The lamprey (Geotria australis) belongs to is a primitive order of jawless fish (Petromyzontiformes). The adults are good climbers and can scale waterfalls, but because of habitat loss and dams blocking their migrations, most populations now occur at lower altitudes (less than 400 m) closer to the coast.
Lamprey juveniles (ammocoetes) live in burrows in silty river edges. As ammocoetes, lamprey are blind and browny-black in colour. Once they reach 100–120 mm (after 3–5 years’ growth), they metamorphose into the adult form, which contains eyes and a vibrant blue colouration. This stage is termed macropthalmia, and these fish will migrate out to sea to feed parasitically on fish and whales.
Lampreys are anadromous – this means they migrate up rivers from the ocean to spawn. The eggs hatch in freshwater where juveniles reside for up to 4 years before heading out to the open ocean. Here, they attach onto the gills and flesh of other fish and marine mammals and live as parasites. They use their specially adapted mouth – a roundish sucker, armed within by series of rasping teeth, with sharper and stronger ones on the tongue – to feed on the host animal’s blood.
Before reaching sexual maturity, the lamprey returns to freshwater to breed and can use its circular sucker to latch onto and surmount obstacles such as rapids and small falls.
The returning adult lamprey spends up to 18 months inland, maturing sexually before spawning. Both sexes will survive spawning for over 3 months before dying. Scientists discovered the first Geotria australis spawning sites in the southern hemisphere on Canterbury's Banks Peninsula.
The adults do not feed in freshwater – so other freshwater fish and people wading in streams will not be preyed on!
Lamprey – also called kanakana or piharau – are a taonga species and were considered a delicacy by Māori.
Watch a lamprey using its sucker mouth to climb a wall in this video.
Acknowledgement: Peter Anderson, Department of Conservation Te Papa Atawhai, Creative Commons 4.0