Description of a new species of the genus Leporinus Spix ( Characiformes : Anostomidae ) from the rio Araguaia , Brazil , with comments on the taxonomy and distribution of L . parae and L . lacustris

A new species of the genus Leporinus is described from the rio Araguaia, in Mato Grosso and Goiás states, Brazil. The new species has the dental formula 4/3, a unique feature within the genus; all other species of Leporinus have dental formulae 3/3, 3/4 or 4/4. In addition, the new species can also be distinguished by the following combination of characters: 36 to 37 scales in the lateral line, 4/4.5 or 4/5 series of scales in the transversal line, 16 circumpeduncular scale series, anal fin surpassing base of lower caudal-fin rays and three blotches along the lateral line. The new species shares with L. parae and L. lacustris a rather deep body, terminal mouth, long anal fin, three small dark blotches on the lateral line, the latter two, particularly the last one, usually fading, and preference for lentic habitats. Comments on the taxonomy and distribution of the species L. parae and L. lacustris are provided.


Introduction
In 1995, Paulo Cesar Venere sent to Museu de Zoologia da Universidade de São Paulo (MZUSP) a collection of fishes made by himself in the rio Araguaia, eastern region of Mato Grosso, central Brazil, including different species of the genus Leporinus.This collection included three specimens of an undescribed species with a unique number of teeth in the jaws; however, considering the small number of specimens available, this species was not described at that time.In the year of 2005, another lot of this new species was deposited at MZUSP, with three specimens collected in the same area by members of the Central Brazilian Expedition (CBE).Since the new species was rediscovered, we contacted Paulo Cesar Venere who recently collected a few more specimens.On the basis of this material now in hands the new species can now be appropriately described.
The first paper on Leporinus from the rio Tocantins basin (including the rio Araguaia drainage) comes from Valenciennes (1850) who, based on material collected by Castelnau, described L. pachyurus and mentioned L. obtusidens and L. maculatus.Other papers by Castelnau (1855), Borodin (1929), Garavello (1979), Santos et al. (1984), Santos & Jégu (1989), Britski (1997), Garavello & Britski (2003), and Santos et al. (2004), reported a total of 18 species of Leporinus for the rio Tocantins basin, including two new species currently under description by Garavello & Santos (Garavello, pers. com.).This makes the rio Tocantins one of the richest in species of the genus Leporinus among all South American river basins.Britski & Garavello (1978), and Britski & Garavello (2005).The number of teeth is ex-pressed as a dental formula and represents the premaxillary number over the dentary counts in each half of the jaw.Counts of vertebrae were taken from radiographed specimens.Vertebral counts included the four vertebrae of the Weberian apparatus and the fused PU1+U1 of the caudal region (counted as a single vertebra).Lateral-line scale counts included the pored scales extending onto the base of the median caudalfin rays.Upper scale counts of transversal series represents the number of scale rows between the median dorsal row and the lateral line (i.e., the count starts at a point just in front of the dorsal-fin origin, and not at the dorsal-fin base, and does not include the median dorsal row); this procedure always eliminates the very confusing count of a half scale in this series.A half scale between the lateral line and the pelvic fin is only counted when the base of the pelvic-fin first ray faces the middle of the scale immediately in front of it.Meristic data of the holotype are indicated in the text by an asterisk.Institutional abbreviations includes: ANSP, Academy of Natural Sciences of Philadelphia; MZUSP, Museu de Zoologia da Universidade de São Paulo and USNM, United States Nation Museum, Smithsonian Institute.

Leporinus venerei, new species
Fig. 1 Diagnosis.Leporinus venerei is distinguished from its congeners by having 4 teeth on the premaxilla and 3 teeth on the dentary yielding the dental formula 4/3 (vs.3/3, 3/4 or 4/4 in all other species of Leporinus).Leporinus venerei is also diagnosed by the following combination of non-unique characteristics: presence of 36-37 pored scales in the lateral line, 4 scales in transversal series from origin of dorsal fin to lateral line and 4.5 to 5 scales from lateral line to base of pelvic fin; 16 series of scales around caudal peduncle; three round dark blotches on lateral line, the first at vertical through dorsal fin, the second at vertical through adipose-fin origin and the third at base of caudal peduncle (the latter two blotches, particularly the last one, usually small or inconspicuous).

Description.
See Table 1 for morphometric data of 21 examined specimens and Fig. 1 for lateral view of holotype.Small sized species for genus Leporinus, largest examined specimen 135.5 mm SL.Body rather elevated and compressed.Dorsal profile straight from anterodorsal portion of snout to posterior tip of supraoccipital; straight or very slightly convex from that point to dorsal-fin origin; straight along dorsalfin base; slightly convex or straight from dorsal-fin base to adipose fin and slightly concave from adipose fin to caudalfin origin.Ventral profile slightly convex from tip of lower jaw to pelvic-fin insertion, (convexity less pronounced below branchial region in some specimens); straight from pelvic-fin base to anal-fin origin; straight at anal-fin base and concave from anal fin to caudal fin.Greatest body depth at origin of dorsal fin.Head somewhat compressed; mouth terminal, anterior opening of mouth positioned at horizontal bisecting eye.Premaxillary with four teeth diminishing in size laterally from the symphyseal tooth.Dentary with three teeth also decreasing in size laterally.Teeth on both jaws of stair-step type.
Dorsal-fin rays ii+11* or iii+11; dorsal-fin origin slightly in front of vertical through pelvic-fin origin; dorsal-fin base extending through seven or eight scales.Pectoral-fin rays i+13, 14* or 15; pectoral fin extending to third or fourth scale anterior to pelvic-fin base.Pelvic-fin rays i+8; pelvic fin extending to four or five scale posterior to fin base.Anal-fin rays ii-9 or iii+9*; anal fin clearly surpassing base of lower caudal-fin rays; distal margin of anal fin straight or slightly convex.Length of last anal fin ray 26 to 47% (mean 36%) length of first branched anal-fin ray.Caudal-fin rays i+17+i; caudal fin forked, upper lobe slightly more developed than lower lobe.Vertebrae 34 (n=4) to 35 (3).
Ecological note.Leporinus venerei is found in lentic environments such as lagoons or borrow pits.
Etymology.The name venerei is given in honor to Paulo Cesar Venere who collected the first known specimens of this new species.

Discussion
The number of teeth in species of the genus Leporinus as discussed by Britski (1997), is a very important feature for the species diagnoses.The species of Leporinus are characterized by having three or four teeth on each premaxilla and dentary and, with the exception of the new species all of them can be placed into three artificial groups according to dental formula (i.e., species with 3/3, 3/4 or 4/4 dental formulae).We have been working exhaustively on Leporinus, examining hundreds of specimens of different species and we have found that variation in dental formula among co-specific individuals is exceptional.In most cases, discrepant individuals were considered anomalous because their teeth were asymmetric (i.e., having either one more or one less tooth on only one side of upper or lower jaw); discrepancy involving both sides of jaws was found only in few examined specimens of L. taeniatus from the rio São Francisco basin.This consistency in number of teeth in species of Leporinus strengthens the reliance of this character in species diagnoses.In addition, we consider it important to provide a list of known species of Leporinus grouped by dental formula: Dental formula 3/3: L aguapeiensis, L.amblyrhynchus, The following species have a doubtful number of teeth or the number of teeth is unknown: L. badueli, L. bleheri, L. jamesi, and L. latofasciatus.
We note that collectors must preserve specimens of Leporinus with mouth open, as they tend to close them very strongly when fixed in formaldehyde.Attempts at opening the mouth of fishes when so fixed usually lead to the breakage of the jaws, particularly the lower jaw, causing loss of the small lateral teeth and therefore making teeth counts unreliable.
There is no consistent hypothesis about relationships within species of Leporinus, a genus with large number of species presenting a great degree of variation in mouth position, tooth morphology and arrangements.Attempts to split Leporinus into subgenera (for example Borodin, 1929) are not presently accepted.Nevertheless, it is necessary to make some comments on similarities between the new species, Leporinus parae Eigenmann, and L. lacustris Campos.The latter two species share with L. venerei a deep body, terminal mouth, anal fin long and dark, and the three blotches on the lateral line small, with the latter two, particularly the last one, usually fading.
Leporinus parae Eigenmann, 1907 was described from the lower Amazon basin in Para state, Brazil.Measurements and counts were taken from 73 of the 279 examined specimens of L. parae from different localities (see comparative material which includes type material).This species is diagnosed by dental formula 4/4, 38 (n=22, including the type), 39 (52), 40 (9), and 41 (1) scales in the lateral line, 5/5 transversal series of scales, and 16 circumpeduncular series of scales (Fig. 1).These data are in agreement with the original description (Eigenmann & Ogle, 1907: 8); but, one of these characters differs from the text figure presented by those authors, as it shows a specimen with four series of scales between the lateral line and the dorsal fin.This should be interpreted as an inaccuracy of the drawer, since the type and all three cotypes have 5 scale series above the lateral line.Specimens of L. parae were found to occur throughout the Amazon and Orinoco basins (see comparative material, fig.2).In some fish collections, specimens from the Orinoco were previously identified as L. subniger Fowler, 1943, described from the Colombian Amazon.Leporinus subniger resembles L. parae in the terminal mouth, dental formula 4/4, and 16 series of scales in the caudal peduncle.Nevertheless, L. parae can be differentiated from L. subniger by the number of scales in the lateral line, 38 to 41 (vs.36 to 38 in L. subniger), 5/5 scales in transversal line [vs. 4/4;although Fowler (1943) mentioned 5/5 scales in transversal line in L. subniger, our examination and that of Garavello (1979), confirmed that there are in fact 4/4 scales series in the transversal line in that species], three dark blotches sometimes fading [vs.three dark blotches always present and supplemented by several smaller blotches over body, see Fowler (1943: figs 10-12 for drawings), or Böhlke (1958: plate 6, fig. 2 for a photographed specimen)], and deep body and short head (vs.body relatively shallower and head relatively larger).
Leporinus lacustris Campos, 1945 was described from the upper rio Paraná basin in São Paulo state, Brazil.Measurements and counts were taken from 109 of the 152 examined specimens of L. lacustris from the upper rio Paraná and rio Paraguay basins (see comparative material which includes type material, fig.2).The species is diagnosed by having dental formula 4/4, 33 (n=4), 34 (69, including the type), or 35 (36) scales in the lateral line, 4/4 or 4/5 transversal series of scales, and 16 circumpeduncular series of scales (Fig. 1).When describing L. lacustris Campos (1945:155) did not comment on the number of teeth and reported 3.5 scales in transverse series above lateral line and 32 to 34 scales in the lateral line.By our counts, the types have 4 and 33 to 34 scales, respectively.In addition, L. lacustris has fewer vertebrae (33, n=6), when compared to L. venerei n.sp.(34 to 35, n=7) and L. parae (35 to 37, n=6).
It is also worth mentioning that to our knowledge these three species are the only in the genus that show preferences for lentic habitats.