Redescription of Gymnotus coatesi (Gymnotiformes, Gymnotidae): A Rare Species of Electric Fish from the Lowland Amazon Basin, with Descriptions of Osteology, Electric Signals, and Ecology
Gymnotus coatesi, a small and rare species of Neotropical electric fish, was originally described by LaMonte from material collected in Pará, Brazil, in 1934. The senior author discovered populations of this species in the vicinity of Tefé, Amazonas, Brazil, and near Iquitos and Jenaro Herrera in the lowland Upper Amazon of Peru. We provide a formal redescription of this species and describe external morphology, osteology, ecology, and electric signals, with emphasis on the Tefé population. Gymnotus coatesi can be distinguished from all congeners by a unique banding pattern and by a unique combination of morphometric and meristic characters. Gymnotus coatesi is known from localities along the main stem of the Amazon River from near the confluence of the Río Marañon with the Río Ucayali (Loreto, Peru) to the Rio Tocantins (Pará, Brazil) but is poorly represented in museum collections. In the Tefé region, G. coatesi inhabits the seasonally flooded lower courses of terra firme rain-forest streams. In the Peruvian Amazon, it also occurs in the upper, nonflooded, reaches of rainforest streams.
Gymnotus coatesi é uma espécie rara e de pequeno porte de peixe elétrico neotropical, descrita originalmente por LaMonte em 1934, com base em material proveniente do Estado do Pará, Brasil. O primeiro autor descobriu populações desta espécie perto de Tefé, Amazonas, Brasil, e perto de Iquitos e Jenaro Herrera na Amazônia Peruana. Fornecemos uma redescrição formal da espécie e descrevemos a morfologia externa, osteologia, ecologia e sinais elétricos da mesma com ênfase na população de Tefé. Gymnotus coatesi diferencia-se inequívocamente das outras espécies do gênero por um padrão de pigmentação único e por uma combinação única de características morfométricas e merísticas. Gymnotus coatesi distribui-se ao longo do trecho principal do Rio Amazonas entre localidades perto da confluência do Río Marañon com o Río Ucayali (Loreto, Perú) e o Rio Tocantins (Pará, Brasil). Contudo, é representada por poucos exemplares em coleções zoológicas. Na região de Tefé G. coatesi ocorre exclusivamente nos trechos baixos e sazonalmente alagá veis de igarapés (riachos) de terra firme. Na Amazônia Peruana esta espécie ocorre também nos trechos altos e não alagáveis de riachos de terra firme.Abstract
Resumen
Map of Tefé area, Brazil, showing collecting localities (black circles) of Gymnotus coatesi. Some symbols represent more than one collection record. All systems south of the Rio Solimões are nutrient-poor blackwater habitats of the Tertiary terra firme. All systems to the north are nutrient-rich Quaternary floodplain habitats. Base map traced from 1999 1:150,000 Landsat TM5 images. Extent of annual flooding plotted from June 1995 NASDA JERS-1 image
Photographs of Gymnotus coatesi from near Tefé, Brazil: (A) adult (MCP 34474); (B) juvenile (MCP 34472). Scale bar = 10 mm. Note diagnostic increase in pale band width from anal-fin base to dorsal midline in adult
Head of adult specimen of Gymnotus coatesi, MCP 34474, illustrating organization of cephalic sensory canals and pores. Centerline of canals (ossified and unossified) indicated by dashed lines. Pores indicated by small circles. Eye and anterior and posterior nares shaded gray. Abbreviations: so, supraorbital; io, infraorbital; pl, posterior lateral-line; pm, preopercular-mandibular; st, supratemporal; m, medial. Scale bar = 5 mm
Diagrammatic representation in left lateral view of neurocranium of Gymnotus coatesi, MCP 34473. Shading: White, bone; Gray, cartilage; Black, foramenae for nerves and blood vessels; Hatched, absence of bone. Abbreviations: MEt, mesethmoid; SOC, supraorbital laterosensory canal; Fro, frontal; SpO, sphenotic; Par, parietal; PtO, pterotic; EpO, epioccipital; SuO, supraoccipital; ExO, exoccipital; VEt, ventral ethmoid; Vom, vomer; OrS, orbitosphenoid; PtS, pterosphenoid; PaS, parasphenoid; PrO, prootic; BaO, basioccipital; F, foramenae for cranial nerves. Scale bar = 1 mm
Diagrammatic representation in left lateral view of suspensorium and jaws of Gymnotus coatesi, MCP 34473. Gray indicates cartilage. Abbreviations: PMx, premaxilla; Max, maxilla; Mes, mesopterygoid; Met, metapterygoid; Hyo, hyomandibula; Den, dentary; Ret, retroarticular; Ang, anguloarticular; Qua, quadrate; POp, preopercle; Sym, symplectic; IOp, interopercle; SOp, subopercle; Ope, opercle; F, foramenae for trigeminal nerve branches (pm, preopercular-mandibular; so, supraorbital; io, infraorbital; pll, posterior lateral line). F. pll is located on medial surface of hyomandibula. Scale bar = 1 mm
Diagrammatic representation in left lateral view of pectoral girdle of Gymnotus coatesi, MCP 34473. Gray indicates cartilage. Abbreviations: PTe, posttemporal; SCl, supracleithrum; MCo, mesocoracoid; Cle, cleithrum; Sca, scapula; PR-1, first pectoral ray; Cor, coracoid; Rad, distal radials. Scale bar = 1 mm. Dotted lines show bone outlines behind cleithrum and supracleithrum
EOD waveform (A) and Fourier Power Spectrum (B) of Gymnotus coatesi. MCP 34473. The EOD is plotted with head-positivity upwards and its component phases labeled P0 through P3. The Power Spectrum was computed from a 2048 point Fast-Fourier-Transform and the Peak-Power-Frequency scaled to 0 dB
Map of northern South America showing collection records for Gymnotus coatesi. 1 and 2 represent alternative type localities (see text). Some symbols represent more than one collection site (see Fig. 1 for details of Tefé region). Base map by M. Weitzman
Contributor Notes
Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611-7800. (WGRC) willc@flmnh.ufl.edu Send reprint requests to WGRC.