Abstract: The population biology of the monogeneans, Dactylogyrus chenminjungae, D. curvicirrus and D. montshadskyi parasitic on gills of Culterichthys erythropterus, from Honghu Lake in Hubei province, are being studied. Prevalence and abandance of the monogeneans show a pattern of seasonal alternation. The abundance of the three species are high in April, June and August respectively. The selectivity of parasitic sites is in relation to the population size, while the seperation of the ecological niche may be resulted from the interspecific competition.