Nannostomus marginatus – Dwarf Pencilfish
Nannostomus marginatus is an active and visually appealing fish that reaches a maximum length of 4.5 centimeters. In terms of both behavior and coloration, it is an attractive species for aquarists. In its natural habitat, there are several distinct color forms. One variation is known as the Peru Gold, which lacks red on its sides and features more yellow between the black stripes. Another variant is the Rio Negro, characterized by a red stripe that runs from the middle of the body to the tail. The Guyana/Suriname variant has a short red stripe, while an other variant displays a red dot at the tail.
Nannostomus marginatus was described in 1909 by Carl H. Eigenmann.
Distribution and habitat
Nannostomus marginatus is a widely distributed species found in major rivers such as the Amazon, Rio Orinoco, and Rio Negro, as well as many smaller tributaries of these rivers. Its habitat extends through Brazil, Peru, Guyana, Colombia, Suriname, and Venezuela. This species thrives in both blackwater and clearwater environments, including rivers, streams, and floodplains. The diverse biotopes in these waters range from blackwater areas filled with wood and leaves to regions abundant with aquatic and marsh plants.
Behavior and compatibility
Nannostomus marginatus should ideally be kept in groups of at least five fish. A minimum surface area of 250 cm² per fish is recommended, as males tend to spar with each other and defend small territories. However, there is generally no real aggression, and other species will be left undisturbed.
Nannostomus marginatus pairs well with tropical species that do not grow too large. They are often used alongside Apistogramma breeding pairs because they can thrive in small groups and have small mouths, which means they won’t quickly eat the young. It is advisable not to keep Nannostomus marginatus with larger carnivorous fish or true subtropical species.
The Aquarium
For a group of 5 to 7 Nannostomus marginatus, a 60 x 30 cm aquarium is sufficient. If you plan to keep more fish, you will need a larger tank. The decoration can vary widely, from densely planted tanks to those featuring wood, stones, and leaves without any plants. In terms of water parameters, a pH level of 5.5 to 7.0 is acceptable, with general hardness (GH) and carbonate hardness (KH) ranging from 0 to 10. The ideal temperature for this species is between 21 and 25 degrees Celsius.
Diet
In the wild Nannostomus marginatus feed on very small animals and zooplankton. In the aquarium, they are not picky eaters; they feed on live food and small dry food.
Sexing and breeding
The difference between males and females is clearly visible in adult fish because the females are much fuller than the males. In a fully planted aquarium with not too many larger species, a young one will sometimes grow up. But if you really want to keep many young ones, it is still important to start breeding with a specially designed breeding tank.
To perform targeted breeding, set up a tank with plenty of Java moss or a spawning mop, along with a small sponge filter. Place one or two well-fed breeding pairs in the tank. Avoid overcrowding, as too many fish can result in the eggs being eaten; thus, one or two pairs work best. After two or three days, you can remove the adult fish. Alternatively, you can replace the spawning mop daily and transfer it to an empty tank to allow the eggs to hatch.
In the first few days after hatching, feed the fry with very fine live food, such as infusoria. As they grow, you can begin to introduce artemia nauplii into their diet.
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Author
jos Rollman
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