The increasing impact of some parasitoses on fish health and its economic relevance in aquaculture and fisheries has enhanced the need for studies on piscine parasites and on the fish-parasite relationships. Fish parasites are an important part of water ecosystems, and thus, changes in these habitats can affect the host-parasite equilibrium. The research teams leaded by the author have studied piscine parasites in Spanish waters since 1970. In this Part 1, the parasite fauna of continental fish (mainly salmonids and cyprinids), mostly collected in rives of the Duero basin (NW Spain) from 1970...