Abstract

In 1997 two and in 1998 six cases of mass mortality in Koi carp (Cyprinus carpio L.) with similar symptoms were examined. Gross examination revealed in each of the cases moderate to extensive epidermal lesions, gill necrosis and enopthalmus. Different ectoparasites were found on the skin only in low numbers, on the gills slight to heavy infestations, mainly with protozoan parasites encountered. Pathological anatomy revealed pale internal organs and an enlarged anterior kidney. Different opportunistic bacteria were isolated from inner organs, with Aeromonas sobria in 7/8 cases. Cohabitation trials confirm the infectious nature of the disease to different breeds of Cyprinus carpio. Transmission electron microscopy (TEM) revealed the presence of virus-like particles in the nuclei and cytoplasm of respiratory epithelial cells of gills.