Hyphessobrycon melanostichos, Carvalho & Bertaco, 2006

Carvalho, Tiago Pinto & Bertaco, Vinicius Araújo, 2006, Two new species of Hyphessobrycon (Teleostei: Characidae) from upper rio Tapajós basin on Chapada dos Parecis, Central Brazil, Neotropical Ichthyology 4 (3), pp. 301-308 : 302-304

Hyphessobrycon melanostichos , new species Figs. 1-3

Holotype. MCP 39510 (34.7 mm SL, female), Brazil, Mato Grosso, Comodoro, rio Doze de Outubro on road BR 364 between Comodoro and Vilhena, 12º58’39"S 60º00’30"W, 14 Jul 2004, R. E. Reis, P. A. Buckup, A. R. Cardoso & E. H. L. Pereira.

Paratypes. MCP 38396 (203, 3 c&s, 13.0- 37.3 mm SL), MZUSP 89646 (25, 13.7-34.5 mm SL), collected with the holotype.

Additional material (non types). MCP 39808 (110, 10.9-26.3 mm SL), collected with the holotype .

Diagnosis. Hyphessobrycon melanostichos is distinguished from all remaining species of the genus by the combination of the following characters: a conspicuous longitudinal broad black band, beginning on the posterior margin of orbit and reaching the distal tip of middle caudal fin rays; humeral spot vertically elongate and distinct from lateral band; and 16 to 18 branched anal-fin rays.

Description. Morphometric data for Hyphessobrycon melanostichos presented in Table 1. Body shape somewhat variable in a depressed to a more lozenge-shaped and deeper form; greatest body depth anterior to dorsal-fin origin. Dorsal body profile gently curved from nostril to supraocciptal spine, moderately convex from that point to dorsal-fin origin; posteroventrally declined at dorsal-fin base; straight from last dorsal-fin ray base to adipose-fin 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 and gently convex. Caudal peduncle elongate, nearly straight to slightly concave along dorsal and ventral margins.

Snout convex from margin of upper lip to vertical through anterior nostrils. Head small. Mouth terminal. Posterior tip of maxilla almost reaching a vertical through middle of orbit. Maxilla positioned at approximately 45 degrees relative to longitudinal body axis. Dorsal border of maxilla nearly straight, anteroventral border concave, and posteroventral border slightly convex.

Premaxilla with two tooth rows; outer row with 2-3, tricuspid to pentacuspid teeth with central cusp larger; inner row teeth 5, gradually decreasing in length from first to fourth teeth, last tooth smaller, with 5-7 cusps and central cusp longer and broader than other cusps. One to 3 maxillary teeth, each with 3-6 cusps, central cusp slightly longer. Five anteriormost dentary teeth larger, with 5-7 cusps, followed by 5-7 smaller sized teeth with 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 interior of mouth ( Fig. 2 ).

Scales cycloid, moderately large. Lateral line incomplete, perforated scales 8-12 (10*, mean = 10.3, n = 24). Longitudinal scale series including lateral-line scales 31-34 (32*, mean = 32.4, n = 22). Scale rows between dorsal-fin origin and lateral line 5-6 (5*, mean = 5.4, n = 24); scale rows between lateral line and pelvic-fin origin 4-5, usually 4 (4*, mean = 4.1, n = 24). Predorsal scales 9-11, arranged in regular series (9*, mean = 10.1, n = 24). Scales rows around caudal peduncle 14 (n = 15). Scale sheath along anal-fin base with 5-8 scales in single series (6*, n = 24), extending posteriorly to base of fifth to seventh branched rays.

Dorsal-fin rays ii,9 (n = 24); first unbranched ray approximately one-half length of second ray, its tip reaching first bifurcation of first branched ray. Dorsal-fin origin posterior to middle of body and posterior to vertical through pelvic-fin origin. Anal-fin rays iii-iv, 16-18 (16*, mean = 16.5, n = 24). Anal-fin profile slightly concave in females and gently convex to straight in males. Anal-fin origin posterior to vertical through base of last dorsal-fin ray. Pectoral-fin rays i,10-11 (11*, one specimen with 9 and other with 12, n = 24). Change of larval pectoral-fin stage to juvenile rayed fin at about 13.1- 13.7 mm SL. Pelvic-fin rays i,7 (7*, n = 24). Pelvic-fin origin anterior to vertical through dorsal-fin origin. Caudal-fin forked, with 19 principal rays (19*, one specimen with 18, n = 24). Dorsal procurrent rays 10-11 (n = 3). Ventral procurrent rays 9 (n = 3). Adipose fin present.

Precaudal vertebrae 15-16; caudal vertebrae 16-17; total vertebrae 32. Supraneurals 4. Gill-rakers 5/ 11 in two specimens and 6/ 8 in one specimen (n = 3).

Color in alcohol. Dorsal and dorsolateral portions of head and body dark. Infraorbitals and opercular region almost plain covered with some sparse scattered dark chromatophores. Scales of mid-dorsal row dark brown. Black longitudinal stripe from posterior margin of orbit to end of middle caudal fin rays. Longitudinal stripe broad approximately two series of scales wide, not expanded on peduncle neither reaching dorsal and ventral edges of caudal peduncle. Longitudinal stripe situated above lateral line and three scale series below dorsal-fin origin. One rounded black humeral spot below longitudinal stripe and vertically elongate, located over three to five lateral line scales and vertically extended over 3-4 horizontal series of scales, including lateral line. Five median caudal-fin rays with a dark stripe ( Fig. 1 ). Small black chromatophores scattered over rays of all fins. Anal-fin with small black chromatophores along its distal border forming a narrow stripe in some specimens.

Color just after fixation. Color pattern similar to described for alcohol preserved specimens. One male examined soon after fixation in formalin had all fins reddish and midlateral and ventral body with scattered red pigment ( Fig. 3 ).

Sexual dimorphism. Five paratypes were dissected ( MCP 38396), including three mature males (26.1-33.8 mm SL) and two mature females (32.4-37.1 mm SL), but no bony hooks were observed on the fin rays. Usually males have a deeper and more lozenge-shaped body ( Fig. 3 ), and females have a less deep and more elongate body ( Fig. 1 ). Anal-fin profile slightly concave in females and gently convex to straight in males. Mature males lack gill gland on first gill arch .

Distribution. Hyphessobrycon melanostichos is known only from rio Doze de Outubro, a tributary of rio Juruena, in the headwaters of the rio Tapajós basin, Chapada dos Parecis, Comodoro, Mato Grosso, Brazil.

Etymology. The specific name melanostichos , from the Greek, melano a black and stichos meaning row, line. Referring to the black longitudinal stripe on the body.

Figures

Fig. 1. Hyphessobrycon melanostichos, MCP 39510, holotype, 34.7 mm SL, female; rio Doze de Outubro, tributary of rio Juruena, rio Tapajós basin, Mato Grosso, Brazil.

Fig. 2. Hyphessobrycon melanostichos, MCP 38396, paratype, 37.3 mm SL. Scanning electron microscope photograph of right side upper and lower jaws.

Fig. 3. Hyphessobrycon melanostichos, MCP 38396, paratype, 33.8 mm SL, male, color just after fixation.