A new species of Boehlkea ( Characiformes : Characidae : Stevardiinae ) from the rio Japurá , Amazon basin , Brazil

A new species of Boehlkea is described from rio Japurá, Amazon basin. The new species differs from B. fredcochui by the presence of a vertically elongate humeral spot (vs. absence), complete lateral line (vs. incomplete), four rows of scales below lateral line (vs. three), and lower number of branched anal-fin rays (17-21 vs. 22-25), and from B. orcesi by the higher number of maxillary teeth (13-14 vs. 5-12), greater head length (27.9-29.9% vs. 24.3-27.5% of SL), and by the color pattern (basal half of dorsal-fin, distal portion of pelvic-fin, lower caudal-fin lobe and anal-fin with black chromatophores vs. absence of black chromatophores in the fins).


Introduction
The genus Boehlkea was proposed by Géry (1966) and considered to be similar to Hemibrycon Günther, 1864 but differing by its smaller size (about 40 mm SL) and by the regression of the lateral line and scales on caudal-fin base.The type-species of the genus, Boehlkea fredcochui Géry was described from 19 specimens from Paramount Aquarium fish importers with uncertain type-locality; "…it is probable that the species occurs along the Upper Amazon (or Marañon) from Iquitos to Leticia downstreams", according to Géry (1966: 213).Géry (1966) grouped Boehlkea along with Bryconacidnus Myers, Bryconamericus Eigenmann, Ceratobranchia Eigenmann, Coptobrycon Ellis, Hemibrycon, Knodus Eigenmann, Microgenys Eigenmann, Nematobrycon Eigenmann, Piabarchus Myers, Rhinobrycon Myers, and Rhinopetitia Géry, in a new subtribe, Hemibryconini, which consists of a group of Tetragonopterinae (sensu Géry, 1977) with four inner premaxillary teeth, frequently having a greatly developed third infraorbital, and, quite often, an irregular implantation of the outer premaxillary row of teeth.Malabarba, Weitzman (2003) assigned Boehlkea to a large clade inside Characidae ("Clade A"), based on the putative derived presence of four teeth in the inner row of the premaxilla and reduced number of dorsal-fin rays (ii,8).Since no specializations related to insemination, development of glands along fins, or modifications on teeth and jaw related to a ventral mouth, which are features found in the majority genera of Clade A, Malabarba, Weitzman (2003) considered Boehlkea and Hemibrycon as the most basal genera in that clade.

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Mirande (2010) elevated the rank of Stevardiinae to include the members of the Clade A, with the addition of Aulixidens Böhlke and Nantis Mirande, Aguilera & Azpelicueta.Although Mirande (2010) did not analyze specimens of Boehlkea in his phylogenetic matrix of Characidae, he pointed out that the genus can be related to Hemibrycon but differing from it by the presence of scales on caudal-fin base.Based mainly on this character, Bertaco, Malabarba (2010) transferred Hemibrycon orcesi Böhlke, 1958 to Boehlkea.In a comparative study of the spermiogenesis and sperm ultrastructure of some stevardiine genera including Boehlkea, Baicere-Silva et al. (2011) concluded that the stevardiines share homologous sperm characteristics, which was considered as an additional evidence supporting the monophyly of the subfamily.
Recently, as part of a molecular-based phylogenetic study of the Stevardiinae, Thomaz et al. (2015) recognized Hemibryconini as a monophyletic group consisting of Acrobrycon Eigenmann & Pearson, Boehlkea, and Hemibrycon, which restricted the tribe to these three genera instead of the 12 that had been proposed by Géry (1966).Despite not including samples of Boehlkea in the study, Thomaz et al. (2015) tentatively classified the genus in the Hemibryconini based on its morphological resemblance with Acrobrycon and Hemibrycon, especially the shared presence of teeth along more than one-half the length of the toothed margin of the maxilla.
The rio Japurá, which drains the northwestern portion of the Amazon basin (near the supposed type-locality of B. fredcochui), is one of the largest rivers in the world regarding water discharge (Latrubesse et al., 2005) and is the fourth major tributary of the rio Amazonas (McClain, Naiman, 2008).The rio Japurá has its headwaters in the Cordillera Oriental of Colombia, where is called as the río Caquetá and lies around two thirds of the Caquetá-Japurá basin; the other one third lies in Brazil (Goulding et al., 2003).Due to the difficulty of access to the rio Japurá, its ichthyofauna is scarcely known, with large sampling gaps mainly on the Brazilian side.Here we describe a new species of Boehlkea based on numerous specimens collected during a recent expedition to the Brazilian stretch of that river, close to the Brazil-Colombia border.

Material and Methods
Counts and measurements were taken as described by Fink, Weitzman (1974), with the exception of the number of scale rows below lateral line, which were counted from the scale row ventral to lateral line to the scale row nearest the first pelvic-fin ray.Measurements were taken point-to-point with an electronic caliper with 0.1 mm of precision on the left side of specimens whenever possible.In the description, counts are followed by the number of specimens examined in parentheses; holotype is indicated by an asterisk.Measurements are given as percent of standard length (SL), except subunits of the head, which are given as percent of head length (HL).
Vertebrae, supraneurals, and procurrent caudal-fin rays counts were taken from cleared and stained specimens (c&s) prepared according to the method of Taylor, Van Dyke (1985).Total vertebral counts include Weberian apparatus, which was counted as four elements, and fused preural centrum 1 plus ural centrum 1 (PU1+U1) counted as a single vertebral element.Teeth and gill-rakers counts included all type-specimens.The gill-raker at the junction of the ceratobranchial and the epibranchial is included in the counting of gill-rakes of lower limb.Scanning electron micrographs (SEM) of teeth and jaws were taken from c&s dissected specimens.
Description.Morphometric data for Boehlkea weitzmani presented in Tab. 1. Body compressed and elongate; greatest body depth located anteriorly to dorsal-fin origin.Dorsal profile of head convex from tip of snout to anterior naris, straight from latter point to tip of supraoccipital spine.Dorsal profile of body slightly convex from tip of supraoccipital spine to dorsal-fin origin; slanted from this point to adiposefin origin and slightly concave along caudal peduncle.Ventral profile of body convex from tip of lower jaw to anal fin; slanted along anal-fin base and slightly concave along caudal peduncle.
Dorsal-fin rays ii,8(32); first unbranched ray smaller than half length of second unbranched ray.Dorsal-fin origin slightly posterior to body midlength and posterior to vertical through pelvic-fin origin.Adipose fin present.Pectoral-fin rays i,9 * (4), 10(20), or 11(8); pectoral-fin tip reaching pelvic-fin origin.Pelvic-fin rays i,6(31); pelvic fin reaching anal-fin origin.Anal-fin rays iii * (18), iv( 13   One conspicuous humeral spot vertically oriented, extending horizontally from second through third lateral-line scales, and over three scale rows dorsal to lateral line.Longitudinal dark stripe along body midline, originating at end of humeral spot, extending to middle of caudal-fin rays, covering two rows of scales.Scattered dark chromatophores above anal-fin base.Distal portion of first to fourth dorsal-fin rays hyaline.Interadial membranes of dorsal fin with dense concentration of dark chromatophores, resulting in dark band.Adipose, pectoral and pelvic fins hyaline.Proximal portion of anal fin with few scattered dark chromatophores or hyaline.Distal portion of interadial membranes of anal fin with dense concentration of dark chromatophores, resulting in dark stripe-like pigmentation.Caudal fin with dark pigmentation along its lateral borders forming broad transversal stripe on both lobes.Tips of caudal-fin lobes hyaline.Middle portion of lower caudal-fin lobe with dark chromatophores forming vertical stripe-like blotch in interadial membranes along lower border without reaching tip of rays.

Color in life.
Overall body color silvery on flanks, with dorsum light olive to yellow from snout tip to near insertion of adipose fin; ventral area silvery white.Black vertically elongated humeral blotch.Scattered melanophores forming faint band along midline just above lateral line scales of posterior half of body.Upper portion of iris red, with some small red markings also on its lower edge.Purple to bluish sheen on scales of caudal peduncle extending to the scales over caudal-fin base.Pectoral fin hyaline; pelvic fin hyaline to whitish.Adipose fin with basal two-thirds opaque white and hyaline outer edge.Dorsal, anal and caudal fins with scattered red chromatophores over interadial membranes, more pronounced on caudal-fin base (Fig. 3).Discussion Géry (1966) proposed Boehlkea based on the presence of two rows of teeth on the premaxilla, four broad pentacuspid teeth in the inner premaxillary row, maxilla generally toothed nearly to its end, dentary with four anteriormost broad, quincuspid teeth, caudal-fin base conspicuously scaled, no apparent caudal gland, and lateral line very rarely complete.Additionally, Géry (1966) noted that Boehlkea has the maxilla moderate in length, without (apparently) a positive allometry in the differential growth as in some Hemibrycon.Other characteristics include body of medium depth and compressed, and head short with cheek entirely covered by the largest suborbital.

Tab. 1. Morphometric data of the holotype and paratypes of
Among the Stevardiinae only Boehlkea and Hemibrycon share the presence of an edentulous portion of maxilla smaller than the toothed portion, associated with the largest number of teeth in the maxilla (Bertaco, Malabarba, 2010;Mirande, 2010).Boehlkea differs from Hemibrycon mainly by the presence of a caudal fin scaled (vs.naked), and by having few vertebrae (36 vs. 38-43) (Bertaco, Malabarba, 2010).Although B. weitzmani has 36 to 38 vertebrae, the vertebral count of Boehlkea still remains smaller to that present in Hemibrycon.Since the systematics of Boehlkea and Hemibrycon are still unresolved, with both genera lacking a phylogenetic diagnosis, the new species is assigned herein to the genus Boehlkea according to the diagnostic characters discussed by Bertaco, Malabarba (2010:767).
In a review of the cis-Andean species of Hemibrycon, Bertaco, Malabarba (2010) transferred H. orcesi to Boehlkea, arguing that the characters observed in the type-specimens (e.g.caudal fin scaled, short lateral line, small number of vertebrae, and color pattern of the fins) are shared with Boehlkea.However, despite all these characteristics, the species was considered as belonging to Hemibrycon by Román-Valencia et al.
We have analyzed the holotype (ANSP 111675) and two paratypes of Boehlkea fredcochui (Fig. 6a); the holotype and one of the paratypes (ANSP 111668) have the lateral line interrupted (14 perforated scales plus 23 remaining scales; last scales perforated or unperforated; totalizing 37 longitudinal series scales), but the other examined paratype (ANSP 111676) has a complete lateral line with 36 perforated scales.Therefore, the main differences between the new species and the types of B. fredcochui were observed in the maxillary teeth (5-12 vs. 14-15) (Tab.2) and number of branched anal-fin rays (17-21 vs. 23-25).Finally, although the types of B. fredcochui have lost most of its coloration, it is possible to notice a large stripe from the posterior border of the orbit to the median region of the lower caudal-fin lobe, but we found no signs of a humeral spot.Conversely, Boehlkea weitzmani presents a large humeral spot, more conspicuous than the faint lateral stripe.
Apparently, Boehlkea is a relatively rare fish.Recent papers about the ichthyofauna of rivers and streams from Colombia, even those sampling localities near the type locality of B. fredcochui, did not report any species of Boehlkea (Mojica et al., 2005;Sanabria-Ochoa et al., 2007;Maldonado-Ocampo et al., 2008).The ichthyofauna of the rio Japurá in Brazilian's territory is scarcely represented in fish collections; most of the preserved samples were obtained from near to the confluence of rio Solimões, at Mamirauá Reserve (Hercos et al., 2008;Slobodian, Bockman, 2013).However, it is possible that Boehlkea weitzmani have a broader distribution in the Western Amazon (the same inferred distribution of B. fredcochui), a kind of aquatic habitat that is much less sampled than larger and more easily assessed rivers, which could partially explain its rarity in ichthyological collections.
According to our field observations related to the species' habitat, Boehlkea weitzmani has an apparently restricted geographical distribution, similar to Moenkhausia agnesae (Characidae), Nannoglanis fasciatus (Heptapteridae), and Bujurquina cf.robusta (Cichlidae).Despite the scarcity of ichthyological records, these results indicate that the sampled region is part of a biogeographical province corresponding to 7 e170026 [7] the Western Amazon Piedmont freshwater ecoregion (Abell et al., 2008;ecoregion 313) that advances to the Brazilian portion of the rio Japurá basin.
It seems that there is a relatively low economic interest in Boehlkea fredcochui as an ornamental fish (Sanabria-Ochoa et al., 2007;Mancera-Rodríguez, Álvarez-León, 2008), which suggests a currently low fishing pressure on the natural populations of the Boehlkea species.This fact, together with the remoteness of large portions of the rio Japurá basin, have resulted in a high degree of preservation of the forest and its aquatic habitats, which indicates positive conservation perspectives for the regional fish fauna.

Fig. 2 .
Fig. 2. Boehlkea weitzmani, INPA 48541, 32.8 mm SL, paratype.Scanning electron micrograph of left side upper and lower jaws.Scale bar = 100μm.Color in alcohol.Overall ground color of body pale yellow.Upper jaw, anterior portion of maxilla, snout, top of head and dorsal portion of opercle with dense concentration of small dark chromatophores.Lower jaw, gular area and infraorbitals clearer.Dorsal surface of body with dark chromatophores from posterior region of supraocciptal spine to caudal peduncle, resulting in dark stripe on the dorsum.One conspicuous humeral spot vertically oriented, extending horizontally from second through third lateral-line scales, Sexual dimorphism.Mature males of Boehlkea weitzmani have slightly curved bony hooks on the pelvic-and analfin rays.Pelvic fin has one hook per segment, which are arranged on the distal portion of the first to fifth (rarely on the sixth) branched rays.One or two pairs of hooks per segmentlocated on the distal portions of the last unbranched anal-fin ray and up to the eighth or ninth (sometimes tenth) branched anal-fin rays.Geographic distribution.Boehlkea weitzmani is currently known only from streams of the rio Japurá basin, a left margin tributary of the rio Solimões basin, Amazonas State, Brazil (Fig.4).

Fig. 5 .
Fig. 5. Type-locality of Boehlkea weitzmani, tributary of the rio Japurá, Amazonas State, Brazil: a. small stream from right margin of rio Japurá, with litter banks; b. small stream from left margin of the river, predominantly composed by pebbles and sand.
A new species of Boehlkea from the rio Japurá