An icosahedral cytoplasmic deoxyvirus has been isolated from moribund sheatfish (Silurus glanis) fry of a commercial warm water recirculation aquaculture unit with cumulative mortalities of up to 100%. The agent replicated in BF-2 and in FHM cells at 20-30 degrees C producing cytoplasmatic inclusion bodies followed by lysis of the cells. The DNA containing virus proved to be labile to chloroform. Infected BF-2 cells revealed hexagonal particles in the cytoplasm measuring about 125-135 nm in diameter. The virus consisted of a central electron-dense core and a electron-translucent zone. The isolate shares characteristics with the Iridoviridae.