Classification: Taxonomic ranks under review (cf. Illustrated Guide to Protozoa, Allen Press). Protista (unicellular eukaryotes) Ciliophora (with cilia, nuclear . Ichthyophthirius multifiliis is a ciliated protozoan that causes. “Ich” or “white spot disease.” This disease is a major prob- lem to aquarists and commercial fish. The name Ichthyophthirius multifilis translates to “fish louse with many children”, a title that fits well, as each parasite may produce more than a.

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Ichthyophthirius multifiliis is a large, ciliated protozoan that causes “Ich” or “white spot disease. All species of freshwater fish are considered susceptible, and the parasite has been found in all areas of the world in both cultured and wild fish. These large parasites cause the characteristic white spots that are often seen on the skin and fins of infected fish.

The disease is highly contagious and spreads rapidly from one fish to another without the need for additional hosts direct life cycle. The disease is particularly severe when fish are crowded. The organism is unusual in that it is an obligate parasite, which means that it cannot survive unless live fish are present. Although Ichthyophthirius multifiliis has a direct life cycle, it is fairly complex and has three distinct life stages: Because of the covering by this epithelial tissue and mucus, the trophont stage is protected from chemical treatment.

Once the trophont is mature, it stops feeding, leaves the fish, and becomes a tomont. The tomont quickly secretes a gelatinous-walled outer cyst that allows it to stick to surfaces in the environment. This can occur in a day or less at warmer water temperatures.


The gelatinous wall of the tomont cyst protects it and the daughter tomites from chemical treatment. The tomites begin to develop and become theronts within the tomont cyst. Following a period of days warm water temperatures or jchthyophthirius cool water temperaturesthe theronts bore out of the tomont cyst and become free-swimming, infective parasites in search of a fish host.

This free-swimming phase is unprotected ichthyophthiriuz, therefore, highly susceptible to chemicals. Treatment protocols should be designed to target this theront stage. Life cycle of Ich. These lesions look like small white dots, blisters, or salt grains on the skin or fins of the fish.

The white spots may not be as obvious on fish that are white or pale in color, or if the infection is limited to the gills. By the time the white spots are visible to the naked eye, the infected fish is very sick. Prior to the appearance of white spots, fish may have shown signs of irritation, flashing, weakness, loss of appetite, and decreased activity. If the parasite is only present in the gills, white spots multiriliis not be seen at all but fish will die in large numbers.

In these fish, gills will often be pale and very swollen. White spots should never be used as the only means of diagnosis because other diseases may have a similar appearance.

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Gill and skin biopsies should be collected and examined with a light microscope when the first signs of illness are observed. To do this testing, a glass coverslip can be lightly scraped down the slide ichthyophthirijs a fish in the direction of head to tail iichthyophthirius remove some skin cells preferably with some of the white spots and mucus. A small area of gill or fin may also be carefully clipped using small, sharp scissors. Keep all tissue pieces small to minimize any harm to the fish.

Further, it is very hard to view the parasites when examining thick tissue sections. Mount the skin, fin, and gill samples separately in drops of tank or other fresh water on a microscope slide and overlay gently with a glass coverslip.

Do not use chlorinated tap water, reverse osmosis water, or distilled water. Bottled spring water can be an acceptable clean, fresh water source.


The mature trophont is large, oval to round, dark in color due to the thick cilia covering the entire celland measures 0. This stage also has a horseshoe- or C-shaped nucleus that may be visible under 40x magnification Figure 3.

The parasite moves slowly in a rolling, sometimes amoeboid motion and, with practice, is easily recognized. The immature, free-swimming ichthyophthriius are smaller, pear- or spindle-shaped, translucent, and move quickly, continuously spinning on its longest axis as it swims. Theronts can resemble other parasites especially Tetrahymenaso if only this juvenile stage is seen, prepare a second slide and examine it closely for the trophont stage to confirm the diagnosis.

Preventing introduction of this parasite is one of the most important reasons all incoming fish should be quarantined. Transport miltifiliis handling can cause newly arrived fish who may be asymptomatic carriers those with no obvious clinical signs to break with active disease, serving as a source of infection for other fish they may come in contact with.

At the warm water temperatures required for many aquarium fish, active disease will often become evident 1—3 weeks after shipping. For this reason, a minimum day quarantine period is recommended for new fish.

The importance of this quarantine period for aquaculture or public aquarium facilities cannot be over-emphasized. Additionally, because the environmental tomont cyst is sticky, it can easily spread between systems. For this reason, nets, siphon hoses, and other equipment that have not been disinfected should not be shared between tanks, ichthyophthiriuz in a quarantine area.

Control of this parasite can be difficult because of its complex life cycle and multiple protected stages. The role of water temperature in determining the timing of treatment application is also critical and is discussed in more detail below. Of the life stages shown Figure 1only the free-swimming ichthyophfhirius are susceptible to chemical treatment. This means that the application of a single dose of a treatment will only kill theronts that have emerged from the tomont cyst and have not yet burrowed into the skin or gills of a host fish.

This single treatment dose will not affect organisms that emerge after the chemical has multfiiliis down or been flushed from the system. Appropriately timed, repeated treatments, however, will continually kill the juvenile, infective theronts, preventing continuation of the infection.

The disease outbreak will be controlled as more adult trophonts drop off the sick fish, encyst, and produce theronts that cannot survive the chemical treatment in the water. In a tank or vat, this process can be greatly enhanced if organic debris is removed following treatment.

Because the sticky cyst of the tomonts may attach to organic material, cleaning this debris will help remove many cysts from the environment, further decreasing the number of emergent theronts.

Any dead fish should be removed as soon as they are seen because mature trophonts will quickly abandon a fish once it has died and begin reproducing in the environment. At these temperatures, chemical treatments should be applied daily and a minimum of 3 to 5 treatments is required.

At cooler temperatures the life cycle is prolonged, and treatments should be spaced further apart. Fish should be closely watched during recovery because the weakened fish may be susceptible to a secondary bacterial infection.

Most aquacultured channel catfish in the southeast United States are reared in ponds. The chemical is effective and relatively inexpensive, an important consideration when large volumes of water are treated. The disadvantage of copper sulfate is that it is extremely toxic, particularly in water of low alkalinity. NEVER use copper sulfate without first testing the total alkalinity of the water, carefully measuring the dimensions of the pond to be treated, and weighing the amount of chemical to be applied.

The concentration of copper sulfate to apply in freshwater is calculated by determining the total alkalinity of the water and dividing that number by Because copper sulfate is an algaecide, its use may lead to severe oxygen depletions; therefore, emergency aeration should always be available.


Use of copper sulfate during hot weather or when algae phytoplankton blooms are dense is strongly discouraged. Formalin is not the ideal treatment for ponds, but it works well in tanks.

Market availability changes, these products are approved to treat external parasites on all species of fish at all life stages. In addition to chemical treatment, cleaning the tank will also decrease the number of parasites. Sick fish may be unable to tolerate a full treatment. If they appear stressed or try to jump out of the tank, flush the chemical from the system immediately with clean, well-oxygenated water.

A slight increase in salinity can help decrease osmoregulatory stress caused by the damage to the external tissues of the fish. Because theronts are intolerant to increased salinity levels of 3—5 ppt, salt is often added to aquaria or tanks that are being treated with formalin to enhance the response to treatment. Most freshwater fish can tolerate 5 ppt salinity for several weeks and many can live in 3 ppt permanently; however, it is important to know the specific tolerances for each species to be treated.

Although potassium permanganate is a good choice for many external fish parasites, the repeated treatments necessary in a short period of time make it a more dangerous choice for control of Ich. Potassium permanganate is a strong oxidizer, and its use more than once a week is discouraged to prevent damage to the skin, gills, and eyes of the fish. A number of commercial preparations are available from pet stores that contain one or more of these agents.

In addition to chemical treatments, cleaning the tank every other day will help remove cysts attached to debris before the theronts emerge thereby helping prevent reinfection of the fish and completion of the life cycle. The most characteristic features of the mature trophont stage of the parasite are a continual rolling, amoeboid motion and a horseshoe-shaped nucleus, both of which are easily recognized during a microscopic examination of infected tissue.

Quarantine is an effective way of preventing this disease. In contrast to most parasitic diseases where the decision to treat or not to treat is based on the degree of infestation and other factors, fish infected with even a single “Ich” parasite should always be treated immediately because of its explosive reproductive rate. A single treatment is not sufficient for this disease because the life stage on the fish trophont and the stage encysted in the environmental tomont are resistant to chemicals.

Only the infective theront stage is susceptible to treatment. Repeating the appropriate chemical treatment will disrupt the life cycle and control the outbreak. Daily cleaning of the tank is also beneficial because tomonts attached to organic matter can be physically removed from the environment.

Fish that have survived an “Ich” infection are known to be potential reservoirs of the parasite and may cause other fish to become infected. Careful attention to management practices, such as quarantine and multiple treatments when outbreaks occur, will minimize economic loss from this disease.

Use of copper in freshwater aquaculture and farm ponds. Use of formalin to control fish parasites. Pages — In P. Fish diseases and disorders — volume 1: Pages 55—72 In P. Ich White Spot Disease. Southern regional Aquaculture Center, Publication No. Original publication date March Visit the EDIS website at http: The Institute of Food and Agricultural Sciences IFAS is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.