Rhamphichthys heleios Carvalho & Albert, 2015

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 : 35-39

Rhamphichthys heleios Carvalho & Albert, 2015

( 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).

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.

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.

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.

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.

Figures

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.

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).

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