Nannostomus marginatus

These fish are indeed miniature — adult specimens reach a length of only 2.5 cm. Sexual dimorphism is weakly expressed, and it is difficult to notice clear differences between males and females. The coloration of the Dwarf Pencilfish is gray, with characteristic horizontal black and white stripes. Their fins often have reddish hues.

The natural habitat of these fish spans South America, including Guyana, Suriname, as well as the lower and middle Amazon River basins in Peru, Colombia, and Brazil. They can be found in small rivers, slow-moving streams, and swamps, as well as in flooded forests and floodplain lakes. Nannostomus prefer areas with dense aquatic vegetation, numerous snags, and fallen leaves.

Nannostomus are peaceful and even somewhat timid fish that prefer to live in schools. Therefore, it is advisable to keep a group of at least 10 individuals. No intraspecific conflicts are observed among them. They get along well with other non-aggressive species of comparable size. They can also coexist with larger bottom-dwelling fish, as they spend most of their time in the upper and middle water layers.

Thanks to their size, Dwarf Pencilfish thrive even in nano-aquariums of 10–20 liters. When setting up such an aquarium, it is recommended to use a dark substrate, place several snags, and provide abundant plants, including floating ones. The latter, as is known, create additional shading. It is important to maintain subdued lighting and stable water parameters. Regular cleaning of the substrate from organic waste and weekly water changes of 10–15% with fresh water are essential procedures. When choosing a filtration system, preference should be given to models that create a weak current, such as sponge air-lift filters. Adding Indian almond leaves or their extract is notably beneficial: they impart a characteristic tea-like tint to the water and enrich it with tannins, recreating natural habitat conditions.

Dwarf Pencilfish readily accept all types of appropriately sized foods. Their diet can consist entirely of dry foods, such as flakes or granules. However, if there is an opportunity and desire to diversify their menu, small crustaceans, such as daphnia and brine shrimp, can be offered.

Under favorable conditions, the Dwarf Pencilfish can breed in a home aquarium. Often, some fry survive even without the aquarist's deliberate intervention. However, to increase the chances of success, the breeding process should be controlled. Dense thickets of low-growing plants, such as Java moss, can be placed at the bottom of the aquarium, or artificial spawning substrates can be used, among which the fish will lay their eggs. Since parental instincts in Nannostomus are weakly developed, the eggs will likely be eaten if not transferred to a separate tank with identical water conditions. It is recommended to place Indian almond leaves from the main aquarium into this tank (if they were present). During decomposition, colonies of microorganisms, such as paramecia, form on the leaves, which will serve as excellent first food for newly hatched fry. Alternatively, specialized foods with particle sizes from 5 to 50 microns can be used, gradually transitioning the growing fish to brine shrimp nauplii.

Health problems in these fish arise only in the presence of injuries or keeping in unsuitable conditions, which leads to a weakening of the immune system and the subsequent occurrence of various diseases. At the first signs of illness, it is necessary first to check the water parameters for exceeding permissible values or the presence of toxic substances (such as nitrites, nitrates, ammonia). If deviations are found, all indicators should be normalized, and then treatment should begin.

When purchasing, choose active individuals that stay in a school and show no visible damage to fins or scales. Avoid fish with signs of emaciation, sunken bellies, or unnatural behavior, such as constantly staying at the surface or alone at the bottom. The coloration of a healthy fish should be clear, without a cloudy film. Since Nannostomus are sensitive to sudden changes in water parameters, inquire about their keeping conditions at the store before purchasing. After purchase, a quarantine in a separate tank for 1–2 weeks is mandatory to prevent the transfer of infections to the main aquarium. During transport and acclimatization, use the method of gradual equalization of temperature and water parameters to minimize stress for the fish.