Salmonids represent a large group of freshwater and migratory fishes of tremendous value in both sport and commercial fisheries; many species have become the subject of intensive breeding in aquaculture both in Europe and other countries. Wild and cultured populations of salmonids are, however, frequently endangered by parasites and other pathogens, which if allowed to go unchecked may cause considerable economic losses or result in the large scale mortality of fish. This also concerns the numerous metazoan parasites dealt with in this monograph; exceptionally, these parasites from fish may be the agents of serious diseases in man. Until now, no monograph on the metazoan parasites of European salmonids has been published and the existing data are contained only in numerous papers in journals or in the books where the parasites of salmonids are treated as the part of the broader subject of fish health. This book is intended primarily for parasitologists, biologists, veterinarians, workers in fisheries and university students.