Characidium xanthopterum ( Ostariophysi : Characiformes : Crenuchidae ) : a new species from the Central Brazilian Plateau

Characidium xanthopterum is described from tributaries of the upper rio Paraná and upper rio Tocantins basins, in the Central Brazilian Plateau, Goiás State, Brazil. The new species is diagnosed among congeners by the absence of dark bars on the sides of the body in adult specimens, and by the deep yellow coloration in all fins. Ontogenetic change of color pattern is recorded for the first time for Characidium species. Specimens smaller than 32 mm SL possess dark bars on body. These bars disappear with growth between 32 and 35 mm SL, and are always absent in individuals larger than 35 mm SL.


Introduction
The genus Characidium Reinhardt contains 51 valid species of small (smaller than 10 cm SL) fishes distributed in most freshwater drainages from eastern Panama to Argentina (Buckup, 2003).The alpha-taxonomy of the genus is still poorly known, and several species have been described in the last few years (e.g., Buckup & Reis, 1997;Buckup & Hahn, 2000;Zarske & Géry, 2001;Melo & Buckup, 2002;Taphorn et al., 2006;Graça et al., in press).Buckup (1993b) provisionally diagnosed Characidium (in a phylogenetic sense) by the presence of a black spot near the base of the middle caudalfin rays.Melo & Buckup (2002) described Characidium stigmosum from the rio Paranã drainage (rio Tocantins basin), remarking that it was the first species of Characidium described from northern areas of the Brazilian State of Goiás, which is located in the Central Brazilian Plateau, an area drained by headwater tributaries of three major South American river basins (Paraná, São Francisco, and Tocantins).An additional species of Characidium from the Central Brazilian Plateau is described herein.It has been collected in tributaries of the upper Paraná and upper Tocantins river basins in the Brazilian State of Goiás.Currently, only four species of Characidium have been formally referred to the upper rio Paraná drainage outside of the Central Brazilian Plateau, Characidium fasciatum Reinhardt, C. gomesi Travassos, C. oiticicai Travassos, and C. schubarti Travassos (Buckup, 2007).Except for C. stigmosum, no other species of Characidium has been formally described from the Tocantins drainage.

Materials and Methods
All measurements were taken with a digital caliper to the nearest 0.01 mm under a stereomicroscope.Definitions of measurements, counts and the descriptive protocol follow Buckup (1993a).Measurements and counts of bilateral structures were obtained on the left side of the specimens.Counts in the text are followed by their frequency in parentheses, and an asterisk indicates values for the holotype.The sex of some specimens was confirmed by dissection.Specimens were cleared and stained according to procedures of Taylor & Van Dyke (1985).Skeletal and tooth counts were taken from cleared and stained (cs) specimens only.Counts or osteological characters from cleared and stained specimens refer to left/right side, respectively.Morphometric data are presented only for specimens larger than 25 mm standard length (SL).The dissection protocol follows Weitzman (1974), except for the ceratohyals, hypohyals and associated branchiostegal rays, which were left attached to the branchial apparatus.Institutional abbreviations are listed in Leviton et al. (1985), with the exception of DZSJRP (Coleção de Peixes do Departamento de Zoologia e Botânica de São José do Rio Preto), and NUP (Coleção Ictiológica do Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura, Universidade Estadual de Maringá).The abbreviation "mun."stands for the Brazilian Portuguese word município (municipality).

Characidium xanthopterum, new species
Figs. 1-3 Characidium sp.Pavanelli et al., 2007:60 [Brazil, Goiás,   compressed.Dorsal profile convex between anterior tip of snout and dorsal-fin origin, except for small concavity at supraoccipital process, almost straight between bases of dorsal and caudal fins.Ventral profile convex from lower lip to pelvic-fin insertion, straight between pelvic-fin insertion and anal-fin origin, slightly concave from anal-fin origin to caudal-fin base.Snout rounded in dorsal view, its tip aligned with ventral margin of orbit.Mouth small, terminal; maxilla moderately elongate, reaching vertical line through anterior third of orbit.Orbit slightly larger than snout length.Cheek shallow, its depth about half of orbit diameter.Nares distinctly separated; posterior naris closer to eye than to anterior naris; margin of anterior naris raised, forming circular rim, without dermal flaps; posterior naris directed backwards, with rim raised and not forming dermal flaps.
Orbitosphenoid slightly rectangular in lateral view, connected anteriorly to rhinosphenoid, with free posterior-ventral margin concave.Pterosphenoid foramen for ophthalmic nerve relatively small, formed by tunnel crossing pterosphenoid diagonally, bordered ventrally by bony crest that conceals the brain cavity from lateral view.

Color in alcohol.
Ground color of head and body brownpurple.Opercular bones and pectoral girdle pale yellow.Chromatophores distributed over entire surface of head, sparse at gular area; dorsal portion of head and body dark, lighter ventrally.All scales, except ventral ones, with chromatophores concentrated at their posterior margin, forming checkered pattern.Adult specimens with brown, dark and pale yellow pigmentation, uniformly checkered, except for inconspicuous midlateral longitudinal stripe, positioned slightly above lateral line.Dark humeral blotch usually conspicuous, vertically elongate.Dark, oblique stripe extending from upper lip to anterior margin of orbit.Black spot slightly vertically expanded near base of middle caudal-fin rays inconspicuous or absent.All fins pale yellow.Specimens smaller than 32 mm SL with eight to 11 vertical bars on sides of body, shaped as inverted isosceles triangles, darker on dorsal portion; humeral blotch partially merged into first bar; black, thin stripe present; dark spot present at base of middle caudal-fin rays.Fins hyaline, with scattered chromatophores along rays (Fig. 2).
Color in freshly preserved specimens.Body almost entirely brown-reddish; cheek, opercular region, and lateral portion of pectoral girdle yellow; fin rays bright yellow.Dorsal portion of head, opercle, and humeral blotch conspicuously dark.Inconspicuous, narrow midlateral longitudinal stripe, running slightly above lateral line, from humeral blotch to caudal peduncle.
Sexual dimorphism.Mature males with sexual hooks on unbranched and branched rays of pectoral and pelvic fins (most evident in MNRJ 11481).Small, inconspicuous hooks observed on pelvic-fin rays of immature males.

Geographic variation.
The description above is based on specimens from the upper rio Paraná basin.To provide comparative morphometric data, specimens from the upper rio Tocantins basin were also measured (Additional examined specimens; Table 1).These specimens differ in the number of scale rows around the caudal peduncle (12 or 14, mode=14 vs 10 or 12, mode=12 in specimens from the upper Paraná basin) and deeper cheek (7.1-10.1, mean= 8.3 vs 10.4-19.8, mean=15.1% of head length in specimens from the upper rio Paraná basin).Due to the overlap and individual variation of meristic data between the samples from these two river drainages, the upper Tocantins population is not considered a different species.

Distribution and habitat.
Characidium xanthopterum is known from tributaries of the rio Paranaíba drainage, upper rio Paraná basin, and tributaries to the upper rio Tocantins basin in the State of Goiás, Brazil (Fig. 3).Most specimens were collected in habitats with riffles, rocky bed with pebbles, and sand deposits.(24.7-33.2, mean = 28.6 vs 18.4-30.7,mean = 26.5% SL), a deeper cheek (10.4-19.8,mean = 15.1 vs 5.7-12.0,mean = 7.7% HL), and a smaller orbital diameter (25.6-33.4,mean = 28.7 vs 28.5-37.9,mean = 34.0%HL).Juvenile specimens from the remaining Characidium species occurring at the upper rio Paraná basin, such as C. fasciatum and C. gomesi, also possess a similar color pattern, but can be easily distinguished from C. xanthopterum by the lack of scales in the isthmus.
Adult males of Characidium occidentale, C. orientale, C. rachovii, and C. vestigipinne are reported as possessing bright orange or red-colored fins (Buckup & Hahn, 2000).In contrast, all fins of Characidium xanthopterum are deep yellow colored in males and females of all size classes.Characidium xanthopterum, however, also lacks the synapomorphy listed by Melo & Buckup (2002) for a putative monophyletic clade that includes those species and C. stigmosum (i.e., black pigmentation of distal portion of anal and pelvic fins).

Fig. 3 .
Fig. 3. Map of central Brazil, showing distribution of Characidium xanthopterum.Arrow indicates type-locality (Caldas Novas, Goiás State, upper rio Paraná basin), complete circles represent localities in the upper rio Paraná basin, and open circles represent localities in the upper rio Tocantins basin.Symbols may represent more than one lot or locality.