Denticetopsis praecox (Ferraris & Brown, 1991)

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 : 213-215

Denticetopsis praecox (Ferraris & Brown, 1991) Figs. 46 , 50 , Tables 16-22

Pseudocetopsis praecox Ferraris & Brown, 1991: 162 , fig. 1 [type locality: río Mawarinuma of the río Baria drainage, Territorio Federal Amazonas, southern Venezuela, (0°55’N, 66°10’W), elevation 120 m].– Ferraris & Vari, 1992: 16 [paratype depository].– Taphorn et al., 1997: 85 [ Venezuela].– Evers & Seidel, 2002: 741 [listing].– Vari & Ferraris, 2003: 259 [in check list; distribution].

Diagnosis. Denticetopsis praecox is distinguished from D. royeroi and D. sauli by the combination of the lack of elongate symphyseal teeth on the dentary, the lateral line extending posteriorly on the body beyond the abdomen onto at least the caudal peduncle, the presence of dentition on the vomer, a dorsal fin with 5 or 6 segmented rays and with the first ray that is spinous basally, a symmetrical, shallowlyforked caudal fin, and the possession of horizontally-elongate, stellate, dark chromatophores when the chromatophores are expanded. Denticetopsis praecox differs from D. epa in the relative length of the pelvic fin (tip of fin falling just short of the anterior margin of the vent versus reaching to the posterior margin of the vent, respectively) and in the number of premaxillary tooth rows (two rows of teeth versus three rows of teeth on premaxilla in all but the smallest examined specimens, respectively). Denticetopsis praecox differs from D. iwokrama in the number of preanal (14 to 15 versus 17, respectively), caudal (27 to 30 versus 32, respectively), and total vertebrae (38 to 40 versus 43, respectively), and in the pigmentation of the caudal-fin (a distinct, pale region present on distal portions of the middle fin rays versus a distinct, pale region in the distal portions of the middle fin rays absent, respectively). Denticetopsis praecox differs from D. macilenta in the relative position of the eye (located at anterior 0.25 of HL versus at anterior 0.18-0.19 of HL, respectively), the number of irregular rows of teeth on the median portions of the premaxilla (two versus three, respectively), in the profile of the postorbital portion of the head in dorsal view (convex versus approximately straight, respectively), and in the width of the head as a proportion of the length of the head (head width/HL 0.71-0.74 versus 0.77-0.84, respectively). Denticetopsis praecox differs from D. seducta in the pigmentation on the caudal fin (the presence of a distinct, pale region in the distal portions of the middle fin rays present versus the absence of a distinct, pale region in the distal portions of middle fin rays, respectively) and in the number of premaxillary tooth rows (two rows of teeth versus typically three rows in all but smallest examined specimens, respectively).

Description. Body moderately-elongate, slightly laterallycompressed anteriorly and becoming progressively distinctlycompressed posteriorly. Body depth at dorsal-fin origin approximately 0.27-0.28 of SL, and approximately equal to distance from anterior margin of eye to posterior margin of opercle. Lateral line on body complete, unbranched, and midlateral; extending from vertical through pectoral-fin base to onto caudal peduncle but falling short of posterior margin of hypural plate. Dorsal profile of body straight from nape to dorsal-fin origin and straight from dorsal-fin origin to caudalfin base. Ventral profile of body convex along abdomen, approximately straight, but posterodorsally-slanted, along base of anal fin. Caudal-peduncle depth nearly two times caudalpeduncle length.

Head in profile acutely triangular overall with bluntlypointed snout. Dorsal profile of head slightly convex from tip of snout to nape. Ventral profile of head slightly convex. Margin of snout in dorsal view rounded to bluntly triangular. Postorbital margins of head running nearly in parallel from dorsal view. Enlarged jaw musculature evident externally on dorsal surface of postorbital portion of head.

Opercular membrane attaching to isthmus only anterior of vertical through pectoral-fin insertion. Opercular opening moderate; extending ventral of pectoral-fin insertion by distance equal to length of snout plus eye and extending dorsal of pectoral-fin insertion by distance equal to width of eye.

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 approximately anterior one-fourth of HL. Eye diameter approximately 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 and ventral of horizontal extending through tip of snout. Distance between anterior nares approximately equal to distance from tip of snout to middle of eye. Posterior narial opening located on dorsal surface of head, situated along vertical through anterior margin of orbit; narial opening nearly round and completely surrounded by flap of skin of nearly uniform height and with posterior margins of flap in contact.

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 two, regular rows of uniform-sized teeth. Vomerine teeth arranged in single, arched row with small median gap in tooth series. Vomerine teeth stout, conical, and becoming progressively larger laterally, with even smallest teeth in series much larger than teeth on premaxilla. Dentary teeth comparable in shape to, but larger in size than, premaxillary teeth. Dentary dentition consisting of two regular rows medially that taper to one tooth row laterally.

Maxillary barbel slender, its length approximately equal to distance from tip of snout to rear of eye, and approximately one-third of HL; barbel origin located ventral to middle of orbit. Medial mental barbel slightly shorter than lateral mental barbel, with latter approximately equal in length to maxillary barbel. Medial mental-barbel origin located along vertical through rictus. Lateral mental-barbel origin situated slightly posterior of vertical through medial mental-barbel origin. Tips of adpressed mental barbels falling short of posterior margin of opercle.

Dorsal fin moderately large overall with length of dorsalfin base approximately 0.32-0.35 of HL. Length of longest branched dorsal-fin ray equal to approximately one-half of HL. Dorsal-fin spinelet absent. First dorsal-fin ray spinous for basal one-half of length but flexible more distally and without distal filament present in some other species of Cetopsinae . Distal margin of dorsal fin convex, with second branched ray longest. Dorsal-fin origin located at approximately anterior 0.36-0.37 of SL and along vertical extending through middle of adpressed pectoral fin. Tip of adpressed dorsal fin falling short of vertical through vent. 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 distinctly posterior of middle of SL and approximately at middle of TL. Anal-fin margin slightly convex. Membranous attachment present between posterior margin of basal one-half of posterior most anal-fin ray and body.

Pelvic fin moderate; distal margin slightly convex with middle fin rays longest. Pelvic-fin insertion located anterior to middle of SL and posterior of vertical through posterior terminus of base of dorsal fin. Tip of adpressed pelvic fin extending past middle of SL, but falling just short of anterior margin of vent. Medial most pelvic-fin ray with membranous attachment to body along basal one-fourth of its length.

Pectoral-fin length approximately one-half of HL. Pectoral-fin margin slightly convex with middle ray longest. First pectoral-fin ray spinous with smooth margins, short with length approximately one-half of first branched ray.

Coloration in alcohol. Overall coloration of head and body dark, only slightly darker dorsally.Abdomen pale. Specimens with more intense overall pigmentation with dark coloration primarily formed of large, stellate, horizontally-elongate chromatophores when chromatophores expanded. Chromatophores appearing as series of dark specks against lighter background in specimens with contracted chromatophores. Head dark dorsally, with dark coloration continuing as far ventrally as horizontal extending through pectoral-fin insertion. Head pale ventrally except in region of lower lip.

Dorsal fin dark across basal one-half except for pale anterior and posterior most rays; distal one-half of fin pale. Anal fin dusky basally, progressively paler distally. Caudal fin dusky except for pale distal portion of middle fin rays. Pelvic fin pale or with scattered, dark chromatophores on basal region. Pectoral fin with scattered, dark chromatophores basally and becoming progressively paler distally.

Maxillary barbel with dusky, basal pigmentation and pale distally. Mental barbels pale or with scattered, dark pigmentation basally.

Sexual dimorphism. Examined specimens of Denticetopsis praecox lack the sexual dimorphism of the dorsal, pectoral, and anal fins that is characteristic of many species within the Cetopsinae , albeit not the other species of Denticetopsis . It appears that the size of sexual maturity may be sexually-dimorphic in this species (see “Biology” below).

Distribution. Denticetopsis praecox is known from the río Baria of the upper río Negro basin in southern Venezuela ( Fig. 46 ).

Biology. According to Ferraris & Brown (1991: 164), specimens of Denticetopsis praecox were captured in a cobblepebble habitat of black water streams that ranged in pH from 4.3-5.0. Stomachs of two examined specimens contained larval chironomids and other larval insect remains. Those authors also reported that females of Denticetopsis praecox of 44.3-52.9 mm SL contained mature ova and that males of 23.7- 42.0 mm SL exhibited obvious testes.

Material examined. 17 specimens (17, 25-48 mm SL). Venezuela. Amazonas: río Baria, above Neblina base camp, in black water tributary, AMNH 74445, 4 (34-46, paratypes of Pseudocetopsis praecox ; 1 specimen cleared and stained); AMNH 74446, 1 (48, holotype of Pseudocetopsis praecox ); AMNH 74447, 2 (27-31, paratypes of Pseudocetopsis praecox ). Río Baria, 5 km above base camp, in tributary, AMNH 74448, 3 (42-44, paratypes of Pseudocetopsis praecox ); AMNH 74449, 5 (25-47, paratypes of Pseudocetopsis praecox ; 1 specimen, 43 mm, cleared and stained). Río Mawarinuma of río Baria, at Neblina base camp, USNM 309184, 2 (35-40, paratypes of Pseudocetopsis praecox ).

Figures

Fig. 46. Map of central and northern SouthAmerica showing geographic distribution of Denticetopsis epa (1 = holotype locality), Denticetopsis iwokrama (2 = holotype locality), Denticetopsis macilenta (3 = holotype locality of Hemicetopsis macilenta), Denticetopsis praecox (4 = holotype locality), Denticetopsis royeroi (5 = holotype locality), Denticetopsis sauli (6 = holotype locality), and Denticetopsis seducta (7 = holotype locality) (some symbols represent more that one locality and/or lot of specimens).

Fig. 50. Denticetopsis praecox, paratype of Pseudocetopsis praecox, AMNH 74445, 46 mm SL; Venezuela, Amazonas, río Baria, above Neblina base camp.