Tetrahymena spp

From Fish
Adult ciliated Tetrahymena spp
Tetrahymena spp invasion of the skin of a hybrid striped bass from a recirculation facility. Note multiple organisms (arrows) in tissues of fish

Tetrahymena corlissi is a ciliated protozoan parasite of fish. Tetrahymena spp may be motile and surface-dwelling but is also occasionally found within tissue, including skeletal muscle and ocular fluids. Similar protozoa, Uronema spp, are found on marine fish[1].

Tetrahymena spp has been recorded throughout the world as a free-living organism commonly found in aquatic and terrestrial habitats ranging from freshwater ponds and streams to salt marshes and soils[2]. However, it has also been found to be parasitic in the tissues of various vertebrate and invertebrate hosts. Infections have been reported in a variety of freshwater fish from Asia, Europe and North America[3].

Life cycle

Tetrahymena spp are pear-shaped and 10-20 µm long, with longitudinal rows of cilia and inconspicuous cytostomes. The optimum temperature for growth and reproduction for some of the Tetrahymena spp. is 280C[4].

Clinical signs

External infestations of Tetrahymena spp are not uncommon on moribund fish removed from the bottom of a tank or aquarium and are often associated with an environment rich in organic material. Most infections have been confined to surface tissues and associated with skin lesions, rased scales, epidermal sloughing and extensive necrosis of the underlying musculature sometimes accompanied by neutrophil infiltration. Systemic infections by Tetrahymena spp have only occasionally been detected in fish in association with moderate to extensive necrosis of various internal organs.


The parasite is readily identified by examining ocular fluids with a light microscope.


As long as Tetrahymena spp are restricted to the external surface of the fish, they are easily eliminated with chemical treatment and sanitation. When they become established internally, they are not treatable and can cause significant mortality. Fish with intraocular infections of Tetrahymena spp develop extreme exophthalmos.


  1. Merck Veterinary Manual
  2. Elliott AM (1973) Biology of Tetrahyrnena. Dowden, Hutchinson & Ross, Stroudsburg
  3. Hoffman GL (1978) Ciliates of freshwater fishes. In: Kreier JP (ed) Parasitic protozoa, Vol. 11. Academic Press, New York, pp:583-632
  4. Pimenta Leibowitz, M. et al (2005) Environmental and Physiological conditions affecting Tetrahymena sp. infection in guppies, Poecilia reticulata Peters. Journal of Fish Dis 28:539-547