Gyrodactylus pisculentus sp. n. is described from the head, body and fins of the northern pipefish, Syngnathus fuscus Storer (Syngnathidae) from the environs of Woods Hole, Massachusetts, USA. The new species is compared with Gyrodactylus shorti and Gyrodactylus syngnathi, species previously recorded from pipefish in the United States and Norway, respectively. Gyrodactylus pisculentus was frequently associated with mortality of northern pipefish held in quarantine at the Woods Hole Science Aquarium during 2002-2005. The clinical account of the infections and treatment protocols are presented.