Emperor tetra
Nematobrycon palmeri
Also known as: Palmeri tetra, Emperor palmeri tetra, Rainbow tetra, Black emperor tetra (black morph)
Emperor tetras are those classy little Colombian characins with the dark horizontal stripe and the males' awesome trident/lyretail look. Keep a decent-sized group and you'll see the males do their little posturing displays without really hurting each other, especially in a planted tank with some shade.
Emperor tetras exhibit vibrant blue and yellow iridescent coloration, with a distinctive long dorsal fin and a sleek, elongated body.
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Quick Facts
Size
4.2 cm (SL)
Temperament
Peaceful
Difficulty
Beginner
Min Tank Size
20 gallons
Lifespan
4-6 years
Origin
South America (Colombia)
Diet
Omnivore/micro-predator — quality flakes/micro pellets plus frozen/live foods (daphnia, brine shrimp, bloodworms)
Water Parameters
23-27°C
5-7.5
1-15 dGH
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Calculate heater sizeCare Notes
- Keep emperors in a proper group (8+ is great). If you only buy a couple, the dominant male will hassle the others nonstop and they'll look stressed and dull.
- A 20-gallon long (or bigger) works way better than a tall tank-give them swimming room, plants, and some driftwood so the shy ones can dip in and out of cover.
- They're pretty forgiving, but they look their best around 74-79°F (23-26°C), pH ~6.5-7.5, and steady water quality; they hate sudden swings more than "slightly off" numbers.
- Flow: don't blast them like a river fish. Moderate filtration with a calm area to cruise keeps them relaxed and shows off that purple/blue sheen.
- Feed small stuff they can nail mid-water: good micro pellets/flakes as a staple, and toss in frozen baby brine, daphnia, or bloodworms a few times a week for color and condition.
- Tankmates: other peaceful community fish (corys, small rasboras, other calm tetras, otos) are fine. Skip fin-nippers and big bullies, and don't pair them with slow long-finned fish they might tempt-nip when squabbling.
- If you want babies, set up a separate small breeding tank with a sponge filter and fine plants/mops; they'll scatter eggs and then snack on them, so adults can't stay in the breeding tank.
- Watch for "mystery deaths" from old-tank syndrome and skipped water changes-these guys are hardy, but they're not fans of rising nitrate and stale water; regular small water changes beat occasional huge ones.
Compatibility
Good Tankmates
- Other small, chill schooling tetras (cardinals, rummynose, lemons) - emperor tetras are pretty peaceful, and they look/act best when everybody's in a calm, midwater community vibe.
- Corydoras (any of the common ones like panda/pepper/bronze) - perfect bottom crew, totally unbothered by emperor tetra posturing, and they keep to their lane.
- Otocinclus - great with emperors in a planted tank, they're small, gentle, and nobody really competes for space.
- Small peaceful dwarf cichlids like Apistogramma or Bolivian ram - works well if the tank has plants/wood and you don't cram it. Emperors just cruise midwater while the cichlids hold the bottom.
- Honey gourami (or other calm gouramis) - nice contrast up top, generally mellow, and emperors don't usually bother them.
- Small, peaceful livebearers (platies/endlers) - usually fine as long as you're not mixing them with super hard-water setups; temperament-wise they're an easy match.
Avoid
- Fin-nippers and rowdy stuff (serpae tetras, tiger barbs) - emperors aren't bullies, but they get stressed and ragged when the tank has constant chasing/biting going on.
- Big aggressive cichlids (convicts, most medium/large Central Americans) - emperors are basically snacks/targets, and they don't enjoy that kind of intensity.
- Slow, long-finned fish (fancy guppies, long-fin bettas) - emperor males can get a bit pushy and curious, and those flowing fins just invite trouble even if nobody 'means' it.
1) Where they come from
Emperor tetras come from Colombia, mostly in calmer tributaries where the water’s often tea-stained from leaves and wood. Think shady banks, tangled roots, and lots of cover. That vibe—dim light, plants, and driftwood—explains why they look and act their best in a “cozy” tank instead of a bright, bare box.
2) Setting up their tank
They’re beginner-friendly, but they reward you for giving them space and structure. A 20-gallon long is a sweet spot for a proper group. They’ll live in smaller, but you’ll see more fin-nipping and posturing when they’re cramped.
- Tank size: 15–20 gallons minimum; 20 long is my go-to
- Group size: 8–12+ (more fish = less drama)
- Filter: any gentle-to-moderate flow; they don’t love a washing machine
- Temp: mid-70s°F (around 24–26°C) keeps them active and colorful
- pH/hardness: they’re flexible, but slightly soft/neutral water tends to bring out better behavior and color
- Lighting: medium to low; floating plants help a lot
Decor-wise, give them a planted middle and sides with a clear swimming lane up front. They like to spar and display in open water, then retreat into plants. Driftwood and leaf litter aren’t mandatory, but the fish act more confident with darker cover and you’ll get that classy “blackwater” look.
If your emperors look washed out or hide all day, dim the tank a bit (floaters, taller plants, darker substrate). It changes their whole vibe.
3) What to feed them
They’re easy eaters. Mine took flakes and small pellets right away, but the real magic happens when you rotate in frozen/live foods. That’s when the males start looking like they’re wearing a tux.
- Daily staples: quality flake, micro pellets, small granules
- Color/conditioning foods (a few times a week): frozen daphnia, baby brine shrimp, cyclops
- Treats: bloodworms (not every day—think “dessert,” not “diet”)
- Feed style: small portions 1–2x/day; they’re not shy and can overeat
If you keep them with slower, timid fish, emperors can outcompete them at feeding time. Spread food across the surface or use sinking foods for bottom dwellers.
4) Behavior + tankmates
Emperor tetras are semi-schoolers with a pecking order. The males do a lot of staring contests and little chase-offs, especially if you only keep a few. In a bigger group, the “boss” spreads his attitude around and everyone settles down.
- Best vibe: 1 male to 2–3 females (or just a larger mixed group)
- They’re active mid-water swimmers and love to display in open areas
- Expect some sparring—usually harmless, but watch for torn fins in tight setups
Tankmates are pretty straightforward: other peaceful community fish that like similar temps. They pair really nicely with corydoras, otos, small rasboras, pencilfish, and calm dwarf cichlids like apistos (if the tank is big and well-scaped). I’d skip long-finned slowpokes—emperors can get a little too curious with flowing fins.
Avoid pairing them with fancy guppies, bettas, or slow long-finned fish. It’s not guaranteed fin-nipping, but if it happens, it’s annoying to fix later.
5) Breeding tips (if you want to try it)
Breeding emperors is doable at home, but it’s not quite “oops, babies everywhere” like livebearers. The adults will snack on eggs and fry if they get the chance, so a separate setup helps a lot.
- Breeding tank: 10 gallons is fine, with a sponge filter and very gentle flow
- Add: fine-leaf plants (java moss) or a spawning mop; dim lighting
- Conditioning: frozen/live foods for a week or two
- Pair/group: one male with one or two females usually works well
They tend to spawn around dawn. If you’re serious, move the adults out after you suspect spawning (or use a mesh/egg grate so eggs fall out of reach). Eggs hatch in about a day or two depending on temperature, and the fry are tiny at first—think infusoria or liquid fry food, then baby brine shrimp once they can handle it.
If you’re not getting eggs, try softer water and a slightly cooler water change in the evening. That little “rainstorm” cue can flip the switch.
6) Common problems to watch for
Most issues I’ve seen with emperors come down to stress: too few fish, too bright/bare of a tank, or unstable water. Fix the setup and a lot of “mystery problems” disappear.
- Fin nipping / torn fins: usually from small groups or cramped tanks; add numbers and cover
- Faded color / hiding: lighting too intense, no plants, or fish feel exposed
- Ich after new additions: they can be a little sensitive to sudden changes—quarantine new fish if you can
- Bloat/constipation: from overeating rich foods; rotate in daphnia and keep portions modest
- Sudden losses: often tied to ammonia/nitrite spikes in newer tanks—these fish don’t forgive cycling mistakes
They handle “pretty good” water, but not dirty water. Keep up with regular water changes, and don’t let the tank swing wildly in temperature or parameters—especially right after you bring them home.
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