Sea & River Lampreys

Lampreys are a primitive type of fish that have a distinctive suckered mouth rather than jaws, quite unlike any other fish in the UK. Eel-like lampreys parasitise other fish; by fastening on to the living fish, lampreys rasp into the flesh and feed on the body fluids.

Sea lampreys (Petromyzon marinus) and river lampreys (Lampetra fluviatilis) are fish that are born in freshwater, spend most of their lives in saltwater, and return (migrate) to freshwater to reproduce.

After around five years in fresh water the river lamprey spends one or two years in the sea (probably staying near the shore) before migrating back up-river, perhaps hitching a ride (and getting a meal at the same time) from another fish. It does not feed once it has reached fresh water and spawns in the upper reaches of the river the next spring.

Sea lampreys are larger than river lampreys but have a similar life cycle. They do, however, venture further out to sea and spawn in lower reaches of the rivers than the river lampreys.

Although there are few records of lampreys in the site, there are known populations within the Cleddau Rivers.

Pollution and obstacles to migration (such as dams or weirs) can cause decline in numbers of both species.