Hyphessobrycon petricolus, Ohara, Willian M., Lima, Flávio C. T. & Barros, Bruno S., 2017

Ohara, Willian M., Lima, Flávio C. T. & Barros, Bruno S., 2017, Hyphessobrycon petricolus, a new species of tetra (Characiformes: Characidae) from the rio Madeira basin, Mato Grosso, Brazil, Zootaxa 4221 (2), pp. 242-250 : 243-247

Hyphessobrycon petricolus new species

( Figs. 1 , 3 )

Holotype. MZUSP 120694, 37.1 mm SL, Brazil, Mato Grosso, Colniza, stream tributary to the rio Roosevelt , 9°8’40”S 60°45’5”W ; 14 Jul 2013, W.M. Ohara & D.B. Hungria.

Paratypes. MZUSP 118564, 6, 2.3–42.8 mm SL (2 c&s, 24.9–30.3 mm SL), 22.9–31.3 mm SL; MZUSP 118565, 5, 33.1–42.1 mm SL; ZUEC 13040, 2, 32.4–42.7 mm SL; ANSP 201030, 2, 35.8–41.9 mm SL; INPA 53140, 2 , 28.8–39.7 mm SL: same data as holotype.

Diagnosis. Hyphessobrycon petricolus differs from all of its congeners with exception of H. cachimbensis Travassos , H. cyanotaenia Zarske & Géry , H. fernandezi , H. melanostichos Carvalho & Bertaco , H. nigricinctus , H. paucilepis García-Alzate, Román-Valencia & Taphorn , H. psittacus Dagosta, Marinho, Camelier & Lima, H. scholzei , H. sovichthys Schultz , H. stegemanni Géry , H. taphorni , H. tuyensis , and H. vilmae Géry , by the presence of a well-defined, relatively narrow dark midlateral stripe on body extending to middle caudal-fin rays (vs. absence of a well-defined longitudinal stripe, or midlateral dark stripe becoming blurred towards caudal peduncle). Hyphessobrycon petricolus differs from all the aforementioned species, with exception of H. cyanotaenia , H. cachimbensis , H. melanostichos , and H. nigricinctus , by the presence of a humeral blotch (vs. humeral blotch absent in H. fernandezi , H. paucilepis , H. psittacus , H. scholzei , H. sovichthys , H. stegemanni , H. taphorni , H. tuyensis , and H. vilmae ). It can be distinguished from H. melanostichos and H. cyanotaenia by midlateral dark stripe starting at trunk, posteriorly to the opercle (vs. midlateral dark stripe starting behind eye); and from H. nigricinctus and H. cachimbensis by having 16–20 branched anal-fin rays (vs. 22–26 in H. nigricinctus ; 21–25 in H. cachimbensis ). It can be additionally distinguished from H. nigricinctus by number of scales above the lateral line (5 vs. 7–8) and by presenting a thinner midlateral stripe, which does not overlap dorsally with the midlateral stripe (vs. midlateral stripe broad, almost completely overlapping humeral blotch except for a small ventral projection); and from H. cachimbensis by presenting 3–6 maxillary teeth (vs. 1–2) and by presenting inner premaxillary teeth with a lower number of cusps (up to 5 cusps, vs. 7 or more).

Description. Morphometric data for the holotype and paratypes presented in Table 1 . Body compressed, moderately short and deep. Greatest body depth situated slightly anterior to vertical through dorsal-fin origin. Dorsal profile of head convex from tip of upper jaw to vertical through anterior nostril; straight or slightly concave from that point to tip of supraoccipital spine. Dorsal profile of body convex from supraoccipital spine tip to base of last dorsal-fin ray, approximately straight from that point to adipose-fin insertion and slightly concave between adipose-fin insertion and origin of anterior most dorsal procurrent caudal-fin ray. Ventral profile of head and body convex from tip of dentary to anal-fin insertion. Body profile along anal-fin base straight and posterodorsally slanted. Ventral profile of caudal peduncle slightly concave.

Jaws equal, mouth terminal. Posterior terminus of maxilla reaching vertical through anterior third of eye. Maxilla approximately at 45 degree angle relative to longitudinal axis of body. Nostrils close to each other, anterior opening circular, posterior opening crescent-shaped. Nostrils separated by narrow flap of skin.

Premaxillary teeth in two rows; outer teeth row with 2(1), 3(10), or 4*(4) tricuspid teeth; inner teeth row with 5*(7) or 6(1) teeth with three to five cusps, symphyseal tooth of inner series narrow and asymmetric with 4(14) cusps. Maxilla with 3(1), 4*(9), 5(3), or 6(2) teeth along anteroventral margin, with one or three cusps ( Fig. 2 ); anterior most tooth usually largest. Dentary with 4(1) or 5(8) tri- to pentacuspid teeth, followed by series of 8(1), 9(2), 10(3), 11(1), or 13(1) small conical or tricuspid teeth, considerably smaller than anterior teeth. Central cusp of all teeth most developed than remaining lateral cusps; cusp tips slightly curved inward on dentary teeth, and outward on premaxillary teeth ( Fig. 2 ).

Scales cycloid, moderately large, with 4 to 8 radii strongly marked; circuli weakly marked proximally. Lateral line slightly deflected downward and incompletely pored, with 5(1), 6(1), 7*(7), 8 (5), or 9(1) perforated scales. Longitudinal scales series including lateral-line scales 30(2), 31(7), or 32*(4). Longitudinal scale rows between dorsal-fin origin and lateral line 5*(15). Longitudinal scale rows between lateral line and pelvic-fin origin 3(9) or 4*(5). Scales in median series between tip of supraoccipital spine and dorsal-fin origin 9(2) or 10*(11). Horizontal scale rows around caudal peduncle 12*(12) or 13(2). Single row of 3(2) or 4(3) scales covering base of anterior most anal-fin rays. Caudal fin with scales only basally.

Dorsal-fin rays ii, 9(15); small ossification anterior to first unbranched ray present in two of the c&s specimens. 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 ray. First dorsal-fin pterygiophore located behind neural spine of 9th (1) vertebrae. Adipose fin present. Anal-fin rays iv, 16(1), 17*(2), 18(8), 19(2), or 20(2), anteriormost rays slightly longer, subsequent rays gradually decreasing in size; distal margin of anal fin slightly concave. Pectoral-fin rays i, 9(1), 10(3) or 11*(11). Tip of pectoral fin reaching vertical at pelvic-fin insertion. Pelvic-fin rays i, 7(15). Tip of pelvic fin falling slightly short of reaching anal-fin insertion (reaching in a single specimen). Principal caudal-fin rays 10+9(15). Caudal fin forked, lobes somewhat pointed and of similar size. Ten (1) or 11 (1) dorsal procurrent caudal-fin rays and 7(1) or 9(1) ventral procurrent caudal-fin rays. Vertebrae 32 (1) or 33 (1). Supraneurals 4 (1) or 5 (1); precaudal and caudal vertebrae 16(1) or 17(1), respectively. Branchiostegal rays 4(2). First gill arch with 1(1) or 2(1) hypobranchial, 8(1) or 9(1) ceratobranchial, 1(1) on cartilage between ceratobranchial and epibranchial, and 6(1) or 7(1) epibranchial gill-rakers.

Color in alcohol. Overall ground coloration of head and body beige ( Fig. 1 ). Dorsal portion of head and body dark. Snout, tip of dentary, maxilla, antorbital and infraorbitals 1 and 2 with a dense concentration of small dark chromatophores, imparting an overall dark coloration. Infraorbitals 3–6, opercle and preopercle with scattered dark chromatophores. Uppermost two scale rows darkened, clearly contrasting with clearer area along third scale row situated immediately above midlateral stripe. Humeral blotch moderately conspicuous, vertically elongated, mostly overlapping with midlateral stripe, relatively diffuse where not overlapping, extending approximately two scales horizontally and one vertically. A conspicuous, relatively broad dark midlateral stripe on body, extending posteriorly along trunk from immediately behind opercle to tip of middle caudal-fin rays. Clear stripe parallel and immediately above to dark midlateral stripe extending from opercle to end of caudal peduncle. Abdominal region with scattered dark chromatophores. Small dark chromatophores scattered on interradial membranes of all fins, sometimes over rays of caudal and dorsal fins. Pelvic, dorsal and anal fins with dark chromatophores scattered along interradial membranes. Adipose fin with scattered dark pigmentation. Caudal-fin median rays with narrow dark stripe continuous with the dark midlateral stripe. Caudal-peduncle blotch absent, midlateral stripe slightly broader at caudal peduncle in two of the examined specimens (MZUSP 120694, holotype, and MZUSP 118564, 42.8 mm SL).

Color in life. Based on photographs taken in the field of three specimens ( Fig. 3 ) Infraorbitals 2, 3, and 4, opercle, preopercle, and abdominal region covered with guanine, imparting a silvery hue. Upper lip and upper half of dentary faintly brown (yellow in juveniles). Top of head and dorsum dark brown, with an olive hue. Humeral blotch and dark midlateral stripe dark, very conspicuous. Yellowish to golden stripe parallel and immediately above to dark midlateral stripe extending from immediately behind opercle to caudal peduncle terminus Dorsal portion of eye red, lower portion clear, with a silvery hue. Dorsal, pelvic, adipose, caudal and anal fins yellow to orange. Pectoral fin hyaline.

Sexual dimorphism. Bony hooks on fins, a common dimorphic feature in characids ( Malabarba & Weitzman, 2003), were not found in any specimens of Hyphessobrycon petricolus .

Distribution. The new species is so far only known from its type locality, a small tributary of the middle rio Roosevelt, rio Aripuanã drainage, rio Madeira basin, northwestern Mato Grosso State, Brazil ( Fig. 4 ).

Ecological notes. The type locality of Hyphessobrycon petricolus is a small, black water stream 1.5–4 m wide and 0.3–1.5 m deep, with swift water current, and rocky bottom ( Fig. 5 a), upstream a large waterfall ( Fig. 5 b). The stream run across a small cerrado-vegetation enclave situated within Amazon forest. Individuals of Hyphessobrycon petricolus were captured near of surface during the night in small groups of 2 to 4 individuals. Other species sampled syntopically were: Aequidens sp., Erythrinus erythrinus, Pyrrhulina sp., Synbranchus sp. and Tatia cf. brunnea .

Etymology. The specific name petricolus derives from the Latin petra meaning rock and colus, to abide, to dwell, referring to the occurrence of the species in a rocky-bottomed stream. An adjective.

Remarks. The new species described herein would be assignable to the Hyphessobrycon heterorhabdus group as defined by Géry (1977), by the presence of a conspicuous midlateral stripe. However, the Hyphessobrycon heterorhabdus group was recently restricted to include only Hyphessobrycon species presenting a midlateral stripe continuous with the humeral blotch that is blurred towards the caudal peduncle, typically not reaching it ( Lima et al. 2014). Among the Hyphessobrycon species presenting a conspicuous midlateral stripe extending to the caudal peduncle, Hyphessobrycon petricolus is more similar to H. cachimbensis , H. cyanotaenia , H. melanostichos , and H. nigricinctus , by sharing with these species the presence of a humeral blotch partially overlapping with the midlateral stripe ( Dagosta et al. 2016). Hyphessobrycon petricolus can be distinguished from the aforementioned species by the characters mentioned in the Diagnosis. Whether the Hyphessobrycon species presenting a conspicuous midlateral stripe represent a monophyletic clade or not is an issue still open to further investigation.

Figures

FIGURE 1. Hyphessobrycon petricolus, holotype, MZUSP 120694, 37.1 mm SL, Brazil, Mato Grosso, stream tributary of rio Roosevelt.

FIGURE 2. Hyphessobrycon petricolus, medial view of right side, premaxilla, dentary and maxilla; MZUSP 118564, paratype, 24.9 mm SL.

FIGURE 3. Hyphessobrycon petricolus, paratypes, immediately after capture.

FIGURE 4. Map showing the type-locality (red star) of Hyphessobrycon petricolus, a tributary from the rio Roosevelt, rio Madeira basin, Mato Grosso, Brazil.

FIGURE 5. The type-locality of Hyphessobrycon petricolus, a small tributary from rio Roosevelt (a), above a great waterfall (b), rio Madeira basin, Mato Grosso, Brazil.

Tables

TABLE 1. Morphometric data for holotype and paratypes of Hyphessobrycon petricolus (n = 15). S. D = Standard Deviation.

Characters	Holotype	Range	Mean±S.D.
Standard length (mm)	37.1	28.8–42.8	39.7
Percentages of standard length
Depth at dorsal-fin origin	33.4	32.4–37.5	34.4±1.7
Snout to dorsal-fin origin	52.3	49.5–54.1	52.5±1.3
Snout to pectoral-fin origin	28.8	26.8–30.9	28.2±1.3
Snout to pelvic-fin origin	48.8	45.2–51.6	48.7±1.8
Snout to anal-fin origin	66.0	61.2–67.4	64.8±1.7
Caudal peduncle depth	10.5	9.9–12.7	11.2±0.8
Caudal peduncle length	13.7	10.6–14.5	13.1±1.2
Pectoral-fin length	21.0	19.7–22.7	21.0±1.0
Pelvic-fin length	17.5	15.1–19.6	17.5±1.2
Pelvic fin to anal-fin distance	17.8	14.5–19.7	17.8±1.5
Dorsal-fin base	13.5	11.9–15.3	14.1±0.9
Dorsal-fin length	29.4	26.4–31.0	29.0±1.4
Dorsal-fin origin to caudal-fin origin	54.4	51.5–57.3	53.8±1.7
Dorsal-fin end to adipose-fin origin	22.9	19.6–24.3	22.8±1.3
Anal-fin base	25.1	25.0–28.9	28.0±1.3
Anal-fin length	21.3	17.4–21.5	20.0±1.3
Posterior margin of eye to dorsal-fin origin	38.0	35.9–40.8	38.5±1.4
Head length	26.4	25.4–28.0	26.3±0.7
Percentages of head length
Horizontal length eye	37.8	35.3–41.8	39.3±2.2
Snout length	25.5	20.5–29.0	25.5±2.2
Least interorbital width	30.6	28.4–37.6	32.6±2.4
Upper jaw length	50.0	46.9–50.8	49.2±1.0