Lamprey (Geotria australis) is not a true bony fish like the similarly shaped eel, but a primitive survivor of an archaic group that has successfully withstood competition from the more specialised true fishes. The lamprey differs from true fishes in the total absence of paired fins, jaws, and other bony structures, the “backbone” being represented by its primitive forerunner, the “notocord”. The mouth is a roundish sucker, armed within by series of rasping teeth, with sharper and stronger ones on the tongue. There are no scales and the skin is slimy. In habits the lamprey is as revolting as is its appearance, for it is predacious. It fastens its disc-shaped mouth to the victim and rasps away the flesh, not eating the tissue but confining its efforts to extracting blood and juices.
Lampreys spend part of their lives in the freshwater rivers and streams, and part in the sea. The eggs are laid far up the rivers, but during its growth the young lamprey descends the river by easy stages and is almost of adult size upon reaching the sea. In the next stage the lamprey spends a certain time in the sea, taking on a new appearance, with a bright silvery and blue coloration. As the breeding season approaches the now adult lampreys, about 18 in. in length, ascend the rivers, gradually losing their bright colours and resolving into a dirty brown.
Maoris esteemed the lamprey as food and formerly captured large numbers of them during the seasonal migration or “runs”, which normally occur at night.
A related but larger species, the hag fish, (Eptatretus cirrhatus) is of similar habits, is larger, and exclusively marine.
by Arthur William Baden Powell, Assistant Director, Auckland Institute and Museum.