Before sharks. Before dinosaurs. Before the first forests had fully established themselves on land. The lamprey was already there, doing more or less exactly what it does today.
Lampreys and its relatives are jawless fish, members of a lineage so ancient that they predate the evolution of jaws in vertebrates by tens of millions of years. The fossil record shows lamprey body plans essentially identical to modern forms dating back 360 million years, making them one of the most morphologically conservative vertebrates known. Whatever the lamprey is doing, it has been working well enough that evolution has seen no reason to substantially revise it.
The adult sea lamprey is a parasite. It attaches to host fish using a circular, tooth-lined sucker mouth, rasps through the scales and skin, and feeds on blood and body fluids for months at a time. A single lamprey can kill its host or leave it severely weakened, and in the Great Lakes of North America, where sea lampreys were introduced through shipping canals in the early twentieth century, they devastated native lake trout and whitefish populations within decades of their arrival.
The Great Lakes lamprey invasion is one of the most economically damaging aquatic invasions in North American history. By the 1940s and 1950s, lake trout populations had collapsed across the Great Lakes, and a fishery worth hundreds of millions of dollars annually had effectively disappeared. Control programs using a selective lampricide called TFM, which kills lamprey larvae while leaving most other species unharmed, have reduced lamprey populations by approximately 90% and allowed lake trout to partially recover, but the control program requires continuous application and costs approximately $20 million per year to maintain.
The Spawning Migration
Adult sea lampreys stop feeding when they reach sexual maturity and undergo a transformation that is essentially a programmed death march. They migrate upstream into freshwater rivers, build nests by moving stones with their sucker mouths, spawn, and die within days of spawning. They do not eat during the entire upstream migration, which can cover hundreds of kilometers. The energy for the migration, the nest building, and the spawning all comes from reserves accumulated during the parasitic feeding phase.
The larvae that hatch from the eggs are filter feeders, living buried in stream sediment for three to seven years before metamorphosing into the parasitic adult form. The larval phase is so different from the adult that early naturalists classified larvae and adults as different species.
The Ancient Blueprint
What the lamprey’s 360-million-year persistence tells us is something worth sitting with. The vertebrate body plan has been elaborated, diversified, and modified into an extraordinary range of forms across that time span, from fish to amphibians to reptiles to birds to mammals. The lamprey watched all of it happen and changed almost nothing. The jawless sucker mouth, the cartilaginous skeleton, the seven gill openings in a row, the absence of paired fins, all of it essentially unchanged since before the Carboniferous period.
It is not a primitive animal in any pejorative sense. It is a solution that was found early and has not needed improving. The ocean is full of experiments. The lamprey is one that worked the first time.