Sea Lamprey Identification Guide
Identify a Sea Lamprey by its jawless sucker mouth, seven gill openings, and mottled marbled body pattern.
Read the full Sea Lamprey encyclopedia entry →
Key identification features
- Long, eel-like, scaleless body with no paired fins
- Round, jawless oral sucker disc lined with concentric circles of sharp, horny teeth
- A single nostril on top of the head, between the eyes
- Seven small, round gill openings in a row behind each eye
- Mottled, marbled olive-brown to gray-green pattern on the back and sides, fading to a lighter belly
- Two dorsal fins set well apart, the second joining a low tail fin
- Large size for a lamprey, commonly 60-90 cm as an adult
Common look-alikes
- American eel has true jaws and paired pectoral fins, and lacks the circular sucker mouth entirely.
- River lamprey is noticeably smaller and shows more uniform coloring rather than the sea lamprey's blotchy marbled pattern.
- Brook lampreys stay under 20 cm and never develop the sea lamprey's large, strongly toothed feeding disc.
Where you'll see one
Sea lampreys are native to coastal waters and rivers of the North Atlantic on both the North American and European sides, migrating from the ocean into freshwater streams to spawn; a landlocked, invasive population also persists in the North American Great Lakes.
Frequently asked questions
How do I distinguish a Sea Lamprey from an eel?
Look at the mouth and fins: a lamprey has a round, jawless sucker disc and no paired fins, while an eel has a hinged jaw and paired pectoral fins.
What separates a Sea Lamprey from smaller lamprey species?
Its large adult size (often over 60 cm), heavily mottled marbled coloring, and well-developed toothed disc set it apart from the smaller, plainer brook and river lampreys.