This ancient jawless fish is seeing for the first time after recently metamorphosing to resemble its more familiar adult form. Juvenile Pacific lamprey (Lampetra tridentate) begin life appearing more like a worm than a fish. As larval lampreys or “ammocoetes” they lack eyes and fins, and spend 5-7 years buried tail first in the river substrate, filter feeding by mouth. Once they reach a length of around 14-16 cm they begin a radical change in physiology and physical appearance. They become silvery, and develop long dorsal fins, large eyes, and a strong sucking mouth with lateral tooth plates. The newly transformed lamprey swim downstream to the ocean where they will begin a novel life as marine predators. Check out our previous Pacific Lamprey post for additional photos and life history information.

Photo source: FISHBIO

The Pacific lamprey, Lampetra tridentate, is an ancient jawless fish that resembles an eel. The adults are parasitic attaching themselves to the side or undersurface of its prey where they use their rasping tooth plates to feed on blood and body fluids. They begin their life cycle as an ammocoete or larvae, usually within a freshwater stream. They burrow tail first into mud or sand where they filter feed on algae and organic matter for 5-7 years before developing eyes and morphing into adults as they migrate downstream to the Pacific Ocean.

Like salmon they are anadromous, migrating to freshwater for spawning, and usually die following spawning. Also like salmon they serve an ecological role transporting nutrients such as nitrogen to freshwater ecosystems. It’s believed that the juvenile lamprey outmigrating to sea were once much more numerous and acted as a buffer to reduce predation on salmon, and provided a good food source for birds, fish, and mammals. Even though Pacific lamprey populations have declined the US Fish and Wildlife Service ruled that they do not warrant listing. We occasionally capture adults lamprey and typically capture thousands of juveniles during our central valley salmon outmigration monitoring.