Silver Lamprey

The silver lamprey (Ichthyomyzon unicuspis) is a jawless, parasitic fish native to freshwater river and lake systems of central and eastern North America, including the Great Lakes, Hudson Bay, and Mississippi River drainages. It belongs to the genus Ichthyomyzon, a group of lampreys found exclusively in North America that includes both parasitic and non-parasitic (brook lamprey) species. Unlike many other lamprey species, the silver lamprey completes its entire life cycle in fresh water, never migrating to the sea. As an adult, it attaches to host fish to feed on blood and body fluids, a habit shared with several related species, though it is native to its range and not considered invasive, distinguishing it ecologically from the introduced sea lamprey found in the same lake systems.

Silver lampreys can be identified through a combination of tooth pattern, coloration, and dorsal fin shape.

Key field marks:

• Oral disc teeth with a single sharp cusp each (unicuspid), rather than multiple points, giving the species its scientific name
• Silvery-grey to bluish back with a metallic sheen, fading to a pale belly
• A single continuous dorsal fin with only a shallow notch, rather than two clearly separated dorsal fins
• Seven round external gill openings on each side of the head
• Adults typically 30-40 cm long

The single-cusped teeth and largely continuous dorsal fin distinguish the silver lamprey from other Ichthyomyzon species such as the chestnut lamprey, which has multi-cusped teeth, and from the sea lamprey, which is larger with a heavily blotched pattern.

Silver lampreys inhabit freshwater lakes and rivers across central and eastern North America, with strongholds in the Great Lakes, upper Mississippi River basin, and Hudson Bay drainage. As adults, they are typically found in larger rivers and open lake waters where suitable host fish populations occur. To spawn, they migrate into smaller tributary streams with gravel or rocky substrate and moderate flow. Larvae burrow into soft silty or sandy sediment along stream margins, where they remain for several years before undergoing metamorphosis. The species requires clean, well-connected freshwater systems throughout its life cycle, as it never enters marine or brackish waters.

Silver lampreys are parasitic as adults, attaching to a range of host fish species with their toothed oral disc and feeding on blood and body fluids over an extended period before detaching, often leaving characteristic circular scars on survivors. They are most active in open water and larger river channels where host fish are abundant. As the spawning season approaches, typically in spring, adults migrate into smaller tributary streams, cease feeding, and construct simple nests in gravel substrate by moving stones with their sucking mouths. Spawning occurs communally, and adults die shortly afterward. Larvae live buried in soft sediment for several years as filter feeders, contributing to nutrient cycling in stream ecosystems before metamorphosing into free-swimming, host-seeking adults.