Brachychalcinus sabaji, Garcia-Ayala & Lima & Gama & Benine, 2024

Garcia-Ayala, James Raul, Lima, Flávio César Thadeo de, Gama, Cecile de Souza & Benine, Ricardo Cardoso, 2024, A new striped species of Brachychalcinus (Ostariophysi: Characiformes) from Amapá and Pará states, northern Brazil, Neotropical Ichthyology (e 230070) 22 (1) : -

Brachychalcinus sabaji , new species

urn:lsid:zoobank.org:act:D5691E3C-67B8-41C4-B98B-53750C4FD622

( Figs. 1–3, 4H, 5A; Tab. 1)

Brachychalcinus aff. reisi (non Garcia-Ayala, Ohara, Pastana & Benine, 2017). ―Garcia-Ayala et al., 2017:571 (rio Tapajós basin; comparative material). ―Garcia-Ayala, Benine, 2020:955 (rio Tapajós basin; comparative material).

Holotype. IEPA 6879 , 69.7 mm SL, Brazil, Amapá, Laranjal do Jari, rio Mapaoni, rio Jari basin, Parque Nacional Montanhas do Tumucumaque ( PNMT), 02º11’36”N 54º35’15”W, 12–13 Jan 2005, C. S. Gama & T. M. Paulino.

Paratypes. All from Brazil . ANSP 208909 , 1 , 52.6 , mm SL ; IEPA 4784 , 2 , 52.1–69.7 mm SL ; IEPA 4980 , 4 , 55.9–70.7 mm SL ; IEPA 4984 , 1 , 64.6 mm SL; LBP 34043, 2, 52.6–53.5 mm SL ; MZUSP 128973 , 2 , 55.9–67.4 mm SL ; ZUEC 17347 , 2 , 60.8–70.7 mm SL, same data as holotype . IEPA 3231 , 2 , 41.0– 50.6 mm SL, Pará , Laranjal do Jari , rio Traíra, rio Jari basin, 00º37’25”S 52º32’49”W, 1 Dec 2011, G. A. Pereira, P. G. Azevedo & F. J. S. Costa .

Non-types: All from Brazil. IEPA 5520 , 1 (SL uncertain, caudal peduncle missing), Amapá, Serra do Navio, rio Amapari , tributary of rio Araguari , PNMT (in front of the park headquarters), 01º11’11”N 52º22’22”W, 13–17 Sep 2021, C. S. Gama, M. H. Sabaj & F. C. T. Lima. LBP 23315, 1 x-ray, 62.6 mm SL, Pará, Itaituba, igarapé Cipó, rio Tapajós basin, 04º52’14”S 56º51’19”W, 29 Sep 2011, R. Britzke .

Diagnosis. Brachychalcinus sabaji can be distinguished from all congeners, except B. reisi , by possessing conspicuous longitudinal dark stripes across the body depth (vs. longitudinal dark stripes absent or restricted to middorsal portion of the body). It can be additionally distinguished from B. copei , B. parnaibae , B. retrospina , and B. signatus by having a lower number of branched dorsal-fin rays (9 vs. 10–11). The new species is distinguished from B. orbicularis by having a comparatively shorter predorsal spine (5.2–6.0 vs. 6.0–9.4% mm SL), a shorter preanal spine (5.0–5.7 vs. 6.0–7.5% mm SL)

( Figs. 5A, B), and by a faint second humeral mark (vs. conspicuous second humeral mark). Brachychalcinus sabaji is differentiated from B. reisi by having a longer predorsal spine (5.2–6.0 vs. 3.2–5.1% mm SL) and longer preanal spine (5.0–5.7 vs. 3.4–4.7% mm SL) ( Figs. 5A, C), by having scales with few curved radii (vs. scales with numerous straight radii), and by having more scale rows between lateral line and midventral scale series (9–10 vs. 7–8). Additionally, B. sabaji can be distinguished from B. nummus by the lower number of longitudinal scale rows between the lateral line and dorsal-fin origin (7–8 vs. 9–11).

Description. Morphometric data summarized in Tab. 1. Largest specimen examined 70.7 mm SL. Greatest body depth at dorsal-fin origin. Dorsal profile of head convex from tip of snout to vertical through anterior nostril; concave from that point to tip of supraoccipital spine; convex from that point to dorsal-fin origin; dorsal-fin base posteroventrally inclined; straight or slightly convex from dorsal-fin terminus to half distance to adipose fin; and convex from this point to adipose fin basis; and straight to slightly concave along dorsal caudal-peduncle profile. Ventral profile of head and body convex from tip of dentary to anal-fin insertion; straight and posterodorsally slanted along anal-fin base; slightly concave at caudal peduncle. Prepelvic region compressed into a sharp keel, with a series of folded and imbricated scales forming a somewhat serrated margin.

Mouth terminal. Maxilla reaches vertical through anterior margin of pupil; its posterior end not extending beyond third infraorbital. Premaxillary teeth in two rows. Outer row with 4*(13) tricuspid teeth. Inner row with 5*(11) pentacupid teeth. Maxilla with 1(6) or 2(5) tri- to tetracuspid teeth. Dentary with 4*(11) pentacuspid teeth, usually central cusp longer, followed by a series of 8 smaller, tri- to unicuspid teeth (1 c&s) ( Fig. 2).

Dorsal-fin rays iii,9*(13). First dorsal-fin element modified into a long, roughly triangular spine in lateral view, with a sharp backward process lying on proximal portion of first unmodified dorsal-fin ray. First unbranched dorsal-fin ray shorter than second. Dorsal-fin origin anterior to vertical through middle of standard length. Adipose fin present. Pectoral-fin rays i,10(9) or i,11*(4). Tip of adpressed pectoral fin extends beyond midlength of adpressed pelvic-fin rays. Pelvic-fin rays i,6*(13). Tip of adpressed pelvic fin reaching first unbranched anal-fin ray. Anal-fin rays iv, 27(1), 28(2), 29(3), 30*(6), or 31(1). First anal-fin element modified into a hook-like preanal spine, with an elongate forward-directed pointed process; second anal-fin element modified into a stiffened simple blunt spine ( Fig. 5A). Caudal fin i,17,i*(1) rays. Dorsal procurrent caudal-fin rays 10(1); ventral procurrent caudal-fin rays 8(1). Caudal-fin forked, lobes somewhat rounded and similar in size.

Scales cycloid, with two to six parallel radii. Lateral line series with 34(6) or 35*(7) perforated scales. Lateral line slightly curved downward. Predorsal scales in an irregular series. Scale rows between dorsal-fin origin and lateral line 7(2) or 8*(11). Scales rows between lateral line and midventral scale series 9*(8) or 10*(5). Circumpeduncular scales 14*(10) or 15(3). Small scales at base of anal fin; two series covering at least anterior most seven rays, which gradually become a single series that extends to over half of anal fin. Small scales covering proximal two-thirds of caudal-fin lobes.

First gill arch with 12(1) rakers on lower limb and 10(1) rakers on upper limb. Total vertebrae 30(1). Supraneurals 3(1).

Coloration in alcohol. Overall background coloration of head and body pale

beige. Dorsal portion of head and body dark. Dark chromatophores concentrated on

snout, jaws, dorsal portion of the neurocranium, and along dorsal midline of body.

Ventral portion of head and body with scattered dark chromatophores. Infraorbital

series with dark chromatophores scattered on the surface of infraorbital bones,

pigmentation more concentrated on infraorbitals 5 and 6. Infraorbitals, opercular

series, and gular area silvery in specimens retaining guanine. Two humeral blotches

separated by a light area. First humeral blotch conspicuous, with concentrated dark

chromatophores lying deeply under scales, rounded, extending across four to five scales

from horizontal series and two scales from the transverse row. Second humeral blotch

faint, formed by scattered dark chromatophores lying deeply under scales, extending

about three scale rows horizontally and four scale rows vertically. Narrow longitudinal

dark line running along horizontal septum of body, extending from humeral region

to caudal peduncle. Sixteen to seventeen, dark, wavy longitudinal stripes formed by

dark pigmentation concentrated on upper and lower scale margins, extending along trunk. Stripes visible along the entire body, more discernible dorsally, except at area of contact between predorsal series of scales and first lateral scale row. Dark wavy stripes more conspicuous dorsally. Pectoral fin with dark chromatophores scattered along edge of lepidotrichia of unbranched and first branched rays. Pelvic fin with dark chromatophores located along fin rays, pigmentation concentrated at posterior half of unbranched and first branched rays. Proximal portion of dorsal fin with concentration of dark chromatophores along interradial membranes; distal portion of fin with dark chromatophores on rays and interradial membranes. Proximal portion of anal fin with concentration of dark chromatophores along interradial membranes; distal margin of fin with dark chromatophores on rays and interradial membranes. Adipose fin with scattered dark chromatophores, more concentrated at fin base. Caudal fin with scattered dark pigmentation on margins of rays ( Fig. 1).

Sexual dimorphism. Mature males with small bony hooks on the branched rays of the anal fin. Anal-fin hooks unevenly distributed on the distalmost segments of the 1 st unbranched ray to the 14 th branched rays, being more numerous in the anteriormost seven branched rays. One to three hooks per segment.

Geographical distribution. Brachychalcinus sabaji is known from the rio Jari, a northern-bank tributary of the lower Amazon River, and the adjacent rio Araguari, an independent coastal river system emptying at the Amazon River delta, Amapá and Pará states, Brazil, respectively. A single specimen from the rio Tapajós is herein identified as B. sabaji , extending the distribution of the new species to this river basin ( Fig. 3).

Etymology. The specific name “ sabaji ” is after Mark Henry Sabaj, fish curator of the Academy of Natural Sciences of Philadelphia of Drexel University, in recognition of his outstanding contribution to the knowledge of South American freshwater fishes. A noun in a genitive case.

Conservation status. Considering that no imminent threats to the species were detected in the area of occurrence, we suggest that Brachychalcinus sabaji has no apparent threat of extinction. According to the International Union for Conservation of Nature ( IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2023), we propose classifying B. sabaji as category Least Concern ( LC).