Rhamphichthys lineatus Castelnau, 1855

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 : 39-41

Rhamphichthys lineatus Castelnau, 1855

( 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).

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.

Body entirely covered by scales in adults, anterior and dorsal areas with smaller scales and naked in juveniles. Scales cycloid, elongate in shape posteriorly, length twice as depth. Lateral line complete with ossified tubules, anterior portion of presenting ventral rami. Pectoral fin with 17–19 (mode 18) rays, dorsal rays longer than ventral rays, distal fin margin slightly rounded. Anal fin with 341–381 (median 355) rays. Unbranched anal–fin rays 14–27. Anal–fin origin at vertical of anterior portion of opercle. Precaudal vertebrae 18–19. Displaced hemal spines 10–11 (n = 2). Sexual dimorphism unknown.

Coloration in alcohol. Ground color of dorsal and lateral surfaces of head and body light brown to pale yellow ( Figs. 31–34 ). Head with scattered dark chromatophores mostly in dorsal region, ventral region less pigmented. Dorsum of body darker lacking conspicuously formed saddles. Lateral region with scattered chromatophores, clear areas forming white stripes in the lateral line and one or two above the line of the anal fin pterygiophores. Faint dark bands sometimes present in the body. Anal fin mostly clear sometimes presenting dark irregular vermiculous areas, especially in juveniles ( Fig. 34 ). Pectoral fin almost entirely clear or hyaline, sometimes with dark pigments forming irregular bars.

Geographical distribution. Rhamphichthys lineatus is known only from the Ucayali, Solimões, and Amazon rivers in Peru and Brazil, apparently not found in the Amazon River downstream mouth of Tapajós River in Brazil ( Fig. 35 ). It is typically found in the main channel of these rivers or tributary lakes.

Electric organ discharge. The electric organ discharge of Rhamphichthys lineatus generates short-pulse-type EOD with a tetraphasic discharge varying in duration 1.5–2 ms mid-high range rates of 40–100 Hz (1.8 kHz) with little day night variation in the EOD rates (Crampton, Albert, 2006).

Material examined. Amazonas Lowlands: ANSP 189537 , 1 (1 specimen measured in Tab. 8, 300 mm LEA), Brazil, Amazonas, rio Amazonas upstream Itacoatiara , 03º15’33”S 58º58’42”W . ANSP 189532 , 1 (1 specimen measured in Tab. 8, 310 mm LEA), Brazil, Amazonas, rio Solimões below mouth of rio Purus , 03º38’41”S 61º27’48”W . CAS 36688 , 1 , Peru, Loreto, Caño Chancho near Pebas , 03º20’S 71º51’W . FMNH 114685, 4 in part (1 cs), Brazil, Amazonas, rio Amazonas between rio Madeira and paraná do Serpa , 03º16’36”S 58º35’09”W . INPA 4725 , 1 , Brazil, Amazonas, Lago do Castanho, Janauacá , 03º49’38”S 60º21’57”W . INPA 9381 , 1 , Brazil, Amazonas, Iranduba, rio Solimões Lago Comprido at ilha da Marchantaria , 03º14’S 59º56’W . INPA 15827 , 3 (1 cs), Brazil, Amazonas, Alvarães, rio Japurá paraná Maiana at reserva do Mamirauá , 02º16’S 66º23’W . INPA 27606 , 1 (1 specimen measured in Tab. 8, 515 mm LEA), Brazil, Amazonas, Manaus, paraná do Xiborena at ilha do Catalão , 03º12’S 59º36’W . INPA 27607 , 1 (1 specimens measured in Tab. 8, 430 mm LEA), Brazil, Amazonas, Manaus, Careiro da Várzea , Paraná do Rei , 03º09’S 59º36’W . INPA 27608 , 2 (2 specimens measured in Tab. 8, 500 mm LEA), Brazil, Amazonas, Manaus, paraná do Curari , 03º14’S 59º56’W . MCP 33456 , 1 , Brazil, Amazonas, Alvarães, praia Caborini at confluence of rio Japurá and rio Solimões , 03º07’08”S 64º47’18”W . MCP 33457 , 3 (1 cs), paraná Maiana at lago Mamirauá system . MNHN 3982 , holotype of Rhamphichthys lineatus , Peru, lake near Río Ucayali . MUSM 6639 , 1 , Peru, Loreto, market at Iquitos , 03º42’S 73º14’W . MZUSP 102703 , 1 , Brazil, Amazonas, rio Solimões downstream mouth of rio Purus , 03º36’16”S 61º21’12”W . UF 116566 , 1 , Peru, Loreto, Maynas, Río Nanay . USNM 320022 , 2 , Brazil, Amazonas, creek connecting rio Solimões and rio Tefé with a black water lake about 15 miles E of Coari.

Figures

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.

FIGURE 33 | Rhamphichthys lineatus, UF 116566, 390 mm LEA, Río Nanay, Loreto, Peru.

FIGURE 34 | Rhamphichthys lineatus, ANSP 189537, 320 mm LEA, rio Amazonas upstream Itacoatiara, Amazonas, Brazil.

FIGURE 35 | Distribution of Rhamphichthys lineatus based on examined museum specimens. Red dot represents the approximate type-locality.