Elephant-nose fish need to twist, pace and shimmy to accurately 鈥渟ee鈥� the shapes of objects when interpreting wobbles in electric fields.
Peters鈥檚 elephant-nose fish (Gnathonemus petersii) is native to the rivers of west and central Africa. It and its close relatives are 鈥渨eakly electric鈥� fish that can produce a small electric discharge too feeble to stun prey. But sensors in their skin can use the resulting electric field around their bodies to detect prey and underwater obstacles.
Electroreception is a truly ancient ability in vertebrates, dating back hundreds of millions of years, says at the New Jersey Institute of Technology, who was not involved with this study. But using a self-generated electric field for perceiving surroundings is a relatively newly evolved sense, independently developed in elephant-nose fish and their relatives, and in South American knifefishes.
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Elephant-nose fish make curious body movements when investigating new objects: angling, tilting and probing. Suspecting this fidgeting may be key to the process of creating an 鈥渆lectric image鈥�, at the University of Oxford and her colleagues tested how shrinking the space a fish occupies affects its electric sense.
The researchers trained six elephant-nose fish to distinguish between two aluminium blocks of different shapes 鈥� sausage-shaped versus cubed or spherical 鈥� set side-by-side behind mesh partitions in a tank. The fish were given food as a reward when they opened a door in the partition that led to the correct object with their 鈥淪chnauzenorgan鈥�, the trunk-like chin appendage that gives them their elephantine look.
After 720 tests, when the fish had sufficient space, they picked the right shape nearly 94 per cent of the time. But then the team put up barriers to make it harder to move around the tank. As the area in which a fish could explore shrank, their accuracy faltered, dropping to 71 per cent when given less than half the starting area. They also took almost four times as long to make a choice in the smallest tank.
The researchers think the fish are using their electric pulses to create a series of snapshots as they move near an object鈥檚 surface. This sequence of scans, working like a flip book animation felt with the skin, can reveal the object鈥檚 shape.
This fits with the 鈥渕ultiple looks hypothesis鈥�, which is thought to play a role in other animal senses such as sight, says Fortune. 鈥淭he idea is that by looking at something more than one time, you can get more information about that thing.鈥�
But with less space to move, the fish may only snap electric images from a fraction of the necessary angles needed to tell the difference between two objects.
Reference: bioRxiv, DOI:
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