Simpsonichthys nigromaculatus Costa 2007

Differs from all other species of the genus by possessing 2-4 black spots on posterobasal portion of dorsal fin in males. In addition, it can be separated from all congeners by the unique combination of the following characters: absence of pelvic fin and pelvic girdle; vertebrae 24-25; absence of second pharyngobranchial teeth; absence of ventral process of posttemporal; anal fin with 17-20 rays in females; body depth 33.5-36.0% SL in males; maximum adult size 25.6 mm SL; bright blue bars on flank in males much narrower than interspace; side of head in males with five alternating bright blue and pink to red bars; short postorbital pink strike connecting pink bars 2 and 3; anterior and posterior margins of iris bright blue; dark gray band bordered by a bright blue line on distal margin of dorsal and anal fins, and posterior margin of caudal fin in males; ground color of dorsal and anal fins orange in males; absence of bars on unpaired fins in males; and presence of yellow dots on the caudal fin in males (Ref. 75131).Description: longitudinal series of scales 24-26; transverse series of scales 9 (Ref. 75131).

Dorsal soft rays (total): 15 - 19; Analsoft rays: 17 - 22; Vertebrae: 24 - 25

Inhabits temporary shallow canals (about 50 cm deep) in the floodplains, with light yellow water (Ref. 75131).

Simpsonichthys nigromaculatus is a species of killifish from the family Rivulidae. It is found in the seasonal canals of the floodplains of the rio da Pratain in the rio Aporé drainage in the upper rio Paraná basin in Brazil. in South America. This species reaches a length of 2.6 cm (1.0 in).