Image of the Day: Eel Compass

Glass eels form a magnetic memory of their estuaries’ currents in order to migrate.

Emily Makowski
Oct 14, 2019

ABOVE: Glass eels (Anguilla anguilla)
A. CRESCI ET AL. (2019)

Transparent European eel (Anguilla anguilla) larvae called glass eels have an internal magnetic compass that helps them migrate. After hatching, they travel from the Sargasso Sea in the middle of the Atlantic Ocean to estuaries throughout Europe, where they live for most of their adult life before returning to the Sargasso to spawn and die. Researchers wondered how eels determine what direction to swim, so they collected 222 glass eels from four estuaries flowing in different directions in Norway. Their findings were published in Communications Biology October 8. 

See “Researchers Track Eels on Their Cross-Atlantic Migration” 

Alessandro Cresci, a graduate student in the at University of Miami and the lead author of the study, worked in collaboration with colleagues at the Norwegian Institute of Marine Research. The scientists placed the eels into tanks with rotated magnetic fields and found that the animals swam in the magnetic direction of the tidal current from where they were collected, even though the tanks did not have water flowing in any specific direction. This shows that the eels formed a memory of the magnetic direction of their estuary’s flow and used that to orient themselves, even when removed from their habitat. 

The life cycle of the European eel
A. CRESCI ET AL. (2019)

A. Cresci et al., “Glass eels (Anguilla anguilla) imprint the magnetic direction of tidal currents from their juvenile estuaries,” Commun Biol, doi:10.1038/s42003-019-0619-8, 2019. 

Emily Makowski is an intern at The Scientist. Email her at

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