The Pacific lamprey is a common parasitic lamprey in Pacific coastal waters. The lamprey has a round, elongate, flexible cartilaginous body, and skin with no scales. Lamprey are very smooth and slimy to the touch. Its mouth is down-turned and adapted for clinging and sucking. The Pacific lamprey are a dark bluish gray or dark brown in color and can reach 30 inches in length and weigh over a pound. The pacific lamprey has no true fins, jaws, or bones. Lampreys have long been used as food for humans. During the Middle Ages, they were widely eaten by the upper classes throughout Europe, especially during fasting periods, since their taste is much meatier than that of most true fish. Especially in Southwestern Europe (Portugal, Spain, France) they are still a highly prized delicacy and fetch up to $25 a pound. Overfishing has reduced their number in those parts. The pacific lamprey is anadromous. Like salmon they are born in freshwater streams, migrate out to the ocean, and return to fresh water as mature adults to spawn. Lampreys have become a major plague in the North American Great Lakes after artificial canals allowed their entry during the early 20th century. They have no natural enemies in the lakes and prey on many species of commercial value, such as trouts. Since North American consumers, unlike Europeans, refuse to accept lampreys as food fish, the Great Lakes fishery has been very adversely affected by their invasion. The lamprey enter streams from July to October; spawning takes place the following spring when water temperatures are between 50 and 60 degrees Fahrenheit. They ascend rivers by swimming upstream briefly, then sucking to rocks and resting. Spawning takes place in low gradient sections of water, with gravel and sandy bottoms. Adults die within four days of spawning, after depositing about 10,000 to 100,000 extremely small eggs in their nest. During its ocean phase of life the pacific lamprey are scavengers, parasites, or predators on larger prey such as salmon and marine mammals. After 2 to 3 years in the ocean they will return to freshwater to spawn.
The sea lamprey is an aggressive parasite - equipped with a tooth-filled mouth that flares open at the end of its eel-like body. When attacking, the lamprey fastens onto its prey and rasps out a hole with its rough tongue. In their natural habitat, sea lamprey are ocean fish that spawn in fresh water. But some sea lamprey have always inhabited Lake Ontario and the St. Lawrence River, which are open to the Atlantic Ocean.
Recent studies reported in nature suggest that lampreys have evolved a unique type of immune system with parts that are unrelated to the antibodies found in mammals. They also have a very high tolerance to iron overload, and have evolved biochemical defenses to detoxify this metal. Lamprey have similar freshwater habitat requirements as do some of the Pacific salmon, therefore they have encountered similar habitat problems.
Though absolute historical population sizes of the lamprey are not known, it is clear that the fish, once a significant tribal subsistence food, have shown severe decline.