Rainbow Tetra
Nematobrycon lacortei
A beautiful small freshwater fish from Colombia, renowned for its iridescent coloration and bright red eyes. Males display a striking extended tail filament during impressive displays.
Water Temperature
23 - 27 °C
pH Value
6 - 7.2
Water type
Freshwater
Tank level
Middle
Adult size
5 cm
Minimum tank volume
>= 80 L
Minimum group
>= 6
GH
3 - 10 dGH
KH
2 - 6 dKH
TDS
65 - 210 ppm
Conductivity
102 - 328 uS/cm
Species description
Geographical Origin and Habitat: This species is native to Western Colombia, specifically found in the San Juan River basin. It inhabits slow-moving forest streams, small tributaries, and quiet pools characterized by dense overhanging vegetation, leaf-litter substrates, and soft, slightly acidic blackwater.
Taxonomy and Morphology: Member of the Characidae family. It features a laterally compressed, slender body. The caudal fin is unique and trilobed, with the middle ray extending into a long black filament (spade-like) in adult males. Grows to a maximum length of about 4.5-5.0 centimeters.
Social Behavior: Schooling species, though males display mild territorial behavior. Dominant males establish temporary territories and engage in non-harmful sparring displays by swimming parallel with flared fins. Should be kept in groups of at least 6-8 individuals.
Coloration and Sexual Dimorphism: The body displays a striking iridescence with hues of pink, green, blue, and gold depending on the light. The eyes are bright red. Sexual dimorphism is clear: males are larger, have brighter red eyes, elongated dorsal and anal fins, and the prominent black caudal filament.
Care, breeding and tankmates
Aquarium Setup: Requires a tank of at least 80 liters with dense lateral and background planting (e.g., Cryptocorynes and Java Moss) while leaving the center open for swimming. A dark substrate and leaf litter (such as Indian Almond leaves) will replicate their habitat and enhance their iridescent colors.
Diet and Feeding: Omnivorous. Readily accepts high-quality commercial flakes and micro-pellets. To encourage vibrant coloration and health, supplement their diet regularly with live or frozen foods such as bloodworms, daphnia, brine shrimp, and tubifex.
Water Quality: Prefers soft, acidic water conditions. Ideal parameters: temperature 22 to 28 °C, pH 6.0 to 7.2, GH 3-12, and KH 2-8. They are sensitive to elevated nitrate levels; regular partial water changes and moderate filtration with gentle water movement are necessary.
Compatibility and Cohabitation: An excellent choice for peaceful community tanks. Suitable tankmates include other tetras, dwarf cichlids, corydoras, and small loricariids. Do not house with large, hyperactive, or predatory species that might prey on them or stress them.
Aquarium Breeding: Oviparous. Spawning is relatively straightforward in a separate breeding tank filled with fine-leaved plants. Parents should be removed immediately after spawning to prevent egg predation. The fry hatch in about 36 hours and require infusoria as first food.
Risks and Diseases: Susceptible to Ich (white spot disease) and velvet if subjected to sudden temperature drops or poor water conditions. They can also contract neon tetra disease (Plistophora). Maintaining stable water quality and quarantining new fish are vital.
Geographic Origin and Distribution
This species is native to Western Colombia, specifically found in the San Juan River basin. It inhabits slow-moving forest streams, small tributaries, and quiet pools characterized by dense overhanging vegetation, leaf-litter substrates, and soft, slightly acidic blackwater.
Origin
Extra-Amazon South America
Fish profile
- Temperament
- Territorial
- While generally peaceful toward other species, males display a striking, semi-aggressive territoriality towards conspecifics. They frequently engage in elaborate lateral displays and mock battles to establish dominance. Despite this internal hierarchy, they are a fascinating and relatively peaceful addition to a mixed community.
- Diet
- Omnivore
- They are opportunistic omnivores that consume small worms, crustaceans, and plant matter in the wild. In the aquarium, they eagerly accept high-quality flakes, granules, and spirulina-based foods. Regular offerings of live or frozen bloodworms and brine shrimp are highly recommended for optimal health.
- Life expectancy
- 3-6 years
- In a well-structured and mature home aquarium, Nematobrycon lacortei exhibits an average lifespan of 3 to 6 years. This species, highly valued for its iridescent coloration and bright red eyes, requires soft and stable water conditions to thrive over the long term. Avoiding temperature fluctuations and high nitrate pollution is critical for preventing debilitating diseases. Providing a varied and high-quality diet supports their overall well-being throughout their life cycle.
- Adult size
- 5 cm
- The catalog's scalar value is 5 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 3.6 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Nematobrycon lacortei (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- Pair
- A ratio with a clear female majority (e.g., 1 male to 2 or 3 females) is strongly recommended. Males are fiercely territorial with each other and will constantly spar, occasionally leading to torn fins. A larger tank with plenty of line-of-sight breaks can accommodate multiple males.
- Feeding frequency
- Twice daily
- Feeding them small, controlled portions twice a day is the most effective approach. This schedule prevents overfeeding and ensures all fish in the hierarchy get a chance to eat. Careful observation during feeding helps confirm that the dominant males are not hoarding all the food.
- Bioload
- The Rainbow Emperor Tetra generates a manageable bioload typical of medium-sized tetras. As a schooling fish, a group will require a mature aquarium with robust biological filtration. Regular water changes are critical to preventing nitrate accumulation, which can negatively affect their vibrant colors.
- Flow
- Strong
- They originate from slow to moderately flowing streams in Colombia and prefer similar conditions in captivity. While they enjoy some current to swim against, they also require calm resting areas. A standard HOB or canister filter provides the appropriate water movement without exhausting them.
- Jump risk
- Yes
- They present a moderate jump risk, particularly during feeding frenzies or when males are actively sparring. A fitted aquarium lid or cover glass is strongly recommended to keep them safely contained. Creating a secure environment with plenty of plants also minimizes flighty behavior.
- Reproduction
- Oviparous
- Breeding involves the typical egg-scattering behavior, but males are highly territorial over breeding sites. A separate breeding tank with soft, acidic water and fine-leaved plants is necessary for successful spawning. Adult fish will predate on the eggs and must be removed once spawning is completed.
- Compatibility & tankmates
- Territorial
- They are generally peaceful but robust enough to hold their own in a moderately active community tank. Good tank mates include Corydoras, dwarf cichlids, rasboras, and other similarly sized tetras. They should not be kept with species that have long, trailing fins, as they may occasionally nip.
- Tank level
- Middle
- They are primarily mid-water swimmers but are confident enough to explore the entire aquarium. They often establish small territories around driftwood or tall plants in the lower-middle sections. During feeding time, they will boldly approach the upper levels.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3 ± 0.3 se
- Resilience
- High (less than 15 months)
- Phylogenetic uniqueness (PD50)
- 0.75
- Bayesian Length-Weight
- a = 0.01122, b = 3.04
- VulnerabilityLow vulnerability (10 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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