A new species of Hemibrycon (Characiformes, Characidae) from the upper San Juan River drainage, Pacific versant, Colombia

Abstract Hemibrycon sanjuanensis, new species, is described from the upper San Juan River drainage, Pacific versant, Colombia. It is distinguished from Hemibrycon boquiae, Hemibrycon brevispini, Hemibrycon cairoense, Hemibrycon colombianus, Hemibrycon mikrostiktos, Hemibrycon metae, Hemibrycon palomae, Hemibrycon rafaelense and Hemibrycon tridens by the presence of a circular or oblong humeral spot that is located two scales posterior to the opercle (vs. 3–4 scales in Hemibrycon palomae, Hemibrycon rafaelense, Hemibrycon brevispini and Hemibrycon cairoense, and 0–1 scales, in Hemibrycon metae and Hemibrycon boquiae). It further differs from Hemibrycon colombianus in having a round or oblong humeral spot (vs. rectangular). It differs from Hemibrycon beni, Hemibrycon dariensis, Hemibrycon divisorensis, Hemibrycon helleri, Hemibrycon huambonicus, Hemibrycon inambari, Hemibrycon jabonero, Hemibrycon jelskii, Hemibrycon mikrostiktos, Hemibrycon polyodon, Hemibrycon quindos, Hemibrycon raqueliae, Hemibrycon santamartae, Hemibrycon surinamensis, Hemibrycon taeniurus, Hemibrycon tridens, and Hemibrycon yacopiae in having melanophores on the posterior margins of the scales along the sides of body (vs. lacking melanophores on margins of scales along entire length of the sides of body). The new species differs from all congeners mentioned above in having, among other features, six teeth in the outer premaxillary row arranged in a straight line (vs. five or fewer teeth not arranged in straight line except Hemibrycon cairoense with two to six teeth in the outer premaxillary row).


Introduction
Today there are 36 species reported in the genus Hemibrycon (Eschmeyer and Fricke 2013). Of these, 21 species are distributed in Colombian watersheds, but only one species, H. dariensis, has been reported from the San Juan drainage on the Pacific coast. The present day distribution of Hemibrycon in Colombia suggests that this genus has its greatest diversity in Andean streams and high mountain habitats. But there are exceptions such as H. dariensis, which occurs in Pacific drainages, H. santamartae and Hemibrycon sp. n. found in northern Colombia, and H. metae from the upper Meta River drainage in the Orinoco River Basin (Bertaco and Malabarba 2010;Román-Valencia and Ruiz-C 2007;Román-Valencia et al. 2009a;Román-Valencia et al. 2013). The discovery of a new species of Hemibrycon from the upper San Juan River Basin, Pacific versant in Colombia, is a result of the authors' ongoing revision of Hemibrycon  and is further proof of undocumented biodiversity in the genus.

Material and methods
Fishes were captured using seines and were preserved in the field with 10% formalin and later stored in 70% ethanol. Measurements and counts follow Armbruster (2012) and . Measurements were made with digital calipers to 0.01 mm precision and are expressed as percentages of standard length (SL) and head length (HL). In reporting counts, values for the holotype are indicated with an asterisk (*). In the list of paratypes, the number of individuals is given immediately after the catalog number, which is followed by the range of SL in mm for that lot. Counts and measurements were taken on the left side of specimens when possible. A multivariate analysis was performed on the morphometric data with the PAST program, version 1.81 for Windows (Hammer et al. 2008), and a variable canonical analysis (CVA) was undertaken assuming allometric growth. All measurements were log transformed, correcting for size using Burnaby methods (Burnaby 1966) in the software PAST to adjust for or eliminate the influence of size and compensate for the allometric growth. In the CVA we included data for H. dariensis (n=71), which is allopatric with the new species in the San Juan River drainage and H. cairoense (n=46), which occurs in nearby watersheds. Morphological analysis based on bivariate or multivariate testing seeks to establish parameters (= morphological characters) for discriminating the closest species to the new taxon from other species present in the area of geographic distribution.
Osteological observations were made on cleared and stained specimens (C and S) prepared according to Taylor and Van Dyke (1985) and Song and Parenti (1995). Bone nomenclature follows Weitzman (1962), Vari (1995), and Ruiz-C and Román-Valencia (2006). Specimens are deposited in the Ichthyology Laboratory at the Universidad del Quindío, Armenia, Colombia (IUQ). Institutional acronyms for comparative material follow Sabaj-Pérez (2010). All collections were made in Colombia.

Taxonomy
Hemibrycon sanjuanensis sp. n. http://zoobank.org/5BF13995-FCD7-42FD-93E3-9B3F62A1BF80 Table 1 beni, H. dariensis, H. divisorensis, H. helleri, H. huambonicus, H. inambari, H. jabonero, H. jelskii, H. mikrostiktos, H. polyodon, H. quindos, H. raqueliae, H. santamartae, H. surinamensis, H. taeniurus, H. tridens and H. yacopiae in having melanophores present on the posterior margins of the scales all along the sides of body (vs. melanophores absent from margins of scales along entire length of sides of body). The new species further differs from all the species mentioned above in having a wide, concave pelvic bone (vs. narrow and straight); the middle part of the dorsal margin of the orbitosphenoid bone flattened and not in contact with frontal (vs. dorsal margin straight and in contact with frontal); ventral tip of supracleithrum bifurcate (vs. not bifurcate); six teeth in the outer premaxillary row arranged in a straight line (vs. five or fewer teeth in outer premaxillary row and not arranged in straight line, except H. cairoense with two to six teeth in the outer premaxillary row).
Description. Body slender and elongate (mean maximum body depth about 26.1% SL). Area above orbits flat between anterior margin of orbits and supraoccipital spine. Dorsal profile of head and body oblique from supraoccipital to dorsal-fin origin and from last dorsal-fin ray to base of caudal fin. Ventral profile of body convex from snout to base of pelvic fin; straight from pelvic-fin origin to anal fin. Caudal peduncle laterally compressed. Head and snout short (21.2% SL and 25.0% HL respectively), jaws equal, mouth terminal, lips soft and flexible, and outer row of premaxillary teeth; ventral border of upper jaw flat; posterior edge of maxilla reaching anterior edge of orbit. Premaxilla with two rows of teeth (Fig. 4). Six teeth of outer row tricuspid with central cusp largest, teeth arranged in straight line. Inner premaxillary row with four pentacuspid teeth that diminish gradually in size. Maxilla long, posterior margin straight, with 5-11 uni-or tricuspid teeth, central cusp slightly longer than outer cusps in tricuspid teeth (Fig. 4). Dentary with three or four large tricuspid teeth with central cusp largest, followed by two to four smaller, uni-to tricuspid teeth (Fig. 4). Six infraorbitals present, the first thin and narrow, extending between the dorsal edge of maxilla and lateral ethmoid, with sensorial canal. Second infraorbital short and wide, not covering dorsal part of angulo-articular. Anterior part of second infraorbital overlaying anterior part of first infraorbital; its posterior margin extending below third infraorbital. Third infraorbital widest and longest, its ventral border in contact with sensorial canal of preopercle. Fourth, fifth and sixth infraorbitals short and wide, covering posterior margin of hyomandibular. Supraorbital absent. Eight to nine supraneurals present between head and anterior part of dorsal fin, without cartilage on upper and lower edges, and with medial sensorial canal. Scales cycloid, moderately large. Lateral line complete with 40-47 pored scales (44*, mean=42.5, n=40). Scale rows between dorsal-fin origin and lateral line 5-6 (5*, mean=5.9); scale rows between lateral line and pelvic-fin origin 4-6 (5*, mean=5, n=40); scale rows between lateral line and anal-fin origin 4-6 (5*, mean=4.8, n=40); predorsal scales 11-14, arranged in regular series 11-14 (12*, mean=12.4, n=40). Dorsal-fin rays iii, 7-8 (iii, 7*, n=40); first unbranched ray approximately one-half length of second ray, its tip not reaching first bifurcation of first branched ray. Anal-fin rays iii-iv, 24-30 (iii, 27*, n=40). Anal-fin origin posterior to vertical through base of last dorsalfin ray. Pectoral-fin rays ii, 9-12 (11*, n=40). Pelvic-fin rays ii, 6 (6*, n=40). Pelvic-fin origin anterior to vertical through dorsal-fin origin. Caudal fin not covered with scales except at its base, forked with short pointed lobes. Total number of vertebra 39-41.
Secondary sexual dimorphism. Males have between 3-11 very short hooks present on all branched pelvic-fin rays, located on both branches of rays, but predominantly on internal and lateral branches; hooks present on one simple pelvic-fin ray. Males have row of very short hooks on first seven to fifteen branched anal-fin rays, each ray has from 3-5 hooks, which extend along the extreme distal branch of rays; no hooks on simple anal-fin rays.
Live colors. Dorsum of body and head silvery green; sides and ventrum silvery white from opercle to caudal peduncle. Caudal peduncle with dark midlateral stripe that extends on to middle caudal-fin rays and has a reddish spot on the ventral portion of the caudal-fin base. Humeral spot dark and rounded or oblong with some dispersed melanophores extending dorsally and ventrally. Pectoral and pelvic fins hyaline, but dorsal, anal and caudal fins with hues of reddish yellow and with dispersed melanophores on interradial membranes.
Pigmentation in alcohol. Body dark brownish-yellow, melanophores more densely concentrated on dorsum and upper sides than on ventrum, most intense on head; with melanophores present on the posterior margins of the scales all along the sides of body. Trunk with dark, midlateral stripe from posterior margin of humeral spot to caudal peduncle, extending on to caudal fin. Humeral spot circular or oblong, located two scales posterior to the opercle, not reaching the first series of scales below the lateral-line canal. Ventral part of body light yellow. Dorsal fin with melanophores concentrated mostly on interradial membranes and rays. Adipose fin hyaline. Dark melanophores present on middle caudal-fin rays, near caudal-fin base. Pectoral and pelvic fins hyaline; anal and caudal-fin lobes dusky and with melanophores concentrated on interradial membranes to form band. Distribution and ecological notes. This species is so far known only from the upper San Juan River Basin, Tatamá River drainage, Pacific versant, Colombia (Fig. 2). Hemibrycon sanjuanensis sp. n. was captured in streams characterized by relatively rapid water running over rocky and sandy substrates with high transparency. The pH was near neutral, dissolved oxygen values were high, and conductivity and total solids were low ( Table 2), typical of oligotrophic environments. The new species is syntopic with Bryconamericus emperador, Astroblepus sp., Pimelodella sp. and Characidium sp. The analysis of stomach contents of four specimens revealed the presence of adults and larvae of two different species of Coleoptera: Hydrophilidae, Promoresia sp. and Elmid sp., Diptera: Simulidae and Sarcophagidae, adult of Odonata Zygoptera, Dytiscidae, Trichoptera, Nematoda, Isopoda and fragments of unidentified arthropods. The presence of autochthonous and some allochthonous items suggest that this species is insectivorous with considerable plasticity in its diet.
Etymology. Hemibrycon sanjuanensis is named for the San Juan River Basin, where the type series was collected (Fig. 2).
Remarks. Canonical Variables Analysis (CVA) of H. sanjuanensis and species found in the San Juan and nearby rivers (including H. dariensis and H. cairoense), revealed significant differences among them, based on several characters, the most important of which are the length of the pelvic fin (variable M) and upper jaw length (related to variable W) (Fig. 3); the first canonical variable explained 84.3% of total variation, the second explained 15.6%. Linear regression analysis of the upper jaw length showed positive increment of these variables in H. sanjuanensis (vs. negative increment in the other species studied) and so separated it from the other species included in the analysis (r=-0.15, P=0.02).
Moreover, this new species is distinguished from H. cairoense (Román-Valencia and Arcila-Mesa 2009) by the number of unbranched dorsal-fin rays (iii vs. ii), by the number of scales rows between the dorsal-fin origin and the lateral line (5-6 vs. 6-7), between the anal-fin origin and the lateral line (5-6 vs. 6-7), and between the pelvic-fin insertion and the lateral line (4-6 vs. 6-7), by the presence of hooks on the males (only on the pelvic fin rays vs. on the anal, pelvic, pectoral and posterior portions of dorsal fin ray). Discussion. Hemibrycon sanjuanensis has all of the synapomorphies observed in other Hemibrycon (Arcila-Mesa 2008, Mirande 2010. Although species of Hemibrycon have a similar color pattern throughout their geographic distribution, subtle differences in the concentration and distribution of black pigment in the humeral and caudal regions have been used to diagnose new species (Bertaco and Malabarba 2010;Román-Valencia et al. 2009a, b, c, 2013Román-Valencia and Arcila-Mesa 2010).
Hemibrycon sanjuanensis has a reddish spot on the ventral portion of the caudal-fin base in life. This characteristic has also been observed in several other species of Hemibrycon (Bertaco et al. 2007;) and has been suggested as a synapomorphy for the genus by Arcila-Mesa (2008) and Román-Valencia et al. (2013).
Two species, H. dariensis and H. microformaa, have been reported previously from the San Juan, Atrato and Leon River drainages (Román-Valencia and Ruiz-C 2007;Román-Valencia and Arcila-M. 2008). The new species is similar and probably related phylogenetically to H. dariensis but is distinguished from it by the following: the presence of a dark lateral stripe that continues on to the middle caudal-fin rays (vs. wide lateral band extending only to bases of middle caudal-fin rays); pectoral fins not reaching pelvic-fin origins (vs. pectoral fins reaching pelvic-fin origins); 39-41 total vertebrae (vs. 37-38); mean length of pelvic fins 11.7% SL, (vs. 15.2% ). From H. microformaa (Román-Valencia and Ruiz-C 2007), the new species differs in attaining a larger adult size (greater than 31 mm SL vs. SL < 31 mm); in not having flat dorsal margins of the orbits and ventral profile of the snout (vs. flat); terminal mouth with upper jaw not surpassing lower (vs. mouth subterminal); greater total number of vertebrae 39-41 (vs. 33-34); and a greater number of branched anal-fin rays 24-30 (vs. 14-16).