Myxozoa is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. Over 2,180 species have been described and some estimates have suggested at least 30,000 undiscovered species. Many have a two-host lifecycle, involving a fish and an annelid worm or a bryozoan. The average size of a myxosporean spore usually ranges from 10 μm to 20 μm, whereas that of a malacosporean spore can be up to 2 mm. Myxozoans can live in both freshwater and marine habitats.
Myxosporea is a class of microscopic parasites, belonging to the Myxozoa clade within Cnidaria. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate and an ectothermic vertebrate, usually a fish. Each host releases a different type of spore. The two forms of spore are so different that until relatively recently they were treated as belonging to different classes within the Myxozoa.
Myxobolus is a genus of myxozoa that includes important parasites of fish like Myxobolus cerebralis. The genus is polyphyletic, with members scattered throughout the myxozoa. Some stages of Myxobolus species were previously thought to be different organisms entirely, but are now united in this group. Some fish species, such as the thicklip grey mullet, can harbour a dozen of Myxobolus species.
Kudoa thyrsites is a myxosporean parasite of marine fishes. 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 causing post-mortem "myoliquefaction", a softening of the flesh to such an extent that the fish becomes unmarketable. It is not infective to humans.
A xenoma is a growth caused by various protists and fungi, most notably microsporidia. It can occur on numerous organisms; however is predominantly found on fish.
The olive flounder, bastard halibut or Korean halibut, is a temperate marine species of large-tooth flounder native to the North-western Pacific Ocean.
Glugea is a genus of microsporidian parasites, predominantly infecting fish.
Ceratomyxa is a genus of myxozoan.
Calyptospora is a genus of parasitic protozoa in the phylum Apicomplexa.
Kudoa paraquadricornis is a myxosporean parasite of marine fishes, first discovered in Australia from 4 carangid species.
Kudoa kenti is a myxosporean parasite of marine fishes, first discovered in Australia from 4 pomacentrid species.
Ceratomyxa hooperi is a myxosporean parasite that infects gall-bladders of serranid fishes from the Great Barrier Reef. It was first found on Epinephelus quoyanus.
Ceratomyxa nolani is a myxosporean parasite that infects gall-bladders of serranid fishes from the Great Barrier Reef. It was first found on Epinephelus quoyanus.
Ceratomyxa whippsi is a myxosporean parasite that infects gall-bladders of serranid fishes from the Great Barrier Reef. It was first found on Cephalopholis boenak.
Enteromyxum leei is a species of myxozoan, histozoic parasite that infects the intestinal tract and sometimes associated organs, like gall bladder and liver, of several teleostean fish species. Myxozoans are microscopic metazoans, with an obligate parasitic life-style. The parasite stages of this species live in the paracelullar space between fish enterocytes. It is the causative agent of enteromyxosis, or emaciative disease, also known as "razor blade syndrome" in sparid fish. E. leei has a wide host and geographical range within marine fish, and even freshwater fish have been infected experimentally. E. leei initially emerged in the Mediterranean in the late 1980s and it is believed to have been unintentionally introduced into the Red Sea. Its pathogenicity and economic impact depend on the host species. In the gilt-head seabream, it is manifested as a chronic disease that provokes anorexia, delayed growth with weight loss, cachexia, reduced marketability and increased mortality. In other species, it has no clinical signs. In sharpsnout seabream, infection results in very high mortality rates, which have pushed fish farmers to abandon the culture of this fish species.
Sphaerospora molnari is a microscopic endoparasite of carp in pond cultures and natural freshwater habitats in Central and Eastern Europe. In natural infections, S. molnari invades the epithelia of gills and surrounding skin regions. It then forms spores in between epithelial cells, causing sphaerosporosis, a pathological condition of the skin and gill tissues. Affected tissues show marked dystrophic changes and necrosis, causing secondary bacterial infections and resulting in osmoregulatory and respiratory failure. Mortalities can reach 100% but little is known about the overall distribution of the parasite species in European carp ponds or its economic impact on carp aquaculture.
Thelohanellus kitauei is a myxozoan endoparasite identified as the agent of intestinal giant-cystic disease (IGCD) of common carp Cyprinus carpio. The species was first identified in Japan, in 1980 and later formally described by Egusa & Nakajima. Fan subsequently reported the parasite in China, and several other reports from carp and Koi carp in China and Korea followed. Reports referred to an intestinal infection, swelling and emaciation of fish due to blockage of the intestinal tract by giant cysts. The intestine of carp was believed to be the only infection site of T. kitauei until Zhai et al. reported large cysts of T. kitauei in the skin, with morphologically similar and molecularly identical spores. T. kitauei has been recognized as the most detrimental disease of farmed carp in Asia with around 20% of farmed carp killed annually. In 2014, the genome of T. kitauei was sequenced, and in 2016, its life cycle was found to include the oligochaete Branchiura sowerbyi. Infected oligochaete worms were first discovered in Hungary and raised concerns of the introduction of T. kitauei into European carp culture ponds, since it was believed to be endemic to Asia. However, the related disease (IGCD) has not yet been reported in Europe.
Henneguya is a genus of myxosporean parasites belonging to the family Myxobolidae.
Carlos José Correia de Azevedo is a Portuguese biologist specialising in microparasites of aquatic organisms, particularly Apicomplexa, Haplosporidia, Microsporidia, and Myxozoa.
Ellipsomyxa is a genus of cnidarian that is part of the family Ceratomyxidae.
