Hemorrhagic thelohanellosis of color carp caused by thelohanellus hovorkai (myxozoa: myxosporea)

Abstract

Morbidity and mortality of adult (2- and 3-year old) color carp were recognized during June and July in 1994 and 1995 at a culture pond in Niigata Prefecture, Japan. The clinical signs were characterized by severe hemorrhages on the body surface, in particular ventrally and in the region of the mouth. The causative agent was identified as a myxosporean parasite, Thelohanellus hovorkai, which parasitized the connective tissues in various organs of color carp. Histopathological examination revealed hemorrhages, edema, extensive inflammatory cell infiltrations and exfoliation of dermal epithelium in the cutaneous lesions, associated with spore dispersion from matured plasmodia. Oligochaetes (Branchiura sowerbyi) in the culture pond were found to be infected with the corresponding aurantiactinomyxon actinosporean, and the prevalence reached a maximum of 81% in June. We propose to designate this disease "hemorrhagic thelohanellosis of carp".