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River Lamprey (Lampetra ayresii)
Species Profile

Did You Know?

Adult river lamprey can be distinguished from other species of lamprey by the presence of three large teeth, including a large middle tooth on the tongue and the absence of posterior teeth on the oral disc.

General Description

The river lamprey is an eel-like fish up to 12 inches in total length. River lampreys are distinguished from other Alaska lampreys by two large teeth on the supraoral bar and one large middle tooth located on the tongue.

Adult river lampreys are dark yellow to silver-gray or blue-black on the dorsal side and silver to white on the ventral side. Metamorphosis of river lamprey from larval to juvenile life stage occurs gradually over time as juvenile lamprey develop eyes, teeth, and the ability to swim freely.

Life History

Growth and Reproduction

River lampreys are anadromous which means it spends part of its life in the ocean and part of its life in fresh water. Anadromous river lampreys may spend months moving to the cool, clear headwaters of streams to make their nest or redds. Both males and females participate in redd building in stream riffles by removing small rocks with their mouths and fanning smaller particles with their tails. Males and females intertwine while simultaneously depositing sperm and eggs into the redd. Depending on her size, a single female can release up to 40,000 eggs. The adults die soon after egg fertilization. The eggs hatch in freshwater in 2 to 4 weeks depending on the water temperature. Larval forms of lampreys, referred to as ammocoetes, are born without eyes and lack sucking mouthparts. Lampreys remain at this stage for three to seven years before metamorphosing into juveniles, which includes the development of a sucking mouth, eyes, and teeth.

Feeding Ecology

Ammocoetes burrow into the silt, mud, or mud of shallow pools and eddies of clear streams and feed by filtering microorganisms, algae, and detritus from the water. Anadromous adult lampreys parasitize other organisms such as other species of fish or even marine mammals by using their sucking mouthparts to attach themselves to the host’s body. They then use their teeth to cut through the scales and skin to get to the host’s blood and body fluid.


Parasitic adult lampreys migrate to the sea after metamorphosing from juveniles and tend to spend one to four years in the marine environment before returning to freshwater to eventually spawn. Anadromous lampreys return to return to fresh water in the fall and overwinter until spring when they spawn. Lampreys tend to migrate upstream in large groups and once upstream migration commences, lampreys do not feed.

Range and Habitat

River lampreys are found only as far north as Stephen Passage and Tee Harbor in Southeastern Alaska.

Status, Trends, and Threats


River lampreys do not appear to be particularly abundant anywhere within its range. It is clear that an understanding of river lamprey genetic population structure is necessary to identify appropriate management units for maintenance of biodiversity and productivity.


Overall strength of river lamprey returns throughout its limited range appears to be quite low.


Potential overharvest from commercial, personal use or subsistence fisheries is the main threat to the resource.

Fast Facts

  • Size
    The river lamprey is smaller than other species of lamprey, measuring between 9 and 12 inches in length.
  • Range/Distribution
    Only known in Southeastern Alaska, as far north as Stephens Passage and Tee Harbor.
  • Diet
    Juveniles are filter feeders of diatoms and algae from the sediment. Adults feed by attaching parasitically to various species of fish such as salmon or sharks or marine mammals such as sperm whales.
  • Predators: Variety of sharks, sea lions, and other marine mammals.
  • Reproduction
    River lampreys are thought to overwinter and remain in freshwater environment for approximately one year before spawning.
  • Remarks
    Managed by the Alaska Department of Fish & Game in Alaska state waters.