Study
Electric fish measure distance in the dark
von der Emde, Gerhard; Schwarz, Stephan; Gomez, Leonel; Budelli, Ruben; Grant, Kirsty
Nature, 1998
Weakly electric fish were trained to choose an object at a particular distance in complete darkness. Object size, shape and material were then varied so that the strength of the electrical image could be matched between objects at different distances, testing whether the fish were using amplitude alone or something else.
- Studied in
- Gnathonemus petersii
- Sample size
- weakly electric fish trained in a two-choice discrimination task
The fish judged distance accurately regardless of object size, shape or conductivity — a discrimination that amplitude alone cannot support.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Weakly electric fish extract distance from the ratio between the width and the peak amplitude of the electrical image, giving true range independent of object properties.
How NatureHQ reads it
Active electrolocation is often described as radar, which gets the effort right and the physics wrong: there is no travelling pulse and no echo delay. The fish surrounds itself with a field and reads the shadow objects cast in it, and the trick shown here is that the *blurriness* of the shadow carries range in a way its brightness does not. Comparing two features of the same image to recover depth is the same solution vertebrate eyes use for focus, arrived at independently in electricity.
- One species in a trained two-choice task, which measures discrimination rather than natural foraging.
- Distances tested are short — centimetres — as the field itself is.
- Whether the fish uses this cue when other information is available is not established.
Asking a fish in total darkness how far away something is
An electric fish reads objects by the shadows they cast in its own field. Can a shadow tell it how far away something is?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Nature PortfolioPublished in a Nature Portfolio journal.
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-02.