Chesapeake Bay Introduced Species Database

Myxobolus cerebralis

Common name(s):
Whirling Disease
Whirling Disease is a trout and salmon parasite discovered in 1893 when Rainbow Trout, a native to the Pacific coast of North America, were imported into Germany and contracted the disease. The parasite is probably associated with the Brown Trout, which is native to central Europe and Northeast Asia. The parasite was spread as Brown Trout and others fish species were moved around the world as part of the push to enhance sport fishing. The disease is especially common in hatcheries and has been seen in several in Virgina and Maryland, but is also widespread in natural waterways. The disease causes the skeleton of juvenile fish to curve, which causes the fish to swim in a circle or whirl.
Image courtesy of Dr. Peter W. Pappas, Ohio State University.


Myxobolus cerebralis


Myxobolus chondrophagus; Myxosoma cerebralis; Lentospora cerebralis; Triactinomyxon gyrosalmo; Triactinomyxon dubium

Potentially Misidentified As:

Myxobolus insidiosus Myxobolus kisutchi; Myxobolus neurobius; Myxobolus squamalis

Common Names:

Whirling Disease


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).

This data was last modified on Wednesday, July 17th, 2013.
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