Maryland Sea Grant Backyard Ecology: Lamprey

In a freshwater tributary of the Corsica River on Maryland’s Eastern Shore, lampreys are wriggling along the bottom and occasionally attaching to small pebbles. Without looking inside their mouths, it’s hard to tell precisely what species of lamprey these are; Maryland has three.
They could be young sea lamprey (Petromyzon marinus), who live in the Bay’s freshwater tributaries for 4-5 years as larvae before metamorphosing into adults. Once that happens, they head for the ocean.
Like all lampreys, they don’t have an actual jaw. Instead, they have sucker-like discs as mouths, and in the sea lamprey these are scary looking indeed, filled with sharp, pointed teeth arranged in concentric circles. Using that mouth to attach to larger fish, the parasitic sea lamprey consumes blood and other tissues.
As adults, sea lamprey can grow to over 700 mm (nearly 28 in) long; they return to freshwater streams to spawn, then die.
Though it looks similar to a young sea lamprey, the American brook lamprey (Lethenteron appendix), which also lives in Maryland, couldn’t be more different. It’s not anadromous; in all stages of its life, it stays in slow-moving, freshwater streams with shady edges. It isn’t parasitic; in fact, the adults they don’t even eat. Larvae live up to 7 years consuming algae before metamorphosing into adults in the fall, spawning in spring, and then dying. As adults, they can grow to about 275 mm (nearly 11 in) long.
Though their populations are stable elsewhere, American brook lamprey are declining in the Mid Atlantic, and in Maryland-where human pressures are degrading or eliminating their habitat-they’re considered threatened.
Last but not least, the least brook lamprey (Lampetra aepyptera) is found in streams on the Eastern Shore and along the western side of the Chesapeake Bay. Like the American brook lamprey, these fish spend about 5-6 years as larvae in freshwater streams eating microscopic plant material until they mature into adults in the fall (when they eat nothing), spawn in spring, and die. Though their populations in Virginia and Pennsylvania are considered “vulnerable,” and in Delaware “imperiled,” in Maryland this lamprey is listed as “apparently secure.”
Fun fact: Like other fish, lampreys breathe through gills. But you can’t see them; lampreys draw water in through a series of openings just behind their eyes, and their gills are internal.