Cyanogaster noctivaga is a species of characin native to the Rio Negro, Brazil. This species is the only known member of its genus and its scientific name translates as the blue-bellied night wanderer, referring to its unique appearance and nocturnal habits. It was first described in 2013, having been discovered in October 2011 on a scientific expedition organised by the University of São Paulo, Brazil.
This fish is only known from a single location in the Rio Negro, but as it is a very small fish and seems to be entirely nocturnal, it is easily overlooked. It was found in an acidic backwater, a similar habitat to that of the smallest known species of fish, Paedocypris progenetica, which occurs in peaty forest swamps and blackwater streams in Asia.