New species of the genus Leporinus Agassiz ( Characiformes : Anostomidae ) from the rio Curuá , rio Xingu basin , Serra do Cachimbo , Brazil , with comments on Leporinus reticulatus

A new species of Leporinus Agassiz is described from the rio Curuá, a tributary of the rio Iriri, rio Xingu basin, Serra do Cachimbo, Pará State, Brazil. The new species is diagnosed by the color pattern, which consists of eight to ten midlateral round dark blotches plus 20 to 40 smaller ones scattered over the body, dental formula 3/4, subinferior to inferior mouth, 37 to 38 lateral line scales, 4/3-4 transversal series of scales, and 12 circumpeduncular scale series. The new species most closely resembles L. octomaculatus and L. reticulatus from the upper Tapajós basin, and L. marcgravii and L. microphthalmus from the rio São Francisco and the rio Paranaíba, respectively. Based on recently collected specimens, L. reticulatus is re-diagnosed as having an allometric elongation of the snout.


Introduction
Leporinus Agassiz is one of the most species-rich genera in the entire order Characiformes, with approximately 90 valid species (Britski & Garavello, 2003, 2005;Britski & Birindelli, 2008;Santos & Zuanon, 2008).Although several species have been described in the last twenty years (see Britski & Garavello, 2003), recent collection efforts in streams and small tributaries of large river drainages, especially in the Amazon basin, have revealed a still greater number of undescribed species.
Fish collections from the Serra do Cachimbo, the highest portion of the Brazilian shield in the Amazon, have revealed a quite rich and endemic fish fauna (Lima & Birindelli, 2006;Birindelli et al., 2009).The area is drained by three major river basins, the rio Curuá, a large tributary of the rio Iriri in the rio Xingu basin, and the rio Teles Pires and the rio Jamanxim, flowing into the rio Tapajós.The rio Curuá near Vila de Cachoeira da Serra (approximately at 08°44'S 54°58'W) drop off from Serra do Cachimbo tablelands in a series of two great waterfalls of approximately 40 and 60 meters deep, separated only by a 50 meters river stretch, that completely isolate the fish fauna in the areas above the falls (Goulding et al., 2003).
During a recent expedition to the Serra do Cachimbo, an undescribed species of Leporinus was discovered from the rio Curuá.The undescribed species most closely resembles L. reticulatus Britski &Garavello, 1993 andL. octomaculatus Britski &Garavello, 1993, both described from the upper rio Tapajós basin, L. marcgravii Lütken, 1875, from the rio São Francisco and L. microphthalmus Garavello, 1989 from the rio Paranaíba (upper rio Paraná basin).
Large specimens of Leporinus reticulatus, a species described based on small specimens, recently collected in the Tapajós basin revealed an unusual snout elongation, and color pattern variation previously unknown for the species.
The aim of the present contribution is to describe the new species, and re-diagnose L. reticulatus based on recently collected material.

Material and Methods
Counts and measurements were taken according to Britski &Garavello (1978) andWinterbottom (1980).Meristic data are given in the description, with the frequency of each count provided in parentheses after the respective count, and an asterisk indicating counts of the holotype.Lateral line scale counts included the pored scales extending onto base of the median caudal-fin rays.The upper transversal series of scales is represented by the number of rows of scales between the lateral line and the dorsal-fin origin (counting neither the scale on the middorsal series immediately anterior to the dorsal-fin origin, nor the small scale at the base of the anteriormost dorsal-fin rays); this procedure always eliminates the very confusing count of a half scale in this series.A half scale between the lateral line and pelvic-fin origin is only counted when the base of pelvic-fin first ray faces anteriorly the middle of the scale immediately in front of it.Tooth counts are expressed as dental formula and represents the premaxillary number of teeth over the dentary in each half of the jaw.Vertebral counts were taken only from x-rayed specimens; vertebrae of the Weberian apparatus were counted as four elements, included in the vertebral counts, and the fused PU1+U1 of the caudal region as a single element.The pattern of circuli and radii was defined on scales sampled from region between the lateral line and the base of dorsal fin.Scanning electron microscopy (SEM) images of the premaxilla, dentary and its teeth were taken from cleared and double stained paratype (cs), prepared according to the method of Taylor & Van Dyke (1985).All examined material is alcohol preserved, except when indicated by cs or sk for dry skeleton.Institutional abbreviations includes: MZUSP, Museu de Zoologia da Universidade de São Paulo, São Paulo, ANSP, Academy of Natural Sciences of Philadelphia, Philadelphia, and INPA, Instituto Nacional de Pesquisas da Amazônia, Manaus.

Leporinus guttatus, new species
Figs  Diagnosis.Leporinus guttatus is diagnosed by its unique coloration, which consists of eight to ten midlateral round dark blotches, and 20 to 40 smaller ones forming one or two irregular series above and two or three irregular series below midlateral blotches.

Description. Morphometric data of holotype and paratypes in Table
Mouth subinferior (reaching slightly ventrally to longitudinal through lower margin of orbit, in specimens around 80 mm SL) to inferior (reaching slightly ventrally to longitudinal through lower margin of infraorbitals, in specimens of 90 mm SL or more).Snout rounded to slightly acute in some specimens (as in holotype, see Fig. 1a).Premaxilla with three incisiform teeth gently diminishing in size from symphyseal tooth.Dentary with four incisiform teeth also gradually decreasing in size laterally (Fig. 3).
Coloration.Overall ground color tan.Head and body slightly countershaded, gradually darker above longitudinal line from mouth, through lower border of orbit to midline of opercle, and body above lateral line.Body with eight to ten dark round blotches along lateral line, three of them slightly larger and more conspicuous (one below posterior insertion of dorsal fin, one above anal-fin origin and one on caudal peduncle), and several (about 20 to 40) smaller blotches scattered over body.Smaller specimens, up to 80 mm SL, with fewer (around 20) smaller blotches forming one or two irregular series above and two or three irregular series below midlateral blotches (Fig. 1b).Larger specimens, from 90 mm SL, with more numerous (around 40) smaller blotches forming two to three irregular series below and above midlateral blotches (Fig. 1a).Ventral surfaces of head and body pale yellow to cream, without chromatophores.Adipose fin with dark distal margin.Remaining fins nearly hyaline, with few chromatophores along margins of rays.
Live coloration as describe above, except for overall ground coloration more tan than yellow (Fig. 2).

Geographic distribution.
Leporinus guttatus is known from the upper rio Curuá, above the great falls of Serra do Cachimbo (Figs. 4 and 5).The rio Curuá is a tributary to the rio Iriri, a large tributary to the lower rio Xingu.The absence of L. guttatus from collections made below the waterfalls indicates that the new species might be restricted to the river portion isolated above the falls (see Birindelli et al., 2009 for discussion on the endemism of the upper rio Curuá Ichthyofauna).
Ecological notes.Specimens of Leporinus guttatus were caught in a clear water stream, near waterfalls (MZUSP 97100 and MZUSP 101300) or in a cofferdam just above a waterfall (MZUSP 96865).Fishes were caught most effectively by gill nets and cast net during the sunset.
Etymology.From the latin guttatus, meaning spotted or dappled, in allusion to the presence of the dark blotches scattered over the body, which are more numerous than those in any other known species of Leporinus.An adjective.

Discussion
Comments on the Leporinus guttatus.The genus Leporinus comprises a great number of species.During the last century, few studies have attempted to split the genus into smaller groups such as subgenus.Fowler (1914) created the subgenus Myocharax for L. desmotes, a species with terminal mouth and symphysal teeth greatly enlarged.Borodin (1929) created the subgenus Hypomasticus for L. mormyrops Steindachner, 1875 (type-species), L. garmani Borodin, 1929 andL. thayeri Borodin, 1929, noting however, that the mouth position in the latter was not as derived as in the first two species.Géry (1960a) redescribed L. despaxi recognizing it, along with L. mormyrops, L. garmani, L. thayeri, and L. crassilabris, in the subgenus Hypomasticus.However, Géry (1960a) noticed that Hypomasticus is an "entité taxonomique commode sans grande valeur phylogénétique".Concomitantly, Géry (1960b) described the subgenus Leporinops, for L. moralesi, based on its terminal, almost upturned mouth and bicuspid symphyseal teeth on the premaxillary, discussing its possible relationship to Abramites.Later on, Géry (1977) recognized three subgenera in the genus Leporinus, in addition to the "subgenus typical Leporinus": Leporinops (with L. moralesi and L. jamesi), Myocharax (with L. desmotes), Hypomasticus (with L. mormyrops, L. thayeri, L. garmani, Leporinus "maculatus" (= L. megalepis), and L. despaxi).On a different approach, Britski & Garavello (1978) recognized three species group within the genus Leporinus, according to adult color pattern: the barred species group (or "fasciatus group") diagnosed by having 8 to 12 transverse (straight or oblique) dark bars on body, the striped species group (or "striatus group") with one to six horizontal dark stripes, and the blotched species group (or "friderici group") with dark blotches over body, usually with three larger midlateral  The study on the morphology of Leporinus guttatus have revealed the presence of three of the four synapomorphies assigned to Hypomasticus, the vertically oriented premaxilla (#46: 0), the wide ascending process of anguloarticular (#55: 1), and the trough formed by the ascending process of the anguloarticular (#56: 1).The other character assigned for Hypomasticus, the lateral process of anterior portion of mesethmoid (#16:1), is absent in L. guttatus.On the other hand, at least two of the five unambiguous synapomorphies assigned to the clade composed by all remaning Anostomids, except Leporellus and Hypomasticus, are present in L. guttatus.In that species, the anterior margin of the antorbitals is positioned distinctly anterior of anterodorsal opening of sensory canal of first infraorbital (#2: 1), and the ectopterygoid vertically oriented with vertical through anterodorsal limit of ectopterygoid passing through ventral portion of ectopterygoid (#72: 1).This combination of characters makes it impossible to securely assign L. guttatus to either Hypomasticus or Leporinus (sensu Sidlauskas & Vari, 2008).The same holds true for the species L. octomaculatus, L. reticulatus, L. microphthalmus and L. marcgravii, all similar to L. guttatus in many aspects (see below).Only through a  phylogenetic analysis focused on the species of Leporinus, expanding the study of Sidlauskas & Vari (2008) by the addition of more species of Leporinus, it will be possible to confidently establish the limits of the groups within the former genus Leporinus.Therefore, for the moment, we conservatively assign L. guttatus, and similar species, to the genus Leporinus (sensu Garavello & Britski, 2003).
The meristic data (e.g., scale and tooth counts), and the general color pattern (more than three large midlateral dark blotches along the body) of L. guttatus are also present in L. marcgravii, L. microphthalmus, L. octomaculatus and L. reticulatus.Nevertheless, in L. reticulatus the dark blotches have different shapes and arrangements (Fig. 6), and the snout is elongate, especially in large specimens (see Comments on Leporinus reticulatus below).The other three species have similar color pattern to the new species, but the blotches are fewer and the largest ones (six to seven in L. marcgravii and L. microphthalmus, or eight in L. octomaculatus, see Fig. 7), are distinctly larger, similarly sized, and aligned over the lateral line, and there is only one series of smaller blotches below the lateral line (inconspicuous or absent in some specimens) and one to two above the lateral line.
Comments on Leporinus reticulatus.Leporinus reticulatus was described by Britski & Garavello (1993) on the basis of 13 specimens from a single locality at riacho Formoso, a small creek in the rio Arinos drainage, in the upper rio Tapajós basin, Mato Grosso State.The specimens utilized for describing this uniquely colored species were very small, ranging from 38.2 to 72.5 mm SL, what let the authors to assume that this was a small sized species of Leporinus.In the last two years we have received collections of L. reticulatus from other localities in the upper rio Tapajós basin (see Comparative Material Examined), which included specimens up to approximately 140 mm SL.These larger specimens possess snout shape completely different, and color pattern slightly differ-ent from that of the type series of L. reticulatus.Therefore, those new specimens make a re-diagnosis of the species necessary.
Leporinus reticulatus is diagnosed by its unique color pattern characterized by a large number of dark blotches scattered on the body, blotches unequal in size and with irregular margins.Blotches usually arranged in transverse dark bars and disrupted by lighter markings in small specimens (up to 60 mm SL; Fig. 6b).In gradually larger specimens (60-80 mm SL), bars fragmenting forming blotches that become separated and irregularly scattered in large specimens (from 80 mm SL; Fig. 6a).In some of the lots (MZUSP 99736), relatively small specimens (around 60 mm SL) already have the same color pattern as described for adults.In addition to the color pattern, L. reticulatus is diagnosed by an elongate snout (especially in larger specimens), snout length 35-50% (mean 43%) of head length (snout length 47-50%, mean 48%, of head length, in specimens larger than 80 mm SL).Furthermore, L. reticulatus can be diagnosed by the following combination of subterminal (in specimens up to 100 mm SL) to subinferior (in specimens from 100 mm SL) mouth, dental formula 3/4, 35 to 37 scales in lateral line, 4/3.5-4.5 transversal series of scales, and 12 circumpeduncular scale series.
Noteworthy in Leporinus reticulatus is the allometric change in the length of snout.Gradually larger specimens (from 80 mm SL) undergo an elongation on the snout (comparatively much greater than associated structures, as for example, eye diameter).Figure 8 shows the allometric growth of the snout in relation to the SL in L. reticulatus.That change is also obvious when comparing snout proportions in two specimens of different sizes, for example, snout length 35% vs. 50% of head length, snout length 10% vs. 14 % of SL, and eye diameter 77% vs. 33% of snout length in a specimen of 42.5 (MZUSP 44782) and another of 135.6 mm SL (MZUSP 99736).Similar allometric development of the snout in any other Leporinus species was only noticed by Borodin (1929: Fig. 6.Leporinus reticulatus, a -MZUSP 99736, 135 mm SL, b -holotype, MZUSP 44781, 66.2 mm SL. 274-275), when he described L. crassilabris (see Borodin, 1929: plate 4 and fig.1), but unlike L. reticulatus, L. crassilabris is a rather large-size species, reaching at least up to 420 mm SL.
The elongation of the snout in Leporinus reticulatus is associated to the elongation of the entire suspensorium, especially the hyomandibula, quadrate, metapterygoid and interopercle; the elongation of the antero-dorsal portion of the cranium, especially the mesethmoid; and the rearrangement of several bones, especially the first and second infraorbitals.In smaller specimens the first infraorbital is parallel to the body axis, and the associated second infraorbital is relatively oblique to the body axis, with its posterior portion more ventral and longer than anterior one (Fig. 9a).In larger specimens the first infraorbital shift to an oblique position in relation to the body axis, with the anterior portion more ventral (than posterior one), directed to the mouth opening, and the associated second infraorbital shifts to a more or less parallel position (relatively to body axis) with the anterior portion longer than the posterior one (Fig. 9b).The most outstanding change is the increased thickness of the lips, and of the anterodorsal portion of the skin over the head.
The fourth and fifth infraorbitals are fused in the two examined clear and stained specimens of L. reticulatus.This is a rather uncommon feature for Leporinus, as several examined species does not possess such characteristic (i.e., L. amblyrhynchus, L. desmotes, L. fasciatus, L. friderici, L. julii, L. macrocephalus, L. obtusidens, L. striatus, L. trifasciatus).Leporinus guttatus and L. octomaculatus were the only other examined species that showed such fusion, what make this another interesting feature shared between these species.This feature is also present in L. megalepis and L. despaxi (Sidlauskas & Vari, 2008: 9), species with subinferior mouth as L. guttatus, L. octomaculatus, and L. reticulatus.

Fig. 5 .
Fig. 5. Rio Curuá, above the great falls, showing one of the collection sites of Leporinus guttatus.