A new species of the genus Pimelodus La Cépède, 1803 from the rio Iguaçu basin and a reappraisal of Pimelodus ortmanni Haseman, 1911 from the rio Paraná system, Brazil (Ostariophysi: Siluriformes: Pimelodidae)

A new species, Pimelodus britskii, is described from the rio Iguaçu in the rio Paraná drainage, on the border of Paraná and Santa Catarina states, Brazil. Specimens of this species were wrongly included in the type series of Pimelodus ortmanni. Pimelodus britskii is distinguished from its congeners by color pattern, having circular dark brown blotches usually smaller than one orbital diameter, regularly and scattered along the trunk. Differs from P. ortmanni by the following characters: body depth at posterior cleithral process greater than head length; lips not prominent; and maxillary barbel reaching or surpassing vertical drawn through median of adipose fin. Pimelodus britskii represents the second species of the genus Pimelodus from the rio Iguaçu basin.


Introduction
The genus Pimelodus La Cépède is the most species-rich genus in the family Pimelodidae, including 26 species and ranging throughout the Neotropical region from Panamá to Argentina (Lundberg & Littmann, 2003;Ribeiro & Lucena, 2006a;Ribeiro & Lucena, 2006b).Eigenmann & Eigenmann (1890) who completed the first comprehensive revision of Pimelodus, identified 12 species and diagnosed the genus using the following: by possessing a vomer with teeth arranged in small patches; pterygoid and palatine regions edentulous; a frontal fontanel not extending posterior to the orbit; a broad posterior cleithral process not spiny and a dorsal fin with I,6 rays, the first of which is a spine.In essence this genus was also diagnosed by Britski et al. (1988) by the combination of the following external morphological characters: supraoccipital process large at its base, elongated distally and in contact with the predorsal plate; unbranched pectoral and dorsal fin rays strong and aculeate; frontal fontanel elongated, interrupted and horizontally aligned with the posterior margin of the orbit; and the base of the adipose fin greater than the base of the anal fin.Lundberg et al. (1991) 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.The new species described herein is considered a member of the "Pimelodus group" because it shares the synapomorphies as proposed by Lundberg et al. (1991).
On the other hand, the continuing studies on pimelodid fishes from the rio Iguaçu drainage conducted by the authors and Renesto et al. (2000), revealed two sympatric species of Pimelodus coexisting within the basin.As a result of a mixed type series, Haseman (1911) produced a confusing original description for P. ortmanni, where the illustrated specimen had a different color pattern of the type.Examination of the holotype and paratypes of P. ortmanni and a new multivariate morphometric ordination obtained from additional fresh specimens collected at the type locality, reveals the presence of both sympatric species within the type series of P. ortmanni.
Counts were obtained for all fins as well as the gill-rakers and are presented as minimum-maximum ranges.Gill-rakers were counted on the first left branchial arch.The following measurements were taken point-to-point with a 0.05 mm precision caliper and are shown in Table 1: 1) standard length; 2) predorsal length (from tip of snout to anterior margin of dorsal fin); 3) dorsal-fin base length (from anterior to posterior margin of dorsal-fin base); 4) dorsal-fin to adipose-fin distance (from posterior margin of dorsal-fin base to anterior margin of adipose-fin base); 5) adipose-fin base length (from anterior to posterior margin of adipose-fin base); 6) adipose-fin to caudalfin base distance (from posterior margin of adipose-fin base to middle of caudal-fin base); 7) pre-pelvic length (from tip of snout to anterior margin of pelvic-fin base); 8) pelvic-fin to anal-fin distance (anterior margin of pelvic-fin base to anterior margin of anal-fin base); 9) anal-fin base length (anterior to posterior margin of anal-fin base); 10) anal-fin to caudal-fin base distance (posterior margin of anal-fin base to middle of caudal-fin base); 11) caudal peduncle depth; 12) snout length (from tip of snout to anterior margin of eye); 13) orbital diameter (in the horizontal); 14) eye-operculum distance (posterior margin of eye to dorsal end of opercular opening); 15) first dorsal-fin ray to the first pelvic-fin ray distance; 16) first pelvic-fin ray to the last dorsal-fin ray distance; 17) last dorsal-fin ray to first anal-fin ray distance; 18) interorbital distance (between bony margins of orbits); 19) pectoral girdle width (across cleithra at base of pectoral spine); 20) head length (from the tip of snout to posterior margin of opercle).The following additional measurements appear within the species descriptions: 21) maxillary barbel length (from the base to tip of structure); 22) dorsal spine length (from base to tip of structure); 23) pectoral spine length (from base to tip of structure); 24) mouth width (between lateral extremities of mouth gap).
The first 19 morphometric variables listed above were used in size-free canonical variates analysis with Statistical Analysis System (SAS) package following Reis et al. (1990).The new species where compared only with P. maculatus because the very similar osteology of both species, plus its congener of the rio Iguaçu, P. ortmanni.The sample of Pimelodus maculatus chosen for comparison includes six specimens from the rio de La Plata and ten specimens from rivers of rio Paraná basin.
Diagnosis.This species can be distinguished from all other Pimelodus, except P. fur (Lütken, ex Reinhardt, 1874), P. heraldoi Azpelicueta, 2001, andP. absconditus Azpelicueta, 1995, by the color pattern composed of small, densely placed oval or circular dots on anterior region of trunk, becoming inconspicuous or disappearing on the caudal peduncle (vs.stripes along the body in P. albicans (Valenciennes, 1840) Ribeiro &Lucena, 2006 andP. punctatus (Meek &Hildebrand, 1913); dots scattered in the trunk in P. coprophagus Schultz, 1944, P. grosskopfi Dahl, 1961, P. maculatus La Cépède, 1803, P. mysteriosus Azpelicueta, 1998, P. navarroi Schultz, 1944, P. paranaensis Britski & Langeani, 1988, P. pictus Steindachner, 1876and P. platicirris Borodin, 1927).Differs from P. fur by smaller maxillary barbell length (1.3-1.8 in SL vs. 0.9 to 1.1), greater snout length (2.1 to 2.4 in HL vs. 3.1 to 3.5), greater eye diameter (3.5 to 4.9 in HL vs. 5.2 to 6.6), greater eye-operculum distance (2.9 to 3.5 in HL vs. 4.8 to 5.1), greater interorbital distance (3.6 to 5.1 in HL vs. 5.5 to 7.6), greater mouth width (2.6 to 3.5 in HL vs. 5.0 to 5.3); from P. heraldoi by smaller predorsal length (2.7 to 2.9 in SL vs. 2.5 to 2.6), smaller caudal peduncle depth (12.2 to 15.0 in SL vs. 11.3-12.6),greater snout length (2.1 to 2.4 in HL vs. 2.9 to 3.3), greater eye diameter (3.5 to 4.9 in HL vs. 5.2 to 6.3), greater eye-operculum distance (2.9 to 3.5 in HL vs. 4.7-5.1),greater mouth width (2.6 to 3.5 in HL vs. 4.3 to 5.4); and from P. absconditus by smaller pre-dorsal length (2.7 to 2.9 in SL vs. 2.4 to 2.6 in SL), smaller pre-pelvic length (2.0 to 2.1 in SL vs. 1.8 to 2.0 in SL), smaller caudal peduncle depth (12.2 to 15.0 in SL vs. 9.8 to 11.9 in SL) and smaller pectoral girdle width (5.4 to 6.2 in SL vs. 4.8 to 5.4). 1. Dorsal profile of head inclined, slightly convex from tip of snout to dorsal-fin origin; slightly concave or almost straight from dorsal-fin insertion to adipose-fin origin; inclined and straight at dorsal-fin base; concave at caudal peduncle.Dorsal fin slightly anterior to median vertical line of trunk.Body depth, anterior to dorsal-fin insertion, less than body width at posterior cleithral process.Shape of head roughly conical in dorsal view, wedgelike in lateral view.Predorsal plate anteriorly V-shaped, surpassing supraoccipital process.Large orbital diameter, 0.7 to 1.4 (mean 1.0) in interorbital distance.Origin of frontal fontanel between posterior nares, not reaching to vertical through posterior orbit; mouth inferior; inferior mandible shorter than superior, fleshy lips in both.Villiform teeth in premaxillary and dentary tooth plates; premaxillary plate with semicircular anterior border, undivided at symphysis; dentary plate elongated, distally pointed, divided at symphysal region; maxillary barbel in adult specimens reaching anterior region of adipose fin, median portion in juvenile specimens.External mental barbel reaching but not surpassing pectoral fin insertion; in juveniles, reaching vertical through dorsal-fin origin; internal mental barbel reaching opercular membrane, sometimes surpassing it, never reaching pectoral-fin origin; ventral profile convex from inferior mouth to anal-fin base, concave on caudal peduncle.Body depth always shorter than head length.Caudal peduncle shallow.Pectoral fin reaching vertical through third or fourth ray of dorsal fin in juvenile specimens.Pelvic fin beginning at vertical through last ray of dorsal fin, not surpassing adiposefin origin when adpressed.Adipose fin elongated, its length similar to head length; anal fin triangular in lateral view, posterior margin concave.Caudal fin bifurcate, upper lobe longer than lower.Posterior cleithral process nearly triangular, short, not reaching vertical through dorsal-fin origin, sometimes reaching vertical through median predorsal plate.Unbranched dorsal-fin ray pointed, anterior margin completely smooth, small and pointed hooks posteroventrally in posterior margin; large hooks covering its superior third on distal region.Anterior margin of pectoral-fin spine smooth, small and pointed hooks on almost entire distal region of posterior margin; hooks absent in base.Dorsal fin rays II,6 (only one specimen II,7); pectoral fin I,8-10; pelvic fin i,5; anal fin i-iv,8-10; caudal fin i,7,8,i.Gill-rakers 19-25 on the first left branchial arch.

Description. Morphometric data presented in Table
Color in alcohol.Dorsal region light gray, ventral region light brown; dark brown oval blotches in series of six to ten, shorter than orbital diameter, neatly positioned in sequence along flanks of body, spots inconspicuous or absent on caudal peduncle; small dark brown dots on parietal, supraoccipital, infraorbital and opercular regions; five dark brown blotches in posterior region of cleithral process; dark brown dots on rays of dorsal fin; inconspicuous gray horizontal line in upper half of dorsal fin; two or three irregular series of small dark dots or ligth adipose fin.Pectoral, pelvic, and anal fin sometimes light gray for almost one-third of fin; pectoral fin completely gray; pelvic fin grayish on base and on distal third; dark dots only on upper lobe of caudal fin, dark brown line crossing three branched rays of lower lobe.

Pimelodus britskii, new species
Figs. 4 and 5 Pimelodus ortmanni (part) Haseman, 1911: 379-380     Diagnosis.Pimelodus britskii differs from its congeners, in its color pattern having circular dark brown blotches usually smaller than one orbital diameter regularly scattered along the trunk (vs.irregular series of dots in P. coprophagus, P. grosskopfi, P. paranaensis, P. navarroi, and P. pictus; small, densely placed oval or circular dots on anterior region of trunk, becoming inconspicuous or disappearing on caudal   Distribution.Distributed broadly throughout the rio Iguaçu basin (Fig. 3).
Etymology.The name Pimelodus britskii is given in honor of the eminent ichthyologist Dr. Heraldo Antonio Britski, of Museu de Zoologia da Universidade de São Paulo, in recognition for his significant contributions to Neotropical systematic ichthyology.
Morphometric analysis.The size-free canonical variate analysis readily discriminated populations of P. ortmanni, P. britskii from rio Iguaçu and P. maculatus from the río de La Plata and rio Paraná basins (Fig. 6), previously diagnosed on the basis of its color pattern.The eigenvalues and their loadings appear in Table 2.The first canonical axis (CAN1) readily separates all three species, while the second canonical axis (CAN2) distinguishes the specimens of P. britskii from the samples of P. ortmanni and P. maculatus, which have similar scores on CAN2.
Pimelodus maculatus has a greater caudal peduncle depth, pectoral girdle width, interorbital and predorsal distance than does P. ortmanni.Pimelodus ortmanni has a larger distance between the bases of the anal and caudal fins, adipose fin length and distance from dorsal to adipose fin.The sample of P. britskii was discriminated from P. ortmanni and P. maculatus on CAN1 and CAN2.Pimelodus ortmanni was discriminated from P. britskii by a longer dorsal-fin base length and greater distance between the terminus of dorsal-fin and anal-fin origin; there are also differences in adipose-fin length.Pimelodus britskii has a larger distance between the orbit and opercular opening, predorsal distance and snout length (Table 2).

Discussion
Because of the absence of a phylogenetically-based diagnosis of Pimelodus, the inclusion of Pimelodus britskii in this genus is based on several plesiomorphic characters like the presence of a foramen with two openings for the passage of the maxillary ramus (dorsalis) and mandibular ramus (ventralis) of the trigeminal nerve as described by Lundberg & Parisi (2002).Haseman (1911) skillfully recognized Pimelodus ortmanni when he splits that species from Pimelodus maculatus, a species described from the major rio Paraná hydrographic system at La Plata.In that article, he recognized the high degree of endemism of the rio Iguaçu ichthyofauna and discussed how it might be acquired in isolation.
However, during a recent visit to the Field Museum of Natural History to study the type series of Pimelodus ortmanni, we discovered that Haseman (1911) had described that species from a mixed type series containing two species.The specimen FMNH 54240 (ex-CM 2856) was designated as the holotype of P. ortmanni, while the specimen FMNH 54241 (ex-CM 2857; now FMNH 105099) was figured.Haseman (1911) incorrectly attributed the differences in color pattern observed within the type series of Pimelodus ortmanni to variation during ontogenetic development.Our examination of the P. ortmanni type series and the additional fresh material revealed that each species maintains a characteristic color pattern throughout ontogeny.The elements of Haseman's type series now included in Pimelodus britskii (FMNH 105098 and 105099), and the additional material of young specimens of this species examined herein, all possess a color pattern with a series of three dark brown blotches on the flanks.Specimens assigned to P. ortmanni all have the contrasting condition of four or five series of dark brown blotches.
The samples of Pimelodus britskii and P. ortmanni analysed confirms that two species are present in the typematerial originally described by Haseman under the name P. ortmanni.Furthermore, Renesto et al. (2000) presented an enzymatic study from internal organs that revealed differences between P. ortmanni and P. britskii.The presence of two species in the type series, with variation in the color pattern, may explain why the original description of Pimelodus ortmanni is so imprecise.Because the figure of P. ortmanni is more informative than the description, subsequent authors have been misled in the identification of Pimelodus ortmanni Haseman (see Severi & Cordeiro, 1994: 65;Azpelicueta, 1995: 75;Nakatani et al., 2001: 277).
It is important to recognize that the color pattern of Pimelodus britskii from rio Iguaçu is an important external diagnostic character for the new species, even given the large diversity of blotches, dots and stripes present in congeners from the rio Paraná-Paraguay basin.On the other hand, P. maculatus and P. platicirris, have fairly similar color patterns to P. britskii.They differ in the size of blotches which are generally larger than one orbital diameter in P. maculatus and P. platicirris and usually smaller than orbital diameter in P. britskii.Borodin (1927) considered P. platicirris to be similar to P. ortmanni in color pattern but differing from it by a longer adipose fin length, greater body depth and longer posterior cleithral process of the pectoral fin.However, the holotype of P. platicirris, the unique specimen examined by Borodin, also differs from P. ortmanni by the greater pre-dorsal length (2.4 vs. 2.7-2.9 in SL), greater adipose-fin to caudal-fin base distance (4.7 vs. 6.2-7.3 in SL), greater pre-pelvic length (1.9 vs. 2.0-2.1 in SL), greater pelvic-fin to anal-fin distance (2.3 vs. 3.8-4.4 in SL), smaller anal-fin to caudal-fin base distance (6.2 vs. 4.9-5.4 in SL), greater caudal peduncle depth (10.2 vs. 12.2-15.0),greater maxillary barbel length (1.2 vs. 1.3-1.8 in SL).
The ten known Pimelodus species from the Paraná-Paraguay river basin include six with a color pattern of blotches or dots on the flanks, but with significant variation from one to another.The species P. absconditus, P. heraldoi and P. ortmanni are similar in color pattern, having small and numerous oval dark brown dots concentrated at the anterior part of the trunk, fading gradually at the posterior region of the caudal peduncle.This color pattern is also found in P. fur from the rio São Francisco basin.Pimelodus paranensis has a unique pattern of several small dark brown circular blotches on the trunk.Pimelodus albicans has three conspicuous dark brown stripes on the trunk and P. argenteus, P. brevis and P. atrobrunneus lack blotches or stripes on the trunk.Pimelodus ornatus, which has two large black stripes on the trunk and a dark brown spot on the dorsal fin is perhaps the most distinctive species of the genus occurring in the Paraná-Paraguay basin.
The dental plate of vomer possessed by some individuals of Pimelodus britskii is also present in P. paranensis and P. absconditus as noted by Britski & Langeani (1988) and Azpelicueta (1995).
Our analysis suggests that Pimelodus britskii is endemic to the rio Iguaçu basin.The examination of a large number of specimens deposited in Brazilian museums (see list of additional material), including those from the rio Paraná basin, did not reveal any P. britskii outside of the rio Iguaçu limits.The old origin of the Iguaçu Falls, as discussed by Garavello (2005), may have isolated the rio Iguaçu from the remaining drainages of the rio Paraná and may perhaps explain the endemicity of Pimelodus britskii and Pimelodus ortmanni.

Fig. 3 .
Fig. 3. Geographical distribution of Pimelodus ortmanni and Pimelodus britskii from Rio Iguaçu.Each symbol may represent more than one sample.
peduncle in P. absconditus, P. fur, P. heraldoi, and P. ortmanni, stripes along the body in P. albicans, P. albofasciatus, P. ornatus, and P. tetramerus; uniform gray coloration or with very weak dark dots on anterolateral region in P. altissimus, P. argenteus, P. atrobrunneus, P. blochii, P. brevis, P. jivaro, P. microstoma, P. pohli, and P. punctatus; blotches larger than one orbital diameter in the trunk in P. maculatus, P. mysteriosus, and P. platicirris).Pimelodus britskii also differs from P. ortmanni in having body depth at posterior cleithral process greater than head length (vs.depth always shorter than head length); lips not prominent (vs.fleshy and prominent lips circumscribing mouth opening); and maxillary barbel reaching or surpassing vertical drawn through median of adipose fin (vs.maxillary barbel reaching but not surpassing vertical drawn through median of adipose fin).cal through posterior margin of orbit; mouth inferior, lower mandible shorter than superior; lips thin.Villiform teeth in premaxillary and dentary tooth plates; premaxillary tooth plates undivided at symphysis, semicircular margins, slightly curved posteriorly.Dentary tooth plate elongate, distally pointed, divided at symphysal region.Teeth absent in vomer and ectopterygoid bones; gill rakers long, slender.Barbels narrow, elongate; maxillary barbel reaching or surpassing vertical drawn through median of adipose fin, it may reach fork of caudal fin in juveniles; external mental barbel generally reaching pectoral fin, sometimes reaching pelvic-fin origin; ventral profile slightly convex from mouth to end of anal fin, concave at caudal infraorbital, parietal and supraoccipital regions.One series of small dark brown dots above and below lateral line, dorsal surface of body, in juveniles; series typically absent in adults.Eyes dark.One to three dark brown circular blotches on posterior cleithral process; dark brown dots on dorsal fin rays and membranes; pectoral, pelvic, anal, and adipose fins uni-

Table 2 .
First two size-free canonical variate axes (CAN1 and CAN2) from the analysis of combined samples of P. britskii, P. ortmanni, and P. maculatus from rio Iguaçu and río de La Plata basins (Total = 59 specimens).