Henneguya Zschokkei

''Henneguya zschokkei'' or ''Henneguya salminicola'' is a species of a myxosporean endoparasite. It afflicts several salmon in the genus ''Oncorhynchus''. It causes milky flesh or tapioca disease. ''H. zschokkei'' is notable for its absence of mitochondria, mitochondrial DNA, aerobic respiration and its reliance on an as yet undiscovered energy metabolism.

Description

''Henneguya salminicola'' is found in fish as an ovoid spore with two anterior polar capsules and two long caudal appendages. Individuals are very small (about 10 micrometers in diameter), but are found aggregated into cysts 3–6 mm in diameter at any place in the muscle mass.

Unknown metabolism

''Henneguya salminicola'' is the only known multicellular animal that does not rely on the aerobic respiration of oxygen. It lacks a mitochondrial genome and therefore mitochondria, making it one of the only members of the eukaryotic animal kingdom to shun oxygen as the foundation of its metabolism. The means by which ''H. zschokkei'' utilizes chemical energy for the sustenance of its life is not yet known.; Lay summary:

''H. zschokkei'' is ultimately a highly derived cnidarian. This obligate internal parasite so little resembles other multicellular animals that it, along with many other species in class Myxosporea, were initially categorized as protozoa. It is nevertheless most closely related to jellyfish. This species, like most myxosporeans, lacks many of the diagnostic criteria that identify cnidarians. It is without nervous, epithelial, gut or muscle cells of any kind.

This parasite has not only lost its mitochondria and the mitochondrial DNA residing in them, but also the nuclear genes that code for mitochondrial reproduction. What genetic instructions for these functions remain are in the form of useless pseudogenes.

Origins

The origin and cause of its highly reduced genome are not yet known. While eukaryotes are known for aerobic respiration, a few unicellular lineages native to hypoxic environments have lost this capacity. In the absence of oxygen these single-celled organisms have lost portions of their genome governing aerobic respiration. Such eukaryotes have developed mitochondria-related organelles (MROs), which fulfil many of the functions of conventional mitochondria. However there is no evidence for such adaptation in the multicellular ''H. zschokkei''.

One theory explaining the highly unsual habit of ''H. zschokkei'' and its fellow myxosporeans invokes the cancers of cnidarians. On this explanation, animals such as ''H. zschokkei'' were originally cancerous growths in free-swimming jellyfish that escaped their parent organism and thereafter became a separate species parasitizing other animals. Such an origin is referred to as a SCANDAL (Speciated by CANcer Development in AnimaLs).

Hosts

Known hosts of ''Henneguya zschokkei'' include:
* ''Oncorhynchus gorbuscha'' (Pink salmon)
* ''Oncorhynchus keta'' (Chum salmon)
* ''Oncorhynchus kisutch'' (Coho salmon)
* ''Oncorhynchus nerka'' ( Sockeye salmon)
* Anadromous forms of ''Oncorhynchus mykiss'' (Rainbow trout)
* ''Oncorhynchus tshawytscha'' (Chinook salmon)
* ''Salmo salar'' (Atlantic Salmon)

See also

;Taxa
* ''Cryptosporidium parvum'', a protist (Apicomplexa) without genes in its mitochondria
* ''Mastigamoeba'', an anaerobic protist (Amoebozoa) without mitochondria
* ''Monocercomonoides'', a protist (Metamonad) without mitochondria
* Loricifera, other metazoans; some species don't require oxygen and may also lack mitochondria

;Structures
* hydrogenosome, an organelle of some anaerobic taxa

References

Further reading

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External links

*
* GBIF
''Henneguya salminicola'' Ward, 1919
Id:6881057, source: World Register of Marine Species
* GBIF
''Henneguya zschokkei'' Ward, 1919
Id:6881028, source: Artsnavnebasen

{{Taxonbar, from=Q16983022

Animal parasites of fish
Myxobolidae
Veterinary parasitology