Gastrodermus

The elegant cory, Gastrodermus elegans, long known as Corydoras elegans, is an armoured catfish from the western Amazon basin in Peru, Ecuador and Brazil. Unlike most congeners it spends a fair amount of time away from the substrate, often forming groups in midwater. It gives its name to the unofficial 'C. elegans group' of similar species, which includes C. nanus and C. undulatus plus many C- and CW-numbered fishes of uncertain status.

Gastrodermus gracilis, long known as Corydoras gracilis, is a small armoured catfish from the central Amazon basin in Brazil, known from the rio Juriti in Pará to the rio Juma in Amazonas. Sometimes called 'shy cory' in the hobby, it has a lightish body with a dark arched stripe along the upper flank, a pattern shared with C. arcuatus, C. narcissus and C. urucu. Only in C. gracilis does the stripe end at the base of the upper caudal-fin rays. It apparently favours minor tributaries with dense riparian vegetation and acidic, tannin-stained water.

The Guaporé cory, Gastrodermus guapore, long known as Corydoras guapore, is an armoured catfish endemic to the rio Guaporé (Río Iténez) in northeastern Bolivia and western Brazil. Unlike most congeners it forms aggregations in midwater and spends much of its time away from the substrate, with a large eye, a more terminal mouth and a strongly forked caudal fin to match. It partly feeds on pelagic zooplankton, so live Daphnia and Artemia belong in its diet. Similar species such as C. similis lack these adaptations.

The tail-spot pygmy cory, Gastrodermus hastatus, long known as Corydoras hastatus, is a tiny armoured catfish with a wide range across the Amazon and Río Paraguay basins. It is known from Brazil, Bolivia, Paraguay and northeastern Argentina. Unlike most congeners it swims in midwater, forming mixed schools with similarly patterned small characids such as Serrapinnus kriegi. It is frequently confused with C. pygmaeus, but has a dark, roughly diamond-shaped spot on the caudal peduncle where C. pygmaeus has a dark lateral stripe.

The Napo cory, Gastrodermus napoensis, long known as Corydoras napoensis, is an armoured catfish from the upper Amazon in Peru and Colombia, including the Rio Napo and Rio Nanay. It belongs to the 'elegans group' of similar species with C. elegans, C. bilineatus and C. nanus. Males show a dark marking in the upper dorsal fin, but females are much harder to identify, especially as C. napoensis and C. elegans occur together and are often sold in mixed shipments.

Nijssen's cory, Gastrodermus nijsseni, long known as Corydoras nijsseni, is an armoured catfish endemic to the Rio Negro basin in Brazil, living in acidic blackwater rivers and creeks. It was first described as a subspecies of C. elegans, and its rounded snout recalls that species, though its colour pattern is closer to C. adolfoi. It suits a Rio Negro biotope or other softwater community.

The pygmy cory, Gastrodermus pygmaeus, long known as Corydoras pygmaeus, is one of a handful of tiny Corydoras species and appears to be endemic to the Rio Madeira basin, Brazil. Unlike most of its congeners it swims in midwater. It is most often confused with C. hastatus, which has a dark diamond-shaped spot at the caudal peduncle, where C. pygmaeus has a dark stripe along the entire lateral line. Easily intimidated by larger tankmates, it is best kept in a group of at least six with other tiny species.