Bryconops chernoffi, Silva-Oliveira & Lima & Bogotá-Gregory, 2018

Silva-Oliveira, Cárlison, Lima, Flávio C. T. & Bogotá-Gregory, Juan D., 2018, A new species of Bryconops Kner (Characiformes: Iguanodectidae) from the Rio Maicuru, lower Amazon basin, Brazil, Zootaxa 4514 (3), pp. 372-382 : 373-380

Bryconops chernoffi , new species

( Figures 1–3 ; Table 1)

Holotype. ZUEC 14796 , 59.6 mm SL, Brazil, Pará State, Monte Alegre, rio Ipixuna , a tributary of rio Maicuru , 1˚29'23" S 54˚15'40" W; 30 Sept 2014, J. D. Bogotá-Gregory.

Paratypes. All from the same locality as the holotype. INPA 56753 , 5 , 39.9 – 69.1 mm SL, collected with holotype. INPA 53232 , 3 , 48.7 – 75.9 mm SL, 7 Dec 2014 , C. Silva-Oliveira & J. D. Bogotá-Gregory. MCP 53173, 5 , 26.3 – 48.8 mm SL; UFOPA-I 656 , 9 , 45.9 – 55.2 mm SL, 4 c& s 41.8 –52.9 mm SL; ZUEC 15719 , 5 , 21.7 – 35.1 mm SL; CAS 245735 , 5 , 29.9 – 54.2 mm SL; FMNH 134476 , 5 , 22.4 – 47.7 mm SL; INPA 53231 , 39 , 24.1 – 48.2 mm SL, 2 c& s 41.8 – 52.9 mm SL; MPEG 36365 , 8 , 25.5 – 43.2 mm SL; MZUSP 123410 , 5 , 22.7 – 49.4 mm SL; UF 239321, 10 , 28.6 – 44.7 mm SL; 11 Aug 2015 , J. D. Bogotá-Gregory. MCP 53172 30, 20.3–41.8 mm SL; ZUEC 11611 , 78 , 22.2 – 61.4 mm SL, 6 c&S, 31.8–41.3 mm SL; ANSP 206083 , 5 , 29.8 – 55.1 mm SL, W.G.R. Crampton, R.E. Reis, C. Silva-Oliveira, J. D. Bogotá- Gregory, B.B. Calegari, E. Cerdeira & F. C. T. Lima, 3 Dec 2015 .

Diagnosis. Bryconops chernoffi is distinguished from all its congeners by presence of an elongated dark blotch immediately posterior to the posterodorsal margin of the opercle, running vertically from the supracleithrum to the distal margin of the cleithrum (vs. absence of a similar blotch), and by having the lateral line reaching the caudalfin interradial membrane (vs. lateral line not extending beyond longitudinal scales of the body). Its differs further from all congeners, with the exception of B. piracolina Wingert & Malabarba , by possessing a mostly dark dorsal fin, with a narrow hyaline band at the middle portion of the dorsal-fin rays (vs. dorsal fin hyaline, or with some dark pigmentation, but never mostly dark). The new species differs further from its congeners, except Bryconops cyrtogaster (Norman) (herein considered a valid species, cf. Géry et al., 1991; Planquette et al., 1996, and pers. obs.) and Bryconops melanurus (Bloch) , by possessing a caudal fin with a prominent black horizontal stripe (vs. caudal fin with dark pigmentation mostly restricted to the upper lobe, or roughly symmetrical between both fin lobes). It can be diagnosed from B. cyrtogaster and B. melanurus by having the dark stripe restricted to the posterior portion of the caudal peduncle and the main caudal-fin rays immediately posterior to the caudal peduncle (vs. dark stripe extending from rays immediately posterior to caudal peduncle onto the distal margin of the lower portion of caudal-fin dorsal lobe). Bryconops chernoffi further differs from its congeners, except Bryconops colanegra Chernoff & Machado-Allison , by possessing dark chromatophores concentrated along the interradial membranes of the anal fin near its base, forming a diffuse band (vs. anal fin lacking a discernible band). It differs further from B. colanegra by having fewer predorsal scales (8–9 vs. 10–11), and by possessing a third infraorbital that contacts the preopercle ventrally (vs. third infraorbital not contacting preopercle ventrally).

Description. Morphometric data presented in Table 1. Body compressed, greatest body depth located just anterior to dorsal-fin origin. Dorsal body profile slightly convex from margin of upper lip to end of supraoccipital spine; more so from that point to dorsal-fin origin, straight and posteroventrally-inclined along dorsal-fin base, straight from end of dorsal-fin base to adipose fin, and slightly concave from that point to anteriormost dorsal procurrent caudal-fin rays. Ventral profile of head and body slightly convex from lower lip to pelvic-fin origin, and straight from this latter point to anal-fin origin. Ventral profile straight and posterodorsally inclined along anal-fin base. Ventral profile of caudal peduncle slightly concave.

Mouth terminal. Posterior extension of maxilla not reaching junction between second and third infraorbital bones; third infraorbital well-developed, reaching preopercle ventrally. Supraorbital bone present. Premaxillary teeth in two rows ( Fig. 2 ), with midcentral cusp more developed than remaining cusps; outer tooth row irregular, with 4 (6) or 5* (23) tri- or pentacuspid teeth; inner tooth row with 5* (29) penta- to heptacuspid teeth. Maxillary with 2* (28) or 3 (1) tri- or pentacuspid teeth on contralateral parts. Dentary with 5* (29) tri-, penta-, or heptacuspid teeth, followed by 7 (2) or 8 (3) smaller, conical teeth.

Dorsal-fin rays ii,9* (29); first unbranched ray about one-half length of second unbranched ray. Dorsal-fin origin situated anterior to vertical through pelvic-fin origin and near middle of body. Posterior margin of dorsal fin straight to slightly concave. Adipose-fin origin approximately at vertical through base of 19th to 20th anal-fin branched rays. Principal caudal-fin rays i,8,9,i* (28) or i,8,10,i (1). Lobes of caudal fin unequal, upper lobe longer than lower lobe. Dorsal procurrent caudal-fin rays 13 (4), ventral procurrent caudal-fin rays 12 (4). Pectoral-fin rays i,11 (5), 12* (24) or 13 (1). Tip of pectoral fin reaching slightly beyond half of distance between pectoral and pelvic fins. Pelvic-fin rays i,7*(29). Pelvic fin originating at vertical through middle of dorsal-fin base, not reaching anal-fin origin. Anal-fin rays iv, 25 (2), 26 (5), 27* (18), or 28 (5). Anal-fin origin located posterior to vertical through base of last dorsal-fin ray. Distal margin of anal-fin slightly falcate, with last unbranched ray and second and third branched rays slightly longer than remaining rays. Distal margin of anal fin slightly concave.

Scales cycloid, moderately large, with few (1–5) well-marked radii; circuli only present proximally. Lateral line surpassing base of caudal-fin rays with canal of lateral line extending on caudal-fin interradial membrane. Total scales in longitudinal series containing lateral line scales 43 (2), 44* (17), or 45 (11). All scales of lateral line pored. Scale rows between lateral line and dorsal-fin origin 7* (29); scale rows between lateral line and pelvic-fin origin 3* (25) or 4 (4). Predorsal scales 8* (6) or 9 (24), arranged in a regular series. Scale rows around caudal peduncle 14 (5), 15* (12) or 16 (12). Precaudal vertebrae 19 (5); caudal vertebrae 22 (3) or 23 (2); total vertebrae 41 (5) or 42 (4). Supraneurals 5 (11). First dorsal fin pterygiophore located between ninth and tenth vertebrae.

Gill rakers of first gill arch 21 (2), 22 (4), or 23 (2): 3 (6) or 4(3) on hypobranchial, 9(3) or 10 (6) on ceratobranchial, 1 (9) on cartilage between ceratobranchial and epibranchial, and 7 (1), 8 (6), or 9 (2) on epibranchial. Gill rakers setiform. Branchiostegal rays 4: 3 (5) on anterior ceratohyal and 1 (5) on posterior ceratohyal.

Color in alcohol. Overall coloration of body dusky brown, darker dorsally. Top of head and snout dark. Infraorbitals, maxillary, and ventral region of opercle silvery. Sixth infraorbital and dorsal portion of opercle with scattered dark chromatophores. Lips and anterior portion of maxilla with dense concentration of dark chromatophores. Gular regions pale brown. Broad, faint midlateral stripe extending from immediately behind dorsal portion of opercle to caudal-fin basis, slightly more conspicuous at vertical through dorsal fin onward, and considerably more conspicuous at caudal peduncle, where extending into middle caudal-fin rays.

Scales on dorsal and dorsolateral portions of body with dark chromatophores concentrated on their edges. Scales below midlateral area with less numerous dark chromatophores. Vertically-elongate, slightly curved and narrow dark patch of pigmentation situated immediately posterior of posterodorsal margin of opercle, running vertically from supracleithrum to distal margin of cleithrum. Dorsal fin dark, especially at its basal and middle portions and corresponding interradial membranes. Adipose fin light grey, with dark chromatophores at its middle and distal portions. Pectoral and pelvic fins hyaline, with few scattered dark chromatophores, especially along outer edge of pectoral fin. Anal fin with dark chromatophores concentrated along interradial membranes of anal-fin base, forming diffuse basal band. Caudal fin with an overall dark coloration, with conspicuous dark stripe along middle caudal-fin rays, in some specimens extending slightly onto upper caudal-fin lobe. Virtually all specimens present irregularly shaped, asymmetrical dark blotches on sides of body.

Color in life. Overall body color plumbeous on lateral portions of body. Snout and lips light brown. Opercle, infraorbital bones, maxilla, and ventral region silvery. Dorsal fin with variably-developed red pigmentation on anteriormost rays. Adipose fin yellowish. Dorsal caudal-fin lobe with patch of red pigmentation running from base to mid-length of fin. Dark pigmentation distribution and conspicuousness similar to that visible in preserved specimens ( Fig. 3 ).

Sexual dimorphism. Two specimens (INPA 53232, 75.9 mm SL and holotype) possess anal- and pelvic-fin hooks and one specimen (INPA 53231, 56.5 mm SL) displays only anal-fin hooks. Pelvic-fin rays of these specimens possess 3–4 small hooks. Anal-fin hooks larger and more numerous (4–8 by ray) than pelvic-fin hooks, and occur from last unbranched ray to 14 th branched ray.

Distribution. Bryconops chernoffi is only known from its type locality, the rio Ipixuna, a tributary of the rio Maicuru, on the left margin of the lower rio Amazonas, about 60 km north from Monte Alegre, Pará State, Brazil ( Fig. 4 ).

Etymology. The specific epithet honors Barry Chernoff, and is in recognition for his contributions to the taxonomy of Bryconops , as well as for ichthyology as a whole.

Ecological notes. The type locality of Bryconops chernoffi , the rio Ipixuna ( Fig. 5 ), is a small tributary of the Rio Maicuru, a tributary of the lower Amazon River draining the southern portion of the Guiana Shield. Four collecting trips were conducted between 2014–2015 at the type locality (September 2014, December 2014, August 2015, and December 2015), where physico-chemical parameters were measured and found to present considerable variation along the year. Water color was dark, with temperature ranging between 27° and 31°C, pH between 4.99 and 8.21, conductivity between 19.99 and 38.9 mS/cm, and turbidity between 0.51 and 6.26 NTU. During the last collecting trip (December 2015), the flow of the rio Ipixuna was interrupted due to a severe dry season exacerbated by an El Niño event. Regarding habitat structure, the rio Ipixuna is characterized as having a rocky and sandy bottom, with alternating riffles and pools, within a patch of a semideciduous, relatively disturbed riparian forest. The type locality lies immediately above a large waterfall, approximately 30 m high. Bryconops chernoffi occur mostly in the river pools. A second Bryconops species similar to B. melanurus was collected syntopically with B. chernoffi , but was lower in abundance. Other fish species collected syntopically with B. chernoffi were Characidium cf. zebra Eigenmann, Hoplias cf. malabaricus (Bloch), Knodus sp., Moenkhausia sp., Jupiaba atypindi Zanata , Ituglanis sp., Lithoxus sp., Ancistrus sp., Pseudancistrus sp., Gymnotus sp., Crenicichla aff. saxatilis (Linnaeus), and Geophagus sp..

Discussion. Bryconops chernoffi exhibits some uncommon and even unique characters among its congeners. The five most prominent features of B. chernoffi are: 1) the dark dorsal fin with a narrow hyaline band along the middle portion of the rays; 2) the elongated patch of pigmentation located immediately posterior to the posterodorsal margin of the opercle; 3) the presence of only five supraneurals, a low count when compared with congeners, which typically have 6 or more supraneurals; 4) the low number (8–9) of pre-dorsal scales; and 5) the lateral line canal extending along the interradial membrane of the caudal fin. Among the characters unique to Bryconops chernoffi within Bryconops is the elongated patch of pigmentation running vertically from supracleithrum to the distal margin of the cleithrum is a very unusual condition among characiforms. A similar patch of pigmentation is known only for some Brycon Müller & Troschel species from northern trans-andean South America and southern Mesoamerica (e.g., Brycon dentex Günther , B. meeki Eigenmann & Hildebrand ) is also reminiscent of the pigmentation found in some Barilius Hamilton species as B. arunachalensis Nath, Dam & Kumar and B. chedra Hamilton ( Cypriniformes , Xenocyprididae ; see photos in Bleher, 2018).

Bryconops chernoffi shares all putative synapomorphies currently used to define the genus, including: the ventral edge of the maxilla curved sharply almost 90 o posteriorly, extending to or beyond the quadrate socket of the anguloarticular; the antorbital with a well-developed infraorbital sensory canal of the infraorbital branch; and the extension of the supraorbital sensory canal extending onto the nuchal scales ( Chernoff & Machado-Allison, 1999, 2005; Wingert & Malabarba, 2011; Silva-Oliveira et al., 2015; Guedes et al., 2016). In addition, Bryconops chernoffi shares the putative characters defining the subgenus Creatochanes as originally proposed by Chernoff & Machado-Allison (1999), except the posterior extension of maxilla not reaching the junction of second and third infraorbital bones.

Among its congeners, only B. piracolina also has a dark dorsal fin. However, the pigmentation pattern on the fin differs between the two species, as detailed in the Diagnosis, above. Nonetheless, in some individuals of that species (larger than 69 mm SL) the dorsal fin is completely dark. The adipose-fin color also distinguishes the species. Bryconops chernoffi has the adipose fin yellowish in life and hyaline in preserved specimens, whereas B. piracolina has a completely dark adipose fin ( Fig. 6 ).

In both Bryconops chernoffi and B. piracolina the dorsal fin originates anterior to a vertical through the first pelvic fin ray, but for distinct reasons. In the new species, the predorsal length is shorter (45.6–48.7 % SL vs. 48.7– 53.1 % SL in B. piracolina ). On the other hand, B. piracolina has a larger prepelvic length (53.3–58.0 % SL vs. 47.8–52.8 % SL in B. chernoffi ). In addition, in Bryconops chernoffi the first dorsal-fin pterygiophore is located between the ninth and tenth vertebrae (vs. first dorsal-fin pterygiophore located between thirteenth and fourteenth vertebrae in B. alburnoides or eleventh and twelfth in the remaining congeners). As a consequence, the proximity of the dorsal fin with the supraocipital spine, results in a smaller number of predorsal scales in B. chernoffi .

Bryconops chernoffi shares with B. inpai Knöppel, Junk & Géry and B. munduruku Silva-Oliveira, Canto & Ribeiro (the latter members of the subgenus Creatochanes ) an irregular outer premaxillary tooth row, with one or two teeth displaced backwards. Knöppel et al. (1968) used this character as one of the main reasons to synonymize the hitherto valid genus Creatochanes within Bryconops . Among its congeners, B. alburnoides Kner is the only species which has three teeth rows in the premaxilla, while other congeners have two regular tooth rows. However, the relationships of the new species with congeners, as well as the relationships of the two subgenera within Bryconops still need to be addressed more thoroughly before any hypothesis of relationships can be advanced.

Comparative material examined. All from Brazil, except if otherwise indicated: Bryconops affinis : BMNH 1969.12.13.1 (holotype) (photo only), Guyana. ZUEC 6557, 10, 69.0–95.0 mm SL, Guyana, Kuribrong River; MZUSP 109100, 11, 72.0– 89.5 mm SL, Guyana, Kuribrong River. Bryconops alburnoides : NMW 5994 (syntype) (photo only), Brazil, Rio Guaporé; INPA 12316, 1, 107.5 mm SL, Rio Tocantins; INPA 30701, 1, 145.7 mm SL, Rio Jaú; INPA 37794, 1, 81.1 mm SL, Rio Negro; INPA 36079, 6, 112.3– 115.1 mm SL, Rio Branco; MZUSP 17586, 7, 92.9– 119.0 mm SL, Rio Jutaí; MZUSP 72877, 1, 124.7 mm SL, Rio Tefé. Bryconops caudomaculatus . INPA 14301, 5, 61.5– 66 mm SL, Lago Curirarra, Rio Caurés; MZUSP 107705, 3, 62.0– 68.0 mm SL, Rio Preto da Eva. ZUEC 9223, 2, 65.0–85.0 mm SL, Goiás, rio Paranã. Bryconops colaroja . UFOPA-I-433, 1, 62.7 mm SL, Rio Cupari. Bryconops colanegra . INPA 10699, 4, 95.9–105.8 mm SL, Rio Araguari; LBP 21170, 42, 31.6–94.7 mm SL, Rio Cassiporé. Bryconops cyrtogaster . BMNH 1926.3.2.515–524 (syntypes); BMNH 2009.9.22.1–6 (syntypes); BMNH 2009.9.22.17–40 (syntypes) (photos only). French Guiana, Oyapock River. Bryconops disruptus . INPA 42819, 14, 30.9–48.6 mm SL, Rio Negro; MZUSP 29492, 644, 36.1– 66.2 mm SL, Rio Arirará; MZUSP 109888, 1, 45.6 mm SL, Rio Negro. Bryconops durbinae : UFOPA-I-337, 109, 18.2– 61.0 mm SL, Lago Verde, Rio Tapajós. Bryconops inpai : INPA 13249, 3, 63.2–72.9 mm SL, Rio Urubu; INPA 29524, 1, 66.7 mm SL, Rio Trombetas; INPA 31573 1, 59.3 mm SL, Rio Anebá; MZUSP 103096, 45, 29.1– 95.9 mm SL, Rio Urubu; MZUSP 17540, 8, 24.8– 78.8 mm SL, Rio Içá; UFRO-ICT 9371, 1, 58.2 mm SL, Rio Madeira. Bryconops munduruku : INPA 46510, 76.6 mm SL (holotype), Rio Tapajós; MCP 48315, 5, 34.0– 79.6 mm SL (paratypes), Rio Tapajós. Bryconops humeralis : INPA19638, 3, 49.8–66.3 mm SL, Rio Negro; INPA 19634, 6, 53.8–83.5 mm SL, Rio Negro; INPA 19636, 7, 31.3–79.6 mm SL, Rio Negro; MZUSP 99439, 1, 94.9 mm SL, Rio Tiquié. Bryconops giacopinii : INPA 32636, 7, 57.1–67.7 mm SL, Rio Negro; MZUSP 92299, 1, 111.3 mm SL, Rio Tiqué; MZUSP 112372, 2, 24.4– 67.5 mm SL, Rio Jufari; Bryconops melanurus : MZUSP 17141, 5, 68.5– 95.6 mm SL, Rio Capim; MZUSP 39909, 19, 51.4–81,9 mm SL, Utinga, Belém; UFOPA-I-336, 16, 84.1–109.7 mm SL, Rio Moju; UFOPA-I-338, 11, 49.1–78.0 mm SL, Rio Curuá. ZUEC 14355, 30, 45.0–91.0 mm SL, Pará, rio Guamá. Bryconops piracolina : MZUSP 105731, 2, 32.9–40.1 mm SL (paratypes), Rio Madeira; MCP 44796, 69.0 mm SL (holotype), Rio Madeira; UFRO-ICT 22726, 69, 24.2–59.9 mm SL, Rio Madeira; UFRO-ICT 22731, 64, 29.0– 70.1 mm SL, Rio Madeira.

Figures

FIGURE 1. Bryconops chernoffi: a) ZUEC 14796, holotype, 59.6 mm SL, b) INPA 56753, paratype, 55.2 mm SL, and c) UFOPA-I 656, paratype, 45.9 mm SL. Brazil, Pará, Monte Alegre, rio Ipixuna, tributary of rio Maicuru.

FIGURE 2. Bryconops chernoffi, UFOPA-I 656, paratype, 49.5 mm SL (c&s). Left side of the premaxillary, maxillary, and dentary. Lateral view. Scale bar = 1 mm

FIGURE 3. Bryconops chernoffi, ZUEC 11611, paratype, 49.2 mm SL, immediately after collection.

FIGURE 4. Map of northeastern South America, showing the type-locality of Bryconops chernoffi (black circle).

FIGURE 5. Type locality of Bryconops chernoffi, Brazil, Pará, Monte Alegre, Rio Ipixuna (a) above, and (b,c) below a great waterfall. Specimens were collected above the waterfall.

FIGURE 6. Bryconops piracolina, UFRO-ICT 22726, a) 70 mm SL; b) 58.4 mm SL, Brazil, Rondônia, Vilhena, Igarapé Piracolina.