Fish Active day and night

Chestnut Lamprey

Ichthyomyzon castaneus

iNaturalist Wikipedia

An ancient, jawless survivor of North American rivers, the Chestnut Lamprey is a marvel of prehistoric evolution. From its parasitic adult life to its mysterious years as a riverbed larva, this unique fish plays a vital role in the health of our freshwater ecosystems.

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Quick Identification

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Size

15 to 38 cm (6 to 15 inches) in length; typically weighs 30 to 80 grams (1 to 2.8 oz)

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Colors

Dull olive, yellowish-tan, or chestnut brown on the back and sides; belly is typically a lighter cream or silver color

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Key Features

Eel-like body lacking scales and paired fins
Circular, sucker-like mouth filled with sharp, radiating bicuspid teeth
Single dorsal fin that is continuous and only slightly notched
Seven small, circular gill openings arranged in a row behind each eye

When You’ll See Them

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Activity pattern Active day and night

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Peak hours 6-10 AM, 5-9 PM

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Season April-June

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Diet Adults are parasitic on larger fish species; larvae (ammocoetes) are filter feeders that consume algae, detritus, and microorganisms from the riverbed.

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Habitat Adults inhabit medium to large rivers and reservoirs; larvae require stable, silty-bottomed areas in smaller tributary streams.

public Geographic range

Where Does the Chestnut Lamprey Live?

Native to the freshwater systems of North America, the Chestnut Lamprey is primarily found throughout the expansive Mississippi River basin and the Great Lakes drainage. Its core range extends from central Canada, including Manitoba and Ontario, southward through the Midwestern United States to the Gulf Coast drainages of Texas and Louisiana. It is a common sight in the river-rich states of Wisconsin, Minnesota, and Arkansas, though it is strictly a freshwater species and does not migrate to the ocean.

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2 Countries

2.5M km² Range

Least Concern Conservation

US United States

Marginal

CA Canada

Marginal

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iNaturalist / Verified observation data

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Behavior

The Chestnut Lamprey is a primitive, jawless fish that exhibits a fascinating dual lifestyle. As adults, they are parasitic, using their specialized suction-cup mouths to attach themselves to the bodies of larger host fish like sturgeon, paddlefish, and catfish. They use a raspy, tooth-covered tongue to break the skin and feed on the host's blood and fluids. While this sounds gruesome, in a healthy ecosystem, they rarely kill their hosts, acting more like a temporary nuisance than a lethal predator.

This parasitic phase is relatively short, lasting about one year, after which the adults migrate into smaller, clear-water streams to spawn. Once they reach the spawning grounds, they move stones with their mouths to create a shallow nest called a redd. Like salmon, Chestnut Lampreys are semelparous, meaning they put all their remaining energy into reproduction and die shortly after the eggs are laid. The young, called ammocoetes, spend several years buried in river sediment as blind filter feeders before transforming into the parasitic adult form.

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Camera Tips

To capture the Chestnut Lamprey on camera, you will need to utilize underwater equipment, as they are rarely visible from the surface. The best time for recording is during the spring spawning season (April to June), when adults move into shallower, clearer tributary streams. Look for gravelly riffles where the water is 1 to 3 feet deep. Secure an underwater action camera to a heavy diving weight or a flat rock to prevent it from being swept away by the current. Point the lens slightly downstream to catch the lampreys as they struggle against the current or move stones to build their nests.

Because river water can be turbid, choose a day after a period of no rain when the water clarity is at its peak. Natural sunlight is your best friend; try to position the camera in a spot that receives direct overhead sun between 10 AM and 2 PM. The Chestnut Lamprey’s skin is non-reflective and brownish, which can make it disappear against a rocky background, so a high-contrast setting or 4K resolution is helpful for picking out detail.

If you are using a trail camera with an external waterproof housing, set it to record short video clips (15-30 seconds) rather than still photos. The unique, undulating swimming motion of the lamprey is its most identifying characteristic and is best captured in motion. Avoid using high-intensity artificial lights at night, as this can spook both the lampreys and their potential host fish. Instead, rely on high-ISO settings for low-light morning or evening shots.

Similar Species

Species that look similar or are commonly confused with Chestnut Lamprey.

Silver Lamprey

Silver Lampreys usually have single-pointed (unicuspid) teeth in the circumoral row, whereas Chestnut Lampreys have two-pointed (bicuspid) teeth.

Sea Lamprey

Much larger (up to 3 feet) with two separate dorsal fins and a more mottled, dark grey-to-black appearance.

Northern Brook Lamprey

This species is non-parasitic as an adult and is significantly smaller, usually reaching only 6 inches in length.

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Frequently Asked Questions

Chestnut Lampreys are active throughout the day and night. However, their spawning activities, including nest building and movement in shallow streams, are most frequently observed during daylight hours, especially in the late morning and early afternoon when water temperatures rise slightly.

Unless your backyard contains a medium-to-large natural river or a clear, silty tributary within their range, you cannot easily attract them. They require specific riverine conditions. Maintaining a healthy, unpolluted local watershed and preventing siltation in spawning streams is the best way to support their populations.

Adult Chestnut Lampreys are parasitic and feed on the blood and body fluids of other fish. They do not eat solid food during this stage. In contrast, the larval stage (ammocoetes) are filter feeders that live in the mud and eat microscopic algae and organic debris.

They are only found in suburban areas that are adjacent to major river systems in the central U.S. and Canada. They are sensitive to heavy pollution and damming, so they are more common in areas with free-flowing, healthy river environments.

The easiest way to tell them apart is by the dorsal fin. The Chestnut Lamprey has one continuous dorsal fin that is slightly notched, whereas the Sea Lamprey has two distinct, separate dorsal fins. Additionally, Sea Lampreys are much larger and usually have a mottled skin pattern.

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