Rhamphichthys Müller & Troschel, 1848

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 : 6-7

Rhamphichthys Müller & Troschel, 1848

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 pirákysé (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 a sa 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).

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 Rhamphichthy s (G1, G2, and G3) and shows statistical significance of species in different groups Rhamphichthys ( Tab. S3; Wilks’ λ: 0.1061; P <0.001; F 18,410.6 = 27.61).

Figures

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

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).