Fish Parasites in a Hypertidal Estuary of the Penzhina River (the Sea of Okhotsk Basin)

Abstract—The species composition of parasites (114 species) has been studied in the estuary of the Penzhina River. The influence of the specific conditions of the estuary on the parasite fauna is shown. High flow velocities, freshwater and seawater mixing, and the abundance of organic matter determine the dominance of parasite species with morphological adaptations for the reliable attachment to fish that are tolerant to changes in salinity and associated with benthos in the life cycle. Transitions of parasites to atypical hosts have been observed. The component communities of parasites of most fish species are characterized by high indices of diversity and evenness and low indices of dominance. In the marginal populations of pike and whitefish, they are strongly depleted with pronounced dominants and their change in ontogeny. The Arctic and Pacific elements of the ichthyoparasite fauna testify to the influence of the Arctic and Pacific oceans on its formation.