Northern Brook Lamprey

Ichthyomyzon fossor


Illustration of a northern brook lamprey
The northern brook lamprey is not parasitic. It lives in streams in the northern Ozarks.
Ted Walke, PA Fish & Boat Commission

Petromyzontidae (lampreys) in the class Agnatha (jawless vertebrates)


All lampreys have snakelike bodies and smooth, slippery skin, lack a lower jaw, and have a mouth that consists of a rounded sucking disk. There are no paired fins. There are 7 pore-like gill openings along each side of the head. Unlike parasitic lampreys, brook lampreys as a group don’t have many teeth in their sucking disk, and the teeth they have are poorly developed, especially near the outer edge of the disk. When expanded, the sucking disk is narrower than the head. The northern brook lamprey has an undivided though shallowly notched dorsal fin, and all the disk teeth are poorly developed. In the innermost circle, all teeth are 1-pointed. Adults ready to spawn are darkish brown, becoming nearly black by the time spawning is completed. The larvae (ammocoetes) of all lampreys resemble the adults but lack eyes, and the mouth is a horseshoe-shaped hood instead of a sucking disk. Larvae and new adults are grayish brown above, yellow on the belly and fins.


Adult length: 6–8 inches long; larvae may grow to nearly 8½ inches long.


Northern Brook Lamprey illustration
Northern Brook Lamprey
The Northern Brook Lamprey is nonparasitic.
Habitat and conservation

Found in medium-sized streams. They avoid both small headwater creeks and large rivers. All brook lampreys require clear, permanent-flowing streams having clean, gravelly riffles for spawning and stable beds of silt, sand and organic debris for larval development. Three other species of brook lampreys occur in Missouri: southern brook lamprey, least brook lamprey and American brook lamprey. All are found in Ozark streams, with the least brook lamprey being much more common than the other two.


All immature or larval lampreys burrow into soft-bottomed areas of streams and feed on microscopic life and organic particles strained from the water and from the bottom sediments. When lampreys undergo the transformation to adults, they stop feeding and can actually become smaller. Brook lampreys never enter a parasitic stage. When they transform into mature adults in late summer and fall, they remain in their smaller streams without feeding until the following spring, when they spawn.

image of Northern Brook Lamprey distribution map
Distribution in Missouri

Streams in the northern Ozarks, particularly the Osage, Gasconade, and Meramec river systems.


This is the most common and widely distributed brook lamprey in the northern Ozarks. It may be more widely distributed than records suggest. There are 5 species of brook lampreys in Missouri. Two of them, the southern brook lamprey (I. gagei) and American brook lamprey (Lampetra appendix), are Species of Conservation Concern, due to their rarity and/or declining populations. The other Missouri brook lampreys are the silver lamprey (I. unicuspis) and least brook lamprey (L. aepyptera).

Life cycle

Spawning in Missouri is in early May. Adults excavate pits, carrying stones with their sucker mouths, or spawn between or beneath rocks. Adult lampreys die shortly after spawning. Larval, or ammocoete, lampreys burrow in bottom sediments, using a sieve apparatus to filter microscopic food from the water. The larval stage can last 3–6 years. Transformation to adult stage takes several months in late summer and fall. As adults, brook lampreys stay in their creeks to spawn and do not eat at all.

Human connections

Brook lampreys do not parasitize or harm other fish. They are primitive survivors from ancient times, remnants of a group of fishes that lived more than 350 million years ago. They are no more closely related to other living fishes than these fishes are to amphibians and other vertebrates.

Ecosystem connections

Anyone who has owned an aquarium understands the importance of a “bottom feeder.” Brook lampreys eat tiny organisms and other materials and in turn become food for something else. The eggs and the young lampreys, like other small fish, are preyed upon heavily by other fish and animals.