title: From the Schnauzenorgan to the back: morphological comparison of mormyromast electroreceptor organs at different skin regions of Gnathonemus petersii.
abstract: The nocturnally active weakly electric fish Gnathonemus petersii is known to employ active electrolocation for the detection of objects and for orientation in its environment. The fish emits pulse-type electric signals with an electric organ and perceives these signals with more than 3,000 epidermal electroreceptor organs, the mormyromasts, which are distributed over the animal's skin surface. In this study, we measured the metric dimensions of the mormyromasts from different body regions to find structural and functional specialization of the various body parts. We focused on the two foveal regions of G. petersii, which are located at the elongated and movable chin (the Schnauzenorgan; SO) and at the nasal region (NR), the skin region between the mouth and the nares. These two foveal regions were compared to the dorsal part (back) of the fish, which contains typical nonfoveal mormyromasts. While the gross anatomy of the mormyromasts from all skin regions is similar, the metric dimensions of the main substructures differed. The mormyromasts at the SO are the smallest and contain the smallest receptor cells. In addition, the number of receptor cells per organ is lowest at the SO. In contrast, at the back the biggest receptor organs with the highest amount of receptor cells per organ occur. The mormyromasts at the NR are in several respects intermediate between those from the back and the SO. However, mormyromasts at the NR are longer than those at all other skin regions, the canal leading from the receptor pore to the inner chambers were the longest and the overlaying epidermal layers are the thickest. These results show that mormyromasts and the epidermis they are embedded in at both foveal regions differ specifically from those found on the rest of the body. The morphological specializations lead to functional specialization of the two foveae.
authors.affiliation: Institute for Zoology, Department of Neuroethology/Sensory Ecology, University of Bonn, 53115 Bonn, North Rhine-Westphalia, Germany. monique.amey@uni-bonn.de
authors.forename: Monique
authors.initials: M
authors.lastname: Amey-Özel
authors.forename: Michael
authors.initials: M
authors.lastname: Hollmann
authors.forename: Gerhard
authors.initials: G
authors.lastname: von der Emde
mesh_terms: D000818:Animals; D001415:Back / Q000033:anatomy & histology; D004555:Electric Fish / Q000033:anatomy & histology* / Q000502:physiology; D004557:Electric Organ / Q000033:anatomy & histology* / Q000166:cytology / Q000502:physiology; D010465:Perception; D011984:Sensory Receptor Cells; D012867:Skin / Q000033:anatomy & histology; D060726:Torso