Description
Kingdom, Phylum - Myxozoa have long been grouped with 'Protozoa', and often placed in the 'Sporozoa' , with what is now the phylum Apicomplexa (Lom 1990). However, the multicellular spores of these organisms suggest Metazoan affinities. A recent morphological and genetic (small subunit ribosomal RNA sequencing) analysis places Myxozoa in the phylum Cnidaria, and identifies the 'polar capsules' of the spores as modified nematocysts. A cladogram based on the RNA analysis showed that Myxozoa were most closely related to a cnidarian parasite of sturgeon eggs, Polypodium hydriforme, class Hydrozoa, phylum Narcomeduseae (Siddall et al. 1995). While Siddall et al.'s evidence seems strong, we've decided to retain Myxobolus cerebralis in the Protista until its reclassification is confirmed by other workers.
Synonymy - The life cycle of Myxobolus cerebralis, and that of the Myxozoa generally, was unknown until recently, but it is now generally accepted that it has two very morphologically different life phases, one of cells proliferating and producing roughly spherical spores in salmonid fishes, and another 'actinosporean' phase taking place in tubificid oligochaetes, producing spores resembling 3-pointed stars. The Actinosporea were formerly recognized as an class of the phylum Myxozoa, and the 'actinosporean' phase of M. cerebralis' life cycle had been known as Triactinomyxon sp. (Kent et al. 1994; Markiw and Wolf 1983; Wolf and Markiw 1984).
Potentially Misidentified Species - The Myxobolus spp. listed are known from North American salmonids including O. kisutch, O. clarki, O. mykiss, and others. Myxobolus neurobius and M. kisutchi also attack the nervous system of salmonids, but are morphologically distinct; M. squamalis and M. insidiosus affect the scales and muscles, respectively. Symptoms of vitamin C deficiency can be mistaken for Whirling Disease (Hoffman 1990).
Taxonomy
| Kingdom | Phylum | Class | Order | Family | Genus |
|---|---|---|---|---|---|
| Protista | Myxozoa | Myxosporea | Bivalvulida | Myxobolidae | Myxobolus |
Synonyms
Invasion History
Chesapeake Bay Status
| First Record | Population | Range | Introduction | Residency | Source Region | Native Region | Vectors |
|---|---|---|---|---|---|---|---|
| 1965 | Established | Expanding | Introduced | Unconfirmed | Europe | Eurasia | Fisheries(Fisheries Accidental) |
History of Spread
Myxobolus cerebralis (Whirling Disease) apparently was an unnoticed non-pathogenic parasite of the Eurasian trout Salmo trutta (Brown Trout), and was not discovered until 1893, when Oncorhynchus mykiss (Rainbow Trout) native to the Pacific slope of North America were imported into Germany, contracting the disease. The native range of the parasite was probably central Europe and Northeast Asia. As S. trutta has been stocked worldwide in suitable streams, together with vulnerable North American salmonids, M. cerebralis has followed. First records for appearance of disease symptoms include: Germany (1893), Italy (1954), Russia (1955), Bulgaria (1960), Sweden (1966), Scotland (1968), Ireland (1974), North America (1956), South Africa (1968), New Zealand 1971, Equador (1971) (Hoffman 1990). The disease is especially common in aquaculture facilities, but is widespread in natural waters as well (Halliday 1976; Hoffman 1990; Bergersen and Anderson 1997).
Myxobolus cerebralis has an obligatory life-cycle phase in which it inhabits oligochaetes of the genus Tubifex. While other genera of worms are apparently not suitable as hosts (Markiw and Wolf 1983), the wide occurrence of the parasite suggests that the availablity of oligochaete hosts is not a constraining factor in the spread of M. cerebralis.
In North America, M. cerebralis first appeared in Benner Spring Fish Research Station, Bellefonte PA (Ohio River Drainage) in 1956. The suspected source of the disease was imported frozen table trout from Europe, accidentally fed to fish, or discarded in streams after cleaning. Attempts to eradicate the parasite were unsuccessful, and it spread to a National Fish Hachery (United States Fish and Wildlife Service) hatchery in Lamar PA in 1960, and to a state fish hatchery in Kensington CT in 1961 (Hoffman et al. 1962). Before 1970, M. cerebralis had reached hatcheries in NJ, MI, OH, and NV, and after 1970 began to spread extensively into natural waters, invading large areas of the Rocky Mountains and Pacific slope after 1980. By 1997, the disease was found in 21 states, and had resulted in decline or elimination of some salmonid year-classes (Bergersen and Anderson 1997).
Myxobolus cerebralis was apparently found in an VA fish hatchery in 1965 (location not given) (Hoffman 1990), and in the 1970's had become widespread on the western side of the Susquehanna drainage in PA. More recently invaded locations include hatcheries on the lower Susquehanna (PA, 1980's), the western border of the Potomac drainage (WV, 1990's) and hatcheries in the James River drainage (VA, 1990's) (Bergersen and Anderson 1997).
History References - Bergersen and Anderson 1997; Hoffman 1990; Halliday 1976; Hoffman et al. 1962; Markiw and Wolf 1983
Invasion Comments
Residency - In the Chesapeake watershed, Myxobolus cerebralis (Whirling Disease) occurs in cool upland streams inhabited by salmonid fishes, and also in aquaculture facilities, in PA, WV, and VA (Bergerson and Anderson 1997). Possible fish hosts of this parasite [Onchorhynchus mykiss (Rainbow Trout); Salmo trutta (Brown Trout); Salvelinus fontinalis (Brook Trout)] occasionally enter tidal waters of the uppermost Bay (Musick 1972a), so the organism could be found within our study limits, but would be unable to complete its life cycle there.
Ecology
Environmental Tolerances
| For Survival | For Reproduction | |||
|---|---|---|---|---|
| Minimum | Maximum | Minimum | Maximum | |
| Temperature (ºC) | ||||
| Salinity (‰) | 0.0 | 0.0 | 0.0 | 0.0 |
| Oxygen | ||||
| pH | ||||
| Salinity Range | fresh-oligo |
Age and Growth
| Male | Female | |
|---|---|---|
| Minimum Adult Size (mm) | ||
| Typical Adult Size (mm) | ||
| Maximum Adult Size (mm) | ||
| Maximum Longevity (yrs) | ||
| Typical Longevity (yrs |
Reproduction
| Start | Peak | End | |
|---|---|---|---|
| Reproductive Season | |||
| Typical Number of Young Per Reproductive Event |
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| Sexuality Mode(s) | |||
| Mode(s) of Asexual Reproduction |
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| Fertilization Type(s) | |||
| More than One Reproduction Event per Year |
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| Reproductive Startegy | |||
| Egg/Seed Form |
Impacts
Economic Impacts in Chesapeake Bay
Myxobolus cerebralis (Whirling Disease) is a parasite of the oligochaete Tubifex spp. and salmonid fishes. It appears to be widespread in cool upland waters of the Chesapeake Bay watershed, but has not been reported from tidal waters.
Fisheries - Since Myxobolus cerebralis affects salmonid fishes which only occasionally stray into Chesapeake Bay, its direct impacts on the Bay are negligable. However, its effects on hatcheries and sport fisheries in the watershed are significant. When M. cerebralis was first observed in PA fish hatcheries, complete eradication of the parasite was attempted, through destruction and incineration or burial of the affected fish, chemical disinfection of hatchery houses, replacement of earthen ponds and raceways with more easily cleaned concrete, and restocking of the hatchery from uncontaminated sources (Hoffman et al. 1962; Hoffman 1990). Eventually, when the parasite was found to be established in wild stocks, and to have a life cycle stage in oligochaete populations (Markiw and Wolfe 1982), eradication was recognized as an unnattainable goal, and management policy shifted to reducing incidence of the disease in hatcheries to tolerable levels and trying to prevent spread of the disease to new regions. Consequently, fish known to carry the parasite are stocked in waters where the disease is known to be established, but in disease-free waters, state agencies attempt to stock only uninfected fish (Hoffman 1990; Markiw 1992). In or near the Chesapeake Bay water shed, at least 4 fish hatcheries in PA, WV, and VA, and 4 feral trout populations (all in PA) tested positive for M. cerebralis, while several hatcheries (3-4) were still apparently free of the disease (Bergersen and Anderson 1997).
References - Bergersen and Anderson 1997; Hoffman et al.1962; Hoffman 1990; Markiw 1992; Markiw and Wolfe 1982
Economic Impacts Outside of Chesapeake Bay
Myxobolus cerebralis (Whirling Disease) is a parasite of the oligochaete Tubifex spp. and salmonid fishes. It appears to be widespread in cool upland waters of the Chesapeake Bay watershed, but has not been reported from tidal waters.
Fisheries - Since its appearance in North America in 1956, Myxobolus cerebralis (Whirling Disease) has been a major issue in the management of salmonid fisheries. Initial management strategies focused on complete eradication of the parasite from hatcheries (Hoffman et al. 1962), but as spread of the parasite continued, and it was recognized as established in natural waters, policy shifted to amelioration of its effects in hatcheries, and prevention of spread of the disease to unaffected streams (Hoffman et al. 1990; Markiw 1992). An antibiotic, Fumagillin, has been found to be effective in reducing the rates of infection in the laboratory, but had yet to be tested in hatchery situations (El-Matbouli et al. 1992).
The impact of M. cerebralis on naturally reproducing salmonid populations is not clear. It appears to have varied regionally, perhaps reflecting varying susceptability of established stocks, development of resistance, or varying degrees of other stresses which might affect vulnerability to disease. Severe reduction of recruitment of Oncorhynchus mykiss has been observed in the Rocky Mountain States (Nehring and Walker 1996), but in the Pacific Coast states, and Eastern and Central states (PA, NY, MI), trout populations seemed to have survived the invasion of M. cerebralis with few notable impacts. In unaffected and newly affected states, concern among fishermen and managers remains strong, and discussions have become rather emotional (Hulbert 1996; Nehring and Walker 1996).
References - Bergersen and Anderson 1997; El-Matbouli et al. 1992; Hoffman et al. 1962; Hoffman 1990; Hulbert 1996; Markiw 1992; Markiw and Wolfe 1982; Nehring and Walker 1996
Ecological Impacts on Chesapeake Native Species
Myxobolus cerebralis (Whirling Disease) is a parasite of the oligochaete Tubifex spp. and salmonid fishes. It appears to be widespread in cool upland waters of the Chesapeake Bay watershed, but has not been reported from tidal waters.
Parasitism - The only salmonid native to the Chesapeake Bay watershed is Salvelinus fontinalis (Brook Trout), which is found in cool upland streams in the upper Piedmont and Mountain regions, but occasionally enters tidal waters of the uppermost Bay (Jenkins and Burkhead 1993; Musick 1972). Salvelinus fontinalis developed clinical signs of the disease (circular swimming motion, body deformities, blackened tails) even in streams with a low incidence of the parasite (O'Grodnick 1979). This species was found to be intermediate in susceptibility to the disease. The parasite appears to be well-established in the Susquehanna drainage (Bergersen and Anderson 1997), but we are not aware of its effects on native S. fontinalis populations. Fisheries biologists in PA believed that trout populations in that state were healthy, in spite of the presence of Whirling Disease (Hulbert 1996). Adverse effects of Myxobolus cerebralis on oligochaetes are not known.
References - Bergersen and Anderson 1997; Hulbert 1996; Jenkins and Burkhead 1993; Musick 1972; O'Grodnick 1979
Ecological Impacts on Other Chesapeake Non-Native Species
Myxobolus cerebralis (Whirling Disease) is a parasite of salmonid fishes. It appears to be widespread in cool upland waters of the Chesapeake Bay watershed, but has not been reported from tidal waters.
Parasitism - Myxobolus cerebralis (Whirling Disease) was apparently orginally a parasite of Salmo trutta (Brown Trout) in Europe and Asia, where it was first discovered in 1903. The spores of the worm-dwelling phase of the parasite ('Triactinomyxon') are ingested by the trout with worms of the genus Tubifex (Oligochaeta). The ingested spores germinate, releasing parasites which multiply in the fish's cartilage (Markiw 1985; Markiw 1992; Markiw and Wolf 1983; Wolf and Markiw 1984). The parasite is well-tolerated by S. trutta and Oncorhychus kisutch (Coho Salmon) and does not produce disease symptoms in those species. Salvelinus namaycush (Lake Trout), and S. namaycush X S. fontinalis hybrids ('Splake') are completely refractory to the disease, while O. nerka (Sockeye Salmon), O. clarki (Cutthroat Trout) and S. fontinalis (Brook Trout) are intermediate in susceptibility . In O. mykiss (Rainbow Trout), infection of the cartilage results in severe skeletal and neural damage, resulting in deformation of growing fish, abnormal swimming (whirling), and up to 90% mortality in fish infected as yolk-sac fry (Hoffman 1990; Markiw 1992; O'Grodnick 1979).
Whirling Disease has appeared when susceptible species were transplanted into the endemic range of Myxobolus cerebralis, as in Europe, when S. trutta has been stocked in native range of susceptable salmonids in North America, and when S. trutta has come into contact with North American salmonids in regions where salmonids were not native (Hoffman 1990). While the disease is devastating to hatchery stocks, and its spread is greatly feared by sports fishermen, the impact of the disease on naturally reproducing salmonid populations is less clear. Within the native range of O. mykiss, in the upper Colorado River CO, M. cerebralis infections have resulted in losses of several successive year-classes of trout. However, in Pacific Coast drainages, and in introduced populations in the Eastern United States, catastrophic decline of O. mykiss populations has not been seen (Nerhring and Walker 1996). In the Chesapeake Bay drainage, populations of O. mykiss are heavily dependent on stocking (Jenkins and Burkhead 1993; Musick 1972), so that M. cerebralis in hatcheries would mainly affect the availability of fish for release.
References - Hoffman 1990; Jenkins and Burkhead 1993; Markiw 1985; Markiw 1992; Markiw and Wolf 1983; Musick 1972; Nerhring and Walker 1996; O'Grodnick 1979; Wolf and Markiw 1984
References
Bergersen, Eric P.; Anderson, Dennis E. (1997) Distribution and spread of Myxobolus cerebralis in the United States, Fisheries 22: 6-7Carlander, Kenneth D. (1969) Handbook of freshwater fishery biology. Vol. 1., In: (Eds.) . , Ames. Pp.
El-Matbouli, Mansour; Theresia; Fischer-Scherl Rudolf W.; Hoffmann, Glenn (1992) Present knowledge on the life cycle, taxonomy, pathology, and therapy of some Myxosporea spp. important for freshwater fish., Annual Review of Fish Diseases 2: 367-402
1996 Potamopyrgus antipodarum (Gray). Web address http://rivers/oscs.montana.edu/dlg/aim/mollusca/potant. Html
Halliday, M. M. (1976) Biology of Myxosoma cerebralis: The causative organism of whirling disease of salmonids, Journal of Fish Biology 9: 359-357
Hoffman, Glenn L. (1990) Myxobolus cerebralis, a worldwide cause of salmonid whirling disease, Journal of Aquatic Animal Health 2: 30-37
Hoffman, Glenn L.; Dunbar, Clarence E., Bradford, Arthur (1962) Whirling disease of trouts caused by Myxosoma cerebralis in the United States, United States Fish and Wildlife Service Special Scientific Report 427: 1-15
Jenkins, Robert E.; Burkhead, Noel M. (1993) Freshwater fishes of Virginia., , Bethesda, MD. Pp.
Kent, M. L.; Margolis, L.; Corliss, J. O. (1994) Demise of a class of protists: Taxonomic and nomenclatural revisions proposed for the protist phylum Myxozoa Grasse, 1970, Canadian Journal of Zoology 72: 932-937
Lom, Jiri (1990) Phylum Myxozoa., In: Margulis, L., Corliss, J. O., Melkonian, M.,(Eds.) Handbook of Protoctista.. , Boston. Pp. 36-52
Markiw, Maria E. (1986) Salmonid whirling disease: Dynamics of experimental production of the infective stage - the triactinomyon spore, Canadian Journal of Fisheries and Aquatic Sciences 43: 521-526
Markiw, Maria E. (1992) Salmonid whirling disease, United States Fish and Wildlife Service Fish Disease Leaflet 17: 1-11
Markiw, Maria E.; Wolf, Ken (1983) Myxosoma cerebralis (Myxozoa: Myxosporea) etiologic agent of salmonid whirling disease requires tubificid worm (Annelida: Oligochaeta) in its life cycle, Journal of Protozoology 30: 561-564
McKeown, Paul E. (1984) Additions to ichthyofauna of the Susquehanna River with a checklist of fishes of the Susquehanna River drainage below Conowingo Dam, Proceedings of the Pennsylvania Academy of Science 58: 187-192
Musick, J. A.; Wiley, Martin L. (1972) Fishes of Chesapeake Bay and the adjacent coastal plain, Special Scientific Report, Virginia Institute of Marine Science 65: 175-212
O'Grodnick, Joseph J. (1979) Susceptibility of various salmonids to whirling disease (Myxosoma cerebralis), Transactions of the American Fisheries Society 108: 187-190
Page, Lawrence M.; Burr, Brooks M. (1991) Freshwater Fishes., , Boston. Pp.
Scott, W. B.; Crossman, E. J. (1973) Freshwater fishes of Canada, , Ottawa. Pp.
Siddall, Mark E.; Martin, Donald S.; Bridge, Daine; Desser, Sherwin S.; Cone, David K. (1995) Demise of a phylum of protists: Phylogeny of Myxozoa and other parasitic Cnidaria, The Journal of Parasitology 8: 961-967
Wolf, Ken; Markiw, Maria E. (1984) Biology contravenes taxononomy in the Myxozoa: New discoveries show alternation of invertebrate and vertebrate hosts., Science 225: 1449-1452