We describe a new species of apteronotid electric fish, Adontosternarchus nebulosus, from the Brazilian and Peruvian Amazon. Adontosternarchus nebulosus differs trenchantly from its congeners in its boldly contrasting color pattern of irregular, dark blotches on the back and sides followed posteriorly by a long pallid area extending far onto the caudal peduncle; relatively few anal-fin rays (112–154, mean 133.2); relatively few vertebrae counted to base of last anal-fin ray (52–57, mean 54.5); and a relatively deep body, 21–33% of distance to origin of dorsal filament. Adontosternarchus nebulosus is common in the Amazon main and tributary river channels.

Key Words: Species novum: Adontosternarchus nebulosus Lundberg and Cox Fernandes