Hemigrammus arua, Lima & Wosiacki & Ramos, 2009

Lima, Flávio C. T., Wosiacki, Wolmar B. & Ramos, Cristiane S., 2009, Hemigrammus arua, a new species of characid (Characiformes: Characidae) from the lower Amazon, Brazil, Neotropical Ichthyology 7 (2), pp. 153-160 : 154-158

Hemigrammus arua , new species

Figs. 1-3

Holotype. MPEG 14755 , 26.8 mm SL, Brazil, Pará State, município de Juruti, lago São Francisco do Alto Aruã, rio Aruã, tributary of rio Arapiuns , tributary of rio Tapajós , 02º36’4”S 55º54’21”W, 20 Feb 2008, W. B. Wosiacki, R. D. O. Rayol & A. S. Bezerra.

Paratypes. All from Brazil, Pará State, município de Juruti : MPEG 14756 , 4 , 20.3-26.3 mm SL, same data as holotype . MPEG 14757 , 138 (29, 14.7-30.0 mm SL), 5 c&s, 16.4-22.0 mm SL ; INPA 28979 , 5 , 15.6-21.4 mm SL ; ANSP 187426 , 5 , 17.2-21.2 mm SL: same locality as holotype, 12 Aug 2004 , W. B. Wosiacki & A. S. Bezerra. MPEG 14758 , 1 , 19.6 mm SL, headwaters of igarapé Juruti Grande, right tributary of rio Amazonas , 02º34’30”S 56º24’12”W, 05 Aug. 2004 , W. B. Wosiacki & A. S. Bezerra. MPEG 14759 , 2 , 17.3-19.2 mm SL, rio Branco, tributary of rio Arapiuns, tributary of rio Tapajós , 02º20’58”S 56º01’22”W, 10 Aug 2004 , W. B. Wosiacki & A. S. Bezerra. MPEG 14760 , 10 , 18.0- 21.8 mm SL, same locality and collectors as MPEG 14759 , 11 Aug 2004 . MPEG 14761 , 3 , 17.3-21.3 mm SL, same locality and collectors as MPEG 14759 , 09 Aug 2004 . MZUSP 100379 , 29 , 13.8 - 24.7 , 3 c&s, 17.2-19.5 mm SL, igarapé São Francisco do Alto Aruã , 02°20’54”S 56°0’42’’W, 11 Aug 2004 , W. B. Wosiacki.

Diagnosis. Hemigrammus arua can be diagnosed from all congeners, except H. stictus (Durbin) , by possessing a large, single humeral spot which is situated from fifth-sixth to posterior margin of eighth-tenth lateral line scales (vs. humeral spot absent, double, or, if single, situated from second-third to posterior margin of fourth-fifth lateral line scales). Hemigrammus arua can be distinguished from H. stictus by possessing a humeral spot roughly rectangular, higher than wide, with a pronounced upper, anteriorly-oriented extension,

conferring an inverted-comma shape to the blotch (vs. humeral spot roughly rounded, not presenting an inverted-comma shape), and life color pattern presenting unpaired fins orangereddish (vs. caudal fin and caudal peduncle bright red in life, remaining fins translucent).

Description. Morphometric data of holotype and paratypes presented in Table 1 . Body compressed, moderately high. Greatest body depth at dorsal-fin origin. Dorsal profile of head convex from upper lip to vertical through middle of orbit; slightly concave from latter point to tip of supraoccipital spine. Predorsal profile of body convex, posteroventrally inclined along dorsal-fin base. Body profile straight to slightly convex from dorsal-fin base terminus to adipose fin; slightly concave between latter point to origin of anteriormost procurrent caudal-fin ray. Ventral profile of head and body convex from lower lip to anal-fin origin, sometimes slightly concave at urogenital opening. Body profile along anal-fin base straight and posterodorsally inclined. Ventral profile of caudal peduncle slightly concave.

Jaws equal, mouth terminal. Posterior tip of maxilla reaching vertical through anterior third of orbit. Premaxillary teeth in two rows ( Fig. 4 ). Outer row with 2(1), 3*(25) 4(3), or 5(2) relatively compressed, tri- to tetracuspidated, elongated teeth. Inner row with 5*(27), 6(4), or 7(1) relatively compressed, penta- to heptacuspidated teeth. Maxilla with 4(2), 5(1), or 6(4) tri- to pentacuspidated teeth. Anteriormost teeth larger. Dentary with 12(1), 13(2), 14 (1), 15(1), 16(1), or 17(1) teeth, sixth to seventh anteriormost teeth larger, relatively compressed, penta- to heptacuspidated, gradually decreasing in size. Remaining dentary teeth considerably smaller, cylindrical, uni- to tricuspidated.

Scales cycloid, with few slightly divergent radii extending to posterior margin of scales. Lateral line slightly decurved ventrally, incompletely pored, with 6*(10), 7(8), 8(8), or 9(1) perforated scales. Lateral series scales including lateral line scales 24(1), 25(2), 26(1), 27(6), 28(9), 29(4), or 30*(5). Horizontal scale rows between dorsal-fin origin and lateral line typically 5*, a single specimen with six. Horizontal scale rows between lateral line and pelvic-fin insertion three. Scales along middorsal line between distal tip of supraoccipital process and origin of dorsal fin 7(2), 8(26), or 9*(1). Horizontal scale rows around caudal peduncle 10(1), 11(8), or 12*(19). Single row of 3-4 scales covering base of anteriormost anal-fin rays. Caudal fin scaled, basalmost scales slightly smaller than caudal peduncle scales. Scales present on basal third of upper and lower caudal lobes (lost in most specimens).

Dorsal-fin rays ii, 9*(28), 10(1), not including small ossification anterior to first unbranched ray, discernible only in c&s specimens, absent in two out of eight c&s individuals. Dorsal fin pointed in juvenile specimens, and rounded in adult specimens (see Fig. 3 ), last unbranched and four anteriormost branched rays considerably more elongated than remaining rays. Dorsal-fin origin slightly anterior to vertical through middle of standard length. Base of posteriormost dorsal-fin ray at vertical through anal-fin origin. First dorsal-fin pterygiophore inserting posterior to neural spine of 8 th (8) vertebrae. Adipose fin present. Anal-fin rays iv(8), 17(2), 18*(3), 19(14), 20(8), or 21(1). Anteriormost anal-fin pterygiophore inserting behind haemal spine of 15 th (2) or 16 th (6) vertebrae. Pectoral-fin rays i, 9(6), 10*(20), 11(3). Tip of pectoral fin reaching vertical through pelvic-fin insertion. Pelvic-fin rays typically i,7*, a single specimen i,8. Caudal fin forked, lobes slightly rounded, similar in size. Principal caudalfin rays 10+9. Dorsal procurrent caudal-fin rays 8(2), 9(5), or 10(1), and ventral procurrent caudal-fin rays 6(2), 7(5), or 8(1). First gill arch with 0(1), 1(1), or 2(2) hypobranchial, 6(1), 8(1), 9(2) ceratobranchial, 1(4) on cartilage between ceratobranchial and epibranchial, and 4(1), 5(1), or 6(2) epibranchial gill-rakers. Vertebrae 31(8). Supraneurals 3(1) or 4(7). Branchiostegal rays four; three branchiostegal rays originating from anterior ceratohyal and one from posterior ceratohyal.

Color in alcohol. Ground color tan, slightly darker dorsally. Guanine pigmentation present on opercular and infraorbital bones. Lower lip, snout, and top of head densely covered by small dark chromatophores, resulting in overall dark pigmentation. Upper half of opercle and fifth infraorbital with large, scattered dark chromatophores. Anterior two-thirds of eye dark pigmented. Gular area clear to tan.

Mid-dorsal and dorsal portion of first lateral scale rows with dense concentration of dark chromatophores, concentrated mainly on scale margins. Large, distinctive blotch, situated immediately above lateral line scales row, extending longitudinally from the fifth or sixth to the posterior margin of eighth to tenth lateral-line scales. Blotch roughly rectangular, higher than wide, with a pronounced upper, anteriorly-oriented extension, giving an invertedcomma shape to the blotch. Thin, subjacent dark midlateral stripe, extending along midline from blotch terminus to anterior portion of caudal peduncle. Scales of dorsal and lateral surfaces of body possessing numerous dark chromatophores, especially over midline. Subjacent dark chromatophores forming thin lines over myomere margins above anal fin base. Scales on abdominal region with few dark chromatophores. Narrow, subjacent stripe of dark pigment located dorsal to anal-fin base, extending approximately along region where hypaxial musculature and muscles of anal fin meet, sub-parallel to anal-fin base. Dark, subjacent pigmentation at base of anal-fin rays, forming a thin longitudinal line. Outer caudal-fin rays with margins dark pigmented, branched rays with few dark chromatophores along dorsal and ventral margins. Inner caudal-fin rays with distal portion more pigmented than remaining fin. Anal-fin rays with scattered chromatophores on interradial membranes. Dorsal, pectoral and pelvic-fin rays with dark pigment along anterior and posterior margins. Adipose fin with scattered dark chromatophores.

Life coloration. Based on a photograph of the holotype ( MPEG 14755 ) and paratypes ( MPEG 14756 ), taken immediatelly after fixation ( Fig. 3 ). Overall ground color brown. Opercular area , facial bones, and abdominal area above pectoral-fin basis bright golden, with a greenish hue. Gular and ventral area below pectoral-fin basis silvery. Dorsal , adipose, caudal, and anal fins, intense orange-reddish, except for their relatively faded distal portions. Pelvic fins yellowish, except in the holotype, which possess orange-reddish pelvic fins. Pectoral fins translucent .

Sexual dimorphism. Not detected. Bony hooks on anal and pelvic fins of mature males, a common dimorphic feature among characids (Malabarba & Weitzman, 2003) were not found.

Geographical distribution. Known from the headwaters of the rio Arapiuns (rio Branco and rio Aruã), rio Tapajós basin,

and from the adjacent headwaters of the igarapé Juruti Grande, a right margin tributary of the rioAmazonas, Pará State, Brazil ( Fig. 5 ).

Ecological notes. The type locality, lago São Francisco do Alto Aruã, is, in spite of its name, not a lake but actually a large river pool (about 200 meters wide). Satellite images of the area suggest that this portion of the rio Aruã is a valley of an ancient ria-lake which is being filled by sediments, as evidenced by the presence of extensive floodplains upstream the lake Aruã (see Klammer, 1984, for a discussion on this type of landscape feature in the Central Amazon region). Specimens of Hemigrammus arua were collected in relatively shallow (1-1.5 meters deep) marginal areas, with abundant aquatic macrophytes, both emergent and non-emergent. Identifiable itens found in gut contents of four specimens (MPEG 14757. 22.0- 27.7 mm SL) were insect larvae (both aquatical and terrestrial forms), winged insects, and vegetal remains.

Etymology. Arua, after lago São Francisco do Alto Aruã, the type locality. A noun in apposition.

Figures

Fig. 1. Hemigrammus arua, holotype, MPEG 14755, 26.8 mm SL: Brazil, Pará State, município de Juruti, lago São Francisco do Alto Aruã. Black spots over body and fins are nematodes’ cysts.

Fig. 2. Hemigrammus arua, paratype, MPEG 14757, 25.4 mm SL: Brazil, Pará State, município de Juruti, lago São Francisco do Alto Aruã.

Fig. 3. Hemigrammus arua, a) holotype, MPEG 14755, 26.8 mm SL, and b-e, paratypes, MPEG 14756 (20.3-26.3 mm SL); immediately after collecting. Black spots over body and fins are nematodes’ cysts.

Fig. 4. Hemigrammus arua, paratype, MZUSP 100379, 19.5 mm SL; scanning electron micrographs (SEM) showing left premaxillary (a), maxillary (b), and dentary teeth (c) in mesial view. Scale bar: (a-c): 100 µm; (b) 30 µm.

Fig. 5. Map of northern South America, showing (inset) the surroundings of Juruti, Pará State, Brazil, and sites of collection of Hemigrammus arua (dots). Star: Type locality.