The pygmy corydoras or pygmy catfish (Corydoras pygmaeus) is a tropical and freshwater fish belonging to the subfamily Corydoradinae of the family Callichthyidae. It originates in tropical inland waters in South America, and is found in the Madeira River basin in Brazil. Taxonomy The first scientific description of the pygmy corydoras was published in 1966 by German biologist and physician Joachim Knaack, in Aquarien und Terrarien-Zeitschrift. One specimen was designated the holotype and one additional specimen was collected as a paratype. It was placed in the genus Corydoras. The scientific name uses the Latin word pygmaeus, meaning dwarf or pygmy, in its scientific name, Corydoras pygmaeus. The common names for the species are "pygmy catfish" and "pygmy corydoras". A species of Corydoras with a similar appearance, Corydoras hastatus was described in the 1880s, and many specimens that were described as Corydoras hastatus between the 1920s and 1950s were subsequently found to be misidentified specimens of the pygmy corydoras. In older literature, the pygmy corydoras is frequently mislabeled because Corydoras hastatus was the only miniature Corydoras species known at the time. Description The pygmy corydoras is a silver-colored fish, with an unbroken black line that runs horizontally along the center of the sides of the fish from the tip of its snout to its caudal peduncle. It has a second thin black line along the lower part of the side of the body, from behind the ventral fins and continuing into the tail. The top part of the body has a light black or dark gray shading that starts on the top of its snout and ends at the tail. Newly hatched fry have vertical stripes along the sides of their bodies that fade by the end of their first month, when the horizontal stripes of the adult fish begin to appear. The maximum length of the species is about , but typical adult sizes are for males and for females. In addition to their larger length, females are also rounder and broader than males, especially when they have eggs. Young fry grow rapidly after hatching, reaching in six to eight weeks. Distribution and habitat The pygmy corydoras is widely distributed in inland waters in Peru in tributaries of the Nanay River, in Ecuador in tributaries of the Aguarico River, and in western Brazil in tributaries of the Madeira River. The holotype was obtained from Calama, Brazil, along the Madeira River