The importance of parasitoses in freshwater fish culture grows parallel with the development of fishbreeding. Especially in intensively cultured fish populations one has to reckon with outbreaks of parasitoses. Although parasite-related problems are different in cultures of salmonids, carp, tilapias, catfishes, eels and ornamental fish protozoan parasites are in general of greatest importance. Among protozoans, myxozoan parasites deserve attention as recent research on this group has brought several new results. Regarding the control of parasitic fish diseases, biological methods might be successful together with prevention and a broader scale of effective medicines.