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Tracheliastes polycolpus is a species of copepod in the family Lernaeopodidae. It is an ectoparasite of a number of freshwater fish in Western Europe, including the beaked dace Leuciscus burdigalensis, the common dace Leuciscus leuciscus, and occasionally a few other fish species. The subspecies Tracheliastes polycolpus baicalensis has been described from Lake Baikal. The parasite attaches itself to the fins of the host, and lives on the mucus and epithelial cells of the host.