Responses of anterior lateral line afferent neurones to water flow

The mechanoreceptive lateral line system detects hydrodynamic stimuli and p lays an important role in a number of types of fish behaviour, including or ientation to water currents. The lateral line is composed of hair cell rece ptor organs called neuromasts that occur as superficial neuromasts on the s urface of the skin or canal neuromasts located in subepidermal canals. Both are innervated by primary afferents of the lateral line nerves. Although t here have been extensive studies of the response properties of lateral line afferents to vibrating sources, their response to water flow has not been reported. In this study, we recorded extracellularly from anterior lateral line afferents in the New Zealand long-fin eel Anguilla dieffenbachii while stimulating the eel with unidirectional water flows at 0.5-4 cm s(-1). Of the afferents, 80% were flow-sensitive to varying degrees, the response mag nitude increasing with flow rate. Flow-sensitive fibres gave non-adapting t onic responses, indicating that these fibres detect absolute flow velocity. Further studies are needed to confirm whether flow-sensitive and flow-inse nsitive fibres correlate with superficial and canal neuromasts, respectivel y.