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sea lamprey

sea lamprey (Petromyzon marinus) [nonnative]
Photo © Sean Landsman/Engbretson Underwater Photography

Features and Behaviors


A typical sea lamprey averages 14 to 19 inches in length and eight to 13 ounces in weight. The average life span is eight to nine years. This fish has two dorsal fins. The mouth is as wide or wider than the head and contains sharp teeth. The body is blue-gray to olive-brown with black mottling and a light belly. The skeleton is made of cartilage.


The sea lamprey adult lives in Lake Michigan. The larval form lives in streams. Adults spawn in riffles and runs of streams and die after spawning. The female deposits 10,000 to 100,000 eggs in a nest on the bottom. Eggs hatch in about two weeks to the ammocoete stage, which is the blind, larval form. The larva burrows into the stream bottom with its head sticking out to filter microscopic organisms that pass by. The larval stage lasts seven years. Upon reaching the adult stage, the lamprey moves to Lake Michigan where it is a parasite of large fishes for about one and one-half years before returning to a stream to spawn and die. It attaches its tooth-filled mouth to the body of a fish and scrapes a hole in the body wall with its rough tongue. Body fluids and tissues are eaten through the hole. The sea lamprey is exotic to Illinois. Native to the Atlantic Ocean and Lake Ontario, this fish usually lives in the ocean and spawns in fresh water. The sea lamprey became able to enter inland waters with the building of the Welland Canal. The first individual sea lamprey was found in Lake Michigan in 1936. By the 1940s it was causing serious problems to fish populations in Lake Michigan. This animal severely decimated the populations of lake trout and whitefish in Lake Michigan in the 1940s and 1950s. In the 1960s a chemical (TFM) was developed and used to kill the larval forms in streams, bringing the population under control.

Illinois Range


​Kingdom: Animalia
Phylum: Chordata
Class: Cephalaspidomorphi
Order: Petromyzontiformes
Family: Petromyzontidae

Illinois Status: common, nonnative