The lateral line can mediate rheotaxis in fish

Rheotaxis is a behavioural orientation to water currents(1). It has been demonstrated physiologically that some lateral-line receptors are particularly well suited to provide information on water currents(2), but their contribution to rheotaxis has been largely overlooked. The accepted view is that rheotaxis is mediated by visual and tactile cues', and that in rheotactic orientation ''the lateral lines play only a minor role''(3). Here we provide a direct demonstration that rheotaxis can be mediated by the lateral line, and indeed by one specific receptor class of this system. In three diverse fish species, pharmacological block of the entire lateral-line system substantially increases the velocity threshold for rheotactic behaviour. The same effect is observed when only superficial neuromasts are ablated, whereas blockade of the other receptor class, canal neuromasts, has no such effect. Our results therefore demonstrate that superficial neuromasts make an important contribution to rheotactic behaviour in fish.