American Brook Lamprey

The American brook lamprey (Lethenteron appendix) is a small, non-parasitic jawless fish widely distributed across clean freshwater streams of eastern and central North America, from the Great Lakes region south through the Mississippi basin to parts of the southeastern United States. It is closely related to the circumpolar Arctic lamprey (Lethenteron camtschaticum) and shares the genus's general body plan, but unlike many relatives, it never undergoes a parasitic feeding phase. The species completes its entire life cycle in fresh water, with the vast majority of its lifespan spent as a burrowing larva, followed by a brief adult stage dedicated entirely to reproduction. It is often used as an indicator of stream water quality due to its sensitivity to pollution and habitat disturbance.

The American brook lamprey is a small stream-dwelling lamprey best identified by its weak dentition and modest adult size.

Key field marks:

• Small, weakly developed teeth on the oral disc, reduced relative to parasitic lamprey species
• Dark grey-brown to olive back, fading to a pale cream belly
• Two closely spaced dorsal fins positioned near the tail
• Seven round external gill openings on each side of the head
• Adults typically 12-18 cm long

It can be distinguished from parasitic species sharing its range, such as the silver or chestnut lamprey, by its smaller size and weaker, blunter teeth, and from the more northerly Arctic lamprey mainly by its distribution and non-parasitic life history.

American brook lampreys inhabit small, clean, well-oxygenated streams and headwater tributaries across a broad swath of eastern and central North America, including parts of the Great Lakes, Ohio, and Mississippi River basins as well as scattered southeastern drainages. They favor stream reaches combining gravel riffles suitable for spawning with soft sandy or silty margins where larvae can burrow. The species is highly sensitive to water pollution and habitat alteration, making its presence a useful marker of good freshwater stream quality. As with other brook lampreys, it never migrates to the sea, spending its multi-year life cycle entirely within local stream systems.

American brook lamprey larvae, or ammocoetes, spend several years burrowed in soft stream sediment, filter-feeding on algae, detritus, and microorganisms. Upon metamorphosis, adults enter a brief non-feeding stage during which the digestive tract regresses, relying entirely on energy reserves accumulated during the larval period. Adults move only short distances within the stream to reach gravel spawning riffles, where they construct simple nests by shifting stones with their sucking mouths and spawn communally in groups before dying shortly afterward. Because adults never feed, the species has no parasitic interaction with other fish. Its larvae serve an important ecological function in nutrient cycling and as prey for other stream organisms.