Abstract
Three parasite species, Anguillicola crassus (Nematoda), Myxidium giardi (Myxozoa) and Eimeria anguillae (Sporozoa) were recorded in the eel, Anguilla anguilla from the Mediterranean Lagoon of Mauguio (Southern France). A. crassus is found in the swim bladder, M. giardi in the kidney and E. anguillae in the intestinal cells of this bony fish. A comparative study of the temporal variations in the population structures of these three endoparasites has been undertaken. This study reveals : a) the regular presence of these endoparasites throughout the year in the eel, and the relative stability of intensities; b) the changes in prevalence are rather cyclic in A. crassus; they increase during spring and autumn. This biannual prevalence change could be related to its biological cycle and this later related to the planktonic blooms in these lagoons; c) the populations of M. giardi increase slightly during spring and autumn. Their periodicity however is less evident; d) E. anguillae is a regular species but does not present any evident cyclic features. The ecopathological consequences of these demographic characteristics are discussed.