Here is what the Baensch states about these little critters:
The larvae stage lasts up to 6 years.......Larvae are harmless, whereas adults are oftentimes parasites, even attacking conspecies........Entering Lake Ontario in 1890, the sea lamprey migrated through the Welland Canal, appearing about 30 years later in Lake Erie. twentyfive years later it had reached Lake Superior. As a consequence, the fisheries in the lake collapsed (lake trout, burbot, lake whitefish). Only through continued management with specific poisons have the native fish populations been able to recover.
Aquarium maintenance for this ENTIRE family is NOT recommended.
Why do you want to keep this fish?
Source: Baensch Photo Index 1-5, p24, 25