Parasitic nematodes (Nematoda) represent an important group of fish parasites. Many species are highly pathogenic, often causing serious diseases or even death to their fish hosts. The significance of recognizing these parasites increases with the development of aquaculture in many countries and with transcontinental transfers of fish. A prerequisite for developing effective control measures in fish culture is the exact identification of these parasites, as well as a knowledge of their, frequently complicated, host-parasite-environment relationships. The present monograph deals, in detail, with all nematodes which are parasites on European freshwater fish, providing contemporary knowledge of the taxonomy, biology and ecology of these parasites. It is divided into introductory chapters, including general morphological, biological and ecological data on fish nematodes, their pathogenicity and methods of study; systematic part/species descriptions, data on hosts, localization, distribution and life cycles and bionomy of all species systematically arranged; and a host-nematode parasite list. This publication is intended for parasitologists, veterinarians, workers in fisheries and university students. It should also be of interest to ichthyologists, museum curators and those engaged in nature conservation.