Moenkhausia rubra , a new species from rio Juruena , upper rio Tapajós basin , Brazil ( Characiformes : Characidae )

Moenkhausia rubra, new species, is described from the upper rio Juruena, rio Tapajós basin, Mato Grosso, Brazil. The new species is distinguished from its congeners, except M. hemigrammoides and M. nigromarginata, by the dark pigmentation on the anteriormost rays of both dorsal and anal fins. Moenkhausia rubra is distinguished from the aforementioned species by the number of branched anal-fin rays 17-20 (vs. 20-25), presence of a dark blotch on the caudal peduncle extending to middle caudal-fin rays, absence of longitudinal black zigzag stripes between longitudinal rows of scales on body, and other details of coloration.

During identification of material deposited in Laboratório de Ictiologia de Ribeirão Preto (LIRP), an undescribed species of Moenkhausia was recognized from rio Juruena, rio Tapajós basin, which is herein formally described.

Material and Methods
Morphometric and meristic data follow Fink & Weitzman (1974) except for counts of scale rows, which follow Lima et al. (2007) and with the addition of pelvic-fin origin to anal-fin origin measured at origin of pelvic-fin through the anal-fin origin.Measurements were taken with a digital caliper.Standard length (SL) is given in millimeters (mm), and morphometric data is given as percentage of SL, or head length for head subunits.The vertebrae of the Weberian apparatus were counted as four elements, and the PU1 + U1 as one element.Counts of maxillary teeth cusps, number and cusps of small dentary teeth, vertebrae, supraneurals, pterygiophores of dorsal and anal fins, procurrent caudal-fin rays, and gill-rakers of the first gill-arch were taken from cleared and stained (c&s) paratypes prepared following the method of Taylor & Van Dyke (1985).Sex was determined based on the pelvic-fin elongation and confirmed by direct examination of gonads in 10 specimens following the methodology described by Vazzoler (1996).In the description, counts are followed by their frequencies in parentheses with an asterisk indicating the count of the holotype.Institutional abbreviations follow Ferraris Jr. (2007).
Color in alcohol.Background body coloration pale yellow (Fig. 1).Dorsal and dorsolateral portion of head grey with dark chromatophores scattered on dorsal surface of head, opercle and infraorbital bones.High concentration of dark chromatophores on dorsal midline of body, from tip of supraoccipital spine to anteriormost dorsal procurrent ray.
Diffuse, dark and round humeral spot with borders not well delimited, extending horizontally along two to three scales, and vertically by three scale rows.Diffuse longitudinally stripe extending along flanks from humeral spot to median caudal-fin rays, more diffuse anteriorly, gradually wider posteriorly.Stripe wider at caudal peduncle and extending onto middle caudal-fin rays.Unbranched and first to third anteriormost branched dorsal-fin rays with dark chromatophores along its length, densely concentrated on its distal portion; remaining rays with few scattered dark chromatophores along their length.Unbranched and first to fifth anteriormost branched anal-fin rays with dark chromatophores along their length, densely concentrated on distal portion; remaining rays with few scattered dark chromatophores along its length.Caudal, pectoral, and pelvic fins with few scattered dark chromatophores mainly on interradial membranes.Color in life.Overall background color ranging from yellowish to reddish, mainly on mid-dorsal area (Fig. 3).Midventral area silvery.Snout and gular area orange.Eye mostly orange, dorsal portion blue to green.Opercular region and circumbital bones silvery.Dark longitudinal stripe at mid-body.Humeral spot round and diffuse.Pectoral and pelvic fins hyaline.Anal and dorsal fins with unbranched and first to third branched anteriormost rays with dark marks.Dorsal, adipose, and caudal fins intense orange to reddish, except for distal hyaline portion on dorsal and caudal fins.
Sexual dimorphism.Males and females/immature specimens were sexed based on the pelvic-fin elongation (Fig. 4).Sex was confirmed by dissection in 10 specimens (male n=5; female n=5).Adult males with pelvic-fin rays slightly longer than females or juvenile specimens, with pelvic-fin length ranging from 17.4-19.5% of SL in mature males (vs.14.7-17.6%SL in mature females/immature specimens).Bony hooks were not observed on fins of any analyzed specimen.Distribution.Moenkhausia rubra is known from rio Juína and rio Juruena, rio Juruena basin, upper rio Tapajós drainage, Mato Grosso State, Brazil (Fig. 5).
Etymology.From the latin ruber (red), in allusion to the reddish coloration of the body, and the dorsal, adipose, and caudal fins in live specimens.An adjective.

Discussion
Although some recent works dealing with the phylogeny of the Characidae have included species of Moenkhausia (e.g., Mirande, 2010;Oliveira et al., 2011, Mariguela et al., 2013), no published account has delved into the definition of the genus which therefore still lacks a phylogenetic definition.Thus, the new species described is herein assigned to Moenkhausia according to the traditional definition of the genus proposed by Eigenmann (1917).
Overall body and life coloration of Moenkhausia rubra resembles M. aurantia Bertaco, Jerep & Carvalho and M. nigromarginata (Fig. 6), both from upland areas of the Brazilian shield (M.aurantia: upper rio Tocantins basin and M. nigromarginata: upper rio Tapajós basin).The new species differs from M. aurantia by the presence of dark pigmentation on the anteriormost rays of anal and dorsal fins and by having fewer number of branched anal-fin rays 17-20 (vs.21 or more).Moenkhausia rubra is further distinguished from M. aurantia by the length of the anal fin ranging from , and by having the pectoral, pelvic and anal fins hyaline in life (vs.reddish).The new species can be diagnosed from M. nigromarginata by the absence of longitudinal black zigzag stripes on both sides of body (vs.presence), and by the absence of dark pigmentation on lateralmost rays of pectoral fins (vs.presence).
The new species was syntopically collected with six other congeners: Moenkhausia lopesi Britski & Silimon, M. cosmops Lima, Britski & Machado, M. cotinho Eigenmann, M. oligolepis Günther, M. phaeonota Fink, and M. pirauba Zanata, Birindelli & Moreira.Besides the absence of dark pigmentation on the anteriormost rays of dorsal and anal fins of the aforementioned species, M. rubra is readily distinguished from M. cosmops, M. oligolepis, and M. pirauba by having 33-34 scales scales on longitudinal series (vs.32 or fewer in M. cosmops, M. oligolepis, and 43 or more in M. pirauba), from M. cotinho by the caudal spot extending posteriorly to the distal margins of the middle caudal-fin rays (vs.not reaching the distal tip of the middle caudal-fin rays), from M. lopesi by the presence of a dark and round humeral spot (vs.humeral spot absent), and from M. phaeonota by the absence of a dark, broad stripe, from the opercle to the end of the caudal peduncle (vs.presence).
In most characids the dorsal and anal fins are hyaline (e.g., Géry, 1977), however several species (e.g., "rosy tetra" species) present dark pigmentation in these fins ranging in size, shape, and position of marks.The evolutionary meaning of these characters have been little studied in Characidae, yet the presence of dark marks in fins seems to have been independently acquired in different lineages of characids.The presence of dark pigmentation along the length of first rays of both the dorsal and anal fins, as found in Moenkhausia rubra (Fig. 1), is uncommon among other Moenkhausia species, with only M. hemigrammoides and M. nigromarginata (Fig. 6b) presenting a condition that resembles the one found on the new species.Nevertheless, the position and shape of the dark marks on the dorsal and anal fins of M. hemigrammoides are similar to the condition found in Hemigrammus unilineatus (Gill), and differs from that seen in M. rubra and M. nigromarginata.In M. hemigrammoides the dark mark of the dorsal fin covers all the dorsal-fin rays (vs.covering up to four anteriormost dorsalfin rays in M. rubra and M. nigromarginata) and the anal-fin dark mark is oblique to the main axis of the fin (vs.perpendicular to the main axis in M. rubra and M. nigromarginata).

Fig. 5 .
Fig. 5. Distribution of Moenkhausia rubra.Black star represents type locality.Symbols may represent more than one lot.