Larval electroreceptors in the epidermis of mormyrid fish: II. The promormyromast

Abstract

Promormyromasts were found in the epidermis of the head of the larvae of five species of mormyrids bred in captivity. The promormyromast is a larval electroreceptor belonging to the specific lateral line system. In 12-day-old larvae this electroreceptor is characterized by a single sensory cell and two types of accessory cells. One type of accessory cell has dark cytoplasm, few microtubules, and contacts the sensory cell directly, whereas a second type has pale cytoplasm, many microtubules, and forms an outer layer not directly in contact with the sensory cell. This second type is referred to as a long pyriform accessory cell. This assembly of cells is situated below an intraepidermal cavity filled with acid polysaccharides. The bordering epidermal cells extend microvilli into the intraepidermal cavity. The apexes of the sensory cell, and of the two types of accessory cells, also open into the intraepidermal cavity but bear no microvilli. The promormyromast is innervated by an unmyelinated sensory nerve fiber passing through the basal membrane, which then splits into several branches between the accessory cells. These branches contact the periphery of the sensory cell with terminal boutons. At the site of each contact a ribbon-like structure surrounded by vesicles is present in the cytoplasm of the sensory cell. In older larvae of Campylomormyrus cassaicus, membrane foldings develop at the periphery of the pyriform accessory cells and accessory cell staining properties change just before transformation to become a mormyromast. The functional role of the promormyromast of the larval mormyrids is discussed.

Group cohesion in juvenile weakly electric fish Mormyrus rume proboscirostris

“…From the day they hatch, Mormyrus rume proboscirostris Boulenger, the species chosen for this study, aggregate, and in spite of the fact that the mormyrid larval electrosensorimotor system is suitable for communication and object location (Bensouilah et al ., 2002; Werneyer & Kramer, 2006; Denizot et al ., 2007), little is known about its function, i.e . the role the electrosense plays during early developmental stages, and whether the transition from a larval, monophasic (EOD) waveform to the adult biphasic EOD (Schugardt, 1997) has any effect on group cohesion.…”

From Sequence to Spike to Spark: Evo-devo-neuroethology of Electric Communication in Mormyrid Fishes

“…Three of these are found only in larvae, two of which degenerate at the onset of the juvenile stage concurrent with degeneration of the larval electric organ (Bensouilah et al, 2002). A third larval electroreceptor is a promormyromast that gives rise to the adult mormyromast through differentiation (Denizot et al, 2007). The remaining two electroreceptors found in larvae are the ampullary organs and knollenorgans that remain in adults.…”

Electric fish: new insights into conserved processes of adult tissue regeneration

“…Of these, approximately 173 species are gymnotiforms, or South American knifefishes, and in all but one group, the electric organ derives from striated muscle cells that suppress many muscle phenotypic properties (Bennett, 1971). Gymnotiforms have been used to study the formation of sensory and motor specializations (Fox and Richardson, 1978;Fox and Richardson, 1979;Kirschbaum and Schwassmann, 2008;Denizot et al, 1998;Denizot et al, 2007;Vischer, 1989a;Vischer, 1989b;Zakon, 1984;Lannoo et al, 1990), animal communication (Zakon et al, 2008;Carr and Friedman, 1999;Hopkins, 1988), speciation (Arnergard et al, 2010;Feulner et al, 2009;Lovejoy et al, 2010), evolution of neural networks (Alves-Gomes, 2001;Bass, 1986;Zakon et al, 2008;Kawasaki, 2009;Arnegard et al, 2010), physiology of membrane excitability and synaptic plasticity (Bell et al, 2005;Gómez et al, 2005;Lewis and Maler, 2004;Markham et al, 2009), and have been a source of material for the isolation of many molecules involved in these biological processes. Not as well known is the considerable regeneration capacity of South American gymnotiform electric fishes.…”