Mylossoma unimaculatum ( Steindachner, 1908 ),

Mateussi, Nadayca T. B., Oliveira, Claudio & Pavanelli, Carla S., 2018, Taxonomic revision of the Cis-Andean species of Mylossoma Eigenmann & Kennedy, 1903 (Teleostei: Characiformes: Serrasalmidae), Zootaxa 4387 (2), pp. 275-309: 299-304

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Mylossoma unimaculatum ( Steindachner, 1908 )

comb. nov.

Mylossoma unimaculatum ( Steindachner, 1908)  comb. nov.

( Figs. 20–23View FIGURE20View FIGURE 21View FIGURE 22View FIGURE 23; Table 5)

Metynnis unimaculatus Steindachner, 1908: 326  [original description; type-locality: "Lagune am Rio Medonho, einem Nebenfluβ des Parnahyba nördich von Sa. Filomena"].— Zarske & Géry, 1999: 188 [cited].

Mylossoma duriventre  (non Cuvier, 1818). — Santos et al., 2004: 65 [lower rio Tocantins].— Lucinda et al. 2007: 78 [Lajeado Reservoir, rio Tocantins, Tocantins]— Mérona et al. 2010: 106 [Lower rio Tocantins, fisheries].— Ferreira et al. 2011: 280 [Cantão State Park, rio Araguaia].

Diagnosis: Mylossoma unimaculatum  differs from M. aureum  by presenting the last abdominal spine reaching the anal-fin origin or almost (vs. last abdominal spine clearly separated from anal-fin origin), 37 vertebrae (vs. 38–39) and a conspicuous black blotch on opercle (vs. black blotch absent or inconspicuous). It differs from M. albiscopum  by presenting 28 to 32 branched rays on the anal fin (vs. 31 to 38), 34 to 40 circumpeduncular scales (vs. 28 to 36) and 95 to 100 perforated scales in the lateral line (vs. 74 to 99). It differs from M. duriventre  by presenting 34 to 40 circumpeduncular scales (vs. 30 to 34), 95 to 110 perforated scales on lateral line (vs. 74 to 97) and 37 vertebrae (vs. 35–36).

Description: Morphometric data presented in Table 5. Body deep, compressed laterally. Dorsal profile concave at posterior region of head and convex between head and dorsal fin. Ventral profile convex; slightly concave at isthmus and strongly convex from this point to end of anal fin. Highest body depth on vertical line passing through dorsal- and pelvic-fin origins. Caudal peduncle deeper than longer.

Eyes lateral, at middle of head; upper margin of eyes below longitudinal axis of lateral-line origin. Frontal and parietal fontanel broadly expanded laterally. Snout short and rounded on lateral view. Nostrils dorsolateraly positioned, above longitudinal axis through upper margin of eye, between tip of snout and orbits.

Mouth terminal to slightly upturned, at same level of orbits. Premaxilla projected forward, with inner premaxillary row over or surpassing dentary teeth. Premaxillary teeth molariform with robust base; outer portion of anteriormost three teeth of outer row and posterior portion of remaining teeth pointed. Inner premaxillary row with two teeth, separated from outer row. Outer premaxillary row with five teeth. Dentary with four or five modified tricuspid, robust, molariform teeth; symphyseal dentary teeth present, with robust base and large conical cusp, behind main row ( Fig. 2View FIGURE 2). Maxilla edentulous.

First gill arch with elongated and conical gill rakers; epibranchial gill rakers 12(4), 13(3) or 14(13); one (21) gill raker at cartilage between epi- and ceratobranchial; ceratobranchial gill rakers 15(2), 16(6), 17(3), 18(8) or 19(2).

Body completely covered by small cycloid scales. Accessory scales covering intersections of major scales, mainly at anterior portion of body. Lateral line complete, with 95(2), 96(1), 97(1), 98(5), 99(1), 100(2), 102(1), 103(1), 104(2), 105(3), 106(1), 107(3), 108(1) or 110(2) perforated scales, extending into caudal fin. Scales above lateral line 56(2), 59(1), 60(3), 61(1), 62(4), 63(3), 64(3), 65(1), 66(1), 67(1), 68(1) or 72(1). Scales below lateral line 46(2), 51(1), 53(2), 54(3), 55(4), 56(2), 57(1), 58(1), 63(2) or 64(1). Circumpeduncular series of scales 34(2), 36(14), 38(9) or 40(3). Ventral keel with well-developed spines forming high serra. Prepelvic spines 29(1), 30(2), 31(3), 32(10), 33(3), 34(2), 35(4), 36(3), 37(2) or 38(1). Postpelvic spines 12(4), 13(4), 14(1), 15(12) or 16(8). Anal spines 6(7), 7(13), 8(8), 9(3) or 10(1).

Dorsal fin not preceded by spine, its origin equidistant from tip of snout and end of hypural plate. First dorsalfin ray much shorter than second ray; in some specimens covered by skin, in such cases discernible only if dissected or x-rayed. Branched dorsal-fin rays gradually decreasing in size; dorsal-fin rays 12(1), 13(2), 14(6), 15(21) or 16(1). Adipose fin short, entirely covered by small scales. Pectoral fins falcate, with i(32) + 13(4), 14(4), 15(16), 16(7) or 17(1). Pelvic fin small, with i(31) + 5(3) or 6(28) branched rays. Anal fin long, with convex edge, median and posterior rays longer than anterior ones, not lobed; sheath of scales covering at least one-third of analfin length; anal-fin rays 28(3), 29(9), 30(13), 31(4) or 32(2). Caudal fin bifurcated, lobes of similar size, with 16(1), 17(25), 18(5) or 19(2) rays. Vertebrae 37(11). Supraneurals 4(5) or 5(2).

Color in alcohol. General body color light brown, darker dorsally ( Fig. 21View FIGURE 21). Fins pale yellow; often with bases of caudal and anal fins and distal margin of anal fin dark. Conspicuous black or brown blotch on opercle. Juvenile specimens presenting several vertical narrow, brown bands on flanks and a round, pale brown, inconspicuous blotch below dorsal fin, sometimes absent ( Fig. 22View FIGURE 22).

Color in life. General body color silvery, darker dorsally; orange to reddish tint on head and around the eyes. Presence of a black blotch on opercle. Anal fin with yellow and orange pigmentation, and a black band at distal margin; remaining fins hyaline ( Fig. 23View FIGURE 23).

Geographic distribution. Mylossoma unimaculatum  is restricted to the rio Tocantins-Araguaia system, Amazon basin, Brazil ( Fig. 3View FIGURE3).

Ecological notes. According to Santos et al. (2004), Mylossoma unimaculatum  inhabits rivers margins and lagoons, feeding primarily on leafs, fruits, seeds and invertebrates, and presents total spawning during the flood season. Given its migratory behavior, Mylossoma unimaculatum  was one of the most affected species after the establishment of the Tucuruí reservoir, since the river impoundment prevents the upstream reproductive migration and also limits the recolonization of downstream stretches ( Mérona et al. 2010).

Molecular data. DNA barcoding showed that the genetic distance between Mylossoma unimaculatum  ( M. duriventre  "group 4" in Mateussi et al. 2016) and the remaining analyzed species ranged from 0.014 to 0.091, being more similar genetically to M. duriventre  ( M. duriventre  "group 3" in Mateussi et al. 2016).

Remarks. Mylossoma unimaculatum  was previously identified from the Tocantins-Araguaia basin as Mylossoma duriventre  (e.g. Santos et al. 2004).In the original description, Steindachner (1908) indicated a lake at rio Medonho, a tributary to the rio Parnaíba (an independent river system flowing at the northeastern Brazilian States of Maranhão and Piauí), as the type-locality. However, this is the only record of Mylossoma  specimens for this river basin. Ramos et al. (2014) have undertaken an extensive survey of the fish fauna from the rio Parnaíba basin, and listed the genus Mylossoma  as occurring in this basin based solely in the literature. During the " Brasilien Expedition" directed by F. Steindachner in 1903, when the type specimens of Metynnis unimaculatus  were collected, not only the rio Parnaíba but also the lower rio Tocantins was sampled, including fish markets at the rio Tocantins ( Böhme 1996), where Mylossoma unimaculatum  is relatively common. We thus consider the typelocality given by Steindachner (1908) as very likely a mistake and we suggest that the type-locality of Metynnis unimaculatus  to be more likely somewhere at the lower rio Tocantins basin.

Material examined. Type material. NMW 56451, 3, 75.9–78.1 mm SL, lake at rio Medonho, Santa Filomena , Brazil [type-locality probably incorrect, see above]. Syntypes of Metynnis unimaculatus  . Non-type material. Brazil. Rio Tocantins-Araguaia basin. Goiás: INPA 46074View Materials, 5View Materials (1 sk), 156.7–184.0 mm SL, Aragarças , rio Araguaia , 15°53'25"S 52°14'25"W, 0 4 May 2014. R. R. Oliveira & J. L. OliveiraGoogleMaps  . MCP 17282, 1, 184.8 mm SL; MCP 17283, 1 (rd), 233.3 mm SL; MCP 17284, 1 (rd), 201.5 mm SL; MCP 17285View Materials, 1View Materials, 256.0 mm SL, Luís Alves, floodplain lakes of the rio Araguaia , 13°14'00"S 50°34'59"W, 21 Apr 1994GoogleMaps  . MCP 44841View Materials, 1View Materials (rd), 226.4 mm SL, Nova Crixás, rio do Peixe (trib. rio Araguaia ), c. 14°11'S, 50°23'W, 13 Jun 2008GoogleMaps  . NUP 13023View Materials, 3, 80.3–85.7 mm SL, São Miguel do Araguaia, lago Piratinga, rio Araguaia basin, 13°04'10"S 50°35'06"W, 0 4 Dec 2011, Nupélia team.GoogleMaps 

NUP 13043View Materials, 1, 84.1 mm SL, Nova Crixás, rio Araguaia , 13°21'53"S 50°37'46"WGoogleMaps  , 0 2 Nov 2011, Nupélia team. NUP 13051View Materials, 1, 90.0 mm SL, São Miguel do Araguaia, rio Crixás –Açu (trib. rio Araguaia ), 13°20'33"S 50°36'41"WGoogleMaps  , 0 2 Nov 2011, Nupélia team. NUP 13087View Materials, 2, 71.8–104.0 mm SL, Nova Crixás, rio Crixás-Açu (trib. rio Araguaia ), 13°21'42.20"S 50°36'22.50"WGoogleMaps  , 0 2 Nov 2011, Nupélia. Mato Grosso: LBP 1823, 2, 177.9– 188.1 mm SL, Barra do Garças, rio Araguaia, 15°32'S 52°12'WGoogleMaps  , 27 Jul 2003, C. Martins et al. LBP 8854, 1, 59.5 mm SL, Cocalinho, Lagoa da Montaria, rio Araguaia , 13°22'36.1"S 50°40'08.4"WGoogleMaps  , 27 Sep 2009, R. Devidé et al. . LBP 15286View Materials, 1, 75.4 mm SL, Cocalinho, lagoa da Boca Franca, rio Araguaia , 13°48'58"S 51°10'46"WGoogleMaps  , 0 6 Sep 2008, J. A. Senhorini et al. LBP 18462View Materials, 5 (rd), 86.8–112.8 mm SL, Cocalinho, rio Araguaia , 13°18'37.3"S 50°36'47.6"WGoogleMaps  , 29 Sep 2009, R. Devidé et al. . MZUSP 20419View Materials, 2View Materials (rd), 199.6–214.8 mm SL, Cocalinho, lago Rico, rio Araguaia , 14°22'00"S 51°00'00"WGoogleMaps  , EMGOPA. NUP 12745View Materials, 1, 72.1 mm SL, Cocalinho, lago Goiaba, rio Araguaia , 12°50'54"S 52°32'02"WGoogleMaps  , 0 5 Dec 2011, Nupélia team. NUP 13030View Materials, 1, 72.2 mm SL, Cocalinho, lago Varal, rio Araguaia , 13°00'52"S 50°36'08"WGoogleMaps  , 0 3 Nov 2011, Nupélia team. Pará: UNT 11125View Materials, 1View Materials (rd), 108.4 mm SL, Marabá, rio Taurizinho , 05°22'33"S 49°00'53"WGoogleMaps  , 17 Dec 2009, Neamb team. Tocantins: INPA 20489View Materials, 1View Materials, 176.2View Materials mm SL, Caseara, lago das Ariranhas, rio Araguaia , 09°20'S, 50°00'WGoogleMaps  , 23 Feb 2000, INPA Ictiofauna team. 


Department of Natural Resources, Environment, The Arts and Sport


Pontificia Universidade Catolica do Rio Grande do Sul


Universidad nacional de Tucumn


Instituto Nacional de Pesquisas da Amazonia














Mylossoma unimaculatum ( Steindachner, 1908 )

Mateussi, Nadayca T. B., Oliveira, Claudio & Pavanelli, Carla S. 2018

Metynnis unimaculatus

Steindachner, 1908 : 326
Zarske & Géry, 1999 : 188

Mylossoma duriventre

Santos et al., 2004 : 65
Lucinda et al. 2007 : 78
Mérona et al. 2010 : 106
Ferreira et al. 2011 : 280