''Cyanogaster noctivaga'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

characin Characiformes is an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-known piranha and tetras.; Buckup P.A.: "Relationsh ...

native to the Rio Negro,

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. 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 The Universidade de São Paulo (, USP) is a public research university in the Brazilian state of São Paulo, and the largest public university in Brazil. The university was founded on 25 January 1934, regrouping already existing schools in ...

, Brazil.

Description

When alive, ''Cyanogaster noctivaga'' is a transparent fish with a blue belly and reddish gill covers, but it quickly loses its bright colours after death. Its eyes are large, and the shape of its snout and its dentition differs from other characins, marking it out as a new genus. The longest specimen found was long. It differs from other members of the subfamily

Stevardiinae Stevardiidae is a large Family (biology), family of freshwater fish in the Order (biology), order Characiformes. It includes many genera previously placed in the family Characidae, which was split into multiple families in 2024. They are found th ...

in having 8 dorsal-fin rays and four teeth in the inner premaxillary tooth series and i+5 pelvic-fin rays and the presence of a single conical tooth in the outer premaxillary tooth series. There are hooks on the rays of the pelvic and anal fins in mature males.

Distribution and habitat

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 ''Paedocypris progenetica'' (also known as Indonesian Superdwarf Fish) is a species of tiny cyprinid fish endemic to the Indonesian islands of Sumatra and Bintan where it is found in peat swamps and slow flowing blackwater streams. It was disc ...

'', which occurs in peaty forest swamps and blackwater streams in Asia.

References

Diapomini Fish described in 2013 {{Improve categories, date=April 2025