Three new Pimelodus species ( Siluriformes : Pimelodidae ) from the rio Tocantins drainage , Brazil

Three new species of Siluriformes from the rio Tocantins drainage of Brazil are placed in the genus Pimelodus, P. stewarti, P. joannis, and P. halisodous. Pimelodus halisodous differs from the sympatric P. joannis and P. stewarti by the number of premaxillary tooth rows (13-16 vs. 5-9). Pimelodus joannis differs from P. stewarti by the presence of two dark blotches on the base of the caudal fin. The three new species differ from all other species of Pimelodus by the possession of a uniform gray coloration along flanks; the relatively short distance between the posterior nostril and the anterior orbital border; a short maxillary barbel, that only slightly surpasses the caudal-fin base.


Introduction
The catfish family Pimelodidae encompasses 29 genera and 94 species distributed exclusively in the Neotropical Region from Panama to Argentina (Lundberg & Littmann, 2003;Ferraris, 2007;Eschmeyer, 2007).The most speciose pimelodid genus is Pimelodus, which consists of 29 species.A cladistic diagnosis of the genus Pimelodus is still lacking, so that a non-cladistic definition has been employed from the latter part of the 19 th century to the present.The first wide-ranging revision of Pimelodus was conducted by Eigenmann & Eigenmann (1890).Those authors defined the genus on the basis of dental characters, fontanel length, width of posterior cleithral process, and the number of dorsal-fin rays.
Examination of the collection of pimelodid fishes housed at the Laboratório de Ictiologia Sistemática, Universidade Federal do Tocantins revealed the existence of three undescribed pimelodid species from the rio Tocantins drainage, which fit into Eigenmann & Eigenmann's (1890) diagnosis of Pimelodus.The purpose of this paper is to name and formally describe these species.

Material and Methods
Measurements and counts follow Lundberg & McDade (1986) and Lundberg et al. (1991b) with the modifications of Lundberg & Parisi (2002) and Ribeiro & Lucena (2006a).Examined specimens belong to the Academy of Natural Sciences, Philadelphia (ANSP), Field Musem of Natural History, Chicago (FMNH), Museu de Ciências e Tecnologia, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre (MCP), Museu de Zoologia da Universidade Estadual de Londrina, Londrina (MZUEL), Museu de Zoologia da Universidade de São Paulo, São Paulo (MZUSP), Laboratório de Ictiologia Sistemática da Universidade Federal do Tocantins, Porto Nacional (UNT), and Departamento de Zoologia de Vertebrados de la Facultad de Humanidades y Ciencias, Montevideo (ZVC-P).Counts and measurements were made on the left side of specimens whenever possible.Measurements are straight-line distances taken point-to-point with digital calipers to the nearest 0.1 mm.All measurements are expressed as percent of standard length (SL), except subunits of the head, which are expressed as percent of head length (HL).Fin-ray counts include all rays.The two posterior most anal-fin rays that are inserted at same pterygiophore were counted as a single element.Gill rakers were counted on the first branchial arch (ceratobranchial and epibranchial).Osteological preparations were cleared and counterstained for cartilage and bone using the method of Taylor & Van Dyke (1985).Tooth rows, branchiostegal rays, procurrent caudal-fin rays and vertebral counts were taken from cleared and stained specimens (c&s).In vertebral counts the fused PU1+ U1 is considered as a single bone, and the Weberian apparatus as having five elements.Osteological terminology follows Lundberg & Luckenbill (2007).Comparative material is that listed by Ribeiro & Lucena (2006a, 2006b, 2007) and additional specimens listed below under "Additional Examined Specimens".

Description. Morphometric data in
Etymology.The specific epithet stewarti is a patronym for Donald Stewart, in recognition of his many contributions to catfish systematics.Color in alcohol.Body color grayish to yellowish.Ventral region brownish to light.Light narrow band along lateral line.
Head surface grayish to brownish.Eyes dark.Some specimens with several dark chromatophores on surface of posterior cleithral process, opercle and below orbit region; sometimes reaching body flanks; such chromatophores more concentrated on lower half of flanks below lateral line.Dorsal fin with black chromatophores on distal portion of rays 2-4.Pectoral, pelvic and anal fins hyaline, base sometimes yellowish.
Adipose fin hyaline with minute uniformly scattered melanophores on distal portion.Black chromatophores along interradial membranes of caudal fin, concentrated on median portion of each caudal-fin lobe.Maxillary barbel dusky on dorsal surface; lighter on ventral surface.Mental barbels pale.
Distribution.Pimelodus halisodous is known from the upper and middle portions of the rio Tocantins drainage (Fig. 2). Etymology.

Diagnosis.
Pimelodus joannis is distinguished from its congeners, except P. halisodous, P. jivaro, P. ornatus, P. pictus, and P. stewarti, by the presence of a dorsal median crest along supraoccipital process (vs.crest absent); 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); a dark spot on the distal portion of dorsal-fin rays 2-4 (vs.no spot); and two dark blotches on the base of the caudal fin (vs.absence of such spots).Pimelodus joannis differs from P. jivaro by having a shorter maxillary barbel, which extends only slightly past caudal-fin base (vs.maxillary barbel extending beyond caudal-fin base); a dark spot in the distal portion of dorsal-fin rays 2-4 (vs.absence of such spot); and two dark blotches on the base of the caudal-fin (vs.absence of such spots).The new species from P. ornatus and P. pictus by the uniform grayish to yellowish coloration (vs.presence of bands or dark dots along flanks, respectively).
Pimelodus joannis differs from P. stewarti by having a shorter posterior cleithral process (10.2-12.4 vs. 12.7-15.6% of SL); by the presence of two dark blotches on the caudal-fin base (vs.absence of such dark blotches); and by the presence of a dorsal median crest along the supraoccipital process (vs.no crest).Pimelodus joannis differs from P. halisodous by having a shorter pectoral-spine (15.5-18.5 vs. 20.0-23.5% of SL); a shorter snout (35.8-41.8 vs. 43.1-47.9% of HL); and by fewer premaxillary tooth rows (5-9 vs. 13-16).ending posteriorly as short free lobe slightly posterior to vertical through tip of last anal-fin ray.Distribution.Pimelodus joannis is known from the upper and medium portions of the rio Tocantins drainage (Fig. 2).

Description. Morphometric data in
Etymology.The specific name joannis is a patronym for John Lundberg, in recognition of his many contributions to catfishes systematic.

Discussion
Pimelodus is a poorly-defined and presumably a paraphyletic assemblage of species (Lundberg & Littmann, 2003).The species level taxonomy of Pimelodus is still poorly known as is the phylogenetic relationships within the genus and with other genera.Given that a cladistic definition (hypothesis of monophyly) of Pimelodus is not available, the traditional non-cladistic diagnosis of Eigenmann & Eigenmann (1890) is still in use.Those authors defined Pimelodus by the following set of non-derived morphological characters: vomerine teeth arranged in small patches; pterygoid and palatine edentulous; frontal fontanel not extending posterior of orbit; broad posterior cleithral process without spines; and first dorsal-fin ray spinous, followed by six branched soft rays.
Several described species of pimelodids fit into the definition above.As a consequence, a large number of species are currently assigned to Pimelodus and several undescribed species would fit the current definition of the genus as well.This, combined with the wide intrageneric variability in morphology and color pattern, pose difficulties for a complete systematic revision of the genus.
The current knowledge on the intrageneric relationships within the Pimelodidae is still under investigation, with most genera (including Pimelodus) lacking a monophyletic hypothesis.In order to properly define Pimelodus with this kind of monophyletic approach, the relationships of related pimelodid genera, e.g.Cheirocerus, Iheringichthys, and Duopalatinus also needs careful review and study.This work goes beyond the scope of this paper.
Some authors have recently provided some insight into the relationships of smaller groups of the Pimelodidae (e.g.Lundberg & McDade, 1986;Lundberg et al. 1991a, b;Lundberg & Parisi, 2002).Lundberg et al. (1991b) delimited the subfamily Pimelodinae, with the genus Pimelodus included in their Pimelodus-group within the "Calophysus-Pimelodus clade", and described synapomorphies for this clade within the subfamily [thereafter, Lundberg & Littmann (2003) raised the Pimelodinae of Lundberg et al. (1991b) to family rank, excluding the genus Conorhynchos].The three species herein described exhibit the character states proposed as synapomorphic for the family Pimelodidae and for the "Calophysus-Pimelodus clade".Following Lundberg et al. (1991b: fig.12B), the synapomorphic character state supporting the monophyly of the Pimelodus-group is the presence of a sutural joint along the entire extension of the transverse processes of the fourth and fifth vertebrae.However, Lundberg & Parisi (2002), reported a submarginal gap between the transverse processes of these vertebrae in small specimens and in some other members of the Pimelodidae (e.g.Pimelodus ornatus, P. grosskopfii, and Duopalatinus).As a consequence, and given this character variation is not satisfactorily understood, we regard the three new species described herein as members of the Pimelodus-group (see Figs. 5-6).
An extensive posterior development of the superficial ossification of the Weberian complex centra that ventrally covers the seventh centrum was proposed by Lundberg et al. (1991b) as synapomorphic for a clade (within the Pimelodus-group) composed of Pimelodus, Cheirocerus, Duapalatinus, Exallodontus, Iheringichthys, and Parapimelodus.Our three new species do not exhibit this condition.Instead, each has centrum 7 exposed ventrally and the superficial ossification is restricted to more anterior vertebrae (Figs.5-6).It is important to emphasize that this character exhibits different ontogenetic states, including an exposed seventh vertebral centrum (Azpelicueta, 2001;Ribeiro & Lucena, 2006b).Lundberg et al. (1991b), and Lundberg & Parisi (2002) also identified one derived state of the trigeminofacial nervecomplex (and respective foramina), which diagnoses a group of Pimelodus species, including P. maculatus (type-species).This character state is also exhibited by species of some other nominal pimelodid genera (e.g.Iheringichthys and Bergiara) and is absent in some species currently assigned to the genus Pimelodus (e.g.P. ornatus and P. altissimus).
Although the three new species described herein lack the derived diagnostic characteristics for the above mentioned group, in the absence of a cladistic definition of the genus and a more comprehensive phylogenetic hypothesis for the group, we opted to describe them as new species of Pimelodus in keeping with the current definition of the genus proposed by Eigenmann & Eigenmann (1890).Given these circumstances, one may question the wisdom of describing three species of such an unstable genus, as opposed to deferring such species descriptions until generic relationships are completely resolved.We argue that the descriptions of such new species are important since (1) these actions make species names available; (2)  they contribute to knowledge of the biodiversity within higherlevel clades, (3) they provide additional published information useful in the future resolution of generic relationships, and (4) these species are seriously threatened by severe alterations from the installation of hydroelectric plants in the middle and upper rio Tocantins basin (Lucinda et al., 2007).
Three additional species have been reported from the rio Tocantins drainage: Pimelodus blochii; P. ornatus; and P. tetramerus.Pimelodus ornatus and P. tetramerus possess a unique color pattern, consisting of dark bands along the sides of the body, which allows for quick recognition and distinction from the three new species herein described.Eigenmann (1912) described two varieties of Pimelodus blochii from the Amazon basin.His variety A, had only a gray ground coloration, and his variety B had black bands along the flanks.Pimelodus joannis, P. halisodous and P. stewarti exhibit a color pattern similar to that of variety A, but they differ from it by the possession of a larger distance between anterior and posterior nostrils (18.1-22.9%HL vs. 11.6-16.9%HL); a dark spot in the distal portion of dorsal-fin rays 2-4 in P. joannis and P. stewarti (vs.absence of such spot); and by the presence of a dorsal median crest along the supraoccipital process in P. halosodous and P. joannis (vs.no crest).
The ichthyofauna of the rio Tocantins drainage is poorly known, especially in the middle and upper portions of this basin.This area contains a large proportion of endemic species for several Neotropical freshwater fish groups.Several new species have been described from this basin during the last few decades.Nonetheless, many species remain unknown to science, exhibit serious taxonomic problems or await formal description.All these facts indicate the poor level of taxonomic knowledge of this ichthyofauna and the need of additional sampling and taxonomic research.

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).
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.

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.
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.Fig.1.Pimelodus stewarti, holotype, MCP 41737, 54.1 mm SL, rio Paranã, rio Tocantins drainage, Brazil.dal-finbase; 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,
The specific name, halisodous from the Greek adjective halis, meaning in crowds, in plenty, sufficient, enough, plus the Greek noun odous, meaning tooth.The name alludes to the several (ca.15) irregular rows of conical and slender teeth on each premaxilla.A noun in apposition.

Table 1
width; orbit oblong, horizontal orbital diameter greater than vertical orbital diameter.Premaxillary tooth patch short, broad, rectangular and transversely elongate; internal border of premaxillary tooth plate straight or slightly concave; premaxilla with eight irregular rows of slender conical teeth.Dentary with