Assessing the importance of American eel (Anguilla rostrata) restoration to freshwater mussel populations in the Susquehanna River

Science Center Objects

The eastern elliptio mussel (Elliptio complanata) is a freshwater mussel that is abundant in many eastern streams and rivers along the Atlantic coast.  Mussels provide important functions in stream ecosystems that help improve water quality such as filtration of algae, sediment, and micronutrients from the water column.  Larval stage (glochidia) eastern elliptio must parasitize a host fish, primarily American eel, to complete metamorphosis to the juvenile life stage.  Although the eastern elliptio is abundant, evidence suggests that populations are comprised of old mussels (sometimes >150 yrs) with limited or no reproduction throughout the Susquehanna River Basin.  In collaboration with US Fish and Wildlife Service, NARL researchers are testing the hypothesis that the loss of eastern elliptio mussels in the Susquehanna Basin is primarily a function of the declining American eel populations that cannot reach their historic upstream habitat due to dams blocking their migration.  Restoring the upstream distribution of American eels and eastern elliptio could have implications for water quality of not only the Susquehanna River, but to the Chesapeake Bay as well. 


Adult American eel (Anguilla rostrata)

Adult American eel (Anguilla rostrata) released into Pine Creek, PA as part of an experimental stocking study investigating the impacts of American eel restoration on eastern elliptio mussel (Elliptio complanata) reproduction.

(Credit: Gary Tyson, Tiadaghton Audubon Society. Public domain.)

Encysted eastern elliptio mussel larvae (glochidia) on its American eel host’s gills

A close-up photograph of an American eel’s (Anguilla rostrata) gill with larval mussels (glochidia) attached.  Larvae will remain on the gills for 2-4 weeks until they metamorphosis into juvenile mussels.  Juveniles detach from the host gills and settle into the river’s sediment where they grow into adult mussels and can live as long as 100+ years.   

(Credit: Carrie Blakeslee, USGS Leetown Science Center. Public domain.)

Juvenile eastern elliptio mussels (Elliptio complanata)

Juvenile eastern elliptio mussel collected during freshwater mussel surveys in Pine Creek, PA, 5 years following experimentally stocking its host fish, the American eel (Anguilla rostrata). 

(Credit: Julie Devers, U.S. Fish and Wildlife Service. Public domain.)