American brook lamprey

American brook lamprey (Lethenteron appendix) [state threatened] Photo © Konrad P. Schmidt, University of Minnesota

The adult American brook lamprey is about six to eight inches in length. Its larval form, the ammocoete, is about eight inches long. The adult is gray to black on the back and upper sides and tan to gray-white below. The larva is dark brown on the back and sides and yellow-brown on the belly and fins. The breeding adult is green-brown to pink-purple or black on the upper surface. Like all lampreys, this fish has no jaws, no scales, no bones, no paired fins, one nostril and seven pairs of gill openings. Its skeleton is made of cartilage. The dorsal fin has two parts with a distinct separation between them. The mouth disc when expanded is narrower than the head. The teeth in the oral disc are arranged in clusters instead of rows.

The American brook lamprey may be found in the northeastern one-fourth of Illinois, although it is rare throughout this range. The adult lives in fast riffles of large creeks and small rivers that have clear water. The ammocoete, or larval lamprey, lives in sandy or silty pools where it burrows into the substrate with only its head sticking out. It feeds by filtering  small organisms from the water. Spawning occurs in late April and early May. More than 1,600 eggs per female are deposited. This lamprey is not parasitic, and the adults do not feed. They die soon after spawning. The eggs hatch in 20 to 22 days under the proper temperature conditions. The larval form takes five years or more to complete development.

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