Nannostomus marginatus – Dwarf Pencilfish
Nannostomus marginatus has been first described in 1909 by Carl H. Eigenmann . Its common name is Dwarf Pencilfish as they only reach a total length of around 4,5 centimeters.
Nannostomus marginatus is a nice and active little fish. Their behaviour and colour make them a nice species to keep. In the wild you can find a couple of different colour morphs. One of them is the Peru Gold, they lack the red coloration on their sides but have a more yellow colour between the black stripes. The Rio Negro variety has a red stripe running from half way their body to their tail. The Guyana/Surinam variety has a short red stripe and another one only has a red dot near their caudal fin.
Distribution and Habitat
Dwarf Pencilfishes have a very wide distribution range. they inhabit the the Amazon, Rio Orinoco and Rio Negro and the many tribituaries that run through Brazil, Peru, Guyana, Colombia Surinam and Venezuala. The water can be clear water, black water, streams and floodlands with a wide range of biotopes ranging from blackwater with wood and leaves to biotopes filled with water- or swamp plants.
Behaviour and Compatibility
Nannostomus marginatus is a schoaling fish and it feels more comfortable in a group of at least 5 specimen but preferably more. Males create a small territory and fight other males to keep them out. Provide them with at least 250 cm2 each to give them the minimum territory they need. Their battles are more show than actual battle, they are not really aggressive. Other species are left alone entirely.
Species that can be housed together with the Dwarf Pencilfish are other tropical species that do not grow too big. They are also used as a dither fish for breeding Apistogramma species. This because they can easily be kept in small groups and have a very small mouth so they won’t eat the Apistogramma fry. It is better not to combine them with the larger carnivores or true subtropical species.
To keep a small group of 5 to 7 Nannostomus marginatus you will need a small aquarium of just 60 x 30 centimeters. If you want to keep a larger group you will need a bigger aquarium. Decoration can vary from densely planted to an aquarium with just some wood, rocks and leaves without any plant at all. Water parameters can vary as well with a pH of 5,5 to 7.0 an GH and KH from 0 – 10. Temperature should be between 21 and 25 degrees Celsius.
In the wild the Dwarf Pencilfish feeds on very tiny invertabrates and zoöplankton. In the aquarium it isn’t a fussy eater, you can feed them with all sorts of live and frozen foods as well as flakes.
Sexual Dimorphism and Breeding Nannostomus marginatus
The difference between males and females is best seen in adult fish. The females are rounder bodied than males who are more slender. In a fully planted aquarium occasionally one of the fry wil make it to adulthood. If you want to breed and raise more of them it is better to setup a special breeding tank.
Set up a Dwarf Pencilfish with lots of Java Moss or a spawning mop, a small spongefilter, aged water and one or more well fed pairs of fish. Too many fish brings the risk they will eat the eggs so one or two pairs works best. After 2 or 3 days you will have to remove the fish or remove the spawning mop daily. You can put the spawning mop in an empty tank with aged water to hatch the eggs.
The first days after hatching the fry will have to be fed with very tiny food particles like infusoria, when they get a little bigger you can feed them with newly hatched brine shrimp.