Electrophorus electricus ( Linnaeus, 1766 )

de Santana, C. David, Crampton, William G. R., Dillman, Casey B., Frederico, Renata G., Sabaj, Mark H., Covain, Raphaël, Ready, Jonathan, Zuanon, Jansen, de Oliveira, Renildo R., Mendes-Júnior, Raimundo N., Bastos, Douglas A., Teixeira, Tulio F., Mol, Jan, Ohara, Willian, Castro, Natália Castro e, Peixoto, Luiz A., Nagamachi, Cleusa, Sousa, Leandro, Montag, Luciano F. A., Ribeiro, Frank, Waddell, Joseph C., Piorsky, Nivaldo M., Vari, Richard P. & Wosiacki, Wolmar B., 2019, Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator, Nature Communications 10 (4000), pp. 1-10 : 6

Electrophorus electricus ( Linnaeus, 1766)

Gymnotus electricus 1;

Gymnoti tremuli ref. 34: 27, pl. 3;

Gymnotus tremulus ref. 35: 111;

Gymnotus electricus ref. 1: 427;

Gymnotus regius ref. 36: 273.

Diagnosis: Ten nucleotides in COI (BOL-COIfishF1/R1; 569- bp fragment): G(8), A(50), T(76), T(77), T(107), C(119), C(182), G(272), G(494), A(560). Ventral outline of head U-shaped, widest at terminus of branchial opening ( Fig. 2a ) and lateral-line pores 88–101 (versus ovoid, widest anterior to branchial opening, Fig. 2b ; 112–146 in E. voltai ). Distinguished by skull depressed, cleithrum lies between vertebrae 5 and 6 ( Fig. 2a ), pectoral-fin rays 32–38, and lateral-line pores 88–101 (versus skull deep, cleithrum lies between vertebrae 1 and 2, Fig. 2c , 20–28, and 124–186 in E. varii , respectively).

Description: Species illustrated in Figs. 2 , 3 , and 5. Maximum size examined specimens 1000 mm TL (total length). Morphometric and meristic data in Supplementary Data 2. Body elongate; sub-cylindrical at pectoral girdle, progressively compressed posteriorly. Mouth superior. Scales absent. Anal and caudal fins seamlessly conjoined. Anus and urogenital papilla separated, located anterior to ventral margin of branchial opening. Head and body color brown to blackish. Clear band along body, below lateral line, variably present.

Low-voltage (Sachs’ organ) EOD and high-voltage (main/ Hunter’ s organ) with head-positive monophasic waveform. Lowvoltage EOD 2.03–2.19 ms duration, n = 2 ( Fig. 4d ). High-voltage EOD 480 V at 760 mm TL, n = 1 ( Fig. 4d ). For distribution see Fig. 1a and Supplementary Data 1.

Figures

Fig. 2 Key morphological features to recognize the three species of Electrophorus. Top, radiographs of lateral view of the anterior portion of body (skull and pectoral girdle highlighted red). The cleithrum lies between the fifth and sixth vertebrae (v) in Electrophorus electricus (a) and E. voltai (b) versus first and second vertebrae in E. varii (c). Bottom, illustrations of ventral view of the head, showing key features listed in Diagnoses. a top: National Museum of Natural History, NMNH 403765, 300 mm TL, Cuyuni River, Guyana; bottom: NMNH 225576, 1000 mm TL, Corantijn River, Suriname. b top: Instituto Nacional de Pesquisas de Amazônia, INPA 39009, 450 mm TL, Teles Pires River, Brazil; bottom: Academy of Natural Sciences of Drexel University, ANSP 197583 (t3539), 1280 mm TL, Xingu River, Brazil. c top: NMNH 306677, 450 mm TL, Lago Janauari, Amazon River, Brazil; bottom: NMNH 196634, 1220 mm TL, Amazon River, Brazil

Fig. 3 Electrophorus tree of life and time of species diversification. Time-calibrated genealogy of Electrophorus based on a maximum clade credibility (MCC) species tree derived from *BEAST2.4 analyses of 10 genes (colored lines) and 94 specimens of Electrophorus (relaxed molecular clock and uncorrelated lognormal model implemented). Purple bars represent 95% highest posterior density distributions for the estimated divergence time of each major node. Voltage measurements made by us are reported below E. electricus (National Museum of Natural History, NMNH 225670, 520 mm TL, Corantijn River, Suriname), E. voltai (Museu Paraense Emílio Goeldi, MPEG 15529; holotype, 1290 mm TL), and E. varii (MPEG 25422; holotype, 1000 mm TL)

Fig. 4 Ecological Niche Model and electric organ discharges for species of Electrophorus. Species niche models generated by MaxEnt for Greater Amazonia: a Electrophorus electricus (red); b E. varii (yellow); and c E. voltai (blue). d Measurements of voltage of high-voltage EODs, low-voltage EODs waveforms from Sach’s organ, and posterior one-third of Hunter's organ (grey lines = individually recorded fish, black lines = averaged waveform for each species). e Nearest-neighbor hierarchical clustering of prominent time-frequency features of the low-voltage Sach’s organ EOD from seven individuals of Electrophorus

Fig. 1 Sampling localities and gene trees for the three species of Electrophorus. a Map of northern South America showing distributions of sampled records and type localities (indicated by numbers) for three electric eel species: Electrophorus electricus (red dots, 1 = Suriname River, Suriname); E. voltai (blue dots, 2 = Rio Ipitinga, Brazil); and E. varii (yellow dots, 3 = Rio Goiapi, Brazil). Bicolor dots (blue/yellow) indicate sympatric co-occurrence of E. voltai and E. varii. The map was created in ArcGIS (https://www.arcgis.com) with images available at Shuttle Radar Topography Mission, Global Multi-resolution Terrain Elevation Data, and HydroSHEDS database. b *BEAST2.4 species tree (top cladogram; 94 specimens:15 E. electricus, 41 E. voltai, 38 E. varii) based on 5 mitochondrial (trees 1–5; 107 specimens: 19 E. electricus, 43 E. voltai, 45 E. varii) and 5 nuclear genes (6–10; 94 specimens). Higher shading densities represent areas where the majority of trees agree in topology and branch lengths (posterior probabilities>0.99), while lower densities represent areas of uncertainty (Supplementary Data 1)