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Nematobrycon palmeri EIGENMANN, 1911

Emperor Tetra


Order: Characiformes Family: Characidae


Endemic to the San Juan and Atrato river basins in Colombia with type locality ‘Condoto, Río Condoto and Novita, Río Tamana, southwestern Colombia’. Wild examples are not as common as they once were in the aquarium hobby, however, with the majority of those in the trade produced on a commercial basis.


Ubiquitous throughout its range in slower-moving sections of rivers, minor tributaries and backwaters.

Sympatric fishes across its range include Priapichthys nigroventralisP. chocoensis, ‘Cichlasoma atromaculatumAndinoacara latifronsA. biseriatus, ‘GeophaguspellegriniLebiasina chocoensis, plus various other characids, gymnotids and loricariids.

Maximum Standard Length

35 – 42 mm.

Aquarium SizeTop ↑

An aquarium with base dimenions of 90 ∗ 30 cm or equivalent should be the smallest considered.

Water Conditions

Temperature23 – 27 °C

pH5.0 – 7.5

Hardness18 – 215 ppm


Likely to be a micropredator feeding on small insects, worms, crustaceans and other zooplankton in nature. In the aquarium it will accept dried foods of a suitable size but should not be fed these exclusively. Daily meals of small live and frozen fare such as DaphniaArtemia and suchlike will result in the best colouration and encourage the fish to come into breeding condition.

Behaviour and CompatibilityTop ↑

One of the best tetras for the ‘general’ community setup. It is lively, peaceful and its colours offer a pleasing contrast to those of many other species. It’s a good tankmate for most commonly available livebearers, danionins, rasboras, other tetras and peaceful bottom dwellers such as Corydoras or smaller Loricariids. It can also be kept with the majority of commonly available gouramis and dwarf cichlids. Obviously it isn’t safe with larger species that may see it as food. In a South American-themed tank as described above, it can be combined with other peaceful tetras, pencil fish, Apistogramma and other dwarf cichlids.

Always buy a group of at least half a dozen of these, preferably 10 or more. It’s a shoaling species by nature, and will fare much better when in the company of its own kind. It actually looks far more effective when maintained like this anyway. Rival males are territorial with one another to an extent, but no serious damage is done during their battles provided the tank is sufficiently large and well-decorated.

Sexual Dimorphism

Males are larger, more colourful and develop much extended dorsal, anal and caudal fins as they mature. It’s one of the few species of characin in which the central ray of the caudal fin also becomes elongated. Males also have a blue iris, whereas that of females is green.


Not a difficult species to breed. You’ll need to set up a separate tank in which to do so, if you want to raise fry in any great numbers. Something around 16″ x 8″ x 8″ in size is fine. This should be very dimly lit and contain clumps of fine-leaved plants such as java moss or spawning mops, to give the fish somewhere to deposit their eggs. Alternatively you could cover the base of the tank with some kind of mesh. This should be of a large enough grade so that the eggs can fall through it, but small enough so that the adults cannot reach them. The water should be soft and acidic in the range pH 6.0-7.0, gH 1-10, with a temperature of around 75-80°F. A small air-powered sponge filter bubbling away very gently is all that is needed in terms of filtration.

It can be spawned in a group, with half a dozen specimens of each sex being a good number. A larger tank would be needed in this situation, to allow males the space they need for territories. Condition the fish with plenty of small live foods and spawning should not present too many problems. The adults can be removed once eggs are noticed, or in a very heavily planted tank left in situ and fry siphoned from the tank as they’re noticed.

In terms of productivity it’s best spawned in pairs. Under this technique the fish are conditioned in male and female groups in separate tanks. When the females are noticeably full of eggs and the males are displaying their best colours, select the fattest female and best-coloured male and transfer them to the spawning tank in the evening. They should spawn the following morning. Only a few eggs are released at a time, so the event can often continue for several hours. If you cannot see eggs after a couple of days remove them and try with a different pair.

The adults will often eat their spawn given the chance and should be removed as soon as eggs are noticed. These will hatch in 24-36 hours, with the fry becoming free swimming 4-5 days later. They should be fed on an infusoriatype food for the first week or so, until they’re large enough to accept microworm or brine shrimp nauplii.

NotesTop ↑

This species can be found in most dealers’ tanks and is one of the best choices for the newcomer to fishkeeping, being attractive, hardy and inexpensive. As virtually all the fish sold in the trade have been captive bred they tend to be relatively unfussy regarding water chemistry and diet.

It’s occasionally confused with N. lacortei, which is currently the only other species in the genus. They can easily be told apart by looking at the eye of the fish in question, as the male N. lacortei has a bright red iris as opposed to the blue iris in male N. palmeri.

The ‘blue’ or ‘purple emperor tetra’, Inpaichthys kerri is also frequently misidentified as N. palmeri. This species is not only in a different (monotypic) genus, but achieves a significantly smaller size and does not develop fin extensions. Inpaichthys also possesses an adipose fin, which is absent inNematobrycon.

In recent years there have been debates surrounding the existence of a third species of Nematobrycon. N. “amphiloxus” possesses a far greater proportion of dark patterning on the body and is usually sold as ‘black emperor tetra’. It’s currently considered a colour morph of N. palmeri by most experts.

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