Fig. 8

Body elongated; greatest depth contained 3.3 to 3.5 and caudal peduncle depth 8.1 to 9.7 times in SL; head length 4.0 to 4.6, predorsal distance 1.9 to 2.1 and caudal peduncle length 6.8 to 9.5 in SL; snout length 3.0 to 3.7, horizontal orbital diameter 2.2 to 2.3 and least interorbital width 2.8 to 3.2 in HL. Mouth terminal; inner row of premaxilla with 4 or 5 teeth, outer with 3-5, dentary with 4 and maxilla with 0 to 2 teeth. Lateral line complete, with 32-34 pored scales; longitudinal series with 32-34 scales; transverse series above lateral line with 5 scale rows and below with 3 scale rows. Dorsal fin with 11 rays, pectoral fin with 12-13 rays, pelvic fin with 8 rays, anal fin with 20-24 rays and caudal fin with 19 rays. Ground color whitish; silver longitudinal stripe (brown or grey in fixed specimens), from humeral spot to caudal peduncle; distal portion of upper caudal-fin lobe darker than lower.

Maximum standard length. 37.0 mm.

Distribution. Upper rio Paraná basin.

Remarks. Some specimens of Moenkhausia cf. gracilima were identified as Hemigrammus marginatus by Graça, Pavanelli (2007). Ota, RP et al. (2015) restricted the distribution of H. marginatus to the rio São Francisco basin and rivers of northeastern Brazil. Moenkhausia cf. gracilima can be distinguished by having a dark-brown humeral spot, lateral line completely pored, median caudal-fin rays hyaline, and the distal portion of upper caudal-fin lobe darker than the lower (vs. dark-brown humeral spot absent, lateral line incompletely pored, median caudal-fin rays darkbrown, continuous with longitudinal stripe, and caudal-fin lobes equally pigmented, in M. bonita, also identified as H. marginatus by Graça, Pavanelli, 2007). Marinho (2009) and Marinho, Langeani (2016) noted a species very similar to M. gracilima, from the Amazon basin, in the influence area of the Ilha Solteira Reservoir, speculating the possibility to be new. The specimens from the upper rio Paraná floodplain, captured there since 2009 by the Nupélia staff, match the description of the specimens from the Ilha Solteira Reservoir. However, as some characters of the specimens from the upper rio Paraná and the Amazon basin are overlapped, M. M. F. Marinho (in an e-mail, manoela.marinho@gmail.com, June 2017), suggested the identification as M. cf. gracilima.