In Southern Yakutia, the common minnow hosts 37 species of parasites, including the most numerous groups, such as Infusoria, Myxozoa, and Monogenea. Specific parasites include Myxobolus lomi, Myxobolus mongolicus, Epistylus phoxini, Apiosoma phoxini, Trichodina mira, Paratrichodina phoxini, Gyrodactylus laevis, Gyrodactylus limneus, Gyrodactylus macronychus, Gyrodactylus magnificus, and Diplostomum phoxini. The component parasite communities are characterized by high rates of evenness and diversity, but the low level of dominance. They possess different structure in dependence to specific conditions of their formation. Pollution of the Chulman River with heavy metals and organic wastewater resulted in changes of the structure of parasite communities and replacement of dominants. The characters of chronic damages of gills in the minnow caused by M. lomi have been reported, including deformations of gill arches and filaments, destructions of lamellae, and substitution of the lamellae by parasite's plasmodia.