Spatial Distribution and Morphological Characteristics of the Trunk Lateral Line Neuromasts of the Sea Bass (<i>Dicentrarchus labrax</i>, L.; Teleostei, Serranidae)

Abstract

The morphology and spatial distribution of the different types of neuromasts encountered on the trunk lateral line of the sea bass (Dicentrarchus labrax) were examined using scanning electron microscopy. The sea bass trunk lateral line exhibits a complete straight pattern. In their basic features, the two types of neuromasts present, canal and superficial, resemble what has been described in other fishes. They are similar in their general cellular organization but differ in sizes, and shapes, as well as in the densities and lengths of their hair bundles. However, the sea bass trunk lateral line distinguishes itself in several ways. For instance, the pores of the canal segments are partially obstructed due to the overlap of scales throughout the trunk. Moreover, based on the density and length of the hair bundles, two distinct areas, central and peripheral, could be distinguished within the maculae of canal neuromasts. Their cupulae are also peculiar as they possess two wing-like extensions and that their central core appears to be organized in layers instead of columns. In addition, the superficial neuromasts, up to 6 per scale, are either round or elliptical and seem to be distributed serendipitously. Finally, within the maculae of both types of neuromasts, a significant number of hair bundles do not follow the two-directional polarity pattern usually described. Although some hypotheses are proposed, the influence of these characteristics in terms of signal encoding and fish behavior is yet to be understood.

Quantitative Aspects of the Spatial Distribution and Morphological Characteristics of the Sea Bass (<i>Dicentrarchus labrax </i>L.; Teleostei, Serranidae) Trunk Lateral Line Neuromasts

“…The remainder exhibited various orientations. Similar ratios were observed within canal neuromasts, whatever the hair bundles' location in the central or the peripheral area of the maculae [Faucher et al, 2003]. The observation of a major pattern of bipolar orientation parallel to the animal's long axis for both types of neuromasts agrees with most reports on teleosts [Flock, 1965;Yamada and Hama, 1972;Münz, 1979;Denton and Gray, 1983;Webb, 1989c;Rouse and Pickles, 1991;Bleckman, 1993;Coombs and Montgomery, 1994;Tsukamoto et al, 1995;Montgomery et al, 2001].…”

“…Similar assertions could be described for non-teleost fishes [Webb and Northcutt, 1997;Maruska and Tricas, 1998;Maruska, 2001;Peach, 2001Peach, , 2003. Few data are available for the sea bass lateral line system [Diaz et al, 2003;Faucher et al, 2003]. Most of the studies listed above are qualitative and to date little is known about the number, the size or orientation of either type of neuromasts and their associated sensory cells along the fish trunk lateral line [Münz, 1979[Münz, , 1989Coombs et al, 1989;Song and Northcutt, 1991;Coombs and Montgomery, 1994;Peach, 2003].…”

“…It can therefore be suggested that there might be a gradient of sensory capacity from the beginning to the end of the trunk lateral line. It has been shown that unlike most teleost fishes [e.g., Flock, 1965;Münz, 1979;Appelbaum and Schemmel, 1983;Coombs et al, 1989;Webb, 1990;Harvey et al, 1992;Kroese and Schellart, 1992], the modified scales of sea bass trunk lateral lines did not present a direct connection between the interior of the canal segment and the external medium [Faucher et al, 2003]. Moreover, the overlap of the pores between contiguous scales appeared to result in the formation of a quasi-continuous tube starting at the operculum and ending at the caudal peduncle.…”

“…observation that both round and elliptical superficial neuromasts exhibited circular maculae [Faucher et al, 2003] and (2) the presence of one third of the hair bundles presenting various orientations. However, as mentioned above, the observation that most hair bundles within the maculae of superficial neuromasts were oriented along the longest axis of the animal body contradicts the possibility of a multi-directional sensitivity.…”

“…They consisted of a single row of modified scales, differing from the others by the presence of superficial neuromasts and the canal tube containing canal neuromasts, running within the midsection of each flank from the operculum up to the tail. No superficial or canal neuromasts were observed on the trunk outside these specific areas [Faucher et al, 2003]. Tissue samples were dissected in an artificial solution (composition in mM: NaCl: 150; KCl: 5; CaCl 2 W 2H 2 O: 3; MgCl 2 W 6H 2 O: 1.5; HEPES: 10) for which the pH was adjusted to 8 with NaOH.…”