Gephyrocharax torresi (Characiformes: Characidae: Stevardiinae), a new species from the río Cascajales basin, río Magdalena system, Colombia

A new species of Gephyrocharax is described from the río Cascajales basin, a tributary of the río La Colorada, río Magdalena system, Colombia. The new species is distinguished from its congeners, except G. melanocheir, by the absence of an adipose fin in most specimens and by the possession of a lateral branched pectoral-fin ray in males with a distal fan-shaped structure with minute bony hooks and a dark blotch or a few scattered dark brown chromatophores along its branches. The new species differs from G. melanocheir by the absence of an intense black pigmentation at the base of the anterior five dorsal-fin rays, the number of vertebrae (40-41 vs. 38-39), the frontals contacting each other anterior to the epiphyseal bar in adults (vs. the absence of contact), the posterior margin of the mesethmoid straight in its central portion (vs. strongly concave at this point), the pouch scale of mature males reaching caudal-fin ray 11 or the area between caudal-fin rays 11 and 12 (vs. reaching only to caudal-fin ray 10 or the area between caudal-fin rays 9 and 10), the number of minute terminal branches of the lateral branched pectoral-fin ray of mature males (60-88 vs. 28-54), a longer black lateral stripe along the body in males (reaching to the base of the caudal-fin rays vs. reaching the middle of the length of the caudal peduncle), and the snout length (28.3-31.8% HL vs. 22.2-28.0% HL). The diagnosis of Gephyrocharax is modified to include species with the adipose fin variably present.


Introduction
Gephyrocharax Eigenmann is the most speciose genus of the tribe Stevardiini, containing twelve valid species (Weitzman & Menezes, 1998;Weitzman, 2003;Menezes & Weitzman, 2009). Species of Gephyrocharax are widely distributed through rivers and creeks of both cis-and trans-Andean basins in southern Central America and South America (Schultz, 1944;Weitzman, 2003).
Gephyrocharax caucanus Eigenmann, G. martae Dahl, and G. melanocheir Eigenmann (Eigenmann, 1912;Dahl, 1943) are the three currently recognized species of the genus in the ríos Cauca-Magdalena system (Schultz, 1944;Weitzman, 2003). Gephyrocharax caucanus occurs in the upper río Cauca, whereas G. martae and G. melanocheir are known from the río Magdalena basin; the latter species being widely distributed in that basin (Eigenmann & Myers, 1929;Miles, 1947;Dahl, 1971), the Lago Maracaibo basin (Taphorn & Lilyestrom, 1984) and some coastal Caribbean versant drainages (Bonilla-Rivero & López-Rojas, 2001). Gephyrocharax melanocheir is distinguished from G. caucanus and G. martae mainly by the presence of a spot of intense black pigmentation at the base of the anterior five dorsal-fin rays in both sexes. Specimens from the río La Colorada basin in the río Magdalena system previously identified as G. melanocheir lack this conspicuous and intense pigmentation and represent a new species of Gephyrocharax described in the present paper.

Material and Methods
The material examined is deposited in the following collections: Asociación Ictiológica, La Plata (AI); American Museum of Natural History, New York (AMNH); Academy of Natural Sciences, Philadelphia (ANSP); California Academy of Sciences, San Francisco (CAS); private collection Carlos Ardila-Rodriguez, Barranquilla (CAR); Colección de Ictiología, Universidad de Antioquia, Medellín (CIUA); Ictiología, Colección Zoológica, Universidad del Tolima, Ibagué (CZUT-IC); Field Museum of Natural History, Chicago (FMNH); Instituto de Ciencias Naturales, Museo de Historia Natural, Universidad Nacional de Colombia, Bogotá (ICNMHN); Ictiología, Colección Zoológica, Measurements and counts follow Fink & Weitzman (1974) and Menezes & Weitzman (2009), with the addition of the distances from the dorsal fin to the pectoral fin (from the base of first unbranched dorsal-fin ray to the base of unbranched pectoral-fin ray), the dorsal fin to the adipose fin (from the base of the first unbranched dorsal-fin ray to the anterior most point of the base of the adipose fin), the pectoral fin to the pelvic fin (from the base of the unbranched pectoral-fin ray to the base of the unbranched pelvic-fin ray), the pelvic fin to the anal fin (from the base of the unbranched pelvic-fin ray to the base of anterior most externally visible anal-fin ray) and the postorbital head length (from the posterior border of the eye to the posterior most point of the bony opercle). The gill-gland length was measured between its anterior and posterior most margins in males. Measurements were taken point to point with a digital caliper under a stereomicroscope and are expressed as percentages of standard length (SL) or head length (HL) for subunits of the head.
Frequency of a particular character value is presented in parentheses with the holotype value indicated by an asterisk. The scales of the median dorsal row and the small scales situated just below the insertion of the anterior most dorsalfin ray are excluded from the counts 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 counts were determined in c&s specimens and radiographs. These include the first preural centrum plus first ural centrum (PU1+U1) counted as one element and the four vertebrae of the Weberian apparatus.
Statistical analyses were performed using PAST 2.15 (Hammer et al., 2001) and SigmaPlot 10.0 for Windows (2006, Systat Software, Inc.) for morphometric variables. The Shapiro-Wilk test was used to test the normality of taken measurements. The non-parametric test of Spearman correlation was performed between the standard length and gill-gland length for the males of the new species. A significant p-value < 0.05 was used to the bivariate statistical tests. The descriptions of sexually dimorphic characters are complemented by regression plots of caudal-peduncle length, pectoral-fin to pelvic-fin length, caudal-peduncle depth, and pelvic-fin length (all as function of SL). Diagnosis. Gephyrocharax torresi is readily distinguished from its congeners (except G. melanocheir) by the absent or vestigial adipose fin (vs. the presence of a well developed adipose fin), the form of lateral branched pectoral-fin ray of males which has a highly developed branching pattern that distally forms a fan-shaped structure with minute branches (vs. less extensive branching pattern not distally forming a fan-shaped structure with such minute branches), and the distal portion of this pectoral-fin ray in males with minute bony hooks (vs. hooks absent) and a dark blotch or a few scattered dark brown chromatophores along its branches (vs. blotch or chromatophores absent). Gephyrocharax torresi differs from G. melanocheir by lacking intense black pigmentation at the base of the anterior five dorsal-fin rays (vs. the presence of such pigmentation), the number of vertebrae (40-41 vs. 38-39), the frontals contacting each other anterior to epiphyseal bar in adults (vs. the absence of contact), the posterior margin of the mesethmoid straight in its central portion (vs. strongly concave at this point), the pouch scale of mature males reaching caudal-fin ray 11 or the area between caudal-fin rays 11 and 12 (vs. reaching only to caudal fin ray 10 or the area between caudal-fin rays 9 and 10), the number of minute terminal branches of the lateral branched pectoral-fin ray of mature males (60-88 vs. 28-54), the longer midlateral black body stripe in males (reaching to the base of the caudal-fin rays vs. reaching to the middle of the caudal peduncle), and the snout length (28.3-31.8% HL vs. 22.1-28.0% HL).

Gephyrocharax torresi, new species
Description. Morphometric data in Table 1. Largest male 37.3 mm SL and largest female 42.0 mm SL. Body laterally compressed, with maximum depth at vertical through pelvicfin origin. Dorsal profile of head slightly convex from margin of upper lip to tip of supraoccipital spine. Dorsal profile of body straight from posterior portion of supraoccipital spine to dorsal-fin origin, slanting posteroventrally along dorsal-fin base, straight from posterior most dorsal-fin ray to caudal peduncle ( Fig. 1). Ventral profile of body convex from tip of snout to pectoralfin origin, slightly convex between vertical through pectoral-fin and pelvic-fin origins, slanting posterodorsally and straight from this point to caudal peduncle. Anterior fontanel absent or reduced to narrow opening anterior to epiphyseal bar. Anterior nostril rounded and separated by skin fold from larger posterior nostril. Groove with at least three rows of neuromasts extending from point half way between posterior pore of nasal bone and nostrils to posterior portion of frontals. Smaller groove with few neuromasts between nostrils and nasal bones. Dorsal-fin rays ii,7* (14) or 8 (23); proximal pterygiophores 9. Dorsal-fin origin located at vertical through base of analfin rays 5 to 8. Adipose fin reduced in size (6) or absent* (31). When present, adipose fin located at vertical through base of four or five posterior most anal-fin rays. Anal fin with 4* (30) or 5 (7) unbranched rays followed by 26 (1), 27 (4), 28 (9), 29* (14), or 30 (9) branched rays. Anal-fin proximal pterygiophores 29-30. Anal-fin origin closer to origin of hypural joint than to snout tip. Pectoral-fin rays i,8 (5), 9 (25), 10* (6), or 11 (1). Pectoral fin long, extending posteriorly to one-third or more of vertical through pelvic-fin origin. Pelvic-fin rays i,6* (37). Pelvic-fin origin located at vertical through lateral-line scales 9 to 11 and slightly anterior to midpoint of body. Caudal fin forked with 10/9 principal rays in all specimens.

Color in alcohol.
Ground color pale yellowish, darker along mid-dorsal line and slightly lighter ventrally. Minute brown chromatophores completely covering body. Black lateral stripe extending from posterior region of opercle to central or posterior portion of caudal peduncle. Dark brown chromatophores present along myosepta between lateral line and upper portion of anal fin. Humeral spot vertically elongate. Large dark brown spot on caudal peduncle. Dorsal fin dusky with dark brown chromatophores concentrated on rays and membranes. Anal fin dusky with dark brown and black chromatophores located on membranes: chromatophores on anterior and distal portions of fin usually more densely concentrated in males. Caudal fin hyaline with few scattered, dark brown or black chromatophores on rays and membranes. Pectoral and pelvic fins hyaline with scattered black chromatophores on rays. Head darker dorsally. Few dark brown chromatophores distributed on opercle and infraorbitals. Premaxilla, anterior portions of maxilla, dentary, and lips with dark brown chromatophores. Snout heavily pigmented by dark brown chromatophores. Variations in color pattern between males and females discussed under sexual dimorphism.

Sexual dimorphism.
Male, but not female, specimens of Gephyrocharax torresi with bony hooks on rays of anal, caudal, pectoral and pelvic fins. Caudal fin with short, slender anterodorsally oriented hooks on unbranched  portions and dorsal branches of rays 14-18 (Fig. 4). All rays of pelvic fin with slender, anterolaterally oriented hooks along nearly entire length of each ray; usually one pair per segment. Pectoral fin with few scattered, minute bony hooks on distal portion of lateral branched ray. Anal fin with slender, anterodorsally placed hooks with broad bases, one pair per segment. From three to 12 pairs of hooks located on posterior most unbranched and up to first seven branched rays. Posterior most unbranched and first 18 branched anal-fin rays gradually decreasing in length in males; females with posterior most unbranched and anterior 1-3 branched anal-rays longer than remaining rays. Mature females with large, usually posteroventrally oriented, conical urogenital papilla (Fig. 1b).
Caudal spot of males only reaching base of caudal-fin rays but extending over middle caudal-fin rays in females. Males with caudal spot chromatophores bounding pouch scale dorsally but leaving clear area in lower portion of caudal peduncle, whereas females with that spot extending completely onto caudal peduncle. Lateral stripe of males bounding caudal spot dorsally versus ending on anterior or middle portions of caudal spot in females. Males differ from females in presence of dark blotch or few scattered dark brown chromatophores on distal portion of lateral branched pectoral-fin ray but rarely on contiguous proximal ray. Distal portion of lateral branched pectoral-fin ray modified in both sexes; branching more complex in males. In males, posterior half of external branched pectoral-fin ray thicker, splitting into two equal branches; each branch dividing into three smaller branches and each one of these six branches splitting further to form distal structure with 60 (1), 61 (1), 62 (2), 64 (1), 70 (3), 72* (1), 78 (1), or 88 (1) minute branches (Fig. 3). In females, lateral branched pectoral-fin ray splits into two principal branches; outer branch divides into four short branches and inner into three short branches. Each of these seven slender branches usually splits one more time.
Males with modified scale forming pouch on lower lobe of caudal fin and with ventral procurrent rays 2 and 3 in form of a claw-shaped structure immediately ventral to ray 9 of lower lobe of caudal fin (lower caudal fulcra free and forming peculiar spur described by Eigenmann, 1912). Tissue of glandular appearance located on caudal-fin rays and medially to pouch scale. Second ventral procurrent ray somewhat longer than third ray. Claw-shaped structure incompletely ossified distally; claw reaching half length of first ventral procurrent ray (Fig. 4). Hypertrophied pouch scale usually with 26 or 30 radii; first 22 radii often located between caudal-fin rays 17 or 18 and second ventral procurrent ray, remaining radii distributed from that point to lateral border of third ventral procurrent ray. Posteroventral portion of pouch scale fused to third ventral procurrent ray. Dorsal surface of pouch scale attached via soft tissue to caudal-fin rays 9 to 15. Posterior margin of pouch scale located between caudal-fin ray 15 and third ventral procurrent ray. Four or five scales in vertical series just below posterior most lateral-line scale and on posterior portion of pouch scale. Median scale with undulated margin located between these scales and pouch scale. Series of minute spinous processes forming patch on dorsal portion of pouch scale. Females with large scale with 20 (1), 21 (3), 22 (2), 24 (2), 26 (2), 27 (1), 28 (2), or 29 (3) radii on lower caudal-fin lobe.
Etymology. The species name torresi is treated as a patronym in gratitude and recognition of Mauricio Torres who collected the material on which the description is based.

Discussion
Gephyrocharax was described by Eigenmann (1912) based on the following characters: "Premaxillary teeth in two distinct series, five teeth in the inner series. Second suborbital covering the entire cheek. Caudal without glandular scales, the lower caudal fulcra free and forming a peculiar spur in the male. Adipose fin present. Origin of dorsal nearer to caudal than the eye, considerably behind the vertical from origin of anal, pectorals large, overlapping the ventrals". Subsequently, Myers (in Eigenmann & Myers, 1929: 477) revised Gephyrocharax and added the character "frontal fontanel present or absent" as part of his diagnosis of the genus. Schultz (1944) and Dahl & Medem (1964) apparently followed Myers's diagnosis of Gephyrocharax.
All the previously described species of Gephyrocharax share the presence of a well-developed adipose fin, a feature widespread among the Characidae. The adipose fin is lacking or much reduced in G. torresi and as such the occurrence of an adipose fin is intragenerically variable. Mirande (2010: 548) proposed two unambiguous losses of the adipose fin within the Characidae: in the Gymnocharacinae and in Phenagoniates macrolepis (Meek & Hildebrand), neither of which is closely related to the Stevardiinae.  Gephyrocharax torresi and G. melanocheir (Fig. 7) are morphologically rather similar and share, among other characters, the presence of minute hooks and the highly developed branching pattern on the distal portion of the lateral branched pectoral-fin ray in mature males (although this pattern is more complex in terms of number of branches in G. torresi than in G. melanocheir: 60-88, mode = 70, n = 10; 28-54, mode = 42, n = 15, respectively). Neither the remaining species of Gephyrocharax nor Corynopoma Gill and Pterobrycon Eigenmann (genera closely related to Gephyrocharax) were observed to have these features. Thus, these features shared by males of G. torresi and G. melanocheir are putative synapomorphies grouping them as sister species. A more extensive phylogenetic analysis of Gephyrocharax is necessary to test this hypothesis.