The lamprey spends most of its life in the sea, where it uses a circular sucker (below) to attach itself to other animals and feeds by rasping a hole in their flesh. The adults, which are over 400 mm long, spawn in fresh water, and thus we find them in our waterways. The adults do not feed while in fresh water, however, and so are not parasitic on other freshwater fish
Extract from http://www.niwa.cri.nz/rc/freshwater/fi ... es/lamprey
As stated above, they do not feed while spawning so would be hard to keep in an aquarium.Although says that young live in fresh water for up to four years so may be possible.
Would love to see one with my own eyes as have heard lots of local Maoris talking about eating them but I have never ever seen one myself.
Very interesting animal though.