Lampreys, along with hagfishes are the sole surviving representatives of the jawless vertebrates. They are conveniently lumped in with the fishes due to the aquatic/ marine habit, but are indeed a totally separate class of animals (Agnantha). Within an evolutionary context, birds are more closely related to reptiles than lampreys are to what people commonly regard as fishes.

Preceding a radical metamorphosis, lampreys have a larval juvenile stage (ammocoetes) lasting several years. After about three years the Short-headed lamprey swims downstream towards the sea. It then parasitises itself to marine fish using its abrasive sucking disk. The adult grows significantly during this stage, then re-enters rivers, migrating upstream, then spawns and dies.

Given the significant changes of its riverine habitat, the migratory behaviour of the Short-headed lamprey is both an advantage and disadvantage. The species is not totally dependent upon the river/ creek environment throughout its life cycle. Thus, to a certain extent avoiding the vagaries of watercourses drying up due to excessive water extraction. Yet even when there is enough water in its chosen stream, the lamprey is faced with climbing over weirs and the like to reach its spawning ground.