Fish and Aquatic Conservation

illustration of a Pacific lamprey

Pacific lamprey

Entosphenus trudentatus (Richardson, 1836)

Cool Facts

The maximum recorded age for Pacific lamprey is 9 years. The maximum weight published for a Pacific lamprey is 500 grams (17.6 oz).

SIZE: Common length for Pacific lamprey is 41 cm (16.1 inches). The maximum recorded length for Pacific lamprey is 76 cm (30 inches).

RANGE: The range of the Pacific lamprey within the North Pacific extends from the Bering Sea coasts of Asia and Alaska, southward to the Yuhuntun River, Hokkaido, northern Japan and southward to Punta Canoas, central Baja California and Mexico. There are some freshwater resident populations existing in Culrus Lake and the Columbia River, British Columbia, the Spague River in Oregon, the Goose Lake in Oregon/California, the Klamath and Shasta rivers and Copco Lake in California.

HABITAT: Adult Pacific lamprey inhabit marine environments in depths ranging from 300 to 2,600 feet (90.9 m – 788.9 m). Pacific lamprey have been recorded at distances of 62 miles off the west coast of the United States. Adult lamprey spawn in habitats similar to adult Pacific salmon, which includes the upstream end of riffles areas in streams with gravel bottoms.

DIET: Pacific lamprey are a parasitic anadromous species that feed on the blood and bodily fluids of other fish species. They attach themselves to other fish by using a round, sucker‐like mouth containing several types of specialized teeth that enable them to attach themselves to other fish.

Natural History

Pacific lamprey are an anadromous species. Adult Pacific lamprey spend between 1 to 3 years at sea before they stop feeding and begin to migrate into freshwater between February and June of the same year. It is believed that once they return to freshwater habitats, they overwinter and inhabit freshwater for about one year before they spawn. During this overwintering period, they may shrink in size by as much as 20 percent.

Pacific lamprey spawning usually occurs between March and July depending on the geographical location of their native range. It is believed that lamprey larvae release some type of fish hormone that enables the adults to locate suitable spawning locations. Both the male and female adults participate in nest construction. After the nest is completed, the females of the species then deposit their eggs in the nest and the male lamprey then fertilizes them by releasing his milt over the eggs.


Pacific lamprey populations have decreased in many river drainages, while some populations have become extinct above impassable river barriers on west coast streams and rivers. Pacific lamprey face significant threats to their habitat. These threats include fish passage barriers, inadequate water flows, poisoning from toxic water spills, poor water quality, impacts from dredging operations from mining and water channel maintenance, and stream and floodplain degradation. During their ocean phase, Pacific lamprey face variable ocean conditions which include prey variability and increased risk of predation.

Migration Behavior

Pacific lamprey are a migratory species. They are born in fresh water and then migrate to the ocean for their adult lives and return to fresh water to reproduce.