Ichthyomyzon fossor    Reighard and Cummins, 1916

Northern Brook Lamprey 

MN Status:
special concern
Federal Status:


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Ichthyomyzon fossor Ichthyomyzon fossor Ichthyomyzon fossor

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Map Interpretation

Map Interpretation


  Basis for Listing

The northern brook lamprey went undiscovered in Minnesota until 1986, when it was collected from the Blackhoof River in Carlton County and the Zumbro River in Olmsted County. It has subsequently been collected in Fillmore, Itasca, Koochiching, Lake of the Woods, Pine, Roseau, St. Louis, Dodge, and Mower counties, and additional populations are expected to be found. These populations represent the northwestern edge of the species' range, which is centered in the Upper Midwest. The northern brook lamprey is at some risk from reduced water quality from land use practices and from lampricide treatments. For these reasons, it was listed as a special concern species in Minnesota in 1996.


The northern brook lamprey has a single, continuous dorsal fin, that may or may not be divided by a shallow notch, connected to a short, round caudal fin. Its mouth is a sucking disc with small, poorly developed teeth. Adult length is usually less than 16 cm (6.3 in.). Adults are grayish brown dorsally, with a pale median line down the back, and lighter ventrally. The posterior portion of the tail is darker, almost black. Ammocoetes, the larval form, lack eyes and are similar in coloration to adults, but have a hood-like mouth instead of a sucking disc. Females tend to be slightly larger. Breeding males have a urogenital papilla and breeding females have an enlarged post-anal fold with eggs often visible through the body wall.


The northern brook lamprey uses different microhabitats during different portions of its life history. Adults are typically found over coarse substrate, sand or gravel, in swifter waters, riffles, or runs. Ammocoetes are found burrowed in fine sediment or organic debris in side channels or other quiet water in areas with embedded woody debris. Spawning occurs in crevices beneath rocks and boulders (Hatch et al. in preparation). The species is most commonly found in clear streams averaging 19 m (62 ft.) wide and 0.7 m (2.3 ft.) deep, and usually in moderately warm water.

  Biology / Life History

The northern brook lamprey is a non-parasitic species. The majority of its life, 3-6 years, is spent as a blind ammocoete partially buried in sandy substrate. Ammocoetes feed on drifting, suspended organic detritus, algae, and bacteria or nutrients drawn from the surrounding sediment. Transformation to adults occurs over 2-3 months in late summer or early fall. As adults, they do not feed. During spring spawning, adults make an oval depression nest by displacing stones and organic material. As many as 7 or 8 individuals can be involved in nest building and they may spawn in aggregations of 10-30 individuals. Adults die a few days after spawning. Eggs hatch 12 days after fertilization and the young become free-swimming (J. T. Hatch, University of Minnesota, pers. comm.).

  Conservation / Management

The apparent decline of the northern brook lamprey in North America is a result of habitat degradation and incidental poisoning. Streams in which they occur should be protected from degradation by maintaining riparian buffers, avoiding contamination, and employing best management practices for timber harvest in surrounding forests. The species may also be adversely affected by lampricide treatments (TFM: 3-trifluoromethyl-4-nitrophenol) for parasitic lampreys, especially in the Blackhoof River population. Although suitable habitat is limited in North Shore streams, TFM may have eliminated populations before discovery (J. T. Hatch, pers. comm.).

  Conservation Efforts in Minnesota

Because the northern brook lamprey has a highly restricted range and little is known about the Minnesota populations, information regarding its distribution, population size, life history, habitat requirements, and genetics are necessary to determine the need for monitoring and/or management. There are currently no management plans directly aimed at the northern brook lamprey.


Becker, G. C. 1983. The fishes of Wisconsin. University of Wisconsin Press, Madison, Wisconsin. 1052 pp.

Cochran, P. A. and A. P. Gripentrog. 1992. Aggregation and spawning by lampreys (genus Ichthyomyzon) beneath cover. Environmental Biology of Fishes 33:381-387.

Cochran, P. A., and T. C. Pettinelli. 1988. Northern and southern Brook Lampreys (Ichthyomyzon fossor and I. gagei) in Minnesota. Minnesota Academy of Science 54:23-27.

Hatch, J. T., G. L. Phillips, and K. P. Schmidt. In preparation. The fishes of Minnesota.

U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Ichthyomyzon fossor. United States Forest Service, Region 9. 16 pp.