Lampetra fluviatilis – River lamprey

Petromyzon marinus – Sea lamprey

River lamprey, courtesy of Jack Perks

Sea lamprey, courtesy of Jack Perks


Sea and River Lamprey are very similar to each other in appearance. Lamprey resemble Eels as they are long and slim ‘snake-like’ fish that have long dorsal fins, however they have many features that differ. Lamprey have a permanently open jawless ‘sucker’ instead of a mouth. This is full of barbed teeth which enable them to latch onto their prey when they are adults. Unlike other fish they don’t have gill covers. Instead they have round open gill ‘pores’. These become their breathing holes when they are attached to their prey. Lamprey are said to be amongst the oldest known vertebrates, and fossils of over 360 million years old have been found of Lamprey that closely resemble the fish we have in our rivers today! River lamprey grow to a maximum length of about 50cms and sea lamprey will grow larger, up to about 1m. Both fish are cartilaginous, meaning they have no bones but have cartilage tissue instead. 


The first few years of a Lamprey’s life are spent burrowed in silty, muddy substrate eating algae and micro-organisms. As they mature they make their way downstream and hunt for food by preying on other fish. They are parasitic. By connecting their ‘sucker’ mouth to another fish they are able to eat their way through their hosts skin and feed on its blood. They are rarely fatal to the host fish. They do this on their migration downstream and into the sea, where Lamprey have been found attached to very large fish, including Basking Sharks! 


Adult River Lamprey make their way downstream into estuaries, and Sea Lamprey will travel further out into the open sea. In rivers they both migrate up rivers to spawning grounds which tend to be shallow, fast flowing rivers with gravel beds. In the River Severn these fish struggle to migrate over the man-made weirs. During spring nights these fish can sometimes be seen gathering at the base of weirs on the River Severn to attempt to ‘sucker’ up the weir and proceed to their spawning ground.  

Did you know?

Baking a Lamprey Pie for the reigning monarch is an ancient tradition. From medieval times to 1836 it was customary for the City of Gloucester to send a lamprey pie to the monarch every ChristmasKing Henry I died ofwhat was thought to be, severe food poisoning after eating this dish in December 1135. Queen Elizabeth II was sent a Lamprey Pie on special occasions, including in 2015 to celebrate her becoming the longest reigning monarch. The fish for this pie were sourced from Canada as they are now a protected species here in the UK. In fact, sea lamprey were accidently introduced into the Great Lakes through shipping where they have become a serious non-native invasive species. Without an ability to return to sea they have to rely on suckering on freshwater fish where they can do a lot of damage and even kill the host fish. 


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