''Henneguya zschokkei'' or ''Henneguya salminicola'' is a species of a myxosporean

endoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

. It afflicts several

salmon Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...

and trout in the genera ''

Oncorhynchus ''Oncorhynchus'', from Ancient Greek ὄγκος (''ónkos''), meaning "bend", and ῥύγχος (''rhúnkhos''), meaning "snout", is a genus of ray-finned fish in the subfamily Salmoninae of the family (biology), family Salmonidae, native to col ...

'' and ''

Salmo ''Salmo'' is a genus of ray-finned fish from the subfamily Salmoninae of family (biology), family Salmonidae, and is part of the tribe (biology), tribe Salmonini along with the sister genera ''Salvelinus'' and ''Salvethymus''. Almost all ''Salmo ...

'','' ''where it causes milky flesh or tapioca disease''. H. zschokkei'' does not require oxygen to survive and is notable for being one of the few multicellular organisms in the animal kingdom to rely on an exclusively anaerobic metabolism. It is also notable for its lack of both

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

and

mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the D ...

.''''

Description

''Henneguya zschokkei'' 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 animal's musculature.

Metabolism

''H. zschokkei'' is incapable of

aerobic respiration Cellular respiration is the process of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cellu ...

, making it one of a handful of truly anaerobic animals.; Lay summary: It also lacks a mitochondrial genome and therefore

. Like all Myxozoans, ''H. zschokkei'' is ultimately a highly derived

cnidarian Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

and is more closely related to

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

and sea anemones than those are to

corals Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

. However, this

obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym '' facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism ...

internal parasite so little resembles cnidarians (let alone other multicellular animals) that it, along with many other species in the 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 lacks nervous, epithelial, gut or

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

cells of any kind. This parasite has not only lost its mitochondria and the

residing in them, but also the nuclear genes that code for mitochondrial reproduction.

Origins

The origin and cause of ''H. zschokkei'''s highly reduced genome are not yet known. While

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s are known for aerobic respiration, a few unicellular lineages native to hypoxic environments have also lost this capacity. In the absence of oxygen, these single-celled organisms lose the portions of their genome that anticipate and govern aerobic respiration. These unusual eukaryotes have developed mitochondria-related organelles (MROs) that fulfill many of the functions of conventional mitochondria. However, there is no evidence of an adaptation in the multicellular ''H. zschokkei''.

Hosts

Known hosts of ''Henneguya zschokkei'' include: * ''Oncorhynchus gorbuscha'' ( Pink salmon) * ''Oncorhynchus keta'' ( Chum salmon) * ''Oncorhynchus kisutch'' (

Coho salmon The coho salmon (''Oncorhynchus kisutch;'' Karuk: achvuun) is a species of anadromous fish in the salmon family (biology), family and one of the five Pacific salmon species. Coho salmon are also known as silver salmon (or "silvers") and is often ...

) * ''Oncorhynchus nerka'' ( Sockeye salmon) * Anadromous forms of ''Oncorhynchus mykiss'' (

Rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributary, tributaries of the Pacific Ocean in North America and Asia. The steelhead (sometimes called steelhead trout) is an Fish migration#Classification, ...

) * ''Oncorhynchus tshawytscha'' ( Chinook salmon) * ''Salmo salar'' (

Atlantic Salmon The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Hucho taimen, Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlan ...

)

References

External links

* * GBIF
''Henneguya salminicola'' Ward, 1919
Id:6881057, source:

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive catalogue and list of names of marine organisms. Content The content of the registry is edited and maintained by scien ...

* GBIF
''Henneguya zschokkei'' Ward, 1919
Id:6881028, source: Artsnavnebasen {{Taxonbar, from=Q16983022 Animal parasites of fish Myxobolidae Veterinary parasitology Taxa described in 1894