Lampreys may not look like fish, but they are. Their round, sucking mouth, lack of pectoral and pelvic fins, and eellike body make Lampreys appear very different from “typical” fish. They also have a unique life history, going through a transformation, or metamorphosis, from larva to adult. Pennsylvania has seven Lamprey species.
The native Ohio Lamprey (Ichthyomyzon bdellium) is found in the Allegheny River and Ohio River watersheds. In Pennsylvania, Ohio Lampreys can sometimes be seen attached to and feeding on stream fish like Smallmouth Bass, Walleyes, Redhorse Suckers and Trout. Native parasitic Lampreys, like the Ohio, are smaller than Sea Lampreys. They evolved with other native fishes, so they do not have a significant effect on populations of their host fishes. The Ohio Lamprey is a Pennsylvania state candidate species.
The Northern Brook Lamprey (Ichthyomyzon fossor) is nonparasitic. This little Lamprey is rare throughout its limited Great Lakes and Midwest range, and is found in Pennsylvania only in a small portion of the northwest part of the state. The Northern Brook Lamprey is a state endangered species.
The Mountain Brook Lamprey (Ichthyomyzon greeleyi) is a state threatened species found in Pennsylvania in the Ohio River watershed. It, too, is nonparasitic.
The Least Brook Lamprey (Lampetra aepyptera) is found in headwater streams. It has been documented in western Pennsylvania’s Ohio River watershed and in the southeast’s lower Susquehanna River watershed. This nonparasitic Lamprey is widespread from Pennsylvania south to the Gulf of Mexico.
The nonparasitic American Brook Lamprey (Lampetra appendix) has a broad range throughout the Midwest. In Pennsylvania it lives in streams in the northern section of the Allegheny River watershed and in the Genesee River and Lake Erie watersheds.
In body structure, Lampreys are primitive fish. They and the marine Hagfishes are considered to be the only living representatives of the ancient jawless fishes. Their extinct relatives, the ostracoderms, were the first vertebrates to appear in the fossil record, about 500 million years ago. In Pennsylvania, Lampreys appeared in the fossil record 280 million years ago.
In Pennsylvania, the Sea Lamprey (Petromyzon marinus) naturally runs up the Delaware River from the Atlantic Ocean to spawn. It is also present in Lake Erie and the other Great Lakes. Sea Lampreys bypassed the barrier of Niagara Falls after the Welland Canal was built. By the 1920s, they had spread all the way to the upper Great Lakes. Thus, although natives of the Delaware watershed, they are non-native to the Great Lakes and Lake Erie. Sea Lampreys feed by attaching themselves by their concave, round, suctiondisk mouth to the exterior of fish. They rasp a hole in the skin with their rough tongue, and feed on the host fish’s body fluids. They may kill their host directly, or weaken it so much that fungus infections and other ills destroy it. The Sea Lamprey invasion of the Great Lakes caused disastrous declines in Lake Trout and Whitefish populations, affecting commercial and sport fisheries. Great Lakes tributary streams where Sea Lampreys spawn are treated with a chemical to reduce this damaging parasite’s numbers. Sea Lampreys have little effect on native fishes in the Delaware River because the adult parasitic form inhabits the Atlantic Ocean.
Lampreys lack the typical jaws of other fishes, in both their larval and adult forms. Larval Lampreys have a sort of oral hood. In parasitic Lampreys, after metamorphosis the hood is replaced by the adult’s concave, circular, sucker-disk mouth, with horny teeth. In nonparasitic Lampreys, the hood does not change. The patterns of the teeth help biologists differentiate among Lamprey species. Lampreys also do not have pectoral or pelvic fins, which are found on most other fishes. The Lamprey’s thin, cylindrical body is eellike or snakelike. It has a single, low, long dorsal fin. The dorsal fin may be notched, but it is never divided in two in Lampreys, and it connects to the curved tail fin.
Lampreys have no body scales, and on the inside they have a poorly developed skeleton of cartilage. Most Lampreys are gray, olive or brown. Some species have plain sides; others are mottled. The adult Lamprey’s eyes are small. Larval Lampreys have no readily visible eyes, although they are present, covered and sightless. Behind the Lamprey’s eyes, on either side, is a row of roundish gill openings.
Female Lampreys grow larger than males. The Sea Lamprey may reach three feet. Of Pennsylvania’s other Lampreys, the Ohio and American Brook grow to about 12 inches. The Mountain Brook and Least Brook Lampreys grow to about seven inches.
Lampreys have an unusual life cycle. They have a long larval stage, during which they are called “ammocoetes.” Then there is a period of resting and metamorphosis to the adult form. In parasitic Lampreys, there is more growth, feeding on host fish for about a year, sexual maturity, spawning and then, immediately following, death. The non-parasitic forms have a shorter life cycle. They become sexually mature during their transformation time, from larva to adult, so they don’t feed after metamorphosis, but go right to the spawning and dying stages. In the nonparasitic species, the spawning adults are often smaller than the ammocoetes just before transformation.
Lampreys move upstream in rivers and creeks before spawning, congregating on gravelly riffles. Males and females help construct the depression that becomes the nest. Parasitic Lampreys pick up and move gravelly particles downstream with their sucking mouths. Several Lamprey pairs may use the same nest for spawning, at the same time, emitting sperm and eggs during their spawning embrace. Parasitic forms lay more eggs (more than 20,000) than do nonparasitic Lampreys (500 to 3,000). All adults die shortly after spawning, while the fertilized eggs sift into the nest gravel. Hatched Lamprey larvae drift downstream and settle to burrow into the silty bottom. There they feed on organic material and bacteria that they filter from the water. They grow for several years until the time of metamorphosis. Stream fishes prey heavily on Lamprey eggs and the small larvae.