Gastrodermus nanus

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Introduction

Gastrodermus nanus, also known as Corydoras nanus, is a small South American armored catfish from the family Callichthyidae. Native to Colombia, it is associated with calm, shallow areas of the upper río Meta basin, where it searches for food close to the bottom. Its small size, peaceful behavior, and group-oriented activity make it an interesting choice for a well-planned community aquarium. Like other armored catfish, it has sensitive barbels and benefits from a soft substrate without sharp edges. Keeping it with several conspecifics and providing stable water conditions makes its natural behavior easier to observe.

General species description

Gastrodermus nanus is a small armored catfish that spends most of its time near the bottom and is generally active in a group. It searches through the substrate with its barbels and may occasionally dart to the surface to take atmospheric air, an adaptation seen in several Callichthyidae. In an aquarium, it should be kept with conspecifics, since a group usually encourages more natural and confident behavior. Its temperament is peaceful, making it suitable for communities of small, non-aggressive fish. It is not a specialized algae eater, and its presence does not replace a complete feeding program. Substrate quality is important: fine sand or very smooth gravel protects the barbels and allows the fish to forage safely. The species is also fairly common in the aquarium trade, making it accessible to many hobbyists.

Geographic origin and biotope

Country of reference: Colombia. The species is associated with the upper río Meta basin, including the río Ariari, within the Orinoco drainage. Its natural habitat consists of warm freshwater environments with calm to moderately flowing sections and soft bottoms made of sand and fine sediment. Leaf litter, roots, and plant debris can provide shelter and concentrate some of the available food. Riparian vegetation shades the water and helps stabilize the banks, while submerged plants and leaf deposits structure the areas explored by the fish. In an aquarium, this setting can be suggested with moderate lighting, plants, roots, and open areas along the bottom. Clean, well-oxygenated, chemically stable water is preferable to a strongly turbulent layout.

Precise location and local name

Gastrodermus nanus is associated with the río Ariari, in the upper río Meta basin of Colombia. This places it in a tropical region of the Orinoco drainage, where streams are bordered by vegetation and experience seasonal changes in water level. In the aquarium trade, the name Corydoras nanus remains widely used, although the genus Gastrodermus is used in current classification. The name “dwarf cory” may also be encountered in English, but it is primarily an aquarium common name rather than a Colombian local name. Correct identification should rely on the combination of size, body structure, and coloration. A clearly stated Colombian origin is useful when distinguishing this species from other small catfish sold under similar commercial names.

Appearance and physical characteristics

The body of Gastrodermus nanus is short and compact, with two rows of bony lateral plates typical of Callichthyidae. The base color is usually silvery gray to brownish, with darker markings that help break up the outline of the fish against the substrate. The fins are translucent and may show yellowish or light brown tones depending on lighting, age, and condition. Its inferior mouth bears sensitive barbels that help locate food particles in the sand. The pectoral and dorsal fins have reinforced rays, so the fish should be handled carefully because these rays can catch in nets. Adult size remains small, reaching about 3.5 cm at most. Mature females are often broader and rounder than males, especially when carrying eggs.

General feeding

Gastrodermus nanus is an omnivorous, bottom-oriented fish. In nature, it feeds on small invertebrates, larvae, microorganisms, and organic debris found while searching through the bottom. In an aquarium, its diet should include quality sinking tablets, micro-pellets, and small frozen or live foods such as mosquito larvae, daphnia, and bloodworms offered in moderation. Food should reach the bottom so the fish can feed without excessive competition from surface-oriented tank mates. Small portions are preferable, sometimes offered after the lights go out, rather than relying on leftovers from other fish. A varied diet supports good body condition and breeding. It should not be treated as a simple cleaner fish: it needs a regular, complete ration containing suitable **protein** and essential nutrients.

Essential data

• River of origin: Río Ariari
• Local name used: Corydoras nanus
• Origin of the scientific name: Gastrodermus is a Greek-derived genus name; nanus is Latin for dwarf.
• Complete-name etymology: Gastrodermus refers to the idea of “belly skin”; nanus means “dwarf.”
• Common/vernacular names: Corydoras nanus; dwarf cory
• Family: Callichthyidae
• Subfamily: Corydoradinae
• Name pronunciation: gas-tro-DER-mus NAN-us
• Discovery: Isaäc J. H. Isbrücker and Han Nijssen, 1967
• Maximum adult size: About 3.5 cm
• Water temperature and pH: 22 to 26 °C; approximately pH 6.0 to 7.5
• Stream appearance and surrounding vegetation: Warm tropical freshwater, calm to moderately flowing sections, soft substrate, leaf litter, roots, and riparian vegetation
• Typical tank mates: Small peaceful characins, small danios, small rasboras, adult shrimp, and other calm bottom fish of similar size
• Temperament and behavior: Peaceful, social, active near the bottom, and generally more comfortable in a group
• Water depth: Shallow areas and calm margins of streams
• Sexual dimorphism: Females are usually larger and broader; males are slimmer
• Bottom structure and flow: Sand or fine sediment, plant debris, and low to moderate flow

In your aquarium

To keep Gastrodermus nanus successfully, use a mature aquarium, a group of several individuals, and a soft substrate. Stable, clean, well-oxygenated water is more important than strong current. Provide hiding places, plants, and open areas where the fish can forage. Regularly offered sinking foods prevent them from depending only on leftovers. Under these conditions, this small catfish displays natural, subtle behavior and remains an excellent choice for a peaceful community aquarium.