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Perhaps the most common, easily identified fish malady is ich. It appears symptomatically as small white specks about the size of table salt on the fins and bodies of fishes. Also indicative of ich infections are lethargy, clamped fins, hiding in corners, "scratching", rapid and labored breathing, and off-gray body coloration in the case of hyper-infections.
Most all fishes, especially in juvenile stages, are susceptible to ich, and under poor environmental conditions for the host fish, e.g. varying temperature (particularly chills), lack of or poor nutrition, etc. These challenges can be fatal and is always debilitating, making the fishes more liable to subsequent parasitic and infectious diseases.
Ich is almost always present in freshwater systems and is parasitic on most if not all freshwater fishes. All that it takes to become pathogenic (actively infectious, disease-causing) is a strong strain of ich (e.g. an import from a newly added specimen), a not-so healthy, poorly-resistant host and/or a poor environment for the fishes. Re the last: Note that all diseases are to degrees environmentally linked. If the fishes are initially in good health, put into a suitable, stable home, the chance of outbreak is small.
The causative agent of white spot disease is a ciliate (meaning it has many fine, hair-like projections for food acquisition and locomotion), protozoan (a single-celled micro-organism) called Ichthyophthirius multifilius ("fish louse you can see with many children"), described by Foque in 1876. This critter burrows under the thin upper layers of fishes skin, gills and fins. Here, these irritations cause the host to produce extra body slime, yielding the visible white spots we identify with ich (not the parasitic organisms themselves which are much smaller). In massive infestations, large sections of the upper layers of skin are sloughed off and the gill filaments become anemic and necrotic... ultimately appearing yellow to gray and slimy.
Ichthyophthirius is a parasite with a direct life cycle, i.e. requiring no intermediate host like a bird, snail, et al. The time per generation is temperature dependent, ranging from a few days for tropical to a few weeks for temperate settings. Starting with a stage feeding (call trophonts) on its fish host:
A) The fully developed adult larvae leaves the fish, drops to the bottom and forms a cyst (called tomonts).
B) Becomes attached to and transmissible by any wet object. For about a day at 78 degrees F. reproduction occurs by binary fission; that is, by each cell dividing into two, until as many as 2,000 individuals are formed.
C) These break out of the cyst and swim (called tomites/theronts) in search of a host fish, which they must find within 3 to 4 days at about 78 F. or will die.
Direct observation of the responsible micro-organism is possible with any medium power microscope, the adult size being up to 1 mm in diameter. Remove some body slime from an infested fish by skimming a microscope slide along its side from the direction of head to tail, and smear this onto the surface of another slide. You might improve contrast by staining the slide specimen with a drop or methylene blue or malachite. Adult ich appears as a roundish blob with two nuclei (a larger C-shaped vegetative macronucleus and smaller reproductive micronucleus), the outside of the cell covered by numerous small "hairs" (cilia).
Prophylaxis "An ounce of prevention...". As mentioned earlier, most maladies of aquatic livestock can be prevented by putting initially healthy organisms into good, constant captive environments and preventing introduction of noxious stimuli and micro-organisms. This being stated, most fish tanks support some latent (non-infectious) level of ich. Keep these under control by keeping the environment healthy (optimized and consistent). Keep out new, possibly more virulent strains of ich by making sure anything wet you add to the tank is safe, if not sterile. Dry out the tank, gear, ornaments prior to use or treat them with a biocide (like dilute bleach solution) to eliminate parasites.
If you can, isolate newcomers, fish and non-fish. In some pet-fish and scientific literature it is said that most ich will die if removed from a host for 70 hours at 80 degrees F., so a few days in quarantine will reveal whether the new fishes have ich or not. Sometimes as good as isolation are baths prior to or in the course of acclimation. Tropicure, copper compounds and potassium permanganate solutions are among the best for this. For permanganate, a 25 mg. per gallon solution using a five to ten second dip is adequate for most fishes.
After the Fact:
The earlier the detection and treatment, the better. Ich can and does kill. Generally ich appears on fins first and in about a day's time spreads to the body. The following are suggested actions in treating ich infestations:
A) Heat: Most all treatments call for an increase in temperature. Depending of the species of livestock you have, it should be slowly (several hours) raised to 82-86 degrees F. Several days after cure, the temperature may be lowered again over a few day's time. The temperature should be raised with or without chemical medication, and it must be kept constant.
B) Medications: First, a mention about pre-treatment. Few fish remedies mention it, but most anything not chemically inert will interfere with the action of chemical treatments. So, it is advised that you remove these "filters", i.e. take out any charcoal, carbon, "new" natural gravel, ornaments, live plants, et al. that might absorb the medications, or treat your affected fishes in a dedicated bare treatment system. Also beneficial are frequent partial water changes, vacuuming prior to treatment to remove organic matter which also acts as a chemical filter. Some treatment chemicals include:
1) 2% Mercurochrome: 4 drops per gallon every 24 hours. Doesn't seem to hurt plants, but be on guard re mercury overdosing.
2) Methylene Blue: 2 drops of 5% solution per gallon. Add as often as blue coloration dissipates. Safe but not very effective.
3) Salts: sodium chloride, sea-salt, ice-cream, kosher... or synthetic saltwater mix can be employed to kill ich as these parasites cannot tolerate more than about 1 ppt salt solutions, whereas most fishes can. The use of salts has an added benefit in alleviating some shock, damage from loss of fish osmotic integrity. Note that addition of salts is deleterious to the health of Ichthyophthirius but may also be bad for your plants, fishes, biological filter.
4) Metallic salts, especially copper and silver solutions (e.g. Nox-ich, Ich-out, Aquari-sol). Not entirely safe for fish or plants but very effective when used properly.
5) Formalin and/or malachite solutions. Together or separately very effective for large scale or advanced infections. Dangerously toxic however.
6) Flavine dyes (e.g. Maracide) safe and pretty effective. May neuter some fishes if remain in prolonged contact.
Treatments should cover a period of seven days minimum to cover the maximum tropical aquarium life cycle, as only the free-swimming (tomite/theront) stages are treatable chemically. Aspects of nutrient cycling (ammonia, nitrites) should be monitored closely (daily) and ready water to make changes kept on hand if these approach dangerous concentrations. The infection and most treatments cause copious effusion of body slime, disturbing respiratory function and ionic balance (exchange) in the blood. Be careful with concentrations of treatment chemicals. Do real calculation (length times width times height of water divided by 231 for gallons of water in a rectangular tank) or measuring of ACTUAL gallonage in the treatment system.
Certain species, sport mutations of fishes seem to be more or less resistant to ich. Angelfishes (knock on wood) hardly ever contact or are the last in a system to contract it. Other fishes, like Clown Loaches and smooth skinned-catfishes seem to be easily afflicted and more difficult to cure... but most fishes can and will contract ich under the right (wrong?) circumstances. The symptoms, white spots, scratching, etc. noted earlier are not restricted to this disease, but thankfully the treatments for various causative agents are about the same.
If you can, avoid outbreaks, and if you can't, catch them quick! It is much more rewarding to avoid this disease by stringent application of preventative measures largely aimed at keeping the parasite from infiltrating your systems.
Related Articles on WWM:
http://www.wetwebmedia.com/FWSubWebIndex/fwdis3setsfactors.htm, The Three Sets of Factors that Determine Livestock Health
http://www.wetwebmedia.com/dips_baths.htm, Net et al. dips to prevent spreading communicable diseases
http://www.wetwebmedia.com/quaranti.htm, Quarantine and treatment procedures
Fenner, Robert. 1976. Pathologically speaking: Ichthyophthiriasis, Ick, White Spot Disease. Tropical Breeze, San Diego Tropical Fish Society 2/76.
Innes, William T. 1968. Exotic Aquarium Fishes. T.F.H. Publications. pp. 37-39
Murawska, Dennis G. 1979. Disease prevention and control. The results of the author's two year study of Ichthyophthirius at Northern Illinois University are presented in this article, illustrating and "ecological" treatment which effectively turns the life cycle limitations of this parasite against itself.
Purser, Philip A. 2001. The science of ich. What every aquarist should know. AFM 5/01. (raised temperature as cure advocated)
Warren, Jonathan Neal. 2000. Ich!!! So now what? The prevention and treatment of Ichthyophthirius. FAMA 8/00.