Knodus shinahota, Ferreira & Carvajal, 2007

Ferreira, Katiane M. & Carvajal, Fernando M., 2007, Knodus shinahota (Characiformes: Characidae) a new species from the río Shinahota, río Chapare basin (Mamoré system), Bolivia, Neotropical Ichthyology 5 (1), pp. 31-36 : 32-34

Knodus shinahota , new species

Fig. 1

Holotype. LIRP 5722 (33.7 mm SL, male), río Shinahota , approximately 150 m upriver from under bridge of new Cochabamba-Santa Cruz road, río Chapare basin ( rio Mamoré system), town of Shinahota, Província de Tiraque, Cochabamba, Bolivia, 16º59’34"S 65º15’4"W, F. M. Carvajal, L. Córdova & C. Flores, 6 Sep 2002.

Paratypes. LIRP 5723 , 7 , 29.6-36.9 mm SL (4, 31.9-36.9 mm SL, c&s), MZUSP 91630, 3 , 33.1 -34.0 mm SL, and UMSS 935, 12 , 29.4 -35.0 mm SL, collected with holotype .

Diagnosis. Knodus shinahota can be distinguished from all congeners except K. chapadae and K. geryi by having six rows of scales between the lateral line and the dorsal-fin origin (vs 4 or 5 rows of scales in the other species). Knodus shinahota differs from K. chapadae by possessing more rows of scales between the lateral line and the pelvic-fin origin (5 vs 3½ or 4, respectively) and more lateral line scales (38-41 vs 36-38, respectively). Knodus shinahota differs from K. geryi

(male): Bolivia, río Shinahota, río Chapare basin, rio Mamoré 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 .

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.

Dorsal-fin rays ii,8* (23). Length of first unbranched dorsal-fin ray less than one-half length of second unbranched ray. Dorsal-fin origin located at middle of SL and posterior to vertical through pelvic-fin origin. First dorsal-fin pterygiophore inserted posterior to neural spine of 11 th (4) vertebra. Adipose fin present, its origin located at vertical through base of last anal-fin ray. Pectoral-fin rays i,8 (3), 9* (16), 10 (4),i. Pelvic-fin rays i,6,i* (23). Anal fin with five unbranched rays followed by 18 (7), 19* (10) or 20 (6) branched rays. First anal-fin pterygiophore inserted posterior to hemal spine of 16 th (4) vertebra. Caudal fin forked; lobes similar in size. Principal caudal-fin rays i,17,i* (23).

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.

Scales cycloid. Lateral line complete, with 36 (5), 37* (15) or 38 (3) perforated scales. Six rows of scales between dorsalfin origin and lateral line. Five rows of scales between lateral line and pelvic fin. Predorsal scales 11* (4), 12 (13) or 13 (6). Circumpeduncular scales 14* (23). Single row of six to nine scales extending along base of anal fin. Basal portion of caudal-fin lobes covered with scales.

First gill arch with 7* (14) or 8 (9) gill rakers on hypobranchial and ceratobranchial, 4* (23) rakers on epibranchial and 1* (23) raker on cartilage between ceratobranchial and epibranchial. Four (4) branchiostegal rays; 3 (4) on anterior ceratohyal and 1 (4) on posterior ceratohyal. Vertebrae 36 (4). Supraneurals 4 (4).

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.

Figures

Fig. 1. Knodus shinahota, holotype, LIRP 5722, 33.7 mm SL system. Photo byAlexandre C. Ribeiro.

Fig. 2. Knodus shinahota, paratype, LIRP 5723, 38.9 mm SL. Upper and lower jaws, right side, lateral view.

Fig. 3. Map of SouthAmerica, star indicates the approximate position of the type locality of Knodus shinahota; 1, rio Madeira; 2, rio Mamoré; 3, rios Paraná-Paraguay.