Pacific Lamprey Identification Guide

Key identification features

• Elongated, scaleless, eel-like body typical of lampreys
• Oral sucker disc bearing a distinctive supraoral tooth plate with three prominent points, the source of its scientific name "tridentatus"
• Single nostril on top of the head
• Two dorsal fins that sit close together, nearly touching, in mature adults
• Dark blue-black to brown back that pales to a lighter belly
• Large adult body size, often 50-80 cm in the ocean-feeding phase
• Smooth, slimy skin with no paired fins

Common look-alikes

• Western river lamprey is noticeably smaller with weaker, fewer teeth and more clearly separated dorsal fins.
• Pacific brook lamprey is a non-parasitic dwarf form with degenerate, blunt oral disc teeth instead of the sharp three-cusped plate.
• Sea lamprey has a more heavily marbled, blotchy color pattern rather than the Pacific lamprey's more uniform dark tone.

Where you'll see one

Pacific lamprey range along the Pacific Rim from Baja California north through Alaska and across to eastern Asia, spending their adult feeding phase in the ocean before returning to coastal rivers and streams to spawn, where their larvae burrow into soft sediment for years.