Hemibrycon divisorensis, Bertaco & Malabarba & Hidalgo & Ortega, 2007

Bertaco, Vinicius A., Malabarba, Luiz R., Hidalgo, Max & Ortega, Hernán, 2007, A new species of Hemibrycon (Teleostei: Characiformes: Characidae) from the río Ucayali drainage, Sierra del Divisor, Peru, Neotropical Ichthyology 5 (3), pp. 251-257 : 252-255

Hemibrycon divisorensis , new species

Figs. 1-3

Holotype. MUSM 28860 , 68.2 mm SL, male, Peru, Loreto, Requena, Zona Reservada Sierra del Divisor, upper río Tapiche , quebrada en la trocha 1, río Ucayali drainage, 07º12’02"S 73º53’00"W, 20 Aug 2005, M. Hidalgo & J. F. P. da Silva.

Paratypes. MCP 41346, 4 (60.5-81.6 mm SL), 2 c&s (62.7-68.4 mm SL) , MUSM 28040 , 19 , 35.0-73.0 mm SL, collected with holotype . MCP 41347, 5 , 48.9 -65.0 mm SL , MUSM 28039 , 11 (43.0- 58.0 mm SL), 1 c&s (55.9 mm SL), Peru, Loreto, Zona Reservada Sierra del Divisor, Ojo de Contaya , quebrada en la trocha 4, río Ucayali drainage, 07º06’54"S 74º35’08"W, 6 Aug 2005, M. Hidalgo & J. F. P. da Silva .

Diagnosis. Hemibrycon divisorensis is distinguished from all other species of the genus by the presence of a wide black asymmetrical spot covering the base of caudal-fin rays and extending along entire length of caudal-fin rays 9 to 12-13 (except from H. surinamensis ), and by the presence of a black band in the lower half of the caudal peduncle from the region above the last anal-fin rays to the caudal-fin base ( Figs. 1-2 ). Furthermore, it is distinguished from most species of the genus by the number of the scale rows below lateral line (4-5 vs 5-9), except from H. jabonero , H. microformaa , H. orcesi , and H. surinamensis . Hemibrycon divisorensis differs from H. orcesi and H. microformaa by the higher number of lateral line scales (39-42 vs 34-35 and 33-37, respectively) and analfin rays (24-30 vs 18 and 14-16, respectively), and by color pattern; from H. jabonero and H. surinamensis by the higher number of scale sheath along anal-fin base (17-22 vs 8-14 and 15-16, respectively), and number of cusps in the inner row of the premaxilla teeth (5-7 vs 5, respectively).

Description. Morphometric data for Hemibrycon divisorensis summarized in Table 1 . Largest male 68.4 mm SL, largest female 81.6 mm SL. Body compressed and moderately elongate; greatest body depth usually nearly to dorsal-fin origin. Dorsal profile of head slightly convex to nearly straight. Dorsal body profile slightly convex from supraoccipital to dorsal-fin origin; posteroventrally slanted from dorsal-fin origin to adipose fin. Ventral profile of head slightly convex. Ventral body profile convex from isthmus to pelvic-fin origin, and straight to slightly convex from this point to anal-fin origin. Body profile along anal-fin base posterodorsally slanted. Caudal peduncle slightly concave along dorsal and ventral margins.

Snout rounded from margin of upper lip to vertical through anterior nostrils. Head small. Mouth terminal, mouth slit nearly at horizontal through middle of eye. Maxilla long, slightly curved, and aligned at angle of approximately 60 degrees to longitudinal body axis, with ventral border slightly convex to nearly straight and dorsal border slightly concave.

Premaxilla with two tooth rows; outer row teeth 4-7 (6*), tricuspid to pentacuspid, central cusp slightly longer; inner row teeth 4, pentacuspid to heptacuspid, central cusp twice or three times longer and broader than other cusps, gradually decreasing in length from first to third teeth and last tooth smallest. Maxilla fully toothed with 10-13 (11*) tricuspid teeth with central cusp longer, except for last six or seven conical teeth. Three anteriormost dentary teeth larger, with 5-7 cusps, followed by medium sized tooth with 3-5 cusps, and 9-12 teeth with 2-3 cusps or conical; central cusp in all teeth two to three times longer and broader than other cusps ( Fig. 3 ). All cusp tips slightly curved posteriorly towards inside of mouth.

Dorsal-fin rays ii,8 (n = 19); first unbranched ray approximately one-half length of second ray. Dorsal-fin origin located slightly posterior to middle of SL and posterior to vertical through pelvic-fin origin. First dorsal-fin pterygiophore inserted between neural spines of 11 th to 12 th vertebrae (n = 3). Profile of distal margin of dorsal fin slightly concave or nearly straight. Males with bony hooks on distal one-third of first to fifth branched dorsal-fin rays. Adipose-fin located approximately at vertical through insertion of last four or five anal-fin rays.

Anal-fin rays iv,25-28 (27*, rarely 24 or 29-30, mean = 26.7, n = 19). Anal-fin profile nearly straight in males and concave in females. Anal-fin origin approximately at vertical through insertion of last two or three dorsal-fin rays. First anal-fin pterygiophore inserted between hemal spines of first and second caudal vertebrae. Anal-fin rays of males bearing one pair of small bony hooks along posterolateral border of each segment of lepidotrichia, usually along first to 12 th anterior branched rays. Hooks more numerous along fourth through seventh branched rays, and usually located along posteriormost branch and distal 1/2 to 2/3 of each ray.

Pectoral-fin rays i,10-13 (11*, mean = 11.1, n = 19). Pecto- ral-fin tip reaching pelvic-fin origin in males, not in females. Males with bony hooks on distal portion of unbranched and all branched pectoral-fin rays. Pelvic-fin rays i,6,i (n = 11) or i,7* (n = 8). Pelvic-fin origin located at vertical through 3-4 predorsal scales anterior to dorsal-fin origin. Pelvic fin of males usually bearing one small bony hook per lepidotrichia segment along ventromedial border of all branched rays.

Caudal fin forked with 19 principal rays (n = 19); lobes similar in size. Basal portion of caudal-fin lobes covered with somewhat irregular scales and smaller than those of body, following by one larger and round shaped scale in each lobe. Dorsal procurrent rays 11 and ventral procurrent rays 10-11 (n = 3).

Scales cycloid, moderately large. Lateral line complete with 39-41 scales (41*, one specimen with 42, mean = 40.2, n = 19). Scale rows between dorsal-fin origin and lateral line 6-7 (6*, mean = 6.5, n = 19); scale rows between lateral line and pelvicfin origin 4-5 (5*, mean = 4.7, n = 19). Predorsal scales 13-15, arranged in regular series (13*, mean = 13.3, n = 19). Scale rows around caudal peduncle 14-16 (14*, mean = 15.5, n = 19). Triangular modified scale on pelvic-fin origin posteriorly covering three scales. Scale sheath along anal-fin base with 17- 22 (18*) scales in single series, extending to base of 18 th to 20 th branched rays.

Precaudal vertebrae 16-17; caudal vertebrae 21-22; total vertebrae 38-39. Supraneurals 5-6 (n = 3). Gill-rakers on upper limb of outer gill arch 7-9, and on lower limb 12-14 (n = 8).

Color in alcohol. General body color yellowish to yellowishbrown. Dorsal and dorsolateral portions of head and body pigmented dark brown. Dorsolateral portion of body with scales bordered by dark pigment and forming reticulate pattern. One black humeral spot vertically elongate, wide in dorsal portion and narrowing ventrally; wide dorsal portion of humeral spot located over two or three scales of two scale series just above lateral line; narrow portion crossing lateral line at fourth and/or fifth scales and extending one or two scale series just below lateral line. Midlateral body silvery. Lower half portion of caudal peduncle from region above last anal-fin rays to caudal-fin base black pigmented, usually from the scale row bearing the lateral line to the scales near analfin base and ventral margin of caudal peduncle. Wide and asymmetric black spot covering base of middle caudal-fin rays and extending along entire length of caudal-fin rays 9 to 12-13. Dorsal and caudal fin with dark pigmentation diffuse. Anal fin with small black chromatophores along its border forming narrow stripe. Other fins without distinctive marks ( Figs. 1-2 ).

Color just after fixation. Color pattern similar to described for alcohol preserved specimens. Specimens examined soon after fixation in formalin with dorsal and adipose fins and caudal peduncle reddish pigmented, and red spot on ventral portion of caudal-fin base.

Sexual dimorphism. Males of Hemibrycon divisorensis are easily recognized by the presence of small bony hooks on the dorsal-, anal-, pelvic-, and pectoral-fin rays (see Description). Also, males and females differ in pectoral and pelvic-fin lengths ( Table 1 ), and anal-fin shape, which is nearly straight in males and concave in females ( Figs. 1-2 ). Mature males do not present gill gland on first arch.

Distribution. Hemibrycon divisorensis is known only from the río Tapiche drainage, a tributary to the río Ucayali, Loreto, Peru. This locality is included in the conservation area “Zona Reservada Sierra del Divisor” recently established by the Peruvian government.

Etymology. The species name, divisorensis , is in reference to the type locality. A noun in apposition.

Ecological notes. The tributaries of río Tapiche where the type specimens were collected are about 2-3 m wide with crystalline water, 0.3-0.5 m deep, medium water current, sandy substrate, and with moderate amount of riparian vegetation.

Spermatozoa. Hemibrycon divisorensis has a typical aquasperm with a spherical to slightly ovoid nucleus (MCP 28040, 62.7 mm SL), suggesting that the species is non-inseminating ( Burns et al., 1995, 1998; Burns & Weitzman, 2005). Due to the lack of mature females, it was not possible to verify the presence of spermatozoa in the ovaries of H. divisorensis .

Figures

Fig. 1. Hemibrycon divisorensis, MUSM 28860, holotype, male, 68.2 mm SL; río Ucayali drainage, Loreto, Peru.

Fig. 2. Hemibrycon divisorensis, MCP 41346, paratype, female, 81.6 mm SL; río Ucayali drainage, Loreto, Peru.

Fig. 3. Hemibrycon divisorensis, MCP 41346, paratype, male, 68.4 mm SL. Scanning electron micrograph of right side upper and lower jaws. The presence of 3-4 teeth in the midlateral of maxilla is an anomaly. Scale bar = 1 mm.