About the Purple Dwarf Pencilfish
Species Type: Freshwater Fish
Care Level: Moderate. May tolerate only a narrow range of water parameters, have specific dietary requirements including frozen or even live foods, may have behaviors that severely limit potential tankmates or may require a specialized aquarium setup.
Origin: Peru: Rio Marano in Loreto Province. Inhabits quiet waters, remaining among branches.
Compatibility/Temperament: Peaceful with other fish. Typical of pencilfish, males can be rough with each other and can drive the females; there should always be a group, with at least as many females as males. The male's aggressiveness is why this fish, though small, requires no less than a 24-inch aquarium so that the females and subordinate males will not be harassed too much. An excellent dither fish for the South American dwarf cichlids, other peaceful small/medium sized characins, Corydoras, Aspidoras, peaceful catfish like Farlowella and Rineloricaria.
This beautiful little pencilfish is now the second of the "red" varieties related to Nannostomus marginatus (the Dwarf Pencilfish) to be described as a distinct species. It has been given the common name of Purple Dwarf Pencilfish due to the almost-magenta red body, although it may also be encountered under the original common name of Dwarf Pencilfish "Red II." Nannostomus mortenthaleri was "Red I."
The "Red" dwarfs are very similar in appearance, but can be readily distinguished by the extent of the red colouration which extends down onto the belly in the subject species, whereas the belly is white on N. mortenthaleri. The sexes in both species can be distinguished by the ventral fins which are coloured and longer in the male but clear on the female. The male fish is also the more colourful, although this can pale when the fish is under any stress, or simply at the fish's whim. The extent of the red colouration can vary from specimen to specimen, as may be observed in the accompanying photos above.
As noted under Origin, this fish remains among branches; collectors must consequently catch each fish individually, something that is reflected in the much higher cost for this species.
A suitable aquarium would be heavily planted, with plenty of bogwood, especially branches and twigs. Floating plants will provide shade to ease the fish (resulting in better colouration) and the leaves and dangling roots will continually be browsed by this fish for particles of food. A substrate of sand or fine gravel with leaf litter completes the hard aquascaping. Tannins from the wood and leaves may stain the water, thus further intensifying the fish's colour. Filtration should be very minimal, with very little water movement. All of this replicates the natural habit of this species.
This species does not possess an adipose fin. In common with all pencilfish, the mouth is always open, and the fish have a diurnal colour pattern. During darkness, the horizontal lines break up into a series of dashes. This has been observed in blind fish, showing that it is an automatic response and not controlled by the fish.
This species was described as a distinct species by Axel Zarske in 2009. The species epithet comes from the Latin rubro [=red] and caudatus [=tail], referring to the red on the caudal fin.
All pencilfish are found in the tribe Nannostomini in the subfamily Pyrrhulininae. Three different genera (Nannostomus, Nannobrycon and Poecilobrycon) were used at various times until Weitzman & Cobb (1975) placed all species in the single genus, Nannostomus, erected by Gunther in 1872 with N. beckfordi as the type species; Gery (1977) separated them into two genera, Nannostomus and Nannobrycon, largely on the basis of the swimming position. Weitzman & Weitzman in Reis et al. (2003) reassigned the species into the single genus Nannostomus which now includes all described pencilfish. The genus name Nannostomus comes from the Greek meaning "small mouth."
Gery, Jacques (1977) "Characoids of the World," TFH Books.
Reis, R.E., S.O. Kullander & C.J. Ferraris Jr. (2003), "Check list of the freshwater fishes of South and Central America."
Weitzman, Stanley H. (1966), "Review of South American Characid Fishes of Subtribe Nannostomina," Proceedings of the United States National Museum (Smithsonian Institution), Volume 119, Number 3538.
Weitzman, Stanley H. & J.S. Cobb (1975), "A revision of the South American fishes of the genus Nannostomus Gunther (family Lebiasinidae)," Smithsonian Contributions to Zoology No. 186.
Zarske, Axel (2009), "Nannostomus rubrocaudatus, sp.n.--ein neuer Ziersalmler aus Peru (Teleostei: Characiformes: Lebiasinidae)," Vertebrate Zoology 59(1), pp. 11-23.
Purple Dwarf Pencilfish Diet
In the wild it feeds on insects, insect larvae, and zooplankton. In the aquarium it accepts prepared foods, but relishes frozen or live artemia (brine shrimp) and small worms.
Male and female attain 3 cm (1.2 inches).
Minimum Tank Suggestion
24 inches, 15 or 20 gallons
Ideal water parameters for Purple Dwarf Pencilfish
Very soft (hardness < 5 dGH), slightly acidic to acidic (pH 5-6.5), temperature 22-27C/71-80F. All fish will be wild-caught, and these parameters are mandatory.