Hyphessobrycon loweae Costa & Géry, 1994

Figs. 6-9

Hyphessobrycon sp. “long dorsal”: Lowe-McConnell, 1991: 68 (Brazil, Mato Grosso State, upper rio Xingu; “Lago do Leo” and “Corrego do Gato”, rio Suiá-Missu drainage, rio Xingu basin).

Hyphessobrycon loweae Costa & Géry, 1994: 71-73, fig. 1 (description; type-locality “ Brazil: Estado de Mato Grosso, córrego Xavante, a tributary of rio Culuene, rio Xingú basin, 40 km S of Paranatinga, 15°01’S, 54°03’W ”; corrected coordinates of type locality approximately 14°43’S 54°04’W).

Diagnosis. Hyphessobrycon loweae can be distinguished from all congeners, with the exception of H. elachys, H. heliacus, and H. peugeoti, by the conspicuously elongated and filamentous dorsal fin in mature males (vs. dorsal and pelvic fins, when elongated, never filamentous). Hyphessobrycon loweae can be distinguished from H. elachys and H. peugeoti by its overall golden color in life (vs. a general clear/silvery color in H. elachys, and reddish color in H. peugeoti). Hyphessobrycon loweae can be distinguished from H. heliacus by the shorter pelvic-fins in fully mature males, reaching only the first anal-fin branched ray (vs. pelvic-fins filamentous, reaching up to the sixth anal-fin branched ray in H. heliacus), and by lacking chevron-like dark markings along the midline (vs. chevron-like dark markings along the midline present in H. heliacus). Additionally, H. loweae can be distinguished from H. elachys by possessing an anal fin with a straight margin in mature males (vs. a distinctly rounded anal-fin lobe present in H. elachys mature males); and from H. peugeoti by possessing a higher number of horizontal scale rows between the dorsal-fin origin and the lateral line (6-7, 5 vs. 5 in H. peugeoti), and by possessing a lower number of branched anal-fin rays (17-21, modally 20, vs. 21-24, modally 22 in H. peugeoti).

Summary of meristic data. Lateral line incompletely pored, five (2), six (5), seven (22), eight (13), nine (3), or 10(1) perforated scales. Lateral series scales including perforated scales 27(1), 28(2), 30(1), 31(5), 32(10), 33(11), 34(10), 35(4), or 37(1). Horizontal scale rows between dorsal-fin origin and lateral line six (39), or seven (7), not including half scale of predorsal series situated just anterior to first dorsal-fin ray. Horizontal scale rows between lateral line and pelvic-fin origin three (1), four (42), or five (1). Scales around caudal peduncle 12(6), 13(14), 14(17), or 15(5). Dorsal-fin rays ii, 8(11), or 9(37). Anal-fin rays iv, 17(1), 18(8), 19(27), 20(9), or 21(3). Pectoral-fin rays i, 9(6), 10(20), 11(20), or 12(2). Pelvic-fin rays i, 6(13), or 7(35). First gill arch with two (5), three (1) epibranchial, eight (1), nine (5), or 10(1) ceratobranchial, and five (5), or six (2) hypobranchial gill-rakers. Vertebrae 31(2), 32(3), or 33(2). Supraneurals four (6). Morphometric data in Table 2.

Color in alcohol. Ground color pale to light yellowish. Guanine pigmentation present on opercular and infraorbital series, and on flank scales of most specimens, except those stored for long time in formalin. Body covered by scattered dark chromatophores, except at ventral regions of head and abdomen, which are clear. Dorsal surface of head and body, from snout to caudal fin, presenting dense concentration of dark chromatophores, mostly on distal portion of scales. Humeral region with vertically elongated, roughly rectangular dark blotch, tapering ventrally, at level of second and fourth lateral line scales. Blotch one and a half scales wide, four to five scales high. Narrow midlateral stripe formed by chromatophores at myosepta between hypaxial and epaxial bundles of muscles, more conspicuous posteriorly to dorsal-fin base. Scattered dark chromatophores scattered across flanks forming ill-defined, broad dark lateral band. Dark chromatophores distributed along myomere junctions, forming thin, angled lines (chevron marks). Caudal peduncle blotch black, variously developed, more developed in males, varying from occupying most of caudal peduncle surface to concentrated on its middle portion, extending across 5-9 last scales of lateral line. Some adult males with blurred, curved dark vertical bars at flanks. Caudal fin with variously developed dark pigmentation on middle caudal-fin rays of adult males, varying from some pigmentation on middle caudal-fin rays to relatively well-defined stripe. Remaining fins clear, with scattered dark chromatophores. Dark chromatophores of dorsal fin more concentrated over its apical portion. Pectoral and pelvic fins hyaline, with few, scattered dark chromatophores. Anal fin hyaline, with some scattered dark chromatophores over its interradial membranes.

Color in life. Based on photographs of two mature males (MZUSP 97435, one depicted in Fig. 9), and the holotype (Costa & Géry, 1994: 72, fig. 1), and cursorial examination in the field of freshly collected specimens from lots MZUSP 97435 and MZUSP 95611 by the second author. Overall coloration (including all fins) golden-yellow; some specimens presenting a large amount of silvery pigmentation, apparently a consequence of infestation by trematodes (“brass-tetras”; cf. Géry & Delage, 1963). Upper portion of eye red.

Sexual dimorphism. Hyphessobrycon loweae presents the same type of sexual dimorphism as observed in H. peugeoti, i.e., mature males with an elongated, filamentous dorsal fin, anal fin with all fin rays with approximately the same size and relatively enlarged, resulting into a straight fin margin, and a more developed caudal-fin blotch. As in Hyphessobrycon peugeoti, mature males of H. loweae lack fin hooks.

Habitat and ecological notes. Hyphessobrycon loweae inhabits streams with clear water, slow current and abundant submerged vegetation. This is the type of habitat found at the type locality, the córrego Xavante (C. R. Moreira, pers. comm.; Costa & Géry, 1994), as well as at the upper rio das Mortes (J. L. Birindelli, pers. comm.) and tributaries of the rio Culuene at Gaúcha do Norte (F. C. T. L., pers. obs.). “Lago do Leo” at the rio Suiazinho, where some paratypes of Hyphessobrycon loweae were collected, is a small lake with dense aquatic vegetation (Lowe-McConnell, 1991: 71). Similarly to some congeners such as H. eques (Steindachner), H. micropterus (Eigenmann), and Hyphessobrycon negodagua Lima & Gerhard (Lima & Gerhard, 2001: 112-113), H. weitzmanorum Lima & Moreira (Lima & Moreira, 2003: 30), and H. bifasciatus Ellis (Lima et al., 2008), it appears that H. loweae favors streams and/or ponds with abundant submerged aquatic vegetation.

Distribution and biogeography. Hyphessobrycon loweae was originally described from tributaries of the rio Culuene and rio Suiá-Missú in the upper rio Xingu basin, Mato Grosso, Brazil. The species is herein recorded from the upper rio das Mortes, a tributary of the rio Araguaia-Tocantins basin (Fig. 5). The species is known from adjacent (less than 20 km apart) headwaters of the rio Culuene and rio das Mortes, and presumably may have been transposed across the water divide via stream capture events. Several fish species are known to occur in adjacent river systems across the southern tributaries of the Amazon basin flowing through the Brazilian shield, presumably due to river capture events resulting from neotectonic reactivation of ancient faults of the Transbrasiliano lineament, which transverses the region (Lima & Ribeiro, 2011).

Remarks. Comparisons between Hyphessobrycon loweae specimens from the rio Culuene (rio Xingu basin) and rio das Mortes (rio Tocantins-Araguaia basin) did not reveal any features that might distinguish these different populations, and thus they are herein considered to represent a single species. The vertically-elongated, curved dark bars in the posterior portion of body (Fig. 7) are present in some mature male specimens from both the rio das Mortes (MZUSP 101404) as well as from the rio Culuene (MZUSP 95611) drainages.

Material examined. Brazil. Mato Grosso State: Rio Araguaia basin: MZUSP 97701, 22, 17.8-29.0 mm SL, Santo Antônio do Leste, tributary to rio das Mortes, near border between Santo Antônio do Leste and Riacho Suspiro, 14°52’30”S, 54°05’00”W. MZUSP 97889, 1, 25.7 mm SL, Santo Antônio do Leste, riacho Gailiro (rio das Mortes basin), road MT-130, 14°53’34”S, 54°04’45”W. MZUSP 97693, 1, 34.8 mm SL, Campo Verde, rio das Mortes, road BR-070, 15°40’22”S, 55°17’53”W. MZUSP 101404, 47, 11.7-29.0 mm SL, Campo Verde, rio das Mortes, road Chapada dos Guimarães / Campo Verde, 15°30’20”S, 55°13’38”W. Rio Xingu basin: MZUSP 45749, 2 paratypes, 21.6 and 21.9 mm SL, Querência, “Lago do Leo” (rio Suiaizinho drainage), ca. 12°43’S 51°50’W. MZUSP 45750, 1, paratype, 22.2 mm SL. MZUSP 45751, 2, paratypes, 21.0 and 23.0 mm SL, ribeirão Cascalheira, “córrego do Gato” (rio Suiaizinho drainage), ca. 12°56’S 51°51’W. MZUSP 95611, 14, 13.1-25.6 mm SL, Gaúcha do Norte, stream tributary of rio Culuene, at MT-020, 13°30’00”S 53°5’35”W. MZUSP 97435, 227, 10 c&s, 10.4-27.6 mm SL, Gaúcha do Norte, stream near Culuene village (rio Culuene drainage), 13°30’29”S 52°46’50”W. MZUSP 102817, 10, 22.4-25.5 mm SL, Canarana, stream tributary to ribeirão Água Limpa (tributary to rio Sete de Setembro), 5 km S of Canarana, 13°35’53”S 52°15’35”W. MZUSP 94214, 21, 12.2- 16.6 mm SL, Campinápolis, rio Culuene, downstream PCH Paranatinga II, 13°49’S 53°15’W. MZUSP 97846, 179, 17.4-30.8 mm SL, Primavera do Leste, córrego Xavante (tributary of rio Culuene), near road MT-130, 14°38’23”S 53°55’37”W. MZUSP 102816, 20, 21.2-34.2 mm SL, Paranatinga, córrego Xavante, tributary of rio Culuene, ca. 23 km from Paranatinga, road MT-130, 14°43’5” S 54°04’37”W.