Rhamphichthys hahni (Meiken, 1937)

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 : 28-33

Rhamphichthys hahni (Meiken, 1937)

( 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).

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 gasbladder, 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.

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 analfin 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.

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).

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 .

Figures

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

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

FIGURE 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.

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 ofRhamphichthys hahni, FMNH 108066, Río Paraguay at Estância Voluntad in Puerto Voluntad, Alto Paraguay, Paraguay.

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