EN
The parasite fauna of autochthonous Cyprinus carpio and introduced Ctenopharyngodon idella, Hypophthalmichthys molitrix and Aristichthys nobilis, cultured together in fish ponds, was analyzed. In common carp four introduced parasites were found, while in introduced fishes 19 autochthonous parasite species occurred. The transfer of parasites between native and introduced fishes requires that the parasites have a rather wide circle of hosts. The autochthonous parasites which occurred in both autochthonous and introduced fishes were generally more frequent in introduced fishes, and vice versa. This fact can indicate a greater susceptibility of new hosts toward non specific parasites, and lack of balance in new host-parasite systems.