Rhamphichthys rostratus (Linnaeus, 1766)

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 : 55-63

Rhamphichthys rostratus (Linnaeus, 1766)

( Fig. 49–60 ; Tab. 10)

Gymnotus rostratus Linnaeus, 1766:428 (original description, type-locality: America). — Bloch, Schneider, 1801:522 (illustrated).

Rhamphichthys rostratus (Linnaeus, 1766) . —Müller, Troschel, 1849: (new combination). —Kaup, 1856:135 (redescription). —Steindachner, 1868:8 (redescription). —Günther, 1870:5 (redescription). —Eigenmann, Ward, 1905:168 (listed). Ihering, 1907:279 (redescription and key). —Ellis, 1913:137; fig.1 (redescription, feeding and skull illustration). —Santos et al., 1984:19 (illustrated and briefly described). —Planquette et al., 1996:400–01 (illustrated, briefly described and distribution in French Guiana). —Frery et al., 2001:453 (mercury contamination). —Maldonado-Ocampo, Albert, 2003:157 (listed). —Santos et al., 2004:106 (illustrated and briefly described). —Lasso et al., 2004 (listed). —Lucinda et al., 2007:81 (listed). —Montag et al., 2009:246 (listed). —Vari et al., 2009:46 (listed). —Ortega et al., 2011:41 (listed). —Mol et al., 2012:277 (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). —Giora, Carvalho, 2018:1060 (accessory electric organ anatomy). —Janzen et al., 2022: tab. 1 (Barcode library). —Taphorn et al., 2022:40 (listed).

Gymnotus longirostratus Lacepède, 1800:145 , 178 (original description, type-locality: South America).

Rhamphichthys blochii Kaup, 1856:133 , fig. 9 (original description: type-locality: No locality stated. Holotype: ZMB 4089 ). —Günther, 1870:5 (redescription).

Rhamphichthys reinhardti Kaup, 1856:132 , fig. 8 (original description: type-locality: No locality. Holotype: MNHN 3956 ). —Eigenmann, Ward, 1905:169 (listed).

Rhamphichthys schneideri Kaup, 1856:136 , fig. 11 (original description: type-locality: Cayenne. Holotype: MHNH 3957 ).

Rhamphichthys schomburgki Kaup, 1856:135 , fig. 10 (original description: type-locality: Rivers of Demerara, British Guiana. Holotype: MNHN 3958 ). —Steindachner, 1868:10 (redescription).

Diagnosis. Rhamphichthys rostratus differs from all congeners by a greater number of caudal vertebrae (111–117), vs. lower number of vertebrae (90–109). Rhamphichthys rostratus also differs from all congeners, except from R. apurensis , by a longer snout (58.8–

65.1% of HL), vs. shorter snout (46.4–59.1% of HL), and a longer caudal appendage

(18.4–35.6% of LEA), vs. shorter caudal appendage (5.8–20.3% of LEA; except in R.

pantherinus, 9.1–28.8 %). Rhamphichthys rostratus further differs from all congeners except R. apurensis and R. pantherinus by the intercalated pattern of the saddles on the mid dorsum, vs. a sickle shaped or absence of saddles. Rhamphichthys rostratus typically has darkly pigmented distal ends of the anal fin rays, forming a longitudinal stripe ( Fig.

61), vs. anal fin varying in pigmentation but not forming a distal darkened stripe.

Description. Morphometrics and meristics given in Tab. 10. Adult body size large as compared with other congeners, maximum size 850 mm LEA, maturing at about

420–460 mm LEA. Mouth subterminal. Snout very long, more than 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 fourth 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 small, positioned laterally. Urogenital papilla developed and anteriorly positioned below eyes in specimens larger than 400 mm LEA. Urogenital papilla small.

Posterior gas bladder small and membranous in between viscera. Caudal appendage long, 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 of presenting ventral rami. Pectoral fin with 17–22 (mode 18) rays, dorsal rays longer than ventral rays, distal fin margin slightly rounded. Anal fin with 365–455 (median 395) rays. Unbranched 17–34 anal–fin rays in the anterior portion of the anal fin. Anal–fin origin at vertical of anterior portion of opercle. Precaudal vertebrae 19–20 ( Tab. 5). Vertebrae to end of anal fin 111–117 ( Tab. 5). Displaced hemal spines 13–15 (n = 2). Sexual dimorphism unknown.

Coloration in alcohol. Ground color of dorsal and lateral surfaces of head and body yellow to dark brown ( Figs. 51–62 ). Head with scattered dark brown blotches of about eye size; snout mostly dark, ventral margin less pigmented. Body presenting dark intercalated saddles, these reaching ventrally the lateral line. Presence of dark lateral pigment bands, slightly diagonally placed along the long axis of the body. Bands sometimes contacting the dorsal saddles; bands diffuse over the pterygiophore region, extending to the proximal region of the anal fin rays. Anal fin mostly clear except for distal portion dark. Pectoral fin clear with broad dark bars. Caudal appendage with dark vertically elongate blotches.

Geographical distribution. Rhamphichthys rostratus is known from the Amazon, Essequibo, Tocantins, and coastal river of Guianas basins ( Fig. 63 ; Tab. 1). It inhabits river channels of medium to large size rivers. It is also found in flooded forest and oxbow lakes.

Ecological notes. Adult specimens of Wismar Guyana are reported to feed on mud-inhabiting worms and insects, including annelids, dipteran larvae, and gyrinid amphipods (Ellis, 1913:173).

Remarks on synonym and geographic variation. The synonyms of Rhamphichthys rostratus were proposed by several authors (see introduction) and were established by Mago-Leccia (1994). After examining Kaup’s (1856) Rhamphichthys type material we concur to this extensive synonymization. A PCA was done using geographic populations of R. rostratus and little geographic variation on morphometrics was observed between Amazon, Negro and Guianas populations. The first three principal components (PC 1, PC 2 and PC 3) explain most of the variance (75.3%; Tab. S10). Scores were plotted for PC 1 vs. PC 2 and show large morphometric overlap of geographic populations of R. rostratus ( Fig. 62 ). Strong loadings separating some of these groups are the interorbital standard length (SL), anal fin length; preorbital length (PR), pectoral–fin length (PFL); branchial opening (BO) and Eye diameter (BD) (Tab. S11). A Multivariate Analyses of Variance (MANOVA) was done using the PC scores of the first three axes of the PCA. Populations of R. rostratus from Amazon marginally differs statistically from Guianas and Negro basin (Tab. S12; Wilks’ λ: 0.3435; P <0.001; F 6,48 = 5.651).

Remarks. The type of Gymnotus rostratus is lost (Mago-Leccia, 1994; Ferraris, 2003). Although Linnaeus’ 1766 description of R. rostratus is very brief and too superficial to distinguish between different species of the genus, R. rostratus is the only species in the genus inhabiting Surinamese rivers (Mol et al., 2012), the likely type-locality of this species ( Albert, Crampton, 2003).

Material examined. ZMB 4089 holotype of Rhamphichthys blochii America. MNHN 3956, holotype of Rhamphichthys reinhardti , cabinet d’ajuda, probably Amazon basin in Brazil. Essequibo: UMMZ 216489, 1, Guyana, Essequibo River at opposite side of Bartica, 06º24’N 58º35’W. Guianas: ANSP 187119, 1 (1 specimen measured in Tab. 10, 580 mm LEA), Suriname, Sipaliwini, Lawa Lawa river Cataract west of base camp 8 km west of Anapaiake. FMNH 53293, 1, Guiana, Demerara River at Wismar. ANSP 187120, 1 (1 specimen measured in Tab. 10, 520 mm LEA), Suriname, Sipaliwini, Lawa Lawa river, Cataract west of base camp 8 km W of Anapaiake, 03º19’31”N 54º03’48”W, 18 Apr 2007. J. Lundberg, M. Sabaj, P. Willink, J. Mol et al. MHNG 2316.17, 1, French Guiana, Antecome Pata upper Maroni. MHNG 2117.007, 1, Suriname, Sipaliwini, Tapahony River Kumaru Konde Sula, 03º21’N 55º25’W. MNHN 3957, holotype of Rhamphichthys schneideri , French Guyana, Cayenne. MNHN 3958, holotype of Rhamphichthys schomburgki , Guyana. MNHN 1998.1569, 1, Suriname, Oulemoni, 03º08’N 54º26’W. MNHN 2000.5923, 1 (1 specimen measured in Tab. 10, 270 mm LEA), French Guyana, Maroni, St. Laurent du Maroni, Antecume Pata, camp nivree, rapids in the main channel upstream the village, 03º18’N 54º05’W. MNHN 2001.2291, 1 (1 specimen measured in Tab. 10, 420 mm LEA), French Guyana, Litany, Saint Laurent du Maroni, port of d’antecume pata. MNHN 2002.816, 1 (1 specimen measured in Tab. 10, 670 mm LEA, French Guyana, Litany, St. Laurent du Maroni, Waterfall Alimina-Emen. USNM 225654, 1, Suriname, Nickerie, Mataway creek approximately 8 km from its intersection with Corantijn River, 04º47’N 57º45’W. ZMB 6433, 1, Suriname, Maroni. Rio Negro: ANSP 189560, 1, Brazil, Amazonas, rio Jauaperi 9.2 km above confluence with rio Negro, 01º35’08”S 61º28’35”W. AUM 43333, 1, Venezuela, Amazonas, Río Casiquiare at mouth of Caño Caripo 36 km WSW of La Esmeralda, 03º06’48”N 65º52’40”W. FMNH 115524, 1, Brazil, Amazonas, Manaus, rio Negro between tributaries igarapé Taruma-Mirim and rio Solimões, 03º07’36”S 60º07’55”W. INPA 4428, 2 (2 specimens measured in Tab. 10, 480–510 mm LEA(Brazil, Amazonas, Manaus, rio Negro near Manaus. MCP 26285, 1, Brazil, Amazonas, rio Jauaperi 9.6 miles upstream São Francisco, 01º34’46”S 61º28’38”W. MCP 26286, 2, Brazil, Amazonas, rio Negro about 9.6 miles downstream Novo Caioe, 01º41’13”S 61º29’02”W. MCP 27756, 23 (5 specimens measured in Tab. 10, 380–450 mm LEA, 1 cs), Brazil, Amazonas, rio Negro 15 miles downstream Moura, 01º33’28”S 61º34’15”W. MCNG 37875, 1, Venezuela, Amazonas, Río Casiquiare at Isla Cuamate downstream Caño Solano, 02º00’N 66º57’W. MZUSP 32217, 1, Brazil, Amazonas, rio Negro downstream mouth of rio Daraá, 00º28’S 64º46’W. MZUSP 32220, 1, Brazil, Amazonas, rio Arira tributary to rio Negro, 00º31’S 63º33’W. MZUSP 32223, 1, MZUSP 32230, 1, Brazil, Amazonas, rio Negro at Anavilhanas, 02º42’S 60º45’W. MZUSP 32231, 1, Brazil, Amazonas, rio Negro at mouth of rio Urubaxi, 00º31’S 64º50’W. MZUSP 32232, 1, Brazil, Amazonas, rio Negro in flooded forest at São Gabriel da Cachoeira, 00º07’S 67º05’W. MZUSP 32233, 1, Brazil, Amazonas, flooded forest near confluence of rio Negro and rio Marauiá, 00º24’S 65º12’W. MZUSP 91650, 1, Brazil, Amazonas, rio Uapés. MZUSP 92251, 1 (1 specimen measured in Tab. 10, 330 mm LEA), Brazil, Amazonas, São Gabriel da Cachoeira, igarapé Curuni 500 m below port of comunidade São José II, tributary to rio Tiquié, 00º13’N 69º36’W. MZUSP 93446, 1 (1 specimen measured in Tab. 10, 530 mm LEA), Brazil, Amazonas, São Gabriel da Cachoeira, rio Tiquié near comunidade Serra do Mucura, 00º10’S 69º07’W. USNM, 373070, 1, Brazil, Amazonas, rio Negro 5.6 km below São Francisco, 01º42’22”S 61º24’27”W. Amazonas Lowlands. ANSP 182428, Peru, Loreto, fisherman catch purchased from canoe in Belen, Iquitos, reportedly from lower Río Itaya, 03º45’S 73º25’W. ANSP 189533, 1, Brazil, Amazonas, rio Amazonas, 162 km downriver Manaus, 31 km upstream Itacoatiara, 03º15’36”S 58º34’12”W. ANSP 189552, 2, Brazil, Amazonas, rio Madeira 4.7 km downstream from Rosarinho and 17.9 km from vila Urucurituba 03º39’17”S 59º03’27”W. ANSP 189555, 1 (1 specimens measured in Tab. 10, 370 mm LEA), Brazil, Amazonas, rio Solimões downstream rio Juruá mouth 21.5 km downstream Tamanicoa, 02º34”38’S 65º30’11”W. ANSP 189556, 1, Brazil, Amazonas, rio Solimões 9 km upstream Santo Antonio do Içá, 03º08’53”S 67º53’29”W. ANSP 189558, 1, Brazil, Amazonas, rio Juruá 9.2 km of Pauapixuna, 02º40’54”S 65º48’57”W. ANSP 189559, 1 (1 specimen measured in Tab. 10, 375 mm LEA), Brazil, Amazonas, rio Solimões 45.9 km downstream of Codajás and 18.2 km upstream of Anori, 03º52’21”S 61º42’49”W. CAS 36690, 1, Peru, Loreto, Caño del Chancho near Pebas, 03º20’S 71º51’W. FMNH 114680, 1(1 specimen measured in Tab. 10, 340 mm LEA), Brazil, Amazonas, rio Solimões between tributaries rio Japurá and lago Caimbe, 03º19’32”S 64º32’18”W. FMNH 114682, 3, Brazil, Amazonas, rio Madeira between Paraná do Canuma and rio Amazonas, 03º40’14”S 59º04’12”W. FMNH 114683, Brazil, Amazonas, rio Solimões between tributaries rio Japurá and lago Caimbe, 03º18’30”S 64º35’25”W. FMNH 115521, 1 (1 specimen measured in Tab. 10, 370 mm LEA, Brazil, Pará, rio Trombetas between tributaries lago Bacabal and lago Samauma, 01º31’03”S 56º09’57”W. FMNH 115523, 1 (1 specimen measured in Tab. 10, 443 mm LEA), Brazil, Pará, rio Trombetas between tributaries lago Bacabal and lago Aracuazinho, 01º31’10”S 56º08’59”W. IAvH-P 3192, 2, Colombia, Amazonas, Letícia, PNN Amacayacu, 03º00’47”S 70º00’01”W. IAvH-P 5342, 2, Colombia, Amazonas, La Chorrera, Lago Grande at río Igará-Paraná, 00º44’S 73º01W. ICNMCN 6671, 1, Colombia, Guiania, San Felipe, Río Negro at San Felipe. INPA 9360, 1 (1 specimen measured in Tab. 10, 640 mm LEA), Brazil, Amazonas, Presidente Figueiredo, igarapé Nazaré tributary to rio Uatuma. INPA 17645, 2 (1 cs), Amazonas, Careiro da Varzea, paraná do Rei at ilha do Careiro, 03º09’S 59º43”W. INPA 27621, 2 (2 specimens measured in Tab. 10, 330–365 LEA), Brazil, Amazonas, Manaus, rio Solimões at Costa do Catalão. MNHG 2552.17, 1, Brazil, Pará, rio Tapajos at Aveiro, 03º36’S 55º19’W. MCP 26455, 2, Brazil, Pará, rio Trombetas 6.25 miles usptream vila Aracua, 01º31’13”S 56º09’20”W. MCP 33444, 1, Brazil, Amazonas, Alvarães, rio Japurá near mouth of lago Mamirauá, 03º07’40”S 64º46’26”W. MCP 33446, 1, Brazil, Amazonas, Alvarães, rio Japurá paraná Maiana. MCP 33447, 1, Brazil, Amazonas, rio Tefé at Toco Preto. MPEG 1299, 1, Brazil, Pará, rio Amazonas at Óbidos, 01º54’S 55º31”W. USNM 52552, 1, Brazil, rio Amazonas. Mamoré-Madre de Dios: FMNH 54701, 1, Bolivia, Río Mamore. MNHN 1988–1029, 1, Bolivia, mouth of Río Ibare. Madeira Brazilian Shield. MZUSP 13957, 1, Brazil, Rondônia, rio Machado at igapó Paraíso. Tocantins-Araguaia. MCN 18986, 2, Brazil, Tocantins, Ananás, ribeirão Curicacas left margin tributary of rio Araguaia, 06º09’30”S 48º16’21”W. MCN 18987, 1, Brazil, Pará, Marabá, rio Taurizinho left margin tributary of rio Tocantins, 05º22’40”S 49º00’54”W. MCN 18988, 2, Brazil, Tocantins, rio Tocantins between Vila Nova dos Martirios and Buriti do Tocantins, 05º16’06”S 48 06’52”W. Amazonas estuary and coastal drainages: ANSP 189541, 1, Brazil, Pará, rio Acarai upstream from confluence with rio Xingu and Porto de Moz, 02º04’34”S 52º20’42”W. MPEG 2300, 1, Brazil, Pará, Gurupá, rio Amazonas downstream Gurupá near Estreito, 01º21’S 51º36’W. MPEG 5466, 1, Brazil, Pará, Castanhal, rio Apeu at Boa Vista do Apeu. MPEG 18693, 3, Brazil, Pará, Cachoeira do Anari, rio Arari. MZUSP 32225, 3, Brazil, Amapá, rio Araguari.

Figures

FIGURE 49 | Linear regression of Rhamphichthys pantherinus populations. Blue circles = Amazon Basin (open circle = holotype of R. pantherinus); red circles = Mearim System (open circle = holotype of R. atlanticus); black circles = Trombetas basin (open circle = holotype of R. longior).

FIGURE 50 | Scatter plots of PCA scores.A. PC 1vs. PC 2;B. PC 1vs. PC 3. PCA of Rhamphichthys pantherinus geographic populations: Red = Amazon; blue = Mearim (including R. atlanticus holotype); pink = Negro; golden = Tocantins (type-locality of R. marmoratus); brown = Tombetas (including types of R. longior); yellow = western Amazon (including R. pantherinus holotype) and grey = Xingu.

FIGURE 51 | Rhamphichthys rostratus, ANSP 187120, 520 mm LEA, Lawa Lawa River Cataract west of base camp 8 km W of Anapaiake, Sipaliwini, Suriname.

FIGURE 52 | Detail of head of Rhamphichthys rostratus, ANSP 187120, 520 mm LEA, Lawa Lawa River Cataract west of base camp 8 km W of Anapaiake, Sipaliwini, Suriname.

FIGURE 53 | Rhamphichthys rostratus, holotype of Rhamphichthys blochii, ZMB 4089, 510 mm LEA, South America.

FIGURE 54 | Rhamphichthys rostratus, holotype of Rhamphichthys blochii, ZMB 4089, 510 mm LEA, South America.

FIGURE 55 | Rhamphichthys rostratus, holotype of Rhamphichthys reinhardti, MNHN 3956, 600 mm LEA, Brazil.

FIGURE 56 | Detail of the head of Rhamphichthys rostratus, holotype of Rhamphichthys reinhardti, MNHN 3956, 600 mm LEA, Brazil.

FIGURE 57 | Rhamphichthys rostratus, holotype of Rhamphichthys schneideri, MNHN 3957, 700 mm LEA, Cayenne, French Guiana.

FIGURE 58 | Detail of the head of Rhamphichthys rostratus, holotype of Rhamphichthys schneideri MNHN 3957, 700 mm LEA, Cayenne, French Guiana.

FIGURE 59 | Rhamphichthys rostratus, holotype of Rhamphichthys schomburgki, MNHN 3958, 700 mm LEA, Demerara, Guyana.

FIGURE 60 | Detail of the head of Rhamphichthys rostratus, holotype of Rhamphichthys schomburgki MNHN 3958, 700 mm LEA, Demerara, Guyana.

FIGURE 61 | Rhamphichthys rostratus, ANSP 182428, 445 mm LEA, fisherman catch purchased from canoe in Belen, Iquitos, reportedly from Lower Río Itaya, Loreto, Peru.

FIGURE 62 | Detail of the head of Rhamphichthys rostratus, ANSP 182428, 445 mm LEA, fisherman catch purchased from canoe in Belen, Iquitos, reportedly from lower Río Itaya, Loreto, Peru.

FIGURE 63 | Distribution of Rhamphichthys rostratus based on examined museum specimens.