Diurnal Movements and Discharge Characteristics of Electric Gymnotid Fishes in the Rio Negro, Brazil

Abstract

Fishes of widely differing evolutionary backgrounds possess organs specifically adapted to produce an external electric field. In most, the field produced by the electric organ is too weak to be of use as a weapon, hence the name "weakly electric fish," to distinguish them from the strongly electric freshwater electric eel (Electro phorus} and electric catfish (Malapterurus) or the marine Torpedo and Stargazers (Family Uranoscopidae) (Lissmann, 1951;Coates, 1947Coates, , 1954.Lissmann and others have shown by behavioral tests that -weakly electric fishes can detect changes in the conductivity of their surroundings (Lissmann, 1958;Lissmann and Machin, 1958 ;Machin and Lissmann, 1960 ;Wantanabe and Takeda, 1963). This is accomplished by using the electric organ as the energy source, and specialized cutaneous receptors as the receivers for a system of active electrolocation, although the actual mechanisms involved are different than first suggested (Machin and Lissmann, 1960;Bennett, 1967).

Population density and habitat of an endangered cave fish Eigenmannia vicentespelaea Triques, 1996 (Ostariophysi: Gymnotiformes) from a karst area in central Brazil

“…Some authors state that Gymnotiformes in general (including Eigenmannia spp.) have low densities (Steinbach, 1970;Marrero, 1987;Peretti, 1997), even lower than those recorded herein. However, these authors were basing these reports on data acquired with indirect methods, such as apparatuses to detect electric-fishes (electrodes with amplifiers or collections with trawls).…”

“…Adaptations related to their predominantly nocturnal activity (see Steinbach, 1970;Bennett, 1971aBennett, , 1971bHopkins, 1974;Westby, 1988;Kramer, 1990Kramer, , 1996, favor the colonization of permanently dark habitats such as those in the subterranean (hypogean) realm. In fact, gymnotiforms are frequently observed in Brazilian caves, with populations regularly found in these habitats, apparently as troglophiles -species with source populations both in hypogean and epigean (surface) habitats, with individuals regularly commuting between them, promoting the introgression of genes selected under epigean regimes into subterranean populations (Trajano, 2012).…”

“…Ecological studies on gymnotiforms are scarce (Lissmann, 1961;Steinbach, 1970;Hagedorn, 1988;Westby, 1988;Alves-Gomes, 1997;Crampton, 1998), and few data on basic aspects of their natural history have been available up to now, most of which consider aspects of their reproduction and feeding biology (Giora et al, 2005;Schaan et al, 2009;Giora et al, 2011). Further, relatively few troglobitic fishes have been studied in detail, focusing on population traits such as population sizes and densities or individual movements and growth (as a life history component) (see Trajano, 2001;Trajano & Bichuette, 2010).…”

Phylogenetic comparative analysis of electric communication signals in ghost knifefishes (Gymnotiformes: Apteronotidae)

“…Comparative studies (>2 species) (Garland and Adolph, 1994) of apteronotid electrocommunication have focused primarily on EOD frequency and waveform because the EOD is constantly emitted and its frequency and waveform are therefore easily measured (Crampton, 1998;Crampton and Albert, 2006;Heiligenberg and Bastian, 1980;Hopkins and Heiligenberg, 1978;Kramer et al, 1981;Steinbach, 1970). These signals vary across species and are sexually dimorphic in some species.…”

Time Domain Processing of Electric Organ Discharge Waveforms by Pulse-Type Electric Fish (Part 2 of 2)

“…3-6) [also see Heiligenberg and Bastian, 1980;Hopkins, 1972;Hop kins and Heiligenberg, 1978;Kramer et al, 1981;Lissman, 1958Lissman, , 1961Steinbach, 1970]. EODs can be mono-, bi-, tri-and even tetraphasic, with durations varying between 1 and 5 ms for many gymnoti forms.…”