In 2002, a deep red dwarf pencil fish from Peru was imported under the names Nannostomus marginatus “Purple” or N. marginatus “Red.” Axel Zarske from the Senckenberg Natural History Collections Dresden, Museum of Zoology formally described this species in 2009 as Nannostomus rubrocaudatus. We had imported the type specimens on which the scientific description is based from Peru.
At first glance, the new species resembles the already known N. mortenthaleri (see https://www.aquariumglaser.de/en/fisharchive/nannostomus-mortenthaleri-2/), but can still be easily distinguished from this species. N. mortenthaleri, for example, always has a white belly. Further species characteristics are listed in the scientific description. The scientific first description is available as a free download at https://www.senckenberg.de/wp-content/uploads/2019/08/02_vertebrate_zoology_59-1_zarske.pdf.
Nannostomus rubrocaudatus does not exhibit very distinct sexual differences. The intensity of the red coloration varies greatly depending on mood. However, females never turn as red as males. What is particularly tricky is that males low in the hierarchy can fade significantly and camouflage themselves as females in terms of color; females can only be reliably identified by their differently shaped anal fins.
The maximum size of this species is around 3-3.5 cm. It is easy to care for, but should not be kept in small aquariums, as the males fight their rivals quite fiercely and the weaker specimen needs space to escape. If this is not available, damage may occur.
The natural range is in Peru, Dep. Loreto. Here, the species is collected for export near the village of Saramirisa on the Maranon (the upper Amazon) between the tributaries Rio Morona and Rio Santiago. The relatively high price of the fish is explained by the fact that the animals live among dense branches in the wild and have to be laboriously picked out individually. Mass catches, as with other Nannostomus species, where thousands of specimens can easily be caught with a net, are not possible with N. rubrocaudatus.
For our customers: Nannostomus rubrocaudatus has – depending on size – code 272261 (sm) to 272265 (lg-xlg) for wild-caught specimens and 272272 for captive-bred specimens on our stock list. Please note that we only supply wholesale customers.
Text & photos: Frank Schäfer
