Simpsonichthys chacoensis,

Wilson J. E. M. Costa, 2007, Taxonomic revision of the seasonal South American killifish genus Simpsonichthys (Teleostei: Cyprinodontiformes: Aplocheiloidei: Rivulidae)., Zootaxa 1669, pp. 1-134: 48-49

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Simpsonichthys chacoensis


Simpsonichthys chacoensis  (Amato, 1986)

(Fig. 30)

Cynolebias chacoensis  ZBK  Amato, 1986: 10 ( type locality: road Mariscal Estigarriba-[ Capitan Pablo] Lagerenza, 624 km NW from Asuncion , 14 km from Comando de Transmisiones Tenente Segundo Americo Picco, Charca Topografo Acevedo, Nueva Asuncion , Paraguay [about 21°00’S 60°00’W]; holotype: MUNHINA 2577GoogleMaps  ).

Material examined

Paraguay, río Paraguay basin: UFRJ 3030, 2 ex.; UFRJ 3170, 1 ex. (c&s); 92 km N of Mariscal Estigarriba, San Juan ; L. Van den Berg, Mar. 1994.  USNM 232295, 1; flooded Chaco, 15 km NE of Ochoa ; M. Ludlow & J. Stallings, 16 Jan. 1981. 


Distinguished from all other species of the subgenus Spectrolebias  by possessing more anal-fin rays in males (26-28, vs. 21-26), and flanks and unpaired fins dark bluish gray in males (vs. never this color in males of other species).


Morphometric data appear in Table 3. Largest specimen examined 35.3 mm SL. Dorsal profile slightly concave on head, convex from nape to end of dorsal-fin base, nearly straight on caudal peduncle. Ventral profile convex from lower jaw to end of anal-fin base, approximately straight on caudal peduncle. Body moderately deep, compressed, greatest body depth at level of pelvic-fin base. Eye positioned on dorsal portion of head side. Snout blunt. Urogenital papilla cylindrical and long in males, pocket-shaped in females.

Tip of dorsal fin pointed in both sexes; tip of anal fin pointed in males, rounded in females; long filamentous rays on tip of anal fin in males, tip reaching vertical posterior to distal edge of caudal fin. Dorsal-fin rays unbranched. Caudal fin rounded. Pectoral fins elliptical. Posterior margin of each pectoral fin reaching vertical through base of 8th anal-fin ray in males, and vertical just anterior to anus in females. Tip of each pelvic fin reaching base of 3rd anal-fin ray in males, and base of 2nd anal-fin ray in females. Pelvic-fin bases in close proximity. Dorsal-fin origin on vertical through base of 5th anal-fin ray in males, and 3rd anal-fin ray in females, between neural spines of vertebrae 8 and 9 in males and vertebrae 10 and 12 in females. Anal-fin origin between pleural ribs of vertebrae 10 and 11. Dorsal-fin rays 23-26 in males, 17-20 in females; anal-fin rays 26-28 in males, 22-24 in females; caudal-fin rays 28; pectoral-fin rays 12; pelvic-fin rays 6-7.

Frontal squamation E-patterned; E-scales overlapping medially; no scale anterior to G-scale; sometimes one supraorbital scale, but this usually absent. Longitudinal series of scales 27-29; transverse series of scales 10; scale rows around caudal peduncle 16. Contact organs absent.

Cephalic neuromasts: supraorbital 11-12, parietal 3, anterior rostral 1, posterior rostral 1, infraorbital 2 + 22-26, preorbital 3, otic 2, post-otic 3, supratemporal 1, median opercular 1, ventral opercular 2, preopercular 18-19, mandibular 11-15, lateral mandibular 2-3, paramandibular 1. One neuromast on center of each scale of lateral line. Two neuromasts on caudal-fin base.

Basihyal subtriangular, width about 60% of length; basihyal cartilage about 20% of total length of basihyal. Six branchiostegal rays. Second pharyngobranchial teeth 3. Gill-rakers on first branchial arch 3 + 11. Vomerine teeth absent. Dermosphenotic absent. Ventral process of posttemporal long. Total vertebrae 29.


Males. Sides of body bluish dark brown, almost black, with white dots. Head dark gray, opercular region dark greenish blue. Iris brownish yellow, with black bar through center of eye. Dorsal and anal fins black with white dots on basal region and subdistal blue stripe. Caudal fin dark gray to black, with light blue shine on posterior portion. Pectoral fins hyaline. Pelvic fins dark blue.

Females. Sides of body light brown, with dark gray marks irregularly arranged, sometimes forming about 10 ill-defined bars; one to three dark greenish gray spots on anterocentral portion of flank. Head pale brown, opercular region greenish blue. Iris yellow, with dark gray bar through center of eye. Fins hyaline, with dark gray spots on posterobasal portion of dorsal and anal fins.


Río Paraguay basin, northern Paraguay and northern Bolivia (Fig. 4).


Temporary pools in the Chaco.