Hyphessobrycon hexastichos, Bertaco & Carvalho, 2005

Bertaco, Vinicius A. & Carvalho, Tiago P., 2005, A new characid fish, Hyphessobrycon hexastichos (Characiformes: Characidae) from Chapada dos Parecis, Mato Grosso, Brazil, Neotropical Ichthyology 3 (3), pp. 439-443 : 440-441

Hyphessobrycon hexastichos , new species Figs. 1-2

Moenkhausia agnesae , non Géry, 1965. - Notare (1994:6-7; misidentification; photo of live specimen).

Holotype. MCP 37648 (53.2 mm SL); Brazil, Mato Grosso, Comodoro, rio Mutum on road BR 364 to cidade de Vilhena, tributary of rio Juruena , upper rio Tapajós drainage, 13 o 05’08"S 59 o 53’32"W, 14 Jul 2004, J. F. Pezzi da Silva , V.A. Bertaco, F. C. Lima, & P. C. Lehmann.

Paratypes. MCP 37649 (145, 4 c&s, 16.9-46.8 mm SL), MZUSP 87242 (20, 19.0-45.0 mm SL), collected with the holotype.

Diagnosis. Hyphessobrycon hexastichos is distinguished from all remaining species of the genus, except H. uruguayensis (Fowler, 1943) , by presence of black zigzag longitudinal lines between longitudinal body rows of scales in the lateral of body. The new species differs from H. uruguayensis by the number of scale rows between lateral line and pelvic-fin origin (3 vs. 4-6), number of maxillary teeth (3-5 vs. 6-11), number of perforated scales on lateral line series (9-13 vs. 6-8), and number and shape of teeth in the premaxillary inner row (5 pentacuspids vs. 6-7 tricuspids), respectively. Furthermore, the presence of bony hooks in all fins of H. uruguayensis (pers. obs.) is unknown on the fins of specimens of H. hexastichos .

Description. Morphometric data for H. hexastichos are summarized in Table 1. Body compressed and moderately deep; greatest body depth anterior to dorsal-fin origin. Dorsal body profile concave from nostril to supraocciptal spine, convex from that point to dorsal-fin origin; posteroventrally slanted at dorsal-fin base; straight from last dorsal-fin ray to adiposefin origin. Ventral profile of head convex. Ventral body profile convex from pectoral-fin origin to anal-fin origin. Body profile along anal-fin base posterodorsally inclined. Caudal peduncle profile nearly straight to slightly concave along both dorsal and ventral margins.

Snout convex from margin of upper lip to vertical through anterior nostrils. Head small. Mouth terminal. Maxilla extending posteriorly to vertical through middle of orbit, slightly curved, forming angle of 45 o with longitudinal axis of body. Anterodorsal border of maxilla concave, posterodorsal bor- der slightly convex, anteroventral border concave, and posteroventral border convex. Maxilla slightly widened posteriorly.

Premaxilla with two tooth rows; outer row with 3-4, rarely 2, pentacuspid teeth with central cusp larger; inner row teeth 5, rarely 6, gradually decreasing in length from first to fourth teeth, last tooth considerably smaller, with 5-9 cusps and central cusp longer and broader than other cusps. Three to 5 maxillary teeth, with 5-7 cusps, central cusp slightly longer. Four or 5 anterior-most dentary teeth larger, with 7 cusps, followed by 1-2 middle sized tooth with 5-7 cusps, and 6-7 teeth with 1-3 cusps or conical in shape; central cusp in all teeth two to three times longer and broader than remaining cusps. Cusp tips slightly curved posteriorly and towards inside of mouth ( Fig. 2 ).

Dorsal-fin rays ii, 9 (n = 20), first unbranched ray approximately half length of second ray. Dorsal-fin origin located anterior to middle of SL and posterior to vertical through pelvic-fin origin. Fleshy flaps on anterior 5 dorsal-fin rays, attached to fin ray and extended over membrane between rays. Adipose-fin located approximately at vertical through insertion of 16th to 19th anal-fin rays bases.

Scale sheath along anal-fin base with 7-11 scales in single series, extending posteriorly to base of fifth to ninth branched rays.

Precaudal vertebrae 14-15; caudal vertebrae 18; total vertebrae 32-33. Supraneurals 4-5. Gill-rakers 6-7/11 (n = 4).

Anal-fin rays iii-iv, 18-22 (x = 19.9, n = 20). First unbranched ray usually only apparent in cleared and stained specimens. Anal-fin distal margin slightly concave in some specimens.Anal-fin origin located posterior to vertical through base of last dorsal-fin ray. Pectoral-fin rays i, 9-10, rarely 12 (x = 9.9, n = 20). Pelvic-fin rays i, 6 (n = 20). Caudal-fin forked, with 19 principal rays. Dorsal procurrent rays 10-12, and ventral procurrent rays 8-10 (n = 4).

Scales cycloid, moderately large. Lateral line incomplete, perforated scales 9-13 (x = 10.7, n = 20). Longitudinal scale series including lateral-line scales 33-35 (x = 33.8, n = 20). Scale rows between dorsal-fin origin and lateral line 4 (n = 20); scale rows between lateral line and pelvic-fin origin 3 (n = 20). Predorsal scales 8-11, usually 9, arranged in regular series (x = 9.6, n = 20). Scales rows around caudal peduncle 14.

Color in alcohol. Dorsal and dorsolateral portions of head and body dark brown. Portion midventral of body above anal fin with red-orange chromatophores in large specimens (38.3 mm SL). Infraorbital and opercular areas covered with scattered, dark chromatophores. Scales on lateral and ventral surface of body with dark brown chromatophores. Black zigzag longitudinal stripes between longitudinal body rows of scales in lateral of body. Specimens larger than 38.1 mm SL with five to six conspicuous longitudinal black stripes, two midlateral longitudinal black stripes densely pigmented above perforated scale series, one faint zigzag above these stripes, and three zigzag longitudinal stripes below perforated scale series. Specimens smaller than 38 mm SL with three or four dark stripes in midlateral body. One black humeral spot, narrow and vertically elongate, upper portion wider, located over first to third lateral line scales and extending over 2-3 horizontal series of scales, including lateral line. Silvery to violet midlateral body stripe extending from humeral region to caudal peduncle, between two longitudinal stripes above perforated scales. Caudal-fin median rays pigmented forming stripe. Small black chromatophores scattered over rays of all fins. Anal fin with small black chromatophores along its distal margin forming narrow stripe in some specimens ( Fig. 1 ).

Color just after fixation. Color pattern similar to described for alcohol preserved specimens, except as follows. Some specimens examined soon after fixation in formalin, with all fins reddish. Lateral surface of body silvery. Body red-orange.

Sexual dimorphism. Secondary characters were not found on examined specimens. Mature gonads were not found on the four dissected cleared and stained specimens (MCP 37649, 32.0- 38.8 mm SL).

Distribution. Hyphessobrycon hexastichos is only known from rio Mutum, tributary of rio Juruena, in the headwaters of the rio Tapajós drainage, Chapada dos Parecis, Comodoro, Mato Grosso, Brazil.

Etymology. The specific epithet hexastichos is from the Greek, hexas, six, and stichos, meaning line or row, referring the presence of six conspicuous black zigzag longitudinal stripes between longitudinal body rows of scales in large specimens.

Ecological notes. All specimens of H. hexastichos were collected along the margin in semilentic stretches of a shallow river with clear water, with sand and scattered small stones on the bottom, and a small amount of riparian vegetation. Species collected syntopically with H. hexastichos were Aequidens epae , Cetopsorhamdia sp. , Characidium sp. , Eigenmannia virescens , Hemigrammus sp. , Hyphessobrycon cf. vilmae , Leporinus sp. , Megalechis thoracata , and Rhamdia sp.

Figures

Fig. 1. Hyphessobrycon hexastichos, MCP 37648, holotype, 53.2 mm SL; Brazil, Mato Grosso, Comodoro, rio Mutum, tributary of rio Juruena, upper rio Tapajós drainage.

Fig. 2. Hyphessobrycon hexastichos, MCP 37649, paratype, 38.8 mm SL. Scanning electronic microscopy of left side upper and lower jaws teeth.