Mass mortalities in Koi carp, Cyprinus carpio, associated with gill and skin disease

In 1997 two and in 1998 six cases of mass mortality in Koi carp (Cyprinus c arpio L.) with similar symptoms were examined. Gross examination revealed i n 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 a nd an enlarged anterior kidney. Different opportunistic bacteria were isola ted from inner organs, with Aeromonas sobria in 7/8 cases. Cohabitation tri als confirm the infectious nature of the disease to different breeds of Cyp rinus carpio. Transmission electron microscopy (TEM) revealed the presence of virus-like particles in the nuclei and cytoplasm of respiratory epitheli al cells of gills.