Neuromast morphology and lateral line trunk canal ontogeny in two species of cichlids: An SEM study

Abstract

A study of neuromast ontogeny and lateral line canal formation in Oreochromis aureus and Cichlasoma nigrofasciatum reveals the existence of two classes of neuromasts: those that arise just before hatching (presumptive canal neuromasts, dorsal superficial neuromasts, gap neuromasts, and caudal fin neuromasts) and pairs of neuromasts that arise on each lateral line scale lateral to each canal segment at the same time as canal formation. In the anterior trunk canal segment, each presumptive canal neuromast is accompanied by a dorsoventrally oriented superficial neuromast forming an orthogonal neuromast pair. It is suggested that each of these dorsoventrally oriented superficial neuromasts is homologous to the transverse superficial neuromast row described by Münz (Zoomorphology 93:73-86, '79) in other cichlids. It is further suggested that the longitudinal lines described by Münz (Zoomorphology 93:73-86, '79) are derived from the pair of superficial neuromasts that arise during canal formation. Distinct changes in neuromast topography are documented. Neuromast formation, scale formation, and lateral line canal formation are three distinct and sequential processes. The distribution of neuromasts is correlated with myomere configuration; there is always one presumptive canal neuromast on each myomere. A single scale forms beneath each presumptive canal neuromast. Canal segment formation is initiated with the enclosure of each presumptive canal neuromast by an epithelial bridge which later ossifies. The distinction of these three processes raises questions as to the causal relationships among them.

The mechanosensory lateral line is used to assess opponents and mediate aggressive behaviors during territorial interactions in an African cichlid fish

“…The OT and PO canals serve as links between IO and SO, PR and trunk (T) canals. Like most cichlids, A. burtoni possesses a disjunct trunk lateral line canal (Webb, 1989), with a dorsally located rostral portion and a medially located caudal portion. Each trunk scale has a single CN with several (1-6, but most commonly 2-3) SNs.…”

“…The functional unit of the lateral line system is a neuromast composed of sensory hair cells and support cells covered by a gelatinous cupula (Dijkgraaf, 1962). Neuromasts are located either superficially on the skin surface (superficial neuromasts, SN) or enclosed within dermal canals (canal neuromasts, CN) (Webb, 1989). Neuromasts are stimulated when the cupula is deflected by viscous drag, activating the mechanotransduction channels in the hair cells, and allowing for sensory perception of water movements relative to the movement of the fish .…”

“…Neuromasts are stimulated when the cupula is deflected by viscous drag, activating the mechanotransduction channels in the hair cells, and allowing for sensory perception of water movements relative to the movement of the fish . Lateral line system morphology is highly variable across fishes (Webb, 1989(Webb, , 2014, and its spatial organization within a species can provide insight into its sensory role(s).…”

The morphology and mechanical sensitivity of lateral line receptors in zebrafish larvae (Danio rerio)

“…Once coated, the periphery of the cupular matrix was visible under differential interference contrast optics. This approach was recently developed (McHenry and van Netten, 2007) as a means of avoiding the shrinkage (Cahn and Shaw, 1962;Blaxter, 1984a;Rouse and Pickles, 1991;Higgs and Fuiman, 1998) and destruction (Webb, 1989;Webb and Shirey, 2003;Carton and Montgomery, 2004;Gibbs and Northcutt, 2004;Faucher et al, 2006) of cupulae that had accompanied previous visualization techniques. After coating the cupulae, larvae were mounted in a 0.3% agarose solution in embryo media and 0.0017 g l -1 MS-222 within a deep-welled glass slide.…”

The flexural stiffness of superficial neuromasts in the zebrafish(Danio rerio) lateral line

“…An understanding of these mechanics would provide a basis for functional interpretations of evolutionary (Northcutt, 1989;Webb, 1989;Webb, 1990) and ontogenetic (Appelbaum and Riehl, 1997;Blaxter and Fuiman, 1989;Poling and Fuiman, 1997;Webb and Shirey, 2003) patterns of variation in lateral line morphology among fishes. Furthermore, research on zebrafish larvae has the potential to relate neuromast dynamics to the biophysics of hair cells because this species is a major model for the study of mechanotransduction (Sidi et al, 2003;Corey et al, 2004).…”