Moenkhausia flava, Britzke & Troy & Oliveira & Benine, 2018

Britzke, Ricardo, Troy, Waldo P., Oliveira, Claudio & Benine, Ricardo C., 2018, Description of a new species of Moenkhausia (Characiformes: Characidae) from the upper Paraguay basin, Central Brazil, with comments on its phylogenetic relationships, Neotropical Ichthyology 16 (2), pp. 1-11 : 3-9

Moenkhausia flava , new species

Figs. 1-7 ; Tab. 1

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Holotype. MZUSP 123719 , 34.0 mm SL, Brazil: Mato Grosso State, Tangará da Serra, Córrego São Jorge, tributary of rio Sepotuba , rio Paraguay basin, 14°27’24.9” S 57°34’32.7” W, 12 Nov 2009, R. Britzke, T. S. Zanini & W. P. Troy.

Paratypes. LBP 9031 , 17 (7 cs), 20.9-36.8 mm SL, collected with holotype . LBP 18414, 15 , 29-38.3 mm SL, same locality as holotype, 2 Apr 2013, W. P. Troy . MZUSP 123720 , 10 , 24.9-35.2 mm SL, same locality as holotype, 2 Apr 2013, W. P. Troy . MZUEL 8139 , 3 , 19.9-23.5 mm SL, Brazil: Mato Grosso State, Tangará da Serra, Ribeirão do Sapo, tributary of rio Sepotuba , rio Paraguay basin, 14°33’24.6” S 57°48’45.8” W, 29 Aug 2013, J. L. O. Birindelli, A. Claro-García, F. Assega & E. Santana .

Non types. Brazil: Mato Grosso State, Tangará da Serra: LBP 8418, 2, 34.9-39.4 mm SL, Córrego São Jorge, tributary of rio Sepotuba , rio Paraguay basin, 14°27’26.3” S 57°34’34” W. LBP 8406, 1, 23.4 mm SL, Riacho Águas Claras, tributary of rio Sepotuba , rio Paraguay basin, 14°21’03.2” S 57°33’07.2” W. Non-types also include dissected, alcoholfixed, and poorly preserved specimens .

Diagnosis. Moenkhausia flava is distinguished from all congeners and members of closely related genera, except Hemigrammus barrigonae Eigenmann & Henn, 1914 ; Hemigrammus lunatus Durbin, 1918 ; Hemigrammus machadoi Ota, Lima & Pavanelli, 2014 ; Hemigrammus ulreyi (Boulenger, 1895) ; Moenkhausia collettii (Steindachner, 1882) ; Moenkhausia conspicua Soares & Bührnheim, 2016 ; Moenkhausia copei (Steindachner, 1882) and Moenkhausia venerei Petrolli, Azevedo-Santos & Benine, 2016 , by the presence of a well-defined dark line at the base of the anal fin. Moenkhausia flava can be easily distinguished from H. barrigonae , H. ulreyi , M. conspicua and M. venerei by the presence of a midlateral dark thin stripe little evident on posterior half of the body (vs. conspicuous dark and well-defined longitudinal midlateral dark stripe from humeral region until caudal peduncle). Moenkhausia flava is quite similar with H. barrigonae and M. conspicua by sharing overall body shape and similar color pattern. In addition, some specimens of H. barrigonae also present complete lateral line (see Géry, 1977:503; Soares, Bührnheim, 2016: 398), similar to the new species and M. conspicua . Moenkhausia flava differs from H. barrigonae and M. conspicua by presenting inner having premaxillary and dentary teeth pentacuspid (vs. inner premaxillary and dentary teeth heptacuspid in both species). Additionally, differs from H. barrigonae by larger body depth (31.0-42.6% SL, mean = 35.8% SL vs. 30.4- 34.8% SL, mean = 32% SL); and differs of M. conspicua by the dorsal-fin length (24.3-31.3% vs. 31.2-36.8% SL, respectively), anal-fin length (14.8-22.1% vs. 22.6-27.1% SL, respectively) and orbital diameter (34.8-43.4% vs. 44.9-56.0% HL, respectively). Moenkhausia flava can be easily distinguished from H. machadoi and H. lunatus by an inconspicuous oval-shaped vertically elongated humeral blotch, extending horizontally from third through five lateralline scales, and vertically from third row above lateral line to first row below it (vs. a conspicuous vertically elongated dark humeral blotch, extending horizontally from second through sixth lateral-line scales, and vertically from third row above lateral line to first row below it in H. machadoi ; and a small roundish humeral blotch in H. lunatus ). The new species differs from M. collettii and M. copei by having six longitudinal rows of scales above lateral line (vs. five longitudinal rows of scales). Additionally, it is distinguished from M. copei by a greater number of branched analfin rays (20-23 vs. 15-17 in M. copei ) and distinguished from H. machadoi , H. lunatus and M. collettii by a threescale deep band of sparse, scattered dark chromatophores extending along midlateral body (vs. a line of concentrated chromatophores along midlateral body).

Description. Morphometric data for Moenkhausia flava summarized in Tab. 1 . Body relatively compressed and elongated, moderately high. Greatest body depth just before the origin of dorsal fin. Snout profile convex. Dorsal profile of head straight or slightly convex. Dorsal profile of body convex from posterior tip of supraoccipital spine to dorsal-fin origin, slightly convex and posteroventrally slanted along dorsal-fin base, slightly convex from posterior terminus of dorsal-fin base to end of adipose-fin origin, and concave along caudal peduncle. Ventral body profile convex from tip of lower jaw to caudal-peduncle origin, slightly concave along caudal peduncle. Prepelvic region transversally flattened, more so proximal to pelvicfin insertion. Postpelvic region transversally flattened proximal to pelvic-fin insertion, becoming somewhat obtuse toward anal-fin origin. Mouth terminal. Maxilla slightly beyond vertical through anterior margin of orbit. Premaxillary teeth in two rows; outer teeth row with 3(19), 4*(21) tricuspid teeth, midcentral cusps longer than remaining cusps; inner teeth row with 4(2), 5*(38) tetra- to pentacuspid teeth, midcentral cusps longer than remaining cusps. Maxilla with 2(21), 3*(19) tricuspid teeth. Dentary with 4(5), 5*(27), 6(8) pentacuspid teeth, followed by a series of small teeth, with 1-3 cusps ( Fig. 6 ). Dorsal profile of head convex from upper lip to vertical through anterior nostril. Suparaoccipital process short, its tip not reaching vertical through posterior margin of opercle. Dorsal-fin rays ii,9(30). Pectoral-fin rays i,10(30), i,11*(10). Tip of pectoral fin not reaching vertical through pelvic-fin insertion. Adipose fin well developed. Pelvic-fin rays i,7(30), when adpressed, its tip reaching first anal-fin ray in a few specimens. Anal-fin rays iv, 20(3), 21*(10), 22(12), 23(3). Caudal fin forked. Principal caudal-fin rays i,17,i. Scales cycloid, with few radii along posterior border. Lateral-line completely pored. Lateral line scales 33(4), 34(17), 35*(11), 36(1). Scale rows between dorsal-fin origin and lateral-line 6; scale rows between lateral-line and pelvic-fin origin 4. Circumpeduncular scale rows 14*(32). Predorsal scales 10*(30). Scale sheath along anal-fin base in a single series of 4 scales, extending from the first to fifth branched anal-fin ray. First gill arch with 9*(18) gill rakers on ventral limb and 5*(18) on dorsal limb.

Sexual dimorphism. Adult males with small hooks on the last unbranched and anterior four branched anal-fin rays. Also, found on the first and second pelvic-fin rays branched. In both fins, there are four to seven hooks per fin ray, located on the distal segments.

Color in alcohol. Humeral region with an inconspicuous oval-shaped vertically elongated humeral blotch located on second to fourth lateral line scales, extending from 3 horizontal series of scales above lateral to the series of scales immediately below the lateral line. Dark chromatophores scattered on infraorbitals and opercle, longitudinal dark lighter stripe along on the eye ( Fig. 2 ). A dark thin stripe extending along horizontal septum, from humeral region to caudal peduncle, more evident on posterior half of the body. A three-scale deep band of sparse, scattered dark chromatophores extending along midlateral body.

Dorsal fin rays with few dispersed chromatophores, more concentrated on anterior half. Anal-fin rays with few dispersed chromatophores, more concentrated along its proximal and distal extension, resulting in a lighter medial area. Tip of anterior anal-fin rays densely pigmented by dark chromatophores resulting in a dark dash in this area. Paired fins hyaline with scattered dark pigmentation, more concentrated on unbranched rays. Caudal fin with a narrow field of dark chromatophores on its distal margin. Conspicuous dark line at anal-fin base. All fins hyaline with few dispersed chromatophores. Anterior rays of the anal fin and base of caudal-fin lobe present orange pigmentation in freshly preserved specimens.

Color in life. Body general color pattern pale yellowish. Dorsal region olive. Abdomen whitish to light yellow. Pelvic fin and adipose fin with yellow-orangish coloration. Dorsal fin and caudal fin with orange-reddish coloration. Anal fin with first rays with orange-reddish coloration and the remaining rays with hyaline coloration. A conspicuous dark line at the base of the anal fin. Pectoral fin yellowish ( Fig. 4 ).

Ecological notes. All specimens of Moenkhausia flava were collected along the margin in semi-lentic stretches of a shallow river with clear water, with sand and scattered small stones on the bottom, aquatic vegetation ( Echinodorus sp., Eleocharis sp., Hygrophila sp. and Mayaca fluviatilis ), and riparian vegetation ( Fig. 3 ). Species collected syntopically were Hyphessobrycon hebertaxelrodi Géry, 1961 , Hyphessobrycon vilmae , Pyrrhulina australis Eigenmann & Kennedy, 1903 , Characidium aff. z ebra Eigenmann, 1909, Corydoras aeneus (Gill, 1858) , Hypostomus sp., Brachyhypopomus sp., Gymnotus inaequilabiatus (Valenciennes, 1839) , and Aequidens rondoni (Miranda Ribeiro, 1918).

Geographic distribution. Only known from tributaries of the upper rio Sepotuba, above the waterfalls Salto das Nuvens and Salto Maciel, rio Paraguay basin, Mato Grosso State, Brazil ( Fig. 5 ).

Etymology. The name of species is derived from Latin flavus, meaning yellow. The name refers to the yellowish color pattern of the body in live specimens. An adjective.

Phylogenetic analysis. Partial sequences of two mitochondrial (16SrRNA and Cytb) and three nuclear genes (Myh6, Rag1 and Rag2) were obtained for 2 species of Hemigrammus and 29 species of Moenkhausia from the final matrix by Mariguela et al. (2013) deposited in TreeBase (treebase.org) under access number 13922, plus the species Hemigrammus barrigonae , H. unilineatus and Moenkhausia flava . The combined sequence data resulted in a matrix with 4,640 base pairs (bp), out of which 1,911 were conserved, 2,726 were variable and 2,196 were information parsimony. The estimated index of substitution saturation (Iss) performed in DAMBE 5.2.31 ( Xia, Xie, 2001) showed that the data were not saturated (i.e., Iss.c value greater than Iss). In our analysis, Moenkhausia flava is more closely related to Moenkhausia collettii , M. copei , Hemigrammus barrigonae and H. ulreyi ( Fig. 7 ). The new species was recovered within the clade 2 (sensu Mariguela et al., 2013), also composed of Aphyodite grammica Eigenmann, 1912 ; Bryconella pallidifrons (Fowler, 1946) ; Hemigrammus barrigonae , H. ulreyi , H. unilineatus (Gill, 1858) ; Moenkhausia comma Eigenmann, 1908 ; M. copei , M. aff. copei , M. collettii , M. hemigrammoides Géry, 1965 ; M. margitae Zarske & Géry, 2001 ; Pristella maxilaris (Ulrey, 1894) , plus Moenkhausia flava . In this analysis, the groups proposed by Géry (1977), reinforce that overall similarities are not sufficient to distinguish groups in Moenkhausia . However, few features seem to be still useful to designate natural groups within Moenkhausia and Hemigrammus (see discussion).

Conservation status. Moenkhausia flava is known exclusively from tributaries of the upper rio Sepotuba, above the waterfalls Salto das Nuvens and Salto Maciel, rio Paraguay basin. Because no specific threats have been detected, the species can be categorized as Least Concern (LC) according to IUCN criteria (IUCN, 2016), however, we emphasize the apparently narrowly distribution of the species, and strongly encourage the preservation of those environments.

Figures

Fig. 1. Moenkhausia flava, holotype, MZUSP 123719, 34.0 mm SL, Brazil, Mato Grosso, small stream tributary of rio Sepotuba.

Fig. 2. Moenkhausia flava, paratype, LBP 18414, 34.1 mm SL. Overall coloration darker, yellowish tan, where most of dark pigments are preserved.

Fig. 3. Type-locality of Moenkhausia flava, upper rio Sepotuba basin, Mato Grosso, Brazil.

Fig. 4. Live specimen of Moenkhausia flava, paratype, MZUEL 8139, 28.5 mm SL.

Fig. 5. Map showing the localities of Moenkhausia flava. Red star represents the type locality. Black square represents the Salto das Nuvens fall and the white square represents Salto Maciel fall.

Fig. 6. Moenkhausia flava. LBP 9031, 31.9 mm SL, paratype: right premaxilla (top), maxilla (middle), and dentary (bottom). Scale bar = 0.5 mm.

Fig. 7. Maximum likelihood phylogenetic tree based on Partial sequences of two mitochondrial genes and three nuclear genes. The series of three numbers (e.g. 100/94/1) at each of the main nodes represents the percentage of bootstrap support obtained by Maximum Likelihood (ML), the percentage of bootstrap support obtained by the Maximum Parsimony (MP) analysis and the posterior probability for that split obtained in Bayesian analysis (B),respectively (1000 bootstrap replicates). Dashes represent values <50% (ML, MP) or <0.5 (B).