Rhamphichthys drepanium Triques, 1999

Carvalho, Tiago P. & Albert, James S., 2023, A taxonomic review of the Neotropical electric fish Rhamphichthys (Gymnotiformes: Rhamphichthyidae), Neotropical Ichthyology (e 230012) 21 (4), pp. 1-76 : 18-27

Rhamphichthys drepanium Triques, 1999

( Figs. 7B–C , 9–14 ; Tab. 4)

Rhamphichthys marmoratus non Castelnau, 1855. —Mago-Leccia, 1994: fig. 61 (illustrated). Maldonado-Ocampo, Albert, 2003:157 (listed). —Lasso et al., 2004:141 (listed). —Rugeles, 2007:17 (illustrated and listed).

Rhamphichthys drepanium Triques, 1999:1 (original description, type-locality: Lago Janauari at the confluence of rio Negro and rio Amazonas. Manaus, Amazonas, Brazil). —Ferraris, 2003:496 (listed). —Maldonado-Ocampo, Albert, 2003:157 (listed). —Lasso et al., 2004:141 (listed). —Campos-da-Paz, 2007:123 (listed). —Carvalho, Albert, 2011:468 (examined). —Carvalho et al., 2011:405 (examined). — 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). —Giora, Carvalho, 2018:1060, fig. 2 (accessory electric organ anatomy). —Janzen et al., 2022: tab. 1 (barcode library).

Rhamphichthys sp. —Lavoué et al., 2012: fig. 2 (illustrated and EOD description).

Diagnosis. Rhamphichthys drepanium differs from all congeners except R. hahni by having paired sickle-shaped saddles along the middorsum interrupted at the midline

( Figs. 15B–C ), vs. absence of saddles or intercalated saddles on the middorsum ( Figs.

15A, D–G). It differs from R. hahni by the shape of the posterior gas–bladder, which is usually reduced with thickened walls, vs. always membranous and balloon like in R.

hahni ( Fig. 16D ). Also, R. drepanium differs from R. hahni by the number of precaudal vertebrae usually 18–20, rarely 20 (mode 19), vs. 19–21, rarely 19 (mode 20; Tab. 5); and by the number of caudal vertebrae 92–94, vs. 90–93 (mode 90; Tab. 5).

Description. Morphometrics and meristic given in Tab. 4. Adult body size moderate to large compared with other congeners, maximum size 604 mm LEA. Mouth subterminal. Snout relatively short and robust, about half of head length. 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 third of 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 small and positioned laterally, about nine times contained in postorbital length. Urogenital papilla developed and anteriorly positioned below eyes in specimens larger than 370 mm LEA. Urogenital papillae large and thickened in adults. Posterior gas bladder variable in shape, typically presenting reduced size and thickened walls, rarely presenting balloon–like gas blader ( Figs. 16A–C ). Caudal appendage laterally compressed, depth about three times 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 of presenting ventral rami. Pectoral fin with 16–19 (mode 18) rays, dorsal rays longer than ventral rays, distal fin margin slightly rounded. Anal fin with 310–390 (median 345) rays. Anal–fin origin at vertical of anterior portion of opercle. Precaudal vertebrae 18–20 (mode = 19, n = 10). Unbranched anal–fin rays at anterior anal fin portion 21–41. Caudal vertebrae to end of anal fin 92–94 (n = 3). Displaced hemal spines 13 (n = 1). Sexual dimorphism unknown.

Coloration in alcohol. Ground color of dorsal and lateral surfaces of head and body light to dark brown ( Figs. 9–14 ). Individuals from the Amazon River basin are overall generally darker ( Figs. 9–12 ) than individuals from the Orinoco River basin ( Figs. 13–14 ). Head mostly dark brown except for scattered, light, irregular small blotches, smaller than eye size; ventral portion of head lighter than dorsal portion. Dorsum of body presenting sickle–shaped dark saddles, these reaching ventrally to lateral line. Presence of lateral darkish lateral bands, slightly diagonally located from anteroventral to posterodorsal axis. Lateral bands sometimes with a light central area. Lateral bands often contacting the dorsal saddles; forming a contiguous band; these usually not contacting the ventrolateral bands over pterygiophores region, which are contiguous with the dark areas of the proximal region of the anal fin. Specimens larger than 500 mm of LEA uniformly dark, with inconspicuous saddles and bands. Anal fin mostly dark with clear and vermiculous areas proximally, and clear spots distally. Pectoral fin mostly clear or hyaline, with dark vertical bars. Caudal appendage with dark vertically elongate bands.

Geographical distribution. Rhamphichthys drepanium is distributed in the Amazon and Orinoco basins ( Fig. 17 ; Tab. 1). In the Amazon basin it is frequently collected in lentic waters, e.g., floodplain oxbow and ria lakes. In the Orinoco basin it is commonly collected in lotic habitats, including flooded savannas and barrow pits in the Llanos, sometimes being found in the main channel of small to medium sized, slowly flowing rivers.

Electric organ discharge. A tetraphasic discharge according to Lavoué et al. (2012, fig. 2d) identified as Rhamphichthys sp.

Comments. Rhamphichthys drepanium has been often erroneously identified as R. marmoratus (currently junior synonym of R. pantherinus ) in the Orinoco River basin (e.g., Mago-Leccia, 1994 and see also synonym list). Rhamphichthys pantherinus has a relatively restricted distribution in the Orinoco, occurring only in the Ventuari, Guaviare and Metica river basins.

Geographic variation. Specimens from the Orinoco basin ( Figs. 14–15 ) are overall less pigmented and relatively clearer than specimens collected in the Amazon basin ( Figs. 9–13 ). Despite their disjunct distribution, the populations in the Amazon and Orinoco basins exhibit relatively little morphological differences. A PCA was conducted using 11 morphometric characters to compare both geographic groups of R. drepanium (Amazon and Orinoco) and the allied species R. hahni from Paraná-Paraguay system. The first three principal components (PC1, PC2 and PC3) explain most of the variance (69.1%; Tab. S4). Scores were plotted for PC1 vs. PC2 and show large morphometric overlap of populations of R. drepanium in the Amazon R. drepanium in the Orinoco and R. hahni . Strong loadings separating these groups are the interorbital diameter (IO), eye diameter (ED), and branchial opening (BO; Fig. 18 ; Tab. S5). A Multivariate Analyses of Variance (MANOVA) was done using the PC scores of the first three axis of the PCA. There are no statistically significant differences between morphometrics between R. hahni and R. drepanium from the Amazon and the comparison between other groups are marginally significant except when comparing the Orinoco population of R. drepanium with R. hahni (Tab. S6; Wilks’ λ: 0.4475; P <0.001; F 6,90 = 7.424).

Material examined. Orinoco Llanos: ANSP 128227 , 2 (2 specimens measured in

Tab. 4, 430–432 mm LEA), Colombia, Meta, Caño Rico at La Defensa NW of Laguna

Mozambique. ANSP 165186 , 1 (1 specimens measured in Tab. 4, 365 mm LEA),

Venezuela, Guárico, Esteros de Camaguan, 6 km N of Camaguan on road between Calabozo and San Fernando de Apure, 08º09’N 67º36’W. ANSP 166566 , 2 (2 specimens measured in Tab. 4, 325–532 mm LEA) , Venezuela, Bolívar, Almacén, Laguna Maldonado, 08º06’N 63º45’W. ANSP 181071 , 2 (2 specimens measured in Tab. 4, 315– 320 mm LEA) , Venezuela, Apure, Río Apure along right bank of channel near Maria Nieves bridge at vicinity of San Fernando de Apure , 07º53’N 67º28’W. ANSP 188935 , 5 , Venezuela, Apure, Río Apure Isla playa del Médio at mouth of Río Portuguesa , 07º55’N 67º31’W. AUM 22668 , 2 , Venezuela, Portuguesa, Río Portuguesa in El Mamón 24 km E of Guanare , 09º04’N 69º30’W. CAS 64326 , 1 (1 specimen measured in Tab. 4, 320 mm LEA) , Venezuela, Portuguesa, Río Maria at bridge on Guanaré-Acarigua highway, 09º10’N 69º35’W. CAS 64425 , 1 (1 specimen measured in Tab. 4, 232 mm LEA) , Venezuela, Portuguesa, Caño Maracá at highway between Guanarito-Guanare km 60. CUMV 72364 , 4 , Venezuela, Apure, Esteros de Camaguán farm pond about 35 km N of San Fernando, 08º07’N 67º36’W. CUMV 72371 , 3 , Venezuela, Apure, San Fernando de Apure, Río Apure east of San Fernando Bridge , 07º54’N 67º28’W. CUMV 82360 , 2 , Venezuela, Apure, Río Apure near mouth of Portuguesa, west of San Fernado , 07º55’N 67º30’W. CUMV 90146 , 1 , Venezuela, Portuguesa, Río Las Marias. FMNH 102111 , 1 (1 specimen measured in Tab. 4, 267 mm LEA) , Venezuela, Barinas, Río Suripa between pumping station of Hato Mercedes and mouth in Río Anaro. FMNH 105141 , 1 , Venezuela, Barinas, Río Anaro about 10 minutes from mouth in Río Suripa , 07º49’N 70º18’W. FMNH 105142 , 8 (2 specimens measured in Tab. 4, 295–315 mm LEA) , Venezuela Barinas, Cano Socopo about 3.5 hours upstream from boat of Hato Mercedes in Río Suripa , 07º47’ N 69º56’W. FMNH 105143 , 1 , Venezuela, Barinas, Playa Los Chicos in the Río Suripa 2.5 hours above Hato Mercedes. IAvH-P 9241 , 4 , Colombia, Arauca, Tame, Caño El Rucio 2 km via Arauca-Tame, 06º40’N 70º30’W. IAvH-P 17545 , 1 , Colombia, Casanare, Paz de Ariporo , Tapa el Venado, 05º36’49”N 71º05’44”W. IAvH-P 17555 , 1 , Colombia, Casanare, Paz de Ariiporo , Tapa las Matas, 05º39’14”N 71º00’31”W. IAvH-P 17559 , 1 , Colombia Casanare, Caño la Hermosa , 05º42’20”N 71º01’11”W. IAvH-P 17972 , 1 , Colombia, Arauca, Arauquita, confluence of stream, río Arauca and brazo Bayonero. IAvH-P 22115 , 1 , Colombia, Arauca, Arauquita, Río Aguas de Limón. ICNMCN 1321 , 1 , Meta Puerto Lopez, Laguna de Menegua. ICNMCN 1727 , Colombia Arauca, Cravo Norte, Caño Negro, Caño Ormedillo on the road to Arauca. ICNMCN 3333 , 1 , Colombia Arauca, Cravo Norte, Caño Negro, Caño Armadillo on the road to Arauca. ICNMCN 5568 1, Colombia, Casanare, Canno Carupana tributary to Río Gachiria. LBP 3040 , 1 , Venezuela, Bolívar, Rio Orinoco upstream Caicara del Orinoco , 07º38’11”N 66º19’04”W. MCNG 2149 , 1 , Venezuela, Barinas, borrow pit 1.2 km south of Bruzual , 08º01’N 69º20’W. MCNG 3110 , 3 , Venezuela, Barinas, flooded area bridge at Bruzual, 08º03’N 69º20’W. MCNG 5256 , 2 , Venezuela, Apure, Rio Sarare , 07º10’N 71º15’S. MCNG 5343 , 1 , Venezuela, Portuguesa / Barinas, Río Bocono , 08º43’N 69º34’W. MCNG 5984 , 6 , Venezuela, Apure, Hato El Frio, 07º53’N 68º52’W. MCNG 12848 , 6 , Venezuela, Barinas, Río Guasimito , 08º13’N 68º25’W. MCNG 14405 , 1 , Venezuela, Portuguesa, stream E of Guayabal. MCNG 14521 , 1 , Venezuela, Guárico, river between Cazorla and Guayabal , 07º57’N 67º09’W. MCNG 15771 , 1 , Venezuela, Apure, creek south to Bruzual. MCNG 19525 , 2 , Venezuela, Guárico, highway Calabozo to Camaguan km 271. MCNG 20694 , 1 , Venezuela, Apure, Río Apure 200 m upstream Maria Nieves bridge, 07º53’N

67º28’W. MCNG 24076 , 3 , Venezuela, Apure , Laguna El Pozón. MCNG 25434 , 1 , Venezuela, Apure , Via Arichuna 4 km from Boquerone. MCNG 25520 , 4 , Venezuela, Guárico , Via Arichuna 4 km from the bridge. MCNG 25533 , 1 , Venezuela, Apure , Río Lagero , Isla Apurito. MCNG 26246 , 1 , Venezuela, Barinas , Río Ticoporo , 07º47’N 69º56’W. MCNG 26648 , Venezuela, Portuguesa , Caño San Jose between Guanaritico and La Capilla , 08º41’09”N 68º56’49”W. MCNG 27371 , 1 , Venezuela, Portuguesa , Caño Ignes tributary to Río Portuguesa . MCNG 28621 , 2 , Venezuela, Apure , Módulos del Apure borrow pit 49, 07º30’N 69º30’W. MCNG 30913 , 1 , Guárico , Infante, Laguna Larga II. MCNG 31166 , 1 , Venezuela, Anzoátegui , Laguna El Venado, 08º10’30”N 63º37’35”W. MCNG 35523 , 2 , Venezuela, Portuguesa , Esteros del Caño Maracá between Papelón y Caño Delgadito , 08º50’N 69º27’W. MCNG 35759 , 1 , Venezuela, Portuguesa , Guanare, Esteros del Caño Maracá, en la finca de Dario Urriola. MCNG 35693 , 1 , Venezuela, Guanare , Caño Maracá at bridge in the road between Guanare / Guanarito about 60 km from Guanare , 08º49’N 69º20’W. MCNG 38804 , 1 , Venezuela, Apure , Caño Guaritico Medanos. MCNG 41735 , 1 , Venezuela, Portuguesa , La Aduana in the road from Guanare to Nueva Florida , 08º55’N 69º12’W. MCNG 48379 , 1 , Venezuela, Guarico , Esteros de Camaguan , 08º07’N 67º36’W. MCNG 49471 , 2 , Venezuela, Barinas , Caño Bravo, 08º00’N 67º59’W. MCNG 50300 , 1 , Venezuela, Apure , Río Apure , Isla Apurito, MCNG 51560 , 2 , Venezuela, Apure , Río Apure at Piedral Abajo . 07º32’27”N 67º18’17”W. MPUJ 6563 , 2 , Colombia, Casanare , Caño Orosio, 05º12’11”N 71º01’56”W. MPUJ 8493 , 1 , Casanare , Trinidad, Caño Varajuste, bridge on main road , 05º24’22”N 71º37’56”W. MPUJ 11694 , Colombia, Casanare , Paz de Ariporo , Tapa el Venado , 05º36’49”N 71º05’44”W. MPUJ 11695 , 1 , Colombia Casanare , Paz de Ariporo, Tapa Las Matas , 05º39’14”N 71º00’31”W. MPUJ 11696 , 1 , Colombia, Casanare , Paz de Ariporo, Tapa la Guayabera , 05º38’41”N 71º13’47”W. UF 37025 , 3 (2 specimens measured in Tab. 4, 171–207 mm LEA; 1 cs), Venezuela, Apure , Hato El Frio borrow pit near Río Guaritico , 07º52’N 69º19’W. UF 78066 , 2 (2 specimens measured in Tab. 4, 247–257, mm LEA, 1 cs), Venezuela, Guárico , borrow pit in palm savannah 2.3 km N of San Fernando de Apure , 07º52’S 68º55’W. UF 80303 , 1 (1 specimen measured in Tab. 4, 277 mm LEA, 1 cs), Venezuela, Portuguesa , old Río Guanare about 12 km S of Arismendi , 08º22’N 68º19’W. USNM 200243 , 1 , Venezuela, Apure , Río Apure 5 km W of San Fernando de Apure , 07º53’N 67º29’W. USNM 260245 , 1 , Venezuela, Apure , Río Apure about 2 km E of bridge at San Fernando de Apure , 07º53’N 67º29’W. USNM 270259 , 4 , Venezuela, Apure , side channel of Río Apure about 3 km W of center of San Fernando de Apure , 07º53’S 67º29’W. ZMB 10015 , 1 , Venezuela, Apure . Orinoco Delta and coastal drainages: USNM 228821 , 1 , Venezuela, Delta Amacuro , Río Orinoco first small caño on W side of Caño Paloma 100 m above its mouth 92 nautical miles upstream from sea buoy, 08º29’N 62º25’W. Rio Negro: INPA 27613 , 1 , Brazil Amazonas, rio Negro at Praia Grande , 03º02’S 60º32’W. Amazonas lowlands: INPA 4805 , 4 (3 specimens measured in Tab. 4, 360– 485 mm LEA), Brazil, Amazonas, Autazes , lago do Castanho , 03º33’S 59º13’W. INPA 4848 , 1 , Brazil, Amazonas, lago do Camaleão at ilha da Marchantaria. INPA 13036 , 2 (1 specimen measured in Tab. 4, 473 mm LEA), Brazil Amazonas , Manaquiri , lago Janauacá , 03º23’S 60º16’W. INPA 13037 , 4 (2 specimens measured in Tab. 4, 420–500 mm LEA), Brazil Amazonas, Manaquiri , lago Janauacá , 03º23’S 60º16’W. INPA 17682 , 6 (2 specimens measured in Tab. 4, 382–395 mm LEA, 1 cs), Brazil, Amazonas, Manaus ,

Costa do Catalão, 03º10’S 59º56’W. INPA 18324 , Brazil, Amazonas, Alvarães, lago Amanã at mouth of igarapé Baré, 02º29’S 64º41’W . INPA 27602 , 1 (1 specimen measured in Tab. 4, 372 mm LEA), Brazil, Amazonas , Manaus, paraná do Xiborena, 03º09’S 59º55’W . INPA 27603 , 1 (1 specimen measured in Tab. 4, 207 mm LEA), Brazil, lago do Padre . MCP 45526 , 1 , Brazil, Amazonas, rio Tefé in ilha do Martelo at lago do Martelo, 03º46’49”S 64º59’29”W . MPEG 10075 , 2 , Brazil, Pará, Juruti, lago da Piranha, 02º12’S 56º06’W . MZUSP 6893 , holotype (1 specimen measured in Tab. 4, 372 mm LEA), Brazil, Amazonas , Manaus , lago Janauari at confluence of rio Negro and rio Solimões, 03º12’S 60º01’W . MZUSP 48509 , 2 paratypes (2 specimens measured in Tab. 4, 325-390 mm LEA), collected with holotype . MZUSP 36144 , 2 (1 specimen measured in Tab. 4, 385 mm LEA), Brazil, Amazonas , lago Amanã mouth of rio Japurá, 02º30’S 64º42’W . USNM 306734 , 1 , Brazil, Amazonas, lago Janauari near its mouth . USNM 306766 , 1 , Brazil, Amazonas, São José, lago do Castanho at Janauacá . USNM 306876 , 1 paratype of R. drepanium , Brazil, Amazonas , lago Janauari at first brick plant. Mamoré-Madre de Dios Piedmont . MNHN 1988–1028 , 1 , Bolívia, Puerto Almacén, Río Ibaré tributary to Río Mamoré, 14º52’S 64º58’W .

Figures

FIGURE 7 | Coloration pattern of the lateral portion of body at about midlenght of LEA in Rhamphichthys. A. Rhamphichthys apurensis, ANSP 162300, 390 mm LEA. B. Rhamphichthys drepanium from Orinoco Basin, ANSP 181071, 320 mm LEA. C. Rhamphichthys drepanium, INPA 17682, 375 mm LEA. D. Rhamphichthys hahni, MZUSP 59297, 355 mm LEA. E. Rhamphichthys lineatus, MCP 26374, 340 mm LEA. F. Rhamphichhtys pantherinus, MCP 24814, 405 mm LEA. G. Rhamphichthys rostratus, ANSP 187120, 520 mm LEA. H. Rhamphichthys heleios, INPA 42308, 335 mm LEA. Anterior portion towards left.

FIGURE 9 | Holotype of Rhamphichthys drepanium, MZUSP 6893, 372 mm LEA, lago Janauari at confluence of rio Negro and rio Solimões, Amazonas, Brazil.

FIGURE 10 | Detail of the head of holotype of Rhamphichthys drepanium, MZUSP 6893, 372 mm LEA, lago Janauari at confluence of rio Negro and rio Solimões, Amazonas, Brazil.

FIGURE 11 | Rhamphichthys drepanium, INPA 17682, 375 mm LEA, confluence of rio Negro and rio Solimões at Costa do Catalão, Amazonas, Brazil.

FIGURE 12 | Detail of the head of Rhamphichthys drepanium, INPA 17682, 375 mm LEA, confluence of rio Negro and rio Solimões at Costa do Catalão, Amazonas, Brazil.

FIGURE 13 | Rhamphichthys drepanium, FMNH 102111, LEA not measured, Río Suripa between pumping station of Hato Mercedes and mouth in Río Anaro, Barinas, Venezuela.

FIGURE 14 | Detail of the head of Rhamphichthys drepanium, FMNH 102111, LEA not measured, Río Suripa between pumping station of Hato Mercedes and mouth in Río Anaro, Barinas, Venezuela.

FIGURE 15 | Coloration pattern of the dorsum in Rhamphichthys. A. Rhamphichthys aprurensis, ANSP 162300, 390 mm LEA. B. Rhamphichthys drepanium, ANSP 181071, 313 mm LEA. C. Rhamphichthys hahni, FMNH108548, 370 mm LEA. D. Rhamphichthys lineatus, FMNH 114685, 290 mm LEA. E. Rhamphichhtys marmoratus MCP 39982, 320 mm LEA. F. Rhamphichthys rostratus, ANSP 187120, 520 mm LEA. G. Rhamphichthys heleios, INPA 42308, 335 mm LEA. Anterior portion towards right.

FIGURE 16 | Posterior gas bladder in lateral view of A. Rhamphichthys drepanium, female, ANSP 128327. B. Rhamphichthys drepanium, female, ANSP 166557. C. Rhamphichthys drepanium, not sexed, ANSP 165186. D. Rhamphichthys hahni, not sexed, MACN 5983, 410 mm LEA. Anterior portion towards left. Scale bars = 10 mm.

FIGURE 17 | Distribution of Rhamphichthys drepanium based on examined museum specimens. Red dot represents the type-locality.

FIGURE 18 | Scatter plots of PC1 vs. PC2 of morphometric data of populations of Rhamphichthys drepanium and R. hahni. Red = Rhamphicthhys hahni; blue = R. drepanium (Amazon) and gray = R. drepanium (Orinoco).