Brycon falcatus Muller & Troschel 1844

Brycon falcatus Müller & Troschel, 1844 (Figs. 84–98) Chalceus labrosus Jardine, in Jardine & Schomburgk, 1841: 212 –213, pl. 13, fig. 1 (Type locality, “river Paduiri”); Lima, 2003: 178 (listed; as a species inquirendae in Brycon; type locality incorrectly stated as situated in Guyana). Brycon falcatus Müller & Troschel, 1844: 90 (Type locality, “In Guiana et Surinam”); Müller & Troschel, 1845: 29, pl. 6, fig. 1 (redescription); Müller & Troschel in Schomburgk, 1848: 635 (“allen flüssen von Britisch-Guiana”; common name); Günther, 1864: 334 –335 (Guyana; Essequibo River; Suriname); Goeldi, 1898: 483 (common name, rio Capim, Brazil); Eigenmann, 1912: 371 –372 (Guyana: Essequibo River at Rockstone; Potaro River at Tukeit); Fowler, 1914: 250 (Rupununi River, Guyana); Cockerell, 1915: 100, pl. 26, fig. 6 (scale morphology; Guyana); Steindachner, 1917: 36 –37 (Albina, Suriname; Brasil, Roraima: Rio Surumú, Serra do Mello; Rio Branco, Bem Querer; Boa Vista; Serra Grande; Conceição; Amazonas: mouth of rio Negro); Géry, 1964: 450 (diagnosis in key); Lowe-McConnell, 1964: 115, 118, 120, 127, 132 (Rupununi and Ireng rivers, Guyana; natural history); Richter & Nijssen, 1980: 123, 125 (Brokopondo reservoir, Suriname River, Suriname; occurrence; abundance, common name); Howes, 1982: 26 –29, fig. 18 (Guyana: Essequibo River; Tukeit; upper Cuyuni River; Rupununi district; Suriname: Nickerie district); Vari, 1983: 12, 16, figs. 3, 13, 14 (branchial arches morphology); Lasso, 1992: 11, 22, fig. 2 (río Suapure, Serranía de Los Pijiguaos, Venezuela); Planquette et al., 1996: 226 –227, fig. (French Guiana, Maroni and Mana rivers); Hardman et al., 2002: 234 (Essequibo and lower Potaro Rivers, Guyana); Mol, 2002: 71 (Kwitaro and Rewa Rivers, Rupununi, Guyana); Lima, 2003: 176 (synonymic list; primary type material; distribution; common names; maximum size); Hoeinghaus et al., 2003: 383 (Río Cinaruco, Rio Orinoco basin, Venezuela); Arrington & Winemiller, 2003: 449, 456 (Río Cinaruco, Río Orinoco basin, Venezuela; sandbank use); Watkins et al., 2004: 46 (Burro-Burro, Siparuni and Essequibo Rivers, Iwokrama forest, Guyana); Layman et al., 2005: 2532 (Río Cinaruco, Río Orinoco basin, Venezuela; trophic position in relation to size); Bejarano et al., 2006: 362, 365, 367–368 (Río Mesay, Río Caquetá drainage, Colombia: abundance); Blanco-Parra & Bejarano-Rodríguez, 2006: 856 –857 (Río Mesay, Río Caquetá drainage, Colombia: diet, reproduction); Mol et al., 2006: 114 (Coppename and Rechter River, Suriname); Mol et al., 2007: 355, 365 (Suriname River, Brokopondo reservoir, Suriname; abundance before and after impoundment); Agostinho et al., 2007: 126 –127 (Lajeado Dam, rio Tocantins, Tocantins, Brazil; density in fish ladder); Agostinho et al., 2007: 163 –165 (Lajeado Dam, rio Tocantins, Tocantins, Brazil; presence in the fish ladder); Silva et al., 2007: 487 (Rio das Mortes, rio Araguaia basin, Mato Grosso, Brazil); Ferreira et al., 2007: 125 (picture; rio Branco, Roraima); Albrecht et al., 2009: 181 –191 (Serra da Mesa dam, upper rio Tocantins basin, Brazil; weight-length relationships, reproduction, diet, persistence in the reservoir); Melo et al., 2009: 424 (Rio das Mortes, rio Araguaia basin, Mato Grosso, Brazil); Camargo & Giarrizzo, 2009: 221, 227 (lower rio Xingu: biological parameters, estimated biomass); Antunes et al., 2010: 676, 679–628 (Lajeado Dam, rio Tocantins, Tocantins, Brazil; nuclear and mitochondrial DNA analysis); Lima & Ribeiro, 2011: 149 (as an example of “Shield” distribution pattern); Venere & Garutti, 2011: 64 (Brazil, Mato Grosso, Parque Estadual da Serra Azul, rio Araguaia basin; short description, photo); Mol et al., 2012: 270 (Suriname: occurrence in Corantijn, Nickerie, Coppename, Saramacca, Suriname, and Marowijne rivers); Mol, 2012: 23, 283–285 (ocurrence in Suriname, local name, photos); Bartolette et al., 2012: 61 (Brazil, Goiás, Serra da Mesa dam); Albrecht et al., 2012: 203, 205 (Brazil, Goiás, Serra da Mesa dam; trophic analysis); Rubio et al., 2012: 173 –182 (Mato Grosso, rio Guaporé: population structure, female maturity, size, age); Pelicice & Agostinho, 2012: 711 (Brazil Tocantins, Peixe Angical dam fish ladder); Lima et al., 2013: 228 –229 (Brazil, Rondônia, rio Madeira basin; distribution in the rio Madeira basin, short description, photo); Correa & Winemiller, 2014: 214, 217, 218, 219, 220, 221 (Colombia, Depto.Vaupés, Río Apaporis: seasonal variation in diet, diet breadth and overlap with other frugivore fishes); Matos et al., 2016: 2016: 1–6 (diet, impact of artificial food supply in wild specimens; Brazil, rio Teles Pires basin). [Doubtful records: Gilbert & Roberts, 1971: 26 (Ecuador, Amazon basin); Saul, 1975: 103 (Ecuador, Napo, Río Conejo, Río Putumayo basin)]. Brycon schomburgkii Müller & Troschel, 1844: 91 (Type locality, “In Guiana”); Müller & Troschel, 1845: 29, pl. 6, fig. 2 (redescription); Müller & Troschel in Schomburgk, 1848: 635 (lower Essequibo River); Eigenmann, 1912: 372 (synonymization with B. falcatus). Brycon hilarii (not Valenciennes, 1850): Valenciennes (in Cuvier & Valenciennes, 1850): 248 (part; “l’Amazone”; syntypes of Chalceus hilarii); Castelnau, 1855: 68, pl. 36, fig. 1 (Brazil. Goiás, “Salinas”); Géry & Mahnert, 1992: 815 (part; paralectotypes from “Salinas”); Lima, 2003: 176 (type material; referred as putative specimens of Brycon falcatus). Brycon brevicauda Günther, 1864: 335 (Type locality, “Rio Jocintins, River Capin”); Boulenger, 1897a: 297 (Brazil, Pará, Ilha de Marajó); Goeldi, 1898: 483 (common name; upper rio Tapajós basin); Géry, 1964: 448, 450, pl. 2, fig. a (Ilha do Bananal, rio Araguaia; diagnosis); Costi et al., 1977: 53, fig. 23 (Pará, at the confluence of rio Araguaia and rio Tocantins); Santos et al., 1984: 41 –42, photo (Pará, rio Tocantins); Lowe-McConnell, 1991: (Mato Grosso, Xavantina: rio das Mortes, rio Araguaia basin; “Sangadina stream”; rio Suiá-Missú, rio Xingu basin); Tejerina-Garro et al., 1998: 402 (Goiás, São Miguel do Araguaia, floodplain lakes; relative abundance); Bergleiter, 1999: 23, 29, 48, 74–75, 113–114, 149 (pl. 10) (Lower rio Xingu, between Porto de Moz and Souzel; diet, feeding habits, social behavior, visual communication); Lima, 2003: 176 (type material; as a synonym of Brycon falcatus); Iglesias-Rios, 2012: 326 (Brazil, Goiás, Serra da Mesa dam: impacts of damming). Brycon bicolor Pellegrin, 1909a: 12 –13 (Type locality, “Orénoque”); Howes, 1982: 11, 13–14, fig.8 (syntypes, redescription); Taphorn, 1992: 80 –81, 128–130, figs. (Río Apure basin, Venezuela; description, ecology, biology); Royero et al., 1992: 49 (Rio Atabapo, Territorio Federal Amazonas, Venezuela); Machado-Allison et al., 1993: 66, 69 (Rio Aguaro and Rio Guariquito, Estado Guarico, rio Orinoco basin, Venezuela); Lima, 2003: 175 (type material; as a possible synonym of Brycon melanopterus). Brycon stübelli Steindachner, 1882a: 176 (Type locality, “Amazonenstome”; brief description); Steindachner, 1882b: 13, pl. 1, fig. 1 (full description; type locality specified as “Rio Amazonas (Iquitos)”). [not Amaral Campos, 1950: 142] Characinus amazonicus (not Agassiz, in Spix & Agassiz): Magalhães, 1931: 141 –142 (Lower Amazon basin; Goiás; natural history, common name). Brycon matrinchao Fowler, 1941: 192 –194, fig. 102 (Type locality, “Rio Parnahyba, Therezina, Piauhy”); Géry, 1964: 450 (diagnosis in key). Brycon melanopterus: Myers & Weitzman, 1960: 99, 101–102 (Los Micos, Cordillera Macarena, 3°20´S 73°56´W, Río Guaviare, rio Orenoco basin, Colombia); Lima et al., 2005: 164 (Rio Tiquié, upper rio Negro basin, Brazil; description, natural history, figure, common indigenous names). Brycon stuebeli: Géry, 1964: 450 (diagnosis in key). Brycon stubelii: Howes, 1982: 45 (comments). Brycon cf. falcatus: Goulding et al., 1988: 124 (Middle and lower rio Negro basin; occurrence). Brycon sp. (aff. bicolor): Géry & Mahnert, 1992: 800 –802 (Rio Aripuanã, Ilha do Castanhal). Brycon sp. (B. falcatus group): Toledo-Piza, 2002: 116 –117 (drawing by A.R. Wallace; “ Rio Uaupés”; common name). Brycon carpophagus (not Valenciennes): Mérona et al., 2001: 387, 391 (Rio Tocantins, Tucuruí; diet before and after river impoundment). Brycon stuebelli: Zarske, 2003: 16, fig. 7 (holotype, MTDF 380); Lima, 2003: 176 (type material; as a synonym of Brycon falcatus). Brycon falcatus group: Phillip et al., 2013: 8, 16 (Trinidad southern coast; occurrence as a vagrant species). Diagnosis. Brycon falcatus can be distinguished from all remaining cis-andean Brycon species, with the exception of B. gouldingi, by typically possessing a V- or crescent-shaped dark blotch on caudal peduncle and caudal fin. Brycon falcatus can be distinguished from B. gouldingi by possessing possessing dark, longitudinal stripes formed by pigmentation concentrated on the mid-distal portion of scales (vs. dark, wavy longitudinal stripes formed by dark pigment concentrated on upper and lower scale margins), paired fins typically clear (vs. paired fins black), and lower lateral line scale counts (47–69, modally 57, vs. 66–82, modally 74). Brycon falcatus is morphologically more similar to B. melanopterus, and an unequivocal diagnosis between both species based only on external morphological characters is not possible due to the great polymorphism in color pattern observed in the species. However, typically, Brycon falcatus does not present an oblique dark solid stripe, presenting instead a V or crescent-shaped blotch on caudal fin (vs. black pigmentation restricted to the upper caudal-fin lobe in B. melanopterus). In addition, Brycon falcatus is typically a higher bodied fish, with higher vertebrae counts. See the item “Comparisons” under Brycon melanopterus, and the item “Variation”, below, for thorough account on the subject. Description. Morphometric data are presented in Tables 21–22; some meristic data (lateral line counts and scales between dorsal-fin origin and lateral line) in Tables 23–24. Middle- to large-sized species, largest examined specimen 434.7 mm SL. Body moderately slender to high. Largest body height slightly ahead of dorsal-fin origin. Dorsal body profile slightly convex from upper lip margin to vertical through anterior naris, straight to moderately convex from latter point to basis of supraoccipital process, moderately to pronouncedly convex from latter point to dorsal-fin origin, straight along dorsal-fin basis, and straight to slightly convex from dorsal-fin basis to adipose-fin origin. Dorsal profile of caudal peduncle slightly concave. Ventral profile slightly to pronouncedly convex from lower lip to pelvic-fin insertion, straight to slightly convex from this point to anal-fin origin and approximately straight along anal-fin base. Ventral profile of caudal peduncle slightly concave. Head profile slightly acute anteriorly, snout obtuse, mouth terminal. Jaws approximately isognathous to slightly anisognathous, outer row of premaxillary teeth partially exposed when mouth is closed. Maxillary moderately long, extending posteriorly to anterior third of pupil. Adipose eyelid well developed. Premaxillary teeth in three rows; teeth of third row largest. Five (2), 6 (5), 7 (29), 8 (65), 9 (118), 10 (99), 11 (53), 12 (8), or 13 (1) relatively small tricuspidate teeth in outer series. Three (30), 4 (229), 5 (107), 6 (6), or 7 (1) tri- to pentacuspidate teeth in second, inner premaxillary row, plus 2 (2), 3 (150), 4 (218), or 5 (7) tricuspidate teeth between the first and third rows. Two teeth in third premaxillary row, medial teeth largest, symphyseal teeth smaller, slightly tilted towards each other, both pentacuspidate. Maxillary margins approximately parallel, straight in profile. Fifteen to 28 maxillary teeth, slightly smaller than teeth of first premaxillary row, anterior teeth tricuspidate, posterior teeth unicuspidate. Dentary with 7 (7), 8 (34), 9 (72), 10 (61), 11 (26), 12 (9), 13 (3), 14 (1), or 15 (1) teeth in main series. Anterior four dentary teeth assymetrical, considerably larger and bulkier than remaining teeth, pentacuspidate, each with central cusp distinctly larger than remaining cusps. Remaining dentary teeth progressivelly smaller, penta- to unicuspidate. Inner (lingual) series consisting of a small, single unicuspid symphyseal tooth, situated immediately posterior to symphyseal dentary teeth of main series, plus row of 13–21 small, aciculated, unicuspidate teeth, originating on lingual crest of dentary replacement trench at the level of fourth to seventh main series dentary teeth. Symphyseal teeth may be lacking in larger (> 350 mm SL) specimens. Scales cycloid. Lateral line complete, from supracleithrum to caudal-fin base. Forty-seven (1), 48 (1), 49 (1), 50 (3), 51 (11), 52 (25), 53 (57), 54 (59), 55 (77), 56 (90), 57 (104), 58 (93), 59 (57), 60 (49), 61 (27), 62 (14), 63 (8), 64 (16), 67 (1), or 69 (1) scales in lateral line series. Laterosensory tube simple in specimens smaller than 100 mm SL, ramified in specimens larger than 100 mm SL. Tubules ramification increasing in complexity along ontogeny, specimens up to 150 mm SL with tubules with two or three branches, three to six branches in specimens between 150–250 mm SL, and with more than 10 branches and developing a dendritic pattern of ramification, with tubules often overlapping each other in larger (> 270 mm SL) specimens. Horizontal scale rows between dorsal-fin origin and lateral line eight (1), 9 (21), 10 (115), 11 (122), 12 (103), 13 (29), or 14 (3). Horizontal scale rows between lateral line and pelvic-fin 4 (21), 5 (156), 6 (169), 7 (27), or 8 (1). Circumpeduncular scales 15 (1), 16 (27), 17 (75), 18 (125), 19 (67), 20 (51), 21 (32), or 22 (6). Dorsal-fin rays ii, 9. Dorsal fin origin slightly ahead, or about at middle of SL. First dorsal-fin pterygiophore inserting behind neural spine of 11th (2), 12th (1), or 13th(1) vertebra. Anal-fin rays iii (not including first, small unbranched ray only visible in cs specimens), 18 (1), 19 (4), 20 (11), 21 (41), 22 (90), 23 (93), 24 (82), 25 (45), or 26 (6). First anal-fin pterygiophore inserting behind haemal spine of 22th (4), or 23th (1) vertebrae. Anal-fin rays decreasing only slightly in size towards anal-fin end. Anal fin displaying several (c. 5–12 per fin-ray main branch) small hooks on posterior main branch of branched rays 2–11, associated with dense, gelatinous tissue in 5 examined specimens (MZUSP 3845, 2, 196.2– 198.9 mm SL, MZUSP 16448, 1, 196.5 mm SL mm SL, MZUSP 91493, 1, 226.0 mm SL, MZUSP 94990, 1, 230.0 mm SL). A single hook per ray segment. Sheath of scales covering basis of anal-fin rays composed of four scale rows, lower scale row formed by 21–25 rectangular scales. Pectoral-fin rays 11 (3), 12 (76), 13 (229), or 14 (58). Pelvic-fin rays typically i, 7 (364), rarely i, 6 (4), or i, 8 (4). Main caudal-fin rays 10/9. Caudal fin forked, lobes slightly emarginated. Laterosensory tube extending over interradial membrane between upper and lower caudal-fin lobes to the distal portion of fin. Laterosensory tube on caudal fin with dorsally and ventrally oriented side branches across its length. Small distal projection in the area of the laterosensory tube present in specimens with relatively intact caudal fin. Four branchiostegal rays, three on anterior ceratohyal and one on posterior ceratohyal. First branchial arch with 12 (14), 13 (24), 14 (40), 15 (32), 16 (22), or 17 (2) lower, 1 at angle, and 11 (1), 12 (15), 13 (38), 14 (51), 15 (20), 16 (6), or 17 (2) upper gill rakers. Vertebrae 39 (1), 40 (1), 41 (7), 42 (5), 43 (2), or 44 (1). Supraneurals 8(2), or 9 (2). Coloration in alcohol. Top of head, snout, supraorbital, and sixth infraorbital light-grey to light-brown. Dorsal portion of body light-grey to dark-brown. Second, third, fourth, and fifth infraorbitals, opercle and cleithrum silvery in specimens retaining guanine, light-brown in specimens that lost this pigment due to a long storage in formalin. Dentary, maxillary, gular area, and lower portion of body light-brown. Lateral portion of body silvery in specimens retaining guanine, light brown in specimens that lost this pigment due to a long storage in formalin. Humeral blotch present, slightly to moderately conspicuous, approximately rounded in shape, situated immediately above lateral line, its anterior margin at level of second, extending longitudinally to posterior margin of fourth to fifth lateral line scales, and vertically one and half scales high. Scales on lateral portions of body with dark pigmentation concentrated on their central portion, forming dark, straight longitudinal stripes, more conspicuous dorsally. Dark, solid, oblique dark stripe extending along anal-fin scales sheath and anal-fin basis in almost all specimens (see item “Variation”, below). Caudal peduncle blotch wide, extending across upper and lower caudalfin rays typically as a V- or crescent-shaped dark blotch, though with a great degree of variation in the development of the pigmentantion in the lower caudal-fin lobe (see item “Variation”, below). Dorsal, anal, pectoral, and pelvicfin rays with a variable amount of interradial dark pigmentantion but typically clear. Adipose-fin light- to darkgrey, with scattered dark spots in large specimens from the upper rio Tapajós basin. Color in life. Description based on pictures of several specimens collected at the lower rio Japurá (Lago Amanã), upper rio Madeira, upper rio Tapajós, upper rio Xingu (Fig. 90), and rio Tocantins in Amazon basin, Río Inirida, Orinoco basin, and Kuribrong River, Essequibo basin, plus published pictures of living specimens (Géry, 1977: 321, upper and lower; Planquette et al., 1996: 227; Ferreira et al., 2007: 125). Top of head and snout light- to dark-grey. Dorsum plumbeous. Lateral surfaces of head and body silvery. Humeral blotch relatively inconspicuous. Dark stripe extending along anal-fin basis and dark, V-shaped caudal peduncle/caudal-fin blotch very conspicuous. Distal border of caudal fin yellowish to reddish. Adipose fin yellowish grey. Remaining fins translucent, dorsal fin with some yellowish pigmentation. Variation. Brycon falcatus is one of the most widespread cis-andean Brycon species, and perharps not unexpextedly, a great degree of variation in body shape and color pattern is observed across its range. Specific features that show a great degree of variation are body height, caudal-fin pigmentation, scale counts, maximum body size, and, to a lesser extent than the previous features, anal-fin pigmentation. Each of these features is treated sequentially below. Body height varies considerably in specimens of Brycon falcatus, to an extent unequalled among cis-andean Brycon species. Specimens range from being relatively elongated (Fig. 89) to high-bodied (Figs. 86, 88, 92). However, there is no consistent geographical variation in this character, and most river systems present specimens ranging from both extremes in body shape. Probably, most of the observed variation in this trait is simply a result of phenotypic plasticity. Caudal-fin pigmentation is the most significant trait to vary among Brycon falcatus populations, and, contrary to body height, exhibits a clear geographical pattern. Brycon falcatus populations from the Guianas, rio Branco, rio Capim, rio Tocantins, and rio Xingu basins possess the characteristic V- or crescent-shaped caudal-fin blotch, with the extent of dark pigmentation approximately symmetrical in both lobes (Figs. 86–87). However, moving westwards into the Brazilian and Guyanese shields, dark pigmentantion on the lower caudal-fin lobe tend to decrease clinally in intensity. Specimens from the rio Tapajós and rio Madeira basins range from possessing an almost symmetrical dark pigmentation in both fin lobes (Figs. 88, 92) to a considerably less pigmented lower caudal-fin lobe. Specimens from the middle and lower rio Negro and middle and middle rio Orinoco basin possess a clearly asymmetrically pigmented caudal fin, with the dark pigmentation much more intense and extensive in the upper, than in the lower caudal-fin lobe (Figs. 93–95). Moving westward into western Amazon, the apparently scattered populations of Brycon falcatus occurring in that vast area possess an even more asymmetrically pigmented caudal-fin, with the lower lobe almost (Fig. 96) or completely (Fig. 97) unpigmented, the latter condition found in specimens from Iquitos area, the most westward known locality for the species. Oddly, specimens from the upper rio Negro (above São Gabriel rapids) and upper rio Orinoco (above its junction with the Río Guaviare) basins present a similar color pattern to the specimens from Iquitos area, presenting no dark pigmentation at all at the lower caudal-fin lobe and the upper caudal-fin lobe pigmentation almost continuous with the anal-fin dark stripe (Fig. 98). Specimens from the Iquitos area and upper rio Negro and upper Río Orinoco basins are thus very similar in color pattern to B. melanopterus, though B. falcatus is typically a higher-bodied species, with lower vertebral counts (see item “Comparisons” of B. melanopterus). See item “Putative examples of mimicry involving Brycon ”, below, for a possible explanation for this similarity. Scale counts vary considerably among distinct populations of Brycon falcatus, with specimens from the Guianas clearly presenting lower counts when compared with specimens from the Orinoco and Amazon basins (see Tables 23 and 24). The lower scale counts presented by Guyanese specimens when compared with specimens from rio Capim and rio Tocantins basins were the main reason supporting the recognition of Brycon brevicauda as a valid species (e.g., Géry, 1964: 450; Howes, 1982: 14). However, the examination of large series of