The sea lamprey is a parasitic, eel-like fish with a fearsome, tooth-covered "oral disk" instead of a regular mouth. When attacking, the lamprey rears its head, and clamps its oral disk onto the skin of other fish. With its grasping tongue, it feeds on blood and body fluids for an average of 76 hours, leaving a bloody scar on the fish's body and often killing it.
Sadistic ancient Romans would throw slaves into a pool of lampreys, condemning them to drawn-out, agonizing deaths for minor misdemeanors and trivial accidents. Pliny the Elder reported that Vedius Pollio, the Roman who devised the lamprey torture, did so "because he took pleasure in beholding a man, torn and plucked in pieces all at once." Pollio evidently enjoyed the "pleasant sight" of death observed close-up. As well as watching the lampreys eat slaves, the Romans liked to eat the fish. Lamprey milt -- the sperm and reproductive organs of male fish -- was considered a delicacy at Roman feasts.
These days humans aren't fed to lampreys, but the fish are nevertheless widely loathed, being held responsible for the devastation of salmon, bass and trout stocks in the Great Lakes of North America. Lampreys are native to the North Atlantic, but probably found their way into the Great Lakes via shipping channels. Despite the parasitic lifestyle, however, there is one thing that loves a lamprey: a female lamprey.