WHIRLING DISEASE OF TROUTS CAUSED BY MYXOSOMA 

 CEREBRALIS IN THE UNITED STATES 



By 



Glenn L. Hoffman, Clarence E. Dunbai;- 

 and Arthur Bradford2^/ 



ABSTRACT 



This disease has recently appeared in North America for the 

 first time. It appeared in a Pennsylvania trout hatchery and may have 

 spread from there to the Lamar National Fish Hatchery which is on 

 the same watershed, and from Lamar to the Kensington State Hatchery 

 in Connecticut in transferred fish. The parasite develops in the car- 

 tilage, primarily of the head of very small trout. Symptoms of black- 

 tail, whirling, spinal curvature and misshapen heads follow SKeletal 

 damage . 



It was not possible to infect rainbow trout fry experimentally 

 with the spores although the incidence was very high in one of the 

 hatcheries . The development of the parasite was studied in infected 

 fish brought from the Benner Spring Hatchery to Leetown. In histo- 

 logical sections the parasite can be seen as a small multinucleate 

 trophosoite at 3 months after infection. The first spores can be seen 

 at 4 months and persist for at least 3 years. Spores can be found in 

 wet mounts prepared from head cartilage . 



A program for control has been started, and the incidence 

 appears to be declining in the Benner Spring Hatchery. The spring 

 water reservoir was chlorinated, the ponds cleaned and potassium 

 cyanamide applied. Acetarsone (Stovarsol) was fed to one lot of 

 small trout at high concentrations with no noticed side effects, but 

 control of whirling disease was not determined. 



This disease, apparently of central repeatedly to form a much larger organism 



European origin, has more recently appeared which finally produces the spores. During the 



in Russia, Italy, and the United States . Trout growth of the parasite much host cartilage is 



usually become infected during the first few eroded and the skeleton weakened, resulting 



weeks of feeding, mortalities ensue and most in the symptoms -- whirling, black tail, gaped 



of the surviviors exhibit disease symptoms for jaws, misshapen heads and trunks. The whirl - 



3 or more years. TTie spores gain entrance to ing is caused by damage to the cartilaginous 



the fish, presumably through accidental ingestion, capsule of the organ of equilibrium; the black - 



and the sporoplasm of the spore emerges and tail is caused by damage to the skeleton in the 



migrates to the cartilage, mainly that of the region of the nerves which control the posterior 



head. The very small sporoplasm, now called pigment cells, 

 a trophosoite, grows and its nuclei divide 



- Eastern Fish Disease Laboratory, Leetown (P.O. Kearneys ville), West Virginia. 



2/ Benner Spring Research Station, Pennsylvania Fish Commission, Bellefonte, Pennsylvania. 



