A predator lurking close by might seem to represent the greatest threat to prey animals. But in zebrafish, flight behaviour is influenced less by a hunter’s proximity than by the speed of its approach.
Malcolm MacIver and his colleagues at Northwestern University in Evanston, Illinois, found that when a threat approached rapidly, zebrafish larvae escaped quickly in a predictable direction or simply froze. Conversely, when an enemy encroached slowly, the larvae paused, then fled in several different directions.
Previous research suggested that Mauthner cells, which trigger escape responses in fish and amphibians, become active once a threat comes close enough. But the team found that the cells were active more often in the presence of fast-moving threats. This suggests that prey fish also command slower, more flexible escape manoeuvres when outsmarting slow-approaching predators, the authors say.
[An earlier version of this highlight erroneously stated that Mauthner ‘reflex’ cells were found to be active only for fast-moving threats. It also implied that zebrafish used non-reflex escape manoeuvres for escaping all kinds of predators.]