Max Size: 4cm

Purple Pencilfish (Nannostomus rubrocaudatus)

The Purple Pencilfish is relatively peaceful and can be somewhat shy. Nevertheless, these Pencilfish make a stunning addition to a planted aquarium or a blackwater biotope aquarium. Like most Pencilfish, they will do best in a group of 10 or more individuals. However, it would be better to have more females than males as they can be rough with each other, frequently sparring during the day and pressuring the females. Due to their boisterous nature, they will require a sizeable spacious aquarium, especially if you plan on keeping them with other species.

Ideally, you should maintain these fish alone or at most with small, non-aggressive tankmates such as other peaceful medium-sized Characins, Corydoras, Aspidoras, and smaller plecos. Purple Pencilfish also make an excellent dither fish Apistogrammas and other South American Dwarf Cichlids.

It would be best to keep Purple Pencilfish in a heavily-planted set-up with a dark substrate making sure you have plenty of hiding places. The hiding places will form a refuge for skittish or subdominant individuals and provide plenty of broken lines of sight. Floating plants are a useful addition, so is dried leaf litter and driftwood branches. These Pencilfish will also appreciate gentle water movement; an air-powered sponge filter will be just fine. In addition, these Pencilfish require stable water conditions so should never be introduced to an immature aquarium.

Purple Pencilfish have a bright reddish-purple colour between the dark stripes on their sides. The middle dark stripe extends to the base of the anal fin, and the dorsal and caudal fin is mainly red in males. Females have a smaller red spot, silvery stripes between the primary and secondary stripes, and a reddish stripe beneath the direct black stripe at the rear.


Purple Pencilfish
Purple Pencilfish
Quick Facts
Scientific NameNannostomus rubrocaudatus
Other NamesPurple Dwarf Pencilfish, Double Red Pencilfish
Aquarium LevelMiddle - Top
DifficultyBeginner - Intermediate
Best kept asGroups 10+
Lifespan3 - 5 years
Water Parameters
Water TypeFreshwater
PH4.0 - 7.0
GH2 - 12
TDS18 - 90
75 - 82℉
23.9 - 27.8℃


In the home aquarium, the Purple Pencilfish will readily accept most good quality dried foods such as granules, flakes and sinking pellets. These modern food products have been developed to provide all adequate nutrition to maintain your fish's health and dietary requirements.

Providing additional foodstuffs such as live, frozen, and freeze-dried meals such as bloodworm, daphnia, and tubifex once or twice a week will provide additional benefits to your fish's health and well-being but is not a must for this fish.

It should be noted that bloodworms should only be given as an occasional treat and should not be used as the staple diet as they are difficult for fish to digest and can potentially cause blockages.

This fish is an omnivore in the wild, meaning it will consume some vegetable matter. Although most modern fish foods take this into account and include them in their products, you can still supplement your fish's diet with blanched vegetables such as spinach, broccoli, and zucchini. Ensure you do not overfeed your fish and remove any leftovers the following day.

Tank Mates

4 interesting tank mate ideas for the Purple Pencilfish could include:

Cherry Barb(Puntius titteya)
Coral Red Pencilfish(Nannostomus mortenthaleri)
Ivantsoffs Blue Eye Rainbowfish(Pseudomugil ivantsoffi)
Peacock Gudgeon(Tateurndina Ocellicauda)

Sexual Dimorphism

Males are easily differentiated from females because males are slimmer and intense, while females have a modified anal fin.

Other Pencilfish of interest

Barred Pencilfish(Nannostomus espei)
Cenepa Red Pencilfish(Nannstomus sp)
Coral Red Pencilfish(Nannostomus mortenthaleri)
Dwarf Pencilfish(Nannostomus marginatus)
Golden Pencilfish(Nannostomus beckfordi)
Hockeystick Pencilfish(Nannostomus eques)
View all Pencilfish
Date Added: 08/02/2022 12:48:51 - Updated: 20/09/2022 15:26:55