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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
International Common Names
- English: Chilodonella infection in fish; killer don
Pathogen/sTop of page
OverviewTop of page
The genus Chilodonella Strand, 1926 comprises many free-living species and two species (C. piscicola and C. hexasticha) infesting freshwater fishes. Both the latter species have cosmopolitan distributions, occur in estuarine and brackish waters (e.g. in the eastern Baltic Sea) and appear to infest most, if not all, teleost fishes. They cause the well-known chilodonellosis, a disease affecting the skin and gills, especially in fish cultures.
[Derived from: Woo, PTK, ed., 2006. Fish diseases and disorders, Volume 1: Protozoan and Metazoan infections. (2nd edition) Wallingford, UK: CAB International]
Host AnimalsTop of page
|Animal name||Context||Life stage||System|
|Bidyanus bidyanus (silver perch)||Aquatic|Adult||Enclosed systems/Ponds|
|Carassius carassius (crucian carp)|
|Clarias batrachus (walking catfish)||Domesticated host; Wild host|
|Ctenopharyngodon idella (grass carp)||Domesticated host; Wild host||Aquatic|Adult; Aquatic|Fry||Enclosed systems/Ponds; Enclosed systems/Tanks|
|Misgurnus anguillicaudatus (oriental weatherloach)||Aquatic|Adult; Aquatic|Fry|
|Oreochromis niloticus (Nile tilapia)||Domesticated host; Wild host|
|Salmo salar (Atlantic salmon)||Domesticated host; Wild host|
|Salmo trutta (sea trout)||Domesticated host; Wild host|
Hosts/Species AffectedTop of page
Chilodonella piscicola and C. hexasticha appear to infest most, if not all, teleost fishes.
DistributionTop of page
Chilodonella piscicola and Chilodonella hexasticha may occur simultaneously on the same host. Most of the information on their biology and relationships to fish was collected at a time when their specific distinction was not recognized. Prost (1952) was the first to confirm that they are indeed distinct species. The data on their distribution in Eurasia came from this period, while more recent records on the occurrence of Chilodonella in South Africa, Israel, the USA, Australia and Malaysia identified the species C. hexasticha (Hoffman et al., 1979; Paperna and Van As, 1983; Shariff, 1984; Langdon et al., 1985); C. cyprini has also been reported in Japan recently by Imai et al. (1985) and Urawa and Yamao (1992).
PathologyTop of page
Under favourable conditions (e.g. in fish and especially fingerlings that are debilitated in early spring or by overcrowding), chilodonellas may virtually cover the body surface in a continuous layer. They disintegrate the body surface using their oral cytoskeletal apparatus and feed on cell debris.
Clinical signs of heavy infestations include increase of mucus, with an overall dark, slimy, patchy or mottled grey appearance. These films of mucus and cellular debris may become detached from the skin surface. Moribund fish may also show signs of hypoxia and uncoordinated swimming, are emaciated and have opaque eyes and abrased skin.
Pathogenesis in skin lesions has not been studied, but has been described in detail in gill infestations with Chilodonella hexasticha (Paperna and Van As, 1983; Shariff, 1984; Langdon et al., 1985). Chilodonella initially cause localized hyperplasia of the gill epithelium, which later becomes more generalized. Proliferating epithelial cells fill the spaces between secondary lamellae, which may fuse together and coalesce into a single mass. The thin respiratory epithelium is covered by the hyperplastic epithelium and this drastically reduces the respiratory surface of the gills. The epithelium may be infiltrated with lymphocytes and eosinophil granulocytes, with an additional increased proliferation of mucus and chloride cells.
The hyperplastic epithelium may undergo changes with dilatation of capillaries, oedema, petechia and haemorrhages. Complete destruction of the epithelium of primary and secondary lamellae may leave the fish with only cartilaginous rays. Pathological manifestations may vary, depending on the intensity of infestations. Sometimes large aggregates of melanin can also be seen along some of the primary lamellae undergoing degeneration. Disintegration of the gills and their necrosis render the gills non-functional. Fish lose osmotic balance and suffocate; this is manifested by their increased sensitivity to oxygen deficiency. Heavily infested fish die.
EpidemiologyTop of page
Chilodonellosis occurs throughout a wide temperature range. Mass infestations with C. piscicola may be found from slightly above zero (e.g. at 4°C) to slightly above 20°C, while C. hexasticha is known to cause morbidities even at 26 to 31°C (Shariff, 1984). Chilodonellosis accounts for the greatest economic losses due to a single disease in commercial tropical fish stores (Leibovitz, 1980). Since chilodonellosis has mostly been reported at low temperatures when fish are under stress, an assumption prevailed that chilodonellas prefer colder waters and basically only occur in commercial set-ups. There is, however, a report on massive mortalities due to chilodonellosis (Chilodonella hexasticha) in free waters. This took place among native fish (bony bream) in Australia in the winter, where the temperature was 8-13°C (Langdon et al., 1985). Unpublished information of the present authors also indicates that chilodonellosis does occur readily in warmer waters; mortalities were observed amongst cichlids on a fish farm in the Okavango River (Botswana) at water temperatures exceeding 25°C.
ReferencesTop of page
Prost M, 1952. Badania nad pierwotniakami pasozytnymi skrzeli ryb. II. Chilodonella cyprini Moroff I Chilodonella hexasticha Kiernik. Annales Universitatis M. Curie-Sklodowska, Lublin - Polonia, 8(C):1-13.