Nanophyetus salmincola - MMFS

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Fish Parasite

Nanophyetus salmincola

Histological section of Nanophyetus salmincola metacercariae

Histological section of Nanophyetus salmincola metacercariae in the gills of an affected steelhead trout. Credit: Paul Hershberger, USGS - Western Fisheries Research Center. (Public domain)

Nanophyetus salmincola is a digenean parasite with a complex life cycle involving freshwater snails as the first intermediate host, freshwater and anadromous fishes as the second intermediate hosts, and birds and mammals as the definitive hosts. Its geographical range in coastal watersheds from northern California through central Washington is determined primarily by the distribution of the first intermediate snail host. However, the encysted parasite commonly occurs in the tissues of marine-phase salmonids beyond this narrow geographic range as infected juveniles outmigrate into the Pacific Ocean.  Current research at the Marrowstone Marine Field Station is directed towards understanding how Nanophyetus infections impact the health and survival of outmigrating steelhead smolts in Puget Sound.