Cetopsis arcana, Vari & Ferraris Jr & de Pinna, 2005

Vari, Richard P., Ferraris Jr, Carl J. & de Pinna, Mário C. C., 2005, The Neotropical whale catfishes (Siluriformes: Cetopsidae: Cetopsinae), a revisionary study, Neotropical Ichthyology 3 (2), pp. 127-238 : 150-153

Cetopsis amphiloxa ( Eigenmann, 1914) Figs. 11 , 12 , Tables 9 -15

Hemicetopsis amphiloxus Eigenmann , in Eigenmann et al., 1914: 14 [type locality: Creek near San Lorenzo, (río) Patia basin; also río San Juan at mouth of río Munguido and Quibdo].– Apolinar-Maria, 1914: 279 [listing of new species described in Eigenmann et al., 1914].– Eigenmann, 1920a: 13 [distribution]; 1920b: 10 [distribution].– Henn, 1928: 81 [type depository].– Gosline, 1945: 54 [listing].– Ibarra & Stewart, 1987: 44 [type depository].– Burgess, 1989: 292 [listing].–Mojica-C., 1999: 565 [in part, citation of species from Colombia, río Patia, río San Juan; not record of species from río Baudó].

Hemicetopsis amphiloxa .– Eigenmann, 1923: 57, pl. 3, fig. 2 [redescription; Colombia, (río) Patia, (río) San Juan, and (río) Atrato basins].– Fowler, 1942: 131 [literature compilation].

Pseudocetopsis amphiloxa .– Schultz, 1944: 252 [in key].– Dahl, 1960b: 454 [comparisons with Pseudocetopsis baudoensis ].– Barriga, 1991: 56 [ Ecuador, Piso Tropical Oriental]; 1994b: 77, 80, 84 [ Ecuador: río Mira, río Mataje, río Santiago; not cited material that originated in río Esmeraldas].–Evers & Seidel, 2002: 741 [listing].–Vari & Ferraris, 2003: 258 [in check list; distribution].

Pseudocetopsis cf. amphiloxa .– Roman-Valencia, 1990: 205 [ Colombia, Choco; occurrence in ríos and quebradas; common name].

Diagnosis. Cetopsis amphiloxa can be distinguished from all of its congeners by the combination of the presence of an eye, the conical teeth on the vomer and dentary, the rounded posterior nares that is distinctly separated from the contralateral nares by a distance greater than the width of posterior nares, the absence of a dark humeral spot, the presence of very small rather than eye-sized or larger spots on the lateral and dorsal surfaces of the body, the lack of a concentration of dark pigmentation at the base of the dorsal fin, the lack of a band of dark pigmentation along the distal portion of the anal fin, the possession of 29 to 33 total anal-fin rays, 23 to 28 branched anal-fin rays, 10 to 12 precaudal vertebrae, 31 to 33 caudal vertebrae, 41 to 43 total vertebrae, 8, or rarely, 9 pectoral-fin rays, and the lack of a concentration of dark pigmentation basally on the dorsal fin.

Description. Body slender, slightly laterally compressed anteriorly, becoming increasingly compressed posteriorly. Body depth at dorsal-fin origin approximately 0.21-0.23 of SL and approximately equal to HL. Lateral line on body complete, unbranched, and midlateral; extending from vertical through pectoral-fin base onto hypural plate and terminating prior to posterior margin of hypural plate. Dorsal profile of body slightly convex from nape to dorsal-fin origin; straight from dorsal-fin origin to caudal-fin base. Ventral profile of body convex along abdomen, approximately straight, but posterodorsally slanted along base of anal fin. Caudal-peduncle depth approximately 1.25 times caudal-peduncle length.

Head triangular in lateral view and broadly rounded anteriorly. Dorsal profile of head nearly straight from tip of snout to posterior of nape. Ventral profile of head ranging from slightly convex to nearly straight. Profile of snout in dorsal view broadly rounded. Portion of head posterior of nares with lateral profiles diverging posteriorly. Dorsal surface of posterior portion of head without enlarged jaw musculature externally apparent.

Opercular membrane attaching to isthmus until point slightly anterior of vertical through pectoral-fin insertion. Opercular opening relatively wide; extending ventral of pectoral-fin insertion by distance approximately equal to distance from tip of snout to middle of eye and extending dorsal of pectoral-fin insertion by distance approximately equal to snout length.

Eye situated on lateral surface of head; located entirely dorsal to horizontal extending through pectoral-fin insertion; eye visible in dorsal view, but not in ventral view, of head. Middle of orbit at slightly less than anterior one-third of HL. Eye diameter approximately one-half of snout length. Interorbital width approximately equal to distance from tip of snout to posterior margin of orbit. Anterior narial opening circular, surrounded by short, anteriorly-directed, tubular rim of skin. Opening of anterior nares located at horizontal extending through tip of snout and slightly dorsal to horizontal running through maxillary-barbel origin. Distance between anterior nares greater than distance from anterior to posterior nares, and approximately equal to distance from tip of snout to middle of eye. Posterior narial opening located near dorsal profile of head; opening rounded, with anterior one-half of aperture bordered by flap of skin. Distance between posterior nares slightly less than distance between anterior nares.

Mouth inferior; its width approximately 0.25 to 0.50 of HL. Margin of lower jaw broadly rounded, its posterior limit falling just short of vertical through middle of eye. Premaxillary tooth patch elongate and crescentic, continuous across midline; anterior margin convex, posterior margin concave. Premaxillary teeth of moderate size, conical, and sharply-pointed, with teeth arranged in two rows medially and reduced to one row on lateral most portion of tooth patch. Teeth of inner most premaxillary tooth row notably larger than those of outer row. Vomerine teeth arranged in one anteriorly-convex row. Vomerine teeth bluntly conical and approximately equal in size to largest premaxillary teeth. Dentary with single row of sharply-pointed, conical teeth; teeth largest medially, with symphyseal teeth somewhat larger than largest premaxillary teeth.

Maxillary barbel slender, its length greater than distance from tip of snout to posterior margin of orbit and nearly equal to one-half of HL; barbel origin located ventral of middle of orbit. Mental barbels approximately equal in size and length to maxillary barbel and to each other. Medial mental-barbel origin located along vertical through posterior margin of orbit. Lateral mental-barbel origin located slightly posterior of vertical through posterior margin of orbit. Tips of adpressed mental barbels falling short of posterior margin of opercle.

Dorsal fin moderately large overall with length of base of dorsal fin approximately 0.32-0.34 of HL. Longest dorsal-fin ray equal in length to postorbital portion of head. Dorsal-fin spinelet absent. First dorsal-fin ray not spinous, and with distal filament absent in limited available sample of specimens. Distal margin of dorsal fin nearly straight, with first ray longest. Dorsal-fin origin located at approximately anterior one-third of SL and along vertical through distal one-third of adpressed pectoral fin. Tip of adpressed dorsal fin reaching to vertical through tip of adpressed pelvic fin. Posterior most dorsal-fin ray without posterior, membranous attachment to body.

Caudal fin shallowly-forked, symmetrical; tips of lobes slightly rounded. Length of longest caudal-fin ray 1.5 times length of middle fin rays.

Base of anal fin long, approximately 0.4 of SL. Anal-fin origin located slightly posterior of middle of SL. Anal-fin margin nearly straight, with limited available population sample not demonstrating sexual dimorphism of distal margin of fin present in many members of Cetopsinae . Posterior most unbranched anal-fin ray longest, with length of subsequent rays gradually decreasing. Posterior most anal-fin ray with posterior, membranous attachment to body for basal one-half of its length.

Pelvic fin moderate, distal margin convex, first and second branched rays longest. Pelvic fin completely in advance of middle of SL, with origin of fin located along vertical through posterior one-half of base of dorsal fin. Tip of adpressed pelvic fin reaching to vent. Medial most pelvic-fin ray with membranous attachment to body for basal two-thirds of its length.

Pectoral-fin length approximately three-quarters of HL. Pectoral-fin margin convex, with second and third branched rays longest. First pectoral-fin ray not spinous and with limited available sample lacking distal filament present in some members of Cetopsinae .

Coloration in alcohol. Scattered, dark pigmentation consisting primarily of very small spots distributed over dorsal and lateral portions of head and body. Abdomen and underside of head virtually without dark pigmentation. Skin overlying lower jaw with some scattered, dark pigmentation, but with pigmentation less intense than that of upper jaw.

Dorsal, anal, and caudal fins with scattered, dark pigmentation over lateral surfaces except along distal margins of fins. Pelvic fin with only few, scattered, dark chromatophores. Pectoral fin with scattered, dark pigmentation on basal onehalf of dorsal surface of anterior fin rays.

Barbels light overall and with scattered, dark chromatophores.

Sexual dimorphism. The sexual dimorphism in the dorsal, pectoral, and anal fins present in many members of the Cetopsinae was not apparent in the limited number of examined specimens of Cetopsis amphiloxa .

Distribution. Cetopsis amphiloxa is known from the northern portions of the río San Juan basin and southern sections of the adjoining río Atrato basin, both in western Colombia, the río Patia basin of southwestern Colombia, and the rivers of northwestern Ecuador ( Fig. 12 ).

Common name. Colombia, río Atrato: “Tariba,” “Baboso” ( Roman-Valencia, 1990: 205).

Remarks. In his summary treatment of the freshwater fishes of northwestern Ecuador, Barriga (1994b: 77, 80, 84) reported Pseudocetopsis amphiloxa from the río Esmeraldas, río Mira, río Mataje, and río Santiago. All samples of the Cetopsinae from the río Esmeraldas basin examined during this study proved to be Paracetopsis esmeraldas and we consequently tentatively consider the Barriga (1994b) reference of Pseudocetopsis amphiloxa from that river system to refer to Paracetopsis esmeraldas . Two of the three specimens of the Cetopsinae examined during this study (MEPN 1525, MEPN 1526) that originated in the río Santiago, the river system to the north of the río Esmeraldas were Cetopsis amphiloxa and represent the southern most records for that species. The third examined specimen of the Cetopsinae from that river basin (CAS 162438) is Paracetopsis esmeraldas and that sample represents the northern record for this species and the only examined specimen of that species originating from outside the río Esmeraldas basin. The occurrence of both Cetopsis amphiloxa and Paracetopsis esmeraldas at relatively closely situated localities in the río Santiago makes that basin the only river system on the western slopes of the Andes where two species of the Cetopsinae apparently live in sympatry. Although we were unable to examine the specimens that served as the basis for Barriga’s (1994b) citation of Pseudocetopsis amphiloxa from the río Mira and río Mataje, both of those river systems lie within the known range of Cetopsis amphiloxa and these records are tentatively assumed to be based on specimens of that species.

Roman-Valencia (1990: 205) reported Pseudocetopsis cf. amphiloxa from the central portions of the río Atrato basin, an area somewhat to the north of the most northerly locality for the specimens of Cetopsis amphiloxa examined in this study. We tentatively consider Roman-Valencia’s report to be a record of Cetopsis amphiloxa in so far as the only other member of the Cetopsinae known to occur in the río Atrato basin is Cetopsis fimbriata . Cetopsis fimbriata is, however, apparently endemic to the río Nercua, a tributary of the río Truando that empties into the río Atrato further to the north than the region sampled by Roman-Valencia (1990).

Cetopsis amphiloxa has the most extensive distribution of any Trans-Andean member of the Cetopsinae , being known from samples that were collected in the area ranging from the río Cayapas basin of northwestern Ecuador to the upper portions of the río Atrato system in northwestern Colombia, albeit with a major gap in the known distribution of the species between the río Patia and río San Juan basins in western Colombia. The river systems between the río Patia and río San Juan systems are poorly sampled ichthyologically and, with one exception, the limited available samples of C. amphiloxa (eight specimens from eight localities) fail to demonstrate any notable differences across that region. The only exception is the single examined specimen from Quibdo in the upper río Atrato basin (CAS 77028, paratype of Hemicetopsis amphiloxus ) that has nine pectoral-fin rays contrary to the eight pectoral-fin rays that are present in all other examined specimens of C. amphiloxa . The examination of additional populations from across the apparent range of C. amphiloxa is necessary to determine whether the variation in the number of pectoral-fin rays within what is herein considered to be that species is perhaps indicative of the presence of more than one species within that material or simply represents intraspecific variation.

Material examined. 8 specimens (22-188 mm SL). Colombia. Choco: río Condoto (approximately 5°06’N, 76°42’W), BMNH 1914.5.18.49, 1 (64). Río San Juan, at Cabeceras (4°18’N, 77°09’W), NRM 10679, 1 (65). Río San Juan at mouth of río Munguido (5°43’N, 76°42’W), CAS 77027, 1 (79, paratype of Hemicetopsis amphiloxus ). Río Patía basin, creek near San Lorenzo (approximately 2°13’N, 78°40’W), FMNH 56519, 1 (65, holotype of Hemicetopsis amphiloxus ). Quibdo, town at junction of río Quito and río Atrato (5 o 42’N, 76 o 38’W), CAS 77028, 1 (42, paratype of Hemicetopsis amphiloxus ; formerly IU 13109). Raspadura (5 o 16’N, 76 o 42’W), FMNH 55170, 1 (22). Ecuador. Esmeraldas: Estero los Indios, Vargas Torres (latter locality at 1°14’N, 79°01’W), MEPN 1525, 1 (45). Estero Sabalera, 600 m from Campamento del MAG, La Chiquita, along highway to Ricaurte, tributary to río Bogotá, río Santiago basin (1°13’47"N, 78°45’19’W), MEPN 1526, 1 (77; specimen cleared and stained).

Figures

Fig. 11. Cetopsis amphiloxa, holotype of Hemicetopsis amphiloxus, FMNH 56519, 65 mm SL; Colombia, Choco, río Patía basin, creek near San Lorenzo (approximately 2°13’N, 78°40’W).

Fig. 12. Map of central and northern SouthAmerica showing geographic distribution of Cetopsis amphiloxa (1 = holotype locality of Hemicetopsis amphiloxus), Cetopsis arcana (2 = holotype locality), Cetopsis baudoensis (3 = holotype locality of Pseudocetopsis baudoênsis), Cetopsis caiapo (4 = holotype locality), and Cetopsis candiru (type locality inexact = rivers of Equatorial Brazil) (some symbols represent more that one locality and/or lot of specimens).