FORM AND FUNCTION RELATIONSHIPS IN LATERAL-LINE SYSTEMS - COMPARATIVEDATA FROM 6 SPECIES OF ANTARCTIC NOTOTHENIOID FISH

The structure and physiology of the anterior lateral line canal system s were studied in six species of fish belonging to two different famil ies within the suborder of antarctic fish Notothenioidei. Many of the canals within the species belonging to the genus Trematomus are relati vely straight sided tubes with diameters around 0.4 mm. Some of the ca nals in Trematomus, and most of the canals in the icefishes (family Ch annichthyidae) are more complex. Relatively small pores lead into larg e tubules, the walls of which appear partially membranous, and the can als not much more than constrictions between adjacent tubules. Dissost ichus mawsoni, a large species, has canals with distinctive wide and n arrow sections, 1.8 mm and 0.48 mm, respectively. Despite these morpho logical differences the frequency response characteristics of anterior lateral line units are remarkably similar in all six species. In the case of D. mawsoni, this functional similarity results from narrow sec tions of the canals, which provide the viscous resistance to flow that preserves the mechanical filtering properties of the canal despite th e huge size difference between D. mawsoni and the other species. It is argued that the most appropriate way to view canals is as high pass f ilters which attenuate lower frequencies, and that this effect is best illustrated by comparing the frequency response characteristics of su perficial and canal neuromasts using a sinusoidal stimulus that has a constant peak-to-peak velocity. The functional contribution of canals is to attenuate low frequencies and improve the signal-to-noise ratio for biologically important signals in the presence of low frequency no ise produced, for example, by the animal's own movements.