In the analysis of the population dynamics of various celozoic Myxosporidians found in Cyprinids of the river Esla (León, NW Spain) a bimodal seasonality was observed for Myxidium macrocapsulare Auerbach, 1910, Myxidium carinae Alvarez-Pellitero et al., 1983 and Chloromyxum complicatum Alvarez-Pellitero et al., 1983. We did not observe a clear influence of the age and sex of the host on the infections. An apparently positive association was observed for Myxidium carinae and Chloromyxum complicatum in Barbus barbus bocagei, and for Myxidium macrocapsulare and Chloromyxum complicatum in Leuciscus cephalus cabeda, which we consider due probably to ecological factors.