Cetopsis orinoco ( Schultz, 1944 )

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 : 181-183

Cetopsis orinoco ( Schultz, 1944)

Figs. 30-33 , Tables 9 -15

Pseudocetopsis plumbeus orinoco Schultz, 1944: 253 , pl. 5, fig. a [type locality: río Torbes, 1 km. above Táriba, Orinoco system, Venezuela].– Gosline, 1945: 54 [in listing of species in Cetopsidae ].– Mago-Leccia, 1970: 82 [ Venezuela; common name].– Fernández-Yépez, 1972b: 14, figs on pages 11 and 14 [ Venezuela, río Yaracuy basin; habitat and common name].–Ferraris & Vari, 1992: 16 [holotype and paratype depository].–Evers & Seidel, 2002: 741 [listing].

Pseudocetopsis plumbeus [not of Steindachner, 1882].– Baskin et al., 1980: 184 [ Venezuela, río Portuguesa basin, piedmont and high Llanos; feeding on terrestrial insects].– Machado-Allison & Moreno, 1993: 86 [ Venezuela, río Orituco basin].– Machado-Allison et al., 1993: 131 [ Venezuela, Llanos].–Mojica-C., 1999: 565 [in part, citations of species from Colombia, río Orinoco, río Cusiana, río Meta, río Arauca].

Hemicetopsis plumbeus orinoco .– Burgess, 1989: 292 [literature compilation].

Pseudocetopsis orinoco .– Taphorn et al., 1997: 85 [ Venezuela].–Vari & Ferraris, 2003: 258 [in check list; distribution, common name].

Diagnosis. Cetopsis orinoco 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 the posterior nares, the presence of a dark humeral spot, the lack of a pattern of dark pigmentation on the pectoral and pelvic fins other than for a thin, clear margin, the presence of dark pigmentation on the caudal fin, particularly on the distal portions of the fin, and the possession of 30 to 35 caudal vertebrae, 43 to 46 total vertebrae, 23 to 30 total anal-fin rays, and 19 to 24 branched anal-fin rays.

Description. Body typically moderately-elongate although specimens with distended abdomens appear somewhat deeper bodied. Body slightly-compressed laterally anteriorly and becoming progressively distinctly-compressed posteriorly. Body depth at dorsal-fin origin approximately 0.25-0.27 of SL and approximately equal to HL in specimens without distended abdomens. Specimens with distended abdomens with body depth approximately 0.32-0.34 of SL and somewhat greater than HL. Lateral line on body complete, unbranched, and midlateral; extending from vertical through pectoral-fin base to hypural plate with short, dorsal bend on hypural plate. Dorsal profile of body slightly convex from nape to dorsal-fin origin and straight or nearly straight from dorsal-fin origin to caudal-fin base. Ventral profile of body convex along abdomen, more so in specimens with distended abdomens, approximately straight, but posterodorsally-slanted, along base of anal fin. Caudal-peduncle depth slightly greater than caudal-peduncle length.

Head in profile acutely triangular overall with bluntlyrounded snout. Dorsal profile of head gently convex from tip of snout to nape. Ventral profile of head slightly convex. Margin of snout in dorsal view rounded. Postorbital margins of head running nearly in parallel from dorsal view. Enlarged jaw musculature slightly evident externally on dorsal surface of postorbital portion of head. Canals and pores associated with laterosensory system on head apparent in some smaller and less intensely pigmented specimens, but canal system masked by pigmentation in larger, more darkly pigmented individuals.

Opercular membrane attaching to isthmus only to region anterior to vertical through pectoral-fin insertion. Opercular opening moderate; extending ventral of pectoral-fin insertion by distance equal to distance from tip of snout to posterior margin of orbit and extending dorsal of pectoral-fin insertion by distance 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 located at approximately anterior one-fourth of HL. Eye diameter slightly less than one-half of snout length. Interorbital width slightly greater than 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 along horizontal extending through maxillary-barbel origin, but ventral of horizontal extending through tip of snout. Distance between anterior nares approximately equal to snout length. Posterior narial opening located on dorsal surface of head, situated along vertical through anterior margin of orbit; narial opening nearly round.Anterior two-thirds of posterior narial opening surrounded by flap of skin with anterior portion of flap highest.

Mouth inferior; its width approximately one-half of HL. Margin of lower jaw gently rounded, its posterior limit reaching to vertical through posterior margin of orbit. Premaxillary tooth patch in form of gently-arched band continuous across midline with anterior margin convex and posterior margin concave and running in parallel to anterior margin. Teeth on premaxilla small, conical, and sharply-pointed, with teeth arranged in three regular rows across entire tooth patch. Vomerine teeth arranged in single, irregular row continuous across midline. Vomerine teeth stout, conical, and much larger than teeth on premaxilla. Dentary teeth comparable in shape and size to vomerine teeth and much larger than premaxillary teeth; with two rows in series medially that taper to one row laterally.

Maxillary barbel slender, its length greater than distance from tip of snout to posterior of orbit, and approximately onethird of HL; barbel origin located ventral to anterior margin of orbit. Mental barbels approximately equal in length to each other, but shorter than maxillary barbel. Medial mental-barbel origin located slightly posterior to vertical through rictus. Lateral mental-barbel origin situated slightly anterior of vertical through middle of adpressed medial mental barbel. Tips of adpressed mental barbels falling far short of posterior margin of opercle.

Dorsal fin moderately large overall with length of dorsalfin base approximately 0.31-0.33 of HL. Longest branched dorsal-fin ray, excluding distal filament on first ray, equal in length to two-thirds to three-fourths of HL. Dorsal-fin spinelet absent. First dorsal-fin ray not spinous but with distal filament present in both sexes; filament barely developed in females and immature males and proportionally longer in mature males. Distal margin of dorsal fin straight, with first ray longest. Dorsal-fin origin located at approximately anterior 0.27-0.29 of SL and along vertical extending through middle of adpressed pectoral fin. Tip of adpressed dorsal fin, excluding distal filament on first ray, falling slightly short of 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 bluntly pointed. Length of longest caudal-fin ray approximately 1.5 times length of middle fin rays.

Base of anal fin moderately long. Anal-fin origin located well posterior of middle of SL, and slightly anterior of vertical through middle of TL. Anal-fin margin straight or slightly concave in females and immature males, with posterior most unbranched anal-fin ray longest and subsequent fin rays becoming gradually shorter. Anal-fin margin very slightly convex in mature males. Posterior most anal-fin ray without posterior, membranous attachment to body.

Pelvic fin moderate; distal margin nearly straight, with first branched ray longest. Pelvic-fin insertion located anterior to middle of SL and along vertical through posterior terminus of base of dorsal fin. Tip of adpressed pelvic fin extending beyond middle of SL and reaching to, or falling slightly short of, anterior limit of vent. Medial most pelvic-fin ray with membranous attachment to body along basal two-thirds of its length.

Pectoral-fin length approximately two-thirds of HL. Pectoral-fin margin straight or slightly convex with first ray longest in females and very slightly concave laterally in males. First pectoral-fin ray not spinous, with first ray longest and prolonged into short filament in some females and into distinct filament in mature males.

Coloration in alcohol. Overall coloration of head and body rather variable ( Figs. 30-32 ). Head uniformly darkly pigmented dorsally and often laterally, with darker pigmentation extending ventrally to horizontal running through origin of maxillary barbel in most specimens. Lateral surfaces of head ventral to that level unpigmented or only partially darkly pigmented, with distinct boundary between pigmented and unpigmented regions. Dark pigmentation extending somewhat more ventrally on posterior portion of head in darkly pigmented individuals ( Fig. 32 ). Ventral surface of head unpigmented. Snout darkly pigmented to tip. Margin of upper lip pale. Body pigmentation variable within and among samples from different portions of species distributional range ( Figs. 30-32 ). Body generally darker dorsally, becoming progressively paler ventrally. Ventrolateral and ventral surfaces of abdomen usually pale ( Figs. 30-31 ), but sometimes with ventrolateral area irregularly pigmented in region above pectoral-fin insertion. Lateral surface of body in many specimens with dark pigmentation formed of very small chromatophores and larger spots that often coalesce into dark spots of various sizes and shapes ( Figs. 31 , 32 ). Resultant spots range from barely evident to prominent and cover large proportion of lateral surface of body ( Fig. 32 ). Diffuse, dark, humeral spot present on lateral surface of body immediately posterodorsal to pectoral-fin insertion. Spot larger than size of eye and apparent to some degree in all specimens that retain dark pigmentation, but somewhat hidden by overall darker body coloration in some individuals ( Fig. 32 ).

Dorsal fin with scattered, dark pigmentation distributed over entire surface except along first unbranched ray and distal margin of fin. Dorsal fin pigmentation distinctly more intense basally and forming dark basal spot. Caudal fin variably darkly pigmented throughout other than for narrow, pale, distal margin, and less heavily pigmented region at the base of each caudal-fin lobe; lightly pigmented areas on caudal fin more obvious in overall more darkly pigmented individuals ( Figs. 31 , 32 ). Pectoral fin with scattered, dark pigmentation basally and occasionally on dorsal surface of interradial membranes of lateral most fin rays. Pelvic fin pale or with some scattered, dark pigmentation basally. Anal fin with scattered, dark pigmentation basally; fin typically pale distally but with irregular dark pigmentation along margin of fin in at least one adult male ( Fig. 31 ).

Barbels with scattered, dark pigmentation on basal portions and otherwise pale.

Sexual dimorphism. The presumed males of Cetopsis orinoco have the filaments on the first rays of the dorsal and pectoral fins proportionally more elongate than those occurring in females and immature males of the species. Mature males also have a convex margin to the anal fin rather than the straight margin of that fin found in females and immature males.

Distribution. Cetopsis orinoco occurs in the rivers of the eastern slope of the piedmont of the Cordillera Oriental and the southeastern slopes of the piedmont of the Cordillera of Merida in the río Orinoco basin of Colombia and Venezuela and in the río Aroa and río Yaracuy basins of the Caribbean Sea versant of northern Venezuela ( Fig. 33 ).

Ecology. Schultz (1944: 255), evidently referring to the holotype, reported that the species was captured in “a mountain stream in very swiftly flowing water among gravel and rubble.” Fernández-Yépez (1972b: 32) reported that the species (cited therein as Pseudocetopsis plumbeus orinoco ) inhabits the middle portions of the water column of high-velocity streams during the night and hides among submerged branches and other obstructions in the river channel during the day. Many of the other lots of Cetopsis orinoco examined in this study also appear to have been captured in piedmont streams that presumably also have rapidly-flowing waters. Some of the examined population samples of the species originated, however, in the apparently more lentic river systems that are characteristic of the upper Llanos the río Orinoco basin.

Figures

Fig. 30. Cetopsis orinoco, INHS 60121, 94 mm SL; Venezuela,Yaracuy, río Guarataro (10°35’N, 68°44’W).

Fig. 31. Cetopsis orinoco, INHS 60096, mature male, 96 mm SL; Venezuela,Yaracuy, río Tupe (10°31’N, 68°53’W).

Fig. 32. Cetopsis orinoco, INHS 27880, 81.5 mm SL; Venezuela, Barinas, Caño Curito (7°22’N, 71°05’W).

Fig. 33. Map of central and northern SouthAmerica showing geographic distribution of Cetopsis orinoco (1 = holotype locality of Pseudocetopsis plumbeus orinoco), Cetopsis othonops (2 = holotype locality of Hemicetopsis othonops), Cetopsis parma (3 = holotype locality), Cetopsis pearsoni (4 = holotype locality), and Cetopsis plumbea (5 = lectotype locality of Cetopsis plumbeus) (some symbols represent more that one locality and/or lot of specimens).