Rainbow Emperor Tetra (Nematobrycon lacortei)

A jewel-toned Colombian tetra with vivid red eyes in males and a peacock shimmer that rivals any nano fish in the hobby.

Care level Medium Temperament Semi-aggressive Adult size 3.6 cm (1.4 in) Min tank 40 L (10.6 gal) Temperature 22–28 °C (72–82 °F)
By The Aquarium DB Team • Updated June 8, 2026 • Also: Rainbow tetra, Lacorte's tetra
Tank-mate checker

Will it live with a Rainbow Emperor Tetra?

We compare each fish against your rainbow emperor tetra on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.

  • African Dwarf Frog✅ Compatible
    Peaceful · 4 cm · Medium care · 22–26 °C (72–79 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Amapá Tetra✅ Compatible
    Peaceful · 4 cm · Medium care · 24–27 °C (75–81 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–27 °C — no size, zone or temperament conflicts.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Amapá Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Assassin Snail✅ Compatible
    Peaceful · 3 cm · Easy care · 22–26 °C (72–79 °F)
    • Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Blue Danio✅ Compatible
    Peaceful · 4 cm · Easy care · 21–26 °C (70–79 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
  • Blue Emperor Tetra✅ Compatible
    Peaceful · 4 cm · Medium care · 23–27 °C (73–81 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Blue Emperor Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Cardinal Tetra✅ Compatible
    Peaceful · 4 cm · Medium care · 23–27 °C (73–81 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 23–27 °C — no size, zone or temperament conflicts.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Cardinal Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Emperor Tetra✅ Compatible
    Peaceful · 4 cm · Easy care · 23–27 °C (73–81 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Emperor Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Flame Tetra✅ Compatible
    Peaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
    • Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Flame Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Ghost Shrimp✅ Compatible
    Peaceful · 4 cm · Easy care · 18–28 °C (64–82 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–28 °C — no size, zone or temperament conflicts.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Ghost Shrimp in a shoal of 6+ or it gets stressed and nippy.
  • Glowlight Tetra✅ Compatible
    Peaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
    • Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Glowlight Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Golden Dwarf Barb✅ Compatible
    Peaceful · 4 cm · Easy care · 18–24 °C (64–75 °F)
    • Compatible on the things that matter: shared water near 22–24 °C, workable temperaments, and no predator-and-prey size gap.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Golden Dwarf Barb in a shoal of 6+ or it gets stressed and nippy.
  • Jelly Bean Tetra✅ Compatible
    Peaceful · 4 cm · Medium care · 20–26 °C (68–79 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Jelly Bean Tetra in a shoal of 10+ or it gets stressed and nippy.
  • Marbled Hatchetfish✅ Compatible
    Peaceful · 4 cm · Medium care · 23–28 °C (73–82 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Marbled Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
  • Otocinclus✅ Compatible
    Peaceful · 4 cm · Medium care · 21–26 °C (70–79 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Otocinclus in a shoal of 6+ or it gets stressed and nippy.
  • Phoenix Tetra✅ Compatible
    Peaceful · 4 cm · Easy care · 23–28 °C (73–82 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Phoenix Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Purple Tetra✅ Compatible
    Peaceful · 4 cm · Medium care · 22–26 °C (72–79 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Purple Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Red Phantom Tetra✅ Compatible
    Peaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
    • Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Red Phantom Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Rosy Tetra✅ Compatible
    Peaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–28 °C — no size, zone or temperament conflicts.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Rosy Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Rummy Nose Rasbora✅ Compatible
    Peaceful · 4 cm · Medium care · 20–26 °C (68–79 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Rummy Nose Rasbora in a shoal of 8+ or it gets stressed and nippy.
  • Sparkling Gourami✅ Compatible
    Peaceful · 4 cm · Medium care · 24–28 °C (75–82 °F)
    • Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Tailspotted Oto✅ Compatible
    Peaceful · 3.5 cm · Medium care · 22–27 °C (72–81 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–27 °C — no size, zone or temperament conflicts.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Tailspotted Oto in a shoal of 6+ or it gets stressed and nippy.
  • Threadfin Rainbowfish✅ Compatible
    Peaceful · 4 cm · Medium care · 24–28 °C (75–82 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–28 °C — no size, zone or temperament conflicts.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Threadfin Rainbowfish in a shoal of 6+ or it gets stressed and nippy.
  • Tiger Otocinclus✅ Compatible
    Peaceful · 4 cm · Medium care · 22–27 °C (72–81 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Tiger Otocinclus in a shoal of 6+ or it gets stressed and nippy.
  • Yellow Phantom Tetra✅ Compatible
    Peaceful · 4 cm · Easy care · 23–27 °C (73–81 °F)
    • Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
    • Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Yellow Phantom Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Black Darter Tetra⚠️ With caution
    Semi-aggressive · 4 cm · Hard care · 21–28 °C (70–82 °F)
    • Rainbow Emperor Tetra and Black Darter Tetra can both be territorial; doable with space and dense planting, but watch for chasing.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Blackwing Hatchetfish⚠️ With caution
    Peaceful · 3.5 cm · Medium care · 23–28 °C (73–82 °F)
    • Rainbow Emperor Tetra and Blackwing Hatchetfish are close in size, but the semi-aggressive one tends to dominate — add blackwing hatchetfish in a group to spread the pressure.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
  • Clown Killifish⚠️ With caution
    Peaceful · 3.5 cm · Medium care · 22–26 °C (72–79 °F)
    • Rainbow Emperor Tetra and Clown Killifish are close in size, but the semi-aggressive one tends to dominate — add clown killifish in a group to spread the pressure.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Clown Killifish in a shoal of 6+ or it gets stressed and nippy.
  • Crimson Red Betta⚠️ With caution
    Peaceful · 3.5 cm · Hard care · 24–29 °C (75–84 °F)
    • Rainbow Emperor Tetra is semi-aggressive and may chase or nip the smaller Crimson Red Betta — plant heavily and break up sight lines.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Endler's Livebearer⚠️ With caution
    Peaceful · 3 cm · Easy care · 22–28 °C (72–82 °F)
    • Expect Rainbow Emperor Tetra to harass Endler's Livebearer at times; give dense cover and watch them at feeding.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Endler's Livebearer in a shoal of 6+ or it gets stressed and nippy.
  • Eyespot Rasbora⚠️ With caution
    Peaceful · 3.5 cm · Medium care · 20–25 °C (68–77 °F)
    • Expect Rainbow Emperor Tetra to harass Eyespot Rasbora at times; give dense cover and watch them at feeding.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Eyespot Rasbora in a shoal of 8+ or it gets stressed and nippy.
  • Fire Red Licorice Gourami⚠️ With caution
    Peaceful · 3.5 cm · Hard care · 23–28 °C (73–82 °F)
    • Rainbow Emperor Tetra and Fire Red Licorice Gourami are close in size, but the semi-aggressive one tends to dominate — add fire red licorice gourami in a group to spread the pressure.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Glowlight Danio⚠️ With caution
    Peaceful · 3 cm · Easy care · 22–26 °C (72–79 °F)
    • Rainbow Emperor Tetra is semi-aggressive and may chase or nip the smaller Glowlight Danio — plant heavily and break up sight lines.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Glowlight Danio in a shoal of 8+ or it gets stressed and nippy.
  • Glowlight Rasbora⚠️ With caution
    Peaceful · 3.5 cm · Easy care · 23–28 °C (73–82 °F)
    • Expect Rainbow Emperor Tetra to harass Glowlight Rasbora at times; give dense cover and watch them at feeding.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Glowlight Rasbora in a shoal of 8+ or it gets stressed and nippy.
  • Gold Ring Danio⚠️ With caution
    Peaceful · 3 cm · Easy care · 18–26 °C (64–79 °F)
    • Expect Rainbow Emperor Tetra to harass Gold Ring Danio at times; give dense cover and watch them at feeding.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Gold Ring Danio in a shoal of 8+ or it gets stressed and nippy.
  • Lambchop Rasbora⚠️ With caution
    Peaceful · 3 cm · Medium care · 23–28 °C (73–82 °F)
    • Rainbow Emperor Tetra and Lambchop Rasbora are close in size, but the semi-aggressive one tends to dominate — add lambchop rasbora in a group to spread the pressure.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Lambchop Rasbora in a shoal of 6+ or it gets stressed and nippy.
  • Northern Glowlight Danio⚠️ With caution
    Peaceful · 3.5 cm · Medium care · 18–24 °C (64–75 °F)
    • Rainbow Emperor Tetra is semi-aggressive and may chase or nip the smaller Northern Glowlight Danio — plant heavily and break up sight lines.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Northern Glowlight Danio in a shoal of 8+ or it gets stressed and nippy.
  • Pygmy Corydoras⚠️ With caution
    Peaceful · 3.2 cm · Easy care · 22–26 °C (72–79 °F)
    • Rainbow Emperor Tetra is semi-aggressive and may chase or nip the smaller Pygmy Corydoras — plant heavily and break up sight lines.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Pygmy Corydoras in a shoal of 8+ or it gets stressed and nippy.
  • Serpae Tetra⚠️ With caution
    Semi-aggressive · 4 cm · Easy care · 23–28 °C (73–82 °F)
    • Rainbow Emperor Tetra and Serpae Tetra can both be territorial; doable with space and dense planting, but watch for chasing.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
    • Keep Serpae Tetra in a shoal of 6+ or it gets stressed and nippy.
  • Strawberry Betta⚠️ With caution
    Peaceful · 4 cm · Medium care · 22–27 °C (72–81 °F)
    • Rainbow Emperor Tetra is a notorious fin-nipper — even though Strawberry Betta is larger, an active shoal will harass its trailing fins. Only safe in a full group of 8+ with plenty of cover.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Tiger Badis⚠️ With caution
    Semi-aggressive · 4 cm · Medium care · 22–24 °C (72–75 °F)
    • Rainbow Emperor Tetra and Tiger Badis can both be territorial; doable with space and dense planting, but watch for chasing.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Alligator Gar⛔ Not recommended
    Aggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
    • Rainbow Emperor Tetra and Alligator Gar are both territorial and at least one is outright aggressive — expect serious fighting.
    • Size gap is too large (250 vs 3.6 cm): Alligator Gar will treat Rainbow Emperor Tetra as food.
    • Rainbow Emperor Tetra is a notorious fin-nipper — even though Alligator Gar is larger, an active shoal will harass its trailing fins. Only safe in a full group of 8+ with plenty of cover.
    • Your 75 L tank is below the ~3785 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Clown Knifefish⛔ Not recommended
    Aggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
    • Two assertive fish, one genuinely aggressive: Rainbow Emperor Tetra and Clown Knifefish will hold territory and clash.
    • Rainbow Emperor Tetra is bite-sized to a 90 cm predatory clown knifefish — it will be eaten.
    • Your 75 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Fire Eel⛔ Not recommended
    Semi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
    • Rainbow Emperor Tetra is bite-sized to a 100 cm predatory fire eel — it will be eaten.
    • Rainbow Emperor Tetra and Fire Eel can both be territorial; doable with space and dense planting, but watch for chasing.
    • Your 75 L tank is below the ~380 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Koi⛔ Not recommended
    Peaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
    • Rainbow Emperor Tetra is bite-sized to a 90 cm koi — it will be eaten.
    • Koi is slow and long-finned; a busy rainbow emperor tetra shoal tends to nip at it. Keep rainbow emperor tetra in a proper group of 8+ and watch them closely.
    • Your 75 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Redtail Catfish⛔ Not recommended
    Aggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
    • Rainbow Emperor Tetra and Redtail Catfish are both territorial and at least one is outright aggressive — expect serious fighting.
    • Redtail Catfish (120 cm) is big enough to swallow the 3.6 cm Rainbow Emperor Tetra whole.
    • Your 75 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Spotted Gar⛔ Not recommended
    Aggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
    • Rainbow Emperor Tetra and Spotted Gar are both territorial and at least one is outright aggressive — expect serious fighting.
    • Rainbow Emperor Tetra is bite-sized to a 90 cm predatory spotted gar — it will be eaten.
    • Rainbow Emperor Tetra is a notorious fin-nipper — even though Spotted Gar is larger, an active shoal will harass its trailing fins. Only safe in a full group of 8+ with plenty of cover.
    • Your 75 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Wels Catfish⛔ Not recommended
    Aggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
    • Rainbow Emperor Tetra and Wels Catfish are both territorial and at least one is outright aggressive — expect serious fighting.
    • Size gap is too large (300 vs 3.6 cm): Wels Catfish will treat Rainbow Emperor Tetra as food.
    • Your 75 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
  • Wolf Cichlid⛔ Not recommended
    Aggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
    • Two assertive fish, one genuinely aggressive: Rainbow Emperor Tetra and Wolf Cichlid will hold territory and clash.
    • Wolf Cichlid (72 cm) is big enough to swallow the 3.6 cm Rainbow Emperor Tetra whole.
    • Wolf Cichlid is slow and long-finned; a busy rainbow emperor tetra shoal tends to nip at it. Keep rainbow emperor tetra in a proper group of 8+ and watch them closely.
    • Your 75 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
    • Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.

Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.

 → Full Rainbow Emperor Tetra tank mates guide: best matches, what to avoid & how to choose
Full specs

Rainbow Emperor Tetra care specs

Care level
Medium
Breeding
Hard
Max size
3.6 cm (1.4 in)
Min tank size
40 L (10.6 gal)
Temperature
22–28 °C (72–82 °F)
pH
6–7.5
Hardness
2–15 dGH
Lifespan
3–5 years
Diet
Carnivore
Swim level
Middle
Group size
8+ (shoaling)
Family
Characidae
Origin
Colombia — San Juan and Calima river basins (Pacific drainage)
Telling sexes apart
Males have striking red eyes, deeper colour and extended dorsal, anal and caudal fins; females have blue-green eyes and a rounder body.
Colour forms
Iridescent blue-green body with violet and gold flanks; males have vivid red eyes

What is a Rainbow Emperor Tetra?

The Rainbow Emperor Tetra (Nematobrycon lacortei) is a small but spectacular characid from Colombia, maxing out at around 3.6 cm (1.4 in) in body length. What it lacks in size it compensates for entirely in colour: the iridescent blue-green flanks shift through violet and gold depending on the light, and breeding-condition males develop a peacock shimmer that competes with fish three times their size. The clincher is the eyes — males carry a vivid, ruby-red iris that is unlike almost anything else in the nano-fish hobby.

Nematobrycon lacortei is the rarer of the two emperor tetras and is less often stocked in fish stores than its relative N. palmeri. That relative scarcity is a shame, because the Rainbow Emperor Tetra is every bit as rewarding to keep and arguably more striking. Its care is rated medium primarily because of water-quality sensitivity and the territorial dynamic between males; the fish itself is robust once settled into a well-maintained tank.

Where do Rainbow Emperor Tetras come from?

Wild Rainbow Emperor Tetras are endemic to the San Juan and Calima river basins in Colombia, both of which drain into the Pacific. These rivers carry soft, gently acidic blackwater through lowland tropical forest — slow-moving, heavily shaded, stained brown with dissolved leaf tannins and driftwood humates. The water is very soft (often below 5 dGH), pH dips toward the acidic end of the species’ tolerance range, and temperatures hold between roughly 22 and 28 °C (72–82 °F) depending on the season and elevation.

Understanding this origin shapes every decision in the care guide. The fish evolved in a stable, chemically gentle environment with abundant cover and relatively little competition for the mid-water column — which explains both its jewel-like colouration and its low tolerance for hard, alkaline or otherwise chemically unstable water.

What tank size and setup does the Rainbow Emperor Tetra need?

The frontmatter minimum is 40 litres (roughly 10 gallons), which can house a small group of eight in a well-planted, well-managed aquarium. In practice, 60–75 L (15–20 gal) is a better target once you account for the territorial spacing that males need, and it leaves margin for a few compatible dither fish.

A blackwater-style layout suits this species perfectly:

  • Substrate: fine dark sand or small, dark gravel — amplifies colour contrast.
  • Plants: dense stands of Cryptocoryne, Java fern and floating plants (Water Sprite or frogbit) to dim the light and break sight lines.
  • Hardscape: driftwood and a layer of dried Indian almond or oak leaves on the substrate; the tannins soften the water and reinforce the natural environment.
  • Flow: gentle — an internal sponge filter or a hang-on filter with a spray bar. Strong flow stresses the fish and scatters the fry if you intend to breed.
  • Lid: essential; like most tetras, N. lacortei will jump.

What water parameters do Rainbow Emperor Tetras need?

  • Temperature: 22–28 °C (72–82 °F). The sweet spot for long-term health and colour is 24–26 °C (75–79 °F).
  • pH: 6.0–7.5. Aim for 6.2–7.0; values above 7.5 suppress colouration and increase stress.
  • Hardness: 2–15 dGH. This species handles moderate hardness, but soft water (under 8 dGH) brings out the best colours and is essential for spawning success.

Consistency is the priority. Weekly partial water changes of 20–25 % prevent the gradual acidification and waste accumulation that erode the health of soft-water species. Do not top up evaporation losses with hard tap water without checking — over time this creeps hardness above the comfortable range.

What do Rainbow Emperor Tetras eat?

Nematobrycon lacortei is a carnivore that hunts small invertebrates in the wild. In the aquarium it accepts a wide range of offerings:

  • Staple: quality micro-pellets or small-particle tropical flake sized appropriately for a 3.6 cm fish.
  • Live and frozen: baby brine shrimp, daphnia, micro-worms, cyclops and finely chopped bloodworm. These are particularly valuable for conditioning adults ahead of breeding.
  • Frequency: two small feedings daily. The fish are active mid-water feeders and will take food before it reaches the substrate.

Variety is genuinely important here. A pellet-only diet keeps the fish alive; a pellet-plus-live/frozen rotation brings out the full iridescent palette, boosts immune resilience and gets males displaying properly.

Are Rainbow Emperor Tetras aggressive — and what fish can they live with?

The Rainbow Emperor Tetra carries a semi-aggressive temperament driven almost entirely by male-to-male rivalry. Males establish loose territories, perform lateral displays with fins fully erect, and will chase or nip fish of similar shape and size — including the Emperor Tetra (N. palmeri) if the two species are mixed. The key management tool is the group structure: a minimum of 8 individuals, with more females than males, spreads the aggression and prevents any single fish from being singled out.

Good community partners are peaceful, occupy the bottom or upper column rather than the middle, and are not long-finned or brightly coloured enough to trigger a male’s territorial response. Pygmy Corydoras, small Loricariids, small peaceful rasboras and danios in the upper column, and dwarf shrimp (with the caveat that fry may be eaten) can all work in a well-planted tank.

For a curated, compatibility-checked list, see Rainbow Emperor Tetra tank mates.

How do you tell male and female Rainbow Emperor Tetras apart?

Sexing this species is one of its most enjoyable aspects — the difference is obvious even to a newcomer:

  • Males have vivid red eyes, deeper and more saturated body colouration, and noticeably extended dorsal, anal and caudal fins. In display mode the finnage fans out impressively for their size.
  • Females have blue-green eyes, a plainer (though still attractive) body colour, and a rounder, deeper belly — most visible when ripe with eggs. Their fins are shorter and neater.

The red-versus-blue-green eye difference is the fastest diagnostic at any age past juvenile. In juveniles, fin extension and eye colour develop gradually over the first few months.

How do Rainbow Emperor Tetras breed?

Breeding N. lacortei is rated hard — achievable for a dedicated intermediate keeper, but it requires deliberate preparation:

  1. Conditioning: feed the target pair or group heavily on live and frozen foods for two to three weeks.
  2. Breeding tank: a bare-bottom or peat-substrate tank of 20–30 L (5–8 gal), very soft water (2–4 dGH), pH around 6.0–6.5, and dim lighting. Fine-leaved plants (Java moss, hornwort) provide spawning sites.
  3. Spawning: the male courts the female with full fin display and lateral shimmering. The pair scatters eggs among the plants, a small number at a time.
  4. Egg care: remove adults after spawning — they will eat the eggs. Eggs hatch in roughly 24–36 hours; fry are free-swimming a few days later.
  5. Fry feeding: infusoria or commercial fry powder for the first week, progressing to freshly hatched baby brine shrimp. Water changes must be tiny and frequent to keep the fry tank clean without crashing the chemistry.

The main challenge is sourcing truly conditioned adults, achieving the correct soft-acid water chemistry, and successfully raising the very small fry. Success is proportionally satisfying.

What diseases affect Rainbow Emperor Tetras?

As soft-water characids, Rainbow Emperor Tetras are susceptible to the standard range of freshwater fish ailments, usually triggered by water-quality lapses:

  • Ich (white spot): tiny white dots on fins and body; caused by temperature drops or stress. Raising temperature slightly and improving water quality often resolves mild cases early.
  • Velvet: fine gold or brown dust on the body, easier to spot under a torch beam; another parasite linked to stress and poor water quality.
  • Fin rot: fraying or receding fins, most commonly in males after prolonged territorial conflict or in deteriorating water. Improving water quality is the first intervention.
  • Neon tetra disease / microsporidiosis: less common but worth being aware of in mixed characid tanks; look for loss of colour along the lateral stripe and wasting.

Prevention is straightforward: maintain soft, stable, well-filtered water; quarantine new fish for a minimum of two to four weeks before introduction; avoid overstocking; and respond to early symptoms promptly rather than waiting.

Health note: medication dosing and disease diagnosis are beyond the scope of a care profile. For a sick fish, confirm symptoms against a reputable veterinary or fish-health resource before treating.

How long do Rainbow Emperor Tetras live?

A well-maintained Nematobrycon lacortei lives 3–5 years. That range is typical for small characids and reflects the difference between baseline survival and genuinely good husbandry — soft, stable water, varied feeding and a stress-managed group dynamic push individuals toward the upper end. Males, which bear the physiological cost of constant display and territorial maintenance, may trend slightly shorter than females all else being equal. Buy from a reputable source, quarantine before introduction, and give them a properly prepared blackwater environment and the species consistently reaches and often exceeds the three-year mark.

FAQ

Frequently asked questions

What is the difference between the Rainbow Emperor Tetra and the Emperor Tetra?

Both belong to the genus Nematobrycon, but they are distinct species. The Emperor Tetra (Nematobrycon palmeri) is the more commonly sold of the two; the Rainbow Emperor Tetra (Nematobrycon lacortei) is slightly smaller and displays an even richer iridescent colour palette and distinctive red eyes in males versus the blue-green eyes of its relative.

Are Rainbow Emperor Tetras aggressive?

Males are territorial toward each other and toward similarly shaped fish — they will spar and flare. Keep a larger group (8+) so aggression is spread out, and avoid other species with flowing fins or similar body shapes. Females and small, fast-moving tank-mates fare much better.

What you need to keep a rainbow emperor tetra

The baseline is a heated, filtered 40 L+ tank: a reliable heater to hold 22–28 °C (72–82 °F), a gentle filter that won't batter a rainbow emperor tetra in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.

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