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Family: Characidae, Nematobrycon Clade

Common Name: Rainbow Emperor Tetra, Red Eye Emperor Tetra

Origin and Habitat: Rio San Juan basin in western Columbia, South America. Occurs in sluggish tributaries and quiet small rivers and streams.

Compatibility/Temperament: Peaceful, though males can be territorial but rarely causing damage to each other. Other characins (tetras) in the tank may also be chased by boistrous males. Must be in a group, preferably nine or more so that the aggressiveness of some males will be spread out and not directed at lone fish. Suitable in community tanks with angelfish, other characins, dwarf cichlids, small catfish and loaches, gourami, rasbora and danios. Not suitable with quieter tankmates as this is an active fish.

Rainbow Emperor Tetra Diet

In nature it feeds on worms and crustaceans; readily accepts most prepared foods including flake and frozen foods like daphnia and bloodworms.


Up to 2 inches, often slightly less.

Minimum Tank Suggestion

30 inches in length.

Water parameters for Rainbow Emperor Tetra

Soft (hardness less than 12 dGH) acidic (pH below 7.0) water, temperature 23-27C/73-81F.


Though less often available, this species is the more colourful of the two "Emperor" tetra. Juveniles can easily be confused with N. palmeri, but the iris of the eye is blue in that species and a bright red in N. lacortei.

This species does not like brightly-lit or sparse environments. In a well-planted aquarium with low light (aided by floating plants) and a dark substrate, their colours truly sparkle. Prefers the middle and upper levels in the water column. Needs to be in groups but frequently swims individually. Will readily mix in with N. palmeri. Neither species in this genus has an adipose fin.

Males are larger, more colourful, and develop extended dorsal, caudal and anal fins; both sexes have the red iris. Will easily spawn in a tank planted with fine leaved plants, very dimly lit, and very soft and acidic water. Adults will readily eat the eggs after spawning. This species is a prolific spawner, and some fry will often survive in well-planted tanks. Males are very aggressive to other fish, especially when enticing females to spawn, and this seems almost continual.

This species was described in 1971 by S.H. Weitzman and W.L. Fink. C.H. Eigenmann initially erected the genus (for N. palmeri) in 1911; the name is derived from the Greek for "Brycon with threads," a reference to the extended filaments of the caudal fin. In some writings the subject species in incorrectly identified as Nematobrycon amphiloxus, a name now considered invalid as a distinct species and designated as a synonym for N. palmeri (Pavanelli in Reis et al., 2003).

The genus Nematobrycon was previously considered within the subfamily Tetragonopterinae, but this classification, as indeed that of the entire Characidae family, has for some time been deemed incertae sedis [Latin for "of uncertain placement"]. Javonillo, et al. (2010) proposed that the subfamily Tetragonopterinae should only be used for species within the genus Tetragonopterus. J. Marcos Mirande (2009) proposed several revisions to the family Characidae based upon phylogenetic diagnosis. Some genera have been moved to a new subfamily, while others are now (temporarily) assigned to a specific clade within the family pending further phylogenetic study.


Javonillo, Robert, Luiz R. Malabarba, Stanley H. Weitzman and John R. Burns (2010), "Relationships among major lineages of characid fishes (Teleostei: Ostariophysi: Characiformes), based on molecular sequence data," Molecular Phylogenetics and Evolution, Vol. 54, No. 2 (February 2010).

Mirande, J. Marcos (2009), "Weighted parsimony phylogeny of the family Characidae (Teleostei: Characiformes)," Cladistics, Vol. 25, No. 6 (July 2009).

Reis, R.E., S.O. Kullander and C.J. Ferraris, Jr. (2003), editors, Check list of the freshwater fishes of South and Central America.

Contributing Members

The following members have contributed to this profile: Byron


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