A taxonomic review of the Neotropical electric fish Rhamphichthys (Gymnotiformes: Rhamphichthyidae)

Tiago P. Carvalho1 and James S. Albert2

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Abstract​


EN

The species diversity and taxonomy of Rhamphichthys is reviewed and seven species are considered valid: Rhamphichthys apurensis from the Orinoco and Cuyuni river basins; R. drepanium from the Amazon and Orinoco river basins; R. hahni from the Paraná-Paraguay River system; R. heleios and R. lineatus from the Amazon River basin; R. pantherinus from the upper Orinoco, Essequibo, Amazon and coastal rivers of North Brazil, and R. rostratus from the upper Orinoco, Amazon and coastal rivers of Guianas. Based on the examination of specimens from nominal species, from across their geographic ranges, including specimen types, the previous synonymization of four species (R. blochii, R. reinhardti, R. schomburgki, and R. schneideri) with R. rostratus, and R. marmoratus with R. pantherinus is confirmed. Two other nominal species, R. atlanticus and R. longior, are proposed as junior synonyms of R. pantherinus. Species are redescribed and diagnosed based on color pattern, morphometric, meristic, and internal anatomy characters. Distribution maps and an identification key based on the examination of a comprehensive list of materials are also provided.

Keywords: Identification key, Ostariophysi, Species diversity, Taxonomy.

PT

A diversidade de espécies de Rhamphichthys é revisada e sete espécies são consideradas válidas: Rhamphichthys apurensis das bacias dos rios Orinoco e Cuyuni; R. drepanium das bacias dos rios Orinoco e Amazonas; R. hahni do sistema do rio Paraná-Paraguai; R. heleios e R. lineatus da bacia do rio Amazonas; R. pantherinus do alto rio Orinoco, Amazonas, Essequibo e rios costeiros do norte do Brasil; e R. rostratus do alto rio Orinoco, Amazonas e rios costeiros das Guianas. Baseado na revisão de material das espécies nominais cobrindo toda a distribuição geográfica, incluindo os espécimes tipos, confirma a sinonímia prévia de quatro espécies nominais (R. blochii, R. reinhardti, R. schomburgki, and R. schneideri) com R. rostratus e de R. marmoratus com R. pantherinus. Duas outras espécies nominais, R. atlanticus e R. longior, são propostas como sinônimo júnior de R. pantherinus. As espécies são redescritas e diagnosticadas baseando-se no padrão de colorido, morfometria, contagens e caracteres de anatomia interna. Mapas de distribuição e uma chave de identificação baseados em uma extensa revisão de material são fornecidos.

Palavras-chave: Chave de identificação, Diversidade de espécies, Ostariophysi, Taxonomia.

Introduction​


The Rhamphichthyidae (Regan, 1911) is a monophyletic group of gymnotiform electric fishes represented by five genera and 28 species (Carvalho et al., 2011; Carvalho, Albert, 2015; Tagliacollo et al, 2016; Ferraris et al., 2017; Fricke et al., 2022). Until recently (Albert, 2001; Ferraris, 2003; Carvalho, Albert, 2011), Rhamphichthyidae was restricted to three long-snouted genera Rhamphichthys Müller & Troschel, 1846, Gymnorhamphichthys Ellis, 1912 and the monotypic Iracema Triques, 1996, and more recently expanded to encompass the short-snouted genera Hypopygus Hoedman, 1962 and Steatogenys Boulenger, 1898, formerly placed in the family Hypopomidae (Tagliacollo et al., 2016; Ferraris et al., 2017; Alda et al., 2018). 

Within the family Rhamphichthyidae, species of the subfamily Rhamphichthyinae are readily characterized by a long and tubular snout, and small oral jaws entirely lacking teeth, which they use in grasp-suction feeding on the substrates of river and lake bottoms, consuming a variety of small-bodied benthic and infaunal animals (Marrero, Winemiller, 1993; Winemiller, Adite, 1997). This group inhabits most water bodies in lowland tropical South America east of the Andes, ranging from the La Plata estuary in Argentina to the Orinoco basin of Venezuela (Ellis, 1913; Ferraris, 2003). Many Rhamphichthys grow to a large body size, sometimes reaching a meter of total length (Santos et al., 1984), thereby possessing one of the largest body length of gymnotiform, together with some species of Sternopygus Müller & Troschel, 1846 and Electrophorus Gill, 1864 (Ellis, 1913; Albert, 2003; de Santana et al., 2019). 

Rhamphichthys includes nine species (Ferraris et al., 2017; Fricke et al., 2022), which together extend throughout the entire geographic range of the family Rhamphichthyidae. Rhamphichthys inhabit deep (5–100 m) river channels or marginal habitats such as oxbow lakes, being collected in relative abundance by bottom trawling in the Amazon and Orinoco basins (Cox Fernandes et al., 2004; Albert, Crampton, 2005; Crampton, Albert, 2006; Kim, Albert, 2018). Juveniles of some species exhibit an ontogenetic shift in habitats, moving from smaller rivers or marginal lakes to larger rivers (Crampton, 1998). There are reports of Rhamphichthys being consumed as food by some indigenous communities (Müller, Troschel, 1848; Ellis, 1913), however, they are not generally an important resource in most Amazonian fisheries; they are infrequently found in the fish markets (Santos et al., 1984) and are rarely encountered in the aquarium trade. 

The name Rhamphichthys appeared for the first time in the literature as “Ramphichthys” in a footnote of Müller, Troschel (1846:194) lacking an “h,” a species description, or a justification (Albert, Campos-da-Paz, 1998; Ferraris, 2003 present as Müller, Troschel, 1844). The authorship and date of the genus Rhamphichthys is either credited to Müller, Troschel (1846) or to Müller, Troschel (1848) where it appeared as a new genus, with the correct spelling and a description (Albert, Campos-da-Paz, 1998; possibly M. T., 1949 according to Fricke et al., 2022). Rhamphichthys was described based on its toothless mouth, head and body laterally compressed, narrow gill slits, anus positioned before the eyes, and body completely scaled except for the head (Müller, Troschel, 1848). By monotypy the type-species was Gymnotus rostratus Linnaeus, 1766, one of the earliest gymnotiform to be formally described. Linnaeus (1766) description was based on Seba (1759; plate 32; Fig. 1A), from material probably originating from somewhere near Paramaribo in Suriname (Albert, Crampton, 2003; Campos-da-Paz, 2003). 

FIGURE 1| Early drawings of Rhamphichthys species. A. Seba’s (1759) illustration of Rhamphichthys, later named by Linnaeus as Gymnotus rostratus (1766). B. Rhamphichthys marmoratus holotype from Castelnau (1855). C. Rhamphichthys rostratus from Bloch, Scheneider (1801), same specimen latter named as R. blochi by Kaup (1855). D. Rhamphichthys pantherinus holotype from Castelnau (1855). Drawings taken from the original publications and slightly modified to a clear white background.

The known diversity of Rhamphichthys was greatly increased by the additions of Castelnau (1855) and Kaup (1856). Castelnau described three species: R. marmoratus Castelnau, 1855 (Fig. 1B) from the Araguaia River in Brazil; and R. pantherinus Castelnau, 1855 (Fig. 1D), and R. lineatus Castelnau, 1855, both from a lake on the Ucayali River in Peru. Castelnau’s species were diagnosed based mostly on color pattern differences and snout length. Kaup (1856) did the most comprehensive review to date of Rhamphichthys. He described six new species (two of this nominal species are currently placed in the monotypic genus Hypopomus Gill, 1864), examining material mostly from Guyana and French Guiana. Kaup’s diagnoses were based mostly on snout length, color pattern and the relative position of the anus. Several authors later criticized this last character due as to ontogenetic variation (e.g., Günther, 1870). 

After this early period of discovery, there was a trend towards synonymization in the genus. Steindachner (1868) considered only three species (R. lineatus, R. pantherinus, and R. marmoratus) of the genus to be valid. Günther (1870) regarded three species to be valid, and proposed R. marmoratus to be a junior synonym of R. pantherinus, which is interpreted as the principle of first reviewer by Ferraris et al. (2017). Later this decision was reversed by Eigenmann, Ward (1905) who considered R. marmoratus to be the senior synonym. Eigenmann, Ward (1905) and Ihering (1907) claimed that the many named species were simply different forms of a single highly variable Rhamphichthys rostratus. Other authors supported this interpretation of low species diversity for the group, with high variation within species. Lahille (1910) proposed that the Rhamphichthys inhabiting the La Plata basin was very similar to the species in the Amazon and Guianas. He considered that the genus comprised a single geographically widespread and phenotypically variable species. Ellis (1913) concurred, synonymizing all species of Rhamphichthys known at that date with the type-species R. rostratus. 

Throughout much of the 20th Century there was no consensus regarding the diversity represented by Rhamphichthys, and the taxonomy of this genus remained poorly resolved. Adding to this confusion, later, two species of Rhamphichthys were described in other gymnotiform genera. Sternarchorhamphus hahni Meinken, 1937 based on superficial resemblance was originally described as a long-snouted apteronotid based on a single specimen from the Paraná River in Corrientes, Argentina. Campos-da-Paz, Paepke (1994) later transferred Sternarchorhamphus hahni to Rhamphichthys, but the authors expressed doubt about the validity of this species. Another Rhamphichthys species described in a different genus was Gymnorhamphichthys apurensis Fernández-Yépez, 1968, from a tributary of the Apure River in Venezuela. The generic allocation of G. apurensis was questioned by Nijssen et al. (1976) and Schwassmann (1989), who considered it an immature specimen of Rhamphichthys. Mago-Leccia (1994:41) considered Rhamphichthys apurensis a valid and probably endemic species of deep river waters in the Orinoco basin. 

In his comprehensive review of Gymnotiformes, Mago-Leccia (1994) recognized seven valid species of Rhamphichthys, some however, of doubtful taxonomic status. Triques (1994, 1999) reviewed the diversity of Rhamphichthyidae, proposing three new species of Rhamphichthys in 1999 (R. atlanticus, R. drepanium, and R. longior), including eight valid species (Ferraris, 2003; Crampton, Albert, 2006; Crampton, 2011). The most recent species addition to Rhamphichthys was the description of Rhamphichthys heleios Carvalho & Albert, 2015 from the Amazon basin with the authors commenting on the species diversity of that basin and assigning R. longior as a junior synonym of R. marmoratus (Carvalho, Albert, 2015; Ferraris et al., 2017). 

Rhamphichthys was first included in a phylogenetic analysis by Triques (1993), who found it to be the sister of Gymnorhamphichthys Ellis (1912). Albert, Campos-da-Paz (1998) and Albert (2001) diagnosed Rhamphichthys from other Gymnotiformes by the presence of four exclusive synapomorphies. In an analysis based on external morphology, Triques (2005a,b) proposed seven putative synapomorphies for Rhamphichthys, including several already proposed by previous studies within Gymnotiformes (Mago-Leccia, 1994; Albert, 2001). Currently, Rhamphichthys is regarded as a monophyletic group, and a sister clade to the monotypic Iracema (Carvalho, Albert, 2011; Tagliacollo et al., 2016). 

Despite this extensive history of taxonomic work, the species diversity within Rhamphichthys remains poorly known and in need of revision (Campos-da-Paz, Paepke, 1994; Albert, Crampton, 2005). The goal of this paper is to review the diversity within this genus, document species distributions, review previously suggested synonyms, and propose new junior synonyms.

Material and methods


Measurements were made to the nearest 0.1 mm with digital calipers or with rulers for larger specimens. The measurements follow those proposed by Carvalho et al. (2011) and Carvalho, Albert, (2011) except for the use of length to the end of anal fin (LEA) instead of standard length (SL; Mago-Leccia, 1976; Crampton et al., 2004). Morphometric data were expressed as percent of length to end of anal fin, except proportions of the head, which are expressed as percent of head length (HL). Osteological terminology follows Albert (2001). Damaged or incompletely regenerated specimens were not included in morphometric analyses, except for R. lineatus where individuals with almost complete regeneration were included due to a lack of fully intact specimens. The number of precaudal vertebrae includes the four of the Weberian apparatus. Caudal vertebrae were counted from the first vertebrae with a hemal spine to the last vertebrae in which the hemal spine is associated with an anal fin pterygiophore (Schwassmann, 1989; Lundberg, 2005). Numbers of vertebrae and displaced hemal spines were counted from radiographs and cleared and stained specimens prepared according to the method of Taylor, Van Dyke (1985). Most pictures were taken in a specially designed thin aquarium, following techniques explained by Sabaj-Pérez (2009), using a Panasonic Lumix DMC-FZ50 or a Nikon D90 digital SLR cameras. Drawings were made using a camera lucida attached to an Olympus SZX12 stereomicroscope. Material examined were listed into Freshwater Ecoregions of the World (FEOW) as proposed by Abell et al. (2008) located with the aid of the color scheme on the Google Earth® available at FEOW web site (feow.org). Material examined coordinates were presented in degrees minutes and seconds, typically georeferenced by GPS; or approximate coordinates shown in degrees and minutes, which are museum georeferenced or whenever possible by using Google Earth® or map charts and the distribution of Rhamphichthys species was mapped using ArcMap v. 10.6.1. Records include all material listed under Material Examined section. Museum acronyms follow Sabaj (2020). 

Statistical analyses. Morphometric analyses were made using all measurements listed above, which are also used and explained in Carvalho et al. (2011) and Carvalho, Albert (2011), except for caudal peduncle depth and caudal appendage length which contains multiple missing entries. The ten measurements were adjusted for size variation. The Aitchinson (1982) log-ratio transformation was applied. In this method every individual is scaled based on the composite of all characters considered and thus does not eliminate the measurement that is adopted for size. The method has been used in size correction in fish morphometrics studies (Peres-Neto, Magnan, 2004; Leal, Sant-Anna, 2007; Delapieve et al., 2020). The size corrected data were then checked for normality using the Shapiro-Wilk test (Shapiro, Wilk, 1965; Shapiro et al., 1968). Outliers were removed after visual inspections of data plots. Principal component analysis (PCA) was used to assess overall differences in morphometric differences among species and within species. PCA on variances-covariances transformations was performed on groups delimited by species or within species by drainage basis. A simple Multivariate Analysis of Variance (MANOVA) was performed on PC1, PC2 and PC3 scores, which are the components that explain most data variation (<10%). MANOVA tests for possible differences between species and groups using the Wilks’ λ test of significance. Bonferroni adjustments were used when doing multiple comparisons to control for type I error (Rice, 1989). Statistical analyses were made using the program PAST v. 2.17 (Hammer et al., 2001).

Results​


Systematic accounts 

Rhamphichthys Müller & Troschel, 1848:640 (type-species: Gymnotus rostratus Linnaeus, 1766. Type by monotypy). 

Altona Kaup, 1856:201 (type-species: Gymnotus rostratus Linnaeus, 1766. Type by monotypy). 

Diagnosis. Rhamphichthys can be diagnosed from other rhamphichthyines by the following 10 characters: (1) absence of the Posterior Lateral Line (PLL) foramen in the hyomandibula, vs. foramen present in the posterior dorsal portion of hyomandibula (Carvalho, Albert, 2011: fig. 5); (2) presence of intermuscular bones in the levator operculi and protactor hyodei (Carvalho, Albert, 2011), vs. absence of intermuscular bones in these muscles; (3) anterior portion of the gas bladder covered in a bony capsule (Mago-Leccia, 1994:40; Albert, Campos-da-Paz, 1998: char. 216), vs. anterior portion of gas bladder membranous not enclosed in a bony capsule; (4) number of pectoral-fin rays 17–22 (Mago-Leccia, 1994:40; Carvalho, Albert, 2011), vs. 10–14 in Gymnorhamphichthys and 14–16 in Iracema; (5) presence of a skin fold inside the branchial opening (Triques, 2005a: char. 3), vs. skin inside the branchial opening smooth; (6) origin of anal fin anterior to vertical of branchial opening (Mago-Leccia, 1994:40), vs. origin of anal fin posterior to branchial opening vertical; (7) more than 300 anal-fin rays (Albert, Campos-da-Paz, 1998: char.197; Albert, 2001:196; Carvalho, Albert, 2011), vs. 260 or less anal-fin rays; (8) more than 90 caudal vertebrae, vs. less than 60 caudal vertebrae; (9) body entirely covered by scales as adult (Mago-Leccia, 1994:40; Albert, Campos-da-Paz, 1998; Albert, 2001; Carvalho, Albert, 2011), vs. anterior portion of body scaleless; (10) presence of a subpectoral accessory electric organ (Giora, Carvalho, 2018), vs. absence of an accessory electric organ below pectoral fin. 

Common names. The common or local names used for Rhamphichthys usually allude to its elongate snout or body form, often being referred to as the “beaked,” “sword,” or “machete” fish. In Argentina R. hahni may be called bombilla (Span. for a straw to drink Yerba Mate), anguiya picuda (pike eel), morenita (Span. little dark girl), or señorita (Span. girl) (Ringuelet et al., 1967). In Paraguay it is known variably as morenita or pirá-kysé (Guaraní for knife–fish) (Neris et al., 2010). In the Paraná, Brazil, it may be called espadão (Port. big sword), peixe-espada (Port. swordfish), or peixe-tatu (Port: armadillo fish) (Godoy, 1986; Graça, Pavanelli, 2007). Rhamphichthys rostratus and R. pantherinus in the Tocantins basin of Brazil is called ituí-terçado (Port. machete gymnotiform) (Santos et al., 1984). Rhamphichthys drepanium in Colombia (Arauca basin) is called cuchillo ossa or caballo ossa (Rugeles et al., 2007). In French Guyana, R. rostratus is commonly known by the Wayana Amerindian people as mapalaine (Fréry et al., 2001), and as asa papi by the Saramaka Marron people (Planquette et al., 1996). In Guyana the same species is called band fish or wabri (Ellis, 1913). 

Geographical distribution. Rhamphichthys is known from most cis-Andean drainages of tropical South America, including the coastal drainages of Guianas, Orinoco, Essequibo, Amazon, Parnaíba basins; and the Paraná-Paraguay system (Fig. 2). The genus is present in nineteen of the Freshwater Ecoregions of the World (Abell et al., 2008; Tab. 1). 

TABLE 1 | Distributional data of species of Rhamphichthys in cis-Andean drainages of South America. Numbers corresponds to FEOW of Abell et al. (2008): Orinoco Llanos-307; Orinoco Guiana Shield-308; Orinoco Delta-309; Essequibo-310; Guianas-311; Negro-314; Amazonas Guiana Shield-315; Amazonas Lowlands-316; Mamoré-318; Guaporé-Itenez-319; Xingu-322; Amazonas estuary and coastal drainages-323; Tocantins-Araguaia-324; Parnaíba-325; Lower Uruguay-332; Chaco-342; Paraguay-343; Upper Paraná-344; and Lower Paraná-345. Asterisk (*) indicate the type-locality. Asterisks (**) indicates that Rhamphichthys hahni is allochthonous in the Upper Paraná (344) ecoregion.

 

 

Orinoco

Guianas

Amazonas

NE Brazil

Paraná-Paraguay

 

307

308

309

310

311

314

315

316

318

319

322

323–324

325

332

342

343

344

345

R. apurensis

X*

X

X

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R. drepanium

X

 

X

 

 

X

 

X*

X

 

 

 

 

 

 

 

 

 

R. hahni

 

 

 

 

 

 

 

 

 

 

 

 

 

X

X

X

X**

X*

R. heleios

 

 

 

 

 

 

 

X*

 

X

 

 

 

 

 

 

 

 

R. lineatus

 

 

 

 

 

 

 

X*

 

 

 

 

 

 

 

 

 

 

R. pantherinus

X

X

 

X

 

X

X

X

X

X

X

X*

X

 

 

 

 

 

R. rostratus

 

 

 

X

X*

X

 

X

X

 

 

X

 

 

 

 

 

 

 

FIGURE 2| Map showing the geographic distribution of Rhamphichthys in South America based on museum examined lots.

Taxonomic account. In this review we recognized seven valid species of Rhamphichthys. Principal component analysis (PCA) was used to investigate morphometric variation of the seven species of Rhamphichthys using 10 linear measurements. Results show that the first three principal components (PC1, PC2 and PC3) account for approximately 70% of the variance (Tab. S1). Scores were plotted for PC1 vs. PC2 and PC1 vs. PC3 that represent 38.49, 16.44 and 15.13% of the total variances, respectively (Figs. 3A–B). The PCA of 10 morphometric measurements indicates three morphologically distinct groups within Rhamphichthys (Fig. 3B). Group (1), formed by R. pantherinus, R. lineatus, and R. heleios, has strong loadings of eye diameter and interorbital distance on component 3 (Tab. S2). Group (2), formed by R. drepanium and R. hahni, has strong loadings of branchial opening and postorbital length on PC1 (Fig. 3; Tab. S2). Group 3, formed by R. rostratus and R. apurensis, is composed of Rhamphichthys with the most elongate snouts, and has strong loadings of head length (HL) and preorbital length (PR) on PC1 (Fig. 3; Tab. S2). A Multivariate Analysis of Variance (MANOVA) was performed using the PC scores of the first three and most important componets of the PCA. There were no statistically significant differences in morphometrics between R. hahni and R. drepanium (G1 species) and between R. apurensis and R. rostratus (G3 species; Tab. S1). Within G2 of species there were no statistically significant differences between R. heleios and R. lineatus and R. pantherinus (Tab. S1). The MANOVA fails to support a distinction of species within the three proposed morpho groups of Rhamphichthys (G1, G2, and G3) and shows statistical significance of species in different groups Rhamphichthys (Tab. S3; Wilks’ λ: 0.1061; P< 0.001; F18,410.6 = 27.61). 

FIGURE 3| Scatter plots of principal component scores of 10 measurements. A. PC1 vs. PC2. B. PC1 vs. PC3. All seven species of Rhamphichthys: red = R. apurensis; blue R. drepanium; pink = R. hahni; yellow = R. heleios; pale green = R. lineatus; brown = R. pantherinus; and grey = R. rostratus. Grey circles in B represent the three putative morpho groups (G 1–3). 

Key to the species of Rhamphichthys.  
A summary of variable characters within Rhamphichthys is given in Tab. 2. 

1a. Snout long (58.4–65.1% of HL); caudal vertebrae to end of anal fin 101–117……….2 

1b. Snout short (46.4–59. % of HL); caudal vertebrae to end of anal fin 90–100……….3 

2a. Anal fin usually clear or hyaline, caudal vertebrae to end of   anal fin 101–109……….Rhamphichthys apurensis (Orinoco basin and Cuyuni River). 

2b. Anal fin usually dark with a terminal dark band, caudal vertebrae to end of  anal fin 111–117……….Rhamphichthys rostratus (Amazon, Tocantins, Essequibo, and coastal drainages of Guianas). 

3a. Dorsal saddles sickle shaped and paired not contacting each other at middorsal line……….4 

3b. Dorsal saddles absent or unpaired and intercalated……….5 

4a. Posterior gas bladder always membranous, large, and not reduced;  19–21, rarely 19 (mode 20) precaudal vertebrae; 90–93 (mode 90) caudal  vertebrae……….Rhamphichthys hahni (Paraná-Paraguay system). 

4b. Posterior gas bladder reduced thick–walled or large and membranous; 18–20, rarely 20 (mode 19) precaudal vertebrae, 92–94 caudal vertebrae……….Rhamphichthys drepanium (Amazon and Orinoco basins). 

5a. Dorsal saddles in an intercalated pattern, extending ventrally to lateral line……….Rhamphichthys pantherinus  (Amazon, upper Orinoco, Tocantins, Parnaíba, and Essequibo basins). 

5b. Dorsal saddles absent……….6 

6a. Body coloration mostly light, sometimes with scattered dark chromatophores in the dorsum, inconspicuous diagonal bands, and dark blotches in the anal fin……….Rhamphichthys lineatus (Amazon basin). 

6b. Body coloration mostly brown, with no saddles in the darker dorsum and series of blotches over lateral line and series of spots in the anal fin……….Rhamphichthys heleios (Amazon basin). 

TABLE 2 | Summary of characters variable within Rhamphichthys species. PCV = precaudal vertebrae; CV = caudal vertebrae; HL = head length; LEA = length to end of anal fin.

 

Characters

R. apurensis

R. drepanium

R. hahni

R. heleios

R. lineatus

R. pantherinus

R. rostratus

Snout length

long; 58.4–63.7% of HL

short; 49.5–54.6% of HL

short; 46.4–54.3% of HL

short; 50.5–55.1% of HL

short; 52.1–56.0% of HL

short; 51.4–59.1% of HL

long; 58.8–65.1% of HL

Caudal appendage length

long; 23.2–36.8% of LEA

short; 5.8–20.3% of LEA

short; 7.3–15.4% of LEA

short; 12.7–16.9% of LEA

short; often damaged

short; 9.1–28.0% of LEA

long; 18.4–35.6%o LEA

Anal fin rays

347–417

310–390

310–360

320–345

341–381

360–444

365–455

Saddles in the dorsum

intercalated saddles

sickle shaped paired saddles

sickle shaped paired saddles

dark, no saddles

clear, no conspicuous saddles

intercalated saddles

intercalated saddles

Anal fin pigmentation

Mostly clear

Mostly dark with reticulated clear areas

Mostly dark with reticulated clear areas

Reticulated dark areas

Mostly clear, sometimes with dark spots

Variable, clear to reticulated dark areas

Terminal dark band

Posterior gas bladder

small, membranous walls

Large, membranous, or thickened walls

Large membranous

Large, thickened walls

small, membranous walls

small, membranous walls

Small, membranous walls

 

(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).  

FIGURE 4| Rhamphichthys apurensis, ANSP 166484, 390 mm LEA, Laguna Mamo at Nuevo Mamo, Anzoátegui, Venezuela.

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). 

FIGURE 5| Detail of the head of Rhamphichthys apurensis, ANSP 166484, 390 mm LEA, Laguna Mamo at Nuevo Mamo, Anzoátegui, Venezuela.

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. 

TABLE 3 | Morphometrics and meristic of Rhamphichthys drepanium. H = holotype, 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

14

86.1–92.5

88.9

1.7

Body depth

14

7.7–9.4

8.4

0.4

Pectoral-fin length

14

4.1–5.5

4.8

0.4

Head length

14

12.9–15.1

13.8

0.6

Caudal filament length

14

23.2–36.8

30.6

4.0

Caudal filament depth

14

1.8–2.3

2.1

0.1

Percents of head length

Interorbital distance

14

9.3–11.6

10.2

0.5

Snout length

14

58.4–63.7

60.9

1.6

Postorbital length

14

34.4–38.1

36.3

1.1

Eye diameter

14

4.2–6.7

5.0

0.6

Post. nares length

14

13.2–17.8

14.8

1.1

Branchial Opening

14

13.2–18.2

15.1

1.4

Meristics

Anal-fin rays

14

347–417

387.1

22.5

Pectoral-fin rays

14

17–21

18.4

1.2

 

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. 

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. 

FIGURE 6| Rhamphichthys apurensis, ANSP 160251, 248 mm LEA, Río Guariquito at confluence of Río Orinoco, Bolívar, Venezuela.

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.

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). 

FIGURE 8| Distribution of Rhamphichthys apurensis based on examined museum specimens. Red dot represents the approximate type-locality.

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. 

(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). 

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.

TABLE 4 | Morphometrics and meristic of Rhamphichthys drepanium. H = holotype, SD = standard deviation, n = number of specimens.

 

 

H

n

Range

Mean

SD

Length to end of anal fin (LEA)

372

24

207–532

344.4

Percents of LEA

Anal-fin length

92.7

24

82.8–92.7

88.9

2.2

Body depth

9.3

24

8.8–12.1

10.1

0.9

Pectoral-fin length

5.1

24

4.5–7.2

5.7

0.6

Head length

13.6

24

12.2–17.6

14.0

1.1

Caudal filament length

20

5.8–20.3

11.9

3.6

Caudal filament depth

20

1.4–2.4

1.8

0.2

Percents of head length

Interorbital distance

10.9

24

9.3–15.0

11.7

1.4

Snout length

50.9

24

49.5–54.6

51.6

1.2

Postorbital length

44.3

24

43.4–48.1

45.6

1.4

Eye diameter

3.8

24

3.9–6.5

5.1

0.6

Post. nares length

18.1

24

13.2–18.6

16.3

1.2

Branchial opening

20.7

24

17.2–27.4

21.9

2.7

Meristic

Anal-fin rays

390

23

310–390

349.0

22.8

Pectoral-fin rays

17

24

16–19

17.5

0.8

 

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). 

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.

TABLE 5 | Number of specimens observed for precaudal vertebrae (PCV) and caudal vertebrae (CV) counts in Rhamphichthys.

 

PCV

18

19

20

21

CV

90

92

93

94

100

101

106

109

111

113

116

117

R. apurensis

3

9

 

 

 

 

 

 

 

 

1

2

2

 

 

 

 

R. drepanium

2

7

1

 

 

 

1

1

1

 

 

 

 

 

 

 

 

R. hahni

 

2

4

1

 

2

1

1

 

 

 

 

 

 

 

 

 

R. heleios

 

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R. lineatus

5

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R. pantherinus

4

3

2

 

 

 

 

 

1

1

 

 

 

 

 

 

 

R. rostratus

 

6

1

 

 

 

 

 

 

 

 

 

 

1

1

1

1

 

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. 

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

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; F6,90 = 7.424). 

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).

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. 

(Fig. 19–24; Tab. 6) 

Rhamphichthys rostratus non (Linnaeus, 1766). —Lahille, 1910:6 (illustrated). —Ringuelet et al., 1967:254 (briefly described). —Caputi et al., 1994:633 (EOD and electric organ description). —Moravec et al., 1997: (parasite description). —Pavanelli, Caramaschi, 1997:26 (listed). —Caputi, 1999 (EOD and electric organ description). —Sverlij et al., 1998:40 (listed and illustrated). —Chernoff et al., 2001:147 (listed). —López et al., 2003 (listed). —Liotta, 2005: (listed and distribution in Argentina). —Shibatta, 2006: (illustrated and briefly described). —Neris et al., 2010:226 (illustrated). 

Rhamphichthys marmoratus non Castelnau, 1855. —Bertoni, 1939:57 (listed). 

Rhamphichthys reinhardti non Kaup, 1856. —Bertoni, 1939:57 (listed). 

Sternarchorhamphus hahni Meiken, 1937:79 (original description, type-locality: Rio Paraná, near Corrientes, Argentina). —Fowler, 1951:430 (listed). —Travassos, 1960:24 (listed). —Ringuelet, Aramburu, 1961:40 (listed). —Ringuelet et al., 1967:262 (listed and briefly described). —Britski, 1972:91 (listed). —Mago-Leccia, 1976:249 (discussion on taxonomic status). —Godoy, 1986:68 (listed). —Zaniboni-Filho et al., 2004:41 (illustrated). 

Rhamphichthys hahni (Meiken, 1937). —Axelrod et al., 1991:310 (new combination). —Campos-da-Paz, Paepke, 1994:155–59 (comments on new combination and resdescription of holotype). —Triques, 1994:92 (phylogenetic analyses). —Britski et al., 1999:86 (illustrated and briefly described). —Willink et al., 2000:87 (listed). —López et al., 2003 (listed). —Ferraris, 2003:496 (listed). —López et al., 2005:318 (listed). —Triques, 2005a:149 (outgroup for phylogeny). —Veríssimo et al., 2005:7. —Liotta, 2005:528 (listed and distribution to Argentina). —Graça, Pavanelli, 2007:187 (illustrated and briefly described). —Britski et al., 2007:110 (illustrated and briefly described). —Langeani et al., 2007:6 (listed). —Ordani, 2007:94 (fish passage). —Campos-da-Paz, 2007:122 (listed). —López et al., 2008 (listed). —Júlio Jr. et al., 2009:712 (listed). —França et al., 2009:2228 (Spermatic cell description). —Takemoto et al., 2009:702 (list of parasites). —Almirón et al., 2010:172 (Illustrated and briefly described). —Neris et al., 2010:227 (illustrated and briefly described). —Bozza, Hahn, 2010:221 (prey item). —Oyakawa, Menezes, 2011:6 (listed). —Mendes et al., 2012:1 (karyotype structure). —Litz, Koerber, 2014:28 (listed). —Carvalho, Albert, 2015:40 (comparative material examined). Mirande, Koerber, 2015:47 (listed). —Tagliacollo et al., 2016:29, fig. 5 (phylogenetic relationships). —Bertaco et al., 2016:422 (listed). —Vera-Alcaraz et al., 2017:6 (listed). Koerber et al., 2017:69 (listed). —Ferraris et al., 2017:28 (listed). —Giora, Carvalho, 2018:1060 (accessory electric organ anatomy). —Reis et al., 2020:463 (listed). —Janzen et al., 2022: tab. 1 (barcode library). 

FIGURE 19| Rhamphichthys hahni, holotype of Sternarchorhamphus hahni, ZMB 31367, 253 mm LEA, Río Paraná near Corrientes, Corrientes, Argentina.

FIGURE 20| Rhamphichthys hahni, detail of head of holotype of Sternarchorhamphus hahni, ZMB 31367, Río Paraná near Corrientes, Corrientes, Argentina.

FIGURE 21| Rhamphichthys hahni, MZUSP 59297, 355 mm LEA, rio Novo at Brejo de Santa Sofia, Mato Grosso do Sul, Brazil.

Diagnosis. Rhamphichthys hahni differs from its congeners, except R. drepanium by having sickle shaped saddles on the dorsal midline, vs. absence of saddles or intercalated saddles on the dorsum. It differs from R. drepanium by the shape of the posterior gas-bladder, which is always membranous and ballon like, vs. a posterior gas bladder usually reduced with thickened walls (Fig. 17). It also tentatively differs from R. drepanium by the number of precaudal vertebrae 19–21 rarely, 19 (mode 20), vs. 18–20 rarely 20 (mode 19; Tab. 5); and by the number of caudal vertebrae 90–93 (mode 90), vs. 92–94 (Tab. 5). 

Description. Morphometrics and meristic given in Tab. 6. Adult body size moderate to large compared with other congeners, maximum size 615 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 360 mm LEA. Urogenital papilla large in adults. Posterior gas bladder large not reduced, membranous (Fig. 16d). Caudal appendage laterally compressed, its depth about three times its width. 

TABLE 6 | Morphometric and meristic data for Rhamphichthys hahni. H = holotype, SD = standard deviation, n = number of specimens.

 

 

H

n

Range

Mean

SD

Length to end of anal fin (LEA)

253

27

230–600

383

Percents of LEA

Anal-fin length

88.9

27

72.7–90.7

86.1

4.4

Body depth

10.1

27

8.0–12.2

10.3

1.2

Pectoral-fin length

6.1

27

4.2–6.4

5.5

0.5

Head length

14.6

27

11.8–15.3

14.0

0.8

Caudal filament length

22

7.3–15.4

10.2

1.7

Caudal filament depth

1.8

25

1.3–2.2

1.7

0.2

Percents of head length

Interorbital distance

10.5

27

8.5–13.6

10.3

1.1

Snout length

51.7

27

46.4–54.3

51.3

1.9

Postorbital length

44.7

27

42.7–48.6

45.8

1.7

Eye diameter

7.0

27

4.6–7.0

5.5

0.6

Post. nares length

17.0

27

14.4–20.2

16.7

1.3

Branchial opening

17.0

27

17.1–25.0

21.0

2.3

Meristic

Anal-fin rays

328

24

310–360

339.6

14.5

Pectoral-fin rays

17

25

16–19

17.7

0.8

 

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 17) rays, dorsal rays longer than ventral rays, distal fin margin slightly rounded. Anal fin with 310–360 (median 340) rays. Anal–fin origin at vertical of anterior portion of opercle. Precaudal vertebrae 19–21 (mode = 20, n = 7). Vertebrae to end of anal fin 90–93 (n = 4). Displaced hemal spines 13 (n = 1). Sexual dimorphism unknown. 

Coloration in alcohol. Ground color of dorsal and lateral surfaces of head and body light brown to pale yellow (Figs. 19–24). Head presenting scattered dark brown blotches of about eye size; snout mostly dark, ventral margin less pigmented. Dorsum of body presenting sickle shaped saddles, these reaching ventrally to lateral line. Presence of lateral darkish lateral bands, slightly diagonally located from anteroventral to posterodorsal axis. Lateral bands sometimes contacting the dorsal saddles; ventrolateral bands diffuse over pterygiophore region, extending to the proximal region of the anal–fin rays and not contiguous with the lateral bands. Anal fin mostly dark with clear vermiculous areas proximally and light spots distally. Pectoral fin almost completely dark except for transverse rows of light spots; these contacting each other sometimes forming clear bars. Caudal appendage with dark vertically elongate bands. 

FIGURE 22| Detail of head of Rhamphichthys hahni, MZUSP 59297, rio Novo at Brejo de Santa Sofia, Mato Grosso do Sul, Brazil.

FIGURE 23| Rhamphichthys hahni, FMNH 108066, 280 LEA, Río Paraguay at Estância Voluntad in Puerto Voluntad, Alto Paraguay, Paraguay.

FIGURE 24| Detail of the head of Rhamphichthys hahni, FMNH 108066, Río Paraguay at Estância Voluntad in Puerto Voluntad, Alto Paraguay, Paraguay.

Karyotype: Rhamphichthys hahni has 50 chromosomes and a formula comprised of 20m+24sm+6a (FN = 94; Mendes et al., 2012). 

Geographical distribution. Rhamphichthys hahni is the single species of the genus known from the Paraná-Paraguay river system (Fig. 25). It is known from the southern La Plata River in Argentina to the northern Paraguay River in Brazil and Paraguay. Is also known from the Uruguay River and Upper Paraná River in Brazil. The presence of this species in the Upper Paraná is due to the construction of Itaipu Dam, which by elevating a portion of the Lower Paraná eliminated the Sete Quedas falls as a barrier for dispersal (Langeani et al., 2007; Júlio Jr. et al., 2009). Another species of the genus was cited for this system (i.e., R. rostratus in Caputi et al., 1994; Shibatta, 2006; Neris et al., 2010, and others), however the only Rhamphichthys species occurring in this system is R. hahni. This species inhabits rivers and lakes, feeding on insect larvae and oligochaetes in the muddy bottom (Ringuelet et al., 1967, Hahn et al., 2004;). Willink et al. (2000) reports R. hahni living under water hyacinths in swamps of the lowlands of Brazilian Pantanal. Presents paternal care and offspring from October to February in the upper Paraná, gonads mature at 444 mm SL in females and 368 mm SL in males (Suzuki et al., 2004).  

FIGURE 25| Distribution of Rhamphichthys hahni based on examined museum specimens. Red dot represents the type-locality.

From the La Plata River region some specimens exhibited an asymmetrical position of the eyes, similar but in a minor degree to what was reported for the apteronotid Orthosternarchus tamandua by Hilton et al. (2007). As for example MACN 6386 (330 mm LEA) which has a preorbital distance of 46.4% of head length on the left side and 53.3% on the right side. 

Also, from the La Plata region a specimen of R. hahni (MPL 6556, 325 mm LEA) was being parasitized by the copepod genus Lernaea. The parasite had about 40 mm found attached inside its gill chamber leaving its posterior body by the opercula. The relationship between Gymnotiformes and this parasite is apparently rare (Takemoto et al., 2009). 

Electric organ discharge. According to Caputi et al. (1994), R. hahni (identified as R. rostratus) has a tetraphasic discharge with 2.5 ms duration (50+-0.2 Hz). Caputi and collaborators studied specimens collected in the Río Uruguay at the gate for migrating fish of Salto Grande Dam (Salto, Uruguay; Caputi et al., 1994:634) and identified as Rhamphichthys rostratus (see Caputi et al., 1994, 1999 for more details on EOD and the EO). 

Material examined. Lower Uruguay: MCP 38709, 1 (1 specimen measured in Tab. 6, 280 mm LEA), Brazil, Rio Grande do Sul, Itaqui, rio Ibicuí, 29º24’S 56º42’W. Chaco: MACN 8034, 1, Argentina, Formosa, Parque Nacional del Pilcomayo, 25º04’S 57º58’W. Paraguay: FMNH 108066, 1 (1 specimen measured in Tab. 6, 280 LEA), Paraguay, Alto Paraguay, Río Paraguay at Estância Voluntad in Puerto Voluntad, 20º42’S 57º57’W. FMNH 108548, 2 (2 specimens measured in Tab. 6, 360–370 LEA), Brazil, Mato Grosso do Sul, rio Negro at road between Nhecolandia and highway BR-262, 19º17’10”S 57º03’23”W. MZUSP 24736, 1 (1 specimen measured in Tab. 6, 480 mm LEA), Brazil, Mato Grosso, Coxipó da Ponte, rio Coxipó da Ponte, 18º38’S 56º03’W. MZUSP 24862, 1 (1 specimen measured in Tab. 6, 560 mm LEA), Brazil, Mato Grosso, Barão de Melgaço, rio Cuiabá at Bocaiúval, 16º11’S 55º57’W. MZUSP 26918, 1 (1 specimen measured in Tab. 6, 360 mm LEA), Brazil, Mato Grosso, fazenda Jofre at Transpantaneira highway 17º21’S 56º46’W. MZUSP 27739, 1 (1 specimen measured in Tab. 6, 470 mm LEA), Brazil, Mato Grosso do Sul, Coxim, rio Taquari, 18º30’S 54º45’W. MZUSP 52514, 1 (1 specimen measured in Tab. 6, 290 mm LEA), Brazil, Mato Grosso do Sul, rio Piquiri at Pantanal de Paiaguas at fazenda Santo Antônio. MZUSP 59297, 2 (2 specimens measured in Tab. 6, 230–345 mm LEA, 1 cs), Brazil, Mato Grosso do Sul, Aquidauana, rio Novo at brejo de Santa Sofia, 19º36’S 56º27’W. NUP 2206, 3, Brazil, Mato Grosso, Chapada dos Guimarães, Manso reservoir, 14º41’S 55º32’. NUP 3162, 5, Brazil, Mato Grosso, Barão do Melgaço, baia Sinhá Mariana tributary to rio Cuiabá, 16º20’S 55º44’W. NUP 3482, 1, Brazil, Mato Grosso, Santo Antônio do Leverger, rio Cuiabá, 15º51’S 56º05’W. NUP 4137, 1, Brazil, Mato Grosso, rio Cuiabá. NUP 9892, 1, Brazil, Mato Grosso do Sul, Porto Murtinho, rio Amonguijá tributary to rio Paraguai, 21º41’10”S 57º52’53”W. UMMZ 208107, 10 (4 specimens measured in Tab. 6, 335–410 mm LEA), Paraguay, Central, río Paraguay overflow at 1 km downstream Puente Remanso, 25º11’S 57º33’W. ZMB 19570, 2, Paraguay. Upper Paraná: LBP 3096, 1, Brazil, Mato Grosso do Sul, Baitapora, rio Bahia, 22º43’19”S 53º17’11”W. LBP 9623, 1, Brazil, Mato Grosso do Sul, Angélica, riacho de Engano, 22º02’37”S 53º43’38”W. MZUSP 44062, 4 (4 specimens measured in Tab. 6, 420–600 mm LEA), Brazil, São Paulo, Rosana, rio Paranapanema at Rosana hydroeletric power plant, 22º35’S 52º52’W. NUP 356, 2, Brazil, Paraná, Porto Rico, mouth of riacho Caracu in the rio Paraná, 22º45’S 53º15’W. NUP 417, 1, Paraná, Porto Rico, island in rio Paraná, 22º45’S 53º16’W. NUP 1708, 3, Brazil, Paraná, Formosa do Oeste, rio Piquiri, 24º11’S 53º19’W. NUP 3367, 1, Brazil, Mato Grosso do Sul, Taquarussu, lagoa dos Patos, 22º49’S 53º33’W. NUP 9623, 2, Brazil, Mato Grosso do Sul, Taquarussu, rio Samambaia tributary to rio Paraná, 22º39’14”S 53º11’ 52”W. Lower Paraná: MACN 1003, 1, Argentina, Buenos Aires, Río de La Plata, Dársena Norte at Buenos Aires, 34º35’S 58º21’W. MACN 4837, 1, Argentina, Buenos Aires, Río de La Plata. MACN 5941, Argentina, Buenos Aires, Pallermo. MACN 5943, 1, Argentina, Santa Fé, Maciel, Río Maciel, 32º27’S 60º50’W. MACN 5971, 1, Argentina, Chaco, Río Paraná Guazu, close to Arroyo Gutierrez. MACN 5983, 4 (2 specimens measured in Tab. 6, 395–410 mm LEA), Santa Fé, Argentina, Rosário, Río Paraná at Rosário, 32º56’S 60º37’W. MACN 6184, 10, Argentina, Buenos Aires, Río de La Plata OSN. MACN 6386, 2 (1 specimen measured in Tab. 6, 330 mm LEA), Argentina, Buenos Aires, Río de La Plata OSN. MACN 6722, 4, Argentina, Buenos Aires, Río de La Plata at SEGBA filters. MLP 259, 1, Argentina, Buenos Aires, Río de La Plata. MACN 7228, 2, Argentina, Corrientes, Corza-Cue. MHNG 2600.077, 1, Paraguay, Canendiyu, Salto Guairá, Río Paraná at Itaipu reservoir, 24º05’S 54º18’W. MLP 48, 1, Argentina, Buenos Aires, Magdalena, Río de La Plata at Punta Atalaya, 35º00’S 57º31’W. MLP 363, 1, Argentina, Buenos Aires, Río de La Plata. MLP 550, 1, Argentina, Buenos Aires, Río de La Plata. MLP 2850, 1, Argentina, Buenos Aires, Ensenada, Río de La Plata at Punta Lara, 34º49’S 57º55’W. MLP 3313, 1, Argentina, Buenos Aires, Ensenada, Río de La Plata at Punta Lara, 34º49’S 57º55’W. MLP 6556, 1, Argentina, Buenos Aires, La Plata, Río Santiago, 34º51’S 57º52’W. MZUSP 23133, 1 (1 specimen measured in Tab. 6, 260 mm LEA), Argentina, Buenos Aires, Río de La Plata (OSN Buenos Aires), 34º33’S 58º23’W. NUP 1515, 1, Brazil, Paraná, Santa Helena, rio Paraná Itaipu reservoir. NUP 1871, 1, Brazil, Paraná, Guaíra, rio Paraná Itaipu reservoir. NUP 4664, Brazil, Paraná, Guaíra, Rio São Francisco Verdadeiro, tributário do rio Paraná, 24º06’37”S 54º18’28”W. NUP 7890, 1, Brazil, Paraná, Candido Rondon, rio Paraná Itaipu reservoir. ZMB 31367, holotype of Sternarchorhamphus hahni, Argentina, Corrientes, Río Paraná near Corrientes. 

(Fig. 26–29; Tab. 7) 

Rhamphichthys heleios Carvalho & Albert, 2015:35 (Original description, type-locality: Brazil, Amazonas, Iranduba, confluence of rio Negro and Solimões at Costa do Catalão, 03°09’S 59°54’W). —Ferraris et al., 2017:28 (listed). —Giora, Carvalho, 2018:1060 (accessory electric organ anatomy). —Janzen et al., 2022: tab. 1 (barcode library). 

FIGURE 26| Holotype of Rhamphichthys heleios, INPA 42309, 375 mm LEA, confluence of rio Amazonas and Solimões at Costa do Catalão, Amazonas, Brazil.

FIGURE 27| Detail of the head of holotype of Rhamphichthys heleios, INPA 42309, 375 mm LEA, confluence of rio Amazonas and Solimões at Costa do Catalão, Amazonas, Brazil.

Diagnosis. Rhamphichthys heleios differs from all congeners by the presence of irregular dark rounded blotches along the lateral body surface over the lateral line, sometimes connected forming an irregular longitudinal dark stripe, vs. diagonally displaced dark bands on the ventrolateral surface of the body over this region sometimes faded in R. lineatus. It differs from R. lineatus by an overall dark, vs. light color pattern of the body. It differs from R. rostratus and R. apurensis by a short snout (50.5–55.1% of HL), vs. long snout (58.4–65.1% of HL); by low number of anal-fin rays (320–345), vs. high number of anal-fin rays (347–455). It differs from R. drepanium, R. hahni, R. rostratus, R. apurensis, and R. pantherinus by the absence of dark transversal saddles on the mid dorsum. 

Description. Morphometrics and meristics given in Tab. 7. Adult body size small to moderate compared with other congeners, maximum size 400 mm LEA. Mouth subterminal. Snout relatively short and robust, size about half of head length. Dorsal profile of snout strongly convex from snout tip to nares; concave from this point to eye and convex from this point to supraoccipital. 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 at vertical of posterior end of anal fin or posterior to end of body cavity. Body tapering posterior to mid body. Eyes relatively large and positioned laterally. Urogenital papilla developed and anteriorly positioned below eyes in specimens larger than 330 mm LEA. Urogenital papilla large. Posterior gas bladder reduced with thickened walls. Caudal appendage laterally compressed, its depth about three times its width. 

 

 

H

n

Range

Mean

SD

Length to end of anal fin (LEA)

333

5

320–400

355.3

Percents of LEA

Anal-fin length

90.1

6

88.0–90.1

89.1

0.8

Body depth

7.8

6

7.5–8.8

8.2

0.5

Pectoral-fin length

4.8

6

4.3–5.1

4.8

0.2

Head length

12.0

6

11.4–13.0

12.4

0.6

Caudal filament length

16.9

3

12.7–16.9

14.5

2.2

Caudal filament depth

1.7

5

1.5–2.0

1.8

0.1

Percent of head length

Interorbital distance

12.3

6

10.3–14.9

12.2

1.7

Snout length

52.8

6

50.5–55.1

52.5

1.5

Postorbital length

45.9

6

41.1–45.9

44.1

1.7

Eye diameter

5.4

6

5.1–6.5

5.8

0.5

Post. nares length

19.0

6

16.2–19.0

17.9

0.9

Branchial opening

22.4

6

16.5–24.4

21.8

2.7

Meristics

Anal-fin rays

342

5

320–345

357.8

15.0

Pectoral-fin rays

17

6

16–19

17.1

0.7

 

TABLE 7 | Morphometric and meristic data for Rhamphichthys heleios. H = holotype, SD = standard deviation, n = number of specimens.

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 19) rays, dorsal rays longer than ventral rays, distal fin margin slightly rounded. Anal fin with 320–345 (median 338) rays. Unbranched 22–33 anal–fin rays anteriorly. Anal–fin origin at vertical of anterior portion of opercle. Precaudal vertebrae 19 (Tab. 5). Displaced hemal spines 12 (n = 1). Sexual dimorphism unknown. 

Coloration in alcohol. Ground color of dorsal and lateral surfaces of head and body light brown to pale yellow (Figs. 26–29). Head with scattered large dark brown blotches of about eye; snout mostly dark, ventral margin less pigmented. Dorsum of body dark, presenting darker irregular marks laterally displaced not forming saddles. Presence of large dark blotches over the midlateral surface of body running from humeral region to a vertical of the end of anal fin; blotches sometimes coalescent forming an irregular longitudinal stripe. Lateral line clearer forming an inconspicuous light longitudinal stripe. Two pairs of whitish stripes running on the lateral surface of body, one over and another below the midlateral region presenting the dark blotches. Lateroventral region brownish with darker rounded or vermiculous blotches over pterygiophores region. Anal fin mostly clear or hyaline, with scattered chromatophores, these forming round blotches on the proximal and posterior regions. Pectoral fin clear with darkish irregular bars. Caudal appendage light brown with scattered darker blotches. 

FIGURE 28| Paratype of Rhamphichthys heleios, juvenile, MCP 45545, 133 mm LEA, ilha do Martelo, Tefé, Amazonas, Brazil. Picture of the right side (figure horizontally inverted).

FIGURE 29| Detail of the head of paratype of Rhamphichthys heleios, MCP 45545, 133 mm LEA, ilha do Martelo, Tefé, Amazonas, Brazil. Picture of the right side (figure horizontally inverted).

Geographical distribution. Rhamphichthys heleios is known from the Solimões and Amazon Rivers in Brazil upstream of the mouth of the Madeira River (Fig. 30; Tab. 1). It is also known from a single locality in the Guaporé River in Brazil. It inhabits mostly lakes in the floodplain of large rivers. 

FIGURE 30| Distribution of Rhamphichthys heleios based on examined museum specimens. Red dot represents the type-locality. 

Material examined. Amazonas lowlands: INPA 42309, holotype, 375 mm LEA, Brazil, Amazonas, Iranduba, confluence of rio Amazonas and Solimões at Costa do Catalão, 5 Feb 1998, C. Cox Fernandes. INPA 17683, 1, paratype, 270 mm LEA, Brazil, Amazonas, Iranduba, ilha da Marchantaria, 19 Nov 1998, C. Cox Fernandes. INPA 18321, 1, paratype, 370 mm LEA, Brazil, Amazonas, Alvarães, rio Japurá at comunidade Caborini, 24 Feb 2000, W. G. R. Crampton. INPA 18323, 1, paratype, 530 mm LEA, Brazil, Amazonas, Alvarães, rio Japurá mouth of Lago Caxinguba at Reserva Mamirauá, 3 Feb 1999. INPA 18331, 1, paratype, 330 mm LEA, Brazil, Amazonas, rio Japurá at paraná Maiana, W. R. G. Crampton. INPA 18332, 1, paratype, 250 mm LEA, Brazil, Amazonas, Alvarães, rio Solimões at Vila Alencar at reserva Mamirauá, 9 Jul 2000, W. G. R. Crampton. INPA 27611, 1, paratype, 235 mm SL, Brazil, Amazonas, Manaus, rio Solimões at paraná do Xiborena, 12 Mar 1998, C. Cox Fernandes. ANSP 195254, 1, collected with holotype; MZUSP 115347, 1, 450 mm LEA, collected with holotype. INPA 42308, 4 (4 specimens measured in Tab. 7, 333–400 mm LEA, 1 cs), paratype, 303–400 m LEA, collected with the holotype. MCP 45545, 1, 133 mm LEA, Brazil, Amazonas, Tefé, ilha do Martelo, 03º46’49”S 64º59’29”W. Guaporé-Itenez: INPA 42306, 1 (1 specimen measure in Tab. 7, 367 mm LEA), Brazil, Rondônia, Guarajá-Mirim, rio Mamoré downstream Surpresa, 11º43’S 65º05’W, 24 Sep 1985, G. M. Santos. 

(Fig. 31–34; Tab. 8) 

Rhamphichthys lineatus Castelnau, 1855:87 (original description, type-locality: Lake of Ucayali River, Peru). —Mago-Leccia, 1994:42 (listed). —Triques, 1999:6 (material examined). —Ferraris, 2003:496 (listed). —Crampton, Albert, 2006:672 (EOD description). —Ortega et al., 2011:41 (listed). —de Santana, Crampton, 2011:1155 (material examined). —Carvalho, Albert, 2015:40 (Comparative material examined). —Ferraris et al., 2017:28 (listed). —Giora, Carvalho, 2018:1060, fig. 2 (accessory electric organ anatomy). —Tagliacollo et al., 2016:29, fig. 5 (phylogenetic relationships). —Meza-Vargas et al., 2021:21 (listed). —Janzen et al., 2022: tab. 1 (barcode library). 

Iracema sp. C. Albert, 2001:117 (Listed). 

FIGURE 31| Holotype of Rhamphichthys lineatus, MNHN 3982, 530 mm LEA, lake near Río Ucayali, Peru.

FIGURE 32| Detail of the head of holotype of Rhamphichthys lineatus, MNHN 3982, lake near Río Ucayali, Peru.

Diagnosis. Rhamphichthys lineatus differs from congeners, except R. heleios, by the absence of clearly marked saddles, vs. presence of sickle shaped or intercalated saddles. It differs from R. heleios by the absence of rounded dark lateral blotches over the lateral line region these sometimes coalescent forming a longitudinal stripe. 

Description. Morphometrics and meristic given in Tab. 8. Adult body size moderate to large compared with other congeners, maximum size 530 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 about midbody, tapering posterior to this portion. Caudal appendage short, rarely intact. 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 400 mm LEA. Urogenital papilla large in adults. Posterior gas bladder absent. Caudal appendage laterally compressed, its depth about three times its width. 

TABLE 8 | Morphometric and meristic data for Rhamphichthys lineatus. H = holotype, SD = standard deviation, n = number of specimens.