Cyanocharax dicropotamicus Malabarba & Weitzman, 2003

Malabarba, Luiz R. & Weitzman, Stanley H., 2003, Description Of A New Genus With Six New Species From Southern Brazil, Uruguay And Argentina, With A Discussion Of A Putative Characid Clade (Teleostei: Characiformes: Characidae), Comun. Mus. Ciênc. Tecnol. PUCRS 16 (1), pp. 67-151 : 109-115

Cyanocharax dicropotamicus Malabarba & Weitzman , new species

( Figs. 1 , 3 , 6 , 14, 24-28, Table 3)

Diagnosis. Cyanocharax dicropotamicus differs from C. itaimbe by the smaller eye diameter (37.8-46.8 versus 43.0-50.0% of HL, respectively); and smaller number of longitudinal scale rows between dorsal-fin origin and pelvic-fin origin (10- 11 versus 11- 13, respectively). Although available specimens are not intensely pigmented, the chromatophore distribution of C. dicropotamicus indicates that the species has the tip of the anal-fin lobe unpigmented, and the adipose fin is darkly pigmented. This distinguishes C. dicropotamicus from C. alburnus , C. lepiclastus , C. macropinna , and C. alegretensis that have the adipose fin not black pigmented and the anal and dorsal-fins distal portions darkly pigmented. The concave distal profile of the anal fin of males also distinguishes C. dicropotamicus from C. lepiclastus , C. macropinna , and C. alegretensis that have a straight or convex anal-fin margin. The complete lateral line (37-39 perforated scales) and the higher number of branched anal-fin rays (22-26, rarely 27 or 28; x ̄= 24.6) differentiate C. dicropotamicus from C. tipiaia (7- 11 perforated scales and 21-23, x ̄= 22.3 branched anal-fin rays).

Description. Morphometric data given in Table 3. Body moderately elongate and compressed. Dorsal and ventral body profiles equally convex from snout to dorsal and anal-fin origins, respectively. Dorsal body profile slightly concave near the insertion of the most posterior dorsal-fin rays, and slightly convex from that point to caudal peduncle. Ventral body profile along anal fin nearly straight. Dorsal and ventral profiles of caudal peduncle slightly concave.

Head small (22.1 -24.8% of SL). Eyes of moderate size (37.8 -46.8% of HL). Maxilla positioned at an angle of 45 degrees or greater, relative to long axis of body. Posterior tip of maxilla usually not reaching further posterior than a vertical line crossing anterior border of pupil.

Two series of premaxillary teeth. Teeth of outer series usually tricuspid, smaller than those of inner series, numbering 3 to 5. Four or 5 teeth with 3, 4 or most rarely 5 cusps in inner series. Those teeth with 4 or 5 cusps with fourth and fifth cusps very small, almost imperceptible. Four to 6 maxillary teeth usually ranging from 3 cusps to conical, from anteriormost to posteriormost teeth. Four large dentary teeth followed by a series of 6 to 10 much smaller ones, ranging from 3 cusps to conical. Anterior large dentary teeth with 3, 4 or 5 cusps. Those teeth with 4 or 5 cusps with fourth and fifth cusps usually very small, almost imperceptible. Second dentary tooth shorter and inserted at a lower position in jaws, in such a way that tip of its longest cusp reaches only as high as tip of second largest cusp of first and third dentary teeth ( Fig. 28 ).

Dorsal-fin rays ii,8 (n = 35). Dorsal-fin origin posterior to mid body length. Adipose-fin origin dorsal to posterior anal-fin ray insertion.

Anal-fin rays iii-v, 22-26, rarely 27 or 28 (x̄ = 24.6, n = 130). Anal-fin origin clearly posterior to a vertical line crossing dorsal-fin origin. Distal border of anal fin concave in both sexes, with anterior 3 -4 branched rays longer, forming a prominent anterior lobe. Anal-fin rays of males with small retrorse bony hooks present on 2/3 of distal length of longest unbranched ray and usually anterior 8 branched rays ( Fig. 6 ). Minute hooks distributed along distal third of some remaining rays. Hooks mostly present on posterior branches of rays. Usually one pair of bony hooks per ray segment; two pairs rarely occur on anterior branched rays.

Pectoral-fin rays i, 9- 11 (x ̄= 9.7, n = 35). Distal ends of longest rays extending to or posterior to pelvic-fin origin. Pelvic fins i, 6 (n = 35). Pelvic-fin origin anterior to a vertical passing through dorsal-fin origin. In females longest pelvic-fin ray may or may not reach anal-fin origin. In males longest ray reaches anal-fin origin. Pelvic fins with ventromedial, usually unpaired retrorse bony hooks on branched rays only ( Fig. 3 ). Principal caudal-fin rays 10/9.

Scales cycloid. Lateral line complete in all specimens in which scales were counted. Total number of scales in lateral line row, 37-39 (x̄= 37.7, n = 14). Scale rows between dorsal-fin origin and lateral line 5-6 (x̄= 6.0, n = 31). Scale rows between lateral line and pelvic-fin origin 3 -4 (x̄= 3.9, n = 35). Predorsal scales 12- 15 (x̄= 12.9, n = 15), usually not arranged in one regular series. Males and females with a scale sheath on anal-fin base consisting of one row with usually 9 to 12 small scales covering bases of unbranched rays and first 9 to 12 branched rays. Vertebrae 36-38 (x ̄ = 36.6, n = 26), including Weberian apparatus and posterior half centrum (counts taken from x-ray negatives from MCP 19510).

Color in alcohol. Available specimens of Cyanocharax dicropotamicus ( Figs. 24-27 ) not as heavily pigmented as available specimens of remaining Cyanocharax species. All C. dicropotamicus specimens were collected during October and December, whereas colorful specimens of C. itaimbe were caught during January and February. Pigmentation may be affected by seasonal and reproductive state. Pigmentation pattern of C. dicropotamicus , however, with a similar distribution to that described to C. itaimbe .

Body pale brownish yellow in specimens preserved in formalin long enough to destroy guanine pigment. Lateral body stripe broad and dark posteriorly, becoming pale and narrow anterior to vertical through dorsal-fin origin. Lateral body stripe remains silvery in some specimens. Dark humeral spot faint, vertically elongate, centered on fourth and fifth scales of scale row just dorsal to lateral line. Middle caudal-fin rays darkly pigmented with pigmentation extending to tips of rays. Exposed borders of scales of back delineated by dark chromatophores. Dorsal and anal fins covered with scattered dark chromatophores, except for distinct unpigmented area at tip of dorsal fin and tip of anterior anal fin lobe. Adipose fin darkly pigmented (most clearly in MCP 19516). Head black to gray dorsally, especially dark near nape. Sides of head and opercles silvery where guanine pigment not destroyed by formalin, sides ofhead otherwise whitish yellow.

Sexual dimorphism. Males have anal and pelvic fin hooks. Additionally, mature males have slightly longer pelvic fins than females (Table 3).

Etymology. Dicro is from the Greek dikros meaning forked and potamicus from the Greek potamus meaning river or stream and is reference to the rio Forqueta, the type locality.

Distribution. Known only from northern tributaries of the rio Jacuí, Laguna dos Patos System, draining from Serra Geral formation ( Fig. 1 ).

Holotype: MZUSP 82262 , male, 42.5 mm SL, rio Forqueta , Marques de Souza, Lageado, Rio Grande do Sul, Brazil; 7 Dec 1979.

Paratypes: all from laguna dos Patos drainage , Rio Grande do Sul, Brazil: MZUSP 18984 (34), USNM 337599 (14), rio Forqueta , Marques de Souza, Lageado; 7 Dec 1979 . MCP 19510 (63: 5 c&s, 22.6-42.6 mm SL), MNRJ 23845 (20, 24.4-30.5 mm SL), USNM 357244 (20), rio Taquari, Cruzeiro do Sul ; 29 Oct 1996 . MCP 19516 (30, 28.3 -40.8 mm SL), rio Taquari, Encantado ; 31 Oct 1996 .

Figures

Figure 1. Map of southern Brazil, Uruguay and eastern Argentina, showing the distribution of examined specimens of Cyanocharax alegretensis, C. dicropotamicus, C. itaimbe, C. lepiclastus, C. macropinna, and C. tipiaia. The detailed portion of the map includes, from North to South, the rio Araranguá, rio Mampituba, rio Três Forquilhas, and rio Maquiné drainages.

Figure 3. Ventral view of the left pelvic fin of a male of Cyanocharax dicropotamicus showing the distribution of the pelvic-fin hooks (MCP 19510, 41.9 mm SL).

Figure 6. Left view of the anal fin of a male of Cyanocharax dicropotamicus showing the distribution of the anal-fin hooks (MCP 19510,41.9 mm SL).

Figure 24. Cyanocharax dicropotamicus, new species, holotype, male, 42.5 mm SL, rio Forqueta, Marques de Souza, Lageado, Rio Grande do Sul, Brazil (MZUSP 18984).

Figure 25. Cyanocharax dicropotamicus, new species, female, 41.8 mm SL, same locality as in Fig. 24 (MZUSP 18984).

Figure 26. Cyanocharax dicropotamicus, new species, male, 37.04 mm SL, rio Taquari, Rio Grande do Sul, Brazil (MCP 19516).

Figure 27. Cyanocharax dicropotamicus, new species, female, 33.63 mm SL, rio Taquari, Rio Grande do Sul, Brazil (MCP 19516).

Figure 28. Teeth of Cyanocharax dicropotamicus (MCP 19510, 40.0 mm SL). Jaws seem decalcified and deformed. A - Maxilla, B - Premaxilla and C - Dentary teeth.