River Lamprey Identification Guide

Key identification features

• Medium-sized, eel-like body, typically 30-50 cm as an adult
• Silvery-blue to brownish back with a paler, more uniform tone than heavily blotched lampreys
• Two dorsal fins with a distinct gap between them
• Oral sucker disc with moderately developed, functional teeth used to grip host fish
• Single nostril on top of the head and seven small round gill openings on each side
• No paired fins, and skin is smooth, scaleless, and covered in protective mucus
• Slim caudal peduncle leading to a low, pointed tail fin continuous with the second dorsal fin

Common look-alikes

• Sea lamprey is considerably larger and shows a mottled, marbled color pattern rather than the river lamprey's more even silvery-brown tone.
• Brook lamprey stays much smaller, under about 15 cm, and its oral disc teeth are weak and degenerate rather than functional.
• Arctic lamprey has dorsal fins that sit closer together, nearly touching, compared with the river lamprey's more clearly separated pair.

Where you'll see one

River lampreys are anadromous, living mainly in coastal seas and estuaries of Western Europe before ascending rivers to spawn over clean gravel beds; their larvae then burrow into silty riverbanks for several years before transforming and migrating back out to sea.