Oligosarcus jacuiensis, Menezes & Ribeiro, 2010

Menezes, Naércio Aquino & Ribeiro, Alexandre Cunha, 2010, Oligosarcus jacuiensis (Characiformes: Characidae), a new species from the Uruguay and Jacuí River basins, southern Brazil, Neotropical Ichthyology 8 (3), pp. 649-653 : 650-651

Oligosarcus jacuiensis , new species

Fig. 1-2a

Holotype. MCP 28980, female, 153 mm SL, Brazil, Rio Grande do Sul, Estrela Velha, rio Jacuí , 29º15’46”S 53º14’05”W, R. E. Reis, E. H. Pereira & V. A. Bertaco, 17 Nov 2001.

Paratypes. Brazil, Rio Grande do Sul. MCP 44405, 8, 132-160 mm SL , MZUSP 104604 , 4, 128-160 mm SL, collected with holotype ; MCP 18876, 6, 178-205 mm SL, rio Uruguay at Marcelino Ramos , 27º18’S 52º20’W, E. Filho , V. Schultz, S. Meurer & P. Iaczinski, 19 Jul 1995 ; MCP 26979, 13 , 92-109 mm SL, Agudo, lake at UHE Dona Francisca, old mouth of lageado do Gringo , rio Jacuí basin, 29º27’10”S 53º15’05”W , R. E. Reis, E. H. Pereira & V. A. Bertaco, 1 Feb 2001 ; MCP 37930, 4, 151-188 mm SL, Nova Roma, rio das Antas, rio Jacuí basin, 29º04’01”S 51º22’48”W, J. D. Latini , V. A. Capatti & S. Rodrigues, Aug 2004 .

Diagnosis. The number of perforated scales on the lateral line (55-65) distinguishes Oligosarcus jacuiensis from O. pintoi (36-40), O. planaltinae (38-40), O. schindleri (45-54), O. argenteus (44-48), O. longirostris (47-51), O. macrolepis (44- 48), O. menezesi (40-48), O. bolivianus (49-55), O. oligolepis (69-81), O. paranensis (47-54) and O. robustus (75-85). There is an overlap in the number of perforated lateral-line scales between Oligosarcus jacuiensis and O. brevioris , but the latter has fewer longitudinal scale rows around the caudal peduncle (17-20) than O. jacuiensis (21-25). Oligosarcus jacuiensis shares with O. jenynsii and O. perdido the absence of a foramen on the premaxillary ( Fig. 2a ) and with respect to this character differs from O. acutirostris , O. solitarius , and O. hepsetus with a conspicuous foramen ( Fig. 2b ). Oligosarcus solitarius can be further distinguished by possessing 18-20 longitudinal scale rows around the caudal peduncle (vs. 21-25 in O. jacuiensis ), but the other two species have all the meristic data largely overlapping those of O. jacuiensis although O. acutirostris has fewer (50-58) and O. hepsetus more (60-75) perforated scales on the lateral line than in O. jacuiensis (55-65). The new species is most similar to O. jenynsii but can be readily distinguished from this species by having a smaller orbital diameter (21.0- 24.5% of the head length vs. 25.0-34.0%) and the tip of the pectoral fin not reaching the pelvic-fin origin (vs. tip of the pectoral fin reaching and extending beyond the pelvic-fin origin in O. jenynsii ).

Description. Morphometrics in Table 1 and meristics in Table 2. Meristic and morphometric data based on all lots for this species since no statistical differences found among samples studied. Body moderately large, females (92-205 mm SL) slightly larger than males (101-188 mm SL) in available samples. Dorsal body profile convex with a slight depression at occipital region, slightly concave above caudal peduncle; ventral body profile slightly more convex than dorsal, also concave at lower portion of caudal peduncle. Snout conical, larger than orbital diameter; lower jaw slightly shorter that upper jaw and first two caniniform premaxillary teeth accommodated into two small furrows when mouth is fully closed. Maxillary widening gradually towards end, its posterior tip not extending beyond vertical crossing posterior edge of orbit; single row of 22-34 nearly conical maxillary teeth, number of teeth increasing in larger specimens. Premaxillary with one anterior and one posterior caniniform teeth, 3 to 4 nearly conical teeth aligned with caniniform teeth and one conical tooth slightly smaller than caniniform teeth slightly more internal than main tooth row. Dentary bearing an anterior canine, followed by three conical teeth about equally developed and a posterior row of 12-25 nearly conical teeth, increasing in number with an increase in standard length. Ectopterygoid with 10-20 nearly conical teeth. All nearly conical teeth on premaxillary ( Fig. 2a ), maxillary, dentary and ectopterygoid with vestigial lateral cusps, anterior edge convex and posterior edge concave, their tips pointing backward. Twenty two to 25 gill rakers on epibranchial and ceratobranchial portions of first gill arch.

Dorsal origin closer to caudal fin base than to tip of snout, dorsal-fin rays ii, 9 in all specimens, including holotype; posteriormost ray branched. Adipose fin present. Anal-fin rays iv-v,22-28 fin origin at vertical crossing base of last dorsal-fin ray. Anal fin of sexually mature males with bilateral hooks on posterior edge of last unbranched ray and anterior and posterior branches of anterior 9 branched rays. Number of hooks increasing from anteriormost to about fifth ray and then decreasing towards ninth ray. One specimen (MCP 44405, 142 mm SL) with 9 hooks on last unbranched ray, 16 on fifth, 12 on seventh and 5 on nineth. Moderately developed anterior anal-fin lobe including anterior unbranched rays and first 8 or 9 branched rays. Pectoral-fin rays i, 13-16, tip of longest rays not reaching pelvic-fin origin, far distant from this origin in larger specimens. Pelvic-fin rays i, 7 in all specimens, including holotype; tip of longest rays reaching and extending beyond anus in some large specimens, but never reaching anal-fin origin; mature males with hooks on ventral portion of branched pelvic-fin rays only, increasing from 2 on external branch and 16 on internal branch of first ray to 20 on external branch and 50 on internal branch of fourth ray and then decreasing to 9 on internal branch and 8 on internal branch of seventh ray; hooks on internal branches of pelvic-fin rays always more developed than those on external branches.

Lateral line complete, perforated scales 55-65; 10-12 horizontal scale rows above lateral line, 8-10 below; 21-25 horizontal scale rows around caudal peduncle; 23-29 scales from tip of occipital to dorsal-fin origin; scale row along both sides of anal-fin base extending to about base of 10 th or 11 th branched anal-fin ray.

Color in alcohol. Body pale yellow darker dorsally due to presence of dark chromatophores, especially concentrated on free edge of scales, lighter ventrally. Dorsal part of head and snout heavily pigmented with dark chromatophores, this pigmentation extending as a narrow stripe over anterior two thirds of maxillary. Lateral head and opercular bones with scattered dark chromatophores. Tip of lower jaw pigmented with dark chromatophores, this pigmentation extending as a narrow stripe along upper lateral portion of lower jaw. Vertically elongate dark blotch at humeral region wider above and gradually narrowing below extending Etymology. The species name jacuiensis is in reference to rio Jacuí in Rio Grande do Sul, Brazil, where most of the specimens were collected. An adjective.

Figures

Fig. 1. Oligosarcus jacuiensis, holotype, MCP 28980, female, 153 mm SL, rio Jacuí.

Fig. 2. a) Oligosarcus jacuiensis, new species, MZUSP 104604, 141 mm SL.b) O. acutirostris, MZUSP 90766,117 mm SL. Right lateral view of premaxillae. Black arrow indicates foramen.