Chrysobrycon eliasi , new species of stevardiine fish ( Characiformes : Characidae ) from the río Madre de Dios and upper río Manuripe basins , Peru

Chrysobrycon eliasi is described from several drainages of río Madre de Dios and upper río Manuripe basins, río Madeira basin, Peru. The new species is distinguished from its congeners by the maxillary teeth, which are tricuspidate, bicuspidate and conical, and the terminal lateral-line tube developed between caudal-fin rays 10-11. Other characters that help to recognize C. eliasi are the possession of maxilla with 6-15 (usually 11) teeth occupying more than 70% of the length of the maxilla in adults, predorsal scales 18-22, dorsal-fin to hypural complex length 36.32-41.17% of standard length (SL), gill-gland length in males 3.57-5.05% SL, maxillary length 33.76-38.75% of head length, and branched anal-fin rays 24-30. The discovery of C. eliasi allows us to extend the geographic distribution of the genus to the southeast, into the río Madeira basin.

The genus has been considered a basal member of the monophyletic tribe Xenurobryconini (Weitzman & Menezes, 1998;Castro et al., 2003;Weitzman et al., 2005;Menezes & Weitzman, 2009;Mirande, 2009Mirande, , 2010)), defined by the presence of a single large pouch scale, with or without hypertrophied radii in males, a synapormophy reported by Weitzman & Menezes (1998).The same authors diagnosed the males of Chrysobrycon by the presence of a pouch scale, relatively small, somewhat elongate, curved and horizontally folded so that its lateral face forms a laterally concave, broadly open pocket; that pouch scale is confined to the dorsal region of the pouch opening; an additional curved scale is situated close to, and nearly completely against, the medially placed surface of the pouch scale, while this medially placed scale sometimes has its ventral border laterally curved around the ventral border of the pouch scale.Furthermore, the two Chrysobrycon species are characterized by the presence of gill gland (Bushmann et al., 2002), insemination habit, and spermatozoa with elongated nuclei (Burns et al., 1995).
Currently, the phylogenetic relationships and the geographic distribution of the Chrysobrycon species are unknown and poorly understood.One of the authors (JAV-R.),examined several lots from the Museo de Historia Natural (Universidad Nacional Mayor de San Marcos, Peru) and the Royal Ontario Museum (Canada), and found several samples identified as Gephyrocharax Eigenmann that actually belong to Chrysobrycon.Further comparisons among Chrysobrycon species confirmed that these specimens constitute a new species herein described; in addition, a key to Chrysobrycon species is provided.

Material and Methods
Measurements and counts are according to Fink & Weitzman (1974) and Menezes & Weitzman (2009), with the addition of the following measurements: dorsal-fin to pectoralfin length, dorsal-fin to adipose-fin length, pectoral-fin to pelvic-fin length, pelvic-fin to anal-fin length (all of them taken from origin to origin), maxillary length (most anterior visible point to posterior margin), and postorbital length.The gillgland length in males was measured from the most anterior to most posterior portions.Measurements were taken point to point with Mitutoyo digital caliper at 0.01 mm under stereomicroscope and are expressed as percentages of standard length (SL) or head length (HL).
In counts, the range is given first, the mode in parentheses, and the holotype counts marked by an asterisk, followed by the number of specimens counted.The scale on the median dorsal row or the small scale just below to dorsal-fin rays insertion is excluded from the count of longitudinal scale rows between the dorsal fin and lateral line.Specimens were cleared and counterstained (C&S) following Taylor & van Dyke (1985).Total vertebral count includes the four vertebrae of Weberian apparatus; preural centrum 1 plus ural centrum 1 (PU1+U1) were counted as one vertebral element.A key for identification of Chrysobrycon species is given based on the examined material; data from Weitzman & Thomerson (1970) was included only in the ranges of counts.
The statistical analyses were performed using PAST 2.07 (Hammer et al., 2001) and SigmaPlot 10.0 for Windows (2006, Systat Software, Inc.) for morphometrics and meristics variables.Tukey box plots were used to describe the variance of counts that showed differences among species and that were considered relevant to diagnose the new species and in the key.Morphometric data was log-transformed (base-10 log) before any subsequent statistical step mentioned herein.Hypothesis of statistical significance of t-test and F-test were of two-tailed, accomplished to compare means and variances among morphometrics variables by sexes into new species (p < 0.05).Test without statistical significance are not presented herein.Principal component analysis (PCA) of morphometric data was used to compare the variation between sexes of new species and among species of Chrysobrycon.Morphometric variables were processed using the covariance matrix.Given that the first component (PC1) is known to be associated to size (Marcus, 1988), the second and third principal component (PC2 and PC3, respectively) were used to analyze the differences in shape.Regression plots by sex were evaluated for each variable measured, but only the plots where the following two conditions are found, are presented herein: 1) evidence for a low overlapping in data, and 2) variables strongly affecting the PC2.
The material examined is deposited in the collections of AI, ANSP, CAS, LACM, and MUSM; acronyms are according to Eschmeyer (1998), except AI, Asociación Ictiológica, La Plata, Argentina.
Description.Morphometric data for holotype (Fig. 1) and 27 paratypes in Table 1.Largest male 39.90 mm SL, largest female 43.50 mm SL.Body laterally compressed, with maximum depth at vertical through half length of pelvic fin.Dorsal profile of body straight over head and convex from supraoccipital region to dorsalfin origin, slanting ventrally and slightly concave or smooth from last dorsal-fin ray to caudal peduncle.Dorsal profile of caudal peduncle straight.Ventral profile of body convex from tip of snout to pelvic-fin origin, slanting dorsally and straight from this point to caudal peduncle.Ventral profile of caudal peduncle straight.Dorsal-fin origin located at vertical through anal-fin rays 8 and 10.Adipose fin located at vertical through last anal-fin ray.Anal-fin origin situated in posterior half of body, always slightly anterior to dorsal-fin origin.Pelvic-fin origin slightly anterior to half length of body.Pectoral fin relatively long, its posterior tip reaching half length or about three quarters of pelvic-fin length (Fig. 2).
Head with anterior portion acute.Frontal fontanel absent.Epiphyseal branch of supraorbital canal absent.Nostrils somewhat rounded separated by one skin fold, posterior opening larger.Mouth superior, lower jaw projecting slightly anterior to upper jaw.Maxilla relatively short, not reaching posteriorly vertical through anterior border of pupil.
Color in alcohol.Ground color pale yellowish in preserved males and females, dorsally darker and slightly lighter ventrally.Scattered chromatophores over all body, dark brown and black, more concentrated dorsally, sometimes forming reticulate pattern.Dark black lateral band extended from   membranes and also on rays 1 and 19.Adipose fin hyaline sometimes with black chromatophores in its base.
Head dark brown dorsally and more yellowish ventrally.Chromatophores dark brown scattered on opercle and infraorbitals.Infraorbitals pale yellowish and sometimes slightly silver.Iris silvery.Maxilla with few chromatophores.Snout heavily covered by black chromatophores.
Sexual dimorphism.The males of Chrysobrycon eliasi are differentiated from females by the presence of bony hooks on rays of the caudal, pelvic, and anal fins.Caudal fin bears 6-21 tiny hooks, anterodorsally oriented on the posterior half of rays 13-17.All rays of pelvic fin bear short, slender hooks, anterolaterally placed almost all over the entire length of the rays; usually two pairs per segment, and more numerous on medial rays.Anal fin has 5-11 husky hooks; one pair per segment, anterodorsally placed on the last unbranched ray and branched rays 1-11; the number of hooks increases in middle rays.The males also differ from females by the presence of modified scales forming a pouch on the lower lobe of caudal fin (Fig. 4).The pattern of scales on the caudal fin includes a pouch scale, somewhat elongate, curved and horizontally folded with its lateral face forming a concave open pocket; the dorsal fold of the pouch scale forms the dorsal region of the pouch opening.An additional small and also curved scale is set under the pouch scale; it is shorter than the length of the pouch scale and its ventral border is not seen in the lateral view.The length of the scale is shorter than the length of the pouch scale.
Distribution.The new species is known from different localities of the río Madre de Dios basin and the upper río Manuripe basin, both flowing into the río Madeira basin, Peru (Fig. 8).

Ecological notes.
Chrysobrycon eliasi is usually found in dark water creeks at 210-250 m a.s.l., often slightly acid with pH ranging between 5.8 and 6.2, and characterized by soft substratum, including sand, clay and fallen leaves, surrounded by primary forest.
Etymology.The species is named as patronym in honor and memory to the late Elias Vanegas G., father of the senior author (J.V-R.).Remarks.Specimens of Chrysobrycon eliasi from río Tambopata (ROM 66378) were listed as non-type specimens.We did not find any clear differences between samples from río Tambopata and the type series, but some variation was found in the gill-gland length of males: 5.33-6.40%SL, n = 2 vs. 3.57-5.05%SL, n = 9, respectively.Statistical tests are not used herein because of the small number of specimens examined of that population; therefore, we considered them as non-type specimens.phylogenetic context describing a new genus, Chrysobrycon, mainly based on secondary sexual characters of males of these two species of Hysteronotus.Therefore the genus Chrysobrycon comprised two species, with C. hesperus as the type species by original designation.Chrysobrycon eliasi shares the synapomorphies described in the diagnosis of the genus.However, males of C. eliasi have a slightly different pattern of pouch scale, in which such scale completely covers the small additional scale under it, in such a way that the ventral border of the underlying scale is not seen in the lateral view.Chrysobrycon hesperus and C. myersi have an additional medial scale near to, and slightly surpassing, the ventral and posterior border of the pouch scale.Weitzman et al. (2005) commented that Chrysobrycon species lack the terminal lateral-line tube; however, C. eliasi has the terminal lateral-line tube developed between caudal-fin rays10-11 (Fig. 5).Mirande (2010) reported the presence of the terminal lateralline tube as synapomophy of the family Characidae.

Key to
Chrysobrycon eliasi is the smallest known species of the genus Chrysobrycon.The size of adult males of C. eliasi ranges between 27.58 and 39.90 mm SL.Weitzman & Thomerson (1970)    examined are also larger than those of C. eliasi, according to the above-mentioned records; this fact is more evident for both sexes of Chrysobrycon in the PC1 (Figs. 6a-b).Bushmann et al. (2002: table 2) observed that the gill-gland length measured in one male in each of several species of Xenurobryconini (including Chrysobrycon hesperus) does not surpass 3.00% of SL; nonetheless, the gill-gland length measured in males of C. hesperus in the present study corresponded to 3.16-5.50%SL, and C. eliasi and C. myersi also exhibited gill glands longer than the known values published for the tribe.Therefore, a comparison using a larger number of males is necessary, because of the scarce information about the gill-gland length, including its intraspecific variation.
The discovery of Chrysobrycon eliasi increases the geographic distribution of the genus to the southeast of the Amazon basin, where the three Chrysobrycon species are allopatric.Chrysobrycon hesperus and C. myersi (Fig. 9) were only known from their type localities (Böhlke, 1958;Weitzman & Thomerson, 1970).However the examination of paratypes of C. hesperus and C. myersi (ANSP 75914, 79512, and 112325) and the comparative study of Chrysobrycon specimens from different drainages of Ecuador and Peru, with data from original descriptions of both C. hesperus and C. myersi, supported the conclusion that C. hesperus and C. myersi have a larger geographic distribution than that previously known, and that distribution of all Chrysobrycon species should be studied more in detail.

Fig. 5 .
Fig. 5. Comparative Tukey box plots showing the variation of (a) number of branched rays of anal fin, (b) number of teeth in maxilla, (c) number of lateral-line scales, and (d) predorsal scales of Chrysobrycon eliasi, C. hesperus, and C. myersi.Number of specimens between parentheses.

Fig. 6 .
Fig. 6.Principal component analyses of morphometric data by sex of Chrysobrycon eliasi (a-b) and comparing Chrysobrycon species (c-d).PC1, PC2 and PC3 correspond to the first, second and third principal components, respectively.

Fig. 8 .
Fig. 8. Geographic distribution of Chrysobrycon eliasi.White circle indicates two localities, including type locality.The inset from upper part of figure is delimited by black line and correspond to a zoom of the rectangle indicate below it.

. 1-4
reported adult males of C. hesperus with SL between 63.40 and 81.80 mm, and adults males of C. myersi with SL between 36.50 and 49.60 mm.Males of C. hesperus (44.44-78.13mm SL) and C

Table 1 .
Morphometric data of holotype and 27 paratypes of Chrysobrycon eliasi from río Madre de Dios and Upper río Manuripe basins.n = number of specimens; SD = standard deviation.The values of the holotype are included in the range of males.