Moenkhausia cambacica, Marinho & Ohara & Dagosta, 2021

Marinho, Manoela Maria Ferreira, Ohara, Willian Massaharu & Dagosta, Fernando Cesar Paiva, 2021, A new species of Moenkhausia (Characiformes: Characidae) from the rio Madeira basin, Brazil, with comments on the evolution and development of the trunk lateral line system in characids, Neotropical Ichthyology 19 (2), pp. 1-20 : 4-11

Moenkhausia cambacica , new species

urn:lsid:zoobank.org:act:329C1539-307D-4E05-B8C9-148888CEB0E3

( Figs. 1–5 ; Tab. 1)

Holotype. MZUSP 125792 , 34.8 mm SL. Brazil, Rondônia State, Municipality of Vilhena, rio Madeira basin, upper rio Machado , tributary of igarapé Ávila , near BR-364 road, 12°30’36.9”S 60°28’20.29”W, 12 Nov 2014, W. M. Ohara, F. C. P. Dagosta & V. Giovannetti.

Paratypes. All from Brazil, Rondônia State, Municipality of Vilhena, upper rio Machado , rio Madeira basin. MCP 39852 , 19 , 16.2–28.5 mm SL, rio Ávila at BR-364 road between Vilhena and Pimenta Bueno, 12º30’18”S 60º28’15”W, 14 Sep 2004, P. Lehmann, V. A. Bertaco & F. C. T. Lima. MZUSP 125793 , 12 , 27.2–35.9 mm SL, 2 CS, 26.5 and 29.0 mm SL, same data of holotype. MZUSP 115277 , 1 , 26.1 mm SL, upper rio Machado , tributary of igarapé Piracolina, near BR-364 road, 12°48’56.5”S 60°6’37.6”W, 14 Sep 2014, W. M. Ohara, D. Hungria & B. Barros. MZUSP 118576 , 5 , 23.7–29.3 mm SL, BR-364 road, km 60 to Porto Velho, 12°30’37.2”S 60°28’20.9”W, 19 Nov 2013, W. M. Ohara, D. Hungria & B. Barros .

Diagnose. Moenkhausia cambacica is distinguished from all congeners, except M. chlorophthalma Sousa, Netto-Ferreira & Birindelli, 2010 , M. petymbuaba Lima & Birindelli, 2006 , M. plumbea Sousa, Netto-Ferreira & Birindelli, 2010 , and M. parecis Ohara & Marinho, 2016 by the presence of a large dark blotch on each scale of the second to seventh longitudinal series of body which are formed by a higher concentration of cromatophores on the anterior portion of scales (vs. pigmentation absent or, when present, concentrated at the middle or posterior margin of scales, forming stripes or a reticulate pattern). Moenkhausia cambacica can be readily distinguished from all the aforementioned species by having a conspicuous, well-defined, horizontally elongate blotch on the caudal peduncle, extending to middle caudal-fin rays, not reaching the upper and lower edges of the caudal peduncle (vs. caudal peduncle blotch absent or poorly defined, continuous with the longitudinal stripe of body in M. clorophthalma , M. petymbuaba , and M. plumbea ; round blotch in M. parecis ). Additionally, it can be distinguished from M. petymbuaba by the absence of a conspicuous longitudinal black stripe on body (vs. black stripe present), from M. plumbea and M. clorophthalma by the absence of a dark, diffuse, slightly concave midlateral stripe on body in live specimens (vs. dark stripe present), and from M. parecis by a shorter upper jaw length (41.5–48.8% HL vs. 50.6–55.0% HL), and, in life, by having a bright golden coloration of the dorsal portion of the eye and a dark shaded line crossing the eye horizontally (vs. eye entirely bright blue, with no horizontal dark line).

Description. Morphometric data of the holotype and paratypes presented in Tab. 1. Body moderately elongate, laterally compressed. Largest specimen examined 35.9 mm SL. Greatest body depth slightly anterior to the vertical through dorsal-fin origin. Dorsal profile of head convex from anterior tip of upper jaw to vertical through anterior nostril. Straight or slightly convex from that point to tip of supraoccipital spine. Dorsal body profile straight or slightly convex from tip of supraoccipital spine to dorsal-fin origin, straight along dorsal-fin base, straight from base of last dorsal-fin ray to adiposefin insertion and slightly concave along caudal peduncle. Ventral profile of body convex from anterior tip of dentary to anal-fin origin, straight at anal-fin base and slightly concave along caudal peduncle.

Mouth terminal, jaws equal. Posterior terminus of maxilla at the vertical through middle of pupil. Maxilla approximately at 45 degrees angle relative to longitudinal axis of body. Frontals with a triangle-shaped fontanel; parietal fontanel large, extending from epiphyseal bar to supraoccipital spine. Infraorbital series with six elements. Nostrils close to each other, anterior opening circular and small, crescent-shaped posterior one, twice in size. Nostrils separated by narrow skin flap.

Premaxillary teeth in two rows. Outer tooth row with 3*(1), 4(25) or 5(1) tricuspid teeth; inner tooth row with 4(1) or 5*(25) teeth with three to five cusps, symphyseal tooth of inner series narrow, asymmetric, with four cuspids. Tooth cusps of inner premaxillary tooth row directed outward and arranged in an arched series. Maxilla with 2*(9), 3(17), or 4(1) teeth along its anterodorsal margin, with one to three cusps ( Fig. 2 ). Dorsalmost tooth usually larger. Dentary with 4*(26) or 5(1) larger tri- to pentacuspid teeth, followed by a series of 9(1) or 11(1) diminute conical teeth. Tooth cusps of larger dentary teeth arranged directed inward and arranged in an arched series. Central cusp of all multicuspid teeth more developed than remaining lateral cusps.

Scales cycloid, moderately large, circuli distributed over whole area of scales. Three to seven radii well defined and slightly divergent posteriorly. Lateral line slightly curved downward anteriorly, with variably developed bony tube. Four specimens (including holotype) with fully developed tube in all lateral-line scales, terminating in a pore (e.g., lateral line complete, with 31(1) and 32*(3) pored scales from supracleithrum to the end of caudal peduncle). Twenty-one specimens with fully developed tube in all lateral-line scales of the anterior and posterior portions of body, and, at the level of the anal-fin base, tubed scales interspersed by scales without bony tube and/or scales with poorly developed tube, with variable count (e.g., 22 tubed scales with pore + 2 scales without tube or pore + 3 scales with poorly developed tube and no pore + 3 tubed scales with pore) ( Fig. 3 ), with a total of 30(2), 31(8), 32(7), or 33(1) scales in the lateral series (see details in the Discussion). Longitudinal scale rows between dorsal-fin origin and lateral line 5*(24). Longitudinal scale rows between lateral line and pelvic-fin origin 3(7) or 4*(17). Predorsal area with 9(11) or 10*(13) scales arranged in one series. Horizontal scale rows around caudal peduncle 14*(24). Single row of 4(7), 5(7), 6(3), or 7*(2) scales covering base of anteriormost anal-fin rays. Caudal fin with small scales on the basal fourth of caudal-fin lobes.

Supraneurals 4(2) with narrow bony lamellae on upper portion. Dorsal-fin rays ii*(27), 9*(27). Dorsal-fin origin at middle of standard length and slightly posterior to vertical through pelvic-fin origin. First unbranched dorsal-fin ray shorter than second unbranched ray. First dorsal-fin pterygiophore located behind neural spine of 9 th (2) vertebra. Adipose fin present. Anal-fin rays v(2), 15(4), 16(15), 17*(7), or 18(1); anteriormost rays longer, subsequent rays gradually decreasing in size. Anteriormost anal-fin pterygiophore inserted posterior to haemal spine of 16 th (2) vertebra. Pectoralfin rays i*(27), 10(1), 11*(14), or 12(12). Tip of adpressed pectoral fin not reaching pelvic-fin origin in most specimens. Pelvic-fin rays i*(27), 7*(27). Tip of adpressed pelvic fin reaching the anal-fin origin. Caudal-fin with i*(26), 9*(26) rays on the upper and i*(26), 8*(26) rays on the lower lobe. Caudal-fin forked, lobes somewhat pointed and of similar size. Twelve (1) or 13(1) dorsal procurrent caudal-fin rays and 10(2) ventral procurrent caudal-fin rays. Total vertebrae 31(2): precaudal vertebrae 16(2) and caudal vertebrae 15(2).

Color in alcohol. Overall ground color pale, with small dark chromatophores spread at the entire head and body, except the ventral portion of abdominal region, and densely concentrated in its dorsal portion, gradually fading ventrally ( Fig. 1 ). Dorsal midline of head and body dark brown. Jaws, opercular, and infraorbital areas pigmented with dark chromatophores. Single, dark humeral blotch, vertically oriented, extending vertically two scale rows above and one scale row below the lateral line. Dorsal portion of humeral blotch wider, over three scales horizontally. Ventral portion narrow, slightly turned anteriorly, over one scale. Thin longitudinal dark stripe at horizontal septum, formed by underlying chromatophores extending from vertical through dorsal-fin origin to caudal peduncle. Conspicuous dark horizontal blotch on caudal peduncle, extending to base of midlle caudal-fin rays, never reaching the upper and lower edges of caudal peduncle. Horizontal blotch on caudal peduncle frequently extending to tip of

middle caudal-fin rays. Lower portion of caudal peduncle with a clear area. Second to seventh horizontal scale rows with scales bearing dark blotches on its anterior portion. All fins with scattered dark chromatophores on interadial membranes. Distal portion of interadial membranes of dorsal fin with concentration of dark chromatophores.

Color in life. Dorsal portion of head and body light brown. Ventral half of head and body pale yellow ( Fig. 4 ). Infraorbital and opercular areas silvery. Dorsal portion of eye bright golden, ventral portion silvery with blue hue. Dark shaded line crossing the eye horizontally ( Fig. 5 ). Vertical arm of preopercle yellow golden. Bright yellow to orange blotch anterior and posteriorly to the humeral blotch ( Fig. 5 ). Second to seventh horizontal scales row with scales bearing brown blotches on its anterior portion. Humeral blotch and caudal-peduncle spot conspicuous in life. All fins with orange to yellow coloration, more intense at the anterior half of caudal-fin lobes. Posterior tip of caudal and dorsal fins hyaline.

Sexual dimorphism. Secondary dimorphic characters were not found in the examined specimens.

Geographical distribution. The new species is so far only known from two headwater tributaries of the upper rio Machado at Chapada dos Parecis, Rondônia State, Brazil ( Fig. 6 ). Intensive ichthyological collecting efforts in the rio Madeira basin (e.g., Queiroz et al., 2013), including the rio Machado drainage (e.g., Perin et al., 2007; Casatti et al., 2013; Costa et al., 2017) have failed to capture M. cambacica in other streams, indicating a very restricted distribution to the tributaries draining the Chapada dos Parecis.

Ecological notes. The type locality of Moenkhausia cambacica is a Balneário (recreation area) upstream the Cachoeira Small Hidroeletric Dam ( PCH, Pequena Central Hidrelétrica), and is located at 415 m above sea level. The stream is small, 2–4 m wide and 0.5–2 m deep, with clear waters with swift current, and bottom composed of sand and dead leaves ( Fig. 7 ). Other species collected syntopically were: Ancistrus verecundus Fisch-Muller, Cardoso, da Silva & Bertaco, 2005 , Astyanax aff. bimaculatus (Linnaeus, 1758) , Bryconops piracolina Wingert & Malabarba, 2011 , Erythrinus erythrinus (Bloch & Schneider, 1801) , Cetopsorhamdia sp. 3 (cf. Bockmann, Slobodian, 2013:25), Aequidens sp. , and Crenicichla sp. A single M. cambacica specimen was collected in a tributary of rio Piracolina near Vilhena at altitude 591 m a.s.l., in a small, clear water stream 1–1.5 m wide and 0.3–1.5 m deep, presenting swift water current and sandy bottom. This specimen was collected syntopically with M. parecis and other species (e.g., A. verecundus , B. piracolina , Cetopsorhamdia sp. 3 , Corydoras hephaestus Ohara, Tencatt & Britto, 2016 , Hyphessobrycon lucenorum Ohara & Lima, 2015 , Hyphessobrycon aff. melanostichos Carvalho & Bertaco, 2006 , Hyphessobrycon aff. notidanos Carvalho & Bertaco, 2006 , and Pyrrhulina sp. ).

Etymology. The specific name, cambacica , is after the one of the Brazilian popular name for Coereba flaveola (Linnaeus, 1758) , a small neotropical bird whose coloration resembles that of the new species, which is bright yellow underparts, dark back coloration and a dark line crossing the region of the eye horizontally, contrasting with a light area above it. A noun in apposition.

Conservation status. Moenkhausia cambacica is another endemic species from the ‘Chapada dos Parecis’ biogeographic region, characterized by high levels of endemicity and large number of restricted-range species (Ohara, Lima, 2015a,b; Dagosta et al., 2020). This biogeographic region was considered by latter authors as one of the Endemic Amazonian Fish Areas (EAFAs), i.e., regions that should be considered as conservation priorities in the basin by presenting imminent threats and low cover of protected areas. Moenkhausia cambacica is endemic to Brazil, known by only two localities. One site is a tourist bathing resort and the other is entirely surrounded by monoculture plantation. Its area of occupancy ( AOO) (B2) 8 km 2 is based on these two known records. The AOO is likely underestimated, although the region has already been largely sampled. A continuing decline in habitat quality b(iii) is inferred based on the deforestation caused by still growing urbanization and agriculture activity in the region. It is not possible to meet subcriterion ‘a’ because the population is not necessarily fragmented. Therefore, we suggest this species is assessed as Near Threatened, close to meeting Critically Endangered (CR) by the following criteria B2b(iii) according to the International Union for Conservation of Nature ( IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2019).

Figures

FIGURE 1 | Holotype of Moenkhausia cambacica, MZUSP 125792, 34.8 mm SL, Brazil, Rondônia State, Municipality of Vilhena, rio Madeira basin, upper rio Machado drainage.

FIGURE 2 | Medial view of left side, premaxillary, maxillary, and dentary of Moenkhausia cambacica, MZUSP 125793, 27.1 mm SL, paratype. Scale bar: 1 mm.

FIGURE 3 | Schematic drawing of Moenkhausia cambacica showing A. lateral-line perforation pattern observed in most specimens. B. Morphology of the lateral-line scales above anal fin: I – scale lacking tube and pore; II – scale with poorly developed tube, with small tube walls; III – scale with poorly developed tube, walls larger but not enclosed; IV– scale with fully developed bony tube, tube walls enclosed, with a posterior pore.

FIGURE 4 | Live coloration of Moenkhausia cambacica, paratype, MZUSP 125793, Brazil, Rondônia State, Municipality of Vilhena, rio Madeira basin, upper rio Machado drainage.

FIGURE 5 | Paratypes of Moenkhausia cambacica, MZUSP 125793, freshly collected, showing other aspects of its live coloration, Brazil, Rondônia State, Municipality of Vilhena, rio Madeira basin, upper rio Machado drainage.

FIGURE 6 | Distribution of Moenkhausia cambacica in the upper rio Machado, rio Madeira basin, Brazil. Black star (type-locality), blue star (other localities).

FIGURE 7 | Type-locality of Moenkhausia cambacica, tributary of igarapé Ávila, upper rio Machado, rio Madeira basin, Vilhena, Rondônia, Brazil.