Hair cell heterogeneity and ultrasonic hearing: recent advances in understanding fish hearing

The past decade has seen a wealth of new data on the auditory capabilities and mechanisms of fishes. We now Irate a significantly better. appreciation of the structure and function of the auditory system in fishes with regard to thier peripheral and central anatomy, physiology, behaviour, sound sour ce localization and hearing capabilities. This paper deals with two of the newest of these findings, hair cell heterogeneity and the detection of ultr asound. As a result of this recent work, we now know that fishes have sever al different types of sensory hair cells in both the ear and lateral line a nd there is a growing body of evidence to suggest that these hair cell type s arose very early in the evolution of the octavolateralis system. There is also some evidence to suggest that the differences in the hair cell types hate functional implications far tlc way the ear and lateral line of fishes detect and process stimuli. Behaviour al studies have shown that, whereas most fishes can only detect sound to 1-3 kHz, several species of the genus Alosa (Clupeiformes, i.e. herrings and their relatives) can detect sounds u p to 180 kHz (or even higher). It is suggested that this capability evolved so that these fishes can detect one of their major predators, echolocating dolphins. The mechanism for ultrasound detection remains obscure, though i t is hypothesized that the highly derived utricle of the inner ear in these species is involved.