infection is at an advanced stage,treatment protocols not followed and the fish are stressed, higher death rates will occur. When a fish has had Ich eradicated, it may develop partial resistance to reinfection. Partially treated fish may initially harbour low numbers of unseen trophozoites, often in the gills. This subclinical carrier will cause another outbreak weeks later, especially when for example stresses occur or uninfected fish are introduced to the aquarium.
[edit] References
[edit] External links
- Life cycle and treatment of Ichthyophthirius in layman's terms.
- Disease profile for ich
- Shirlie Sharpe's Your Guide to Freshwater Aquariums
- Detailed life cycle of Ichthyophthirius multifiliis at MetaPathogen
- Treatment information for freshwater Ich at the Aquarium Wiki
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