Simpsonichthys nielseni Costa 2005

Distinguished from congeners by having a unique color pattern of the caudal fin in males, which includes six or seven light blue stripes diverging from the fin base, terminating in sharp tips on the fin margins. Shares with Simpsonichthys stellatus an apomorphic color pattern consisting of elongated light spots alternating with black zones on the dorsal-fin base in males (Ref. 56725).

Simpsonichthys nielseni is a species of killifish from the family Rivulidae. It is found in the São Francisco River basin in Brazil in South America.