Nannostomus rubrocaudatus

Nannostomus rubrocaudatus is a small schooling fish with a very beautiful red color. They do not grow large but do need a spacious aquarium!

Nannostomus rubrocaudatus

Nannostomus rubrocaudatus was officially described by Zarske in 2009. Before this time, this species was known under the old names: Nannostomus sp. ‘Red’; Nannostomus cf. marginatus “red pencil fish”; Nannostomus sp. “Coral red”.

The scientific name of this species can be broken down into two parts. Nannostomus: from Latin “nannus” = small + Greek, “stoma” = mouth. Rubrocaudatus: from Latin “rubra”, which means “red”, and “cauda”, which means tail.


Nannostomus rubrocaudatus is similar to and closely related to Nannostomus marginatus and Nannostomus mortenthaleri.

They differ from them in that adult males have a bright purplish-red color between the dark stripes on their sides. The middle dark stripe extends to the base of the anal fin. The dorsal fin is predominantly red in the males, in the females it is a smaller red spot.

Nannostomus marginatus is clearly distinguished from the other two in that it lacks the red color on the males’ bodies, but N. mortenthaleri and N. rubrocaudatus are less easily distinguished.

Males of N. rubrocaudatus differ from those of N. mortenthaleri in that the red pigmentation in the back half of the body is more purplish and uniform than in N. mortenthaleri where, outside spawning season, the red color is only seen between the primary and secondary stripe.

In the females of N. rubrocaudatus, the spacing between primary and secondary stripes is silvery with a reddish stripe below the primary black stripe at the back of the body.

Like the other Nannostomus species, they have a different color pattern during the night, with the colors fading considerably and the dark stripes disappearing.

They are definitely schooling fish. The maximum size is approximately 4 centimeters.

Sex difference

Adult males are noticeably less stocky and much more colorful than females.

Distribution / origin

According to reports, they have been captured in the Amazon River in Peru, several hundred kilometers west of Iquitos, at the foot of the Andes Mountains and upstream from where the Río Morona joins the Rio Marañón.


There is little data on the biotope in which they were found. Similar species as N. marginatus and N. mortenthaleri are found in slow-flowing rivers, streams and swampy areas, with many aquatic plants, submerged woody structures and leaf litter. However, these types of habitats are quite uncommon at higher elevations such as the stated area of origin.

Nannostomus rubrocaudatus Care

It is best to keep them in a well-planted aquarium, preferably with a dark bottom. Because of the planting they have enough hiding places and will be less skittish and therefore show their natural behavior more. The less dominant examples can also find hiding here.

Surface floating plants are appreciated by them, as are driftwood, branches and dried leaves. The latter also ensure the development of micro-colonies. Such microorganisms are a valuable additional food source for juvenile fish, while the tannins and other substances released from the leaves also serve to mimic natural conditions for the inhabitants. It is even better to place this fish in a special aquarium with dark and quite acidic water.

The filtration and the resulting flow should be kept on the moderate side. This species needs stable water conditions and should never be added to a not fully matured aquarium.

The minimum size of their tank is 50 liters, with a water temperature between 22 and 28 ° C, we keep the pH between 4.0 – 7.0, but certainly not higher. As indicated earlier, it is a schooling fish, so at least 5 must be kept together, but preferably 10 or more.


In the wild, they are predatory fish, which feed on small invertebrates and other zooplankton. In the aquarium they also accept dry food of a suitable size, but it is advisable to also offer small live or frozen food such as newly hatched brine shrimp and the like.

Behavior and tolerance

They are more aggressive to each other than most relatives and in spaces that are too small can lead to injuries or even death. Keeping them in a large school will spread this aggression across more specimens, while the fish will also show their natural behavior more. A spacious aquarium is recommended if you want to keep a group of both males and females, because males can be particularly aggressive towards each other.

This fish is peaceful compared to other species, but due to its small size and rather timid character it is not a suitable fish for most community aquariums. As mentioned before, one could keep them in a special aquarium or in the company of small, non-aggressive characins and small catfish.

Breeding Nannostomus rubrocaudatus

Breeding reports on the internet show that reproduction in aquariums has been successful, although not yet frequent. Using a special breeding tank significantly increases the chances of success.

In preparation, the adult animals are fed well, while at the same time one or more breeding tanks are set up with “old” water. These breeding tanks are decorated with a lot of Java moss or a “spawning mop” and possibly some fine-leaved plants, further it is equipped with a small sponge filter.

If the adults are well fed, you can place one or more pairs in a breeding tank. If you put more than 1 pair in it, arrange the plants or mops so that separate areas are created, eg place two groups of spawning media at both ends of the tank at a considerable distance. Too many fish cause many eggs to be eaten, 1 or 2 pair(s) actually works best.

After 2 or 3 days you can remove the parents. Another option is to replace the spawning mop daily and put it in an empty aquarium to let the eggs hatch there. The eggs hatch after 2 days.

In the first days you feed them very fine live food or very small dry food of sufficient quality. After that Artemia nauplii and the like can be given as soon as the young are big enough to eat them.

The (color) patterns of adult specimens become visible in the offspring after about 8 weeks.



Menno van Veen

Copyright images

Peter Maguire

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