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Ichthyophthirius Multifiliis (White Spot) Infections in Fish
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Diagnosis of "Ich"
Diagnosis of "Ich" is easily confirmed by microscopic examination of skin and gills. Remove several white spots from an infected fish, then mount them on a microscope slide with a few drops of water and a cover glass. The mature parasite is large, dark in color (due to the thick cilia covering the entire cell), and has a horseshoe-shaped nucleus which is sometimes visible under 100 x magnification ( Figure 2 ). The adult parasite moves slowly in a tumbling manner and, with practice, is easily recognized. The immature forms (tomites) are smaller, translucent, and move quickly. The tomites ( Figure 3 ) closely resemble another protozoan parasite called Tetrahymina ( Figure 4 ). Tetrahymina usually does not require treatment, so it is important to recognize the difference between the two parasites. If only tomites are seen, prepare a second slide and examine it closely for the adult parasite to confirm the diagnosis. Observation of a single organism is sufficient to make treatment necessary.




Prevention of "Ich"
Prevention of "Ich" is preferable to treating fish after a disease outbreak is in progress. All incoming fish should be quarantined for at least three days when temperatures are 75 to 83F. At cooler temperatures a 3-day quarantine will be inadequate for "Ich" because of its lengthened life cycle. For this reason, and to prevent introduction of other diseases which have incubation periods greater than 3 days, a longer quarantine is strongly recommended. Three weeks is generally considered a minimum period for adequate quarantine of new fish.


Treatment of "Ich"
Control of "Ich" outbreaks can be difficult because of the parasites' unusual life cycle and the effect of water temperature on its life cycle. Review the life cycle of L. multifiliis presented in Figure 1 . Of the life stages shown, only the free-swimming tomites are susceptible to chemical treatment. This means that application of a single treatment will kill tomites which have emerged from cysts and have not yet burrowed into the skin of host fish. This single treatment will not affect organisms which emerge after the chemical has broken down or been flushed from the system. Repeated treatments, however, will continually kill the juvenile tomites, preventing continuation of the infection. The epizootic will be controlled as more adult parasites drop off the sick fish, encyst, and produce young which cannot survive because of the repeated application of chemicals. This process will be greatly accelerated if organic debris can be removed from the tank or vat following treatment. This will remove many cysts from the environment, decreasing the number of emergent tomites.

Water temperature has a tremendous influence on how fast the life cycle for "Ich" ( Figure 1 ) is completed. At warm temperatures (75-79F), the life cycle is completed in about 48 hours, which means that chemical treatments should be applied every other day. At cooler temperatures the life cycle is prolonged and treatments should be spaced further apart. For example, at a water temperature of 60F, treatments should be spaced 4 or 5 days apart. In warm water, a minimum of three treatments applied 2 to 3 days apart is required. In cooler water, a minimum of five treatments should be applied 3 to 5 days apart. Treatments should never be discontinued until all mortality from "Ich" has stopped. Fish should be closely watched during recovery; the weakened fish may be susceptible to a secondary bacterial infection. The choice of chemical used to treat "Ich" will be based upon water quality conditions, species of fish to be treated, and the type of system fish are housed in. In general, copper sulfate, formalin, and potassium permanganate are all effective against "Ich" when applied at the correct concentration in a repetitive manner as described above.


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