A taxonomic review of the Neotropical electric fish Rhamphichthys (Gymnotiformes: Rhamphichthyidae) Author Carvalho, Tiago P. Author Albert, James S. University of Louisiana at Lafayette, Department of Biology, P. O. Box 42451, Lafayette, LA 70504, USA. jalbert @ louisiana. edu. USA.jalbert@louisiana.edu text Neotropical Ichthyology 2023 e 230012 2023-12-11 21 4 1 76 http://dx.doi.org/10.1590/1982-0224-2023-0012 journal article 10.1590/1982-0224-2023-0012 1982-0224 13326894 Rhamphichthys apurensis (Fernández-Yepéz, 1968) ( Figs. 4-6 , 7A ; Tab. 3 ) Gymnorhamphichthys apurensis Fernández-Yepéz, 1968:5 (original description, type-locality: Río Bucaral (Paso Don Pancho), tributary to Río Apure , Orinoco basin, Venezuela ). —Nijssen et al ., 1976:60–61 (comments on species validity). —Provenzano et al ., 1998:10 (listed). Rhamphichthys apurensis (Fernández-Yepéz, 1968) . —Schwassmann, 1989:166 (new combination). —Mago-Leccia, 1994:42, fig. 62 (listed and illustrated). —Triques, 1994:109 (diagnosed). —Triques, 1999:1 (examined). — Albert, 2001:124 (examined and listed). —Ferraris, 2003:495 (listed). —Maldonado-Ocampo, Albert, 2003 : tab. 2 (listed). —Lasso et al ., 2004:141 (listed). —Machado-Allison, 2006:26 (listed). —Vari et al ., 2009:46 (listed). — Carvalho, Albert, 2015:40 (comparative material examined). —Tagliacollo et al ., 2016:29, fig. 5 (phylogenetic relationships). —Ferraris et al ., 2017:28 (listed). —DoNascimiento et al ., 2017:66 (listed). —Urbano-Bonilla et al ., 2018:73 (listed, included in key). —Giora, Carvalho, 2018:1060 (accessory electric organ anatomy). — Alda et al ., 2018 : tab. 1, fig. 2 (phylogenetic relationships). —Janzen et al ., 2022: tab. 1 (barcode library). —Taphorn et al ., 2022:40 (listed). Diagnosis. Rhamphichthys apurensis differs from its congeners, except from R. rostratus and R. pantherinus by the larger snout (58.4–63.7% of HL; Figs. 5 , 7 ), vs . shorter snout (46.4–59.1% of HL); larger caudal appendage (23.2–36.8% of LEA), vs . shorter caudal appendage (5.8–20.3% of LEA). Rhamphichthys apurensis differs from R . rostratus by having a lower number of caudal vertebrae to end of anal fin (106–109), vs . higher number of caudal fin vertebrae (109–115; rarely 109); and by having a clear anal fin membrane, vs. anal fin membrane usually distally pigmented forming a longitudinal dark stripe. Rhamphichthys apurensis differs from R . pantherinus by the relatively larger snout (58.4–63.7% of HL), vs . shorter snout (51.4–59.1% of HL); and by the large number of caudal vertebrae to end of anal fin (101–109), vs . lower number of caudal vertebrae (91–100). Description. Morphometrics and meristics given in Tab. 3 . Adult body size moderate to large as compared with other congeners, maximum size 520 mm LEA. Mouth subterminal. Snout relatively long, more than half of head length ( Fig. 5 ). Dorsal profile of snout strongly concave in front of eye, head profile slightly convex posteriorly. Anterior nares positioned terminally, posterior nares located closer to snout than eyes, at about one fourth of head length. Body profile almost straight to slightly concave dorsally. Ventral body profile slightly concave from anal–fin origin to end of anal fin. Greatest body depth slightly posterior to end of body cavity. Body tapering posterior to mid body. Eyes relatively large and positioned laterally, about seven times contained in postorbital length. Urogenital papilla developed and anteriorly positioned below eyes in specimens larger than 480 mm LEA. Urogenital papilla relatively small. Posterior gas bladder absent. Caudal appendage laterally compressed, its depth about three times its width. Body entirely covered by scales in adults, anterior and dorsal areas naked in juveniles. Scales cycloid elongate in shape posteriorly, length twice as depth. Lateral line complete with ossified tubules, anterior portion with ventral rami. Pectoral fin with 18–21 (mode 19) rays, dorsal rays longer than ventral rays, distal fin margin slightly rounded. Anal fin with 347–417 (median 403) rays. Anal-fin origin at vertical with anterior portion of opercle. Unbranched anterior anal–fin rays 23–42. Precaudal vertebrae 18–29. Vertebrae to end of anal fin 101–109. Displaced hemal spines 16 (n = 1). Sexual dimorphism unknown. FIGURE 4 | Rhamphichthys apurensis , ANSP 166484, 390 mm LEA, Laguna Mamo at Nuevo Mamo, Anzoátegui, Venezuela. FIGURE 5 | Detail of the head of Rhamphichthys apurensis , ANSP 166484, 390 mm LEA, Laguna Mamo at Nuevo Mamo, Anzoátegui, Venezuela. TABLE 3 | Morphometric and meristic of Rhamphichthys apurensis . SD = standard deviation, n = number of specimens.

n	Range	Mean	SD
Length to end of anal fin (LEA)	14	252–520	401.0	–
Percents of LEA
Anal-fin length Body depth Pectoral-fin length Head length Caudal filament length Caudal filament depth	14 14 14 14 14 14	86.1–92.5 7.7–9.4 4.1–5.5 12.9–15.1 23.2–36.8 1.8–2.3	88.9 8.4 4.8 13.8 30.6 2.1	1.7 0.4 0.4 0.6 4.0 0.1
Percents of head length
Interorbital distance Snout length Postorbital length Eye diameter Post. nares length Branchial Opening	14 14 14 14 14 14	9.3–11.6 58.4–63.7 34.4–38.1 4.2–6.7 13.2–17.8 13.2–18.2	10.2 60.9 36.3 5.0 14.8 15.1	0.5 1.6 1.1 0.6 1.1 1.4
Meristics
Anal-fin rays Pectoral-fin rays	14 14	347–417 17–21	387.1 18.4	22.5 1.2

Coloration in alcohol . Ground color of dorsal and lateral surfaces of head and body pale yellow ( Figs. 4–6 ). Head surface covered with scattered dark-brown blotches of about eye size; snout mostly dark, ventral head margin less pigmented. Epaxial body surface with many intercalated and dark pigment saddles across the mid-dorsum extending ventral to the lateral line. Hypaxial body surface with many dark pigment bands oriented at a slight diagonal to the long axis, sometimes contacting dorsal saddles, generally diffuse over pterygiophores region, and extending to proximal portion of anal–fin rays. Anal-fin membrane mostly clear or hyaline ( Figs. 4 , 7A ), except for ventral extensions of lateral bands and some scattered dark round pigment blotches ( Fig. 6 ). Pectoral fin clear or hyaline in most specimens, sometimes with scattered dark pigment blotches. Caudal appendage with dark vertically elongate pigment blotches. Geographical distribution. Rhamphichthys apurensis is distributed throughout the Orinoco basin and its larger tributaries and in the Cuyuni drainage of Essequibo ( Fig. 8 ; Tab. 1 ). Rhamphichthys apurensis inhabits mostly the deep waters of the main channel of Orinoco River and large size tributaries (Mago-Leccia, 1994). Material examined. Orinoco Llanos: ANSP 160251, 1, Venezuela , Bolívar , Río Guariquito at confluence of Río Orinoco, 07º39’36”N 66º20’W . ANSP 162300, 60 ( 12 specimens measured in Tab. 3 , 330–520 mm LEA; 1 cs), Venezuela , Bolívar , Río Orinoco near mouth of Río Caura, 07º38’N 64º52’W . ANSP 162707, 3, Venezuela , Bolívar , Río Orinoco about 50 m above mouth of Río Cuchivero, 07º40’N 65º57’W . ANSP 166845, 9, Venezuela , Bolívar , Laguna Castillero at Caicara del Orinoco, 07º38’20”N 66º09’00”W . ANSP 166484, 3, Venezuela , Anzoátegui , Laguna Mamo at Nuevo Mamo, 08º28’N 63º02’W . ANSP 188936, 1, Venezuela , Apure , Río Apure Isla Playa del Medio, near mouth of Río Portuguesa, 07º55’47”N 67º31’12”W . ANSP 190968, 1, Venezuela , Anzoategui , Río Orinoco deep channel upstream Los Baranacos, 08º21’N 62º43”W. AUM 53707, 4, Venezuela , Bolívar , Río Orinoco at Caicara del Orinoco ferry boat landing, 07º38’44”N 66º10’46”W . CUMV 72365, 2, Venezuela , Apure , San Fernando de Apure , Río Apure east of San Fernando Bridge, 07º 54’N 67º28’W . CUMV 82347, 2, Venezuela , Apure , San Fernando de Apure , Río Apure east of San Fernando Bridge, 07º54’N 67º28’W . FMNH 85503, 1, Venezuela , Apure , Río Arauca 32.5 km south of Biruaca, 07º34’N 67º38’W . IAvH-P 1021, 1, Colombia , Meta, Puerto Gaitán, Estero el Carrizal, Río Manacancias, 4º23’N 72º04’N . IAvH-P 17554, 1, Colombia , Casanare, Paz de Ariporo, Tapa El Venado, 05º39’14”N 71º00’31”W . IAvH-P 17587, 1, Colombia , Casanare, Paz de Ariporo, Tapa El Venado, 05º36’49”N 71º05’44”W . IAvH-P 17558, 2, Colombia , Casanare, Paz de Ariporo, Caño la Hermosa, 05º42’20”N 71º01’11”W . IAvH-P 18415, 2, Colombia , Casanare, Pore Caño Curimina, 05º35’09”N 71º50’19”W . IAvH-P 19994, 1, Colombia , Casanare, Orocué, Caño Aguaverde, Reserva Paralmarito-Casambá, 04º52’09”N 71º38’27”W . IAvH-P 24332, 4, Venezuela , Río Orinoco near mouth of Río Caura, 07º38’N 64º52’W . IAvH-P 25042, 1, Colombia , Meta, Caño Carrestilar. IAvH-P 25726, 3, Colombia , Vichada, Puerto Carreño, Caño Charapa, 06º05’33”N 67º30’03”W . IAvH-P 25784, 1, Colombia , Vichada, Puerto Carreño, Río Orinoco, 05º59’58”N 67º25’18”W . IAvH-P 28420, 2, Colombia , Vichada, Puerto Carreño, Río Orinoco, upstream Caño D’agua, 05º45’04”N 67º37’14”W . IAvH-P 28482, 1, Colombia , Vichada, Puerto Carreño, REserva Natural Bojonawi, 06º07’04”N 67º30’37”W . IAvH-P 28484, 1, Colombia , Vichada, Puerto Carreño, Laguna El Pañuelo, 06º07’04”N 67º30’32”W . ICNMCN 3456, 1, Colombia , Meta, Puerto Lopez, Laguna de Menegua. ICNMCN 5359, 1, Colombia , Vichada, Río Orinoco. LBP 10226, 1, Venezuela , Guárico , Río Apure at Cabruta, 07º37’24”N 66º24’48”W . MCNG 5985, 1, Venezuela , Apure , Hato El Frio, 07º53’N 68º52’W . MCNG 13143, 1, Venezuela , Apure , Río Apure at San Fernando. MCNG 20360, 1, Venezuela , Apure , Río Apure at Isla del Medio. MCNG 26351, 1, Venezuela , Apure , Muñoz, borrow pit at Módulo Fernando Corrales, 07º32’N 69º42’W . MCNG 31124, 1, Venezuela , Bolívar , Laguna Maldonado, 08º06’N 63º46’W . MCNG 31232, 1, Venezuela , Anzoátegui , Laguna de Tineo, 08º11’N 63º28’W . MCNG 33241, 13, Venezuela , Bolívar , Laguna Bartolico 07º38’N 66º06’W . MCNG 37462, 2, Venezuela , Apure , Río Arauca at El Yagual, 07º28’N 68º25’W . MCNG 51559, 5, Venezuela , Apure , right margin of Río Apure at Piedral. MPUJ 6564, 3, Colombia , Casanare, Caño Orosio. MPUJ 11697, 1, Colombia , Casanare, Caño La Hermosa, 05º42’20”N 71º01’11”W , MPUJ 12007, 1, Colombia , Casanare, Paz de Ariporo, Tapa Las Matas, 05º39’14”N 71º00’31”W . Orinoco Guiana Shield: MCNG 36173, 2, Venezuela , Bolívar , Río Caura at Salto Pará, 06º18’N 64º30’W . Orinoco Delta and coastal drainages: ANSP 149461, 1, Venezuela , Monagas , inlet on Isla Chivera below Barrancas 145 nautical miles from sea bouy 08º40’12”N 62º12’W . ANSP 188934, 1, Venezuela , Delta Amacuro , Río Orinoco just downstream los Castillos, 08º31’N 62º22’W . ANSP 192671, 1, Venezuela , Delta Amacuro , Río Orinoco, Brazo Imataca near S shore, 08º21’N 62º43’W . CAS 51077, 1, Venezuela , Delta Amacuro , Río Orinoco at El Toro, 08º31’N 61º29’W . MZUSP 44495, 2 ( 2 specimens measured in Tab. 3 , 252–282 mm LEA ), Venezuela , Delta Amacuro , Río Orinoco at Isla Tres Caños, 08º38’N 61º59’W . UMMZ 211324, 2, Venezuela , Delta Amacuro , Shallow channel of Río Orinoco across from Isla Tres Caños, 08º40’N 62º01’W . USNM 228767, 1, Venezuela , Delta Amacuro , Río Orinoco first small caño on W side of La Paloma 100 m above its mouth 92 nautical miles upstream of sea Buoy, 08º29”N 61º25’W . USNM 228768, 1, Venezuela , Monagas , Isolated lagoon on Isla Tapatapa at Río Orinoco 163 nautical miles from sea buoy, 08º31’36”S 62º26’42”W . USNM 233796, Venezuela , Delta Amacuro , Río Orinoco downstream Isla Portuguesa about 116.5 nautical miles from sea buoy, 08º36’12”N 61º46’24”W . USNM 388748, 1, Venezuela , Río Orinoco. Essequibo: USNM 404246, 1, Guyana , Cuyuni River, Cuyuni River about 15 km upstream from Waikuni mountains in Vicinity of mouth of Toropaur River, 06º41’31”N 59º34’38”W . USNM 402687, 1, Guyana , Cuyuni-Mazaruni , sand beach in the Cuyuni River immediately downstream Kanaima falls, 06º52’28”N 60º14’54”W . USNM 402688, 1, Guyana , Cuyuni-Mazaruni , Cuyuni River about 15 km upstream from Waikuni mountains in Vicinity of mouth of Toropaur River, 06º41’31”N 59º34’38”W .