The alien of the freshwater world. This is a fish that looks like it forgot to evolve. Lampreys appear to have swum out of the Jurassic and stopped changing. They have no jaws and no scales. The body is long, muscular and eel-like. It ends in a circular mouth full of rows of sharp, yellow teeth. They are nature's living fossil. A remnant of an ancient lineage of jawless fish that once ruled the seas. It is a design that raises questions. Parasites with a passport define the adult stage. Lampreys latch onto the sides of whales, sharks and large fish. They use a rasping tongue to drill through scales. They suck blood and body fluids. Feeding continues for up to three years in the ocean. They grow fat and long. Then an ancient instinct takes hold. Feeding stops. They swim back to the exact river where they were born. They climb waterfalls and damp rocks using that suction-cup mouth. It is a fish that travels thousands of kilometres to die. The spawning run is a spectacle of desperation. They gather in huge, writhing balls. They wrap around each other in the gravel. After laying their eggs, the adults die. Their bodies feed the stream with a burst of nutrients. The young hatch as blind, toothless ammocoetes. They burrow into the mud for up to six years. Then they transform into the adult form. It is a fish that lives most of its life as a larva. To see a piharau climbing a wet rock face is to watch a survivor. It is a creature that has been doing the same impossible journey since before the dinosaurs. The waterfall is wet. The lamprey climbs, suction-cup mouth gripping the rock, body writhing, inching upward. It has come from the ocean. It will spawn and die. It does not know why. It just climbs. It has been doing this for 300 million years. It does not need to know why.