Kudoa thyrsites

Kudoa thyrsites
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Myxosporea
Order:	Multivalvulida
Family:	Kudoidae
Genus:	Kudoa
Species:	K. thyrsites
Binomial name
Kudoa thyrsites (Gilchrist, 1924)

Kudoa thyrsitesis amyxosporeanparasiteofmarinefishes.It has a worldwide distribution, and infects a wide range of host species. This parasite is responsible for causing economic losses to the fisheries sector, by causingpost-mortem"myoliquefaction", a softening of the flesh to such an extent that the fish becomes unmarketable. It is not infective to humans.

Taxonomy

The spores ofK. thyrsitesare stellate in shape, with 4 valves and 4polar capsules.Upon infection by theactinosporeanstage thesporoplasmmigrates to amuscle fibrewhere it forms apseudocyst.Within these pseudocysts are the developing spore stages. Comparison of18S rDNAsequences ofKudoaspecies and other myxozoan species to determine their relationships. They show thatKudoaspecies are distinct from other myxozoans analyzed (Myxidiumsp.,Myxobolussp., andHenneguya zschokkei).^[1] Kudoa thyrsitesis an interesting member of this group in that apparently has very broad host specificity, infecting many fish species around the world (Table 1).

Pathology

Members of thegenusKudoa primarily infectmuscletissue of marine fishes, where they form nodules or pseudocysts containing a great number of individual spores. In lighter infections these pseudocysts are isolated from the fish'simmune systemwithin the muscle fibre. More intense infections can result in severeinflammationsurrounding infected muscle fibres.^[2]Although apparently asymptomatic in all but heavy infections, they are associated with post-mortem degeneration of the tissue. This softening of flesh is most likely a result the release ofproteolytic enzymesby the parasite.^[3] This causes losses to bothaquacultureoperations, for instance, wheresalmonare being reared in "sea-pens", and tocapture fisheries.Losses are both direct, through the degradation of fish products, and indirectly, through the perception of theconsumerthat fish from a particular area are of a lower quality. The intensity ofK. thyrsitesinfection ispositively correlatedwith the severity of flesh softening in Atlantic salmon fillets.^[4]Softening of flesh always occurred with heavily infected fillets, while lightly infected fillets showed no softening. Prevention and/or control ofK. thyrsitesinfections is problematic especially in open water netpens. Currently there are no available treatments. One approach to control may be to disrupt the life cycle in some way thereby minimizing the likelihood of infection.

Table 1. Distribution and species infected byKudoa thyrsites

Location	Species	Common name
North America	Merluccius productus	Pacific hake
	Oncorhynchusspp.	Pacific salmon
	Icelinus filamentosus	Threadfin sculpin
	Ophiodon elongatus	Lingcod
	Aulorhynchus flavidus	Tube-snout
	Salmo salar	Atlantic Salmon
	Reinhardtius stomias	Arrowtooth Flounder
	Eopsetta jordani	Petrale sole
	Hippoglossus stenolepis	Pacific halibut
	Microstomus pacificus	Dover sole
	Lepidopsetta bilineatus	Rock sole
	Platichthys stellatus	Starry flounder
	Parophrys vetula	English sole
	Theragra chalcogramma	Alaskan pollock
	Merluccius capensis	Cape hake
Australia	Engraulis australis	Australian anchovy
	Thunnus maccoyii	Southern Bluefin Tuna
	Engraulis japonicus	Japanese anchovy
	Sardinella lemuru	Bali sardinella
	Sardinops neopilchardus	Australian pilchard
	Spratelloides delicatulus	Blue sprat
	Coryphaena hippurus	Mahi Mahi
South Africa	Sardinops ocellatus	South African pilchard
	Thyrsites atun	Snoek
Chile	Paralichthys adspersus	Fine flounder
Japan	Cypselurussp.	Flying fish
Ireland	Salmo salar	Atlantic Salmon
	Clupea harengus	Herring
Spain	Salmo salar	Atlantic Salmon
United Kingdom	Scomber scomber	Mackerel
	Salmo trutta	Brown trout

Life cycle

The myxosporeans have been shown to have complex life cycles using more than one host. Usually a fish and anoligochaeteorpolychaeteworm, and in one case abryozoan. The life cycle ofK. thyrsitesis poorly understood. It has been hypothesized thatK. thyrsiteshas an indirect life cycle involving some marine invertebrate. Experiments have shown direct transmission of the marine myxosporeanMyxidium leeiinsea bream.^[5]However, direct transmission of K. thyrsites failed when native fish were fed fresh myxospores.^[6]If K. thyrsites does have an indirect life cycle, the intermediate host has yet to be identified.

References

1. ^Hervio, D.M.L., Kent, M.L., Khattra, J., Sakanari, J., Yokoyama, H., Devlin, R.H. (1997). "Taxonomy ofKudoaspecies (Myxosporea), using a small-subunit ribosomal DNA ".Canadian Journal of Zoology.75(12): 2112–2119.doi:10.1139/z97-846.{{cite journal}}:CS1 maint: multiple names: authors list (link)
2. ^Kent, M.L.; T.T. Poppe (1988). "Diseases of netpen-reared salmonid fishes".Pacific Biological Station, Nanaimo, BC.:293pp.
3. ^Tsuyuki, H., Williscroft, S.N., Kabata, Z., Whitaker, D.J. (1982). "The relationship between acid and neutral protease activities and the incidence of soft cooked texture in the muscle tissue of Pacific hake (Merluccius productus) infected withKudoa paniformisand/orK. thyrsitis,held for varying times under different prefreeze chilled storage conditions ".Canadian Technical Report on Fisheries and Aquatic Sciences.1130:39 pp.{{cite journal}}:CS1 maint: multiple names: authors list (link)
4. ^St-Hilaire, S., Hill, M., Kent, M.L., Whitaker, D.J., Ribble, C. (1997)."A comparative study of muscle texture and intensity ofKudoa thyrsitesinfection in farm-reared Atlantic salmonSalmo salaron the Pacific coast of Canada ".Diseases of Aquatic Organisms.31:221–225.doi:10.3354/dao031221.{{cite journal}}:CS1 maint: multiple names: authors list (link)
5. ^Diamant, A. (1997)."Fish-to-fish transmission of a marine myxosporean".Diseases of Aquatic Organisms.30:99–105.doi:10.3354/dao030099.
6. ^Moran, J.D.W., Whitaker, D.J., Kent, M.L. (1999). "Natural and laboratory transmission of the marine myxosporean parasiteKudoa thyrsites(Gilchrist, 1924) to Atlantic salmon (Salmo salar) ".Journal of Aquatic Animal Health.11(2): 110–115.doi:10.1577/1548-8667(1999)011<0110:NALTOT>2.0.CO;2.ISSN1548-8667.{{cite journal}}:CS1 maint: multiple names: authors list (link)