Knodus shinahota ( Characiformes : Characidae ) a new species from the río Shinahota , río Chapare basin ( Mamoré system ) , Bolivia

*Laboratório de Ictiologia de Ribeirão Preto (LIRP), Depto. Biologia, FFCLRP-USP, Av. Bandeirantes, 3900, 14040-901 Ribeirão Preto, SP, Brazil. katiane@usp.br ** Laboratorio de Ictiología, Unidad de Limnología y Recursos Acuáticos, Facultad de Ciencias y Tecnología, Universidad Mayor de San Simón, Calle Sucre frente al parque La Torre s/n, Cochabamba, Bolivia. fmcvalle@yahoo.com Knodus shinahota (Characiformes: Characidae) a new species from the río


Introduction
Knodus Eigenmann, 1911, is a genus of the Characidae that consists of 20 valid species (Lima et al., 2003;Lima et al., 2004;Zarske & Géry, 2006;Ferreira & Lima, 2006).Knodus species occur in the Paraná-Paraguay, Parnaíba, São Francisco, and Amazonas basins, with the greatest diversity of the genus in the latter drainage system.The monophyly of Knodus has been disputed, and the genus was considered a synonym of Bryconamericus by some authors (see Lima et al., 2004, for a discussion of the topic).Currently, the presence of scales on the basal portion of the caudal fin in the species of Knodus is the sole feature used to distinguish that genus from Bryconamericus.
Knodus was recently considered within Characidae as incertae sedis (Lima et al., 2003), and until now no phylogenetic hypothesis has been proposed concerning the mono-phyly or lack thereof of the genus.Only two phylogenetic studies, one based on osteology (Malabarba & Weitzman, 2003) and the second on molecular data (Calcagnotto et al., 2005), included Knodus.According to Malabarba & Weitzman (2003), Knodus belongs to a clade that also includes the subfamily Glandulocaudinae and Attonitus, Boehlkea, Bryconacidnus, Bryconamericus, Caiapobrycon, Ceratobranchia, Creagrutus, Cyanocharax, Hemibrycon, Hypobrycon, Microgenys, Monotocheirodon, Odontostoechus, Othonocheirodus, Piabarcus, Piabina, Rhinobrycon and Rhinopetitia.In the study by Calcagnotto et al. (2005), Knodus was a member of a clade that also included Bryconamericus, Creagrutus, Hemibrycon, and two genera of the Glandulocaudinae (Gephyrocharax and Mimagoniates).The interrelationships among the species of Knodus remain uncertain.In light of the uncertainty as to the monophyly and relationship of Knodus we describe the new species of Knodus using Eigenmann's (1918) original concept of the genus.According to Eigenmann, Knodus is characterized by the combination of the presence of the expanded second infraorbital that is in contact ventrally with the horizontal limb of the preopercle, two rows of teeth on the premaxilla, with four teeth present on the inner tooth row, a caudal fin that is scaled basally, and a slightly decurved lateral line.
The new species described herein is the fourth species of Knodus reported from the upper Madeira-Mamoré basin.We provide comparisons between the new species and the remaining three congeners from that basin and also with Bryconamericus bolivianus, the only species of that genus known from the upper Madeira-Mamoré basin.Leviton et al. (1985) with the addition of LIRP, Laboratório de Ictiologia de Ribeirão Preto, Departamento de Biologia da FFCLRP, Universidade de São Paulo, Ribeirão Preto, Brazil; and UMSS, Universidad Mayor de San Simón, Facultad de Ciencias y Tecnología, Unidad de Limnología y Recursos Acuáticos, Laboratorio de Ictiología, Cochabamba, Bolivia.

Institutional abbreviations follow
Counts and measurements follow Fink & Weitzman (1974) except for counts of the horizontal scale rows below the lateral line which were counted to the pelvic-fin insertion because this region presents a minor degree of deformation making counts more precise.In Table 1, standard length (SL) is expressed in mm and all other measurements are expressed as percentage of SL, except for subunits of the head which are expressed as percentages of head length (HL).Counts are presented in the description, followed by frequency of particular values in parentheses.Asterisks indicate values of the holotype.Counts of vertebrae and supraneurals were taken from cleared and stained (c&s) paratypes.Counts of total vertebral include the four vertebrae of the Weberian appara-tus and the terminal centrum.Specimens were cleared and stained following the method of Taylor & Van Dyke (1985).Osteological terminology follows Weitzman (1962) with the modifications listed by Vari & Harold (2001).Comparisons were based on the examination of type-specimens of species of Knodus made by the first author, with the exception of Bryconamericus bolivianus and K. longus, in which case the comparison was based on photographs of the holotype and data provided in the original description.
With objective of verifying the presence of insemination, tissue samples for histology were removed from specimens initially fixed in 10% formalin and subsequently transferred to 70% ethanol.Tissue samples were dehydrated in an ethanol series, embedded in paraffin, sectioned at 6 µm and stained with hematoxylin and eosin.by possessing more rows of scales between the lateral line and the pelvic-fin origin (5 vs 4, respectively); fewer branched anal-fin rays (17-20 vs 15-17, respectively), and in lacking the two symmetric, large, dark, blotches that are present on the base of the caudal-fin lobes in K. geryi.

Knodus shinahota, new species
Description.Morphometric and meristic data for holotype and paratypes presented in Table 1.Body laterally compressed, largest specimen 37.0 mm SL.Greatest body depth situated at dorsal-fin origin.Dorsal profile of head distinctly convex from margin of upper lip to tip of supraoccipital spine.Dorsal profile of body convex from tip of supraoccipital spine to dorsal-fin origin; straight along dorsalfin base; straight from posterior terminus of dorsal-fin base to adipose-fin insertion, and slightly concave from latter point to caudal-fin origin.Ventral profile of body convex from tip of lower jaw to anal-fin insertion.Anal-fin base straight to slightly concave.Ventral profile of caudal peduncle slightly concave.
Mouth terminal.Premaxilla extending slightly anterior of vertical through anterior limit of dentary.Premaxilla with two rows of teeth (Fig. 2).Outer tooth row aligned in gentle arch, with 4* (18) or 5 (5) tricuspid teeth, with median cusps largest.Inner premaxillary tooth row with 4 teeth.Symphyseal tooth in row with four cusps and remaining teeth with five cusps.Maxilla with 2 (4) or 3* (19) teeth; teeth with seven cusps with median cusps slightly more developed.Dentary with four large teeth with five cusps followed by 2 (3), 3* (16) or 4 (4) smaller teeth with three to five cusps.
Sexual dimorphism.Sexually mature males easily recognized by presence of hooks on anal-fin rays, by possession of proportionally longer pectoral and pelvic fins, by tip of pectoral fin reaching pelvic-fin origin, and by tip of pelvic fin reaching anal-fin origin.
Anal-fin hooks small, slightly curved dorsally, with one or two hooks on each ray segment along posterior margin of ray.Hooks more numerous on longest unbranched to seventh to ninth branched rays.Longest unbranched ray with 10 to 12 hooks limited to central portion of ray.Branched rays with hooks distributed along entire fin margin.One to four hooks located basal to split of ray and 9 to 20 hooks distal  that point.All pelvic-fin rays with hooks.Pelvic-fin hooks small, curved, and distally-projected, with one or two hooks per ray segment along both anterior and posterior margins of rays.Three to 12 hooks located basal to first split of ray and nine to 15 hooks distal of that point.
Color in alcohol.Overall ground coloration yellowish tan.Specimens retaining guanine on body and head silvery in these areas.Dorsal surface of head and lips with dense concentration of dark chromatophores.Scattered dark chromatophores covering dorsal one-third of opercle along with fifth and sixth infraorbitals.Dark chromatophores concentrated on scales of dorsal portion of body, mainly along scale margins.Concentration of chromatophores decreasing progressively from middorsal region to lateral line where dark pigmentation limited to margins of scales.Scales below lateral line without chromatophores along margins.One narrow, vertically-elongate humeral mark present over second or third lateral line scale; extending more than two series of scales dorsal to lateral line and one scale ventral of lateral line.Humeral mark is darkest immediately above lateral line and more diffuse dorsal and ventral of that area.Diffuse midlateral stripe on body extending from humeral mark to onto middle caudalfin rays.Pectoral, pelvic and caudal fins hyaline, with scattered, dark chromatophores outlining rays.Dark chromatophores more concentrated along margin of distal portions of membranes of anal and dorsal fins.Adipose fin hyaline, with small, dark chromatophores concentrated over center of fin.

Histological analysis.
No evidence of insemination was found.
Examined females of K. shinahota lack spermatozoa inside ovary.The spermatozoa nucleus was rounded.
Distribution.Known only from the type locality (Fig. 3).
Etymology.The specific name, shinahota, is in reference to the río Shinahota, the type locality.A noun in apposition.
Ecological notes.The río Shinahota is a typical Andean piedmont drainage, with medium water velocity and with the substrate composed primarily of gravel and pebbles.In some years the river has an intermittent flow.The riparian forest is degraded and, the river is polluted by domestic waste.

Discussion
Three Knodus species (K.mizquae, K. longus and K. smithi) that occur in the Madeira-Mamoré system were compared with K. shinahota.Knodus mizquae and Knodus longus occur in tributaries of the río Beni, Bolivia.Knodus mizquae differs from K. shinahota in the number rows of scales above and below the lateral line (5 and 3½-4 in K. mizquae vs 6 and 5 in K. shinahota), in the head length (22.5-28.0% SL in K. mizquae vs 32.3-36.2% SL in K. shinahota), and in the number of cusps on the maxillary teeth (5 in K. mizquae vs 7 in K. shinahota).Knodus longus differ from K. shinahota in the number of anal-fin branched rays (15-16 in K. longus vs 18-20 in K. shinahota), perforated scales in the lateral line (41-42 in K. longus vs 36-38 in K. shinahota), and in number of predorsal scales (17-18 in K. longus vs 11-13 in K. shinahota).Knodus smithi was described from a small tributary of the rio Madeira near Porto Velho, Brazil, and differs from K. shinahota in the number of branched anal-fin rays (25-26 in K. smithi vs 17-20 in K. shinahota), in the number of scale series above and below the lateral line (5 and 4 in K. smithi vs 6 and 5 in K. shinahota), in the number of cusps on the maxillary teeth (5 in K. smithi vs 7 in K. shinahota), in the number of cusps on the teeth of the inner row of the premaxilla (7 in K. smithi vs 5 in K. shinahota), in the distance between the snout and pelvic-fin origin (41.9-43.3%SL in K. smithi vs 43.1-49.6%SL in K. shinahota), in the caudal-peduncle length (8.8-10.6%SL in K. smithi vs 10.0-12.4% SL in K. shinahota) and in the interorbital width .
As noted in the Introduction, some authors consider Knodus as a synonym of Bryconamericus and we consequently extend our comparisons of Knodus shinahota to the members of Bryconamericus that occur in the rio Madeira basin.Bryconamericus bolivianus that occurs in upper Madeira basin (río Beni) belongs to the B. diaphanus group as defined by Géry (1977).The B. diaphanus group is characterized by the presence of 15-25 branched anal-fin rays and 4-6 transverse scales above the lateral line.Bryconamericus bolivianus has a shallower body than K. shinahota , and fewer branched anal-fin rays (15-16 in B. bolivianus vs 18-20 in K. shinahota), the number of maxillary teeth (4-5 in B. bolivianus vs 2-3 in K. shinahota), and the number of scale series above (to origin of the dorsal fin) and below (to origin of the pelvic fin) the lateral line (4 and 2½-3 in B. bolivianus vs 6 and 5 in K. shinahota).