Arctic Lamprey, Lampetra japonica

There are two forms of arctic lamprey; the more common form is that of a parasitic, anadromous fish; the other is non-parasitic, dwarf, and inhabits fresh water. The parasitic form attacks some commercially important species such as salmon, lake trout and lake whitefish.

The arctic lamprey has a similar body form to other lampreys, including the characteristic circular, sucking disc mouth and the slightly compressed cylindrical body. In contrast, they have two dorsal fins, which are continuous with their caudal fin. To distinguish the fins, note that the dorsal fins are low and rounded, while their caudal fin is higher and pointed. Lamprey skin is smooth and leathery because it lacks scales. Those lamprey that inhabit fresh water are dark brown to blue-black, but their marine counterparts are blue on their upper body and silvery coloured on their underside.

During late spring, arctic lamprey migrate to fast-flowing stretches of clear streams to spawn. Spawning behaviour is dramatic: a group of 2 to 8 males and females carry stones and thrash their bodies in the gravel substrate to create a nest. Eggs and sperm are expelled into the long, shallow nest simultaneously. The male wraps his body around the female, using his sucker-like mouth as an anchor to her head. Females often spawn with more than one male during the breeding season. The eggs hatch within a few weeks and the resulting larvae burrow into the soft mud of the river bank. By autumn, the larvae have become smaller versions of their parents. The young of anadromous populations make their way towards the sea, while those of freshwater populations seek out deep, cold lakes.

Parasitic adults feed on the bodies of large-bodied fish, such as trout and salmon. They are, in turn, eaten by inconnu, northern pike, and burbot. During the spring migration to spawning grounds, arctic lamprey gather in large swarms in shallow water, becoming easy prey for gulls. The eggs and young are also eaten by sculpins.

The arctic lamprey occurs along the Pacific coast of Alaska and into the Mackenzie River system of the Northwest and Yukon Territories. Populations of freshwater arctic lamprey are known in Great Slave Lake and in the tributaries of the Slave River. Populations occurring in Alaska were once considered to be a separate species, known as the Alaskan lamprey, Lethenteron alaskense.