Sphaerothecum destruens (the rosette agent) is a parasite of fish. It was first discovered in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in association with invasive species

Invasive species

"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

 including topmouth gudgeon but was found to be the causative agent of a disease in the UK affecting salmonid species such as Atlantic salmon

Atlantic salmon

The Atlantic salmon is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the north Atlantic and the north Pacific....

 and brown trout

Brown trout

The brown trout and the sea trout are fish of the same species....

. It is thought to pose more of a risk in Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 than in the USA as native species there are more susceptible to the parasite. The disease causes high rates of morbidity and mortality

Death

Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

 in a number of different salmonid species and can also infect other UK freshwater fish such as bream, carp

Carp

Carp are various species of oily freshwater fish of the family Cyprinidae, a very large group of fish native to Europe and Asia. The cypriniformes are traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain...

 and roach

Rutilus

Rutilus is a genus of fishes in the family Cyprinidae, commonly called roaches. Locally, the name "roach" without any further qualifiers is also used for particular species, particularly the Common Roach Rutilus (Latin for "shining, red, golden, auburn") is a genus of fishes in the family...

. The genus Sphaerothecum is closely related to the genera Dermocystidium

Dermocystidium

Dermocystidium is a genus of cyst forming parasitic protists of fish, which are the causative agents of dermocystidiosis.- Taxonomic History :...

and Rhinosporidium.