Lampetra tridentata (Gairdner, 1836): Pacific lamprey

Biological Description

Body elongate, almost cylindrical, round in cross section from head to dorsal fin, posterior from dorsal fin origin, gradually more laterally compressed. Skin smooth and leathery. Lateral line absent. Skeleton cartilaginous, no vertebrae; notochord persists. Head without jaws; mouth a funnel-like disc, directed downward, with a margin of leaf-like lamellae; the inner part of the funnel lined with many series of sharp teeth; supraoral lamina, or bar, of three large cusps, three pair of inner lateral teeth, some tricuspid, scattered bicuspid and single teeth and a ring of small marginal teeth; the tongue is also armed with rasping teeth; eyes are small and high on head with a median single nostril between and slightly forward, and seven pairs of lateral gill openings behind. Dorsal fins two, separated by a cleft; first dorsal low and rounded; second dorsal longer, higher, rounded to pointed; caudal fin rounded; anal fin very low and inconspicuous; no paired fins. Color is dark bluish gray to dark brown paler below.

Life History

The spawning run of adult lampreys usually enter fresh water from May to September, but do not spawn until the following March or April. The males usually arrive on the spawning ground first, however, both sexes build a nest in sandy gravel by body vibrations or moving rocks with the suctorial disc. When the next is ready the female attaches to a rock and the male goes through various courting motions and at the proper time eggs and sperm are emitted together and the fertilized eggs fall into the nest. A female may lay from 30,000 to 100,000 eggs. The elliptical eggs hatch in two to three weeks. After hatching the ammocoetes burrow in the mud downstream from the nest where they remain for five or more years. At the end of this period, the transformation from larvae to adult is complete and they migrate downstream to the ocean where they become parasitic. There are landlocked populations that metamorphose and remain in fresh water where they prey on fresh-water fishes throughout their adult life. Such is probably the case in Pend Oreille Lake. The period of parasitism in both fresh and salt water may last one or two years before they return to spawn.

Geographic Distribution

The natural range is restricted to the Pacific Coast from the Aleutians Islands to Baja California and Hokkaido, Japan. It enters all major rivers including the Columbia. In Idaho it once migrated into all of the waters where salmon and steelhead migrated. Several small (8 inch) specimens were collected from Pend Oreille Lake in 1967 which were parasitic and attached to Kamloops trout. Its presence here is puzzling. They had not been observed previously to 1967 and have only been once since that date. Larval lampreys were impounded in Dworshak Reservoir (North Fork of the Clearwater River) when the dam was closed in 1971. By the 1973 angling season many lamprey scars on rainbow trout and kokanee were observed and six small metamorphosed lampreys collected. Since that time the incidence of parasitism has decreased rapidly and during the 1976 season only 11 incidences of parasitism were reported. There are some 25 species that inhabit the waters of the north temperate zone.

Habits and Habitats

Some lampreys may be restricted to freshwater whereas others spend a portion of their life in the ocean and return to freshwater to spawn (anadromy).


The larvae feed on desmids and diatoms. When lampreys turn parasitic they attach themselves to the side or undersurface of fishes. The toothed tongue rasps through the scales and skin and the blood and body fluids are consumed. An anticoagulant fluid is produced by the parasite which prevents the host's blood from solidifying.

Idaho Conservation Status

Considered critically imperiled by the State of Idaho.


Idaho Native or Import




Simpson and Wallace 1982. Wydoski and Whitney 1979. Image Copyright Joseph Tomelleri. Used by permission.