River lamprey.

River lamprey (Lampetra fluviatilis)

The river lamprey is native to Ireland, and it is distributed throughout Europe. Like all lampreys, they lack gill covers or paired fins and have an oral sucker disc instead of a mouth with jaws. 

River lamprey spawn in rivers in mid to late spring in nests called redds, which they evacuate from the bed of gravelly or sandy rivers using their suckers to remove stones. After hatching, larval lamprey drift downstream until they find a suitable muddy or silty part of the riverbed to burrow into. Lamprey then spend several years in a blind, worm-like juvenile form known as ammocoetes, which filter feed microscopic organisms from the water and mud. After about four years, river lamprey ammocoetes develop eyes and turn silvery, transforming into free-swimming adults as they make their way downstream and migrate to sea.

Adult river lamprey are external parasites that attach to host fish with their oral disc to feed on their flesh and blood. River lamprey remain relatively close to the coast for about 18 months before migrating back up into the river to spawn.

Although they are not considered to be at risk in this country, impacts including pollution, instream works in river channels and barriers to migration remain potential threats to river lamprey.

River lamprey caught in the Avoca Estuary.

Parietal eye, also called a pineal eye, visible on the top of the head of a river lamprey caught in the Avoca Estuary, 2010.

River lamprey climbing barrier during upstream migration.

River lamprey preparing spawning redd.