Pimelodus stewarti, Ribeiro & Lucena & Lucinda, 2008

Ribeiro, Frank R. V., Lucena, Carlos A. S. & Lucinda, Paulo H. F., 2008, Three new Pimelodus species (Siluriformes: Pimelodidae) from the rio Tocantins drainage, Brazil, Neotropical Ichthyology 6 (3), pp. 455-464 : 456-458

Pimelodus stewarti , new species

Fig. 1

Pimelodus sp. B - Lucinda et al., 2007: 79.

Holotype. MCP 41737, 54.1 mm SL, rio Paranã, near lagoa Verde , approximately 12 o 30’S 48 o 12’W, Paranã, Tocantins, Brazil, 8 Jul 2000, Neamb-UFT.

Paratypes. Brazil. Tocantins State. All collected by Neamb-UFT staff. MCP 41920, 5 , 38.4-40.6 mm SL, and UNT 5642 , 38 (1 c&s), 35.0- 50.8 mm SL, Ipueiras, rio Tocantins near rio Manoel Alves , approximately 11 o 19’S 48 o 28’W, 20 Jan 2000. UNT 5649 , 2 , 60.6 - 60.5 mm SL , Paranã, rio Paranã, approximately 12 o 30’S 48 o 12’W, 7 Jan 2001. UNT 5748 , 1 , 61.7 mm SL , Paranã, rio Paranã, approximately 12 o 29’S 48 o 12’W, 8 Feb 2000. UNT 5754 , 8 , 44.4- 48.8 mm SL, Porto Nacional, rio Tocantins, 10 o 43’15"S 48 o 25’14"W, 23 Mar 2000. UNT 5756 , 2 , 47.8 -48.0 mm SL, São Salvador, rio Maranhão, approximately 12 o 45’S 48 o 48’W, 10 Mar 2005. UNT 5766 , 2 , 44.8-49.8 mm SL, Porto Nacional, rio Tocantins, 10 o 43’15"S 48 o 25’14"W, 24 Mar 2000. UNT 5798 , 1 , 40.2 mm SL, Pedro Afonso, rio Tocantins, approximately 08 o 59’S 48 o 10’W, 15 Jan 2001. UNT 5801 , 1 , 43.2 mm SL, Porto Nacional, rio Tocantins, 10 o 43’15"S 48 o 25’14"W, 24 Feb 2000. UNT 5856 , 3 , 58.6-66.1 mm SL, collected with the holotype .

Diagnosis. Pimelodus stewarti is distinguished from its congeners, except P. halisodous , P. joannis , P. ornatus and P. pictus , by the presence of a dark spot in the distal portion of dorsal-fin rays 2-4 (vs. absence of such spot); dark transverse band just anterior to dorsal fin (vs. absence of such band); shorter distance between the posterior nostril and the anterior orbital border (posterior nostril closer to anterior orbital border vs. posterior nostril closer to anterior nostril than to anterior orbital border). Pimelodus stewarti differs from P. ornatus and P. pictus by its uniform gray coloration along the flanks, and a light narrow band along the lateral line (vs. two bands or dark dots along flanks, respectively). Pimelodus stewarti differs from P. joannis by having a greater posterior cleithral-process length (12.7-15.6 vs. 10.2-12.4% of SL) and by the absence of dark blotches on the caudal-fin base (vs. two dark blotches) and from P. halisodous by a smaller pectoral-spine length (15.4-19.6 vs. 20.0-23.5% of SL); a shorter snout (36.1-40.9 vs. 43.1-47.9% of HL); and by having fewer rows of premaxillary teeth (5-8 vs. 13-16).

Description. Morphometric data in Table 1. Body deeper than wide. Dorsal profile of body convex from snout tip to supraoccipital process origin, straight from that region to dorsal-fin origin; straight from dorsal insertion to adipose-fin origin, then gently sloping to anterior extent of caudal peduncle. Dorsal and ventral profiles of caudal peduncle slightly concave. Ventral profile of head anterior to isthmus straight. Preventral profile of body slightly convex or straight. Anal-fin base straight. Head covered by thin skin. Skull roof ornamented with numerous small granulations and osseous tubercles, more visible in larger specimens. Snout not very long, projecting beyond mandibular symphysis by distance less than internarial length. Mouth subterminal; margins curved in ventral view when mouth closed and exposing approximately anterior half of premaxillary tooth rows. Upper lip thick, fleshy, not striated. Lower lip posterior to vertical passing through anterior margin of anterior nostril. Fleshy rictal fold in pocket behind corner of mouth. Posterior nostril closer to anterior orbital margin than to anterior nostril. Anterior nostril with fleshy rim slightly raised posteriorly; posterior nostril thin, fleshy, rim anteriorly elevated. Eye large, elliptical, margin completely free and dorsolaterally positioned on head; horizontal orbital diameter greater than interorbital width orbit oblong, horizontal orbital diameter greater than vertical orbital diameter. Premaxillary tooth patch short, broad, rectangular and transversely elongated; internal border of premaxillary tooth plate straight or slightly concave; premaxilla with eight irregular rows of slender conical teeth; 5- 8 tooth rows on dentary (n = 10). Vomerine and pterygoid tooth plates absent.Anterior cranial fontanel triangular in dorsal view, open from mesethmoid to frontals, and terminating before vertical through posterior margin of eye. Posterior cranial fontanel ovoid or circular, foramen in center of supraoccipital. Supraoccipital process wide; dorsal surface rounded, ornamented with numerous small granulations; lateral margins of supraoccipital process converging posteriorly, process covered by narrow sheath of opaque hyaline skin. Anterior nuchal plate with short anterior process fitting into bifid supraoccipital tip. Anterior and middle nuchal plates ornamented sparsely with tuberculated ridges. Posterior nuchal plate with long posterior process trespassing line through origin of first branched dorsal-fin ray. Three pairs of barbels, flattened at base. Maxillary barbel inserted at vertical through anterior edge of lower lip; slightly surpassing anal-fin base. Mental barbels inserted in advance of gular fold apex, in curved line parallel to mandibular margin. Inner mental barbel reaching base of pectoral fin. Tip of outer mental barbel reaching tips of middle pectoral-fin rays, almost to tip of pectoral spine. Gill membranes free, diverging just behind gular fold apex and supported by 7 branchiostegal rays. Gill rakers well-ossified, sharp and slender; 12-17 (mode = 14) on first branchial arch; 2-4 on epibranchial (mode = 3), 10-13 on ceratobranchial (mode = 12; n = 61). Dorsal fin rays II,6-7 (mode = 6; n = 63), fin inserted near anterior one-third of SL; its origin slightly posterior to vertical through tip of posterior cleithral process. Spinelet narrow, sharply angular or low crest in front. Dorsal spine straight, strong, pungent, shorter than first branched ray, continued in filamentous ray reaching nearly edge of first soft dorsal-fin ray; approximately as long as pectoral spine length. Dorsal spine with 1-3 anterior distal serrae (n = 12). Posterior margin of dorsal spine moderate sharp retrorse spines distally, becoming gradually erect near spine base. First branched dorsal-fin ray longest, last dorsal-fin ray slightly longer than one-half length of first ray; distal margin of dorsal fin nearly straight. Adipose fin large, posterior to middle of body. Adipose-fin margin rounded and moderately deep, its apex near to vertical through base of rays 4-6 of anal fin, ending posteriorly as short free lobe slightly posterior to vertical through tip of last anal-fin ray. Caudal fin i,7,8,i (n = 63); 20 dorsal and 15 ventral procurrent caudal-fin rays; fin deeply forked, with pointed lobes; dorsal lobe slightly longer than ventral lobe, outer principal rays non-filamentous.Anal fin inserted on posterior one-third of SL; fin margin concave, not forming distinct lobe anteriorly; tips of three longest anterior and posterior branched rays meet when depressed. Anal fin ivvi,7-8 (mode = 8; n = 63), last rays simple, first and second branched rays longest. Pectoral fin i,8-9 (mode = 9; n = 63); its posterior margin obliquely truncate, first soft ray longer than spine tip. Pectoral spine strong, distally pointed, dorsal and ventral surfaces smooth; numerous, regularly spaced, uniformly retrorse unicuspid dentations along posterior margin; antrorse and straight dentations along anterior margin, becoming progressively less prominent and more crowded proximally; anterior dentations much larger in juveniles. Pelvic fin i,5 (n = 10); first branched ray almost same length of last branched ray; first branched ray longest, inserted near vertical through last dorsal-fin ray. Lateral-line canal complete, extending onto caudal-fin base; canal nearly straight, with superficial tubular ossicles directed posteroventrally and more developed anteriorly; no accessory laterosensory canals posterior to nuchal area. Posterior cleithral process broad, narrowing posteriorly; ventral margin nearly straight, dorsal margin somewhat concave; granular osseous tubercles on lateral surface. Urogenital papilla short, located in shallow depression immediately posterior of anus. No apparent sexual dimorphism. Superficial ossifications of Weberian complex centrum not covering seventh centrum. Total vertebrae 40 (15 precaudal and 25 caudal). First pleural rib on sixth vertebra. Ten pairs of pleural ribs.

Color in alcohol. Body light brownish to yellow, with white unpigmented stripe on lateral line. Ventral region light to yellowish. Head surface with blackish area on supraoccipital process. Eye dark. Dark transverse band just anterior to dorsal fin. Several dark chromatophores on posterior cleithral process, opercle and below orbital region. Dark spot on distal portion of second to fourth branched dorsal-fin rays. Pectoral, pelvic, and anal fins hyaline. Black chromatophores along interradial membranes of caudal fin, mainly concentrated on median portion of ventral lobe.Adipose fin with few black chromatophores scattered on distal surface. Maxillary barbel dusky on dorsal surface; lighter on ventral surface. Mental barbels pale.

Distribution. Pimelodus stewarti is known from the upper and middle portions of the rio Tocantins drainage ( Fig. 2 ).

Description. Morphometric data on Table 2. Body deeper than wide. Dorsal profile of body convex along snout, straight from orbital region to dorsal-fin origin, dorsal insertion to adiposefin origin gently sloping to anterior extent of caudal peduncle. Dorsal and ventral profiles of caudal peduncle slightly concave. Ventral profile of head straight to anterior region of isth- Etymology. The specific epithet stewarti is a patronym for Donald Stewart, in recognition of his many contributions to catfish systematics.

Figures

Fig. 1. Pimelodus stewarti, holotype, MCP 41737, 54.1 mm SL, rio Paranã, rio Tocantins drainage, Brazil.

Fig. 2. Rio Tocantins drainage showing the collection localities of Pimelodus stewarti (triangles, 1), P. halisodous (squares, 2), and P. joannis (circles, 3). Numbers represent type-localities. Some symbols represent more than one lot or locality.