How does a sea lamprey feed on game fish?

The sea lamprey (Petromyzon marinus) is a parasitic fish that feeds on game fish and other hosts using a specialized, jawless mouth disc.12

To feed, the sea lamprey attaches itself to the side of a host fish by creating suction with its circular oral disc, which is lined with sharp, hooked teeth. Once securely attached, it uses a toothed, tonguelike structure to rasp a hole into the host's flesh. To facilitate feeding, the lamprey secretes an enzyme from its mouth that acts as an anticoagulant, preventing the host's blood from clotting. This allows the lamprey to ingest the host's blood and muscle tissue.123

While sea lampreys generally do not kill their hosts in their native oceanic habitats, they are highly destructive as an invasive species in the Great Lakes. In that ecosystem, they have been known to kill more than half of the fish they parasitize, significantly impacting populations of species such as lake trout, walleye, and northern pike.1