Knifefish is energy efficient


Scientists have developed a new computer based model which can help predict the strategies that animals will use to catch their prey using the Black ghost knifefish (Apteronotus albifrons) as their subject.

Like dolphins and bats and other electric fish, this nocturnal fish from the Amazon actively searches out its prey using a weak three-dimensional electrical field around its body.

However, this method of detecting prey can be very costly in terms of energy expended as electric signals fall off rapidly with distance.

Using video footage and computer modelling, Malcolm MacIver and James Snyder from Northwestern University have discovered that knifefish fish have an area surrounding them in which they can sense prey that is almost directly limited to the distance they can move in time to catch it.

The knifefish can move at 10cm/sec and so have a cylindrical electrical field about 3.5cm around its body with which they can actively sense prey. This ensures that the fish invests just enough energy into active sensing to detect prey in time to stop.

Where other animals tend to have a conical forward facing ~detection zone for prey, the knifefish has an omni-directional cylinder; as unlike other animals, the knifefish can respond to prey (in this case water fleas Daphnia magna) both behind and to the side of it and move immediately both forwards and backwards using a modified anal fin.

The model was also used on a number of other animals and it was predicted that where the detection and movement zones are roughly equal then a rapid response to prey is expected, but where animals can sense further, as is the case with dolphins that can detect prey up to 100m away, then longer range planning strategies of capturing prey are more likely.

Snyder JB, Nelson ME, Burdick JW, MacIver MA (2007) Omnidirectional sensory and motor volumes in electric fish. PLoS Biol 5(11): e301. doi:10.1371/journal.pbio.0050301