Sea lampreys are parasites in their adult stage. They attack a wide range of salt- and freshwater fish, including herring, mackerel, salmon, trout and even some sharks, using its 'sucker' to attach to its host and rasp out a whole with its rough tongue.

Yes, sea lampreys can and do harm sharks, although they are more commonly associated with bony fish like trout. Known as the "vampire fish," lampreys are jawless parasites that use a suction-cup mouth filled with concentric circles of sharp teeth to latch onto their hosts. Once attached, they use a raspy tongue to bore through the shark's skin—which is made of tough "dermal denticles"—to feed on its blood and bodily fluids. While a single lamprey attachment is rarely fatal to a large shark, it causes significant stress, blood loss, and open wounds that can become infected. Researchers have documented lampreys attached to various shark species, including Blue Sharks and Basking Sharks. In some cases, multiple lampreys have been found on a single shark, which can significantly weaken the animal and affect its swimming efficiency. Unlike the "remora," which has a symbiotic relationship with sharks, the lamprey is a true parasite that offers no benefit to the shark and leaves behind distinctive circular scars that are frequently seen by divers and marine biologists.