Cyanocharax obi, Casciotta, Jorge, Almirón, Adriana, Piálek, Lubomír & Říčan, Oldřich, 2012

Casciotta, Jorge, Almirón, Adriana, Piálek, Lubomír & Říčan, Oldřich, 2012, Cyanocharax obi, a new species (Characiformes: Characidae) and the first record of the genus from tributaries of the río Paraná basin, Argentina, Zootaxa 3391, pp. 39-51 : 42-48

Cyanocharax obi sp. nov.

( Figs. 3–8 , Tab. 2 )

Holotype. MACN-ict 9560, 53.3 mm; Argentina: Misiones: río Paraná basin, tributary of the arroyo Paranay–Guazú, 26°52’28.9” S, 54°42’22.8” W, col: Casciotta et al., December 2010 ( Fig. 3 ).

Paratypes. All from Argentina: Misiones: río Paraná basin:

MACN-ict 9557, 9 ex., 41.0– 52.7 mm; same data as holotype. AI 284, 2 ex., 52.2–57.4 mm, tributary of the arroyo Paranay-Guazú in trail from road 14 to Monte Carlo city, 26°49'03.5" S, 54°26'58.9" W, col: Říčan et al., December 2007. MACN-ict 9558, 3 ex., 38.1–46.6 mm, tributary of the arroyo Paranay–Guazú, road 11 between Aristóbulo del Valle and El Alcazar, 26°48'27.1" S, 54°45'37.7" W, col: Říčan et al., December 2007. MACN-ict 9559, 3 ex., 48.4–56.7 mm, tributary of the arroyo Paranay–Guazú, road 11 between Aristóbulo del Valle and El Alcazar, 26°48'27.1" S, 54°45'37.7" W, col: Casciotta et al., December 2010. AI 282, 1 ex. (C&S), 58.7 mm, tributary of the arroyo Paranay–Guazú, road 11 between Aristóbulo del Valle and El Alcazar, 26°48'27.1" S, 54°45'37.7" W, col: Říčan et a l., December 2007.

Diagnosis. Cyanocharax obi can be distinguished by the following combination of characters: lateral line interrupted or with alternated series of perforated and non perforated scales, 22–24 (mode=24) branched anal-fin rays, body depth at dorsal-fin origin (34.5–40.8, mean=37.9 % SL), and distal border of anal fin in matures males nearly straight.

Cyanocharax obi differs from C. alburnus , C. itaimbe , and C. dicropotamicus in having the lateral line interrupted or with alternated series of perforated and non perforated scales vs. usually complete. Also, Cyanocharax obi differs from C. alburnus by the number of sheath scales on anal-fin base (7–14 scales vs. 6–8), body depth at dorsal-fin origin (2.5–2.9 vs. 3.1–4.7 in SL), anal-fin base length (2.9–3.4 vs. 3.5–3.8 in SL), and interorbital width (2.7–2.9 vs. 2.9–3.7 in HL); from C. itaimbe by the number of scales on longitudinal series (34–38 vs. 37–40), and horizontal eye diameter (35.9–42.1 vs. 43.0–50.0% SL); from C. dicropotamicus by the body depth at dorsal-fin origin (34.5–40.8 vs. 26.6–33.1% SL), snout length (24.0–27.3 vs. 19.5–23.5% HL), and upper jaw length (42.0–46.9 vs. 33.3–41.9% HL); from C. tipiaia by the number of maxillary teeth (3–6 vs. 2–3), pelvic-fin length (14.5–18.1 vs. 13.1–14.5% SL), snout to pelvic-fin origin (44.4–50.6 vs. 42.3–45.3% SL), and body depth at dorsal-fin origin (34.5–40.8 vs. 28.5–31.3% of SL); from C. lepiclastus by a sheath of scales on anal-fin base consisting of row with 7–14 scales vs. 13–20, number of branched anal-fin rays (22–24 vs. 24–29), snout to anal-fin origin (59.4–65.3 vs. 52.1–58.8% SL), and snout to pelvic-fin origin (44.4–50.6 vs. 38.6–44.6% SL); from C. alegretensis by the number of branched anal-fin rays (22–24 vs. 23–30), snout to anal-fin origin (59.4–65.3 vs. 53.4–58.2% SL), and snout to pelvic-fin origin (44.4–50.6 vs. 38.9–43.5% SL); and from C. uruguayensis by the number of branched anal-fin rays (22–24 vs. 28–35) and distal margin of anal-fin in mature males nearly straight vs. convex.

Description. Morphometric data of the holotype and paratypes are given in Table 2 . Body moderately elongate and compressed. Predorsal body profile convex, usually with a concavity at nape. Dorsal body profile nearly straight from dorsal fin to caudal peduncle. Ventral body profile convex from snout tip to anal-fin origin. Nearly straight in females and slightly convex in mature males along anal-fin base. Ventral and dorsal borders of caudal peduncle slightly concave.

Head small, posterior tip of maxilla surpassing the anterior margin of orbit.

Two series of premaxillary teeth. Teeth of outer series tricuspid, smaller than those of inner series ( Fig. 4 ). Four teeth with 3 to 5 cusps in inner series (19* ex.). Three to six maxillary teeth with 1 to 4 cusps, four tricuspid teeth in the holotype ( Fig. 4 ). Dentary with three large anterior teeth followed by one medium-size teeth and 8 smaller ones, ranging from tricuspid to unicuspid, from anteriormost to posteriormost teeth ( Fig. 5 ). Anterior larger dentary teeth tri- or pentacuspid. Second dentary tooth shorter and inserted at lower position in jaws (1 ex., C&S), tip of its longest cusp reaches only as high as tip of second largest cusp of first and third dentary teeth.

Holotype Range Mean SD Standard length 53.3 38.1–58.7

Anal-fin rays iv–v,22–24 (mode=iv,24*, n=19). Anal-fin origin posterior to vertical through dorsal-fin origin at middle of body length. Anal-fin distal border concave in females and juveniles, nearly straight in mature males. Anal-fin rays of males with small retrorse bony hooks present on 2 to 19 branched rays. Hooks mostly present on posterior branches of rays and posterior border of lepidotrichia. One or two pairs of bony hooks per ray segment.

Pectoral-fin rays i,10–12 (mode: i,11*, n=19). Distal ends of longest rays may or may not reach pelvic-fin insertion in both males and females. Pelvic-fin rays i,6. Pelvic-fin origin anterior to dorsal-fin origin. Distal ends of longest rays not reaching anal-fin origin. Pelvic fins with ventromedial, usually unpaired retrorse bony hooks on third to sixth branched rays in sexually mature males. Principal caudal-fin rays 10/9. Scales cycloid. Lateral line never complete, with anterior series of 8 to 12* pored scales (mode=11, n=19), followed by a median non-perforated scales series, and a posterior perforated series of 1 to 3 scales (in 7 ex.). Total number of scales in longitudinal series 34–38 (mode=36*, n=19). Scale rows between dorsal-fin origin and lateral line 5–6* (mode=6, n=19). Scale rows between lateral line and pelvic-fin origin 4. Predorsal scales 13–17 (mode=14*, n=19). Males and females with sheath of scales on anal-fin base consisting of row with 7–14 scales (mode=11*, n=19), covering bases of unbranched rays and first 12 to 14 branched rays. Vertebrae 37 (1 ex., C&S).

Color in alcohol. Body pale brownish. Lateral body stripe broad and dark posteriorly, becoming pale anterior to dorsal-fin origin. Dark humeral spot vertically elongated. Scales of dorsal portion of body with scattered dark chromatophores. Fins translucent, with scattered black chromatophores on distal third of anal fin, middle caudal-fin rays, dorsal and ventral caudal-fin lobes, along branched pelvic-fin rays, along unbranched and branched pectoral-fin rays, and on the distal two thirds of dorsal-fin rays. Tip of all unbranched and 1st to 3rd branched anal-fin rays unpigmented.

Adipose fin darkly pigmented with an unpigmented area in the middle. Head gray dorsally, especially dark near nape. Sides of head and opercle pale brown.

Color in life. Body between silvery and sky-blue. Black humeral spot elongated vertically. A wide silvery lateral band more evident at the caudal peduncle. Scattered black chromatophores on all fins without additional obvious markings. Base of caudal-fin lobes orange ( Fig. 6 ).

Sexual dimorphism. Males of C. obi differ from females in the nearly straight or slightly convex distal border of the anal fin (vs. concave in females), first branched pelvic-fin produced in a short filament (4* ex., n= 10 males), hooks on anal and pelvic-fin rays.

Distribution. Cyanocharax obi is only known from tributaries of the arroyo Paranay–Guazú, río Paraná basin, Misiones Province, Argentina ( Fig. 7 ).

Ecological notes. The localities where Cyanocharax obi was collected had a turbid and rapidly flowing water after heavy rain. The depth of the arroyo Paranay–Guazú is variable, 0.40 to 2 m. The bottom consists of mud, sand, and stones. Some areas have scarce submerged vegetation ( Fig. 8 ).

Etymology. The specific epithet obi is a Guaraní word that means blue in allusion to the ground color of the body.

Figures

FIGURE 3. Cyanocharax obi, male, holotype, MACN-ict 9560, 53.3 mm; Argentina: Misiones: río Paraná basin, tributary of the arroyo Paranay-Guazú, 26 ° 52 ’ 28.9 ” S, 54 ° 42 ’ 22.8 ” W.

FIGURE 4. Cyanocharax obi, AI 282, paratype, 58.7 mm, lateral view of right upper jaw. Scale bar: 1 mm.

FIGURE 5. Cyanocharax obi, AI 282, paratype, 58.7 mm, lateral view of right lower jaw. Scale bar: 1 mm.

FIGURE 6. Cyanocharax obi, live specimen, female, paratype MACN-ict 9559, 56.7 mm.

FIGURE 7. Hydrological map of the Misiones Province. The type locality is marked with number 1.

FIGURE 8. Tributary of the arroyo Paranay-Guazú on a side trail from national road 14 to the town of Monte Carlo, 26 ° 49 ' 03.5 " S, 54 ° 26 ' 58.9 " W.

Tables

TABLE 2. Morphometrics data of the holotype and 18 paratypes of Cyanocharax obi. Standard length is expressed in mm. SD: standard deviation.

Percents of SL
Snout to anal-fin origin	63.2	59.4–65.3	62.8	1.60
Snout to dorsal-fin origin	57.6	54.1–59.1	56.8	1.56
Snout to pelvic-fin origin	49.4	44.4–50.6	47.9	1.52
Dorsal-fin base length	11.7	10.2–12.6	11.7	0.65
Anal-fin base length	30.8	29.2–34.1	31.6	1.36
Caudal peduncle length	12.7	10.0–12.9	11.9	0.82
Caudal peduncle depth	11.1	9.7–11.7	11.0	0.53
Depth at dorsal-fin origin	40.2	34.5–40.8	37.9	2.23
Dorsal-fin height	23.4	20.5–23.9	22.5	1.12
Pelvic-fin length	17.2	14.5–18.1	16.8	0.97
Pectoral-fin length	23.3	21.3–24.5	23.3	0.90
Bony head length	22.9	21.3–24.3	22.7	0.70
Percents of head length
Snout length	25.8	24.0–27.3	25.7	0.91
Upper jaw length	43.4	42.0–46.9	45.1	1.42
Horizontal eye diameter	38.5	35.9–42.1	39.2	1.77
Least interorbital width	36.7	34.3–37.5	35.9	1.04