Hyphessobrycon nicolasi, Miquelarena & López, 2010

Miquelarena, Amalia M. & López, Hugo L., 2010, Hyphessobrycon nicolasi (Teleostei: Characidae) a new species from the Uruguay River basin in the Mesopotamian Region, Argentina, Neotropical Ichthyology 8 (1), pp. 1-6 : 1-4

Hyphessobrycon nicolasi , new species

Figs. 1-3

Holotype. ILPLA 1808 , 49.1 mm SL, female, Argentina, Entre Ríos Province, Colón Department, El Pelado stream, 32º19’S 58º14’W, Nov 2005, A. Miquelarena, H. López, L. Protogino, E. Etcheverry . Paratypes. Same data as holotype : ILPLA 1809 , 20 , 33.7-49.7 mm SL ; ILPLA 1810 , 6 c&s, 36.6-43.9 mm SL ; MLP 9746 , 9 , 41.7-51.4 mm SL (2, 44.4-46.2 mm SL). Same locality as holotype, Oct 2004 ,

A. Miquelarena, H. López, R. Menni, L. Protogino: ILPLA 1811,

8, 37.5-43.6 mm SL; ILPLA 1812, 7 c&s, 34.1-44.7 mm SL.

Diagnosis. Hyphessobrycon nicolasi can be distinguished from congeners by the presence of a well-defined, oblique and marginal black stripe on each lobe of the caudal fin. In addition, the following combination of characters permits the differentiation of the species: maxilla with 1-3 teeth, bearing 3-10 cusps; outer premaxillary row with 2-3 small teeth, bearing 5 or 7 cusps; iv-v, 27-36 anal-fin rays; 33-36 scales on the longitudinal series; two vertically elongated dark humeral spots; black caudal spot rounded or fan-shaped; dorsal and anal fins with the first rays dappled in black; and presence of minute bony hooks on the dorsal, anal and caudal fins of the mature males.

Description. Morphometric data are shown in Table 1. Body compressed and rhomboidal, greatest body depth at dorsalfin origin. Predorsal body profile convex, slightly concave at level of supraoccipital process. Body profile slightly straight between dorsal-fin origin and adipose-fin origin. Ventral profile almost symmetrical with dorsal counterpart. Dorsal and ventral margins of caudal peduncle straight or slightly concave. Caudal peduncle relatively high. Head short. Snout short. Eye relatively large. Frontals broad at interorbital area, its width slightly less than or equal to eye diameter. Mouth terminal. Maxilla short not reaching anterior edge of orbit.

Dorsal-fin origin almost equidistant from tip of snout and base of caudal-fin rays. Tip of pectoral fin not surpassing pelvic-fin origin. Pelvic-fin tip not surpassing the anal-fin origin. Presence of bony hooks on rays of dorsal, anal and caudal fins of mature males. Dorsal-fin rays ii,8 (5), i,9 (2), ii,9* (30), or iii,9 (6). In the latter specimens, first unbranched ray very small and only visible in cleared and stained specimens. Posterior margin of dorsal fin rounded, last unbranched ray and first two branched rays longest. Adipose fin well developed. Pectoral- fin rays i,10 (19), i,11* (17), or i,12 (5). Pelvic-fin rays i, 6 in all specimens. Pelvic fin with axillary scale. Anal-fin rays iv,27 (5), v,27 (2), vi,27 (1), iv,28 (6), v,28 (6), iv,29 (7), v,29 (2), iv,30 (5), v,30* (6), iv,31 (2), iv,35 (1), or iv,36 (1). Anal-fin origin aligned to vertical through base of third to sixth dorsal-fin ray, except in one female (37.4 mm SL) with anal and dorsal fin origins aligned. Posterior end of pelvic fin falling short of anal fin by 1-2 scales. Caudal fin forked, lobes rounded, and similar in size. Principal caudal-fin rays i,16,i (1), i,17,i (9), or i,18,i (1). Dorsal procurrent rays 9 (5), 10 (3), 11 (2), or 12 (1). Ventral procurrent rays 7 (2), 8 (6), or 9 (3).

Scales cycloid. Lateral line incomplete, perforated scales 6 (2), 7 (4), or 8* (5). Longitudinal scale series 33 (1), 34 (12), 35* (14), or 36 (4). Scales row between dorsal-fin and anal-fin origins 15* (13), 16 (9), 17 (7), or 18 (2). Predorsal scales 12* (20), 13(8), or 14 (3) arranged in irregular series. Single row of scales covering base of anteriormost anal-fin rays. Infraorbital bones 6 (11). Distal margin of third infraorbital not reaching sensory canal of preopercle. Supraneurals 5 (1), 6 (11), or 8 (1). Total vertebrae 32 (1), 34 (6), 35 (4), or 36 (2). Gill-rakers 7/ 15 (2), or 8/18 (2).

Maxilla short and somewhat expanded ( Fig. 2a ), with 1-3 teeth (typically 2*), each one with 3-10 cusps (usually 7). Premaxilla with two tooth rows. Outer row with 2-3 teeth (typically 3), with 5 or 7 cusps. Inner row with 4 or 5 (typically 5), with 6-11 cusps; teeth broadened distally and overlapping on its borders ( Fig. 2b ). Three or 4 anteriormost dentary teeth larger, with 7-11 cusps, followed by medium sized tooth with 7-8 cusps, and 2-3 smaller teeth with 5-6 cusps or conical in shape ( Fig. 2c ).

Color in alcohol. Dorsal and dorsolateral portions of head and body light brown. Dense concentration of chromatophores along dorsal profile, more conspicuous from end of dorsal fin to dorsal procurrent rays. Scales above lateral longitudinal stripe darkened by higher concentration of small chromatophores. Infraorbital and opercular areas with scattered, dark chromatophores. Two dark blotches above and below the eye’s pupil, which are reddish in living and 1-2 horizontal scale rows below lateral-line perforated scales. Second humeral spot, usually well developed, separated from anterior spot by three less pigmented scales. Posterior to latter spot, sparse melanophores form a well defined narrow midlateral stripe (one scale high); stripe more conspicuous upon caudal peduncle and broader at caudalfin base and connected to, a dark rounded or fan-shaped spot somewhat expanding over caudal-fin rays. Pectoral and pelvic fins translucent, with few melanophores on rays. Dorsal fin usually with first seven rays black. Proximal half of first anal-fin rays black. Caudal fin with two oblique black stripes on dorsal and ventral margins of each lobe. These stripes variably developed, reaching tips of fin lobes in some specimens. Snout, lips, and maxilla with scattered dark chromatophores. Ventral body light brown. Scales above the base of anal fin with dark chromatophores. Interradial membrane of paired and unpaired fins with small dark chromatophores, distributed along borders of the rays ( Fig. 1 ).

individuals.

Two dark humeral spots, vertically elongated and narrower ventrally. First spot located over third to fourth lateral-line scales and extending over 3-4 horizontal scale rows above Color in life. Ground color in life iridescent with yellow and turquoise hues. Iris with two reddish blotches above and below, the upper one with a dark lower edge. Dorsal fin yellow with first seven rays black. Generally, first two unbranched rays and first two branched rays more heavily pigmented. On remaining rays, dark pigmentation only reaching proximal third of ray length. Anal fin reddish yellow with anterior third intense red and proximal half of first rays black. Pectoral fin translucent with yellow hues and pelvic fin reddish yellow. Adipose fin yellowish. Caudal fin red with tips of lobes and middle caudal rays yellow; two oblique black stripes of variable length. Stripe on upper lobe of caudal fin involving upper marginal and first branched principal rays; stripe on lower lobe involving last branched and lower marginal principal rays. Two dark humeral spots vertically elongated and a rounded or fan-shaped dark spot on caudal-fin base ( Fig. 3 ).

Small dark chromatophores scattered over body and often on rays of all fins. Upper and lower lips with fine dark dotting.

Sexual dimorphism. Males with minute and blunt bony hooks on dorsal, anal and caudal fins. Dorsal fin with one or two bony hooks at the distal end branched 6 th or 7 th rays. Bony hooks especially numerous on anal fin, with one bony hook in each ray segment, distributed from last unbranched ray to usually, the 26 th branched ray. In one male specimen (39.7 mm SL) bony hooks on anal and dorsal fins only. In specimens larger than 40 mm SL hooks also on central principal rays of caudal fin. Morphology of anal fin similar for both sexes, somewhat more concave in females.

Distribution. Hyphessobrycon nicolasi is known from the type locality El Pelado stream, tributary of Uruguay River in the vicinity of the city of Colón, Entre Ríos Province, Argentina ( Fig. 4 ).

Habitat notes. At the type locality, El Pelado stream has clear water and rocky/sandy bottom, with irregularly distributed small stones, cobbles and boulders. The stream has shallower sectors with fast-running water up to 60 cm deep, and deeper portions with around 2 m depth and abundant submerged vegetation ( Fig. 5 ). Species collected with H. nicolasi were Apareiodon affinis , Australoheros scitulus , Cnesterodon decemmaculatus , Corydoras paleatus , Crenicichla lepidota , Cyphocharax spilotus , C. voga , Characidium rachovii , C. tenue , Charax stenopterus , Cheirodon interruptus , Diapoma terofali , Heptapterus mustelinus , Hypostomus commersoni , Loricariichthys anus , Macropsobrycon uruguayanae , Oligosarcus jenynsii , Pseudocorynopoma doriae , and Rineloricaria isaaci .

Etymology. This species is dedicated to Nicolás Bonelli, whose affection and company we have enjoyed for the last few years.

Figures

Fig. 1. Hyphessobrycon nicolasi, ILPLA 1808, holotype, female, 49.1 mm SL. El Pelado stream, Uruguay River basin.

Fig. 2. Hyphessobrycon nicolasi, ILPLA 1812, paratype, male, 44.7 mm SL: (a) left maxilla, external view; (b) right premaxilla, external view; (c) right dentary, external view.Scale bar = 1 mm.

Fig. 3. Hyphessobryconnicolasi, MLP 9746, paratype, 51.4 mm SL.El Pelado stream, Uruguay River basin. Photographed in life.

Fig. 4. Type locality of Hyphessobrycon nicolasi (triangle).

Fig. 5. El Pelado stream, 32º19’S 58º14’W, Entre Ríos, Argentina, type locality of Hyphessobrycon nicolasi.