Ichthyophthirius
Encyclopedia
Ichthyophthirius multifiliis (commonly known as freshwater white spot disease, freshwater ich, or freshwater ick) is a common disease
of freshwater fish
. It is caused by the protozoa
Ichtyopthirius. Ich is one of the most common and persistent diseases.
The protozoan is an ectoparasite. White nodules that look like white grains of salt or sugar of up to 1 mm appear on the body, fins and gills. Each white spot is an encysted
parasite.
The ich protozoa goes though the following life stages:
This life cycle is highly dependent on water temperature, and the entire life cycle takes from approximately 7 days at 25 °C (77 °F) to 8 weeks at 6 °C (42.8 °F).
Marine ich is a similar disease caused by a different ciliate
, Cryptocaryon irritans.
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.
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 myself, the mutifiliis trophozoites.
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.
and goldfish
, but even in those cases, a higher water temperature will accelerate the life-cycle of the parasite, allowing other treatments to take effect sooner.
, chelated copper, copper sulfate, potassium permanganate
and quinine
. There are also a large number of proprietary treatments available for the treatment of white spot, and the related Oodinium
(velvet disease). All treatments target the free-living theronts and tomont
s, which only survive about two to three days in the absence of a host fish.
Partially treated fish may initially harbour low numbers of unseen trophozoites, often in the gills. This subclinical carrier will cause another outbreak weeks later, most likely when stresses occur or uninfected fish are introduced to the aquarium.
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
of freshwater fish
Freshwater fish
Freshwater fish are fish that spend some or all of their lives in freshwater, such as rivers and lakes, with a salinity of less than 0.05%. These environments differ from marine conditions in many ways, the most obvious being the difference in levels of salinity...
. It is caused by the protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
Ichtyopthirius. Ich is one of the most common and persistent diseases.
The protozoan is an ectoparasite. White nodules that look like white grains of salt or sugar of up to 1 mm appear on the body, fins and gills. Each white spot is an encysted
Microbial cyst
A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed down and...
parasite.
Description
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.The ich protozoa goes though the following life stages:
- Feeding stage : The ich trophozoite (a protozoan in active stage of life) feeds in a nodule formed in the skin or gill epithelium.
- After it feeds within the skin or gills, the trophozoite falls off and enters an encapsulated dividing stage (tomontTomontTomont is a protozoan, especially of the Apicomplexa, in the active stage of its life cycle, which develops into an encyst....
). The tomont adheres to plants, nets, gravel or other ornamental objects in the aquarium. - The tomont divides up to 10 times by binary fission, producing infective theronts, thus dividing rapidly and attacking the fish.
This life cycle is highly dependent on water temperature, and the entire life cycle takes from approximately 7 days at 25 °C (77 °F) to 8 weeks at 6 °C (42.8 °F).
Marine ich is a similar disease caused by a different ciliate
Ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...
, Cryptocaryon irritans.
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 presence 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.Diagnosis
Typical behaviours of clinically infected fish include:- AnorexiaAnorexia (symptom)Anorexia is the decreased sensation of appetite...
(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.
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.Eyes
The eye becomes cloudy almost to the point of whiteness and the fish lose vision. The causes behind this disease can vary. An increase in parasites in the aquarium is the most common cause but severe stress, old age, or malnutrition can all lead to this condition. Treating this condition requires an investigation of water quality. Once the water quality is high enough, the fish will usually recover by themselves within 1–2 weeks. Thus, it is advisable to wait for 1–2 weeks before administering antibiotics.Gills
GillGill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
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 myself, the mutifiliis trophozoites.
Treatment
Unfortunately, an efficient prevention of the disease by vaccination is not possible, although several studies identified potential vaccine candidate proteins, i.e. i-antigens, of the parasite.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. However, it can only be used on fish that can tolerate high water temperatures, and is unsuitable for cold water fish like koiKoi
or more specifically , are ornamental varieties of domesticated common carp that are kept for decorative purposes in outdoor koi ponds or water gardens....
and goldfish
Goldfish
The goldfish is a freshwater fish in the family Cyprinidae of order Cypriniformes. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish....
, but even in those cases, a higher water temperature will accelerate the life-cycle of the parasite, allowing other treatments to take effect sooner.
Chlorine
For treating koi & goldfish, chlorine, in the form of tapwater, is very effective in removing not only the threadlike parasites, but eventually the persistent cysts. Thread like infestations on fish will disappear overnight, cysts will take a couple of weeks and possibly a couple of water changes to eliminate. Aquarium lighting is used to detect the presence of parasites, as the filament like threads fluoresce at these light frequencies.Salt
One 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 4 °C (39.2 °F)), would require large quantities of salt. Fish can be dipped in a 0.3% (3g/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 (0,5g)/L; pure water at 4 °C).Chemical treatments
Chemical treatments include formalin, malachite greenMalachite green
Malachite green is an organic compound that is used as a dyestuff and has emerged as a controversial agent in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper...
, chelated copper, copper sulfate, potassium permanganate
Potassium permanganate
Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4− ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely purple solutions, the...
and quinine
Quinine
Quinine is a natural white crystalline alkaloid having antipyretic , antimalarial, analgesic , anti-inflammatory properties and a bitter taste. It is a stereoisomer of quinidine which, unlike quinine, is an anti-arrhythmic...
. There are also a large number of proprietary treatments available for the treatment of white spot, and the related Oodinium
Oodinium
Oödinium is a genus of microscopic parasitic dinoflagellates. They live off salt and fresh water fish, causing a type of fish velvet disease . One species has also been recorded on various cnidarians .The host typically develops small yellow or gold dust scattered on its head, fins and body...
(velvet disease). All treatments target the free-living theronts and tomont
Tomont
Tomont is a protozoan, especially of the Apicomplexa, in the active stage of its life cycle, which develops into an encyst....
s, which only survive about two to three days in the absence of a host fish.
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 are 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, most likely when stresses occur or uninfected fish are introduced to the aquarium.
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