The river lamprey (Lampetra fluviatilis) is much smaller than its larger relative, the sea lamprey. It is a migratory fish spawning in rivers and spending its adult life in estuaries and around the coast.
Just like the much larger sea lamprey, river lamprey are migratory, spawning in clean sandy gravels in rivers. The young larvae then swim off to the soft marginal silt of the river to grow, feeding on the algae, bacteria and detritus. They can spend five years in the mud before metamorphosing into adults and migrating down towards the sea. There they will feed parasitically on fish, such as herring, by attaching themselves with their sucker-like mouths.
Appearance: Adults are eel-like in size and shape, but they have no gill plates, paired fins or a jawed mouth. They have a silver colouration with a uniform grey dorsal and silvery flanks, and obvious gill holes/pores.
Typical size: 30-50cm as an adult
Lifespan: 4 to 8 years
When to see them: Juvenile river lamprey spend their time in the mud so you won’t see them. However, adults migrate up the rivers during the winter and start to spawn in April/May.
Last date edited: 24 December 2020