Ciliates (including Ich and Tetrahymena)

Ich or Ichthyophthirius multifiliis, Tetrahymena spp.

Ciliates are protozoans, the most common fish parasites in the guppy tank. They are single-celled and have a direct life cycle, with no intermediate host.

Ciliates have hair-like structures projecting from their bodies for locomotion. They do not seem to bother the fish in small numbers, but when water conditions deteriorate they multiply quickly and cause fatal damage to the guppies.

Ich or Ichthyophthirius multifiliis (a.k.a. white spot disease) is so well known to hobbyists as to not require description in depth. It often shows up when the guppy is suddenly chilled. It can attack the body or gills. When it is seen on the body, it shows as small white spots. It encysts under the epidermis of the fish. These mature and fall off to the bottom of the tank, divide up to free-swimming tomites that re-infect the guppies. Sometimes they can be present and not visible. If the infection is only in the gills, the disease will be hard to diagnosis without the aid of a microscope. The cyst is resistant to chemical treatment, so the disease requires a five-day course of treatment. In cooler water it may require substantially longer.  If it is not caught early its spread and the mortality of the fish can be swift.

According to Doc Johnson, new strains of ich have developed that are resistant to high temperatures, with one strain surviving temperatures over 90F (32C), according to research at the University of Florida. Another strain was discovered at the University of Oklahoma that remains under the skin until it matures, making it impervious to treatment until it reaches the free-swimming stage.

Guppies can develop immunity to ich. This explains why a new guppy introduced to a tank often falls ill with it, while the tank mates do not. Scientists are actually trying to develop a vaccine against it. Until this vaccine is developed, salt is still the most effective treatment.

Tetrahymena spp. is a free-swimming oval ciliated protozoa about 50-70 microns long. It's a close relative of ich. It's favorite hosts are the fry of the guppy (Guppy Disease), cichlids, tetras and the Northern Pike, although some report infection of Discus. It invades the skin, often penetrating through the muscle and ultimately the body cavity. It can become fatal. One treatment is usually enough to kill this parasite.

If the parasite has penetrated into the body it is untreatable. One sign that it has penetrated the body is bulging eyes. It's difficult to diagnosis or treat the disease when it is internal.

Signs that your guppy has been infected by Tetrahymena include: an area of the body dies or hemorrhages, usually in the ventral area. Black spots appear on the guppy that eventually ulcerate as bacteria take advantage of the rupture in the scales. In severe cases the body wall ruptures and the guppy eviscerates.

According to Jeong-Ho Kim , Craig James Hayward, Gang-Joon Heo in Nematode worm infections (Camallanus cotti, Camallanidae) in guppies (Poecilia reticulata) imported to Korea (Aquaculture 205 (2002) 231– 235):
Tetrahymena corlissi also causes serious mortalities among guppies. Although it has not been generally considered as a major threat to tropical fishes, sometimes it is fatal to its fish host because it can penetrate scales and reach muscles and internal organs (Imai et al., 2000). It is now considered as a serious pathogen of guppies, especially in Southeast Asian countries, and causes economic losses.

Another study identifies a secondary infection after Tetrahymena:

"Effect of Tetrahymena on the occurrence of achlyosis in the guppy" Lawhavinit, K. Chukanhom, K. Hatai,
Tetrahymena infection has become the most problematic parasitic disease of the guppy Poecilia reticulata in Southeast Asia. Tetrahymena corlissi was isolated from guppies with a fungal infection in Thailand, and the fungus was identified as Achlya bisexualis. Male and female guppies were artificially infected with both organisms. The results showed that guppies could easily be artificially infected with a culture of Tetrahymena corlissi and that female guppies were more sensitive than male guppies. Achlya bisexualis infection was shown to be a secondary infection after the Tetrahymena infection.

Symptoms and Behavioral Signs
An early sign of infection is guppy flashing (rubbing on filters or sides of aquariums) or heavy breathing, indicating irritation of the skin or gills respectively.

Causative Condition
Ciliates thrive on the organic material on the sides of the tank, in the filters and on the bottom of the tank. They easily hitch a ride on wet hands, nets and water splashing from one tank to another. Guppies imported from Asia should be suspected carriers.

Diagnosis
Some forms of Ich are readily identifiable as white spots on the surface of the fish. Most ciliates are large enough to be viewed under a microscope.

Prevention and Treatment
Tetrahymena corlissi and Ich are usually not a problem until overcrowding occurs and the water quality deteriorates (high organic content).

Ciliates should be eliminated from the tank through treatment.

Salt treatment is effective against ciliates. Formalin and Potassium Permanganate are also effective. Salt is the preferred treatment as the guppy can easily tolerate it. Both formalin and PP may damage the guppy's gills and adversely affect the nitrogen cycle. While tetrahymena usually only requires one treatment, Ich can be persistent. Its usual life cycle is 2 to 5 days, but if the tank is cool, 70F (21C) or lower, the treatment regime should be extended up to two weeks.