Rivulus rossoi, Costa, 2005

Costa, Wilson J. E. M., 2005, Seven new species of the killifish genus Rivulus (Cyprinodontiformes: Rivulidae) from the Paraná, Paraguay and upper Araguaia river basins, central Brazil, Neotropical Ichthyology 3 (1), pp. 69-82 : 74-75

Rivulus rossoi , new species

Fig. 5

Holotype. UFRJ 5976, male, 18.9 mm SL; Brazil: Estado de Mato Grosso do Sul: Município de Campo Grande: stream at the road BR-060, 21.5 km SW from Campo Grande, rio Inhanduí drainage, rio Paraná basin, about 20 o 40’S 54 o 40’W, altitude about 500 m; A. Rosso, 30 Mar 2004.

Paratypes. UFRJ 5977, 6 males, 17.2-21.5 mm SL, 1 female, 16.9 mm SL; UFRJ 5978 , 2 males, 16.5-18.8 mm SL, 2 females, 16.5- 17.2 mm SL (c&s); collected with the holotype. UFRJ 5923, 1 female, 19.7 mm SL ; MCP 36122; 2 males, 17.8-18.1 mm SL; same locality and collector, 7 Mar 2004 .

Diagnosis. Distinguished from all other species of the R. punctatus group by having 1 + 6 Gill rakers on the first branchial arch (vs. 1 + 7-8) and a unique color pattern of caudal fin in males, in which the fin is hyaline, the anterior half with red dots and narrow light orange stripe on the dorsal and ventral margins (vs. never a similar color pattern). Differs from all congeners from the rio Paraná basin by having oblique rows of red dots (vs. oblique red bars or horizontal rows of red dots) on the flank, dark gray stripe along midline of flank (vs. no distinctive dark stripe), 28-29 caudal-fin rays (vs. 30-34).

Description. Morphometric data in Table 3. Largest specimen 19.7 mm SL, male. Dorsal profile weakly convex from snout to end of dorsal-fin base, approximately straight to gently concave on caudal peduncle. Ventral profile convex on head, slightly convex from anterior portion of venter to end of analfin base, nearly straight to slightly concave along caudal peduncle. Body slender, subcylindrical anteriorly, slightly deeper than wide, to compressed posteriorly. Greatest body depth at level of pelvic-fin base.

Dorsal fin rounded to slightly pointed in male, rounded in female. Anal fin pointed in male, rounded to slightly pointed in female. Caudal fin rounded. Pectoral fin rounded, posterior margin on vertical through pelvic-fin base in male, just anterior to it in female. Tip of pelvic fin reaching between urogenital papilla and anal-fin origin in male, and between anus and urogenital opening in female. Pelvic-fin bases in close proximity. Dorsal-fin origin on vertical through base of 10th or 11th anal-fin ray, and between neural spines of 19th and 21st vertebrae. Anal-fin origin between pleural ribs of 13th and 14th vertebrae. Dorsal-fin rays 8-9; anal-fin rays 13-14; caudal-fin rays 28-29; pectoral-fin rays 13; pelvic-fin rays 7.

Scales large, cycloid. Trunk scaled; head scaled except on its anteroventral surface. Body scales slightly extending over caudal-fin base; no scales on dorsal and anal fins. Frontal squamation F-patterned; E-scales not overlapping medially; scales arranged in circular pattern around central A-scale without exposed margins. Longitudinal series of scales 31-32; transverse series of scales 8; scale rows around caudal peduncle 16. Contact organs absent. Supraorbital neuromasts 3 + 3. Six branchiostegal rays. Gill rakers of first branchial arch 1 + 6. One vomerine teeth. Total vertebrae 30.

Coloration. Male: Side of body light purplish brown with oblique chevron-like rows of red dots, with vertex anteriorly directed; laterodorsal gray spots on anterior portion of body; dark gray stripe between eye and caudal-fin base, darker on anterior portion and when exposed to light. Dorsum light brown, venter white. Postorbital region silver. Infraorbital region and ventral surface of head white. Lower jaw dark gray to black. Iris light yellow. Dorsal fin hyaline with red dots. Anal fin light yellow, base bright blue with red dots. Caudal fin hyaline with red dots on anterior half, dots larger on dorsal and ventral portions; narrow light orange stripe on anterior portion of dorsal and ventral edges. Pelvic fin pale yellow. Pectoral fin hyaline.

Female: Side of body light brown with oblique rows of dark reddish brown small spots; laterodorsal gray spots on anterior portion of body; dark gray to black stripe between eye and caudal-fin base, darker when exposed to light. Dorsum light brown, venter white. Postorbital region gray. Infraorbital region and ventral surface of head white. Lower jaw dark gray to black. Iris light yellow. Dorsal fin hyaline with pale red dots; dark gray distal stripe. Anal fin light yellow, base blue with pale red dots, and dark gray distal stripe. Caudal fin hyaline with dark gray small spots; dark gray zone along fin margin; round black spot on dorsobasal portion, not contacting fin margin. Paired fins hyaline; anterior margin of pelvic fin dark gray.

Distribution. Known only from the type locality, upper rio Inhanduí drainage, rio Paraná basin, central Brazil ( Fig. 2 ).

Etymology. The name rossoi after Aldovan Rosso, the first collector of the new species.

Figures

Fig. 5. Rivulus rossoi, UFRJ 5976, male, holotype, 18.9 mm SL (five days after collection); Brazil:Mato Grossodo Sul: Campo Grande. Photo by W. J. E. M. Costa.

Fig. 2. Geographic distribution of species of the genus Rivulus in the Paraná, Paraguay, and upper Araguaia river basins, central Brazil.