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Nematobrycon lacortei WEITZMAN & FINK, 1971

Rainbow Tetra


Nematobrycon: from the Ancient Greek νῆμα (nêma), meaning ‘thread’, in reference to the extended filamentous rays in the caudal-fin of member species, and βρύκω (brúkhō), meaning ‘devour, gobble, bite, chew, gnash’, a term which was originally used in reference to possession of fully-toothed maxillae but subsequently applied to the generic names of many characiform species in order to demonstrate their putative relatedness.

lacortei: named for aquarist Rosario LaCorte.


Order: Characiformes Family: Characidae


Considered endemic to the Río San Juan river system, which drains the departments of Choco and Valle de Cauca in western Colombia. All records of N. lacortei appear to correspond to the Río Calima, a tributary in the lower part of the basin.

Type locality is ‘probably from Río Calima, Colombia’.


Apparently restricted to small, isolated forest pools in headwaters of the Río Calima, presumably above the Calima Dam.

Maximum Standard Length

The largest officially-recorded specimen measured 36.0 mm.

Aquarium SizeTop ↑

An aquarium with dimensions of 120 ∗ 30 ∗ 30 cm or equivalent should be the smallest considered.


Choice of décor is not especially critical, although this species tends to show better colouration when maintained in a well-furnished aquarium with live plants. A natural-looking arrangement might consist of a soft, sandy substrate with wood roots and branches placed such a way that plenty of shady spots are formed.

The addition of dried leaf litter would further emphasise the natural feel and with it the growth of beneficial microbe colonies as decomposition occurs. These can provide a valuable secondary food source for fry, whilst the tannins and other chemicals released by the decaying leaves are considered beneficial.

Water Conditions

Temperature20 – 28 °C

pH5.0 – 7.2

Hardness18 – 179 ppm


Probably an opportunistic omnivore by nature. In the aquarium it is easily-fed but the best condition and colours offer regular meals of small live and frozen foods such as chironomid larvae (bloodworm), DaphniaArtemia, etc., alongside good quality dried flakes and granules.

Behaviour and CompatibilityTop ↑

This species is relatively peaceful making it an ideal resident of the well-researched community aquarium, although adult males are territorial and aggressive to an extent, and this behaviour may sometimes extend to similarly-shaped species. It is perhaps best-maintained alongside similarly-sized characids, gasteropelecids, lebiasinids, smaller callichthyid or loricariid catfishes and non-predatory, medium-sized cichlids.

Try to buy a group of at least 8-10 specimens comprising both males and females, include other schooling fishes to provide security, and you will be rewarded with a more natural-looking spectacle. The interaction between rival males is fascinating to watch and they will display their best colours when competing for female attention or hierarchical position.

Sexual Dimorphism

Adult males possess red eyes and more-extended dorsal, anal, and caudal fins than females, plus they are generally more colourful. Adult females possess blue-green eyes and typically appear fuller-bodied than males, especially when gravid.


Said to breed in a similar way to its congener N. palmeri. A small, very dimly-lit aquarium containing clumps of fine-leaved plants or spawning mops should be used. Alternatively, the aquarium base can be covered with some kind of mesh of a large enough grade so that 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 5.0-7.0, gH 1-8, with a temperature of around 75-80°F. A small air-powered sponge filter can also be included.

The fish are best conditioned in separate male and female groups. When the females are noticeably gravid a single pair should be selected and transferred to the small aquarium in the evening, with spawning tending to occur the following morning. Eggs are deposited in small batches, thus spawning may continue for several hours. If you cannot see eggs after a couple of days remove the fish and repeat the process with a different pair.

The adults will eat their eggs given the chance and should be removed post-spawning. The eggs typically hatch in 24-36 hours, with the fry free swimming 4-5 days later. They should be fed on an infusoria-grade food for the first week or so, until they are large enough to accept microworm , Artemia nauplii, and suchlike.

NotesTop ↑

The genus Nematobrycon currently comprises two species, both of which are endemic to western Colombia with N. palmeri the more widespread. They are quite similar morphologically, differing only in modal pectoral-fin ray counts (9 in N. lacortei vs. 10 in N. palmeri), number of premaxillary teeth in the outer row (2 vs. 3), mean number of anal-fin rays (25.8 vs. 28.1), and dorsal-fin length (29.1-30 vs. 31.3-49.0 % SL), but possess highly distinctive colour patterns.


  1. Weitzman, S. H. and W. L. Fink, 1971 - Beaufortia 19(248): 57-77
    A new species of characid fish of the genus Nematobrycon from the Rio Calima of Colombia.

7 Responses to “Nematobrycon lacortei – Rainbow Tetra”

  • hidebeetle

    This maximum length seems much too small. I have seen a number of specimens over 6cm body length for sale and LFS staff said they grow to 3 inches. LFS staff also described them as “chasers” rather than “fin nippers” but as an active species not suitable as dither fish and slightly more aggressive than emperor tetras (Nematobrycon palmeri). This matched the behavior I saw in the store tank-males seem pretty aggressive to each other (though N. palmeri is supposed to have aggression between males but be peaceful with other species). Re your photos: the adult fish I saw as N. lacortei all had red eyes; the N. palmeri had blue or green eyes.

  • Darrell Ullisch

    Females of this species have blue-green eyes. The males are the only ones with red eyes. In N. palmeri, the males have blue eyes, while the females have greenish eyes. Very young fish start off with female colors, and the red eyes develop with maturity. However, the lower photo to the right is a female based not only on eye color, but the lack of an extension at the center of the caudal fin.

    I have kept this species, and the males are extremely aggressive toward other males, and fairly rough on females. The size they can reach is about the same as N. palmeri, about 3 inches (70-75mm). They are said to breed much the same as N. palmeri, though I had no success with them.

  • Hi guys, updating this now. Is that 70-75 mm SL or TL?

  • Darrell Ullisch

    I would say TL. For SL I would call it 65mm.

  • Great, thanks Darrell!

  • hidebeetle

    Due to LFS identifying males only as this species, I have 5 adult males, 0 females in a 29 gal well-planted community tank. They are tolerant of each other, in spite of some being twice the size of others. Aggression seems mostly limited to visual displays. I would not want this situation in a smaller or bare tank, though.

  • Characid Kid

    Any information on sympatric fish species?

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