Phylum: Chordata - Class: Hyperoartia - Order: Petromyzontiformes - Family: Petromyzontidae
There are three kinds of lampreys found in British rivers: Brook Lamprey Lampetra planeri, Rver Lamprey Lampetra fluvitilis and Sea Lamprey (Petromyzon marinus. These are very primitive fishes; they have no scales and they feed parasitically upon other fish species, including Salmon migrating towards river estuaries.
The Sea Lamprey seen here attached to an angler's wader is the largest of the three lamprey species found in our rivers. It can grow to more than 5lb (2.2kg) in weight, and as thick and as long as a man's arm.
Lampreys have sucker mouths with rasp-like teeth and seven circular gill openings on each side. They attach themselves to the flank of a passing fish and feed upon the blood of their victim.
Sea Lampreys migrate up the rivers of Wales in the spring, and in May and June they cut redds in the gravel in much the same way as salmon and trout do. Once in fresh water it is rare for sea lampreys to feed.
In recent times lampreys have become scarce and are now protected by wildlife legislation.